Dissertations / Theses on the topic 'Diffusion cooling'

Solar thermal driven or assisted absorption cooling machines are gaining increasing importance due to the continually growing demand for airconditioning in domestic housing as well as office and hotel buildings. Presently there are no thermally driven absorption cooling machines available on the market that can provide a smaller cooling capacity than 10kW for cooling buildings. For this reason, two single-effect solar heated ammonia/water (NHJlH20) Diffusion-Absorption Cooling Machines (DACM) with a design cooling capacity of 2.SkW at evaporator temperatures between -10°C and +soC were designed, built and operated. The indirectly heated, solar powered generator (bubble pump) is the main new feature of this cooling machine. Data acquisition was conducted under laboratory conditions as well as under simulated field conditions for vacuum-tube collectors. The first pilot plant showed that coefficient of performance values (COP) range from 0.1 to 0.2 and the evaporator cooling capacity of the pilot plant could reach 1.SkW, but that the operation stability was insufficient. The second optimised and compacted pilot plant showed stable and continuous temperature and pressure levels. The reached COPs were between 0.2 and O.S and the continuous cooling performance between 1.0kW and 1.6kW. A maximum cooling performance of 2.0kW could be reached if the evaporator temperature was set to the relatively high value of 2SoC. The Diffusion-Absorption Cycle has been modelled using the constant characteristic equation of sorption chillers. An expanded, steady-state model which includes additional specific components of the DACM was developed based on the exact solution of the internal mass and energy balances of each component as well as the heat transfer between external and internal temperature levels. The internal enthalpies are calculated at each time interval using the simulation environment INSEL. The compared experimental and simulated data showed a good accordance.

Previous studies indicate that increasing the diffusion angle in conical film-cooling holes leads to an improvement in their film cooling effectiveness. Discharge coefficient and film cooling effectiveness measurements are conducted to characterize this behavior. Part of the focus of this investigation is to find out how this trend develops and attempt to ascertain the optimum cone angle, if possible. Six test plates, each with one row of eight conical-shaped cooling holes of equal diffusion angles of 0, 1, 2, 3, 6, or 8 [degrees], with respect to the hole axis are used in this study. The ratios of the hole exit areas to the inlet areas range from 1 to 2.85. Coolant injection angle for all holes is at 35 degrees to the horizontal, in the direction of the main flow. Coefficients of discharge of all holes are reported under flow conditions. Temperature sensitive paint, TSP, is the technique used to find the temperature distribution downstream of the cooling holes and determine the laterally averaged film-cooling effectiveness. Data are obtained for blowing ratios ranging from 0.5 to 1.5, at a constant density ratio of 1.26. Results and trends are compared with established literature, which also recommends that a cylindrical entry length for diffused holes should be at least 4 diameters long. The effect that an added entry length has on the 3-degree conical plate's cooling effectiveness is also explored. Data are compared to baseline cylindrical holes, as well as to fan-shaped film holes found in open literature. Results indicate that the conical holes with larger diffusion angles provide strikingly even film protection and outperform fan shaped and cylindrical holes under certain conditions over extended downstream distances. Also, the addition of a cylindrical entry length to a conical hole, by providing a manageable metering diameter, should ease their usage while providing the full benefits of the conical geometry which may one day lead to numerous industrial applications.
M.S.M.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering

Several steps are followed in order to evaluate the cycle as the title suggests. The diffusion absorption refrigerator (DAR) cycle performance is evaluated when using helium or hydrogen as auxiliary gas. A slight increase in COP is found when using helium, but it is not sufficient to justify the cost. A secondary simulation of an alternate dual-pressure cycle using a pump is done as feasibility comparison with the same parameters as the diffusion cycle. It was found that the second cycle is not acceptable due to high evaporator temperatures needed to ensure liquid enters the pump instead of partially evaporated solution. This would greatly increase the work input required for what essentially becomes a compressor. Optimisation of the DAR is evaluated by simulating the use of a rectification column and the effects of different design points on overall performance. Meteorological data for Potchefstroom, South Africa is used to perform a yearly analysis on the simulated cycle and to specify a suitable design point. The use of a radiative cooling system as heat sink for the system is then investigated and incorporated into the system model. Finally, the performance characteristics of the simulated DAR cycle are discussed, verified and compared with available data from similar research. It is shown that a 40% solution aqua-ammonia-hydrogen cycle driven by 526 kW of solar thermal energy at 130°C and a system pressure of 1.5 MPa can easily achieve a COP over 0.4 with an air-cooled absorber at 40°C and a water-cooled condenser at 35°C. A 231 kW refrigeration capacity at an average evaporator temperature of –20°C is achieved, satisfying the requirements for a domestic refrigeration system.
Thesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013.

