Effects of Pressure and a Microporous Coating on HFC-245fa Pool Boiling Heat Transfer

2013 ◽  
Author(s):  
Gilberto Moreno ◽  
Jana R. Jeffers ◽  
Sreekant Narumanchi
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Reduced Pressure ◽  
Heat Transfer Coefficients ◽  
Hfc 134A ◽  
Microporous Coating ◽  
Two Phase Cooling

A study was conducted to experimentally characterize the pool boiling performance of hydrofluorocarbon (HFC)-245fa. The motivation for this research is to characterize the performance of candidate refrigerants for potential use in automotive power electronics two-phase cooling systems. The HFC-245fa pool boiling experiments were conducted using horizontally oriented 1-cm2 heated surfaces to quantify the effects of pressure and a microporous-enhanced coating on heat transfer coefficients and critical heat flux (CHF) values. Experiments were carried out at pressures ranging from 0.15 MPa to 1.1 MPa (reduced pressure range: 0.04–0.31). To enhance boiling heat transfer, a copper microporous coating was applied to the test surfaces. The coating was found to enhance heat transfer coefficients by as much as 430% and CHF by approximately 50%. Increasing pressure decreased the magnitude of the heat transfer coefficient enhancements but had minimal effect on CHF enhancements. The experimental data were then used to generate correlations for the boiling heat transfer coefficients and CHF values. Finally, the performance of HFC-245fa was compared to the performance of hydrofluoroolefin (HFO)-1234yf and HFC-134a at conditions of equivalent saturation temperatures and reduced pressures.

Effects of Pressure and a Microporous Coating on HFC-245fa Pool Boiling Heat Transfer

2014 ◽  
Vol 136 (10) ◽  
Author(s):  
Gilberto Moreno ◽  
Jana R. Jeffers ◽  
Sreekant Narumanchi
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heat Transfer Performance ◽  
Pool Boiling ◽  
Transfer Coefficients ◽  
Enhanced Heat Transfer ◽  
Reduced Pressure ◽  
Heat Transfer Coefficients ◽  
Hfc 134A ◽  
Microporous Coating

A study was conducted to experimentally characterize the pool boiling performance of hydrofluorocarbon HFC-245fa at pressures ranging from 0.15 MPa to 1.1 MPa (reduced pressure range: 0.04–0.31). Pool boiling experiments were conducted using horizontally oriented 1-cm2 heated surfaces to quantify the effects of pressure and a microporous-enhanced coating on heat transfer coefficients and critical heat flux (CHF) values. Results showed that the coating enhanced heat transfer coefficients and CHF by 430% and 50%, respectively. The boiling heat transfer performance of HFC-245fa was then compared with the boiling performance of HFC-134a and hydrofluoroolefin HFO-1234yf.

Pool Boiling Heat Transfer Characteristics of HFO-1234yf With and Without Microporous-Enhanced Surfaces

2011 ◽  
Author(s):  
Gilberto Moreno ◽  
Sreekant Narumanchi ◽  
Charles King
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Fundamental Study ◽  
Heat Transfer Coefficients ◽  
Hfc 134A ◽  
Lower Heat

This fundamental study characterizes the pool boiling performance of a new refrigerant, HFO-1234yf (hydrofluoroolefin 2,3,3,3-tetrafluoropropene). The similarities in thermophysical properties with HFC-134a and low global warming potential make HFO-1234yf the prospective next generation refrigerant in automotive air-conditioning systems. This study examines the possibility of using this refrigerant for two-phase cooling of hybrid and electric vehicle power electronic components. Pool boiling experiments were conducted with HFO-1234yf and HFC-134a at system pressures ranging from 0.7 to 1.7 MPa using horizontally oriented 1 cm2 heat sources. Results show that the boiling heat transfer coefficients of HFO-1234yf and HFC-134a are nearly identical at lower heat fluxes. HFO-1234yf yielded lower heat transfer coefficients at higher heat fluxes and lower critical heat flux (CHF) as compared with HFC-134a. To enhance boiling heat transfer, a copper microporous coating was applied to the test surfaces. The coating provided enhancement to both the boiling heat transfer coefficients and CHF, for both refrigerants, at all tested pressures. Increasing pressure decreases the level of heat transfer coefficient enhancements while increasing the level of CHF enhancements.

