scholarly journals Effects of heat flux, mass flux, vapor quality, and saturation temperature on flow boiling heat transfer in microchannels

2009 ◽  
Vol 35 (2) ◽  
pp. 142-154 ◽  
Author(s):  
Stefan S. Bertsch ◽  
Eckhard A. Groll ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Vapor Quality ◽  
Flow Boiling Heat Transfer

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.

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).

Effect of Inlet Restriction on Flow Boiling Heat Transfer in a Horizontal Microtube

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
YanFeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Mass Fluxes ◽  
Flow Boiling Heat Transfer ◽  
Low Mass

Flow boiling heat transfer in a horizontal microtube with inlet restriction (orifice) 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 microtubes with smaller diameters are assembled at the inlet of main microtube to achieve the restriction ratios of 50% and 20%. The experimental measurement is carried out at mass fluxes ranging from 160 to 870 kg/m2·s, heat fluxes varying from 6 to 170 kW/m2, inlet temperatures of 23 and 35 °C, and saturation pressures of 10 and 45 kPa. The effects of the orifices on two-phase pressure drop, critical heat flux (CHF), and flow boiling heat transfer coefficient are studied. The results show that the pressure drop caused by the orifice takes a considerable portion in the total pressure drop at low mass fluxes. This ratio decreases as the vapor quality or mass flux increases. The difference of normal critical heat flux in the microtubes with different orifice sizes is negligible. In the aspect of flow boiling heat transfer, the orifice is able to enhance the heat transfer at low mass flux and high saturation pressure, which indicates the contribution of orifice in the nucleate boiling dominated regime. However, the effect of orifice on flow boiling heat transfer is negligible in the forced convective boiling dominated regime.

scholarly journals Alumina Nanoparticle Pre-Coated Tubing Enhancing Subcooled Flow Boiling Critical Heat Flux

2009 ◽  
Author(s):  
Bao Truong ◽  
Lin-wen Hu ◽  
Jacopo Buongiorno ◽  
Thomas McKrell
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Subcooled Flow Boiling ◽  
Nanoparticle Deposition ◽  
Subcooled Flow ◽  
Flow Boiling Heat Transfer

Nanofluids are engineered colloidal dispersions of nano-sized particle in common base fluids. Previous pool boiling studies have shown that nanofluids can improve critical heat flux (CHF) up to 200% for pool boiling and up to 50% for subcooled flow boiling due to the boiling induced nanoparticle deposition on the heated surface. Motivated by the significant CHF enhancement of nanoparticle deposited surface, this study investigated experimentally the subcooled flow boiling heat transfer of pre-coated test sections in water. Using a separate coating loop, stainless steel test sections were treated via flow boiling of alumina nanofluids at constant heat flux and mass flow rate. The pre-coated test sections were then used in another loop to measure subcooled flow boiling heat transfer coefficient and CHF with water. The CHF values for the pre-coated tubing were found on average to be 28% higher than bare tubing at high mass flux G = 2500 kg/m2 s. However, no enhancement was found at lower mass flux G = 1500 kg/m2 s. The heat transfer coefficients did not differ much between experiments when the bare or coated tubes were used. SEM images of the test sections confirm the presence of a nanoparticle coating layer. The nanoparticle deposition is sporadic and no relationship between the coating pattern and the amount of CHF enhancement is observed.

Flow Boiling Heat Transfer Characteristics of a Minichannel Up to Dryout Condition

2009 ◽  
Author(s):  
Rashid Ali ◽  
Bjo¨rn Palm ◽  
Mohammad H. Maqbool
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Working Fluid ◽  
Flow Boiling Heat Transfer ◽  
The Heat Transfer Coefficient

In this paper the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.7mm and a uniformly heated length of 220mm. R134a was used as working fluid and experiments were performed at two different system pressures corresponding to saturation temperatures of 27 °C and 32 °C. Mass flux was varied from 50 kg/m2 s to 600 kg/m2 s and heat flux ranged from 2kW/m2 to 156kW/m2. The test section was heated directly using a DC power supply. The direct heating of the channel ensured uniform heating and heating was continued until dry out was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux while mass flux and vapour quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures.

