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Journal articles on the topic 'Flat Evaporator'

Author: Grafiati

Published: 6 September 2023

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1

Szymanski, Pawel, Richard Law, Ryan MᶜGlen, and David Reay. "Recent Advances in Loop Heat Pipes with Flat Evaporator." Entropy 23, no. 11 (October 20, 2021): 1374. http://dx.doi.org/10.3390/e23111374.

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The focus of this review is to present the current advances in Loop Heat Pipes (LHP) with flat evaporators, which address the current challenges to the wide implementation of the technology. A recent advance in LHP is the design of flat-shaped evaporators, which is better suited to the geometry of discretely mounted electronics components (microprocessors) and therefore negate the need for an additional transfer surface (saddle) between component and evaporator. However, various challenges exist in the implementation of flat-evaporator, including (1) deformation of the evaporator due to high internal pressure and uneven stress distribution in the non-circular casing; (2) heat leak from evaporator heating zone and sidewall into the compensation chamber; (3) poor performance at start-up; (4) reverse flow through the wick; or (5) difficulties in sealing, and hence frequent leakage. This paper presents and reviews state-of-the-art LHP technologies; this includes an (a) review of novel manufacturing methods; (b) LHP evaporator designs; (c) working fluids; and (d) construction materials. The work presents solutions that are used to develop or improve the LHP construction, overall thermal performance, heat transfer distance, start-up time (especially at low heat loads), manufacturing cost, weight, possibilities of miniaturization and how they affect the solution on the above-presented problems and challenges in flat shape LHP development to take advantage in the passive cooling systems for electronic devices in multiple applications.

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2

Chien, L. H., and Y. C. Shih. "An Experimental Study of Mesh Type Flat Heat Pipes." Journal of Mechanics 27, no. 2 (June 2011): 167–76. http://dx.doi.org/10.1017/jmech.2011.18.

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ABSTRACTFlat heat pipes having mesh capillaries were investigated experimentally in this study. An apparatus was designed to test thermal performance of plate type copper water heat pipe having one or two layers of #50 or #80 mesh capillary structures with 5 to 50 W heat input. The working fluid, water, is charged in volumes equivalent to 25%, 33%, or 50% of the internal space. In addition to horizontal orientation, heat pipes were tested with the evaporator section elevated up to 40 degree inclination angle. Temperature distribution of the heat pipe was measured, and the evaporator, adiabatic and condensation resistances were calculated separately. The effects of mesh size, charge volume fraction, and inclination angle on thermal resistance were discussed. In general, the #80 mesh yielded lower thermal resistance than the #50 mesh. Inclination angle has a more significant effect on condenser than evaporator. Analysis of evaporation and condensation in flat heat pipes was conducted and semi-empirical correlations were derived. The present evaporation correlation predicts evaporation resistance between −20% and +30%, and the condensation correlation predicts most condensation resistance data within ±30% for 25% and 33% charge volume fraction.

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3

Hu, Wenju, and Xin Zhang. "Study on the Coupling Effect of Heat Transfer and Refrigerant Distribution in the Flat Tube of a Microchannel Evaporator." Energies 15, no. 14 (July 20, 2022): 5252. http://dx.doi.org/10.3390/en15145252.

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Refrigerant maldistribution severely deteriorates the heat transfer performance of a microchannel evaporator. Compared with the refrigerant distribution among flat tubes along the header, refrigerant distribution among microchannels in the flat tube in the airflow direction has barely been paid attention. In this paper, a heat transfer mathematical model of a microchannel evaporator’s flat tube composed of vertically placed parallel microchannels in the airflow direction was developed. The Refrigerant distribution among the microchannels was evaluated and its influence on heat transfer between air and refrigerant was analyzed. The results showed that the refrigerant distribution and heat transfer performance between air and refrigerant were interrelated and interacted with each other. The temperature of the air leaving the microchannel evaporator changed along the microchannel because of uneven refrigerant distribution among the microchannels, and the air temperature difference between air leaving out of the bottom and the top of the evaporator was approximately 2.13 °C. Ignoring the heat transfer from adjacent microchannels will lead to a small heat transfer deviation for the flat tube; thus, heat transfer among microchannels can be neglected.

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4

Santos, Paulo, Thiago Alves, Amir Oliveira, and Edson Bazzo. "Analysis of a flat capillary evaporator with a bi-layered porous wick." Thermal Science 24, no. 3 Part B (2020): 1951–62. http://dx.doi.org/10.2298/tsci180419240s.

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A numerical evaluation of the heat and mass transfer concerning a flat capillary evaporator provided by a bi-layered porous wick is presented. The wick has a shape of a flat disc and is assembled between the liquid feeding channel and the vapor chamber. An external heat input is applied into the upper surface of the bi-layered wick, where the working fluid evaporates. The mass and heat transfer are modeled using the mass and energy conservation equations. The model allows to verify the effect of design variables, such as working fluids, dimensions, permeability, average pore radius and thermal conductivity of the wick, in the performance of the capillary evaporator. It can be used as a predictive tool to design similar capillary pumping systems for thermal control of satellite or electronics systems in general.

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5

Gai, Dongxing, Wei Liu, ZhiChun Liu, and JinGuo Yang. "Temperature Oscillation of mLHP with Flat Evaporator." Heat Transfer Research 40, no. 4 (2009): 321–32. http://dx.doi.org/10.1615/heattransres.v40.i4.40.

