The Simulation of Heat Pipe Evaporator in Concentration Solar Cell

2010 ◽  
Vol 44-47 ◽  
pp. 1207-1212 ◽  
Author(s):  
Zi Long Wang ◽  
Hua Zhang ◽  
Hai Tao Zhang
Keyword(s):  
Heat Flux ◽  
Solar Cell ◽  
Heat Pipe ◽  
Saturation Temperature ◽  
High Heat ◽  
Maximum Temperature ◽  
Working Fluid ◽  
High Heat Flux ◽  
Two Phase ◽  
Solar Cell Performance

Considering the problem of the concentrating solar cell efficiency restricted by the temperature. The closed two-phase thermosyphon was used to dissipation heat in concentrating solar cell at high heat flux, which adopted water as the working fluid. The temperature distribution of evaporator had significant effect on solar cell performance and heat pipe efficiency. A numerical simulation model of evaporator was established by FLUENT. During the computing process, the heat flux, filling ratio of liquid and saturation temperature were taken into account. It was found that the maximum temperature of evaporator was less than 85°C, when the solar cell operated in 140 to 180 suns, in the conditions of evaporator size (Length×Width×Height, 100×100×30 mm), the optimum charging ratio of liquid is between 27%～30%. The smaller saturation temperature would bring the better heat transfer characters.

A Numerical Model of a Reciprocating-Mechanism Driven Heat Loop for Two-Phase High Heat Flux Cooling

2016 ◽  
Vol 8 (4) ◽  
Author(s):  
Olubunmi Popoola ◽  
Ayobami Bamgbade ◽  
Yiding Cao
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Model ◽  
Performance Optimization ◽  
Numerical Study ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Two Phase ◽  
Transfer Device

An effective design option for a cooling system is to use a two-phase pumped cooling loop to simultaneously satisfy the temperature uniformity and high heat flux requirements. A reciprocating-mechanism driven heat loop (RMDHL) is a novel heat transfer device that could attain a high heat transfer rate through a reciprocating flow of the two-phase working fluid inside the heat transfer device. Although the device has been tested and validated experimentally, analytical or numerical study has not been undertaken to understand its working mechanism and provide guidance for the device design. The objective of this paper is to develop a numerical model for the RMDHL to predict its operational performance under different working conditions. The developed numerical model has been successfully validated by the existing experimental data and will provide a powerful tool for the design and performance optimization of future RMDHLs. The study also reveals that the maximum velocity in the flow occurs near the wall rather than at the center of the pipe, as in the case of unidirectional steady flow. This higher velocity near the wall may help to explain the enhanced heat transfer of an RMDHL.

Working Fluid Inventory Effect on Heat Transfer Performance of a Grooved Micro Heat Pipe

2013 ◽  
Vol 589-590 ◽  
pp. 559-564
Author(s):  
Xi Bing Li ◽  
Yun Shi Ma ◽  
Xun Wang ◽  
Ming Li
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Pipe ◽  
Heat Transfer Performance ◽  
Mathematic Model ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Transfer Performance ◽  
Flux Concentration

As a highly efficient heat transfer component, a micro heat pipe (MHP) has been widely applied to the situations with high heat flux concentration. However, a MHPs heat transfer performance is affected by many factors, among which, working fluid inventory has great influence on the security, reliability and frost resistance of its heat transfer performance. In order to determine the appropriate working fluid inventory for grooved MHPs, this paper first analyzed the working principle, major heat transfer limits and heat flux distribution law of grooved MHPs in electronic chips with high heat flux concentration, then established a mathematic model for the working fluid inventory in grooved MHPs. Finally, with distilled water being the working fluid, a series of experimental investigations were conducted at different temperatures to test the heat transfer performances of grooved MHPs, which were perfused with different inventories and with different adiabatic section lengths. The experimental results show that when the value of α is roughly within 0.40±0.05, a grooved MHP can acquire its best heat transfer performance, and the working fluid inventory can be determined by the proposed mathematic model. Therefore this study solves the complicated problem of determining appropriate working fluid inventory for grooved MHPs.

