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1
Tanguy-Sai, Gaëlle. "Concentration de produits laitiers dans les évaporateurs à flot tombant : facteurs limitants et alternatives technologiques". Thesis, Rennes, Agrocampus Ouest, 2018. http://www.theses.fr/2018NSARB318/document.
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Les poudres laitières sont obtenues par concentration du produit liquide (membranes, évaporation sous vide) puis séchage du concentré. Contrairement au séchage par atomisation, peu de travaux ont été menés sur la concentration par évaporation sous vide. Pourtant, la maîtrise du schéma global de production des poudres gagnerait en une meilleure compréhension de cette opération réalisée dans des évaporateurs à flot tombant. Le présent travail vise à étudier comment améliorer les performances des évaporateurs ; il s’appuie sur deux facteurs limitants de l’opération : l’encrassement des surfaces d’échange et la viscosité maximale en sortie des évaporateurs. La contribution des différents constituants des produits à l’encrassement a été étudiée grâce à une méthodologie développée sur un évaporateur pilote.Les résultats obtenus ont permis d’identifier les éléments minéraux qui contribuent à l’encrassement lors de la concentration de microfiltrat et d’ultrafiltrat de lait, de lactosérums acides chlorhydrique et lactique. Afin de dépasser l’extrait sec maximal en sortie des évaporateurs à flot tombant, deux évaporateurs rotatifs à couche mince, de conceptions différentes, ont été testés à l’échelle pilote. Les études de faisabilité ont été menées jusqu’à la poudre. Le potentiel des équipements a été évalué suivant les propriétés fonctionnelles des poudres et le coût énergétique d’élimination de l’eau. Dans l’un des cas, le remplacement de la tour de séchage par deux évaporateurs rotatifs en série constitue une rupture technologique pour la production de poudres de perméat et dimiDairy powders are produced using a two-step process: concentration of the liquid product (membrane, concentration by vacuum evaporation) and drying of the concentrate. Contrary to spray-drying, vacuum concentration has been poorly investigated. However, a better understanding of this unit operation carried out in falling-film evaporators would lead to an improved control of the global process scheme for the production of powders. This PhD project aims to highlight how to enhance the performances of falling-film evaporators; it focuses on two limiting factors of the vacuum concentration: the fouling of the heating surfaces and the maximal viscosity at the outlet of the falling-film evaporators. The contribution of the different product components to the fouling was investigated using a methodology developed at pilot-scale.Our results showed which mineral elements favored the fouling of falling-film evaporators during the concentration of milk microlfiltrate and ultrafiltrate as well as hydrochloric and lactic acid wheys. Besides, two thin-film rotative evaporators of different designs were tested at pilot-scale in order to exceed the maximum dry matter achieved in falling-film evaporators. The feasibility studies were conducted up to the production of powders. The capabilities of the equipment were evaluated according to the functional properties of powders and the specific energy costs relative to the removal of water. In one case, the combination of two rotative evaporators replacing the spray drier constitutes a technological breakthrough in the production of permeate p
2
Caldas, Pereira Silveira Arlan. "Caractérisation expérimentale et comportement de constituants protéiques et minéraux laitiers en concentration sous vide". Thesis, Rennes, Agrocampus Ouest, 2015. http://www.theses.fr/2015NSARB269/document.
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Les évaporateurs à flot tombant (EFT) sont largement utilisés dans les industries chimiques, de la réfrigération, du raffinage du pétrole, et alimentaires. Dans l'industrie laitière, les EFT sont appliqués pour la concentration de solutions avant l'étape de séchage. Malgré l'importance économique du procédé d'évaporation sous vide dans la fabrication de produits laitiers déshydratés, la connaissance du procédé est essentiellement empirique. Des recherches visant à améliorer l'efficacité du procédé sont donc nécessaires. L'objectif de ce projet de doctorat est de caractériser expérimentalement un EFT lors de la concentration de produits laitiers, par des approches thermo et hydro-dynamiques, afin d'étudier les interactions entre les propriétés des produits et les paramètres opérationnels. Un évaporateur à flot tombant, simple effet, à l’échelle pilote, qui décrit le même processus que celui à l'échelle industrielle, d'un point de vue hydrodynamique, a été instrumenté et utilisé pour établir les bilans massiques et énergétiques. La capacité évaporatoire et le coefficient global de transfert de chaleur ont été calculés à partir des données expérimentales. Une méthodologie pour la détermination expérimentale des fonctions distribution des temps de séjour (DTS) a été développée. En effet, les fonctions de DTS fournissent des informations essentielles sur l'écoulement des produits lors de la concentration dans un EFT. L'augmentation de la concentration, du débit massique et de la distance parcourue par le produit entraîne une augmentation de la dispersion des particules dans le flux. Ces fonctions ont été modélisées par une combinaison de réacteurs en cascade, parfaitement agités. D’après l'interprétation de ce modèle, deux flux, un principal et un secondaire, correspondant à deux couches superposées de produit circulant à travers des tubes d'évaporateur, a été proposé. La méthodologie développée pour le calcul des fonctions de DTS a été appliqué pour la concentration de produits laitiers (lait écrémé, lactosérum doux et acide). Par la suite, l'étude a été