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6

Ninolin, Emerald, Godson Asirvatham Lazarus, and K. Ramachandran. "Thermal Performance of a Compact Loop Heat Pipe with Silver-Water Nanofluid." Applied Mechanics and Materials 852 (September 2016): 666–74. http://dx.doi.org/10.4028/www.scientific.net/amm.852.666.

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The thermal performance of a compact loop heat pipe is fabricated and tested for different heat inputs ranging from 30 W to 500 W using water and silver-water nanofluid with low volume concentrations of silver nanoparticles (0.03% and 0.09%) in vertical orientation. A flat square evaporator having a bottom area of 30 mm × 30 mm and a height of 15 mm is used in the present study. The effect of heat input on the thermal resistance, evaporation and condensation heat transfer coefficient is experimentally investigated. The results showed that a reduction in the evaporator thermal resistance of 26.45% is achieved with 0.09 volume percentage of silver nanoparticles when compared with that of water. Further an enhancement in the convective heat transfer coefficient of 25.23% has been observed with the same volume concentration of silver nanoparticles. Addition of small amount of nanoparticles enhanced the operating range of heat pipe beyond 500 W and without the occurrence of any dry out conditions. From the outcome of this study, it is concluded that the compact loop heat pipe with flat square evaporator can be used for thermal control of electronic equipments with limited space.

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7

Gabsi, Inès, Samah Maalej, and Mohamed Chaker Zaghdoudi. "Modeling of Loop Heat Pipe Thermal Performance." Journal of Advanced Research in Fluid Mechanics and Thermal Sciences 81, no. 1 (March 5, 2021): 41–72. http://dx.doi.org/10.37934/arfmts.81.1.4172.

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The present work deals with the heat transfer performance of a copper-water loop heat pipe (LHP) with a flat oval evaporator in steady-state operation. Modeling the heat transfer in the evaporator was particularly studied, and the evaporation heat transfer coefficient was determined from a dimensionless correlation developed based on experimental data from the literature. The model was based on steady-state energy balance equations for each LHP component. The model results were compared to the experimental ones for various heat loads, cooling temperatures, and elevations, and a good agreement was obtained. Finally, a parametric study was conducted to show the effects of different key parameters, such as the axial conductive heat leaks between the evaporator and the compensation chamber cases, the capillary structure porosity and material, and the groove dimensions.

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8

Merzah, Basil Noori, Majid H. Majeed, and Fouad A. Saleh. "Numerical study of flat plate solar collector performance with square shape wicked evaporator." Al-Qadisiyah Journal for Engineering Sciences 12, no. 2 (June 30, 2019): 90–97. http://dx.doi.org/10.30772/qjes.v12i2.592.

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In this work, a system of a heat pipe is implemented to improve the performance of flat plate solar collector. The model is represented by square shape portion of the evaporator section of wicked heat pipe with a constant total length of 510 mm, and the evaporator section inclined by an angle of 30o. In this models the evaporator, adiabatic and condenser lengths are 140mm, 140mm, and 230mm respectively. The omitted energies from sunlight simulator are 200, 400, 600, 800 and 1000 W/m2 which is close to the normal solar energy in Iraq. The working fluid for all models is water with fill charge ratio of 240%. The efficiency of the solar collector is investigated with three values of condenser inlet water temperatures, namely (12, 16 and 20o C). The numerical result showed an optimum volume flow rate of cooling water in condenser at which the efficiency of collector is a maximum. This optimum agree well with the ASHRAE standard volume of flow rate for conventional tasting for flat plate solar collector. When the radiation incident increases the thermal resistance of wicked heat pipe is decreases, where the heat transfer from the evaporator to condenser increases. The numerical results showed the performance of solar collector with square shape evaporator greater than other types of evaporator as a ratio 15 %.

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9

Dongxing, Gai, Sun Jingyu, Chen Chen, and Chen Ting. "Hysteresis phenomena in flat-type loop heat pipe." Thermal Science, no. 00 (2020): 166. http://dx.doi.org/10.2298/tsci191010166d.

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Testing of loop heat pipes (LHPs) showed that the heat-load dependence of the operating temperature was not always unambiguous. It may have hysteresis phenomena. The temperature hysteresis had a certain relationship with previous history of the power variation, and also related to the initial parameters of the LHP. It has been found that the temperature hysteresis of the LHP was related to the gas-liquid distribution in the compensation chamber (CC) which depended on the interaction between heat leak of evaporator and the reflux liquid from condenser. The temperature of the LHP evaporator rose with the gas phase in the compensation chamber increased.

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10

Khrustalev, D., and A. Faghri. "Thermal Characteristics of Conventional and Flat Miniature Axially Grooved Heat Pipes." Journal of Heat Transfer 117, no. 4 (November 1, 1995): 1048–54. http://dx.doi.org/10.1115/1.2836280.

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A detailed mathematical model of low-temperature axially grooved heat pipes (AGHP) is developed in which the fluid circulation is considered along with the heat and mass transfer processes during evaporation and condensation. The results obtained are compared to existing experimental data. Both capillary and boiling limitations are found to be important for the flat miniature copper-water heat pipe, which is capable of withstanding heat fluxes on the order of 40 W/cm2 applied to the evaporator wall in the vertical position. The influence of the geometry of the grooved surface on the maximum heat transfer capacity of the miniature AGHP is demonstrated.

