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1
Al-Hinai, Hilal Ali Zaher. „Natural Cooling Techniques For Buildings“. Thesis, Cranfield University, 1992. http://hdl.handle.net/1826/3591.
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Modern development in many Third World countries in the
hot regions of the world,, have been accompanied by the
construction of highly energy-wasteful buildings. The
interiors of these buildings have to be mechanically airconditioned
in order to achieve thermal-comfort conditions.
The consequence of this, has been the rapid increase in
electricity-generating plant capacity to match demand (of
which, for example at present in Oman, more than 70%
nationally is used for air-conditioning modern, energyinefficient
buildings).
The aim of this work was to find the most suitable way
of stabilising or even reducing the electricity demand in a
country like Oman. The first step taken to achieve this aim,
was to study and draw out lessons from the vernacular
architecture of the different climatic regions in Oman. This
has been followed by a literature survey that looks at
passive and active natural cooling techniques for buildings
in hot climates. Mathematical models were then developed to
analyze and compare those passive techniques that are most
suitable for an environment like that of Oman. Different ways
of reducing the heat gain through the roof were investigated
and compared. These include the addition of insulation,
shading, air-cooling of the roof when the ambient air
temperature is lower than that of the roof, and roof ponds.
Roof ponds were found to be the most effective of those
techniques analyzed. An improved design of the roof pond (the
Water Diode roof pond) that eliminates the need for covering
the roof pond during the day and uncovering it at night, was
suggested and analyzed. The analysis showed promising
results. Mathematical models were also developed to analyze and
compare dif f erent ways of reducing the heat gain through the
walls. These included the use of closed cavities, naturally
ventilated cavities, the addition of insulation, and the
effect of using brick as compared to concrete block. The
analysis suggested that the combination of a Water Diode roof
pond and insulated brick wall construction will reduce the
heat gain through the envelope of a single room by more than
90%, when compared to a room with un-insulated roof and
single-leaf concrete block walls.
An empirical validation of the mathematical models was
conducted. The results showed a good agreement between the
actual and predicted values. An economical analysis of the
commonly used roof and wall constructions in Oman, was also
conducted. This compared the life-cycle cost of nine
different construction techniques, with eight different airconditioning
schedules. The result of this analysis showed a
clear advantage of using roof insulation, reflective double
glazing, and insulated walls with brick outer-leaf and
concrete block inner-leaf.
2
Worthington, D. R. E. „The cooling of electronic power supplies by natural convection“. Thesis, University of Exeter, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380691.
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3
Van, Der Merwe Daniel. „Evaluation of natural draught wet-cooling tower performance uncertainties“. Thesis, Stellenbosch : Stellenbosch University, 2007. http://hdl.handle.net/10019.1/50709.
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Thesis (MScEng)--Stellenbosch University, 2007.ENGLISH ABSTRACT: A natural draught wet-cooling tower (NDWCT) was modelled using the Merkel method with an improved energy equation as recommended by Kloppers and Kroger (2005a) - referred to as the Improved Merkel method. The improved energy equation is used for calculating the heat rejection rate of the tower and includes the energy associated with water evaporation. The sensitivity indexes of a NDWCT were calculated numerically with the Improved Merkel method model. It was found that the perfonnance of a NDWCT is most sensitive to the fill Merkel number. The "Natklos" fill test facility at Stellenbosch University was used to estimate typical uncertainties found in fill performance characteristics. The zeroth order uncertainty for the Merkel number and loss coefficient was calculated to be 0.2100 m-1 and 0.4248 m- 1 , respectively, while the first order uncertainty for the Merkel number and loss coefficient was calculated to be 0.1933 m- 1 and 0.2008 m-1 , respectively. ASME requires that the uncertainty in tower capability has to be less than 6 % for a NDWCT perfonnance test to be deemed ASME approved. Propagating typical measurement uncertainties found in NDWCT test standards and experimental data into the tower capability showed that the 6 % uncertainty limit imposed by ASME is unrealistic and too stringent. Performance curve generator (PCG) is a software package developed that generates NDWCT perfonnance curves. With these performance curves it is possible to easily and effectively adjust the off-design test results in order to detennine whether the NDWCT has met its guarantee or not.
AFRIKAANSE OPSOMMING: Die werksverrigting van 'n natuurlike trek nat koeltoring (NTNT) is gemodelleer deur gebruik te maak van die Merkel metode met 'n verbeterde energie vergelyking, soos aanbeveel deur Kloppers en Kroger (2005a) - Verbeterde Merkel metode. Die energie vergelyking word gebruik om die toring se tempo van warmteoordrag te bereken en sluit die energieverlies as gevolg van verdamping in. Die Verbeterde Merkel metode model was gebruik om die sensitiwiteits-indekse van 'n NTNT te bepaal. Die analise toon dat die toring se werksverrigting die sensitiefste is vir die pakking se Merkel getal. Die Natklos pakkingstoetsfasiliteit aan die Universiteit van Stellenbosch was gebruik om tipiese onsekerheid in die pakkingsprestasiekarakteristieke te bepaal. Die zero-orde onsekerheid in die Merkel getal en verlieskoeffisient was bereken as 0.2100 m· 1 en 0.4248 m· 1 , onderskeidelik, terwyl die eerste-orde onsekerhede bereken was as 0.1933 m·1 en 0.2008 m· 1 , onderskeidelik. Die toelaatbare onsekerheid in toringvennoe vir 'n NTNT aanvaardingstoes volgens ASME is 6 %. Deur tipes meetonsekerhede, soos gegee deur NTNT aanvaardings-toesstandaarde sowel as eksperimentele data, deur te propageer, word 'n onsekerheid veel groter as die toelaatbare 6 % gegenereer. 'n Renekaarpakket, genaamd Performance Curve Generator (PCG), is ontwikkel om werksverrigtinskurwes vir 'n NTNT te genereer. PCG se werksverrigtinskurwes maak dit moonltik om maklik te bepaal of a NTNT sy ontwerpskriterea bereik het of nie.
4
HEINERUD, VICTOR, und ANDRÉ SAHLSTEN. „Natural Refrigerants in Data Center Cooling with Thermosiphon Application“. Thesis, KTH, Energiteknik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-192880.
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Ever since the computer was invented, there has been a need of data storage and the demand has strictly grown since. This has resulted in a huge amount of data centers and the trend has shown no signs of changing. The data centers are powered by electricity and in 2010 the electricity consumption for data centers stood for 1.3% of the world’s electricity usage. The most energy consuming part of a data center is the servers themselves, but the second largest energy consuming part is the cooling system which, in a normal data center, stands for two fifths of the energy usage. Besides the energy consumption, the cooling systems are in most cases a cooling machine using HCFC and HFC refrigerants. These refrigerants are all bad for the environment since HCFCs have high ODP and GWP values and HFCs have high GWP values. The purposes of this work is: A) Find a way to make the cooling systems more efficient. Previous work has shown that using free cooling from the ambient air is an effective method of reducing the yearly electricity demand. Further the systems use a two-phase thermosiphon to move heat from the servers to the ambient, which means that there is no need of pumping power. B) Find solutions using natural refrigerants that have no ODP and very low or zero GWP. C) Evaluated if there is a possibility to recover the waste heat from the data center to e.g. an office building. This work contains two systems being mathematically modeled with the software Engineering Equation Solver: a direct R744 system and an indirect system running with R290 and R744. Both systems are using a thermosiphon application, connected to a condenser, to use free cooling up to a certain set point temperature and the rest is covered with a vapor compression cycle. These systems are then matched to temperature profiles for five cities, Stockholm, Paris, Phoenix, Tokyo and Madrid, to see how many hours of the year are covered by free cooling. The systems are then evaluated considering both energy consumption and cost. To be able to compare these systems to a present cooling system, a reference system is modeled which uses R22 as refrigerant, that is the most commonly used refrigerant in the world today for the data center cooling application. The results show that a direct R744 system or an indirect system with R290/R744 with a thermosiphon application have both energy and economical savings compared to the reference system. The energy savings are up to 88% and the total annual cost savings are up to 69%. The Power Usage Effectiveness is reduced with up to 6% and up to 8% if only cooling is considered. These savings are for an optimized condenser with a 2000 m2 fin area and 6 fans with a set point temperature of 22°C. The indirect R290/R744 system is the best in all cities considering energy efficiency. Both systems are also well suited for use with heat recovery. The Seasonal Performance Factor for the heat recovery is between 8.3 and 15.2, which is a consequence of the high evaporation temperature and low supply temperature to the heating system.Ända sedan datorn uppfanns har det funnits ett behov av datalagring, ett behov som ökat stadigt. Detta har resulterat i en stor mängd datacenter och det finns inget som tyder på att trenden kommer ändras. Datacenter drivs av el och under 2010 var elförbrukningen för datacenter 1.3% av världens totala elanvändning. Den mest energikrävande delen av ett datacenter är de faktiska servrarna och den näst största energikrävande delen är kylsystemet, vilket i ett normalt datacenter står för två femtedelar av energianvändningen. Förutom energiförbrukningen, är kylsystemen i de flesta fall, en kylmaskin med HCFC- och HFC-köldmedier. Dessa köldmedier är dåliga för miljön eftersom HCFC har högt ODP- och GWP-värden och HFC har höga GWP-värden. Syftet med detta arbete är: A) Hitta ett sätt att göra kylsystem effektivare. Tidigare arbeten har visat att användning av frikyla från den omgivande luften är en effektiv metod för att minska det årliga elbehovet. Det finns även system som använder en två-fas termosifon för att flytta värme från servrar till den omgivande luften, vilket innebär att det inte behövs några pumpar. B) Hitta systemlösningar med naturliga köldmedier som har noll ODP och mycket låg eller noll GWP. C) Utvärdera om det finns möjlighet att återvinna spillvärme från ett datacenter till exempelvis en kontorsbyggnad. Detta arbete innehåller två system vilka modelleras matematiskt med hjälp av programvaran Engineering Equation Solver: ett direkt R744-system och ett indirekt system som använder R290 och R744. Båda systemen använder en termosifonslinga som är ansluten till en kondensor för att kunna använda frikyla upp till en viss brytpunktstemperatur och det resterande behovet täcks av en kylmaskin. Dessa system matchas sedan mot temperaturprofiler för fem städer, Stockholm, Paris, Phoenix, Tokyo och Madrid, för att se hur många timmar av året som frikylakan användas. Systemen utvärderas sedan utifrån både energiförbrukning och kostnad. För att kunna jämföra dessa system mot ett befintligt kylsystem modelleras ett referenssystem med R22 som kylmedel, vilket är det vanligaste köldmediet i världen idag för kylning av datacenter. Resultaten visar att ett direkt R744-system eller ett indirekt system med R290/R744, båda med en termosifonslinga, är både energieffektivare och ekonomiskt fördelaktigare jämfört med referenssystemet. Energibesparingen uppgår till 88% och de totala årliga kostnadsbesparingarna uppgår till 69%. Power Usage Effectiveness värdet reduceras med upp till 6% och om enbart hänsyn tas till nedkylning, upp till 8%. Dessa besparingar är för en optimerad kondensor med en flänsyta på 2000 m2 samt 6 stycken fläktar då kondensatorn har en brytpunktstemperatur på 22° C. Det indirekta R290/R744-systemet är det bästa i alla städer vad gäller energieffektivitet. Båda systemen är också väl lämpade för användning med värmeåtervinning. Årsvärmefaktorn för värmeåtervinningen är mellan 8.3 och 15.2, vilket är en följd av den höga förångningstemperaturen och den låga framledningstemperaturen till värmesystemet.
5
Gallarotti, Maura. „CFD ANALYSIS ON THE COOLING OF NON GUIDED OIL NATURAL AIR NATURAL TYPES OF TRANSFORMERS“. Thesis, KTH, Mekanik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-203970.