The objective of this research work was to understand the molecular mechanism of gas transport through amorphous glassy polymers. Especially, emphasis was placed on determining whether or not gas transport in amorphous glassy polymers is directly correlated with the free volume content. Free volume arguments are indeed commonly used to explain the gas transport process. The gas transport properties of bisphenol-A polycarbonate films were examined as a function of the cooling rate, physical aging, and orientation. Such conditions affect the free volume content and its size and shape distribution. Results obtained from permeation experiments were accompanied with dynamic mechanical and density measurements. The experimental results suggest that the diffusion coefficient of small gas molecules in glassy polycarbonate is influenced by the local dynamics or mobility of the polymer chains rather than by the overall free volume content. Indeed, the diffusion coefficient of nitrogen for instance was reduced in fast-cooled samples, despite of the fact that those samples possessed a greater overall free volume content. Fast cooling rates may generate highly restricted conformations which hinder local motions, and therefore tend to increase the activation energy of diffusion. As expected, the greater the free volume content, the greater was the solubility coefficient. The increase in the polymer relaxation times with aging time is believed to restrict the local chain motions, leading to enhanced activation energies of diffusion, and therefore to reduced diffusion coefficients. The change in the solubility coefficients with physical aging revealed that the aging process might not affect all the cavity sizes in polycarbonate equally. According to free volume arguments, one would anticipate that the physical aging of fast-cooled samples (which possess more free volume) should be enhanced compared to that of slowly-cooled samples. Quite interestingly, the decrease in the diffusion coefficient with aging was found to occur much slower in fast-cooled samples, despite of the higher initial free volume content. In contrast, properties directly related to the free volume content, such as density or isothermal DMTA measurements actually showed a greater aging rate in the sample containing the greatest amount of free volume. Slow-cooled samples that are in a low energy conformational state may loose their internal degrees of freedom more rapidly, due to the closer interchain packing and the possibly restricted segmental motions. Studies dealing with orientation and gas transport were complicated by several factors. For instance the fact that the permeation experiments were performed perpendicularly to the orientation of the chains and not along the orientation axis limited the sensitivity of the gas transport properties to orientation. This work points out that dynamic rather than static models should be developed to predict the gas transport phenomenon.
Ph. D.