étendue à la formation de l'encrassement pendant la concentration par évaporation sous vide. Il a été montré que le temps de séjour moyen était plus sensible pour identifier l'encrassement que le coefficient global de transfert de chaleur et la capacité évaporatoire. Ainsi, cette étude a souligné le rôle crucial de l’importance de la caractérisation des EFT sous vide afin d’en améliorer leurs performances et la qualité des produits qui en sont issuFalling film evaporators (FFE) are widely used in the chemical, refrigeration, petroleum refining, desalination and food industries. In the dairy industry FFE is applied for the concentration of solutions prior to the drying step. Despite the economic importance of the vacuum evaporation process in the manufacture of dairy dried products, the knowledge about the process is mostly empirical. Research aiming to improve the efficiency of the process is therefore necessary. The objective of this PhD project was to characterize experimentally a FFE during the concentration of dairy products by means of thermodynamic and hydrodynamic approaches, in order to study the interactions between the products properties and the operating parameters. A pilot-scale, single-stage falling film evaporator that describes the same process as that of an industrial scale from a hydrodynamic point of view was instrumented and used to establish the mass and energy balances. The evaporation rate and the overall heat transfer coefficient were calculated from the experimental data to follow up the process. A methodology for the determination of the experimental residence time distribution (RTD) functions was developed. RTD functions provide global information about the flow of the products during concentration in a FFE. Increasing of the concentration of skim milk, mass flow rate and the distance covered by the product resulted in an increase in the dispersion of the products particles. The experimental RTD functions were modelled by a combination of two perfectly mixed reactor tanks in series. From the interpretation of this model, two different flows, a main and a minor flow, were identified. The RTD methodology developed on skim milk was applied to sweet whey and lactic acid whey and the study was extended to the formation of fouling during a 5-hour concentration. The mean residence time was more sensitive to identify fouling than the overall heat transfer coefficient and the evaporation rate. This study emphasized the crucial role of process characterization to improve the performance of FFE and product quality
3
Aza-Gnandji, Cocou Davis Ruben. "Salinity of irrigation water in the Philippi farming area of the cape flats, Cape Town, South Africa". University of the Western Cape, 2011. http://hdl.handle.net/11394/2921.
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Magister Scientiae - MScThis research investigated the nature, source and the spatial variation of the salinity of the water used for irrigation in the urban farming area of Philippi, which lies in the Cape Flats region of the Cape Town Metropolitan Area, South Africa. The irrigation water is mainly drawn from the Cape Flats aquifer, and pumped into ponds for eventual crop irrigation. Water samples were collected in summer and in winter from fifteen selected sites using standard water sampling procedures. Each site consisted of one borehole and one pond. The samples were routinely analyzed for salinity levels, and concentrations of major and minor ions. From the same boreholes and ponds, water was sampled in summer for isotope analysis to assess effects of evaporation on the water quality and salinity. Descriptive statistics were used to display the variation in range of specific ions in order to compare them with the recommended ranges. Geographical Information Systems analysis described the spatial distribution of the salinity across the study area, and hydrogeochemical analysis characterized the various waters and detected similarities between the water samples in the study area and other waters found in the Cape Flats region. In addition, the US salinity diagram classification of irrigation water developed by Richards (1954) was used to assess the current suitability of groundwater and pond water samples collected during the entire sampling period for irrigation activities. The research indicated that the concentrations of some ions such as chloride, nitrate, potassium and sodium exceeded in places in the study area, the target range values set by the Department of Water Affairs and Forestry (DWAF, 1996) and the Food and Agriculture Organization (Ayers and Westcot, 1985). It revealed that borehole and pond water were mostly brackish across the area regarding their total dissolved salts content, and fresh water was only found in the middle part of the study area. The research found that sea water does not intrude into the aquifer of the study area, and the accumulation of salts in groundwater and soil in the study area is mainly due to the agricultural activities and partially due to the natural movement of water through the geological formation of the Cape Flats region. The conceptual model of the occurrence of the salinization process supported these findings. From this investigation it is understood that the groundwater and pond water in the study area were generally suitable for irrigation purposes but they have to be used with caution as the vegetables are classified as sensitive and moderately sensitive to salt according to DWAF Irrigation water guidelines (1996). The quality of these waters was mainly affected by the land use activities.
South Africa
4
Ali-Adib, Tarif. "Estimation et lois de variation du coefficient de transfert de chaleur surface/ liquide en ébullition pour un liquide alimentaire dans un évaporateur à flot tombant". Phd thesis, AgroParisTech, 2008. http://pastel.archives-ouvertes.fr/pastel-00004544.