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ABB is moving towards more powerful and compact transformers and an efficient cooling is of paramount importance in order to avoid overheating.In this master thesis, transformers without guides for the oil flow have been analysed: they allow a faster and cheaper manufacturing process, but at the same time the absence of guides makes the cooling design more difficult.In order to be able to perform several parametric studies, a script with the Pointwise mesher has been developed for the automatic generation of the geometry and mesh of transformer windings. This has allowed to analyse transformer windings with a different shape, assessing the effect of a certain number of geometrical parameters on the cooling efficiency.The software ANSYS Fluent was used to perform 2D axisymmetric unsteady simulations on the company cluster and the simulation set up was validated thanks to comparison with experimental measurements in ABB in Vaasa (Finland), that showed an average relative error below 2%.A remarkable result of this study is the identification of a periodic pattern in the temperature of the windings from the inlet to the outlet of the transformer, with hot spot locations every 10-20 disc windings. This conclusion has also been confirmed by the experimental measurements performed in Vaasa on a test transformer. Furthermore, a periodic behaviour of the temperature of the windings and of the oil in time has also been identified.Finally, transformers with an additional cooling channel in the disc windings have been studied, revealing that an accurate design is needed when adding oil channels through the windings in order to avoid the formation of unexpected hot spots.
6
Reuter, Hanno Carl Rudolf. „Performance evaluation of natural draught cooling towers with anisotropic fills“. Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/5440.
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Thesis (PhD) -- University of Stellenbosch, 2010.ENGLISH ABSTRACT: In the design of a modern natural draught wet-cooling tower (NDWCT), structural and performance characteristics must be considered. Air flow distortions and resistances must be minimised to achieve optimal cooling which requires that the cooling towers must be modelled two-dimensionally and ultimately threedimensionally to be optimised. CFD models in literature are found to be limited to counterflow cooling towers packed with film fill, which is porous in one direction only and generally has a high pressure drop, as well as purely crossflow cooling towers packed with splash fill. This simplifies the analysis considerably as the effects of flow separation at the air inlet are minimised and fill performance is determined using the method of analysis originally employed to determine the fill performance characteristics from test data. Many counterflow cooling towers are, however, packed with trickle and splash fills which have anisotropic flow resistances, which means the fills are porous in all flow directions and thus air flow can be oblique through the fill, particularly near the cooling tower air inlet. This provides a challenge since available fill test facilities and subsequently fill performance characteristics are limited to purely counter- and crossflow configuration. In this thesis, a CFD model is developed to predict the performance of NDWCTs with any type of spray, fill and rain zone configuration, using the commercial code FLUENT®. This model can be used to investigate the effects of different: atmospheric temperature and humidity profiles, air inlet and outlet geometries, air inlet heights, rain zone drop size distributions, spray zone performance characteristics, variations in radial water loading and fill depth, and fill configurations or combinations on cooling tower performance, for optimisation purposes. Furthermore the effects of damage or removal of fill in annular sections and boiler flue gas discharge in the centre of the tower can be investigated. The CFD modelling of NDWCTs presents various options and challenges, which needed to be understood and evaluated systematically prior to the development of a CFD model for a complete cooling tower. The main areas that were investigated are: spray and rain zone performance modelling by means of an Euler-Lagrangian model; modelling of air flow patterns and flow losses; modelling of fill performance for oblique air flow; modelling of air pressure and temperature profiles outside and inside the cooling tower. The final CFD results for the NDWCT are validated by means of corresponding one-dimensional computational model data and it is found that the performance of typical NDWCTs can be enhanced significantly by including protruding platforms or roundings at the air inlet, reducing the mean drop size in the rain zone, radially varying the fill depth and reducing the air inlet height.
AFRIKAANSE OPSOMMING: By die ontwerp van ‘n moderne natuurlike trek nat koeltoring (NTNK), moet strukturele en werkverrigtings eienskappe in ag geneem word. Wanverdeelde lugvloei en vloeiweerstande moet geminimaliseer word om optimale verkoeling te bewerkstellig, wat vereis dat die koeltorings twee-dimensioneel en uiteindelik driedimensioneel gemodelleer moet word om hulle te kan optimeer. Dit is gevind dat berekeningsvloeidinamika (BVD of “CFD” in engels) modelle in die literatuur, beperk is tot teenvloei koeltorings gepak met film tipe pakking, wat net in een vloeirigting poreus is en boonop gewoonlik ook ‘n hoë drukval het, sowel as suiwer dwarsvloei koeltorings met spatpakking. Hierdie vergemaklik die analise aansienlik omdat die effekte van vloeiwegbreking by die luginlaat verklein word en die pakking se werkverrigtingsvermoë bereken kan word met die analise metode wat oorspronklik gebruik is om die pakkingseienskappe vanaf toets data te bepaal. Baie teenvloei koeltorings het egter drup- (“trickle”) of spatpakkings met anisotropiese vloeiweerstand, wat beteken dat die pakking poreus is in alle vloeirigtings en dat die lug dus skuins deur die pakking kan vloei, veral naby die koeltoring se lug inlaat. Hierdie verskaf ‘n uitdaging aangesien beskikbare pakking toetsfasiliteite, en dus ook pakking karakteristieke, beperk is tot suiwer teenvloei en dwarsvloei konfigurasie. ‘n BVD model word in hierdie tesis ontwikkel wat die werkverrigtingsvermoë van NTNK’s kan voorspel vir enige sproei, pakking en reënsone konfigurasie deur van die kommersiële sagteware FLUENT® gebruik te maak. Hierdie model kan gebruik word om die effekte van verskillende: atmosferiese temperatuur- en humiditeitsprofiele, lug inlaat en uitlaat geometrië, lug inlaat hoogtes, reënsone druppelgrootteverdelings, sproeisone werkverrigtingskarakteristieke, variasie in radiale waterbelading en pakking hoogte, en pakking konfigurasies of kombinasies op koeltoringvermoë te ondersoek vir optimerings doeleindes. Verder kan die effekte van beskadiging of verwydering van pakking in annulêre segmente, en insluiting van ‘n stoomketel skoorsteen in die middel van die toring ondersoek word. Die BVD modellering van NTNK bied verskeie moontlikhede en uitdagings, wat eers verstaan en sistematies ondersoek moes word, voordat ‘n BVD model van ‘n algehele NTNK ontwikkel kon word. Die hoof areas wat ondersoek is, is: sproeien reënsone modellering mbv ‘n Euler-Lagrange model; modellering van lugvloeipatrone en vloeiverliese; modellering van pakking verrigting vir skuins lugvloeie; modellering van lugdruk- en temperatuurprofiele buite en binne in die koeltoring. Die BVD resultate word mbv van data van ‘n ooreenstemmende eendimensionele berekeningsmodel bevestig en dit is bevind dat die werkverrigting van ‘n tipiese NTNK beduidend verbeter kan word deur: platforms wat uitstaan of rondings by die luginlaat te installeer, die duppelgrootte in die reënsone te verklein, die pakkingshoogte radiaal te verander, en die luginlaathoogte te verlaag.
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Aboul, Naga Mohsen M. „Natural ventilation and cooling by evaporation in hot-arid climates“. Thesis, University of Leeds, 1990. http://etheses.whiterose.ac.uk/4043/.
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In hot climates, outside air is too hot during the day. In hot arid climates, low humidity increases discomfort. For comfort, hot air should be cooled before flowing into dwellings and moisture in the moving air increased. For the poor, comfort must be sought cheaply. In places without electricity only 'natural' ventilation is feasible. The air temperature difference between the sunny and the shaded side of a building can be exploited to promote ventilation. Ventilation cooling can be enhanced with an 'evaporative cooling cavity' attached to a dwelling on its shaded side. The cavity has a top external inlet and a bottom internal outlet, and incorporates one or two wet partitions. The air within the cavity, being moist. descends. drawing the outside warm and dry air into the cavity. Evaporation cools the air and raises its humidity. The cool incoming air will reduce inside air temperature and improve comfort. The performance of a typical cavity to induce cooling ventilation by evaporation was investigated theoretically and experimentally with a full scale model. The temperature drop. velocity and relative humidity of the air were measured. The pattern of the air flow in the cavity was observed. The optimum dimensions of the cavity were established. Buoyancy air flow and fan-assisted air flow were analysed in the steady state. Since a convective heat transfer coefficient for air flowing between two parallel vertical surfaces was not found in the literature, appropriate convective heat and surface mass transfer coefficients were derived from measurements. The results show the convective heat transfer coefficient to be independent of the separation of the wet surfaces, and that with separation greater than 3Omm, each wet surface behaves as a 'free' surface. The optimum separation between wet surfaces was assessed, and the water removed by evaporation was determined, and found to be small. The Admittance Method was used to assess comfort. Ventilation and evaporation effectiveness were evaluated. An outlet air velocity of O.3m/s accompanied with a temperature drop of about 6K was achieved. Design proposals for hot arid climates are offered.
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Ehlers, Frederik Coenrad. „Condition-based monitoring of natural draught wet-cooling tower performance-related parameters“. Thesis, Stellenbosch : Stellenbosch University, 2011. http://hdl.handle.net/10019.1/17904.
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Thesis (MScEng)--Stellenbosch University, 2011.ENGLISH ABSTRACT: The meteorological conditions at Eskom’s Majuba Power Station are measured, evaluated and trended in this dissertation. The results are used to evaluate the current natural draught wet-cooling tower (NDWCT) design- and performance test specifications and to compare these to the original design- and performance test specifications. The evaluation reveals that the design parameters for the NDWCTs at Majuba Power Station, a cooling system that was originally designed optimally, could have been determined differently and arguably more accurately by using the wet-bulb temperature (Tawb) as the main design variable instead of the dry-bulb temperature (Ta). A new technique to determine optimal NDWCT design and performance test conditions is consequently proposed. In order to satisfy the atmospheric conditions required for a successful NDWCT performance test, it is also proposed that the tests be undertaken between 12:00 and 14:00 during Summer. It is found that the NDWCT inlet Tawb, measured at specific heights, does not compare well to the far-field Tawb measured at the same heights when a Tawb accuracy of 0.1 K is required. It is proposed that a more representative far-field Tawb measuring height of 10 m should be used in future NDWCT designs as the NDWCT design temperature reference height. The industry-standard reference height should, however, still be used during temperature profile calculations. A parametric study of the water-steam cycle and wet-cooling system at Majuba indicates that during full load conditions, the generated output (Pst) is primarily dependent on the condenser saturation pressure (pc). The latter is reliant on Tawb, the temperature lapse rate (LRT) that is represented by the temperature profile exponent (bT), the main cooling water flow rate (mcw), atmospheric pressure (pa), and wind speed (VW). Using historical plant data relatively simple methods, enabling the quick and effective determination of these relationships, are proposed. The plant-specific and atmospheric parameters required for these analyses are also tabulated. Two NDWCT effectiveness models, one mathematical (Kröger, 1998) and one statistical artificial neural network (ANN) model are presented and evaluated. ANNs, which are not often used to evaluate NDWCT effectiveness, provide accurate NDWCT temperature approach results within 0.5 K of measured values for varying dependent variables. This motivates that an ANN, if set up and used correctly, can be an effective condition-monitoring tool and can be used to improve the accuracy of more empirical NDWCT performance models. The one-dimensional mathematical effectiveness model provides accurate results under NDWCT design conditions. The dependency of Majuba’s NDWCT to the rain zone mean drop diameter (dd) is evaluated by means of the one-dimensional mathematical model. A reduction in dd from 0.0052 m to 0.0029 m can reduce the NDWCT re-cooled water temperature (Tcwo) so that the rated pc is reduced by 0.15 kPa, which relates to a combined financial saving during peak and off-peak periods of R1.576M in 2013 and R1.851M in 2016. Similar improvements can result in higher savings at other wet-cooled stations in the Eskom fleet due to less optimally-designed wet-cooling systems. The proposed techniques should be considered in future economic evaluations of wet-cooling system improvements at different power stations.