Analysis of the Evaporating Characteristics of the Grooved Micro Heat Pipe with Alkali Metals as Working Fluid

2012 ◽  
Vol 516-517 ◽  
pp. 84-87 ◽  
Author(s):  
Lei Yu ◽  
Wei Qiang Liu
Keyword(s):  
Thin Film ◽  
Mathematical Model ◽  
Heat Flux ◽  
Heat Pipe ◽  
Alkali Metals ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Working Fluids ◽  
High Temperature Heat Pipe

This paper has built a mathematical model for the evaporating characteristics of the grooved micro heat pipe’s thin film region and computed them in a specific working condition. The evaporating model of Wayner was employed in this mathematical model. The results from computation showed, for the H2O and NH3 as working fluid, at the beginning of the thin film region, the heat flux raised rapidly to a peak value and then declined to almost 0 also rapidly in a very short distance. Differently, for the Na and K as working fluid, the heat flux raised quickly but declined slower. Therefore, the alkali metals working fluids had larger area of high heat flux covered. The results indicated that the alkali metals working fluid has better evaporating characteristics for the high-temperature heat pipe than normal working fluids.

Experimental and Analytical Studies of Reciprocating-Mechanism Driven Heat Loops (RMDHLs)

2008 ◽  
Vol 130 (7) ◽  
Author(s):  
Yiding Cao ◽  
Mingcong Gao
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Electronics Cooling ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Two Phase ◽  
Condenser Section ◽  
Analytical Studies ◽  
Evaporator Section

This paper conducts experimental and analytical studies of a novel heat-transfer device, reciprocating-mechanism driven heat loop (RMDHL) that facilitates two-phase heat transfer while eliminating the so-called cavitation problem commonly encountered by a conventional pump. A RMDHL normally includes a hollow loop having an interior flow passage, an amount of working fluid filled within the loop, and a reciprocating driver. The hollow loop has an evaporator section, a condenser section, and a liquid reservoir. The reciprocating driver is integrated with the liquid reservoir and facilitates a reciprocating flow of the working fluid within the loop, so that liquid is supplied from the condenser section to the evaporator section under a substantially saturated condition and the so-called cavitation problem associated with a conventional pump is avoided. The reciprocating driver could be a solenoid-operated reciprocating driver for electronics cooling applications and a bellows-type reciprocating driver for high-temperature applications. Experimental study has been undertaken for a solenoid-operated heat loop in connection with high heat flux thermal management applications. Experimental results show that the heat loop worked very effectively and a heat flux as high as 300W∕cm2 in the evaporator section could be handled. A working criterion has also been derived, which could provide a guidance for the design of a RMDHL.

Development of an R245fa for Electronics Cooling System for High Heat Flux Applications

2009 ◽  
Author(s):  
Farhad Saffaraval ◽  
Amir Jokar
Keyword(s):  
Heat Flux ◽  
Heat Exchanger ◽  
Cooling System ◽  
Electronics Cooling ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Two Phase ◽  
Microchannel Heat Exchanger ◽  
Mass Flow Rates

The objective of this study is to experimentally explore thermodynamic performance of R245fa, as a low-pressure and environmentally-friendly refrigerant, in a microchannel heat exchanger. This heat exchanger is used in an electronics cooling application with high-power density. Due to the large amount of latent heat that is released during evaporation process, the two-phase microchannel coolers are able to remove much more energy compared to single-phase cooling systems. In this study, R245fa is used as the working fluid in a refrigeration pump loop that mainly includes an evaporator, a condenser, a refrigerant pump, and a pressure regulator valve. The goal is to obtain optimal mass flow rates and system pressures while the temperatures in evaporator and condenser are kept constant for specific conditions. The results obtained from this study are then compared to the results previously obtained for water as the working fluid in a similar cooling system. It is expected the evaporative cooling through the microchannel heat exchanger be a viable and effective solution, especially for higher heat flux applications.

