scholarly journals Refrigerant flow boiling heat transfer in parallel microchannels as a function of local vapor quality

2008 ◽  
Vol 51 (19-20) ◽  
pp. 4775-4787 ◽  
Author(s):  
Stefan S. Bertsch ◽  
Eckhard A. Groll ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Vapor Quality ◽  
Flow Boiling Heat Transfer ◽  
Parallel Microchannels

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.

Flow Boiling Heat Transfer of R-22 in Small-Diameter Horizontal Round Tubes

2003 ◽  
Author(s):  
K. S. Park ◽  
W. H. Choo ◽  
K. H. Bang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Vapor Quality ◽  
Flow Boiling Heat Transfer ◽  
Boiling Heat Transfer Coefficient

The flow boiling heat transfer coefficient of R-22 in small hydraulic diameter tubes has been experimentally studied. Both brass and aluminum round tubes of 1.66 mm inside diameter are used for the test section. The ranges of the major experimental parameters are 300∼600 kg/m2s of refrigerant mass flux, 10∼20 kW/m2 of the wall heat flux, 0.0∼0.9 of the inlet vapor quality. The experimental result showed that the flow boiling heat transfer coefficient in this small tubes are in the range of 2∼4 kW/m2K and it varies only by heat flux, independent of mass flux and vapor quality. It is also observed that the heat transfer coefficients in the aluminum tube are up to 50% higher than in the brass tube.

Review: General Issues and Correlations for Predicting Flow Boiling Heat Transfer Coefficients in Micro-Scale Channels

2015 ◽  
Vol 23 (04) ◽  
pp. 1530003 ◽  
Author(s):  
Chang Yong Park
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Inertial Force ◽  
Viscous Force ◽  
Vapor Quality ◽  
Micro Scale ◽  
Continuous Decrease ◽  
Flow Boiling Heat Transfer

A review study was performed for basic heat transfer mechanism and quantitative analysis of correlations for flow boiling heat transfer in micro-scale channels. Several criteria for determining threshold diameter for micro-scale channels were discussed and the concept of confinement number was commented. The distinctive feature of flow boiling in micro-scale channels were considered and it was found out that the effect of the heat flux, latent heat, viscous force, surface tension, and inertial force was more significant. Important dimensionless parameters were summarized and it was pointed out that the boiling number, capillary number, and Weber number could be expected to play important roles at flow boiling in micro-scale channels. 17 correlations for flow boiling in micro-scale channels were reviewed in this study, and they were categorized by three types of correlations such as an equivalent Nusselt number correlation, a correlation with superposition of nucleate and convection boiling mechanism, and a flow pattern-based correlation. The predicted values by the correlations were compared with 536 experimental data from four different literatures and a correlation with smallest prediction errors was found. Some correlations showed distinct trends of convection heat transfer coefficient (h) change with respect to the variation of vapor quality. The trends are categorized by three trends such as noticeable increase of h with the increase of vapor quality and significant continuous decrease after dryout point, minor increase and decrease or decrease and increase of h, and gradual and continuous decrease of h with the increase of vapor quality. For each trend of h change, recommendable correlations and their basic equation forms were proposed to compare the prediction results with experimental data or to develop a new correlation by modifying existing correlations.

Pressure Effect on Flow Boiling Heat Transfer of Water in Minichannels

2009 ◽  
Author(s):  
Kwang-Hyun Bang ◽  
Kyung-Kyu Kim ◽  
Ok-Keun Choi ◽  
Hui-Seong Jeong
Keyword(s):  
Heat Transfer ◽  
Test Section ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Test Tube ◽  
Gear Pump ◽  
Vapor Quality ◽  
System Pressure ◽  
Flow Boiling Heat Transfer ◽  
Experimental Apparatus

The effect of pressure on the flow boiling of water in minichannels has been experimentally studied. The range of pressure was 2 to 16 bars in the experiment. The experimental apparatus consisted mainly of the 1.73 mm inner-diameter round tube test section, gear pump, pre-heater, pressurizer, pre-evaporator, and condenser. The pre-evaporator was used for varying the vapor quality entering the test section. The pressurizer controls the desired system pressure. The test tube is made of 316 stainless steel and the test tube and the pre-evaporator tube were heated by DC electric current through the tubes. The measured flow boiling heat transfer coefficients were in the range of 10000∼40000 W/m2K and showed the general convection dominant trend in terms of vapor quality. The data also indicates that the pressure does not alter the heat transfer coefficient significantly. Comparisons of the experimental data to the existing correlations showed large discrepancy, implying that these correlations are not correctly accounted for pressure.