AFRIKAANSE OPSOMMING: Die meteorologiese toestande by Eskom se Majuba-kragstasie is deur die navorser gemeet en -evalueer. Die resultate word gebruik om die Natuurlike-trek, Nat koeltoring (NTNKT) se ontwerp- en werkverrigting toetsspesifikasies te evalueer en vergelyk met die oorspronklike toetsspesifikasies. Die resultate dui daarop dat die ontwerpsparameters vir die NTNKTs by Majuba-kragstasie, ‘n verkoelings-sisteem wat aanvanklik optimaal ontwerp is, op ‘n ander, selfs meer akkurate manier bepaal kon word deur die natbol-temperatuur (Tawb) te gebruik as die hoof-ontwerpsparameter inplaas van die droëbol temperatuur (Ta).’n Nuwe tegniek wat gebruik kan word om akkurate NTNKT ontwerp- en werkverrigting toetsspesifikasies te bepaal word voorgestel. Die tydperk vir die mees optimale atmosferiese toestande, wanneer NTNKT-toetse uitgevoer moet word, word vasgestel as tussen 12:00 en 14:00 tydens Somermaande. Dit word bewys, vir ’n Tawb akkuraatheid van 0.1 K, dat die NTNKT inlaat-Tawb, gemeet by verskillende hoogtes, nie vergelykbaar is met Tawb wat ver van die NTNKT af op dieselfde hoogtes gemeet word nie. ’n Meer aanvaarbare hoogte van 10 m word voorgestel as die NTNKT ontwerpstemperatuur verwysingshoogte vir toekomstige NTNKT ontwerpe wanneer die Tawb ver van die NTNKT af meet word. Die industrie-standaard temperatuur verwysingshoogte moet wel steeds gebruik word tydens temperatuur-profielberekeninge. ’n Parametriese studie van die turbine se water-stoom siklus en die nat-verkoelingstelsel by Majuba dui daarop dat die generator se uitset (Pst) hoofsaaklik afhanklik is van die kondensator se druk (pc) gedurende vol-vrag toestande. Druk (pc) is weer afhanklik van Tawb, die temperatuur vervaltempo (LRT) wat voorgestel word deur die temperatuur profiel eksponent (bT), die verkoelingswater-vloeitempo (mcw), atmosferiese druk (pa) en windspoed (VW). Deur die gebruik van historiese data word redelike eenvoudige metodes voorgestel om dié verhoudings doeltreffend te bepaal. Die atmosferiese- en stasie-spesifieke parameters wat benodig word vir dié ontleding is ook getabuleer. Twee modelle vir NTNKT-effektiweit, ’n wiskundige (gebaseer op Kröger, 1998) en statistiese kunsmatige neurale-netwerk (KNN) model, word aangebied en geëvalueer. KNNe, wat nie gereeld gebruik word om NTNKTe se effektiwiteit te evalueer nie, lewer akkurate NTNKT temperatuur-benadering resultate binne 0.5 K van die gemete resultate vir wisselende afhanklike parameters. Dié resultate motiveer dat ’n KNN wat korrek opgestel is doeltreffend gebruik kan word om die toestand van NTNKTs te bepaal en om die akkuraatheid van ander NTNKT-modelle te verbeter. Die eendimensionele, wiskundige model lewer akkurate resultate onder NTNKT ontwerpspesifikasies. ’n Wiskundige NTNKT-model word gebruik om die afhanklikheid van Majubakragstasie se NTNKTe tot die reënsone druppelgrootte (dd) te bereken. 'n Vermindering in dd van 0,0052 tot 0,0029 m kan die NTNKT se afgekoelde watertemperatuur (Tcwo), van só 'n aard verlaag dat pc verminder met 0,15 kPa. Só kan ’n gesamentlike vol- en gedeeltelike vrag finansiële besparing van R1.576M in 2013 en R1.851M in 2016 behaal word. Soortgelyke verbeterings aan verkoelingstelsels sal lei tot meer en hoër besparings by ander Eskom nat-verkoelde stasies. Dié tegnieke moet in ag geneem word tydens toekomstige ekonomiese evaluasies van verbeterings tot nat-verkoelingstelsels by ander kragstasies.
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Villarreal, Guerrero Federico. „Enhanced Greenhouse Cooling Strategy with Natural Ventilation and Variable Fogging Rates“. Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/202717.
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High-pressure fog (HPF) systems have advantages for greenhouse cooling compared to traditional systems, such as pad and fan. Such advantages include the potential of improving climate uniformity. Water is distributed throughout the greenhouse space thus reducing water use and energy operation costs, especially if used within naturally ventilated greenhouses. Fog cooling in combination with natural ventilation is difficult to manage, primarily because accurate estimation of air exchange rates is required to determine the precise amount of fog required. This limitation on automated control has been the main reason restricting the widespread commercial use of HPF systems. The goal of this research was to develop and implement a control strategy for a naturally ventilated greenhouse with a variable HPF system. The strategy that was developed included variable rate of fog introduced into the greenhouse, a dynamic control of the air ventilation openings, and it considered the contribution of cooling and humidification from the crop by evapotranspiration. Three evapotranspiration models, including Penman-Monteith, Stanghellini and Takakura, were calibrated and evaluated in terms of prediction accuracy. The Stanghellini model provided the best overall performance for several growing seasons and under two different evaporative cooling systems (i.e. pad and fan and natural ventilation with HPF), and was selected and implemented in the cooling control strategy. The strategy utilized enthalpy and vapor pressure deficit (VPD) of the greenhouse atmosphere for the control parameters. Using a calibrated greenhouse mechanistic climate model, a computer algorithm was created to simulate the capabilities of the proposed. The control strategy that was developed was able to maintain the greenhouse climate closer to the pre-established set points while consuming less water and energy, compared to a constant HPF system based on VPD control. Finally, the strategy was implemented in a single span research greenhouse. A four-day validation study provided good agreement for measured and simulated greenhouse climate values, as well as for water and energy use. Moreover, the strategy was able to maintain VPD around its set point for all the experiments and temperature remained around its set point when outside enthalpy was lower than the enthalpy set point.
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Rai, Roby. „Cooling multi-family residential units using natural ventilation in the Central U.S“. Thesis, Kansas State University, 2016. http://hdl.handle.net/2097/34565.
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Master of ScienceDepartment of Architecture
Michael D. Gibson
The use of Natural Ventilation (NV) to cool buildings in mixed climates can conserve significant cooling energy. In mixed climates it is particularly important during the fall and the spring, where appropriately designed buildings should use very little energy for heating or cooling. Natural ventilation is also important in residential buildings, where internal heat gain can be managed, making cooling by natural ventilation easier. Earlier investigations have clearly shown the economic, social, and health benefits of the use of NV in built environment. Studies have shown that increased airflow or air-speed during ventilation can bring a significant rise in comfort range which further reduces the cooling energy required to maintain comfort. The climatic data of the central United States (U.S.) shows that the availability of frequent high speed wind and favorable seasonal humidity conditions make natural ventilation feasible in late spring and early fall, where NV can offset most of the cooling demand for a home or multifamily residential unit, though it is not possible to maintain thermal comfort during the entire summer with NV alone. In mixed climates, NV for multifamily residential units has not been investigated thoroughly. According to 2009 International Residential Code, multifamily residential buildings are typically designed to use a code minimum amount of operable or ventilating windows, 4% of the floor area being ventilated, while also using lightweight construction methods (such as wood framing) that is prone to fast thermal response during the overheated periods of the year. While climate may favor the use of NV in these building types, the sizing of windows and the building construction type limit the potential to save energy with NV. This study hypothesized that the maximum benefits from NV in the climate of the central U.S. requires further optimization of window openings beyond the energy code minimum, and a construction system incorporating mass that can slow thermal response during overheated periods. During the study, the climatic data of the central US was scrutinized to understand the most suitable time frames where NV could be applied in order to maintain indoor thermal comfort in various construction systems in residential buildings: mainly lightweight using wood framing, and heavier construction using concrete and masonry. The location of the housing unit, first level or second level, was also examined to account for the differences in thermal gains and losses as a result of ground coupling and additional heat gain from the roof. Further, computational fluid dynamics evaluated the comfort achieved with different ventilation areas. Change in comfort hours by using NV tested the practicability of the use of NV to maintain indoor thermal comfort for different scenarios. The study concluded with design recommendations for building orientation, operable window size, and construction type as these factors relate to thermal comfort and the optimization of multifamily residential buildings to utilize NV for energy savings in the U.S.
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Storm, Heinrich Claude. „CFD investigation of flow in and around a natural draft cooling tower“. Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4353.
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Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: Cooling tower inlet losses and effective flow diameter under no crosswind conditions and the pressure distribution around a circular cylinder subjected to a crosswind are modelled using CFD. The CFD model used to evaluate the inlet losses is validated with data measured in an experimental cooling tower sector model and data obtained from literature. The effect of different inlet geometries on the inlet loss coefficient and the effective diameter are investigated in order to improve cooling tower inlet designs. CFD models are developed to investigate the pressure distribution around infinite and finite circular cylinders. The infinite cylinder is modelled with a smooth surface and a rough surface so that the results can be compared to experimental data from literature. Ultimately a finite cylinder model with a rough surface is developed and the results are compared to experimental data from literature.
AFRIKAANSE OPSOMMING: Koeltoring inlaatverlies en effektiewe vloei deursnit onder geen teenwind toestande en die drukverdeling rondom ‘n sirkelvormige silinder, onderworpe aan ‘n teenwind, word gemodelleer deur gebruik te maak van “CFD”. Die “CFD” model wat gebruik word om die inlaatverlies te evalueer is gevalideer met data verkry vanaf ‘n eksperimentele koeltoring sektor model. Verder word die “CFD” model gebruik in ‘n ondersoek om te bebaal wat die effek is van verskillende inlaat geometrieë op die inlaat verlies koeffisiënt en die effektiewe diameter sodat die inlaat geometrie van koeltorings verbeter kan word. ‘n “CFD” model word dan ontwikkel om die druk verdeling rondom ‘n sirkelvormige silinder te ondersoek. Die silinder word as oneindig gesimuleer met ‘n glade en ruwe wand sodat die resultate vergelyk kan word met eksperimentele data verkry vanaf literatuur. Die afdeling word afgesluit deur die silinder as eindig met ‘n ruwe wand te simuleer en dan word die resultate vergelyk met eksperimentele data verkry vanaf literatuur.
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Farija, Ghassan Mahmood. „Wind induced natural ventilation for wind tower houses in maritime desert climates with special reference to Bahrain“. Thesis, University of Reading, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270325.
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Du, Preez Abraham Francois. „The influence of cross-winds on the performance of natural draft dry-cooling towers“. Thesis, Link to the online version, 1992. http://hdl.handle.net/10019.1/1426.
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Baudoin, Antoine. „Cooling Strategies for Wave Power Conversion Systems“. Doctoral thesis, Uppsala universitet, Elektricitetslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-306706.
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The Division for Electricity of Uppsala University is developing a wave power concept. The energy of the ocean waves is harvested with wave energy converters, consisting of one buoy and one linear generator. The units are connected in a submerged substation. The mechanical design is kept as simple as possible to ensure reliability. The submerged substation includes power electronics and different types of electrical power components. Due to the high cost of maintenance operations at sea, the reliability of electrical systems for offshore renewable energy is a major issue in the pursuit of making the electricity production economically viable. Therefore, proper thermal management is essential to avoid the components being damaged by excessive temperature increases. The chosen cooling strategy is fully passive, and includes no fans. It has been applied in the second substation prototype with curved heatsinks mounted on the inner wall of the pressurized vessel. This strategy has been evaluated with a thermal model for the completed substation. First of all, 3D-CFD models were implemented for selected components of the electrical conversion system. The results from these submodels were used to build a lumped parameter model at the system level. The comprehensive thermal study of the substation indicates that the rated power in the present configuration is around 170 kW. The critical components were identified. The transformers and the inverters are the limiting components for high DC-voltage and low DC-voltage respectively. The DC-voltage—an important parameter in the control strategy for the WEC—was shown to have the most significant effect on the temperature limitation. As power diodes are the first step of conversion, they are subject to large power fluctuations. Therefore, we studied thermal cycling for these components. The results indicated that the junction undergoes repeated temperature cycles, where the amplitude increased with the square root of the absorbed power. Finally, an array of generic heat sources was optimized. We designed an experimental setup to investigate conjugate natural convection on a vertical plate with flush-mounted heat sources. The influence of the heaters distribution was evaluated for different dissipated powers. Measurements were used for validation of a CFD model. We proposed optimal distributions for up to 36 heat sources. The cooling capacity was maximized while the used area was minimized.