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Le coefficient de transfert de chaleur est nécessaire pour concevoir et dimensionner un évaporateur utilisé pour concentrer un liquide, tel que rencontré couramment dans les industries alimentaires. Le coefficient de transfert de chaleur le plus variable et le plus incertain est du coté produit, entre paroi et liquide, noté « h ». Il varie à la fois avec les propriétés thermo-physiques du liquide traité (ηL, σL, λL, ρL , CpL, ω, ...) et avec les paramètres du procédé (type d'évaporateur, φ ou Δθ, Γ (δ), P, rugosité de la surface, encrassement, etc), ces grandeurs étant définies dans le texte. Mais h est aussi lié au régime d'ébullition (nucléée ou non nucléée), et pour les évaporateurs de type « flot tombant », au régime d'écoulement laminaire ou turbulent, selon le nombre de Reynolds en film Ref. Nous avons étudié le cas des évaporateurs « à flot tombant », très utilisés dans les industries alimentaires pour concentrer le lait et les produits laitiers, les jus sucrés, les jus de fruits et légumes. L'objectif de notre travail était de définir une méthode fiable et économique pour évaluer a priori le coefficient de transfert de chaleur h coté liquide en ébullition, dans un évaporateur flot tombant. La première partie de la thèse a été consacrée à l'analyse bibliographique, qui a révélé une grande incertitude actuelle dans la prévision de h, sur la base des formules de la littérature, et des paramètres descripteurs proposés. La deuxième partie de la thèse a été de concevoir et construire un pilote utilisable pour estimer h, dans des conditions stationnaires connues et reproductibles. Dans la troisième partie, on présente les résultats et commente les lois de variations de h en fonction de la concentration de matière sèche du liquide XMS, de la température d'ébullition de liquide θL (ou P), du flux de chaleur φ ou (Δθ), et du débit massique de liquide par unité de périmètre de tube Γ, pour des propriétés de surface de chauffe fixées (ici, paroi en acier inoxydable poli Rs ≈ 0,8 μm). On commente l'effet sur h de chaque variable isolément, les autres étant maintenues constantes, ce qui confirme l'importance de la transition du régime non-nucléé au régime nucléé, cette transition variant avec la nature du liquide, sa concentration, et le flux de chaleur. On a montré la possibilité de modéliser un produit donné dans l'ensemble du domaine expérimental, où tous les paramètres peuvent varier simultanément, avec peu de coefficients, selon deux types d'équations (polynomiale et puissance). On a comparé le cas d'un liquide Newtonien (jus sucré) et non-Newtonien (solution de CMC dans l'eau). On a aussi observé le débit de mouillage critique Γcri et ses lois de variation. On a aussi démontré la possibilité de simplifier le plan d'expérience, aussi bien pour les liquides Newtoniens que non-Newtoniens, tout en gardant un coefficient de corrélation satisfaisant dans le domaine Γ > Γcri, cette modélisation pouvant servir de base de données produit pour l'ingénierie.
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Wang, Yu-Hsuan, i 王御軒. "Preliminary Study of Dual Loops LHP with Flat Evaporator". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/87967754299842194091.
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碩士淡江大學
機械與機電工程學系碩士班
97
This paper presented an preliminary study on a copper- methanol based Loop Heat Pipes(LHP) with a 82 mm long, 42mm wide and 10 mm thick flat rectangular evaporator. A novel concept to have dual vapor lines and liquid lines loops design from evaporator to condenser was devised to achieve higher vapor flow rate and reduce the heat leakage to compensation chamber. Thermal performance of loop heat pipe was evaluated experimentally in a fan-heat sink CPU test apparatus with heating area of 31mm x 31mm. After the evaluation, the LHP with 40% filling rate showed the lowest evaporator-to-ambient resistance of 0.83 K/W , corresponding to a heater temperature of 80 ℃ at an input power of 60 watts.
6
Anand, A. R. "Investigations on Miniature Loop Heat Pipe with Flat Evaporator". Thesis, 2017. http://etd.iisc.ac.in/handle/2005/4308.
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The present investigation on a miniature loop heat pipe (LHP) with flat evaporator is motivated by two factors. Firstly, miniature loop heat pipes are required for thermal management of small electronics in spacecraft with heat dissipation ranging from 50 W to 100 W (heat flux up to ~ 10 W/cm2). An LHP with flat evaporator is easier to mount on an electronic package (heat source) without a saddle. Though axially grooved aluminium – ammonia heat pipes are being used for thermal management in spacecraft, when the electronic package is located far away from the radiator, conventional heat pipes are no longer useful as the number of bends in axially grooved heat pipes is restricted. LHPs can overcome this issue since they have smooth walled tubes for vapour and liquid transport lines that can easily be bent and routed inside the spacecraft. Furthermore, high pressure fluids such as ammonia require thick-walled container to withstand the high operating pressure and are more hazardous to humans in human space programs. For thermal management of small electronics with heat dissipation in the above range, there is scope for alternate working fluids that are less hazardous. Thus, issues related to design, miniaturization of the heat transport devices and use of working fluids that are less hazardous are still open for research. Secondly, the operating characteristics of an LHP are strongly influenced by the flow and heat transfer characteristics in the wick which need to be explored in detail. Thus, the present research focuses on the investigation of an LHP with a flat evaporator with various working fluids – acetone, methanol, n-pentane and ethanol.