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11

Joung, Wukchul, Keesool Gam, Kwangmin Park, Sungpil Ma, and Jinho Lee. "Transient responses of the flat evaporator loop heat pipe." International Journal of Heat and Mass Transfer 57, no. 1 (January 2013): 131–41. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2012.10.025.

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12

Jung, Eui Guk, and Joon Hong Boo. "A Novel Analytical Modeling of a Loop Heat Pipe Employing Thin-Film Theory: Part II—Experimental Validation." Energies 12, no. 12 (June 22, 2019): 2403. http://dx.doi.org/10.3390/en12122403.

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Part I of this study introduced a mathematical model capable of predicting the steady-state performance of a loop heat pipe (LHP) with enhanced rationality and accuracy. Additionally, investigation of the effect of design parameters on the LHP thermal performance was also reported in Part I. The objective of Part II is to experimentally verify the utility of the steady-state analytical model proposed in Part I. To this end, an experimental device comprising a flat-evaporator LHP (FLHP) was designed and fabricated. Methanol was used as the working fluid, and stainless steel as the wall and tubing-system material. The capillary structure in the evaporator was made of polypropylene wick of porosity 47%. To provide vapor removal passages, axial grooves with inverted trapezoidal cross-section were machined at the inner wall of the flat evaporator. Both the evaporator and condenser components measure 40 × 50 mm (W × L). The inner diameters of the tubes constituting the liquid- and vapor-transport lines measure 2 mm and 4 mm, respectively, and the lengths of these lines are 0.5 m. The maximum input thermal load was 90 W in the horizontal alignment with a coolant temperature of 10 °C. Validity of the said steady-state analysis model was verified for both the flat and cylindrical evaporator LHP (CLHP) models in the light of experimental results. The observed difference in temperature values between the proposed model and experiment was less than 4% based on the absolute temperature. Correspondingly, a maximum error of 6% was observed with regard to thermal resistance. The proposed model is considered capable of providing more accurate performance prediction of an LHP.

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13

Mihai, Ioan, Cornel Suciu, and Claudiu Marian Picus. "Considerations for the Maximum Heat Load and Its Influence on Temperature Variation of the Evaporator in Flat MHPs in Transient Regimes." Micromachines 13, no. 6 (June 20, 2022): 979. http://dx.doi.org/10.3390/mi13060979.

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The present paper describes a series of considerations for the occurrence of capillary boundaries in flat micro heat pipes (flat MHPs) and the conditions required for their stable operation in relation to the working circumstances and to the type of liquids inside the pipes. Particularities of heat transfer in a flat MHP are analyzed for situations of either excessive or deficient working liquid. Depending on the physical properties of the working liquids (acetone, methanol and distilled water), the maximum rate of heat flow that can be applied to a flat MHP is determined analytically. The calculus is made with the assumption that constant vaporization of the liquid is ensured in the flat MHP’s evaporator, with no overheating. The considered analytical models allow for the evaluation of the liquid film thickness and the mass flow corresponding to the vaporization region. The temperature difference between the inner and outer walls of a flat MHP is found in the case of a transient regime and a variable thermal flow is applied in the evaporation region. The interior of flat MHPs was modeled in MATLAB using an FTCS (Forward-Time Central-Space) method, which is a finite difference method used for numerically solving the heat equation.

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14

Varughese, Allen, A. Brusly Solomon, Benny Raj, Mohsen Sharifpur, and Josua P. Meyer. "Heat transfer characteristics and flow visualization of anodized flat thermosiphon." Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 234, no. 2 (February 13, 2020): 182–92. http://dx.doi.org/10.1177/0954408920905400.

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Use of environmentally safe refrigerants is the need of the hour to minimize the carbon footprints and to reduce the ozone depletion. The application of such environmentally safe refrigerants in the thermosyphon with the micro/nanoporous coating is expected to operate efficiently. In this study, a simple cost-effective anodizing technique to form a uniform thin micro/nanoporous coating at the inner wall of the thermosiphon is undertaken, and the resulting performance enhancement is presented. Also, the effect of fill ratio, heat input and the porous coating on the heat transfer characteristics of flat thermosiphon are studied. The heat transfer coefficient in the evaporator of anodized and nonanodized thermosiphon is enhanced to a maximum of 3587 and 2742 W/m2 K, respectively. The number of pores present in the anodized evaporator surface is estimated as 3.4 × 109. The width (pore size) and depth of pore are measured as 0.25 µm and 16 nm respectively. The porosity of the coating is around 55%, and the contact angle is ≤10°. As a result, the heat transfer coefficient at the evaporator and condenser of anodized thermosyphon is enhanced to a maximum of 24% and 13% respectively, when compared to that of the nonanodized thermosiphon.

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15

Singh, Randeep, Aliakbar Akbarzadeh, Chris Dixon, and Masataka Mochizuki. "Novel Design of a Miniature Loop Heat Pipe Evaporator for Electronic Cooling." Journal of Heat Transfer 129, no. 10 (February 9, 2007): 1445–52. http://dx.doi.org/10.1115/1.2754945.