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Van, der Westhuizen Pieter Hermanus. „Dynamic modelling of the natural convection water cooling principle / by Pieter v.d. Westhuizen“. Thesis, North-West University, 2007. http://hdl.handle.net/10394/1949.
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Gdhaidh, Farouq Ali S. „Heat transfer characteristics of natural convection within an enclosure using liquid cooling system“. Thesis, University of Bradford, 2015. http://hdl.handle.net/10454/7824.
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In this investigation, a single phase fluid is used to study the coupling between natural convection heat transfer within an enclosure and forced convection through computer covering case to cool the electronic chip. Two working fluids are used (water and air) within a rectangular enclosure and the air flow through the computer case is created by an exhaust fan installed at the back of the computer case. The optimum enclosure size configuration that keeps a maximum temperature of the heat source at a safe temperature level (85°C) is determined. The cooling system is tested for varying values of applied power in the range of 15-40W. The study is based on both numerical models and experimental observations. The numerical work was developed using the commercial software (ANSYS-Icepak) to simulate the flow and temperature fields for the desktop computer and the cooling system. The numerical simulation has the same physical geometry as those used in the experimental investigations. The experimental work was aimed to gather the details for temperature field and use them in the validation of the numerical prediction. The results showed that, the cavity size variations influence both the heat transfer process and the maximum temperature. Furthermore, the experimental results ii compared favourably with those obtained numerically, where the maximum deviation in terms of the maximum system temperature, is within 3.5%. Moreover, it is seen that using water as the working fluid within the enclosure is capable of keeping the maximum temperature under 77°C for a heat source of 40W, which is below the recommended electronic chips temperature of not exceeding 85°C. As a result, the noise and vibration level is reduced. In addition, the proposed cooling system saved about 65% of the CPU fan power.
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Gdhaidh, Farouq A. S. „Heat Transfer Characteristics of Natural Convection within an Enclosure Using Liquid Cooling System“. Thesis, University of Bradford, 2015. http://hdl.handle.net/10454/7824.
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In this investigation, a single phase fluid is used to study the coupling between natural convection heat transfer within an enclosure and forced convection through computer covering case to cool the electronic chip. Two working fluids are used (water and air) within a rectangular enclosure and the air flow through the computer case is created by an exhaust fan installed at the back of the computer case. The optimum enclosure size configuration that keeps a maximum temperature of the heat source at a safe temperature level (85℃) is determined. The cooling system is tested for varying values of applied power in the range of 15−40𝑊.
The study is based on both numerical models and experimental observations. The numerical work was developed using the commercial software (ANSYS-Icepak) to simulate the flow and temperature fields for the desktop computer and the cooling system. The numerical simulation has the same physical geometry as those used in the experimental investigations. The experimental work was aimed to gather the details for temperature field and use them in the validation of the numerical prediction.
The results showed that, the cavity size variations influence both the heat transfer process and the maximum temperature. Furthermore, the experimental results
ii
compared favourably with those obtained numerically, where the maximum deviation in terms of the maximum system temperature, is within 3.5%. Moreover, it is seen that using water as the working fluid within the enclosure is capable of keeping the maximum temperature under 77℃ for a heat source of 40𝑊, which is below the recommended electronic chips temperature of not exceeding 85℃. As a result, the noise and vibration level is reduced. In addition, the proposed cooling system saved about 65% of the CPU fan power.
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Williamson, N. J. „Numerical modelling of heat and mass transfer and optimisation of a natural draft wet cooling tower“. Connect to full text, 2008. http://ses.library.usyd.edu.au/handle/2123/4035.
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Thesis (Ph. D.)--University of Sydney, 2007.Title from title screen (viewed February 12, 2009). Includes graphs and tables. Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Aerospace, Mechanical and Mechatronic Engineering. Includes bibliographical references. Also available in print form.
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Musskopf, Diego Boschetti. „Estudos exploratórios sobre ventilação natural por tubos enterrados“. reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2006. http://hdl.handle.net/10183/11803.
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O uso do solo como massa inercial para condicionamento térmico de edificações por contato direto é uma prática antiga, porém, seu uso como trocador de calor através de dutos enterrados, para ventilação natural de edificações é recente. A prática consiste em enterrar dutos a profundidades entre 0,5m e 1,5m – com extensões e diâmetros variáveis – por onde o ar circula do exterior para o interior dos ambientes através da ação do vento externo e da convecção natural. Durante o trajeto, o ar troca calor com o solo e ingressa no ambiente a temperaturas mais amenas. Embora seja um sistema já empregado na arquitetura bioclimática, existem poucos estudos conclusivos sobre a sua real eficácia. Dessa forma, o objetivo do trabalho é investigar o comportamento higrotérmico de uma edificação construída no sul do Brasil com o sistema e compreender a atuação dos fatores climáticos responsáveis pelo deslocamento de ar no seu interior. O estudo foi realizado através do monitoramento do Protótipo Ventura, localizado em Viamão (Brasil – 30º01'59"S, 51º13'48"W) no período de verão. No deslocamento de ar, foi estudada a influência do vento e da diferença de temperatura nos 2 diâmetros, nas 2 inclinações e nas 2 orientações dos dutos existentes, bem como a influência da chaminé solar. O desempenho higrotérmico foi avaliado comparando o ar na sala ventilada com uma sala de referência (de mesmas dimensões, porém de orientação distinta) e com o exterior. Os resultados demonstram que o solo de Viamão é eficiente para o condicionamento térmico da edificação, pois a pequenas profundidades, ele apresenta uma temperatura mais estável que o ar, próxima à média anual de temperatura do ar local (18ºC). Dessa forma, ao passar pelo duto, o ar externo é aquecido nos períodos frios e refrigerado nos períodos quentes, mantendo o ar interno próximo da zona de conforto. Também foi possível observar que o principal fator responsável pelo deslocamento de ar observado é o vento externo, porém as diferenças de temperatura entre as extremidades dos tubos, bem como entre o interior e exterior da edificação, não podem ser desprezadas, pois geram velocidades de mesma magnitude que o primeiro. Por fim, conclui-se que a ventilação da sala reduziu seu retardo térmico, porém não prejudicou o seu conforto térmico, apresentando inclusive uma redução de sua umidade interna.The use of the ground as an inertial mass for thermal conditioning of buildings, such as the Italians cellars, is an old practice. However, its use as a heat exchanger with buried pipes for natural indoor ventilation is quite recent. The system uses pipes with variable length and diameter buried at a depth between 0.5m and 1.5m. The air flows trough the pipes from the outside to the inside by convection or wind effects. Although it’s already a bioclimatic architecture system, there are few conclusive studies about its real effectiveness. The objective of this study is to investigate the benefits of natural ventilation through buried pipes in a building located in the south of Brazil. A prototype building and a buried pipe system have been built and measured during a period in the summer of 2005-2006, in Viamão (30º 01'59"S, 51º13'48"W). The influence of the pipes diameter, inclination and orientation has been studied as well as the thermal comfort indoors. The system is efficient for thermal building conditioning and air renovation. At small depths, the ground presents a more steady temperature than the air, close to the annual average temperature (18ºC), cooling the air in hot days, warming it in cold nights – a similar effect is expected on a yearly period. The main factor responsible to the air flow is the outside wind, but the air temperature differences between the pipes, the room and the solar chimney edges are very relevant. The room ventilation reduces its thermal delay without interfering with its thermal performance, and also shows a decrease in its internal humidity.
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Williamson, Nicholas J. „Numerical modelling of heat and mass transfer and optimisation of a natural draft wet cooling tower“. University of Sydney, 2007. http://hdl.handle.net/2123/4123.
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Doctor of PhilosophyThe main contribution of this work is to answer several important questions relating to natural draft wet cooling tower (NDWCT) modelling, design and optimisation. Specifically, the work aims to conduct a detailed analysis of the heat and mass transfer processes in a NDWCT, to determine how significant the radial non-uniformity of heat and mass transfer across a NDWCT is, what the underlying causes of the non-uniformity are and how these influence tower performance. Secondly, the work aims to determine what are the consequences of this non-uniformity for the traditional one dimensional design methods, which neglect any two-dimensional air flow or heat transfer effects. Finally, in the context of radial non-uniformity of heat and mass transfer, this work aims to determine the optimal arrangement of fill depth and water distribution across a NDWCT and to quantify the improvement in tower performance using this non-uniform distribution. To this end, an axisymmetric numerical model of a NDWCT has been developed. A study was conducted testing the influence of key design and operating parameters. The results show that in most cases the air flow is quite uniform across the tower due to the significant flow restriction through the fill and spray zone regions. There can be considerable radial non-uniformity of heat transfer and water outlet temperature in spite of this. This is largely due to the cooling load in the rain zone and the radial air flow there. High radial non-uniformity of heat transfer can be expected when the cooling load in the rain zone is high. Such a situation can arise with small droplet sizes, low fill depths, high water flow rates. The results show that the effect of tower inlet height on radial non-uniformity is surprisingly very small. Of the parameters considered the water mass flow rate and droplet size and droplet distribution in the rain zone have the most influence on radial noniv uniformity of heat transfer. The predictions of the axisymmetric numerical model have been compared with a one dimensional NDWCT model. The difference between the predictions of tower cooling range is very low, generally around 1-2%. This extraordinarily close comparison supports the assumptions of one dimensional flow and bulk averaged heat transfer implicit in these models. Under the range of parameters tested here the difference between the CFD models predictions and those of the one dimensional models remained fairly constant suggesting that there is no particular area where the flow/heat transfer becomes so skewed or non-uniform that the one dimensional model predictions begin to fail. An extended one dimensional model, with semi-two dimensional capability, has been developed for use with an evolutionary optimisation algorithm. The two dimensional characteristics are represented through a radial profile of the air enthalpy at the fill inlet which has been derived from the CFD results. The resulting optimal shape redistributes the fill volume from the tower centre to the outer regions near the tower inlet. The water flow rate is also increased here as expected, to balance the cooling load across the tower, making use of the cooler air near the inlet. The improvement has been shown to be very small however. The work demonstrates that, contrary to common belief, the potential improvement from multi-dimensional optimisation is actually quite small.
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Williamson, Nicholas J. „Numerical modelling of heat and mass transfer and optimisation of a natural draft wet cooling tower“. Thesis, The University of Sydney, 2008. http://hdl.handle.net/2123/4123.