Pool Boiling Heat Transfer Characteristics of HFO-1234yf on Plain and Microporous-Enhanced Surfaces

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Gilberto Moreno ◽  
Sreekant Narumanchi ◽  
Charles King
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heated Surface ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Automotive Air Conditioning ◽  
Hfc 134A ◽  
Lower Heat

This study characterizes the pool boiling performance of HFO-1234yf (hydrofluoroolefin 2,3,3,3-tetrafluoropropene). HFO-1234yf is a new, environmentally friendly refrigerant likely to replace HFC-134a in automotive air-conditioning systems. Pool boiling experiments were conducted at system pressures ranging from 0.7 to 1.7 MPa using horizontally oriented 1-cm2 heated surfaces. Test results for pure (oil-free) HFO-1234yf and HFC-134a were compared. The results showed that the boiling heat transfer coefficients of HFO-1234yf and HFC-134a were nearly identical at lower heat fluxes. HFO-1234yf yielded lower heat transfer coefficients at higher heat fluxes and lower critical heat flux (CHF) values as compared with HFC-134a. To enhance boiling heat transfer, a copper microporous coating was applied to the test surfaces. The coating enhanced both the boiling heat transfer coefficients and CHF for both refrigerants at all tested pressures. Increasing pressure decreased the level of heat transfer coefficient enhancements and increased the level of CHF enhancements. The experimental data were then used to develop a correlation for predicting the CHF for a smooth/plain heated surface.

Forced Convective Boiling of Refrigerant HCFC123 in a Mini-Tube

2010 ◽  
Author(s):  
Koichi Araga ◽  
Keisuke Okamoto ◽  
Keiji Murata
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Pool Boiling ◽  
Constant Heat Flux ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Convective Boiling ◽  
Frictional Pressure Drop ◽  
Heat Transfer Coefficients

This paper presents an experimental investigation of the forced convective boiling of refrigerant HCFC123 in a mini-tube. The inner diameters of the test tubes, D, were 0.51 mm and 0.30 mm. First, two-phase frictional pressure drops were measured under adiabatic conditions and compared with the correlations for conventional tubes. The frictional pressure drop data were lower than the correlation for conventional tubes. However, the data were qualitatively in accord with those for conventional tubes and were correlated in the form φL2−1/Xtt. Next, heat transfer coefficients were measured under the conditions of constant heat flux and compared with those for conventional tubes and for pool boiling. The heat transfer characteristics for mini-tubes were different from those for conventional tubes and quite complicated. The heat transfer coefficients for D = 0.51 mm increased with heat flux but were almost independent of mass flux. Although the heat transfer coefficients were higher than those for a conventional tube with D = 10.3 mm and for pool boiling in the low quality region, they decreased gradually with increasing quality. The heat transfer coefficients for D = 0.30 mm were higher than those for D = 0.51 mm and were almost independent of both mass flux and heat flux.

Nucleate Pool Boiling Heat Transfer Coefficients of Distilled Water (H2O) and R-134a/Oil Mixtures From Rib-Roughened Surfaces

1997 ◽  
Vol 119 (1) ◽  
pp. 142-151 ◽  
Author(s):  
Shou-Shing Hsieh ◽  
Chun-Jen Weng
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Distilled Water ◽  
Transfer Coefficients ◽  
Pool Boiling Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Oil Mixtures ◽  
R 134A ◽  
Rib Roughened

Measurements of pool-boiling heat transfer coefficients in distilled water and R-134a/oil mixtures with up to 10 percent (by weight) miscible EMKARATE RL refrigeration lubricant oil are extensively studied for a smooth tube and four rib-roughened tubes (rib pitch 39.4 mm, rib height 4 mm, rib width 15 mm, number of rib element 8, rib angle 30 deg–90 deg). Boiling data of pure refrigerants and oil mixtures, as well as the influences of heat flux level on heat transfer coefficient, are presented and discussed. A correlation is developed for predicting the heat transfer coefficient for both pure refrigerants and refrigerant-oil mixtures. Moreover, boiling visualizations were made to broaden our fundamental understanding of the pool boiling heat transfer mechanism for rib roughened surfaces with pure refrigerants and refrigerant-oil mixtures.

Pool Boiling Heat Transfer From Plain and Microporous, Square Pin Finned Surfaces in Saturated FC-72

1999 ◽  
Author(s):  
K. N. Rainey ◽  
S. M. You
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Large Scale ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Small Scale ◽  
Surface Microstructure ◽  
Transfer Coefficients ◽  
Microporous Coating ◽  
Nucleate Boiling Heat Transfer

Abstract The present research is an experimental study of “double enhancement” behavior in pool boiling from heater surfaces simulating microelectronic devices immersed in saturated FC-72 at atmospheric pressure. The term “double enhancement” refers to the combination of two different enhancement techniques: a large-scale area enhancement (square pin fin array) and a small-scale surface enhancement (microporous coating). Fin lengths were varied from 0 (flat surface) to 8 mm. Effects of this double enhancement technique on critical heat flux (CHF) and nucleate boiling heat transfer in the horizontal orientation (fins are vertical) are investigated. Results showed significant increases in nucleate boiling heat transfer coefficients with the application of the microporous coating to the heater surfaces. CHF was found to be relatively insensitive to surface microstructure for the finned surfaces except in the case of the surface with 8 mm long fins. The nucleate boiling and CHF behavior has been found to be the result of multiple, counteracting mechanisms: surface area enhancement, fin efficiency, surface microstructure (active nucleation site density), vapor bubble departure resistance, and re-wetting liquid flow resistance.