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Miniature loop heat pipes (mLHPs) are coming up with a promising solution for the thermal management of futuristic electronics systems. In order to implement these devices inside compact electronics, their evaporator has to be developed with small thickness while preserving the unique thermal characteristics and physical concept of the loop scheme. This paper specifically addresses the design and testing of a mLHP with a flat evaporator only 5mm thick for the cooling of high performance microprocessors for electronic devices. A novel concept was used to achieve very small thickness for the mLHP evaporator in which the compensation chamber was positioned on the sides of the wick structure and incorporated in the same plane as the evaporator. This is unlike the conventional design of the flat evaporator for mLHP in which the compensation chamber, as a rule, adds to the overall thickness of the evaporator. The loop was made from copper with water as the heat transfer fluid. For capillary pumping of the working fluid around the loop, a sintered nickel wick with 3–5μm pore radius and 75% porosity was used. In the horizontal orientation, the device was able to transfer heat fluxes of 50W∕cm2 at a distance of up to 150mm by using a transport line with 2mm internal diameter. In the range of applied power, the evaporator was able to achieve steady state without any temperature overshoots or symptoms of capillary structure dryouts. For the evaporator and condenser at the same level and under forced air cooling, the minimum value of 0.62°C∕W for mLHP thermal resistance from evaporator to condenser (Rec) was achieved at a maximum heat load of 50W with the corresponding junction temperature of 98.5°C. The total thermal resistance (Rt) of the mLHP was within 1.5–5.23°C∕W. At low heat loads, the mLHP showed some thermal and hydraulic oscillations in the transport lines, which were predominately due to the flow instabilities imposed by parasitic heat leaks to the compensation chamber. It is concluded form the outcomes of the present investigation that the proposed design of the mLHP evaporator can be effectively used for the thermal control of the compact electronic devices with high heat flux capabilities.

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16

Gai, Dongxing, Yang Yin, and Chen Chen. "Investigation of instability on loop heat pipe with flat evaporator." IOP Conference Series: Earth and Environmental Science 467 (April 9, 2020): 012024. http://dx.doi.org/10.1088/1755-1315/467/1/012024.

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17

Gai, Dongxing, Zhichun Liu, Wei Liu, and Jinguo Yang. "Operational characteristics of miniature loop heat pipe with flat evaporator." Heat and Mass Transfer 46, no. 2 (December 2009): 267–75. http://dx.doi.org/10.1007/s00231-009-0563-0.

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18

Yang, Yang, Zhu Kai, Wang Yabo, Wei Jie, and Sarula Chen. "Experimental analysis of a Vapour-Liquid Separated Flat Loop Heat Pipe Evaporator System." MATEC Web of Conferences 307 (2020): 01055. http://dx.doi.org/10.1051/matecconf/202030701055.

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In this paper, a unique operation mechanism of loop heat pipe (LHP) was proposed. To test the performance of LHP under this new mechanism, a visual flat LHP evaporator prototype and an open experimental system were designed and assembled, and start-up experiment and variable heat load experiment were done respectively to obtain the actual operation characteristics, such as the evaporator thermal resistance (Re), total thermal resistance (Rt), start-up time and temperature of base plate. The proposed LHP had better overall performance during the start-up tests when He value of EC was set to 0.5mm, and its corresponding Re and Rt value were 0.035 K/W and 0.451 K/W when the heating power was 208w. Meanwhile, as per the heat load applied to the base plate, the whole variable heat load experiment could be divided into three distinct stages: low heat load stage, efficiency operation stage and dry-out stage. Moreover, the results also showed that the circulation driven head formed inside of the EC played an important role in promoting the operation performance, especially when the wick, the vapour-liquid interface and the bottom of the evaporator arrived at a reasonable situation.

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19

Quitiaquez, William, José Estupiñán-Campos, César Nieto-Londoño, and Patricio Quitiaquez. "CFD Analysis of Heat Transfer Enhancement in a Flat-Plate Solar Collector/Evaporator with Different Geometric Variations in the Cross Section." Energies 16, no. 15 (August 2, 2023): 5755. http://dx.doi.org/10.3390/en16155755.

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There is a growing demand from the industrial sector and the population to cover the need for water temperature increases that can be covered with systems such as heat pumps. The present research aims to increase the heat transfer to the working fluid in a collector/evaporator, part of a solar-assisted direct expansion heat pump. This research was developed using a numerical analysis and by applying computational fluid dynamics; different simulations were performed to compare the performances of collector/evaporators with models exhibiting variations in the cross-section profile under similar conditions. An average incident solar radiation of 464.1 W·m−2 was considered during the analysis. For the comparison, profiles with hexagon-, four-leaf clover-, and circular-shaped sections with floral shapes, among others, were analysed, resulting in a temperature increase at the outlet of the working fluid of 1.3 °C. In comparison, the collector/evaporator surface temperature varied between 4 and 13.8 °C, while the internal temperature of the fluid reached 11.21 °C. Finally, it is indicated that the best results were presented by analysing the profile corresponding to the circular section with the flower shape.

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20

Wong, Shwin-Chung, Jhan-Hong Liou, and Chia-Wei Chang. "Evaporation resistance measurement with visualization for sintered copper-powder evaporator in operating flat-plate heat pipes." International Journal of Heat and Mass Transfer 53, no. 19-20 (September 2010): 3792–98. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2010.04.031.

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21

Wu, Shen Chun, Shih Syuan Yan, Chen Yu Chung, and Shen Jwu Su. "The Study of PTFE Wicks Application to Loop Heat Pipes with Flat Evaporator." Applied Mechanics and Materials 775 (July 2015): 54–58. http://dx.doi.org/10.4028/www.scientific.net/amm.775.54.