Flow Boiling Heat Transfer in Horizontal Metal-Foam Tubes

2009 ◽  
Vol 131 (12) ◽  
Author(s):  
C. Y. Zhao ◽  
W. Lu ◽  
S. A. Tassou
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Metal Foam ◽  
Flow Boiling ◽  
Vapor Quality ◽  
Flow Rates ◽  
Flow Boiling Heat Transfer ◽  
Mass Flow Rates

The two-phase flow and boiling heat transfer in horizontal metal-foam filled tubes are experimentally investigated. The results show that the heat transfer is almost doubled by reducing the cell size from 20 ppi to 40 ppi for a given porosity, thanks to more surface area and strong flow mixing for the smaller cell size. The boiling heat transfer coefficient keeps steady rising, albeit slowly, by increasing the vapor quality for high mass flow rates, while the same story does not hold for the cases of low mass flow rates. The flow pattern can be indirectly judged through monitoring the cross-sectional wall surface temperature fluctuations and wall-refrigerant temperature difference. As the operating pressure increases, the boiling heat transfer at low vapor quality (x<0.1) exhibits similar behavior with pool boiling heat transfer, namely, the heat transfer is enhanced by improving the pressure. However the flow boiling heat transfer is suppressed to some extent as the pressure increases. The heat transfer coefficient of copper foam tubes is approximately three times higher than that of plain tubes.

scholarly journals Experimental Approaches to Measurement of Vapor Quality of Two-Phase Flow Boiling

2020 ◽  
Author(s):  
Mehdi Kabirnajafi ◽  
Jiajun Xu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Phase Flow ◽  
Vapor Quality ◽  
Two Phase ◽  
Thermal Boundary Conditions ◽  
Flow Boiling Heat Transfer ◽  
Experimental Approaches

Vapor quality is one of the crucial parameters substantially affecting the flow boiling heat transfer coefficient. Hence, the reliability and accuracy of vapor quality measurements is of a great significance to accurately investigating the effect of vapor quality on the local flow boiling heat transfer coefficients. In the present study, various experimental approaches are represented to measure and control local vapor quality for flow boiling tests. Experimental approaches are classified based on the type of thermal boundary conditions imposed on the tube wall, that is, known constant wall heat flux and constant wall temperature (unknown variable wall heat flux). In addition, in-situ techniques are also investigated to measure local vapor quality regardless of the governing thermal boundary conditions within two-phase flow experiments. Finally, the experimental methodologies are compared based on their level of reliability and accuracy in measurement, costliness and affordability, and simplicity in execution to address their potential merits and demerits.

Flow Boiling in Minichannels of Copper, Brass, and Aluminum Round Tubes

2004 ◽  
Author(s):  
K. H. Bang ◽  
W. H. Choo
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Wall Heat Flux ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Flow Boiling Heat Transfer

The past work on flow boiling heat transfer in minichannels ranging one to three millimeters of hydraulic diameter has indicated that the local heat transfer coefficients are largely independent of mass flux and vapor quality, but mainly a function of wall heat flux. The present work is a revisit of flow boiling in minichannels by conducting experiment using 1.67 mm inner diameter tubes of three different materials; aluminum, brass, and copper, to investigate an effect of the tube inner surface conditions with the focus on an effect on nucleate boiling. Tests were conducted for R-22, a fixed mass flux of 600 kg/m2s, 5∼30 kW/m2 of wall heat flux, 0.0∼0.9 of local vapor quality. The present experimental data confirmed that the flow boiling heat transfer coefficient in a minichannel varies only by heat flux, independent of mass flux and vapor quality. The effect of tube material was found small for the tubes used in the present work. The present data were well predicted by the correlation proposed by Tran et al. (1996).

An Analytical Model of Flow Boiling Heat Transfer for Slug Flow in a Single Circular Horizontal Micro-Channel

2012 ◽  
Author(s):  
Amen M. Younes ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Film ◽  
Transfer Coefficient ◽  
Slug Flow ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Micro Channel ◽  
Vapor Quality ◽  
Flow Boiling Heat Transfer

Slug flow is one of the most common flow patterns that occur during flow boiling in horizontal micro-channels. In the present work, an analytical model of flow boiling heat transfer is developed for slug flow in a single circular horizontal micro-channel under a uniform heat flux. The heat transfer is affected mainly by the liquid film thickness confined between the vapor slug and the channel wall. For more physical and reliable flow boiling heat transfer model, the liquid film thickness variation and pressure gradient effects on the flow boiling heat transfer coefficient are considered. The influence of vapor quality on heat transfer coefficient, vapor velocity and liquid film velocity is studied. The model is constructed based on the conservation equations of the separated two phase flow. The interphase surface is assumed to be smooth and the flow is a laminar flow. The obtained model applied for flow boiling of R-134a refrigerant in the slug flow at a narrow vapor quality range (0.0 < x < 0.1). The heat transfer coefficient showed a high increase close to the low vapor quality while decreases gradually after the peak. Furthermore, the vapor velocity increases linearly by increasing the vapor quality while, the liquid film velocity decreases.

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