For the year ending March 2014 the Office for National Statistics (ONS) estimated there were 573,000 domestic burglaries in England and Wales. Using the Home Office Integrated Offender Management Value for Money Toolkit valuation (2011) the cost to society of this is £1.9 billion. The financial and resulting emotional cost is a heavy burden for the UK. Better understanding crime prevention approaches and their impact on reducing residential burglary is of obvious relevance to policing, government and society as a whole. This study examined the wider impact of traceable liquid property marking strategies on reducing residential burglary and other acquisitive crime. It monitored levels of crime in trial areas. It observed if crime displacement or diffusion of benefits effects occurred to a distance of 750m, in 250m intervals, surrounding the trial areas. By doing so it added to the body of knowledge that surrounds situational crime prevention. It also surveyed households, which were participants of the trial, some 6 months following the deployment to measure any impact on their confidence in policing and on their fear of crime. To do this, 10 x London trial sites, comprising of 500 households areas were purposively selected that had both a persistent and a long-term chronic residential burglary offence rate. Two such sites were selected on each of five London Boroughs. The residential homes within these areas were then visited by a police officer or a PCSO and occupants had their property marked using a unique traceable liquid property marking solution. This strategy was supported by stickers saying their property had been marked being placed on external display on front and back doors and windows, signs being put up on street furniture in the surrounding area telling people they were entering a property marked area and the use of press and media releases to wider market the approach to offenders. Trap cars and houses were utilised and arrests advertised to ‘prove’ the approach to offenders. Finally control areas of similar characteristics to the trial areas were identified and observed on each of the 5 x borough sites. Once the marking had been implemented to the point of 85% saturation (where able), key data was observed over a 12-month period and compared against the previous year. These included: o Residential burglary crime levels within the target area. o Residential burglary crime levels in displacement zones of 250m, 500m, and 750m, surrounding the targeted area. o Robbery, theft of motor vehicle (M/V), theft from motor vehicle and total notifiable offences (TNO’s) offence levels within the target and displacement areas to measure displacement effects. o An online survey of the trial households of police satisfaction and fear of crime levels. o Interviews with key staff that implemented the trial. The study deduces that the following effects occurred within the trial areas: o A 45% reduction in residential burglaries, a 21% reduction in robberies, no significant change in M/V crime and 22% less TNO’s. Once offset against the control area performance the results indicated: o Overall average residential burglary was reduced by 21% with the best BOCU achieving an 88% reduction. o Personal robbery offences reduced by 16% and overall TNO’s by 20%. o There was no statistically significant change in M/V crime offence levels. o There was no significant crime or offence displacement within the target areas and indeed clear diffusion of benefits effects occurred. When the trial areas were widened to include the 250m, 500m and 750m displacement zones the following results were found to 750m: o A 23% reduction in residential burglaries, a 15% reduction in robberies, a 3% reduction in theft of M/V, 1% reduction in theft from M/V and a 9% less TNO’s. Once offset against the control area performance the results indicated: o Residential burglary reduced by 12% in the 250m-displacement zones, increased by 7% in the 500m zones, decreased by 19% in the 750m zones and cumulatively resulted in a 17% reduction. o Robbery increased by 8% in the 250m-displacement zones, decreased by 7% in the 500m zones, increased by 13% in the 750m zones and cumulatively resulted in a 5% increase. o Theft of M/V increased by 27% in the 250m-displacement zones, increased by 4% in the 500m zones, increased by 5% in the 750m zones and cumulatively resulted in a 10% increase. o Theft from M/V increased by 24% in the 250m-displacement zones, increased by 16% in the 500m zones, increased by 11% in the 750m zones and cumulatively resulted in a 15% increase. o TNO’s increased by 3% in the 250m displacement zones, decreased by 4% in the 500m zones, increased by 5% in the 750m zones and cumulatively resulted in a 1% increase. The results of the on-line survey found the following: o 51% of householders felt safer in their area. o 52% of householders felt safer in their home. o 33% had an improved opinion of the police. The study concludes that traceable liquid property marking is highly effective at reducing residential burglary. It found that when deployed with high levels of saturation to an area, diffusion of benefits effects for this crime type are likely to occur out to at least 750m from that area. This strategy led to a reduction in the fear of crime and if distributed by the police family, leads to an increase in public confidence for at least 6 months after the distribution period. However in achieving these positive impacts there will be offence displacement outside the targeted area, where offenders will move from residential burglary to other offences types. The most likely change is into theft of and from M/V crime. These crimes are arguably less harmful and impactive on crime victims and occurred at a lower rate than the residential burglary offences prevented.

We have carried out detailed thermometric and cooling history studies of several LL-, L- and H-chondrites of petrologic types 5 and 6. Among the selected samples, the low-temperature cooling of St. Severin (LL6) has been constrained in an earlier study by thermochronological data to an average rate of similar to 2.6 degrees C/My below 500 degrees C. However, numerical simulations of the development of Fe-Mg profiles in Opx-Cpx pairs using this cooling rate grossly misfit the measured compositional profiles. Satisfactory simulation of the latter and low temperature thermochronological constraints requires a two-stage cooling model with a cooling rate of similar to 50-200 degrees C/ky from the peak metamorphic temperature of similar to 875 degrees C down to 450 degrees C, and then transitioning to very slow cooling with an average rate of similar to 2.6 degrees C/My. Similar rapid high temperature cooling rates (200-600 degrees C/ky) are also required to successfully model the compositional profiles in the Opx-Cpx pairs in the other samples of L5, L6 chondrites. For the H-chondrite samples, the low temperature cooling rates were determined earlier to be 10-20 degrees C/My by metallographic method. As in St. Severin, these cooling rates grossly misfit the compositional profiles in the Opx-Cpx pairs. Modeling of these profiles requires very rapid cooling, similar to 200-400 degrees C/ky, from the peak temperatures (similar to 810-830 degrees C), transitioning to the metallographic rates at similar to 450-500 degrees C. We interpret the rapid high temperature cooling rates to the exposure of the samples to surface or near surface conditions as a result of fragmentation of the parent body by asteroidal impacts. Using the thermochronological data, the timing of the presumed impact is constrained to be similar to 4555-4560 My before present for St. Severin. We also deduced similar two stage cooling models in earlier studies of H-chondrites and mesosiderites that could be explained, using the available geochronological data, by impact induced fragmentation at around the same time. Diffusion kinetic analysis shows that if a lower petrological type got transformed by the thermal effect of shock impacts to reflect higher metamorphic temperature, as has been suggested as a possibility, then the peak temperatures would have had to be sustained for at least 10 ky and 80 ky, respectively, for transformation to the petrologic types 6 and 4. Finally, we present a model that reconciles textural data supporting an onion-shell parent body of H-chondrites with rapid cooling rate at high temperature caused by impact induced disturbance, and also discuss alternatives to the onion shell parent body model. (C) 2016 Elsevier Ltd. All rights reserved.

