Effect of Operating Pressure on Flow Boiling Heat Transfer in Microchannels

2005 ◽  
Author(s):  
K. H. Bang ◽  
T. Y. Yoon
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Working Fluid ◽  
Operating Pressure ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer ◽  
Experimental Apparatus

This paper reports an experimental study of flow boiling in a microchannel and this work has been focused on the investigation on the effect of operating pressure. The experimental apparatus consisted mainly of peristaltic pump, preheater, microchannel test tube, and vacuum chamber for control of operating pressure. Deionized water was used as the working fluid. The test section was a round tube of 310 μm inside diameter, made of 304 stainless steel. The experiment has been performed for the conditions of heat flux of 35∼85 kW/m2, mass flux of 200∼300 kg/m2s (160∼250 of liquid Reynolds numbers), and the operating pressure of 10∼20 kPa. The measured flow boiling heat transfer coefficients in the microchannel were in the range of 3.0 to 27 kW/m2K and the experimental data showed that the flow boiling heat transfer coefficients in microchannels were affected mainly by the wall heat flux and the operating pressure.

scholarly journals Flow boiling heat transfer coefficient of R-134a/R-290/R-600a mixture in a smooth horizontal tube

2008 ◽  
Vol 12 (3) ◽  
pp. 33-44 ◽  
Author(s):  
Raja Balakrishnan ◽  
Lal Dhasan ◽  
Saravanan Rajagopal
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer ◽  
R 134A

An investigation on in-tube flow boiling heat transfer of R-134a/R-290/R-600a (91%/4.068%/4.932% by mass) refrigerant mixture has been carried out in a varied heat flux condition using a tube-in-tube counter-flow test section. The boiling heat transfer coefficients at temperatures between -5 and 5?C for mass flow rates varying from 3 to 5 g/s were experimentally arrived. Acetone is used as hot fluid, which flows in the outer tube of diameter 28.57 mm, while the test fluid flows in the inner tube of diameter 9.52 mm. By regulating the acetone flow rate and its entry temperature, different heat flux conditions between 2 and 8 kW/m2 were maintained. The pressure of the refrigerant was maintained at 3.5, 4, and 5 bar. Flow pattern maps constructed for the considered operating conditions indicated that the flow was predominantly stratified and stratified wavy. The heat transfer coefficient was found to vary between 500 and 2200 W/m2K. The effect of nucleate boiling prevailing even at high vapor quality in a low mass and heat flux application is high-lighted. The comparison of experimental results with the familiar correlations showed that the correlations over predict the heat transfer coefficients of this mixture.

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.

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.

The Effect of Inlet Orifice on Critical Heat Flux and Flow Boiling Heat Transfer in Single Horizontal Microtube

2013 ◽  
Author(s):  
Yanfeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Saturation Pressure ◽  
Working Fluid ◽  
Flow Boiling Heat Transfer

Flow oscillation is a crucial issue for the development of flow boiling heat transfer in the applications. Inlet orifice has been proven be an option to eliminate the oscillation. However, the effects of inlet orifice on critical heat flux and flow boiling heat transfer coefficient are lack of study. In this work, the effects of inlet restriction on critical heat flux and heat transfer coefficient in single horizontal microtube under uniform heating condition is experimentally investigated using FC-72 as working fluid. A stainless steel microtube with an inner diameter of 889 μm is selected as main microtube. Two smaller microtubes are assembled at the inlet of main microtube to achieve the restriction configurations of 50% and 20% area ratios. The experimental measurement is carried out at mass fluxes ranging from 160–870 kg/m2·s and heat fluxes varying from 6–170 kW/m2. Two saturation pressures, 10 and 45 kPa, are tested. The experimental results of critical heat flux and two phase heat transfer coefficient obtained in the microtube without orifice are compared with the existing correlations. The addition of an orifice does not enhance the normal critical heat flux but increases the premature critical heat flux. In aspect of heat transfer, the orifice shows improvement on heat transfer coefficient at low mass flux and high saturation pressure.

New correlations of flow boiling heat transfer coefficients based on R1234yf data

2017 ◽  
Author(s):  
Fernando Neves Quintino dos Santos ◽  
Matheus Barroso ◽  
Juan Jose Garcia Pabon ◽  
Hélio Augusto Goulart Diniz ◽  
Paulo Eduardo Lopes Barbieri
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer
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