An LHP with a flat evaporator has been built and tested with acetone, methanol, n-pentane and ethanol for heat inputs starting from 25 W till deprime for two coolant set points (-20 °C and 0 C). The LHP is also provided with a visualization arrangement to observe the phenomena occurring inside the compensation chamber (CC). Experimental results reveal that methanol has the highest deprime limit, followed by acetone, ethanol and n-pentane in decreasing order. It was also found that n-pentane has the lowest operating temperature followed by acetone, methanol and ethanol in increasing order. It was observed that increase in the sink temperature causes an increase in the operating temperature, a decrease in the deprime limit and a decrease in the total thermal resistance offered by the LHP to the heat transport from the evaporator to the sink. Visualization studies reveal that the LHP operates without any nucleation in the CC for all the heat inputs till deprime. However, the deprime of the LHP is characterised by intense nucleation inside the CC, an increase in the operating temperature and a decrease in the condenser exit temperature indicating ceasing of the fluid flow inside the LHP. Since the LHP evaporator will be directly in contact with the electronic package for its temperature control, the evaporator wall temperature will influence the electronic package temperature and its life. Hence, a model for prediction of the evaporator wall temperature under the assumption that the wick is always saturated with liquid is developed which can serve as a design platform for miniature LHPs for thermal management of electronic packages. The maximum underprediction of the evaporator wall temperature with respect to the measured evaporator wall temperature in the model is found to be 16.4 °C. Based on the results of this model, it is inferred that there exists a vapour blanket in the wick causing an additional resistance for the heat flow from the evaporator to the working fluid for its vapourization and another model is developed to estimate the vapour blanket thickness.
By balancing the loop pressure drop with the capillary pressure, an equivalent apparent contact angle which is a measure of wettability of a working fluid is estimated on a relative scale for each working fluid. It was found that ethanol has the highest wetting, followed by methanol, acetone, and n-pentane in decreasing order, or the lowest contact angle, followed by methanol, acetone, and n-pentane in increasing order. It was also found that fluid with less wetting recedes faster into the wick.
The impact of the location of liquid-vapour interface on the evaporative heat transfer coefficient is studied for all the fluids. It was found that decrease in the evaporative heat transfer coefficient is mainly due to increase in the vapour blanket thickness in the wick.
In order to compare different working fluids with respect to their operating characteristics, an improved LHP figure of merit with a correction factor is presented. This figure of merit clearly distinguishes the operating temperatures of a given LHP with different working fluids and is superior to other figures of merit available in literature. The proposed figure of merit can serve as a predictive tool for making qualitative assessment of the operating characteristics of an LHP.
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Chen, Chung-Wei, i 陳仲威. "Visualization and Evaporation Resistance Measurement for Groove-Wick Evaporator of Operating Flat-Plate Heat Pipes". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/56864342489570572865.
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Wu, Cheng-Yu, i 吳昌瑀. "Effect of wick evaporation area on thermal performance for loop heat pipe with flat evaporator". Thesis, 2014. http://ndltd.ncl.edu.tw/handle/09314070664185237929.
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碩士中華科技大學
飛機系統工程研究所在職專班
102
This study investigates the effects of increasing the evaporating area of wick in a Flat Loop Heat Pipe(FLHP). This work attempts to improve the performance of the FLHP by increasing the number of grooves and thereby the surface area of the wick. The number of grooves is increased from 0%(grooves 8) to 90%(grooves 16). Production results are limited that we cannot be successfully produced the wick structure of 16 grooves, so the thermal permormance of the test and wick parameters of testing only for grooves 8~14. Experimental results show that increasing the number of grooves not only increases the surface area of the wick but also enhances FLHP performance. When the evaporating surface area increases by 45%(grooves 12),which corresponds to increasing the number of grooves 8 to 14, We can get most of the heat transfer performance, also the heat transfer capacity increases to 260W and enhance the heat transfer performance about 30%. Wick permeability:13-20×〖10〗^(-13)(m^2)、pore size:3.1~3.7(μm)、porosity:60~66%. The rate of change of the wick is tiny,also good production within the range suggested in the literature. Produced by the simplicity and success rate, we recommend that the evaporation area is increased by 45%(grooves 12),thermal resistance is reduced to 0.2℃/W, The heat transfer raised to 260W, enhancethe heat transfer performance about 30%.
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YU, YEN-YI, i 游晏宜. "Design and discuss of the flat tubes and parallel flow evaporator". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/t8c67v.
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碩士國立中央大學
機械工程研究所
94
This project will discuss the flat tubes and parallel flow heat exchangers air-conditioner. The traditional round tube evaporator and condenser in an air-conditioner will be replaced by flat tube parallel flow evaporator. In this project not only design the flat tube parallel flow evaporator but also test the flat tube evaporator. The compressor, expansion valve and other components in the air-conditioner will also be modified according to the changes of heat transfer and pressure loss of the heat exchangers. This project will be performed by the cooperation with the TECO Electric and Machinery Co., Ltd. The ME department will design and test the flat tube evaporator and condenser and the TECO will take charge of other components. A compact, low noise and high performance air-conditioner will be developed in this project.
10
GUN-NING, KUO, i 郭君寧. "Thermal Performance of a Loop Heat Pipe with a Flat Evaporator". Thesis, 2004. http://ndltd.ncl.edu.tw/handle/38977099709502269606.
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碩士國立臺灣科技大學
機械工程系
92
The heat transfer characteristics of a loop heat pipe with flat-shaped evaporator was studied experimentally . Thermocouples were used to measure temperatures along the loop. Trends of steady-state operating temperature are presented and explained for two different tilt angles of the loop. Temperature hysteresis and low-power start-up problems were observed and discussed. The maximum heat transport capacity was up to 100W with a thermal resistance of 0.212℃/W and an operating temperature around 60℃.