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This study investigates the application of PTFE wicks to flat-plate loop heat pipes (FLHPs). PTFE’s low heat transfer coefficient effectively prevents heat-leakage, which is a problem with using metal wicks, lowering the operating temperature and pressure. This paper uses PTFE particles to form wicks, and the effect of PTFE on flat-plate LHP performance is investigated. Experimental results shows that the highest heat load reached was 100W, with lowest thermal resistance of 0.61°C/W, and heat flux of about 10W/cm2, For the wick properties, the wick had an effective pore radius of the wick was around 9.2μm, porosity of 47%, and permeability of 1.0 x 10-12m2. Compared to the highest heat flux reported in literature thus far for PTFE flat-plate LHPs, the heat flux in this study was enhanced by around 50%.

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22

Zhang, Xian Feng, and Shuang Feng Wang. "Experimental Investigation of Heat Transfer Performance of a Miniature Loop Heat Pipe with Flat Evaporator." Applied Mechanics and Materials 71-78 (July 2011): 3806–9. http://dx.doi.org/10.4028/www.scientific.net/amm.71-78.3806.

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The present work experimentally investigated the operating characteristics of a miniature loop heat pipe (LHP) under different power cycle. The miniature LHP with flat evaporator of 8mm thick is made of copper. The evaporator with sintered copper power wick is in series structure with compensation chamber. Water is working fluid. It is found that the LHP can start up at heat load of 15W with temperature oscillation and the maximum heat load is 160W with Rl=0.068°C/W. The LHP operates unstably under low heat load. The oscillating frequency of temperature rises with heat load increased. The operating performance of the LHP is affected by the power cycle.

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23

Liu, Zhichun, Dongdong Wang, Chi Jiang, Jinguo Yang, and Wei Liu. "Experimental study on loop heat pipe with two-wick flat evaporator." International Journal of Thermal Sciences 94 (August 2015): 9–17. http://dx.doi.org/10.1016/j.ijthermalsci.2015.02.007.

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24

Phan, Nguyen. "Flat-evaporator-type loop heat pipe with hydrophilic polytetrafluoroethylene porous membranes." Physics of Fluids 32, no. 4 (April 1, 2020): 047108. http://dx.doi.org/10.1063/1.5143561.

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25

Singh, Randeep, Aliakbar Akbarzadeh, Chris Dixon, Mastaka Mochizuki, and Roger R. Riehl. "Miniature Loop Heat Pipe With Flat Evaporator for Cooling Computer CPU." IEEE Transactions on Components and Packaging Technologies 30, no. 1 (March 2007): 42–49. http://dx.doi.org/10.1109/tcapt.2007.892066.

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26

Singh, Randeep, Aliakbar Akbarzadeh, and Masataka Mochizuki. "Operational characteristics of a miniature loop heat pipe with flat evaporator." International Journal of Thermal Sciences 47, no. 11 (November 2008): 1504–15. http://dx.doi.org/10.1016/j.ijthermalsci.2007.12.013.

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27

Adnan, Samah Ihsan, Aouf Abdulrahman Ahmad, and Adnan Abdulamar Abdulrasool. "Experimental Study of Wickless Heat Pipe with Flat Evaporator for Used in Cooling of Electronic Components." Journal of University of Babylon for Engineering Sciences 27, no. 2 (May 26, 2019): 125–37. http://dx.doi.org/10.29196/jubes.v27i2.2303.

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In this paper, systematic experimental investigations were carried out for a wickless heat pipe with flat evaporator having dimensions (100x100x30) mm. Flat-square electrical element was used to simulate the heat source of electronic part with dimensions of (100x100) mm. The aim of this paper presents the effect of fill ratio and cooling water mass flow rate on thermal performance of a wickless heat pipe. Experiments were performed to evaluate performance of wickless heat pipe for range of input power from 10 W to 100 W. The fill ratios used in the present work were 15%, 25%50% and 85%. The cooling water mass flow rate was also changed from 0.0083 kg/s to 0.033 kg/s. Experimental results showed that the maximum value of wall evaporator temperature was 115°C at input power of 100 W and a fill ratio of 15%. Results also showed that the maximum value of the total resistance was 0.8°C/W.

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28

Kuzmich, M. A., and A. A. Artsiukh. "Intensification of heat transfer in the zone of the thermosyphon evaporator when changing the boiling surface shape." Proceedings of the National Academy of Sciences of Belarus, Physical-Technical Series 67, no. 1 (April 6, 2022): 49–56. http://dx.doi.org/10.29235/1561-8358-2022-67-1-49-56.

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In present paper the influence of the boiling surface treatment types of thermosyphon evaporator on the heat transfer coefficient was studied. An experimental setup «Loop thermosyphon with replacing lower part of the evaporator» has been developed and assembled. This feature makes it easy to replace samples with various surface modifications as the lower part of the evaporator. The description of the experimental setup, equipment and research methods is given. Heat transfer coefficients for the samples at various applied thermal loads (from 5 to 200 W) were calculated. In case of flat aluminum plate (boiling surface) concentric grooves and uneven coating of aluminum oxide particles, an increase of the heat transfer coefficient from h1 = 5760 W/(m2·K) to h2 = 28339 W/(m2·K) at the supplied heat flux density q = 250 kW/m2 was observed. The heat transfer coefficient for a sample without concentric grooves, but with an uneven coating of aluminum oxide particles was h3 = 16952 W/(m2·K) at q = 250 kW/m2. Results of the study can be used for further increase of thermosyphon evaporator efficiency.