Two-Phase Spray Cooling With Water/2-Propanol Binary Mixture: Investigation of Mass Diffusion Resistance

2016 ◽  
Author(s):  
Sai Sujith Obuladinne ◽  
Huseyin Bostanci
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Performance ◽  
Pure Water ◽  
Spray Cooling ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Two Phase ◽  
High Heat Transfer

Two-phase spray cooling has been an emerging thermal management technique offering high heat transfer coefficients (HTCs) and critical heat flux (CHF) levels, near-uniform surface temperatures, and efficient coolant usage that enables to design of compact and lightweight systems. Due to these capabilities, spray cooling is a promising approach for high heat flux applications in computing, power electronics, and optics. The two-phase spray cooling inherently depends on saturation temperature-pressure relationships of the working fluid to take advantage of high heat transfer rates associated with liquid-vapor phase change. When a certain application requires strict temperature and/or pressure conditions, thermophysical properties of the working fluid play a critical role in attaining proper efficiency, reliability, or packaging structure. However, some of the commonly used working fluids today, including refrigerants and dielectric liquids, have relatively poor properties and heat transfer performance. In such cases, utilizing binary mixtures to tune working fluid properties becomes an alternative approach. This study aimed to conduct an initial investigation on the spray cooling characteristics of practically important binary mixtures and demonstrate their capability for challenging high heat flux applications. The working fluid, water/2-propanol binary mixture at various concentration levels, specifically at x1 (liquid mass fraction of 2-proponal in water) of 0.0 (pure water), 0.25, 0.50, 0.879 (azeotropic mixture) and 1.0, represented both non-azeotropic and azeotropic cases. Tests were performed on a closed loop spray cooling system using a pressure atomized spray nozzle with a constant liquid flow rate at corresponding 20°C subcooling conditions and 1 Atm pressure. A copper test section measuring 10 mm × 10 mm × 2 mm with a plain, smooth surface simulated high heat flux source. Experimental procedure involved controlling the heat flux in increasing steps, and recording the steady-state temperatures to obtain cooling curves in the form of surface superheat vs heat flux. The obtained results showed that pure water (x1 = 0.0) and 2-propanol (x1 = 1.0) provide the highest and lowest heat transfer performance, respectively. At a given heat flux level, the HTC values indicated strong dependence on x1, where the HTCs depress proportional to the concentration difference between the liquid and vapor phases. The CHF values sharply decreased at x1≥ 0.25.

Geometric Evaporator Enhancements of an Oscillating Heat Pipe

2015 ◽  
Author(s):  
Mitchell P. Hoesing ◽  
Gregory J. Michna
Keyword(s):  
Heat Pipe ◽  
Electronics Cooling ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Straight Channel ◽  
Two Phase ◽  
Oscillating Heat Pipe ◽  
Meandering Channels ◽  
Channel Configuration

The oscillating heat pipe (OHP) is a passive two-phase cooling device that is capable of transferring large amounts of thermal energy. Previous research conducted on OHPs indicates that it is a viable option for developing high-heat flux cooling requirements, particularly in the field of electronics cooling. OHPs consist of evaporator, adiabatic, and condenser sections connected by multiple interconnected meandering channels. A two-phase working fluid, in this study acetone, fills the channels and acts as the heat transfer medium. The focus of this study is to further the development of OHPs to improve performance and operation by conducting a comparison between two different evaporator geometries. The first was a traditional straight channel geometry. The second consisted of circular pins centered in the channels with circular cavities surrounding the pins to allow fluid flow. The results of this study showed that the traditional straight channel configuration preformed best. The lowest fill ratio, 35%, performed best for all cases. The lowest thermal resistance observed was 0.11 K/W for the straight channels, and 0.16 K/W for the enhanced channels. The enhanced channels likely did not improve the performance because of an increase in pressure drop through the evaporator section.