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Chen, Jia-Ruei, i 陳嘉瑞. "Investigates the application of PTFE wicks to Loop Heat Pipe with flat evaporator". Thesis, 2015. http://ndltd.ncl.edu.tw/handle/28403727381712240959.
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Chang, Chia-Wei, i 張家瑋. "Visualization and Measurement for Sintered-Wick Evaporator in an Operating Flat-Plate Heat Pipe". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/48869875797606783280.
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Lai, Shih-Ru, i 賴世儒. "Investigation of the Effect of Heat Leak in Loop Heat Pipes with Flat Evaporator". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/48037703193312162536.
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碩士國立臺灣大學
機械工程學研究所
95
Loop heat pipes (LHPs), which are generally and widely used with cylindrical evaporators, have a great potential for applications of spacecrafts and electronic cooling due to the advantages of high transfer capacity, low thermal resistance and long transport distances. However, the cylindrical evaporators of loop heat pipes cannot work on a flat thermo-contact surface without saddle. The saddle not only creates an extra thermal resistance but also makes evaporators less isothermal. To avoid the above disadvantages, we adopt the flat evaporators of loop heat pipes. According to the literature, however, the heat leak problem is more serious in the flat evaporators than the cylindrical evaporators. This problem also makes the thermal resistance of flat evaporators higher. Hence this study tries to solve the difficulties and provides two solutions. The first method is to increase the thermal resistance of the wick by raising the wick thickness. The second method, we design a double-decked wick, which is composed of the primary wick sintered with metal powder and the secondary wick made of the low thermal conductivity polymer. The material wick generates higher capillary forces and the polymer has lower thermal conductivity. Such design can ease the heat leak problem. The results show that both methods can ease heat leak problem. When primary wick thickness of double-decked wick is 4 mm, the temperature of the evaporators is less than 100oC and the sink temperature is at 30oC. The maximum heat capacity increases from 40W to 180W. In addition, the thermal resistance decreases from 0.69 K/W to 0.38 K/W
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Basha, Mulla Saleem. "Heat Transfer and Visualization Studies in the Evaporator of a Flat Loop Heat pipe". Thesis, 2020. https://etd.iisc.ac.in/handle/2005/4493.
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Heat pipes are extensively used in spacecraft thermal control and electronics cooling for transfer of heat from high heat flux zones to low heat flux zones. The major advantage of heat pipe is it can transfer high heat flux with minimum temperature difference between the source and sink. Capillary forces generated by wick drives the fluid between condenser and evaporator. The working fluid collects heat in the evaporator, vaporizes and moves towards condenser. The vapour condenses back to liquid in the condenser by releasing the heat to surroundings. This condensed liquid flows back to the evaporator by capillary forces generated by wick.
Loop heat pipes (LHPs) are provided with wick at evaporator region unlike in conventional heat pipes to reduce the pressure drop and increase heat transport distances. The flat plate LHPs are always preferred due to their simple construction and can be mounted directly onto the electronics package without any saddle. But large heat leak from evaporator to compensation chamber (CC) of flat LHPs is their major drawback, which needs to be studied meticulously.
Extensive research has been carried out for understanding the steady state and transient characteristics of an LHP with different heat loads and working fluids. However, the literature lacks in the study of heat leak into the CC and its effect on its operating characteristics, particularly at high heat loads or catastrophic operating conditions.
The present study of heat leak into the CC of an LHP evaporator is a step forward for better understanding of the phenomena occurring in the CC and their effect on the heat transfer characteristics with acetone as working fluid. An optically accessible evaporator setup is built to visualize the phenomena inside the CC of capillary evaporator using high speed camera and two different thermal conductive material wicks, i.e., Bronze and UHMW-PE. Visualization inside the CC is carried out for bubble dynamics and correlated against heat loads. Heat transport capability at different operating regimes is evaluated and it is found that the highest evaporative heat transfer coefficient is achieved at the onset of nucleate boiling. Wick temperature overshoot is witnessed during start-up of the flow while using Bronze wick, but no such phenomenon is observed for UHMW-PE wick. This is attributed to higher thermal conductivity of Bronze wick, which would delay to attain required motive temperature head (second serviceability condition) to displace liquid into CC. The start-up duration decreases steeply with increase in heat load for both the wicks. It was found the probability of bubble size mostly depends on the wick pore size and marginally on heater power. As the bubble frequency (which is the measure of energy carried by bubbles) changes significantly with heater power, bubble dynamics have substantial implication on the evaporative heat transfer coefficient.
Global heat balance across the capillary evaporator is carried out and presented. Heat leak through the wicks (i.e., heat leak through temperature measurement and heat leak estimated from correlation) are compared and their effects on the heat transfer characteristics are also discussed.
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Wei, Kai-chin, i 魏愷進. "Experimental Investigation on the Thermal Performance of a Loop Heat Pipe with a Flat Evaporator". Thesis, 2005. http://ndltd.ncl.edu.tw/handle/07098029413457812793.