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The main contribution of this work is to answer several important questions relating to natural draft wet cooling tower (NDWCT) modelling, design and optimisation. Specifically, the work aims to conduct a detailed analysis of the heat and mass transfer processes in a NDWCT, to determine how significant the radial non-uniformity of heat and mass transfer across a NDWCT is, what the underlying causes of the non-uniformity are and how these influence tower performance. Secondly, the work aims to determine what are the consequences of this non-uniformity for the traditional one dimensional design methods, which neglect any two-dimensional air flow or heat transfer effects. Finally, in the context of radial non-uniformity of heat and mass transfer, this work aims to determine the optimal arrangement of fill depth and water distribution across a NDWCT and to quantify the improvement in tower performance using this non-uniform distribution. To this end, an axisymmetric numerical model of a NDWCT has been developed. A study was conducted testing the influence of key design and operating parameters. The results show that in most cases the air flow is quite uniform across the tower due to the significant flow restriction through the fill and spray zone regions. There can be considerable radial non-uniformity of heat transfer and water outlet temperature in spite of this. This is largely due to the cooling load in the rain zone and the radial air flow there. High radial non-uniformity of heat transfer can be expected when the cooling load in the rain zone is high. Such a situation can arise with small droplet sizes, low fill depths, high water flow rates. The results show that the effect of tower inlet height on radial non-uniformity is surprisingly very small. Of the parameters considered the water mass flow rate and droplet size and droplet distribution in the rain zone have the most influence on radial noniv uniformity of heat transfer. The predictions of the axisymmetric numerical model have been compared with a one dimensional NDWCT model. The difference between the predictions of tower cooling range is very low, generally around 1-2%. This extraordinarily close comparison supports the assumptions of one dimensional flow and bulk averaged heat transfer implicit in these models. Under the range of parameters tested here the difference between the CFD models predictions and those of the one dimensional models remained fairly constant suggesting that there is no particular area where the flow/heat transfer becomes so skewed or non-uniform that the one dimensional model predictions begin to fail. An extended one dimensional model, with semi-two dimensional capability, has been developed for use with an evolutionary optimisation algorithm. The two dimensional characteristics are represented through a radial profile of the air enthalpy at the fill inlet which has been derived from the CFD results. The resulting optimal shape redistributes the fill volume from the tower centre to the outer regions near the tower inlet. The water flow rate is also increased here as expected, to balance the cooling load across the tower, making use of the cooler air near the inlet. The improvement has been shown to be very small however. The work demonstrates that, contrary to common belief, the potential improvement from multi-dimensional optimisation is actually quite small.
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Williamson, Nicholas J. „Numerical modelling of heat and mass transfer and optimisation of a natural draft wet cooling tower“. Phd thesis, School of Aerospace, Mechanical and Mechatronic Engineering, 2008. http://hdl.handle.net/2123/4035.
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SESINI, PAULA A. „Analise das instabilidades termo-hidraulicas em um circuito operando em regime de circulacao natural bi-fasico“. reponame:Repositório Institucional do IPEN, 1998. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10686.
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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PENDSE, RAHUL S. „Incorporation of Natural Ventilation in a Commercial HVAC System Using Temperature as a Comfort Parameter“. University of Toledo / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1083031216.
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Jacobs, Louis Egbert. „A conceptual study of a natural circulation cooling loop for a PWR containment / Jacobs L.E“. Thesis, North-West University, 2011. http://hdl.handle.net/10394/7608.
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The removal of heat from the containment building is an important consideration in the design of a
nuclear power plant. In this investigation a simple rectangular natural circulation loop was simulated to
determine whether it could possibly be used to remove usable quantities of heat from a containment
building. The loop had a vertical pipe on the inside and outside of the containment building. These pipes
acted as heat exchangers. Single phase and two phase cases were simulated by imposing a
temperature on the respective vertical leg pipe walls and determining the heat absorption from the
containment building. The heat was conveyed from the inside of the building to the outside via the
natural circulation phenomenon.
A literature study was done to cover topics relevant to this investigation. A theoretical model using
conservation equations and control volumes was derived. This model was based largely on knowledge
gleaned from the literature study. The theoretical model was a simple homogenous model, which was
sufficiently detailed for a conceptual investigation. The theoretical model was then manipulated into a
form suitable for use in a computer simulation program. Simplifications were made to the simulation
model and underlying theory due to the nature of the investigation. The simulation model was validated
against published experimental results.
During the simulation phase a number of cases were investigated. These cases were divided into base
cases and parametric studies. During the base case simulations the change of key fluid variables along
the loop was examined. During the parametric studies the hot and cold leg inside wall temperatures, loop
geometry and pipe diameter were varied. The effect of these parameters on the heat absorption from the
containment was determined.
The simulations showed that with the current assumptions about 75 to 120 of the natural circulation
loops are needed depending on their geometry and containment conditions. The heat removal rates that
were calculated varied from 50 kW to 600 kW for a single loop. As explained in the final chapter, there
are many factors that influence the results obtained. The natural circulation concept was deemed to be
able to remove usable quantities of heat from the containment building.Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2012.
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Willson, Thomas D. „A study of natural convection cooling of multiple discrete heat sources in a vertical channel“. Thesis, Monterey, California. Naval Postgraduate School, 1988. http://hdl.handle.net/10945/23126.
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This thesis is a study of missile and target parameters used in second and third order modeling of the tracking subsystem used in radar guided guided missiles. Guidance methods are analyzed to determine which method is optimum in a search for an ideal missile. Target parameters which have an effect on the missile tracking system are analyzed and a target acceleration probability model is discussed. A two dimensional third order tracking model is simulated utilizing a Kalman filter for target parameter estimation and prediction. Linear second and third order tracking models are simulated and compared with the third order Kalman filter tracker. This thesis concludes that a proportional navigation guidance method, with a non linear third order tracking Kalman filter, is the better model. Benefits of using a non linear third order Kalman filter may not overide the cost and complexity of implementation of the model
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Paje, Rufino A. „Experiments on liquid immersion natural convection cooling of leadless chip carriers mounted on ceramic substrate“. Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/25932.
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Theunissen, Ruhan. „Investigation of a radiative cooling system with natural circulation for regulating a heat sink / Theunissen R“. Thesis, North-West University, 2011. http://hdl.handle.net/10394/7593.
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The global energy demand has seen a significant increase over the past decade. Our inseparable need for energy has created a number of serious concerns. The most important concern is the environmental impact of our energy generating methods. Another looming concern is our global fossil fuel resources that are diminishing progressively. These two major concerns have turned attention to research and development of energy efficient and alternative energy systems.
A field of alternative energy that has been untapped is nocturnal radiative cooling. The idea behind this is to utilise the cooling effect between a hot surface and the night sky. The setup is similar to that of a solar water heating system but is used for cooling instead of heating.
Previous studies on radiative cooling systems have all focussed on forced circulation systems. The aim of this study is to analyse the performance of a natural circulating system. The current knowledge on radiative cooling systems is limited and experimental research is often a costly and time consuming exercise. As a result it is difficult to get an understanding of the performance of a radiative cooling system in various operating environments. The aim of this study is to overcome this limitation by developing a theoretical model to simulate the performance of a natural circulating radiative cooling system.
A natural circulating solar water heater model was used as a basis for the natural circulating radiative cooling model. A night sky radiation model replaced the solar radiation component to give the radiative heat transfer of the panel to the night sky. Fundamental heat transfer and fluid flow theories also formed part of the model.
The theoretical model was able to give realistically accurate predictions compared to data from an experimental setup. The model made it possible to study the impact of various parameters on the system performance without the constraints of experimental setups. The performance of a natural circulating radiative cooling system was simulated over a year under different operating climates by using historical weather data.
The results obtained with the help of the model indicated that natural circulating radiative cooling is indeed able to provide a sufficient cooling effect that can be utilised in a practical manner. This study gives indication that radiative cooling systems are worthy of further development to ensure that it forms part of the current line–up of alternative energy systems.Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2012.
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Li, Y. „Thermal performance analysis of a PCM combined solar chimney system for natural ventilation and heating/cooling“. Thesis, Coventry University, 2013. http://curve.coventry.ac.uk/open/items/0bca9412-8b49-4d3c-84e5-453e315d4c6b/1.
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Solar chimney is an important passive design strategy to maximize solar gain to enhance buoyancy effect for achieving adequate air flow rate and a desired level of thermal comfort inside a building. Therefore, solar chimney has the potential advantages over mechanical ventilation systems in terms of energy requirement, economic and environmental benefits. The main aim of this project is to study the technical feasibility of a solar chimney incorporating latent heat storage (LHS) system for domestic heating and cooling applications. The research work carried out and reported in this thesis includes: the development of a detailed theoretical model to calculate the phase change material (PCM) mass for solar chimney under specific climatic condition, the development of a CFD model to optimise the channel depth and the inlet and outlet sizes for the solar chimney geometry, experimental and numerical investigations of the thermal performance of the proposed system using a prototype set-up, a parametric study on the proposed system to identify significant parameters that affect the system performance was carried out by using the verified numerical model. The numerical and experimental study showed that the numerical model has the ability to calculate the PCM mass for the proposed system for the given weather conditions. The optimum PCM should be selected on the basis of its melting temperature, rather than its other properties such as latent heat. The experimental work on the thermal performance of the proposed system has been carried out. The results indicated that the LHS based solar chimney is technically viable. The outlet air temperature and the air flow rate varied within a small range during phase change transition period which are important for a solar air heating system. A numerical model was developed to reproduce the experimental conditions in terms of closed mode and open mode. The model results were in a close agreement with the experimental results particularly the simulated results for the discharging process. With the verified model, a comprehensive parametric analysis intended to optimise the thermal performance of proposed the system was performed. The results analysed are quantified in terms of charging/discharging time of the PCM, temperature difference between outlet air and inlet air of the solar chimney, and mass flow rate of the chimney, which are the most important quantities of the proposed system.
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MACEDO, LUIZ A. „Atuação de um sistema passivo de remoção de calor de emergência de reatores avançados em escoamento bifásico e com alta concentração de não-condensáveis“. reponame:Repositório Institucional do IPEN, 2008. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11622.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
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Radosavljevic, Dejan. „The numerical simulation of direct-contact natural-draught cooling tower performance under the influence of cross-wind“. Thesis, Imperial College London, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261786.
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Thompson, Ronald G. Jr. „Natural convection heat transfer studies of simulated and actual electronic components using dielectric liquids for immersion cooling“. Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23978.
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Approved for public release; distribution is unlimitedTwo experimental studies of the natural convection characteristics of heated protrusions immersed in dielectric liquids were conducted. the first study used a three by three array of simulated 20 pin dual-in-line chips which were made from aluminum blocks with full heaters. The second set of experiments used a three by three array of thermal evaluation devices mounted on an alumina substrate. The devices were 8.9 mm square chips which contained resistors and a type of temperature sensing transistor. Both studies used an insulated Plexiglas enclosure with a top mounted heat exchanger maintained at a constant 10 degrees C. Each array was mounted on a Plexiglass substrate, and spacers were used to vary the horizontal distance from the components to the enclosure wall. Five separate enclosure widths were used, with a maximum spacing of 40 mm. The vertically oriented aluminum blocks were tested with FC-71 and power levels ranging from 0.115 W/chip to 2.9 W/chip. The non-dimensional data obtained was used to develop an empirical correlation which predicts Nusselt number as a function of Rayleigh number and enclosure width. The correlation was accurate to within 4% of the array averaged data, and the maximum uncertainty in the Nusselt number was 7.4%. The actual electronic components were tested with FC-71, FC-43 and FC-75. Power levels ranged from 0.34 W/chip to 1.48 W/chip. Again, the data obtained was used to develop a Nusselt number correlation. In this case a better correlation of the data was achieved using Grashof number and enclosure width. The correlation is accurate to within 2% of the array averaged data. The maximum Nusselt number uncertainty was 4.7%
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Gaiser, Alfred O. „Natural convection liquid immersion cooling of high density columns of discrete heat sources in a vertical channel“. Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/26097.
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Fronk, Brian Matthew. „Modeling and Testing Of Water-Coupled Microchannel Gas Coolers for Natural Refrigerant Heat Pumps“. Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16247.