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29

Maydanik, Yury, Mariya Chernysheva, and Sergey Vershinin. "High-Capacity Loop Heat Pipe with Flat Evaporator for Efficient Cooling Systems." Journal of Thermophysics and Heat Transfer 34, no. 3 (July 2020): 465–75. http://dx.doi.org/10.2514/1.t5845.

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30

Singh, R., A. Akbarzadeh, and M. Mochizuki. "Thermal Potential of Flat Evaporator Miniature Loop Heat Pipes for Notebook Cooling." IEEE Transactions on Components and Packaging Technologies 33, no. 1 (March 2010): 32–45. http://dx.doi.org/10.1109/tcapt.2009.2031875.

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31

Siedel, Benjamin, Valérie Sartre, and Frédéric Lefèvre. "Complete analytical model of a loop heat pipe with a flat evaporator." International Journal of Thermal Sciences 89 (March 2015): 372–86. http://dx.doi.org/10.1016/j.ijthermalsci.2014.11.014.

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32

Celata, Gian Piero, Maurizio Cumo, and Massimo Furrer. "Experimental tests of a stainless steel loop heat pipe with flat evaporator." Experimental Thermal and Fluid Science 34, no. 7 (October 2010): 866–78. http://dx.doi.org/10.1016/j.expthermflusci.2010.02.001.

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33

Chen, B. B., W. Liu, Z. C. Liu, H. Li, and J. G. Yang. "Experimental investigation of loop heat pipe with flat evaporator using biporous wick." Applied Thermal Engineering 42 (September 2012): 34–40. http://dx.doi.org/10.1016/j.applthermaleng.2012.03.006.

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34

Bhargava, R., S. Khanam, B. Mohanty, and A. K. Ray. "Simulation of flat falling film evaporator system for concentration of black liquor." Computers & Chemical Engineering 32, no. 12 (December 2008): 3213–23. http://dx.doi.org/10.1016/j.compchemeng.2008.05.012.

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35

Yang, Peng, Xinlei Yang, Qingshan Liu, Dawei Li, Jing Li, Guoxin Yu, and Yingwen Liu. "Performance improvement of a household freezer with a microchannel flat-tube evaporator." Case Studies in Thermal Engineering 49 (September 2023): 103394. http://dx.doi.org/10.1016/j.csite.2023.103394.

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36

Zeng, Liping, Xing Liu, Quan Zhang, Jun Yi, Xiaohua Li, Xianglong Liu, and Huan Su. "Experimental and Simulation Study of Micro-Channel Backplane Heat Pipe Air Conditioning System in Data Center." Applied Sciences 10, no. 4 (February 13, 2020): 1255. http://dx.doi.org/10.3390/app10041255.

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This paper mainly studies the heat transfer performance of backplane micro-channel heat pipes by establishing a steady-state numerical model. Compared with the experimental data, the heat transfer characteristics under different structure parameters and operating parameters were studied, and the change of heat transfer coefficient inside the system, the air outlet temperature of the back plate and the influence of different environmental factors on the heat transfer performance of the system were analyzed. The results show that the overall error between simulation results and experimental data is less than 10%. In the range of the optimal filling rate (FR = 64.40%–73.60%), the outlet temperature at the lowest point and the highest point of the evaporation section is 22.46 °C and 19.60 °C, the temperature difference does not exceed 3 °C, and the distribution gradient in vertical height is small and the air outlet temperature is uniform. The heat transfer coefficient between the evaporator and the condenser is larger than the heat transfer coefficient under the conditions of low and high liquid charge rate. It increases gradually along the flow direction, and decreases gradually with the flow rate of the condenser. When the width of the flat tube of the evaporator increases from 20 mm to 28 mm, the internal pressure drop of the evaporator decreases by 45.83% and the heat exchange increases by 18.34%. When the number of evaporator slices increases from 16 to 24, the heat transfer increases first and then decreases, with an overall decrease of 2.86% and an increase of 87.67% in the internal pressure drop of the evaporator. The inclination angle of the corrugation changes from 30° to 60°, and the heat transfer capacity and pressure drop increase. After the inclination angle is greater than 60°, the heat transfer capacity and resistance decrease. The results are of great significance to system optimization design and engineering practical application.

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Cerza, M., and B. Boughey. "The Effects of Air Infiltration on a Large Flat Heat Pipe at Horizontal and Vertical Orientations." Journal of Heat Transfer 125, no. 2 (March 21, 2003): 349–55. http://dx.doi.org/10.1115/1.1532020.

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In the satellite or energy conversion industries flat heat pipes may be utilized to transfer heat to the thermal sink. In this investigation, a large flat heat pipe, 1.22m×0.305m×0.0127m, fabricated from 50 mil Monel 400 metal sheets and Monel 400 screens was videographed at horizontal and vertical orientations with an infrared video camera. The heat pipe evaporator section consisted of a 0.305m×0.305m area (one heated side only) while the side opposite the heated section was insulated. The remaining area of the heat pipe served as the condenser. In the horizontal orientation the heated section was on the bottom. In the vertical orientation the evaporator was aligned below the condenser. The sequence of photographs depicts heat inputs ranging from 200 W to 800 W, and the effect of air infiltration on heat pipe operation for both orientations. For the horizontal orientation, the air is seen to recede towards the small fill pipe as the heat input is increased. For the vertical orientation, the air and water vapor exhibit a buoyant interaction with the result that the air presence inhibits heat transfer by rendering sections of the condenser surface ineffective. The effects depicted in this paper set the stage for future analytical and experimental work in flat heat pipe operation for both normal and variable conductance modes.