Le présent travail est consacré en premier lieu à l'investigation des limites de fonctionnement et de performances des machines frigorifiques à absorption et absorption-diffusion utilisant des mélanges d'alcanes comme fluides de travail et l'analyse en second lieu du processus d'absorption le long d'un absorbeur à film tombant en présence d'un gaz inerte. Dans le cas d'un refroidissement à l’eau les meilleures performances réalisées sont celles d'une machine utilisant le binaire C₃H₈/n-C₉H₂₀ avec un COP de l'ordre de 0.51 dans l'intervalle de la température de la chaleur motrice [110-125℃]. Une machine à absorption-diffusion utilisant ce même mélange en combinaison avec l’hydrogène permet de réaliser un COP de l'ordre de 0.44 pour une température de la chaleur motrice ne dépassant pas 120℃. Une étude approfondie est par suite menée sur l’absorption en présence d’un gaz inerte. Les résultats des l’étude ont montré entre autres que les deux résistances aux transferts de chaleur et de matière sont toutes les deux prédominantes en phase vapeur et ont révélé un taux d'absorption de l'ordre de 34% à travers une surface d'échange de 0.15m². Pour évaluer la réponse du système aux variations de ses principaux paramètres caractéristiques une étude paramétrique a été menée. Cette étude a permis d'appréhender le comportement complexe du processus d'absorption en présence d'un gaz inerte
This work is aimed primarily to investigate the feasibility limits and the performance of absorption and absorption-diffusion cooling machines using light alkane mixture as working pairs and secondarily to analyze the absorption process along a falling film absorber in the presence of an inert gas. It is shown that in the case of water cooling the best performances are those of an absorption machine using the C₃H₈/n-C₉H₂₀ binary mixture with a COP of about 0.51 in the heat driving temperature range 110-125℃. A COP of about 0.44 is attained with an absorption-diffusion cooling machine using the same mixture in combination with hydrogen with a heat driving temperature of 120℃. A detailed study of the absorption process with the C₃H₈/n-C₉H₂₀ pair and hydrogen as inert gas is conducted. The study results show that the heat and the mass transfer resistances are both prevalent in the vapor phase. An absorption rate of about 34% through an exchange surface of 0.15m² is calculated. A parametric study is carried out to evaluate the system response to the changes of its main characteristic parameters. This study allows a better understanding of the complex behavior of the absorption process in the presence of an inert gas

The commercial polycrystalline superalloy RR1000 developed for turbine disc applications contains a large number of alloying elements. This complex alloy chemistry is required in order to produce appropriate microstructures and the required mechanical properties, such that the most important strengthener γʹ displays complex alloy chemistry. The broad aim of this project is to develop an approach to measuring the composition of γʹ precipitates at a broad range of length scales from nanometres to hundreds of nanometres, and subsequently develop a better understanding of the role of thermodynamics and diffusion kinetics on γʹ phase separation and precipitate growth. A solution of the absorption-corrected EDX spectroscopy to spherical particles was developed in our work, therefore enabling the quantitative analysis of precipitates' composition using an absorption-corrected Cliff-Lorimer approach. By performing this quantification, size-dependent precipitate compositional variations were obtained. Examination of this quantitative approach was compared to thermodynamic calculations of primary γ' precipitates possessing equilibrium compositions. Given the development of semi-quantitative compositional measurements for spherical γʹ precipitates and that cooling is one of the most common and critical regimes in physical metallurgy of Ni-based superalloys, this approach was then applied to study the local compositional variations that are induced in γ' precipitates when the alloy RR1000 undergoes different cooling rates. These measured compositions have been compared to detailed thermodynamic calculations and provide new experimental evidence of the importance of the dominant role of aluminium antisite diffusion in determining the low-temperature growth kinetics of fine-scale γ' precipitates. We have applied a similar analysis approach to study the compositional variations of γʹ cores within the class of secondary precipitates upon cyclic coarsening and reversal coarsening. It was shown that supersaturated Co in secondary γʹ exhibits an overall trend towards the equilibrium but Co content can significantly increase as γʹ coarsens. It was demonstrated that the limited elemental diffusivity in γ and γʹ compared to the observed coarsening rate in the coarsening regime results in the long-lasting Co supersaturation in γʹ and builds up elemental enhancements or depletions. These inhomogeneous elemental distributions produce compressive elastic constraints on large-scale secondary γʹ, therefore inducing morphological instability of these γʹ and causing the reversal coarsening. These results enable us to better understand the role that both thermodynamics and limited diffusion kinetics plays in controlling the complex microstructures of γ' precipitates.