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An experimental and analytical investigation on a water-coupled microchannel gas cooler was conducted in this study. With a relatively low critical temperature (31.1°C/89.9°F) and pressure (73.7 bar/1070 psi), CO2 is a supercritical fluid on the high side of a vapor compression cycle under warmer ambient conditions. This results in a non-isothermal heat rejection through the component known as the gas cooler. The large temperature glide in the heating of tap water matches well with the supercritical temperature glide of carbon dioxide. Unlike in a condensation process, here the non isothermal heat rejection can be used to advantage in a counterflow gas cooler, in which the water outlet temperature can rise to the desired high value. This minimizes temperature pinch and keeps gas cooler size economical. The focus of this thesis was to develop and experimentally validate a heat transfer model for a water-coupled microchannel gas cooler. The heat exchanger was tested in a small capacity experimental heat pump system. The heat pump system was designed to simulate conditions for heating domestic tap water to a usable temperature. A matrix of test points varying refrigerant inlet temperature, refrigerant mass flow rate, water inlet temperature and water volumetric flow rate were used to characterize the performance of the heat exchanger and validate the model.
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Bradley, Joseph Matthew. „Natural convection cooling of a three-by-three array of leadless chip carrier packages in a dielectric liquid“. Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA282298.
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Thesis (M.S. in Mechanical Engineering and Mechanical Engineer) Naval Postgraduate School, March 1994.Thesis advisor(s): Yogendra Joshi. "March 1994." Includes bibliographical references. Also available online.
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Osman, Medhat. „Evaluating and enhancing design for natural ventilation in walk-up public housing blocks in the Egyptian desert climatic design region“. Thesis, University of Dundee, 2011. https://discovery.dundee.ac.uk/en/studentTheses/5f07394c-7eb6-4fac-8469-ecea3233dc34.
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This work is concerned with evaluating and studying the possibilities of enhancing natural ventilation performance and its use as a passive cooling strategy in walk-up public housing blocks within the Egyptian desert climatic region. This research attempts to maximize the benefits from the vast investments made in housing projects in Egypt through providing thermally comfortable housing prototypes that could use by contrast less energy for cooling purposes. This is considered essential in the light of the current concerns about energy all over the world. Egypt was devided to seven different climatic regions by the Egyptian organization for energy conservation and planning. The Egyptian desert climatic region, which was chosen as the research context, is the largest climatic region of Egypt. Most of the Egyptian new cities that accommodate the majority of the recent public housing projects are located within this desert climatic region that represents the typical hot arid climate characteristics. Nationally, the problem of the misuse of the housing prototyping was spotted. According to previous researchers, the same basic prototypical designs are being built all over the country without giving enough consideration to the actual effects of different climates and the diversity in the residents social needs. Regionally, within the Egyptian desert climatic region, the harsh climatic conditions rate the problem of achieving thermal comfort within these housing prototypes as the most urgent problem that needs to be examined in depth. A pilot study that used observation and monitoring methods was conducted in the New Al-Minya city (The representative city of the desert climatic design region) in order to closely investigate this problem and identify its dimensions. The results confirmed thermal discomfort conditions of the housing prototypes built there, especially during the hot summer period. The passive design strategies analysis of the climatic context indicated that night purge ventilation is the most effective passive strategy that could enhance thermal comfort. These results go along with the rule of natural ventilation in reducing the used energy for cooling and the actually massive national income spent on these housing prototypes encourage this work so to concentrate on natural ventilation. Different studies using multi-approaches research techniques were employed in order to achieve the main aim of the research. These techniques included; literature review, monitoring, questionnaire and computer simulation.A critical literature review was conducted including; the physical science of natural ventilation, its strategic design as well as the design measures that control natural ventilation and the airflow in; the macro, intermediate and micro design levels. The results of the investigations were discussed and interpreted in the light of this review. A representative case study was chosen for the study. The natural ventilation performance in the case study was quantitatively and qualitatively evaluated through conducting field objective and subjective assessment respectively. In evaluation study, the thermal performance of the case study under different ventilation scenarios was monitored, the airflow inside it was simulated using CFD (computational fluid dynamics) software “FloVent” and a sample of residents were questioned. This study identified many problems associated natural ventilation uses and indicated its poor performance within the case study. A number of design measures were formulated based on the literature review and considering the evaluation study results along with the research context nature. The proposed natural ventilation design measures were applied to the case studies and their effectiveness in terms of enhancing the natural ventilation performance was quantified using “FloVent”. Results reported that the proposed natural ventilation design measures could significantly enhance the natural ventilation performance inside the case study quantitatively and qualitatively. This in turn maximizes the potential of providing thermal comfort by using both natural ventilation strategies; comfort ventilation and night purge ventilation. However, all the applied measures could not achieve neither an acceptable airspeed at any of the case study spaces nor a good airflow circulation at some of its spaces. It can be concluded that the current design of the case study can not achieve quality airflow without the use of the mechanical assisted ventilation. In general, it seems very difficult to optimize the air velocity within all spaces in a very dense multi-space design like this case study. A new design that considers natural ventilation and its drivers has to be introduced.
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Mehrtash, Mehdi. „Numerical Investigation Of Natural Convection From Plate Finned Heat Sinks“. Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613530/index.pdf.
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Finned heat sink use for electronics cooling via natural convection is numerically investigated. An experimental study from the literature that is for vertical surfaces is taken as the base case and the experimental setup is numerically modeled using commercial CFD software. The flow and temperature fields are resolved. A scale analysis is applied to produce an order-of-magnitude estimate for maximum convection heat transfer corresponding to the optimum fin spacing. By showing a good agreement of the results with the experimental data, the model is verified. Then the model is used for heat transfer from inclined surfaces. After a large number of simulations for various forward and backward angles between 0-90 degrees, the dependence of heat transfer to the angle and Rayleigh number is investigated. It is observed that the contributions of radiation and natural convection changes with the angle considerably. Results are also verified by comparing them with experimental results available in literature.
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Rocha, André Damiani 1977. „Convecção natural em placa nas posições vertical e inclinada contendo elementos protuberantes aquecidos“. [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263471.
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Orientador: Marcelo Moreira GanzarolliDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: No presente trabalho o resfriamento por convecção natural de uma placa plana, disposta em um meio infinito, contendo elementos protuberantes aquecidos e distribuídos uniformemente sobre uma das paredes da placa é analisado experimentalmente sob a condição de aquecimento uniforme. A parede oposta da placa de teste é isolada utilizando um aquecedor de proteção que possui as mesmas dimensões da placa de teste. Os testes experimentais utilizam um aparato com placa de fibra de vidro contendo elementos protuberantes de alumínio de seção quadrada, em cujo interior passa uma resistência. A placa de teste é posicionada em uma estrutura de ferro que foi projetada para permitir a variação da inclinação da placa. As trocas de calor por condução, através da placa de fixação dos elementos protuberantes, e por radiação, entre as superfícies das protuberâncias foram consideradas. Testes experimentais foram realizados variando a potência entre 30 e 70W para uma variação angular entre 0° e 60° a partir da posição vertical. Do presente trabalho concluiu-se que foi possível avaliar o número de Nusselt em função do número de Rayleigh para placa protuberante e inclinada através de uma única correlação, desde que a componente da aceleração gravitacional paralela à placa seja utilizada no cálculo do número de Rayleigh modificado
Abstract: In the present work, cooling with natural convection of a plate, disposed in an infinite middle, containing protruding heated elements and distributed evenly on one of the walls of the plate it is analyzed experimentally about the condition of uniform heating. The opposite wall of the test plate is considered isolated using a guard heater that possesses the same dimensions that the test plate. Experimental tests are performed in a apparatus containing fiberglass plates with protruding, square section, aluminum elements. The test plate is positioned in a structure of iron that was projected to allow the angular variation of the plate. The conduction heat transfer through the plate and radiation heat transfer among the surfaces of the protruding were considered. Tests were accomplished varying the power between 30 and 70W for an angular variation between 0° and 60° starting from the vertical position. The investigation shows that it is possible to evaluate Nusselt number as a function of the modified Rayleigh number for inclined and protruding plate through an only correlation, since to component of the gravitational acceleration parallel to the plate it is used in the calculation ofthe modified Rayleigh number
Mestrado
Termica e Fluidos
Mestre em Engenharia Mecânica
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Goulart, Solange V. G. „Thermal inertia and natural ventilation : optimisation of thermal storage as a cooling technique for residential buildings in Southern Brazil“. Thesis, Open University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.418513.
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Eriksson, Rebecca. „Legionella i kyltorn : Enkätundersökning gällande kommuners och länsstyrelsers tillsyn på kyltorn och behovet av ökad prioritering“. Thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-153228.
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If cooling towers are poorly maintained there is a risk of microbial growth such as Legionella which in turn might spread via aerosols and infect humans. This may lead to an outbreak of legionnaires’ disease. The purpose of this study was to highlight the risks of Legionella and cooling towers along with investigating the legal responsibility of businesses and supervision authorities in this regard. The study also investigated whether business should be obligated to register their cooling towers at supervising authorities. The study was partly based on a survey which was sent to Sweden’s 290 municipalities and 21 county administration boards to investigate their knowledge regarding Legionella and cooling towers and if they had inventoried which of their facilities that uses cooling towers. The results of the survey showed that 16% of the municipalities and none of the county administration board had inventoried which of their facilities that uses cooling towers. Half of the municipalities do not have any knowledge if any of their facilities uses cooling towers. Moreover, 45% of the municipalities and 30% of the county administration boards consider that business should register their cooling towers. The results showed that many of Sweden’s municipalities and county administration boards have shortcomings in their knowledge and supervision. Legislation and priorities need to be assessed and regulatory guidance from the Public Health Agency of Sweden is necessary for future progress.
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Pesic, Nikola. „Geo-climatic potential for advanced natural ventilation comfort cooling approach in mid-rise office buildings in the north-western Mediterranean“. Doctoral thesis, Universitat Politècnica de Catalunya, 2020. http://hdl.handle.net/10803/670793.
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The objective of this investigation is to evaluate the geo-climatic potential for comfort cooling energy savings in mid-rise office buildings applying advanced natural ventilation (ANV) approach based on the stack-effect. The region of interest is the Mediterranean coastline of Catalonia with selected reference geographical locations—the cities of Barcelona, Terrassa and Tarragona. In the first part of this research is evaluated the climatic potential for natural ventilation (CPNV) for each location, as a theoretical level of availability of natural ventilation (NV) based on the model of adaptive thermal comfort. For a comparison of geo-climatic potentials in a wider regional context, additional reference locations are chosen along the Northern Mediterranean: Valencia, Marseille, Rome, Koper, Split, Athens and Nicosia. Generated results confirm that NV is feasible mainly from April to October while in July and August is considerably limited due to unfavourable climate conditions. The second part of the work examines cooling energy savings of the hypothetical mid-rise office-type building model “A”. Applied building performance simulations (BPS) demonstrates achieved total yearly cooling energy savings in the region of Catalonia between 22% and 51%. The same model positioned along the Northern Mediterranean displays cutting in yearly cooling energy loads in a wider range—from 6% to 51%.The following section evaluates levels of climate change vulnerability applying climate scenarios for the selected time-slices—the years 2050 and 2080. It is indicated that the potential of ANV will be reduced close to zero in July and August in 2080. However, the introduction of selected assisted cooling techniques demonstrates that this impact can be absorbed approximately back to the previously evaluated scale in the horizon of 2050. In the last part of the investigation, the new defined building model “B” displays an improvement of comfort cooling energy efficiency: selected NV techniques are merged in order to take advantage of lower nocturnal outdoor temperatures by passive means, whose potential is reflected on the decrease of active day-time cooling loads. For this purpose, the positioned model in Barcelona achieves the yearly reduction of cooling energy loads by 65% in present-time weather conditions. At the conclusion, under projected climate configurations for 2050 and 2080, in Barcelona Terrassa and Tarragona, the series of BPS displays a higher level of climate resilience and the overall reduction of cooling energy loads within 53% and 59%.
