Reciprocating-Mechanism Driven Heat Loops and Their Applications

2003 ◽  
Author(s):  
Yiding Cao ◽  
Mingcong Gao
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Electronics Cooling ◽  
Working Fluid ◽  
High Heat Flux ◽  
Two Phase ◽  
Condenser Section ◽  
Evaporator Section ◽  
Two Phase Heat Transfer ◽  
Transfer Device

This paper introduces a novel heat transfer mechanism that facilitates two-phase heat transfer while eliminating the so-called cavitation problem commonly encountered by a conventional pump. The heat transfer device is coined as the reciprocating-mechanism driven heat loop (RMDHL), which 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 300 W/cm2 in the evaporator section could be handled. The applications of the bellows-type reciprocating heat loop for gas turbine nozzle guide vanes and the leading edges of hypersonic vehicles are also illustrated. The new heat transfer device is expected to advance the current two-phase heat transfer device and open up a new frontier for further research and development.

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.

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.

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.

High-Flux Thermal Management With Supercritical Fluids

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Brian M. Fronk ◽  
Alexander S. Rattner
Keyword(s):  
Heat Flux ◽  
Thermal Management ◽  
Heat Sink ◽  
Electronics Cooling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Management Approach ◽  
High Heat Flux ◽  
Two Phase ◽  
Pump Design

A novel thermal management approach is explored, which uses supercritical carbon dioxide (sCO2) as a working fluid to manage extreme heat fluxes in electronics cooling applications. In the pseudocritical region, sCO2 has extremely high volumetric thermal capacity, which can enable operation with low pumping requirements, and without the potential for two-phase critical heat flux (CHF) and flow instabilities. A model of a representative microchannel heat sink is evaluated with single-phase liquid water and FC-72, two-phase boiling R-134a, and sCO2. For a fixed pumping power, sCO2 is found to yield lower heat-sink wall temperatures than liquid coolants. Practical engineering challenges for supercritical thermal management systems are discussed, including the limits of predictive heat transfer models, narrow operating temperature ranges, high working pressures, and pump design criteria. Based on these findings, sCO2 is a promising candidate working fluid for cooling high heat flux electronics, but additional thermal transport research and engineering are needed before practical systems can be realized.

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.

High Heat Flux Absorption Utilizing Porous Materials With Two-Phase Heat Transfer

1997 ◽  
Vol 119 (3) ◽  
pp. 171-179 ◽  
Author(s):  
J. T. Dickey ◽  
G. P. Peterson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Porous Materials ◽  
Metal Flow ◽  
High Heat ◽  
High Heat Flux ◽  
Two Phase ◽  
Macro Scale ◽  
Flow Through ◽  
Two Phase Heat Transfer

By combining two-phase heat transfer with forced convective flow through a porous material, a new heat transfer scheme emerges with the ability to absorb high heat fluxes without the corresponding temperature increase encountered in single-phase systems. In general, flow-through sintered metals are characterized by high thermal conductivity due to the metallic media, and a fluid flow which on the macro scale can be described as slug flow in nature. These same characteristics are exhibited by liquid metal flow cooling systems. To predict the heat transfer attributes of this two-phase flow process, a semi-analytical model was developed using the conservation equations of mass, momentum, and energy along with the apparent physical properties of the composite material. The results indicate that when a heat flux is applied to one side of the bounding surface and adiabatic conditions exist on the remaining sides, the surface temperature asymptotically approaches the same value regardless of the mass flow rate. In addition to the analytical results, definitions for the convection coefficient and Nusselt number for flow-through porous materials with phase change are presented.

Mathematical Modeling of Novel Two-Phase Heat Transfer Device for Thermal Management of Light Emitting Diodes

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Karthik S. Remella ◽  
Frank M. Gerner ◽  
Ahmed Shuja
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Thermal Management ◽  
Light Emitting Diodes ◽  
Working Fluid ◽  
Two Phase ◽  
Light Emitting ◽  
Phase Mixture ◽  
Two Phase Heat Transfer ◽  
Transfer Device

The paper introduces a novel two-phase heat transfer device (TPHTD) which is employed in the thermal management of light emitting diodes (LEDs). The heat transfer device structurally resembles a conventional loop heat pipe (LHP) without a compensation chamber, but operates very differently from it. The device is comprised of a central evaporator package and a circular coil that acts as a heat exchanger loop. The working fluid leaving the evaporator has a two-phase mixture quality of approximately 0.2. Having introduced the device, the paper delineates a mathematical model for predicting its thermal performance. The primary objective of the model is to provide a fundamental understanding of the operation of the device. A one-dimensional thermal resistance model (TRM) is utilized in modeling the evaporator. The paper presents a detailed discussion on obtaining these resistances from experiments conducted on the device. A correlation for the external heat transfer coefficient of the heat exchanger loop is proposed based on experiments and is found to be in good agreement with literature. The model predicts performance parameters such as board temperature, two-phase mixture quality, and saturation and subcooled temperatures (Tsat and Tsc) of the working fluid for different input thermal powers (Qtot). Based on experimental evidence, it is concluded that the majority of Qtot (∼75%) is utilized in phase change of the working fluid, and the rest reheats the working fluid from a lower subcooled temperature (Tsc) to the saturation temperature (Tsat) of the evaporator.

Visualization of Two-phase Bursting Flow Effect on the Two-Phase Closed Thermosyphon

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Yeonghwan Kim ◽  
Dong Hwan Shin ◽  
Jin Sub Kim ◽  
Seung M. You ◽  
Jungho Lee
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cylindrical Channel ◽  
Nucleate Boiling ◽  
Liquid Pool ◽  
Working Fluid ◽  
Two Phase ◽  
Evaporator Section

Abstract Two-phase flow inside the two-phase closed thermosyphon (TPCT) including evaporator, adiabatic and condenser sections was visually investigated in order to qualitatively analyze the complicated behaviors of both liquid film and vapor flows simultaneously. The semi-cylindrical channel which is 650 mm long was formed in the long copper block and the flat face of the channel was covered with a flat Pyrex glass for visual observation. The inner diameter of the semi-cylindrical channel was 25 mm and distilled water was used as a working fluid. The filling ratio of the thermosyphon was fixed at 0.5 and the inclination angle was set to 60º. As the heat flux increases, nucleate boiling becomes dominant and the bursting motion starts to begin in the liquid pool at the evaporator section. The bursting liquid flow reaches the condenser section and changes the condensation regime from dropwise to filmwise by flooding the condenser wall, which results in the decrease of condensation heat transfer coefficient. In addition, the vigorous vapor generation which occurs in the liquid pool at the evaporator section disturbs the circulation of the condensate film from the condenser to the evaporator section. As a result, the local dry-out occurs on the evaporator section with increasing heat flux, so the boiling heat transfer coefficient is decreased. [This research was supported by the Ministry of Science and ICT through the National Research Foundation of Korea (NRF-2018H1D3A2000929).]

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