Cavitation-Enhanced Microchannel Heat Exchanger Demonstration and Heat Transfer Correlation Development Using R-134a

2012 ◽  
Author(s):  
Joshua D. Sole ◽  
Bradley J. Shelofsky ◽  
Robert P. Scaringe ◽  
Gregory S. Cole
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
High Heat ◽  
High Heat Flux ◽  
Heat Transfer Correlation ◽  
Two Phase ◽  
Microchannel Heat Exchanger ◽  
Military Aviation ◽  
R 134A ◽  
Two Phase Heat Transfer

Electronics of all types, particularly those in the military aviation arena, are decreasing in size while at the same time increasing in power. As a result, newer high-heat-flux electronic components are exceeding the cooling capabilities of conventional single-phase military aviation coldplates and coolants. It is for this reason that we have been investigating new methods to cool the next generation of high-heat-flux military aviation electronics. In this work, a novel method of inducing two-phase conditions within a microchannel heat exchanger has been developed and demonstrated. Micro-orifices placed upstream of each microchannel in a microchannel heat exchanger not only cause an improvement in flow distribution, but can also induce cavitation in the incoming subcooled refrigerant and result in favorable two-phase flow regimes for enhanced heat transfer. In this study, R-134a is used as the coolant in the cavitation enhanced microchannel heat exchanger (CEMC-HX) which has been integrated into a vapor compression refrigeration system. Multiple micro-orifice geometries combined with a fixed microchannel geometry (nominally 250 μm × 250 μm) were investigated over a range of applied base heat fluxes (10–100 W/cm2) and mass fluxes (500–1000 kg/m2-s). Two-phase heat transfer coefficients exceeding 100,000 W/m2-K at refrigerant qualities of less than 5% have been demonstrated due to the achievement of preferential, cavitation-induced, flow regimes such as annular flow. To the author’s knowledge, this is the highest heat transfer coefficient ever reported in the literature for R-134a. Additionally, a four term two-phase heat transfer correlation was developed that achieved a mean absolute error (MAE) of 25.5%.

Investigation of Two Phase Heat Transfer Coefficients of Cryogenic Mixed Refrigerants

2013 ◽  
Author(s):  
Seungwhan Baek ◽  
Sangkwon Jeong
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Microchannel Heat Exchanger ◽  
Heat Transfer Coefficients ◽  
Evaporation Heat ◽  
Two Phase Heat Transfer

Mixed Refrigerant Joule Thomson (MR-JT) refrigerators are widely used in various kinds of cryogenic systems these days. Although heat transfer coefficient estimation for a multiphase and multi-component fluid in cryogenic temperature range is necessarily required in the heat exchanger design of MR-JT refrigerator, it has been rarely discussed so far. In this paper, condensation and evaporation heat transfer coefficients of mixed refrigerant are measured in a microchannel heat exchanger. Printed Circuit Heat Exchanger (PCHE) has been developed as a compact microchannel heat exchanger and used in the experiment. Several two-phase heat transfer coefficient correlations are examined to discuss the experimental measurement results. The result of this paper shows that cryogenic mixed refrigerant heat transfer coefficients can be estimated by conventional two-phase heat transfer coefficient correlations.

scholarly journals Effect of Pressure on the Performance of Passive Two-Phase Closed Thermosyphon System Using R-134a

2020 ◽  
Vol 7 (1) ◽  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
High Heat ◽  
High Heat Flux ◽  
Two Phase ◽  
Heating Load ◽  
R 134A ◽  
The Heat Transfer Coefficient

Two-phase closed thermosiphon system for cooling high heat flux electronic devices was constructed and tested on a lab scale. The performance of the thermosyphon system was investigated using R-134a as a working fluid. The effect of heat flux and the refrigerant pressure on the evaporator side heat transfer coefficient were investigated. It was found that the heat transfer coefficient increases by increasing the heat flux on the evaporator or by reducing the inside pressure. The effect of heat transfer mode of the condenser (natural or forced) also affected the overall heat transfer coefficient in the cycle. At the 200W heating load, the values of the heat transfer coefficients were 32 and 1.5 kW/m². ˚C, for natural and forced convection modes, respectively. The temperature difference between the evaporator and the refrigerant saturation pressure was found to be dependent on heat flux and the pressure inside the system. At 40 W heating load, the heat transfer coefficient was calculated to be 500, 3000 and 7300 W/oC.m2 at 0.152, .135 and 0.117 reduced pressure, respectively. It can be concluded that such a thermosyphon system can be used to cool high heat flux devices. This can be done using an environmentally friendly refrigerant and without any need for power to force the convection at the condenser.

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 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.

Experimental investigation on two-phase heat transfer of R-134a during vaporization in a plate heat exchanger with rough surface

2020 ◽  
Vol 160 ◽  
pp. 120221
Author(s):  
Jutapat Soontarapiromsook ◽  
Lazarus Godson Asirvatham ◽  
Ahmet Selim Dalkılıç ◽  
Omid Mahian ◽  
Somchai Wongwises ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Heat Exchanger ◽  
Rough Surface ◽  
Plate Heat Exchanger ◽  
Two Phase ◽  
Plate Heat ◽  
R 134A ◽  
Two Phase Heat Transfer

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.

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.

Thermoreflectance Wall Temperature Measurement in Annular Two-Phase Flow

2019 ◽  
Author(s):  
Jason Chan ◽  
Brian E. Fehring ◽  
Roman W. Morse ◽  
Kristofer M. Dressler ◽  
Gregory F. Nellis ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Wall Temperature ◽  
Annular Flow ◽  
High Heat ◽  
High Heat Flux ◽  
Phase Flow ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Dry Out

Abstract A thermoreflectance method to measure wall temperature in two-phase annular flow is described. In high heat flux conditions, momentary dry-out occurs as the liquid film vaporizes, resulting in dramatic decreases in heat transfer coefficient. Simultaneous liquid and vapor thermoreflectance measurements allow calculations of instantaneous and time-averaged heat transfer coefficients. Validation, calibration and uncertainty of the technique are discussed.

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