The key-contribution and the novelty of this research is in the performed series of experimental BPS of the building model “A” where are detected ANV system’s weaknesses as a result of estimated unfavourable climate effects. Relative to observed limited cooling performances, ANV is shifted from an autonomous comfort cooling concept to being a part of a complex ventilative system with specific day- and night-time cycles. Such a new established design approach based on dynamic heat storage is associated with an introduction of lower nocturnal and early morning outdoor air temperatures, as being less affected with future regional climate change. An achieved advantageous momentum in energy performances is categorized through strengths and opportunities. Thereby, the building model “B”, the outcome of this investigation, represents the climate responsive building form with an integrated climate sensitive comfort cooling system, which delivers a higher level of energy efficiency—seen as an acquired factor of resilience towards estimated climate change threats. Such a conceptualised hypothetical building prototype may prove to be a beneficial contributor in the current process of rapid deployment of renewable energy sources in the regional building sector, observed as well from the perspective of the ongoing European Union’s energy transition.El objetivo de esta investigación es evaluar el potencial geo-climático para el ahorro de energía de enfriamiento de confort en los edificios de oficinas de mediana altura aplicando el concepto de ventilación natural avanzada (ANV). El enfoque es en la costa Mediterránea de Cataluña y las ubicaciones geográficas seleccionadas: Barcelona, Terrassa y Tarragona. La primera parte de investigación evalúa el potencial climático de ventilación natural (CPNV), un nivel teórico de disponibilidad de ventilación natural (NV) aplicando el modelo de confort térmico adaptativo. Para una comparación de los potenciales geo-climáticos en un contexto regional más amplio, están elegidas las ubicaciones a lo largo del Mediterráneo Norte: Valencia, Marsella, Roma, Koper, Split, Atenas y Nicosia. Los resultados confirman que NV es factible principalmente desde abril hasta octubre, mientras que en julio y agosto es considerablemente limitada. La segunda parte del trabajo examina los ahorros de energía de enfriamiento de un hipotético modelo “A” del edificio de oficinas de media altura. Las simulaciones de rendimiento de edificios (BPS) en la región de Cataluña demuestran una reducción anual de cargas de enfriamiento entre 22% y 51%. El mismo modelo posicionado a lo largo del Mediterráneo Norte muestra la reducción de las cargas anuales en un rango más amplio, entre 6% y 51%. La siguiente sección evalúa los niveles de vulnerabilidad al cambio climático aplicando escenarios climáticos para los años 2050 y 2080. Se indica que el potencial de ANV se reducirá cerca de cero en julio y agosto de 2080. Sin embargo, la introducción de unas técnicas de enfriamiento asistidas demuestra que ese impacto puede ser absorbido aproximadamente a la escala previamente evaluada en el horizonte de 2050. La última parte de investigación exhibe que el modelo “B” tiene un mejor nivel de la eficiencia energética del enfriamiento de confort: se fusionan técnicas de NV seleccionadas para aprovechar las temperaturas exteriores nocturnas más bajas por medios pasivos, cuyo potencial se refleja sobre la disminución de las cargas de enfriamiento activo diurno. Para este propósito, el modelo posicionado en Barcelona consigue la reducción anual de las cargas de enfriamiento en un 65% en las condiciones meteorológicas actuales. En conclusión, bajo las configuraciones climáticas proyectadas para 2050 y 2080, en Barcelona, Terrassa y Tarragona, la serie de BPS muestra un mayor nivel de resiliencia climática con la reducción de las cargas de enfriamiento entre 53% y 59%. El aporte clave de la investigación se encuentra en BPS experimentales del modelo “A” donde se detectan las debilidades del sistema ANV como consecuencia del cambio climático estimado. En relación con los rendimientos de enfriamiento limitados, ANV se cambia de un concepto autónomo a ser parte de un sistema de ventilación más complejo con los ciclos específicos diurnos y nocturnos. Este nuevo enfoque de diseño establecido basado en el almacenamiento dinámico de calor se asocia con una introducción del aire exterior con temperaturas más bajas durante la noche y las primeras horas de la mañana, como menos afectado por el futuro cambio climático regional. Un impulso ventajoso logrado en el desempeño energético se categoriza a través de las fortalezas y oportunidades. Por lo tanto, el modelo "B" representa la forma del edificio receptivo al clima con un sistema de enfriamiento de confort integrado sensible, lo que ofrece un mayor nivel de eficiencia energética, visto también como un factor adquirido de resiliencia frente a las amenazas estimadas del cambio climático. Tal prototipo de edificio hipotético puede resultar como un contribuyente beneficioso en el proceso actual de despliegue rápido de fuentes de energía renovables en el sector de la construcción regional, observado también desde la perspectiva de la transición energética en curso de la Unión Europea
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Kloppers, Johannes Christiaan. „A critical evaluation and refinement of the performance prediction of wet-cooling towers“. Thesis, Link to the online version, 2003. http://hdl.handle.net/10019.1/1476.
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Solmus, Ismail. „An Experimental Study On The Performance Of An Adsorption Cooling System And The Numerical Analysis Of Its Adsorbent Bed“. Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613973/index.pdf.
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In this thesis, firstly, the equilibrium adsorption capacity of water on a natural zeolite at several zeolite temperatures and water vapor pressures has been experimentally determined for adsorption and desorption processes. Additionally, the modified Dubinin-Astakhov adsorption equilibrium model has been fitted to experimental data and separate correlations are obtained for adsorption and desorption processes as well as a single correlation to model both processes. Experimental results show that the maximum adsorption capacity of natural zeolite is nearly 0.12 kgw/kgad for zeolite temperatures and water vapor pressures in the range 40-150 C and 0.87-7.38 kPa. Secondly, a thermally driven adsorption cooling prototype using natural zeolite-water as working pair has been built and its performance investigated experimentally at various evaporator temperatures. Under the experimental conditions of 45 C adsorption, 150 C desorption, 30 C condenser and 22:5 C, 15 C and 10 C evaporator temperatures, the COP of the adsorption cooling unit is approximately 0.25 and the maximum average volumetric specific cooling power density (SCPv) and mass specific cooling power density (SCP) of the cooling unit are 5.2 kWm-3 and 7 Wkg-1, respectively. Thirdly, in order to investigate the dynamic heat and mass transfer behavior of the adsorbent bed of an adsorption cooling unit, a transient local thermal non equilibrium model that accounts for both internal and external mass transfer resistances has been developed using the local volume averaging method. Finally, the influence of several design parameters on the transient distributions of temperature, pressure and amount adsorbed inside the cylindrical adsorbent bed of an adsorption cooling unit using silica-gel/water have been numerically investigated for the one and two dimensional computational domains. Moreover, validity of the thermal
equilibrium model assumption has been shown under the given boundary and design conditions. Generally, for the conditions investigated, the validity of the local thermal equilibrium and spatially isobaric bed assumptions have been confirmed. To improve the performance of the bed considered, eorts should be focused on reducing heat transfer resistances and intra-particle mass transfer resistances but not inter-particle mass transfer resistances.
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Karlgren, Johansson Mikael, und Kevin Leong. „Auxiliary Heater for Natural Gas Trucks“. Thesis, Linköpings universitet, Maskinkonstruktion, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-139687.
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As alternative fuels are becoming more common, technologies need to adjust to them. Natural gas is one of the alternative fuels that has grown during the latest years in the transport sector. Natural gas consists of around 97 % methane and is the cleanest fossil fuel. The use of natural gas can make it easier to transition to biogas as it has equivalent properties. Today Scania CV AB's trucks fuelled by natural gas are using auxiliary cabin heaters driven by diesel. This means that the natural gas trucks have two fuels on-board the truck. The goal of this project is to find a concept to eliminate the diesel fuel and replace it with an auxiliary cabin heater driven by another energy source. It will improve the heating solution and make it superior from an environmental perspective. The result of the project lead to a short-term solution with an auxiliary heater fuelled by natural gas. A long-term solution is to have a cooperation with a manufacturer to develop a better natural gas auxiliary heater that fulfils more of the requirements in the technical specification. An experiment plan is devised to test parameters out of reach of the project.
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Benedict, Terry J. „An advanced study of natural convection immersion cooling of 3 x 3 array of simulated components in an enclosure filled with dielectric liquid“. Thesis, Monterey, California. Naval Postgraduate School, 1988. http://hdl.handle.net/10945/22860.
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Approved for public release; distribution is unlimited.An experimental study has been conducted to examine the three dimensional natural convection heat transfer from an array of simulated electronic components immersed in a chamber filled with Fluorinert FC-75, a commercially available dielectric liquid. The top and bottom walls of the chamber were maintained at uniform temperature while all other surfaces were insulated. The simulated components were in the form of a 3 x 3 array of discrete protruding aluminum blocks, each with geometrical dimensions of a 20 Pin Dual-inline-Package. The components were electrically powered resulting in a range of energy dissipation levels from 0.1 to 3.1 watts. Flow visualization in steady state was accomplished using Magnesium particles illuminated by a Helium Neon laser plane. Component surface temperature measurements allowed determination of the heat transfer characteristics. Timewise fluctuations of temperature at several locations were measured with increasing power levels. Keywords: Computer programs, Electronic cooling, Protruding heat sources, Flow visualization, Convective heat transfer, Immersion cooling, Dielectric liquids, Theses. (jhd)
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Desai, Chetan Prabhakar. „An experimental and numerical investigation of natural convection in open ended annuli and its application to the cooling of an aircraft brake assembly /“. The Ohio State University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487863429091573.
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Sittmann, Ilse. „Inside-pipe heat transfer coefficient characterisation of a one third height scale model of a natural circulation loop suitable for a reactor cavity cooling system of the Pebble Bed Modular Reactor“. Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6708.
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Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011.ENGLISH ABSTRACT: The feasibility of a closed loop thermosyphon for the Reactor Cavity Cooling System of the Pebble Bed Modular Reactor has been the subject of many research projects. Difficulties identified by previous studies include the hypothetical inaccuracies of heat transfer coefficient correlations available in literature. The aim of the research presented here is to develop inside-pipe heat transfer correlations that are specific to the current design of the RCCS. In order to achieve this, a literature review is performed which identifies reactors which employ closed loop thermosyphons and natural circulation. The literature review also explains the general one-dimensional two-fluid conservation equations that form the basis for numerical modelling of natural circulation loops. The literature review lastly discusses available heat transfer coefficient correlations with the aim of identifying over which ranges and under which circumstances these correlations are considered accurate. The review includes correlations commonly used in natural circulation modelling in the nuclear industry in aims of identifying correlations applicable to the modelling of the proposed RCCS. One of the objectives of this project is to design and build a one-third-height-scale model of the RCCS. Shortcomings of previous experimental models were assessed and, as far as possible, compensated for in the design of the model. Copper piping is used, eliminating material and surface property uncertainties. Several sight glasses are incorporated in the model, allowing for the visual identification of two-phase flow regimes. An orifice plate is used allowing for bidirectional flow measurement. The orifice plate, thermocouples and pipe-in-pipe heat exchangers are calibrated in-situ to minimize experimental error and aid repeatability. Twelve experiments are performed with data logging occurring every ten seconds. The results presented here are limited to selected single and two-phase flow operating mode results. Error analyses and repeatability of experimental measurements for single and two-phase operating modes as well as cooling water mass flow rates are performed, to show repeatability of experimental results. These results are used to mathematically determine the experimental inside-pipe heat transfer coefficients for both the evaporator and condenser sections. Trends in the heat transfer coefficient profiles are identified and the general behaviour of the profiles is thoroughly explained. The RCCS is modelled as a one-dimensional system. Correlations for the friction factor, heat transfer coefficient, void fraction and two-phase frictional multiplier are identified. The theoretical heat transfer coefficients are calculated using the mathematical model and correlations identified in the literature review. Fluid parameters are evaluated using experimentally determined temperatures and mass flow rates. The resulting heat transfer coefficient profiles are compared to experimentally determined profiles, to confirm the hypothesis that existing correlations do not accurately predict the inside-pipe heat transfer coefficients. The experimentally determined coefficients are correlated to 99% confidence intervals. These generated correlations, along with identified and established twophase heat transfer coefficient correlations, are used in a mathematical model to generate theoretical coefficient profiles. These are compared to the experimentally determined coefficients to show prediction accuracy.