Failure to maintain thermal equilibrium can cause uncontrollable increases in body core temperature beyond critical upper limits. In selecting clothing, consideration must be given to the heat transfer properties of clothing that may restrict the cooling capacity of the human body under heat stress conditions, most importantly, apparent total evaporative resistance (Re,T,a). This study calculated and compared Re,T,a for five clothing ensembles under varying heat stress conditions, including three relative humidity (RH) levels and three stages of heat stress to determine if Re,T,a values varied or remained the same with changes in heat stress conditions. A four-way mixed model analysis of variance demonstrated significant differences for estimated Re,T,a values among ensembles, RH levels, heat stress stages, and interactions among ensembles and RH levels and ensembles and heat stress stages (p < 0.0001). No significant interaction among RH levels and heat stress stages was found (p = 0.67). A Tukey's Honestly Significant Difference multiple comparison test was used to identify where significant differences occurred (p < 0.05). The results of the study indicated that Re,T,a values do change with RH levels and stages of heat stress and that the theoretical framework for explaining heat-exchange in hot environments is not yet well-established. Also confirmed was the dominance of the convection pathway over the diffusion pathway in hot environments.

The temperature at which steam condenses stays more or less constant throughout the aircooler while the temperature of the cooling water increases, a temperature rise of 12 °C being a typical figure for cooling tower operation. Those parts of the aircooler where the cooling water enters therefore condense more steam than equal areas where the cooling water leaves. The orifice plates used to feed the separate compartments of the aircooler therefore need to be sized to cater for different mass flows. Up until now aircooler designs have used the same diameter for the orifices in each compartment. This project describes the generation of a computer program which, by combining steam-air mixture mass flow and pressure drop computation with the condensation heat transfer in the corresponding compartment of an aircooler with up to 20 compartments, enables engineers to specify orifice plate sizes which will optimise mass and heat flow to produce the best venting of the condenser. The program was written and compared with field test results. The computer results gave valid explanations for corrosion found in one major condenser and suspected backflow from the collecting duct to the compartments. They also validated an earlier design decision to apply variable aircooler inlet orifice cross sections in order to achieve equal pressure in the aircooler compartments along the tube bundle. The program was applied to a 300 MW el condenser to verify the results of a new design method. Design modifications to the condenser were then introduced to allow for more detailed future comparison between computer results and field test results. The program was written in Fortran after investigation of several major already existing software packages assessed them as being inappropriate for this application to steam power station condensers.