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Hopkins, R., A. Faghri, and D. Khrustalev. "Flat Miniature Heat Pipes With Micro Capillary Grooves." Journal of Heat Transfer 121, no. 1 (February 1, 1999): 102–9. http://dx.doi.org/10.1115/1.2825922.

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Flat miniature heat pipes (FMHP’s) are shown to be very promising in the cooling of electronic component systems. This investigation presents a detailed experimental and theoretical analysis on maximum heat transfer capabilities of two copper-water FMHP’s with diagonal trapezoidal micro capillary grooves and one copper-water FMHP with axial rectangular micro capillary grooves. Maximum heat flux on the evaporator wall of the 120-mm long axial grooved heat pipe, with a vapor channel cross-sectional area of approximately 1.5 × 12 mm2 and rectangular grooves of dimensions 0.20 mm wide by 0.42 mm deep, exceeded 90 W/cm2 in the horizontal orientation and 150 W/cm2 in the vertical orientation. Theoretical prediction of the capillary limitation in the horizontal orientation agreed reasonably well with the experimental data.

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Wang, Huanfa, Guiping Lin, Xiaobin Shen, Yong Liu, and Yuandong Guo. "Experimental Study and Visual Observation of a Loop Heat Pipe with a Flat Disk-Shaped Evaporator under Various Orientations." Energies 16, no. 13 (June 30, 2023): 5068. http://dx.doi.org/10.3390/en16135068.

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In this study, visualization treatment was applied to the flat disk-shaped evaporator of a loop heat pipe. By observing the liquid/vapor behavior inside the evaporator and compensation chamber, the effects of orientation on the performances during startup and during a step-increase in heat load were investigated. With water as the working fluid, the loop heat pipe was tested under three typical orientations of φ = −90°, φ = 0°, and φ = +90°. The startup time was the shortest for the φ = −90° orientation but there could be a slight temperature overshoot, resulting in an unsmoothed startup process. The startup speeds under the φ = 0° and φ = +90° orientations were similar, both without any significant temperature overshoot. The orientation could significantly change the heat leak and, therefore, the operating temperature and the heat-transfer limit. For the φ = +90° and φ = −90° orientations, the heat-transfer limits were about 71% and 157% of the value at the φ = 0° orientation, respectively. Based on visual observations, for the loop heat pipe operating in gravity-driven mode, there could be two different paths for the working fluid to return to the evaporator, namely, along the vapor line for low heat loads and along the condenser and liquid lines for relatively large heat loads, respectively.

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Ito, Sadasuke, Nakatsu Miura, Jin Qi Wang, and Miwako Nishikawa. "Heat Pump Using a Solar Collector With Photovoltaic Modules on the Surface." Journal of Solar Energy Engineering 119, no. 2 (May 1, 1997): 147–51. http://dx.doi.org/10.1115/1.2887894.

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It is known that the higher the evaporation temperature, the higher the coefficient of performance of a heat pump for hot water supply. Flat-plate solar collectors which were insulated on the back and bonded with flexible polycrystalline silicon-type photovoltaic modules on the upper surfaces were used in a heat pump system as the evaporator in order to increase the coefficient of performance and to generate electric power. The total area of the collectors was 3.24 m2 and the photovoltaic modules covered 76 percent of the area. The characteristics of the photovoltaic array and the thermal performance of the heat pump were studied experimentally. The results indicated that a coefficient of performance (COP) of the heat pump as high as six could be obtained at 40°C of the water temperature at the inlet of the condenser in the daytime in winter. The peak electric power generated was 120 W. It was found that the photovoltaic modules on the collectors did not influence the performance of the heat pump appreciably. When there was little solar radiation, the COP of the heat pump became two which was very low. This defect was improved by using an evaporator, which had a high convective heat transfer coefficient, arranged in parallel with the fiat-plate collectors.

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Amin, Zakaria Mohd, M. N. A. Hawlader, and YE Shaochun. "ANALYSIS AND MODELING OF SOLAR EVAPORATOR-COLLECTOR." IIUM Engineering Journal 16, no. 2 (November 30, 2015): 13–29. http://dx.doi.org/10.31436/iiumej.v16i2.601.

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Solar energy is considered a sustainable resource that poses little to no harmful effects on the environment. The performance of a solar system depends to a great extent on the collector used for the conversion of solar radiant energy to thermal energy. A solar evaporator-collector (SEC) is basically an unglazed flat plate collector where refrigerants, such as R134a is used as the working fluid. As the operating temperature of the SEC is very low, it utilizes both solar irradiation and ambient energy leading to a much higher efficiency than the conventional collectors. This capability of SECs to utilize ambient energy also enables the system to operate at night. This type of collector can be locally made and is relatively much cheaper than the conventional collector.Â Â At the National University of Singapore, the evaporator-collector was integrated to a heat pump and the performance was investigated for several thermal applications: (i) water heating, (ii) drying and (iii) desalination. A 2-dimensional transient mathematical model of this system was developed and validated by experimental data. The present study provides a comprehensive study of performance.Â KEYWORDS: heat pump; evaporator-collector.