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碩士國立臺灣科技大學
機械工程系
93
In this study, a two-phase closed loop cooling system aimed to be used in electronic system is designed and tested. The cooling system consists of a flat evaporator with wick structure inside, a tube-and-fin condenser, and two connecting tubes between evaporator and condenser. The connecting tubes are transparent silicon tubes which can be used for flow pattern observation. Water is used as the working fluid. The cooling system is charactered by a parametric study which determined the effect of charging capacity, the tilt angle of the system on the thermal performance of the closed loop. Experimental data show that the system has optimal performance under vertical operating condition with 22cc water charging capacity. The thermal resistance of the system is around 0.384℃/W under this configuration.
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林宇中. "Visualization and Measurement for Evaporator in Operating Flat-Plate Heat Pipes－Different Working Fluids and Wettabilities". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/56220279196942776357.
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Lu, Chien-Ming, i 盧建銘. "Effect of Sintering Rising Temperature Slope in Wick Manufactured for Loop Heat Pipe with Flat Evaporator". Thesis, 2014. http://ndltd.ncl.edu.tw/handle/70701179540159460535.
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碩士中華科技大學
飛機系統工程研究所在職專班
102
Loop heat pipe (LHP), which are generally and widely used with cylindrical evaporators, have a great potential for applications of spacecrafts and electronic cooling due to the advantages of high transfer capacity, low thermal resistance and long transport distances. However, the cylindrical evaporators of loop heat pipes cannot work on a flat thermo-contact surface without saddle. The saddle not only creates an extra thermal resistance but also makes evaporators less isothermal. To avoid the above disadvantages, we adopt the flat evaporators of loop heat pipe. This investigation examines the effect of the effect of the sintering temperature curve in manufacturing nickel powder capillary structure (wick) for a loop heat pipe (LHP) with flat evaporator. The sintering temperature curve is composed of three regions: a region of increasing temperature, a region of constant temperature, and a region of decreasing temperature. The most important region is the increasing temperature region, as the rate of temperature increase directly affects the performance of the wick.When the slope of the region of increasing temperature is 0.8 (equivalent to 8℃/min), the structure of the manufactured wick is complete, with the best heat transfer performance result. Experimental resultsshowed that the optimal heat transfer performance is 160W, the minimal total thermal resistance is approximately 0.43℃/W, and the heat flux is 17W/cm2; the optimal wick manufactured has an effective pore radius of 5.2 μm, a permeability of 8.5×10-13m2, and a porosity of 64%.
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Lo, Kuei-Chi, i 羅貴淇. "Effect of Sintering Temperature and Time in Nickel Wick for Loop Heat Pipe with Flat Evaporator". Thesis, 2014. http://ndltd.ncl.edu.tw/handle/73084329970070502961.
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碩士中華科技大學
飛機系統工程研究所在職專班
102
This paper specifically addresses the effect of changing the constant temperature region of the sintering temperature curve in manufacturing nickel powder capillary structure (wick) on the performance of a flat loop heat pipe (FLHP). The sintering temperature curve is composed of three regions: a region of increasing temperature, a region of constant temperature, and a region of decreasing temperature, with the sintering time and temperature in the region of constant temperature having significant effect on the permeability of the wick. In this study, for wick manufacturing the temperatures in this region tested range from 550°C to 650°C and the time from 30 minutes to 60 minutes. The properties and internal parameters of the wick are measured, and the wick is placed into FLHP for performance testing. Experimental results show that at sintering temperature of 550°C and lasting about 45 minutes, maximum heat load is 200W, minimum thermal resistance is 0.32°C/W, permeability is 1.2×〖10〗^(-12) m^2, porosity is 66%, effective porosity is 3.8 μm, and heat flux is around 21W/cm2; related literatures have only reported maximum heat load increase of 25%.
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Wu, Wei-Ting, i 吳韋廷. "Heat Transfer Enhancement of Loop Heat Pipe with Flat Plate Evaporator using 2-Butanol Aqueous Solution". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/r7gj95.
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碩士中華科技大學
飛機系統工程研究所
106
Under the rapid development of the electronics, consumer electronic product, the demand of cooling increases with the raises of power density. Loop Heat Pipe (LHP) system often characterized by high heat transfer capacity and long transport distancing. It shows great potential for electronic cooling. The objective of this study is the application of self-rewetting fluid as the working fluid on Loop Heat Pipe with flat evaporators (FLHP) to increases the heat transfer performance. Use the 2-butanol aqueous solution as the working fluid on FLHP, with nickel as the capillary structure material. Self-rewetting fluid shows better wettability compared with pure water. At a certain temperature, a self-rewetting fluid, contrary to common fluids, has the ability to reverse its surface tension’s trend, inducing colder fluid to flow to the heated surface and delaying the occurrence of dry-out in FLHP, it is advantageous to use self-rewetting fluid as working fluid on heat-transfer devices. Heat transfer performance test results shows that water and 2-Butanol(20wt%) aqueous solution in nickel wick FLHP, the maximum heat load from 150W to 425W, can improve heat transfer performance about 180%, the thermal resistance decreased from 1.2℃/W to 0.61℃/W, the heating area is 961mm2 and the maximum heat flux from 15W/cm2 to 41W/cm2.
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YEN, SHIH-HSUAN, i 顏士軒. "Study of Self-Rewetting Fluid Applied to PTFE Wick structure of Loop Heat Pipe with flat evaporator". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/00634478782462936917.