Two-Phase Pressure Drop and Boiling Heat Transfer in a Single Horizontal Microchannel

2006 ◽  
Author(s):  
Cheol Huh ◽  
Moo Hwan Kim
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Local Flow ◽  
Heat Transfer Coefficients ◽  
Phase Pressure

With a single microchannel and a series of microheaters made with MEMS technique, two-phase pressure drop and local flow boiling heat transfer were investigated using deionized water in a single horizontal rectangular microchannel. The test microchannel has a hydraulic diameter of 100 μm and length of 40 mm. A real time observation of the flow patterns with simultaneous measurement are made possible. Tests are performed for mass fluxes of 90, 169, and 267 kg/m2s and heat fluxes of from 100 to 600 kW/m2. The experimental local flow boiling heat transfer coefficients and two-phase frictional pressure gradient are evaluated and the effects of heat flux, mass flux, and vapor qualities on flow boiling are studied. Both the evaluated experimental data are compared with existing correlations. The experimental heat transfer coefficients are nearly independent on mass flux and the vapor quality. Most of all correlations do not provide reliable heat transfer coefficients predictions with vapor quality and prediction accuracy. As for two-phase pressure drop, the measured pressure drop increases with the mass flux and heat flux. Most of all existing correlations of two-phase frictional pressure gradient do not predict the experimental data except some limited conditions.

Nucleate Pool Boiling Heat Transfer of R134a and R134a-PVE Lubricant Mixtures on Smooth and Five Enhanced Tubes

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
Wen-Tao Ji ◽  
Ding-Cai Zhang ◽  
Nan Feng ◽  
Jian-Fei Guo ◽  
Mitsuharu Numata ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Saturation Temperature ◽  
Transfer Coefficients ◽  
Pool Boiling Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Enhanced Tubes ◽  
Mass Fractions

Pool boiling heat transfer coefficients of R134a with different lubricant mass fractions for one smooth tube and five enhanced tubes were tested at a saturation temperature of 6°C. The lubricant used was polyvinyl ether. The lubrication mass fractions were 0.25%, 0.5%, 1.0%, 2.0%, 3.0%, 5.0%, 7.0%, and 10.0%, respectively. Within the tested heat flux range, from 9000 W/m2 to 90,000 W/m2, the lubricant generally has a different influence on pool boiling heat transfer of these six tubes.

Effect of Nano-Particles on Pool Boiling Heat Transfer of Refrigerant 141b

2007 ◽  
Author(s):  
Da-Wei Liu ◽  
Chien-Yuh Yang
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heat Transfer Performance ◽  
Pool Boiling ◽  
Nano Particles ◽  
Test Results ◽  
Tube Surface ◽  
Transfer Coefficients ◽  
Pool Boiling Heat Transfer ◽  
Heat Transfer Coefficients

Fluids with nano-sized particles have been proved that may effectively enhance the single-phase convective heat transfer performance. For pool boiling heat transfer, the published test results seems conflicted to each other. Some measured heat transfer coefficient decreased with increasing particle concentration but some showed no appreciable difference. This study provides an experimental investigation on pool boiling heat transfer performance of refrigerants R-141b with and without nano-sized Au particles on horizontal plain tubes. The test results show that the boiling heat transfer coefficients increase with increasing nano-particles concentration. At particles concentration of 1.0%, the heat transfer coefficient is more than twice higher than those without nano-particles. However, the heat transfer coefficients decreased for each test after every 5 days and finally close to those of R-141b without nano-particles. The SPM investigation shows that the test tube surface roughness decreased from 0.317 μm before boiling test to 0.162 μm after test. Further investigation by TEM and Dynamic Light Scattering particle analyzer shows that the nano-particles aggregated from 3 μm before test to 110 μm after test. This results show that the nano-sized Au particles are able to significantly increase pool boiling heat transfer of refrigerant R-141b on plain tube surface. The tube surface roughness and particle size changed after boiling test. Both of these effects degrade the boiling heat transfer coefficients.

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