scholarly journals Boiling Heat Transfer and Flow Regimes in Microchannels—A Comprehensive Understanding

2011 ◽  
Vol 133 (1) ◽  
Author(s):  
Tannaz Harirchian ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
High Speed ◽  
Flow Boiling ◽  
Electronics Cooling ◽  
Flow Regimes ◽  
Operating Conditions ◽  
Comprehensive Understanding ◽  
Transfer Coefficients ◽  
Cross Sectional

Flow boiling in microchannels has been investigated extensively over the past decade for electronics cooling applications; however, the implementation of microchannel heat sinks operating in the two-phase regime in practical applications has lagged due to the complexity of boiling phenomena at the microscale. This has led to difficulties in predicting the heat transfer rates that can be achieved as a function of the governing parameters. From extensive experimental work and analysis performed in recent years, a clear picture has emerged that promises to enable prediction of flow boiling heat transfer over a wide parameter space. Experiments have been conducted to determine the effects of important geometric parameters such as channel width, depth, and cross-sectional area, operating conditions such as mass flux, heat flux, and vapor quality, as well as fluid properties, on flow regimes, heat transfer coefficients, and pressure drops in microchannels. A detailed mapping of flow regimes occurring under different conditions has been facilitated with high-speed flow visualizations. In addition, quantitative criteria for the transition between macro- and microscale boiling behaviors have been identified. In this paper, these recent advances toward a comprehensive understanding of flow boiling in microchannels are summarized.

Augmented Performance of Flow Boiling Heat Transfer in a Tube With Axial Micro-Grooves and its Augmentation Mechanisms

1999 ◽  
Author(s):  
Lixin Cheng ◽  
Tingkuan Chen
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Axial Direction ◽  
Smooth Tube ◽  
Absolute Pressure ◽  
Transfer Coefficients ◽  
Frictional Pressure Drop ◽  
Flow Boiling Heat Transfer ◽  
Enhanced Tube

Abstract Experiments of upward flow boiling heat transfer with water in a vertical smooth tube and a tube with axial micro-grooves were respectively conducted. Both of the tested tubes have a length of 2.5 m, an inner diameter of 15 mm and an outlet diameter of 19 mm. The tube with axial micro grooves has many micro rectangle grooves in its inner wall along the axial direction. The grooves have a depth of 0.5 mm and a width of 0.3 mm. The tests were performed at an absolute pressure of 6 bar. The heat flux ranged from 0 to 550 kW/m2 and the mass flux was selected at 410, 610 and 810 kg/m2s, respectively. By comparison, flow boiling heat transfer coefficients in the enhanced tube are 1.6 ∼ 2.7 fold that in the smooth tube while the frictional pressure drop in the enhanced tube is slightly greater than that in the smooth tube. The augmentation of flow boiling heat transfer in the tube with axial micro-grooves is apparent. Based on the experimental data, a correlation of flow boiling heat transfer is proposed for the enhanced tube. Finally, the mechanisms of heat transfer enhancement are analyzed.

Flow Boiling Heat Transfer, Pressure Drop, and Flow Pattern for CO2 in a 3.5mm Horizontal Smooth Tube

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Chang Yong Park ◽  
Pega Hrnjak
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer

Abstract C O 2 flow boiling heat transfer coefficients and pressure drop in a 3.5mm horizontal smooth tube are presented. Also, flow patterns were visualized and studied at adiabatic conditions in a 3mm glass tube located immediately after a heat transfer section. Heat was applied by a secondary fluid through two brass half cylinders to the test section tubes. This research was performed at evaporation temperatures of −15°C and −30°C, mass fluxes of 200kg∕m2s and 400kg∕m2s, and heat flux from 5kW∕m2 to 15kW∕m2 for vapor qualities ranging from 0.1 to 0.8. The CO2 heat transfer coefficients indicated the nucleate boiling dominant heat transfer characteristics such as the strong dependence on heat fluxes at a mass flux of 200kg∕m2s. However, enhanced convective boiling contribution was observed at 400kg∕m2s. Surface conditions for two different tubes were investigated with a profilometer, atomic force microscope, and scanning electron microscope images, and their possible effects on heat transfer are discussed. Pressure drop, measured at adiabatic conditions, increased with the increase of mass flux and quality, and with the decrease of evaporation temperature. The measured heat transfer coefficients and pressure drop were compared with general correlations. Some of these correlations showed relatively good agreements with measured values. Visualized flow patterns were compared with two flow pattern maps and the comparison showed that the flow pattern maps need improvement in the transition regions from intermittent to annular flow.

Single Phase and Flow Boiling Heat Transfer of Water and Ethanol in a Mini-Channel Array

2010 ◽  
Author(s):  
M. W. Alnaser ◽  
K. Spindler ◽  
H. Mu¨ller-Steinhagen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Speed ◽  
Single Phase ◽  
Flow Boiling ◽  
Video Camera ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Speed Video Camera

A test rig was constructed to investigate flow boiling in an electrically heated horizontal mini-channel array. The test section is made of copper and consists of twelve parallel mini-channels. The channels are 1 mm deep, 1 mm wide and 250 mm long. The test section is heated from underneath with six cartridge heaters. The channels are covered with a glass plate to allow visual observations of the flow patterns using a high-speed video-camera. The wall temperatures are measured at five positions along the channel axis with two resistance thermometers in a specified distance in heat flow direction. Local heat transfer coefficients are obtained by calculating the local heat flux. The working fluids are deionised water and ethanol. The experiments were performed under near atmospheric pressure (0.94 bar to 1.2 bar absolute). The inlet temperature was kept constant at 20°C. The measurements were taken for three mass fluxes (120; 150; 185 kg/m2s) at heat fluxes from 7 to 375 kW/m2. Heat transfer coefficients are presented for single phase forced convection, subcooled and saturated flow boiling conditions. The heat transfer coefficient increases slightly with rising heat flux for single phase flow. A strong increase is observed in subcooled flow boiling. At high heat flux the heat transfer coefficient decreases slightly with increasing heat flux. The application of ethanol instead of water leads to an increase of the surface temperature. At the same low heat flux flow boiling heat transfer occurs with ethanol, but in the experiments with water single phase heat transfer is still dominant. It is because of the lower specific heat capacity of ethanol compared to water. There is a slight influence of the mass flux in the investigated parameter range. The pictures of a high-speed video-camera are analysed for the two-phase flow-pattern identification.