The Advisory Council of Aeronautical Research in Europe (ACARE) has set record emission reduction targets for 2020, in response to increased awareness of global warming issues and the forecast high level of growth in global air traffic. In order to meet this legislation engine designers have to consider new and unconventional designs. An intercooled aero-engine with a heat exchanger (HX) positioned between the IP and HP compressors has the potential to reduce emissions and/or reduce specific fuel consumption relative to conventional engine cycles. In such an engine a coolant delivery system is required to bleed a proportion of the bypass flow, from behind the fan outlet guide vane (FOGV), rapidly diffuse the flow (to reduce pressure loss through the HX modules) and present it to the intercooler (i.e. heat exchanger) modules for cooling. This spent cooling air is then fed back into the bypass duct. To realise the benefits of the intercooled cycle the coolant delivery system must diffuse the flow, within the geometrical constraints, with minimal pressure loss and present it to the heat exchanger modules with suitable flow characteristics over a range of operating conditions. Therefore, a predominately experimental study, complemented with CFD predictions, was undertaken to investigate the design and performance of a coolant delivery system aimed at providing high pressure recovery in a relatively short length. For this to be achieved some pre-diffusion of the flow is required upstream of the offtake (i.e. by making the offtake larger than the captured streamtube), with a controlled diffuser or hybrid diffuser arrangement located downstream of the offtake. Although targeted at an intercooled aero-engine the concept of a system that produces a high pressure recovery in a limited length is applicable to a variety of applications. Experimental data were obtained on a modified existing low speed isothermal annular test facility operating at nominally atmospheric conditions. The offtake must operate aft of the FOGV in a highly complex flow field environment. Hence, a 1½ stage axial flow compressor (IGV, rotor and modified OGV) was used to simulate the unsteady blade wakes, secondary flows, loss cores and other turbo-machinery features that can significantly influence offtake performance. Preliminary numerical (CFD) studies enabled an offtake configuration to be determined and provided understanding of the governing fluid mechanic processes. A relatively small scale, low speed test facility was designed that had the capability to evaluate aerodynamic processes in isolation (i.e. pre-diffusion, controlled diffusion, hybrid diffusion) and full system modelling to enable the complex interaction between these flow processes to be assessed. Hence an optimal system could be characterised in terms of total pressure loss, static pressure recovery and flow profiles at HX inlet. Measurements and numerical predictions are initially presented for a baseline configuration with no offtake present. This enabled the OGV near field region to be characterised and provided a datum, relative to which the effects of introducing an offtake could be assessed. The results showed that in the near field region (i.e. within one chord downstream of the FOGV) the high velocity gradients in the circumferential direction, and associated turbulent shear stresses, dominate the profile mixing and loss production. There is little mixing out of profiles in the radial direction. Furthermore, the relatively large amount of kinetic energy associated with the compressor efflux and its subsequent mixing to a more uniform profile (i.e. reduced blockage) results in a significant static pressure recovery (Cp=5.5%). With the offtake present a variety of configurations were investigated including different levels of pre-diffusion, prior to the offtake, and different offtake positions. This enabled evaluation of the upstream pressure effects and interaction with the upstream FOGV. For very compact systems of short length, such that the gap between the OGV and offtake is relatively small, the amount of pre-diffusion achievable is limited by the offtake pressure field and its impact on the upstream OGV row. This pressure field is also influenced by parameters such as the non-dimensional offtake height and splitter thickness. For systems of increased length a significant amount of flow pre-diffusion can be achieved with little performance penalty (relative to the datum configuration). Hence, the loss associated with mixing blade wakes and secondary flows in an adverse pressure gradient is relatively small. However, the pre-diffusion level is eventually limited, to approximately 1.5, by the increased distortion and pressure losses associated with the captured streamtube. Further measurements were made with various controlled diffuser and hybrid diffusers (of varying area ratio) downstream of the offtake and various levels of pre-diffusion. The flow profile that is presented to the controlled diffuser is directly influenced by the upstream pre-diffusion process. Hence, in this case the upstream-downstream interaction is relatively strong. Conversely, the downstream-upstream interaction, between the controlled diffuser and pre-diffusion process, is relatively weak and thus has little effect on the upstream flow field. The data enabled an optimal system to be characterised (pre-diffusion/controlled diffusion split) in terms of total pressure loss, static pressure recovery and flow profiles at HX inlet. A total system diffusion of 1.8 was achievable with a pre-diffusion of 1.4 and controlled diffusion of 1.25, with further increases in either the pre-diffusion level or the controlled diffuser area ratio destabilising the system. This was achieved with an absolute mass weighted total pressure loss of 11% measured from FOGV inlet to the controlled diffuser exit plane. Utilising a hybrid bled diffuser, combined with the pre-diffusion, enabled a total system diffusion of 2.24 to be achieved. The system incorporated a 6% bleed from the hybrid diffuser and a system total pressure loss of 13%. Experimental and computational results obtained in the current research have provided an understanding of the governing flow mechanisms and quantified the geometric and aerodynamic interaction of the offtake with the FOGV and between the diffusion processes. This has enabled a design methodology to be outlined that provides approximate information on system geometry and performance (in terms of optimal diffusion split and total pressure loss) for future coolant delivery systems with minimal effort. Preliminary design maps have been developed to define the magnitude of the interaction between the offtake and FOGV in terms of the offtake height, pre-diffusion level, the splitter thickness and the axial distance between the fan OGV and offtake. In this way systems of optimal diffusion split, minimum pressure loss and minimal axial length can be determined.