Combined Pulsating and Capillary Heat Pipe Mechanism for Cooling of High Heat Flux Electronics

1999 ◽  
Author(s):  
Z. Jon Zuo ◽  
Mark T. North ◽  
Lee Ray
Keyword(s):  
Heat Flux ◽  
Theoretical Model ◽  
Heat Pipe ◽  
Internal Flow ◽  
Thermal Conditions ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Test Results ◽  
Sintered Metal

Abstract This paper discusses an advanced heat pipe mechanism for cooling of high heat flux electronics. The mechanism combines the capillary effect of sintered metal powder wicks with a pulsating motion of the working fluid to maintain sufficient liquid supply to high heat flux regions. The pulsating motion is driven by thermal conditions in the heat pipe evaporator and condenser and can be sustained with proper internal flow channel design. A theoretical model was developed to describe the pulsating motion of the working fluid. Proof-of-concept copper/water heat pipes were tested to verify the heat flux capability of this advanced mechanism. The test results demonstrated over 220W/cm2 heat flux capability, a fourfold improvement over present state of the art heat pipe performance. Comparisons between the test results and the model predictions validated the theoretical model.

Loop Thermosyphon Design for Cooling of Large Area, High Heat Flux Sources

2007 ◽  
Author(s):  
John R. Hartenstine ◽  
Richard W. Bonner ◽  
Jared R. Montgomery ◽  
Tadej Semenic
Keyword(s):  
Saturation Temperature ◽  
High Heat ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Working Fluid ◽  
High Heat Flux ◽  
Flow Loop ◽  
Large Area ◽  
Two Phase ◽  
Porous Wick

Two-phase flow loop technologies capable of acquiring high heat fluxes (>1kW/cm2) from large area heat sources (10cm2) are being considered for the next generation naval thermal requirements. A loop thermosyphon device (∼1 meter tall) was fabricated and tested that included several copper porous wick structures in cylindrical evaporators. The first two were standard annular monoporous and biporous wick designs. The third wick consists of an annular evaporator wick and an integral secondary slab wick for improved liquid transport. In this configuration a circular array of cylindrical vapor vents are formed integral to the primary and secondary transport wick composite. Critical heat fluxes using these wick structures were measured between 240W/cm2 and 465W/cm2 over a 10cm2 area with water as the working fluid at 70°C saturation temperature. A thermosyphon model capable of predicting flow rate at various operating conditions based on a separated flow model is presented.

Passive Thermosyphon Cooling System for High Heat Flux Servers

2015 ◽  
Author(s):  
Sylwia Szczukiewicz ◽  
Nicolas Lamaison ◽  
Jackson B. Marcinichen ◽  
John R. Thome ◽  
Peter J. Beucher
Keyword(s):  
Heat Flux ◽  
Cooling System ◽  
Cost Savings ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Net Benefit ◽  
Operation Performance ◽  
Two Phase ◽  
Cooling Loop

The main aim of the current paper is to demonstrate the capability of a two-phase closed thermosyphon loop system to cool down a contemporary datacenter rack, passively cooling the entire rack including its numerous servers. The effects on the performance of the entire cooling loop with respect to the server orientation, micro-evaporator design, riser and downcomer diameters, working fluid, and approach temperature difference at the condenser have been modeled and simulated. The influence of the thermosyphon height (here from 5 to 20 cm with a horizontally or vertically oriented server) on the driving force that guarantees the system operation whilst simultaneously fulfilling the critical heat flux (CHF) criterion also has been examined. In summary, the thermosyphon height was found to be the most significant design parameter. For the conditions simulated, in terms of CHF, the 10 cm-high thermosyphon was the most advantageous system design with a minimum safety factor of 1.6 relative to the imposed heat flux of 80 W cm−2. Additionally, a case study including an overhead water-cooled heat exchanger to extract heat from the thermosyphon loop has been developed and then the entire rack cooling system evaluated in terms of cost savings, payback period, and net benefit per year. This approximate study provides a general understanding of how the datacenter cooling infrastructure directly impacts the operating budget as well as influencing the thermal/hydraulic operation, performance, and reliability of the datacenter. Finally, the study shows that the passive two-phase closed loop thermosyphon cooling system is a potentially economically sound technology to cool high heat flux servers of datacenters.

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