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碩士中華科技大學
飛機系統工程研究所
104
This study investigated the application of self-rewetting fluid to Nickel and PTFE wick structure of Loop Heat Pipe with flat evaporators (FLHP) and its effect on the heat transfer performance of FLHP. PTFE wick structure can prevent FLHP heat leakage problem, however, PTFE material with strong hydrophobic nature, cannot use the water as the working fluid. Therefore, this study attempts to use Self-rewetting fluid's good wettability to overcome the PTFE wick's hydrophobicity. At a certain temperature, a self-rewetting fluid, contrary to common newtonian fluids, has the ability to reverse its surface tension's trend, inducing colder fluid to flow to the heated surface and delaying the occurrence of dry-out in FLHP during operation. Thus, this study focused on a few self-rewetting fluids; the surface tensions of these fluids were measured, and then it was applied to FLHP as working fluid to investigate its effect on the heat transfer performance. Heat transfer performance test results shows that DI water and 1-Butanol;1-Heptanol aqueous solution in nickel wick’s FLHP, the maximum heat load can be up to 280W,Compared to DI water's 140W can improve heat transfer performance about 70 to 100% . DI water and 1-Butanol;1-Heptanol aqueous solution in PTFE wick's FLHP, the maximum heat load can be up to 240W,Compared to DI water's 40W can improve heat transfer performance about 300 to 500% .
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Liou, Jhan-Hong, i 劉展宏. "Visualization and Measurement for Evaporator of Different Sintered-Wicks and Working Fluids in Operating Flat-Plate Heat Pipes". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/50107468376505893258.
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DONG, HONG-WEI, i 董宏威. "Research on the Liquid-side Grooves of Wick in Loop Heat Pipe With Card-type of Flat Evaporator". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/9r38hn.
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碩士中華科技大學
飛機系統工程研究所在職專班
106
In this study, we tried to design and make liquid-side grooves on the surface of the wick next to the compensation chamber, which is in the card-type flat evaporator. By this, the absorbing surface area of working fluid increased and thereby decreased the flow resistance in loop heat pipe with card-type of flat evaporator. We used PTFE as material of wick, because of its low thermal conductivity, and acetone as working-fluid. Results indicated that heat transfer performance increases in the wick structure with liquid-side grooves , of which the critical heat load（dry-out heat load）reached 175W, the thermal resistance was 0.77℃/W and the heat flux reached 28W/cm². Comparing with the structure without liquid-side grooves under 100℃, the typical operating temperature of electronic devices, our design increased the heat load about 50%. As the reason, wick structure with liquid-side grooves has a great potential to improve the performance of loop heat pipe.
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LO, CHUN-CHENG, i 羅浚誠. "Study of Performance Enhancement with the Double-Side Grooves Wick Applied to Loop Heat Pipe with Card-Type of Flat Evaporator". Thesis, 2019. http://ndltd.ncl.edu.tw/handle/6pcxa4.
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碩士中華科技大學
飛機系統工程研究所
107
This study is to manufacture more liquid groove on the wick structure and apply to the card-type flat loop heat pipe. The purpose is to enhance the heat transfer of performance. Besides the single side vapor groove and 5 liquid grooves designed on the wick structure before. In order to increase the liquid receiving surface absorption and in a limited space condition, we manufacture the 10 liquid grooves to make the working fluid easier to absorb. This design has the effect of reducing the flow resistance and increasing the liquid receiving surface absorption, and also helps to enhance the heat dissipation effect. In this study, we use a low thermal conductivity of Teflon (polytetrafluoroethylene, PTFE) as the material of the wick. Due to the hydrophobic nature of PTFE, this study uses acetone with a lower operating temperature and good compatibility as the working fluid, and make it simply absorbs to the wick. We also hope it can exert phase change effect when the system is operating, thereby improving the heat transfer performance in card-type flat loop heat pipe. The experimental results show that the maximum heat transfer capacity of the 10 liquid grooves of wick is about 300W, and the lowest thermal resistance value is about 0.598°C/W, which can reach the heat flux to 44.4W/cm2,and if the evaporator wall set about 100°C of limitation, the heat load is more than 92% to the single side vapor groove of wick, and it also more than 67% to the 5 liquid grooves of wick. It can be proved that the 10 liquid grooves of wick has the best heat transfer performance no matter to the single vapor groove or 5 liquid grooves of wick in the card-type flat loop heat pipe.
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王維文. "Experimental investigation of R-22 evaporation inside aluminum flat tubes". Thesis, 1993. http://ndltd.ncl.edu.tw/handle/88253181223435959898.
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Chao, Chi, i 趙淇. "Evaporation Resistance of Flat Heat Pipe Having Metallic Mesh Wick". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/44230452291185835598.
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Chu, Yi-Ming, i 褚伊銘. "Study on the Performance of flat Loop Heat Pipe in the Wick of Compensation Chamber and Evaporation Zone". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/59a75e.