AFRIKAANSE OPSOMMING: Die haalbaarheid van ‘n natuurlike sirkulasie geslote lus vir die Reaktor Holte Verkoeling Stelsel (RHVS) van die Korrelbed Modulêre Kern-Reaktor (KMKR) is die onderwerp van talle navorsings projekte. Probleme geïdentifiseer in vorige studies sluit in die hipotetiese onakkuraatheid van hitte-oordrag koëffisiënt korrelasies beskikbaar in literatuur. Die doel van die navorsing aangebied is om binne-pyp hitte-oordrag koëffisiënt korrelasies te ontwikkel spesifiek vir die huidige ontwerp van die RHVS. Ten einde dit te bereik, word ‘n literatuurstudie uitgevoer wat kern-reaktors identifiseer wat gebruik maak van natuurlike sirkulasie lusse. Die literatuurstudie verduidelik ook die algemene een-dimensionele twee-vloeistof behoud vergelykings wat die basis vorm vir numeriese modellering van natuurlike sirkulasie lusse. Die literatuurstudie bespreek laastens beskikbare hitte-oordrag koëffisiënt korrelasies met die doel om te identifiseer vir welke massavloei tempo waardes en onder watter omstandighede hierdie korrelasies as korrek beskou is. Die ontleding sluit korrelasies in wat algemeen gebruik word in die modellering van natuurlike sirkulasie in die kern industrie met die hoop om korrelasies vir gebruik in die modellering van die voorgestelde RHVS te identifiseer. Een van die doelwitte van die projek is om ‘n een-derde-hoogte-skaal model van die RHVS te ontwerp en te bou. Tekortkominge van vorige eksperimentele modelle is geidentifiseer en, so ver as moonlik, voor vergoed in die ontwerp van die model. Koper pype word gebruik wat die onsekerhede van materiaal en opperkvlak eindomme voorkom. Verkseie deursigtige polikarbonaat segmente is ingesluit wat visuele identifikasie van twee-fase vloei regimes toelaat. ‘n Opening plaat word gebruik om voorwaartse en terugwaartse vloeimeting toe te laat. Die opening plaat, termokoppels en hitte uitruilers is gekalibreer in plek om eksperimentele foute te verminder en om herhaalbaarheid te verseker. Twaalf eksperimente word uitgevoer en data word elke tien sekondes aangeteken. Die resultate wat hier aangebied word, is beperk tot geselekteerde enkel- en tweefase vloei meganismes van werking. Fout ontleding en herhaalbaarheid van eksperimentele metings, om die herhaalbaarheid van eksperimentele resultate te toon. Hierdie is gebruik om wiskundig te bepaal wat die eksperimentele binne-pyp hitte-oordrag koëffisiënte is vir beide die verdamper en kondenseerder afdelings. Tendense in die hitte-oordrag koëffisiënt profiele word geïdentifiseer en die algemene gedrag van die profiles is deeglik verduidelik. Die RHVS is gemodelleer as 'n een-dimensionele stelsel. Korrelasies vir die wrywing faktor, hitte-oordrag koëffisiënte, leegte-breuk en twee-fase wrywings vermenigvuldiger word geïdentifiseer. Die teoretiese hitte-oordrag koëffisiënte word bereken deur middle van die wiskundige model en korrelasies wat in literatuur geidentifiseer is. Vloeistof parameters is geëvalueer met eksperimenteel bepaalde temperature en massa-vloei tempos. Die gevolglike hitte-oordrag koëffisiënt profiles is vergelyk met eksperimentele profiele om die hipotese dat die bestaande korrelasies nie die binne-pyp hitte-oordrag koëffisiënte akkuraat voorspel nie, te bevestig. Die eksperimenteel bepaalde koëffisiënte is gekorreleer en die gegenereerde korrelasies, saam met geïdentifiseerde twee-fase hitte-oordrag koëffisiënt korrelasies, word gebruik in 'n wiskundige model om teoretiese koëffisiënt profiele te genereer. Dit word dan vergelyk met die eksperimenteel bepaalde hitteoordrag koëffisiënte om die akkuraatheid van voorspelling te toon. Tekortkominge in die teoretiese en eksperimentele model word geïdentifiseer en aanbevelings gemaak om hulle aan te spreek in die toekoms.
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Jensen, Mark. „Energy Process Enabled by Cryogenic Carbon Capture“. BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/5711.
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Global climate change concerns help shape current environmental regulations, which increasingly seek to reduce or capture CO2 emissions. Methods for capturing CO2 emissions from energy processes have been the focus of numerous studies to provide support for those seeking to reduce the environmental impact of their processes. This research has (1) simulated a baseline case of energy-storing cryogenic carbon capture for implementation on a 550 MWe coal fired power plant, (2) presented a novel cryogenic carbon capture process for removing CO2 from natural gas down to arbitrary levels, (3) presented a natural gas liquefaction process that has the ability to be highly CO2 tolerant, and (4) developed theoretical models and their experimental validation of CO2 capture predictions for all aforementioned processes.
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Loubser, Karl Albie. „An experimental study of an inherently-safe, natural circulating, flash-tube type system for a nuclear reactor steam supply concept“. Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/96050.
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Thesis (MEng) -- Stellenbosch University, 2014.ENGLISH ABSTRACT: This project investigates aspects of a novel inherently safe nuclear power steam supply system as safety is of paramount importance. The system envisaged has unique features namely: a) a two-phase flow flash-tube type natural circulating primary loop (also the secondary radioactive particle containment); b) a twophase flow thermosyphon heat pipe type heat exchanger secondary loop is used to transfer heat from the primary loop to the steam generators, thereby physically separating the two flow streams from one another; c) a natural convection air cooled condenser for the removal of the reactor’s residual heat; d) a unique core using TRISO type fuel (acting as the primary radioactive particle containment) with life of at least 8.9 years; e) a steel containment vessel acting as a tertiary radioactive product containment; f) a concrete containing structure with air vents to allow air to pass over the main steel containment vessel for cooling purposes in the case of an emergency, and for the removal of parasitic heat during operation. In particular the primary and secondary loops of the proposed system are investigated. This is done by design, construction and testing of a small scale experimental set-up of the primary and secondary loops as well as the development of theoretical models for the two loops. A literature survey focusing on nuclear technology, thermosyphon loops, natural circulating loop instabilities, heat pipes, and two-phase flow modelling is presented to give a brief overview of the technologies as well as tools used in the work undertaken. Observations of the inside flow behaviour of the primary loop experimental set-up were made possible by windows providing many insights into the inner workings, such as plume formation and geysering. The transient response of the secondary heat pipe loop start-up is also investigated. A thermal resistance theoretical model was developed for the secondary loop using heat transfer formulae from theory as well as experimentally semiempirical correlated formula. Different states of operation of the secondary loop were observed during testing with the theoretical model of the condensing regime correlating well, two-phase regime correlating acceptably and liquid regime correlating poorly to experimental results and thus were modelled using an experimentally determined overall heat transfer coefficient. The secondary loop model of the liquid regime is coupled with the primary loop theoretical model to predict the system’s performance. A homogeneous, one-dimensional, simple theoretical model for the primary loop was derived and computer simulated. The results did not compare well with experimental results for single phase flow and failed to capture the onset of two-phase flow. The assumptions of one dimensional model with a unidirectional flow, a hydrostatic pressure problem, a constant volumetric flow rate and the inability of the implementation of the code to handle expansion are noted as some of the flaws in the theoretical model. The following recommendations are made: a more advanced design of the pressuriser should be incorporated into the experiment; the secondary loop’s theoretical model should be characterised under a broader set of operating conditions; the computer program can be used as the basis for further research and implementation of alternative solution algorithms and models.
AFRIKKANSE OPSOMMING: Hierdie projek ondersoek aspekte van ’n ongewone, essensieel veilige kernkrag stoomtoevoer-stelsel, omdat veiligheid van kardinale belang is. Die stelsel wat voorgestel is, het unieke eienskappe, naamlik: a) ’n twee-fasevloei flits-buistipe natuurlik sirkulerende primêre lus (wat ook die sekondêre inperking van radioaktiewe materiaal bevat); b) ’n twee-fasevloei termo-heweleffek sekondêre lus hitte-pyp hitte-uitruiler word gebruik om die hitte vanaf die primêre lus oor te dra na die stoomkragopwekkers en daardeur word die twee strome se vloei fisies geskei van mekaar; c) ’n natuurlike konveksie lugverkoelde kondensor word gebruik vir die verwydering van die reaktors se oortollige hitte; d) ’n unieke kern gebruik TRISO-tipe brandstof (wat as die primêre inperking van radioaktiewe materiaal optree) met ’n lewe van minstens 8.9 jaar; e) ’n inperkingshouer van staal wat optree as ’n tersiêre radioaktiewe produkhouer; f) ’n betonstruktuur met lugventilasie om toe te laat dat lug oor die hoof staalhouer vloei vir verkoeling in ’n noodgeval, en vir die verwydering van parasitiese hitte tydens werking. Hoofsaaklik word die primêre en sekondêre lusse van die voorgestelde stelsel ondersoek. Dit word gedoen deur die ontwerp, konstruksie en die toets van ’n eksperimentele opstelling van die primêre en sekondêre lusse op klein skaal, sowel as die ontwikkeling van teoretiese modelle vir die twee lusse. ’n Literatuurstudie wat fokus op kerntegnologie, termo-heweleffeklusse, natuurlik sirkulerende lus instabiliteit, hitte-pype, en twee-fase vloeimodellering word aangebied om ’n kort oorsig te gee van die tegnologie, sowel as gereedskap gebruik in die werk wat onderneem is. Om die interne vloeigedrag van die primêre lus se eksperimentele opstelling waar te neem, word daar gebruik gemaak van vensters wat dien as ’n manier om die innerlike werking van die proses soos pluimvorming en die kook van die water in die warmwaterkolom te toon. Die oorgangsreaksie van die sekondêre hittepyplus aanvangs is ook ondersoek. ’n Teoretiese termiese weerstandmodel is ontwikkel vir die sekondêre lus met behulp van hitte-oordragformules waarvoor hitte-oordragteorie gebruik is, wat met eksperimentele semi-empiriese formules gekorreleer is. Verskillende toestande van die sekondêre lus se werking is waargeneem gedurende die toetse. Die teoretiese model het goed met die kondensasiestaat gekorreleer, terwyl by die twee-fasewerkswyse aanvaarbare korrellasies aangetref is en die uiteindelike vloeitoestand swakker gekorrelleer het met eksperimentele resultate en dus gemodelleer is met behulp van die NTU-effektiwiteitsmetode. Die sekondêre lusmodel van die vloeistoftoestand is gekoppel met die primêre lus teoretiese model om die werking van die stelsels te voorspel. ’n Homogene een-dimensionele eenvoudige teoretiese model van die primêre lus is afgelei en ’n rekenaar simulasie is uitgevoer. Die resultate vergelyk nie goed met die eksperimentele resultate vir enkelfasevloei en kon nie die aanvang van twee-fasevloei beskryf nie. Die aannemings van ’n een-dimensionele model met eenrigting vloei, ’n hidrostatiese druk probleem, ’n konstant volumetries vloeitempo en die onvermoë van die implementering van die kode om uitbreiding te hanteer is bekend as ’n paar van die foute in die teoretiese model. Die volgende aanbevelings word gemaak: ’n meer gevorderde ontwerp van drukreëlaar moet in die eksperiment ingesluit word; die sekondêre lus se teoretiese model moet gekenmerk word onder ’n wyer stel bedryfsomstandighede, en die rekenaar program kan gebruik word as die basis vir verdere navorsing en die implementering van alternatiewe algoritmes en modelle.
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Aytar, Erol. „Natural convection immersion cooling of an array of heated protrusions in an enclosure filled with dielectric liquid : effects of enclosure width and fluid Prandtl number“. Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28387.
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