Eine kompakte Integration der Leistungselektronik in einem Fahrzeuggetriebe des Hybridfahrzeugs stellt hohe Anforderungen an die Lastwechselfestigkeit der Halbleiter-Leistungsmodule. Gefordert wird die Auslegung für die Kühlmitteltemperatur von 125°C und für die Sperrschichttemperatur von 200°C. Für die Untersuchung der Lastwechselfestigkeit bei geforderten hohen Temperaturen werden neue Prüfstandskonzepte und Messmethoden vorgestellt. Mit realisierten Testständen wird die Lastwechselfestigkeit der neuen Aufbau- und Verbindungstechnologien „gehärtete Aluminiumbonddrähte”, „Diffusionslöten”, „Lötung mit vertikalen Strukturen” und „Niedertemperatur-Verbindungstechnik” untersucht
High power density of the power electronics in a hybrid electric vehicle demands a high power cycling capability of the semiconductor power module. Requirements are: 125°C coolant and 200°C junction temperature. For the investigation of the power cycling capability at high temperatures new test benches and measurement methods are introduces. With realized methods the reliability of following new interconnection technologies is investigated: doped aluminium bond wires, diffusion soldering, solder layer with vertical microstructures, low temperature sinter technology

Eine kompakte Integration der Leistungselektronik in einem Fahrzeuggetriebe des Hybridfahrzeugs stellt hohe Anforderungen an die Lastwechselfestigkeit der Halbleiter-Leistungsmodule. Gefordert wird die Auslegung für die Kühlmitteltemperatur von 125°C und für die Sperrschichttemperatur von 200°C. Für die Untersuchung der Lastwechselfestigkeit bei geforderten hohen Temperaturen werden neue Prüfstandskonzepte und Messmethoden vorgestellt. Mit realisierten Testständen wird die Lastwechselfestigkeit der neuen Aufbau- und Verbindungstechnologien „gehärtete Aluminiumbonddrähte”, „Diffusionslöten”, „Lötung mit vertikalen Strukturen” und „Niedertemperatur-Verbindungstechnik” untersucht.
High power density of the power electronics in a hybrid electric vehicle demands a high power cycling capability of the semiconductor power module. Requirements are: 125°C coolant and 200°C junction temperature. For the investigation of the power cycling capability at high temperatures new test benches and measurement methods are introduces. With realized methods the reliability of following new interconnection technologies is investigated: doped aluminium bond wires, diffusion soldering, solder layer with vertical microstructures, low temperature sinter technology.

Thesis (M.S.)--University of Wisconsin--Madison, 1996.
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The Ediacaran to Cambrian (600-500 Ma) intraplate Petermann Orogeny significantly affected the crustal architecture of Central Australia, resulting in the exhumation of the Musgrave Province from beneath the Centralian Superbasin. In the western Musgrave Province response to intensive deformation is variable, with pervasive mylonitic reworking and localised migmitisation in the western Mann Ranges, and discrete mylonitisation in the eastern Mann Ranges. The duration of this period of intraplate orogenesis is a currently debated topic. Ti-in-zircon thermometry coupled with SHRIMP U-Pb zircon geochronology indicate that peak temperatures of 733±23°C in the western Mann Ranges occurred at circa 540 Ma. Combined diffusion-cooling modelling, U-Pb rutile and titanite isotopic data and calculated phase equilibria of recrystallised metagranites from the Cockburn Shear Zone and kyanite-bearing mylonites from the Mt. Charles Thrust indicate exhumation driven cooling from peak P-T conditions of 12-14 kbars and 700-750°C to 6-7 kbars and 550-600°C at c. 500 Ma occurred at a rate of 3.75-5.6°C/ My. These results indicate a slow-cooling and long-lived thermal regime and additionally suggests that final exhumation of the Musgrave Province had not occurred by c. 500 Ma, much younger than previously estimated. These findings suggest that granulite-facies metamorphism in the Musgrave Province was regional and that other factors such as fluid, control the variations in style of structural reworking. This study lends support to the notion that the intraplate Petermann Orogeny was long-lived and does not advocate short-lived orogenesis or the theory that shear heating is the driving force for metamorphism.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2010

This thesis presents an experimental and computational fluid dynamics (CFD) study on a rectangular S-bend with straight and diffusing passages with passive effusion cooling. Experimental tests were performed at both cold and hot flow conditions over a range of Reynolds numbers from 2.5e5 to 4.5e5. Hot flow testing was conducted with the primary flow temperature up to 300 °C. Severe backpressure penalties occurred with full-surface passive effusion injection in cold flow tests. Moderate penalties occurred with reduced surface coverage whereby the performance was affected by the S-bend secondary fields with injection at different locations. High surface cooling effectiveness with full-coverage of cooling film was measured; the impacts from the S-bend secondary flow fields were measured to be minimal. The CFD study revealed the importance of using experimental flow boundary conditions for simulations. Using the standard k-ε model with wall functions was confirmed as appropriate for simulating the S-bend flow with effusion cooling. A coarse-grid CFD methodology using a porous wall boundary condition to simulate the effects of effusion cooling was investigated. From a design perspective, this model is preferable for quantifying the injection flow rate since the actual mass flow rate is not known. Comparison to the alternative solution using uniform mass flow boundary conditions showed that both models incorrectly predicted the momentum. The porous wall model, however, is promising for practical design applications of S-duct flow fields with effusion injections.
Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2013-12-23 14:20:32.38