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碩士國立臺北科技大學
機電整合研究所
98
Loop Heat Pipe is a kind of heat pipe with both vapor chamber based on the theory of two-phase change thermal conductivity of the passive cooling system. Compared to the conventional heat pipe, loop heat pipe has a high heat transfer capacity, transmission distance of a long and low thermal resistance performance in cooling, space technology or military technology and other thermal applications. The flat loop heat heating element can be placed on the heat source directly without using saddle. During the startup process, the working fluid in the system will be distributed and phase transition including evaporation, condensation and boiling will occur, leading to the thermal status for each component unstable. In addition, boiling bubbles and thermal leakage also influence the system stability. Therefore, the start up and stable operation for the loop heat pipe is the aim to investigate in various research fields. In this study, two different sizes, different material powder were used. The wick structure of flat loop heat pipe can be fabricated to green tape with sinter process by using doctor blade casting. The first part, the sintered 400 mesh copper powders have higher capillarity and the better the heat transfer rate. In secondary part, 150 mesh nickel powders, have good permeability and lower capillarity to resist heat leaking to compensation chamber. The green tape made by doctor blade casting can be sintered to chamber of flat loop heat pipe for single time. It can decrease the error during the manufacturing. In the experiment, various water contents of 6.2g, 8.6g and 10.6g were injected to measure the performance. According to the characterization, the flat loop heat pipe has no obvious thermal oscillation and performs freely during the operation. The results show that the 6.2g water content injection has the lowest heat resistance of 0.21 ℃ / W. In addition, the compensation chamber for additional cooling can increase the operation stability and decrease the system thermal resistance.
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Pei, Shan-Yung, i 裴善永. "A Study of Convective Evaporation in a One-side Heated Flat Channel of a Liquid Cooling Device for Chips". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/7w9vw4.
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碩士國立臺北科技大學
能源與冷凍空調工程系碩士班
95
This study investigates the influence of the heat flux and mass velocity on convective heat transfer performance of two fluids (water and FC-72) in a rectangular channel subjected to one side heating. The fluid passes through a rectangular channel, having either a smooth surface or a pin fin surface, with a flow rate from 80ml/min to 960ml/min. The inlet fluid temperature is maintained at 30oC. The cross section of the test channel is 20mm wide and 2 mm high. The total length of the test channel is 113 mm, with a heated length of 25mm. The heat flux varies between 32 and 98 W/cm^2. A high speed camera system is used to record the phenomenon of flow boiling. The observation is compared with experimental data and found that the flow patterns depend on heat flux and flow rate. For water, single phase convection is the dominant heat transfer mechanism during the present tests except for the flow rate less than 160 ml/min and heat flux > 50 W/cm^2. At a fixed flow rate, the pin fin surface yields up to 40% higher heat transfer coefficient and greater critical heat flux than those of a smooth surface. The pin fin surfaces and the smooth surface yield similar performance in FC-72, where convective boiling is the main heat transfer mode. In the present FC-72 tests, bubbly flow is the dominant flow regime. Plug flow and churn flow occur at high heat fluxes. The convective heat transfer coefficient of FC-72 is greater than water at low flow rate (80~ 160 ml/min) and heat flux = 15 ~ 35 W/cm^2, where the thermal resistance is about 0.22 K/W. However, the convection performance of water is superior to FC-72 at high flow rates.
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Ruben, Aza-Gnandji Cocou Davis. "Salinity of irrigation water in the Philippi farming area of the cape flats, Cape Town, South Africa". Thesis, 2011. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_8633_1365586459.
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This research investigated the nature, source and the spatial variation of the salinity of the water used for irrigation in the urban farming area of Philippi, which lies in the Cape Flats region of the Cape Town Metropolitan Area, South Africa. The irrigation water is mainly drawn from the Cape Flats aquifer, and pumped into ponds for eventual crop irrigation. Water samples were collected in summer and in winter from fifteen selected sites using standard water sampling procedures. Each site consisted of one borehole and one pond. The samples were routinely analyzed for salinity levels, and concentrations of major and minor ions. From the same boreholes and ponds, water was sampled in summer for isotope analysis to assess effects of evaporation on the water quality and salinity. Descriptive statistics were used to display the variation in range of specific ions in order to compare them with the recommended ranges. Geographical Information Systems analysis described the spatial distribution of the salinity across the study area, and hydrogeochemical analysis characterized the various waters and detected similarities between the water samples in the study area and other waters found in the Cape Flats region. In addition, the US salinity diagram classification of irrigation water developed by Richards (1954) was used to assess the current suitability of groundwater and pond water samples collected during the entire sampling period for irrigation activities. The research indicated that the concentrations of some ions such as chloride, nitrate, potassium and sodium exceeded in places in the study area, the target range values set by the Department of Water Affairs and Forestry (DWAF, 1996) and the Food and Agriculture Organization (Ayers and Westcot, 1985). It revealed that borehole and pond water were mostly brackish across the area regarding their total dissolved salts content, and fresh water was only found in the middle part of the study area. The research found that sea water does not intrude into the aquifer of the study area, and the accumulation of salts in groundwater and soil in the study area is mainly due to the agricultural activities and partially due to the natural movement of water through the geological formation of the Cape Flats region. The conceptual model of the occurrence of the salinization process supported these findings. From this investigation it is understood that the groundwater and pond water in the study area were generally suitable for irrigation purposes but they have to be used with caution as the vegetables are classified as sensitive and moderately sensitive to salt according to DWAF Irrigation water guidelines (1996). The quality of these waters was mainly affected by the land use activities.