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.

Flow Boiling of Water in Minichannels: Effect of Pressure

2007 ◽  
Author(s):  
Kwang-Hyun Bang ◽  
Kun-Eui Hong ◽  
In-Seon Hwang
Keyword(s):  
Heat Transfer ◽  
Test Section ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Gear Pump ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Effect Of Pressure ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer

This paper reports an experimental study on flow boiling of water in a minichannel. Flow boiling heat transfer coefficients and pressure drops were measured and the data were compared with existing correlations. The effect of pressure was the major objectives in this study and the range of pressure was 1 to 18 bars. The experimental apparatus consisted mainly of a minichannel test section, gear pump, pre-heater, pressurizer, condenser and evaporator. The evaporator was used for variation of vapor quality at the inlet of test section. The pressurizer controls the desired system pressure. The test section is a round tube of 1.73 mm inside diameter, made of 316 stainless steel. The test section and the evaporator tubes were heated by DC electric current through the tubes. The measured flow boiling heat transfer coefficients showed two distinct regions; relatively high heat transfer coefficients at low vapor quality and lower heat transfer coefficients at higher vapor quality. This observation implies the change of flow regime, slug to annular flow. Comparisons of the experimental data and the prediction of correlations (Gungor & Winterton, 1987; Tran et al., 1996; Kandlikar, 2003) showed large discrepancy in both regions.

Subcooled Water Flow Boiling Heat Transfer in a Short SUS304-Tube With Twisted-Tape Insert

2010 ◽  
Author(s):  
Koichi Hata ◽  
Suguru Masuzaki
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Test Tube ◽  
Heat Fluxes ◽  
Effective Length ◽  
Twisted Tape ◽  
Subcooled Boiling ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

The subcooled boiling heat transfer (HT) and the steady-state critical heat fluxes (CHFs) in a short SUS304-tube with twisted-tape insert are systematically measured for mass velocities (G = 4016 to 13850 kg/m2s), inlet liquid temperatures (Tin = 285.82 to 363.96 K), outlet pressures (Pout = 764.76 to 889.02 kPa) and exponentially increasing heat input (Q = Q0exp(t/τ), τ = 8.5 s) by the experimental water loop comprised of a multistage canned-type circulation pump controlled by an inverter. The SUS304 test tube of inner diameter (d = 6 mm), heated length (L = 59.5 mm), effective length (Leff = 49.1 mm), L/d (= 9.92), Leff/d (= 8.18) and wall thickness (δ = 0.5 mm) with average surface roughness (Ra = 3.18 μm) is used in this work. The SUS304 twisted tape with twist ratio, y [= H/d = (pitch of 180° rotation)/d], of 3.39 is used. The relation between inner surface temperature and heat flux for the SUS304-tube with the twisted-tape insert are clarified from non-boiling to CHF. The subcooled boiling heat transfer for SUS304-tube with the twisted-tape insert is compared with our empty SUS304-tube data and the values calculated by our and other workers’ correlations for the subcooled boiling heat transfer. The influences of the twisted-tape insert and the swirl velocity on the subcooled boiling heat transfer and the CHFs are investigated into details and the widely and precisely predictable correlations of the subcooled boiling heat transfer and the CHFs for turbulent flow of water in the SUS304-tube with twisted-tape insert are given based on the experimental data. The correlations can describe the subcooled boiling heat transfer coefficients and the CHFs obtained in this work within −25 to +15% difference.

A General Correlation for Saturated Two-Phase Flow Boiling Heat Transfer Inside Horizontal and Vertical Tubes

1990 ◽  
Vol 112 (1) ◽  
pp. 219-228 ◽  
Author(s):  
S. G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Experimental Investigations ◽  
Mean Deviation ◽  
Transfer Coefficients ◽  
Flow Boiling Heat Transfer ◽  
Dependent Parameter ◽  
Vertical Tubes

A simple correlation was developed earlier by Kandlikar (1983) for predicting saturated flow boiling heat transfer coefficients inside horizontal and vertical tubes. It was based on a model utilizing the contributions due to nucleate boiling and convective mechanisms. It incorporated a fluid-dependent parameter Ffl in the nucleate boiling term. The predictive ability of the correlation for different refrigerants was confirmed by comparing it with the recent data on R-113 by Jensen and Bensler (1986) and Khanpara et al. (1986). In the present work, the earlier correlation is further refined by expanding the data base to 5246 data points from 24 experimental investigations with ten fluids. The proposed correlation, equations (4) and (5), along with the constants given in Tables 3 and 4, gives a mean deviation of 15.9 percent with water data, and 18.8 percent with all refrigerant data, and it also predicts the correct hTP versus x trend as verified with water and R-113 data. Additional testing with recent R-22 and R-113 data yielded the lowest mean deviations among correlations tested. The proposed correlation can be extended to other fluids by evaluating the fluid-dependent parameter Ffl for that fluid from its flow boiling or pool boiling data.

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