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Jung, Eui Guk, and Joon Hong Boo. "A Novel Analytical Modeling of a Loop Heat Pipe Employing the Thin-Film Theory: Part I—Modeling and Simulation." Energies 12, no. 12 (June 22, 2019): 2408. http://dx.doi.org/10.3390/en12122408.

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In this study, steady-state analytical modeling of a loop heat pipe (LHP) equipped with a flat evaporator is presented to predict the temperatures and pressures at each important part of the LHP—evaporator, liquid reservoir (compensation chamber), vapor-transport tube, liquid-transport tube, and condenser. Additionally, this study primarily focuses on analysis of the evaporator—the only LHP component comprising a capillary structure. The liquid thin-film theory is considered to determine pressure and temperature values concerning the region adjacent to the liquid-vapor interface within the evaporator. The condensation-interface temperature is subsequently evaluated using the modified kinetic theory of gases. The present study introduces a novel method to estimate the liquid temperature at the condensation interface. Existence of relative freedom is assumed with regard to the condenser configuration, which is characterized by a simplified liquid–vapor interface. The results obtained in this study demonstrate the effectiveness of the proposed steady-state analytical model with regard to the effect of design variables on LHP heat-transfer performance. To this end, the condenser length, porosity of its capillary structure, and drop in vapor temperature therein are considered as design variables. Overall, the LHP thermal performance is observed to be reasonably responsive to changes in design parameters.

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43

Wu, Shen Chun, Shih Hsuan Yen, Wei Chen Lo, Chen Yu Chung, and Shen Jwu Su. "Study of Nickel Wick Structure Applied to Loop Heat Pipe with Flat Evaporator." Key Engineering Materials 723 (December 2016): 282–87. http://dx.doi.org/10.4028/www.scientific.net/kem.723.282.

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This study investigated the use of sintered Nickel powder as the wick material of Loop heat pipe with flat evaporator (Flat loop heat pipe, FLHP) and its effect on the heat transfer performance. Add the 1-heptanol into water and form Self-rewetting Fluid (SRF), resulting in the Marangoni effect. The colder liquid can be transport to the heating surface, delaying the occurrence of dry-out and increasing the critical heat load. This paper use Surface tension measurements to measure the change of 1-heptanol SRF, then it was apply to nickel wick FLHP as working ﬂuid to investigate its effect on the heat transfer performance. This study successfully established production process of Nickel wick structure. Results of wick structure for the effective pore radius of 2.6 μm, porosity of 62%, permeability of 5.7 × 10-13m2. Results of Surface tension measurements show that 1-heptanol aqueous solution’s surface tension increases with increasing temperature, Results from applying 0.1% 1-heptanol aqueous solution to FLHP as working fluid. For performance testing show that the critical heat load was 240 W and the total thermal resistance was 0.77 ° C/W. Compared with FLHP with pure water, SRF raised the maximum heat flux of 70%, the total thermal resistance of the system reduces 40%, SRF has the potential to enhance the heat transfer performance of FLHP.

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Chernysheva, M., Svetlana I. Yushakova, and Yury F. Maydanik. "RESEARCH ON OPERATING PARAMETERS OF COPPER-WATER LOOP HEAT PIPES WITH FLAT EVAPORATOR." Heat Pipe Science and Technology, An International Journal 5, no. 1-4 (2014): 327–34. http://dx.doi.org/10.1615/heatpipescietech.v5.i1-4.360.

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Gabsi, I., S. Maalej, and M. C. Zaghdoudi. "Thermal performance modeling of loop heat pipes with flat evaporator for electronics cooling." Microelectronics Reliability 84 (May 2018): 37–47. http://dx.doi.org/10.1016/j.microrel.2018.02.023.

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Nguyen, Xuan Hung, Byung Ho Sung, Jeehoon Choi, Seong Ryoul Ryoo, Han Seo Ko, and Chulju Kim. "Study on heat transfer performance for loop heat pipe with circular flat evaporator." International Journal of Heat and Mass Transfer 55, no. 4 (January 2012): 1304–15. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2011.09.010.

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Wong, Shwin-Chung, and Chung-Wei Chen. "Visualization and evaporator resistance measurement for a groove-wicked flat-plate heat pipe." International Journal of Heat and Mass Transfer 55, no. 9-10 (April 2012): 2229–34. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2012.01.045.

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48

Wang, Dongdong, Zhichun Liu, Jun Shen, Chi Jiang, Binbin Chen, Jinguo Yang, Zhengkai Tu, and Wei Liu. "Experimental study of the loop heat pipe with a flat disk-shaped evaporator." Experimental Thermal and Fluid Science 57 (September 2014): 157–64. http://dx.doi.org/10.1016/j.expthermflusci.2014.04.017.

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49

Song, He, Liu Zhi-chun, Zhao Jing, Jiang Chi, Yang Jin-guo, and Liu Wei. "Experimental study of an ammonia loop heat pipe with a flat plate evaporator." International Journal of Heat and Mass Transfer 102 (November 2016): 1050–55. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2016.07.014.

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50

Becker, S., S. Vershinin, V. Sartre, E. Laurien, J. Bonjour, and Yu F. Maydanik. "Steady state operation of a copper–water LHP with a flat-oval evaporator." Applied Thermal Engineering 31, no. 5 (April 2011): 686–95. http://dx.doi.org/10.1016/j.applthermaleng.2010.02.005.

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