Flow Boiling Heat Transfer Characteristics of a Minichannel up to Dryout Condition

2011 ◽  
Vol 133 (8) ◽  
Author(s):  
Rashid Ali ◽  
Björn Palm ◽  
Mohammad H. Maqbool
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Working Fluid ◽  
Flow Boiling Heat Transfer ◽  
The Heat Transfer Coefficient

In this paper, the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.70 mm and a uniformly heated length of 220 mm. R134a was used as a working fluid, and experiments were performed at two different system pressures corresponding to saturation temperatures of 27°C and 32°C. Mass flux was varied from 50 kg/m2 s to 600 kg/m2 s, and heat flux ranged from 2 kW/m2 to 156 kW/m2. The test section was heated directly using a dc power supply. The direct heating of the channel ensured uniform heating, which was continued until dryout was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux, while mass flux and vapor quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that the dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures.

Flow Boiling of R134a and R245fa in a 1.1 mm Diameter Tube

2013 ◽  
Author(s):  
Emily A. Pike-Wilson ◽  
Mohamed M. Mahmoud ◽  
Tassos G. Karayiannis
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Experimental Conditions ◽  
Local Flow ◽  
Flow Boiling Heat Transfer ◽  
Vapour Quality

New refrigerants are required for cooling systems due to the fact that refrigerants like R134a are about to be phased out. This paper presents a comparison between the flow boiling heat transfer and pressure drop results of refrigerants R245fa and R134a. The experiments with R245fa were conducted in a vertical cold drawn stainless steel tube with an inner diameter of 1.1 mm and heated length of 150 mm. Experimental conditions include: mass flux range 100–400 kg/m2s, heat flux range 10–60 kW/m2, pressures of 8 and 10 bar and 1.9 and 2.5 bar for R134a and R245fa corresponding to saturated temperatures 31 °C and 39 °C and exit vapour quality range 0–0.95. The data for R134a were obtained earlier using the same experimental facility at the same experimental conditions and with the same test tube. The results demonstrated that refrigerant properties have a significant effect on heat transfer and pressure drop. The pressure drop of R245fa is higher by up to 300% compared to that of R134a at similar conditions. In addition, the effect of mass flux and heat flux on the local flow boiling heat transfer coefficient was different. Heat transfer coefficients of R245fa showed a greater dependence on vapour quality. The agreement with past heat transfer correlations is better with R134a than with R245fa.

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.

scholarly journals Experimental Study on the Flow Boiling Heat Transfer Characteristics in a Mini-Channel with Offset Fins

Proceedings ◽  
2018 ◽  
Vol 2 (22) ◽  
pp. 1376
Author(s):  
Tao Wen ◽  
Hongbo Zhan ◽  
Yimo Luo ◽  
Dalin Zhang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Saturation Pressure ◽  
Rectangular Channels ◽  
Flow Boiling Heat Transfer

The present study studied the flow boiling heat transfer performance of a mini channel with offset fins experimentally. The hydraulic diameter for it is 1.59 mm with 9 offset rectangular channels. The influences of saturation pressure, mass flux and heat flux on heat transfer coefficient were investigated. The experimental results reveal that when the vapor quality of refrigerant is less than 0.6, the mass flux has negligible influence on heat transfer coefficient. While it increases with both the saturation pressure and heat flux. Differently, in the high quality region, the heat transfer coefficient has an ascending trend with the increase of mass flux and is not affected by heat flux and saturation pressure.

scholarly journals Impact of selected thermal and flow parameters on flow boiling heat transfer in a minichannel

2019 ◽  
Vol 213 ◽  
pp. 02079
Author(s):  
Kinga Strąk ◽  
Magdalena Piasecka
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Inlet Pressure ◽  
Flow Parameters ◽  
Flow Boiling Heat Transfer

This paper reports an impact of selected thermal and flow parameters i.e., mass flux and inlet pressure on flow boiling heat transfer in a minichannel. Research was carried out on the experimental set up with the test section fitted with a single, rectangular and vertically oriented minichannel 1.7 mm deep. Infrared thermography was used to determine changes in the temperature on the outer side of the heated minichannel wall in the central part of the minichannel. The heated element for HFE-649 flowing in the minichannel was a thin alloy plate, made of Haynes-230. Local values of heat transfer coefficient for stationary state conditions were calculated using a simple one-dimensional method. Analysis of the results was based on experimental series obtained for the same heat flux, various mass fluxes and average inlet pressures. The experimental results are presented as the relationship between the heat transfer coefficient and the distance along the minichannel length and boiling curves. The highest local heat transfer coefficients were obtained for the lower average inlet pressure and for the highest mass flux at lower heat flux.

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