碩士
國立臺北科技大學
能源與冷凍空調工程系碩士班
97
Phase change materials were employed in industrial applications very often. The solidification of a binary solution is one of them (for example, casting of binary alloys). In the past, one of the main issues to study the solidification of a liquid binary alloy focused on how to remove or weaken the “double-diffusive convection” because it is the main reason to cause the poor quality of alloys. The objective of this project is to investigate the effect of periodic lid-driven flow on the development of double-diffusive convection and to find a method to erase or reduce the double-diffusive convection. A hypereutectic aqueous ammonium chloride (NH4Cl-H2O) solution was adopted as the test sample in this project and it was put into an enclosure cooled from the lateral side to investigate the flow field, heat and mass transport phenomena during solidification. The experiments of temperature and concentration distributions, movement of liquid-solid interface, and flow visualization by shadowgraph technique were conducted in this study. According to the experimental results, it is known that larger external disturbance can suppress the development of double-diffusive convection and result in more layers of circulation flows moving downward in the initial stage of solidification. At later stage of solidification, without or with periodic lid-driven flow has insignificant effect on development of double-diffusive convection.

碩士
國立臺北科技大學
能源與冷凍空調工程系碩士班
97
Phase change materials were employed in industrial applications very often. The solidification of a binary solution is one of them (for example, casting of binary alloys). In the past, one of the main issues to study the solidification of a liquid binary alloy focused on the development of “double-diffusive convection” because it is the main reason to cause the poor quality of alloys. The objective of this study is to investigate the effect of the slope of the side wall on the development of double-diffusive convection. An aqueous solution of 27 wt.% NH4Cl, with a liquidus temperature corresponding to 18.9℃, was adopted as the test sample in this study and it was put into an enclosure cooled from the lateral side to investigate the flow field, heat and mass transport phenomena during solidification. Experiments conducted in this study include PIV measurement on the flow field, flow visualization by shadowgraph technique, measurement of the growth of the mushy zone with time, transient temperature distribution within the test cell and the concentration distribution within the cavity. According to the experimental results of PIV measurement and flow visualization by shadowgraph, the development of double-diffusive convection became stable at later stage of solidification. Four kinds of slopes of the side wall were employed in this study, including 0, 5, 10 and 15 degrees. The larger the slope is, the earlier the double-diffusive convection occurred among the slopes of 0, 5 and 10 degrees. However, the double-diffusive convection grew the slowest for the slope of 15 degrees.

碩士
國立臺北科技大學
能源與冷凍空調工程系碩士班
100
Solidification of liquid binary alloys is found in various industrial applications, such as marine science, silicon crystal growth process, the ice storage system in HVAC, the food processing and cold storage in food industry, the metal alloys casting and low-temperature biotechnology applications. The natural convection phenomenon, also known as double-diffusive convection, which occurs during the solidification process owing to the effects of temperature and concentration gradients, is likely to cause poor quality of alloy castings. The factors contributing to the formation of double-diffusive convection and the means to eliminate or weaken such phenomenon have been the focus of research in the past. This study focused on the effect of slanted lateral cooling wall with negative slope on the formation of double-diffusive convection during the solidification of a 25 wt. % hyper-eutectic binary solution (NH4CL-H2O). Particle Image Velocimetry (PIV) techniques, thermochromic liquid crystal (TLC) and Schlieren method were employed to observe the flow development of the binary solution in the liquid. The experimental results showed that the water-rich fluid was continuously released through the mushy layer during solidification, resulting in the formation of a red color layer on the thermochromic liquid crystal. The image processing software was used for temperature field visualization. The experimental results also indicated that the lateral cooling wall with different slope has significant effects on the formation of double-diffusive convection during solidification. The growth process of double-diffusive convection varies apparently between the lateral cooling walls with higher slopes, such as in the case of 0 and 5 degrees compared to those with lower slopes, such as in the case of 10 and 15 degrees. As the slope of lateral cooling wall decreases, the filling-box process becomes faster and the time for the flow development to reach steady state becomes shorter.