Evaporative Heat Transfer in Microtubes With Diameters From 244 μm to 792 μm

2005 ◽  
Author(s):  
Yun Wook Hwang ◽  
Min Soo Kim
Keyword(s):  
Heat Transfer ◽  
Nucleate Boiling ◽  
Transfer Coefficients ◽  
Average Deviation ◽  
Heat Transfer Coefficients ◽  
Experimental Heat ◽  
New Correlation ◽  
Experimental Heat Transfer ◽  
Flow Heat ◽  
Evaporative Heat Transfer

The characteristics of the evaporative heat transfer in microtubes were investigated with three circular tubes with inner diameters of 244, 430, and 792 μm, respectively. The interrelation between the heat flux and the mass flux about the heat transfer coefficients was expressed by the boiling number, which was considered to be a very important parameter to predict the trend of the heat transfer coefficients in microtubes versus the quality. A new correlation for the evaporative heat transfer coefficients in microtubes was developed by considering the following factors; the laminar flow heat transfer coefficient of liquid-phase flow, the enhancement factor of the convective heat transfer, and the nucleate boiling correction factor. The correlation developed in this study predicts the experimental heat transfer coefficients within an absolute average deviation of 8.4%.

Experimental Heat Transfer Coefficients from Ice-Roughened Surfaces for Aircraft Deicing Design

1999 ◽  
Vol 36 (6) ◽  
pp. 948-956 ◽  
Author(s):  
Nihad Dukhan ◽  
K. C. Masiulaniec ◽  
Kenneth J. De Witt ◽  
G. James Van Fossen
Keyword(s):  
Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Experimental Heat ◽  
Experimental Heat Transfer

Experimental Study of Condensation Inside a Horizontal Single Square Minichannel

2009 ◽  
Author(s):  
Marko Matkovic ◽  
Stefano Bortolin ◽  
Alberto Cavallini ◽  
Davide Del Col
Keyword(s):  
Heat Transfer ◽  
Mass Velocity ◽  
Saturation Temperature ◽  
External Heat ◽  
Copper Tube ◽  
Transfer Coefficients ◽  
External Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Experimental Heat ◽  
Experimental Heat Transfer

This work is aimed at presenting experimental heat transfer coefficients measured during condensation inside a single square cross section minichannel, having a 1.18 mm side length. The experimental heat transfer coefficients are compared to the ones previously obtained in a circular minitube. This subject is particularly interesting since most of the mini and microchannels used in practical applications have non circular cross sections. The test section used in the present work is obtained from a thick wall copper tube which is machined to draw a complex passage for the water; its geometry has been studied with the aim of increasing the external heat transfer area and thus decreasing the external heat transfer resistance. This experimental technique allows to measure directly the temperature in the tube wall and in the water channel. The heat flux is determined from the temperature profile of the coolant in the measuring sector. The wall temperature is measured by means of thermocouples embedded in the copper tube, while the saturation temperature is obtained from the saturation pressure measured at the inlet and outlet of the measuring sector. On the whole, more than seventy thermocouples have been placed in the 23 cm long measuring section. Tests have been performed with R134a at 40°C saturation temperature, at mass velocities ranging between 200 and 800 kg m−2s−1. As compared to the heat transfer coefficients measured in a circular minichannel, in the square minichannel the authors find a heat transfer enhancement at the lowest values of mass velocity; this must be due to the effect of the surface tension. No heat transfer coefficient increase has been found at the highest values of the mass velocity where condensation is shear stress dominated.

scholarly journals Experimental Study of Nucleate Boiling of Flammable, Environmentally Friendly Refrigerants

Energies ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 160 ◽  
Author(s):  
Bartosz Gil ◽  
Beata Fijałkowska
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
New Correlation ◽  
Boiling Process ◽  
The Heat Transfer Coefficient

This paper investigates the nucleate boiling process of dimethyl ether and selected hydrocarbons. The main goal of this study is to measure the heat transfer coefficients of RE170, R600a, and R601, and to compare them with R134a. The experiments were carried out for heat fluxes up to 70 kW/m2. Experimental results have shown a typical trend that the heat transfer coefficient of flammable refrigerants increases as the heat flux increases. Among the tested fluids, the highest values of heat transfer coefficient were obtained for RE170. Available correlations describing this coefficient showed a deviation of up to 93%, as compared to the data obtained. The new correlation was developed by regression analysis taking into account dimensionless variables affecting the boiling process.

Nucleate boiling heat transfer coefficients of halogenated refrigerants up to critical heat fluxes

2009 ◽  
Vol 223 (6) ◽  
pp. 1415-1424 ◽  
Author(s):  
K-J Park ◽  
D Jung ◽  
S E Shim
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Nucleate Pool Boiling ◽  
Transfer Coefficients ◽  
Average Deviation ◽  
Heat Transfer Coefficients

In this work, nucleate pool boiling heat transfer coefficients (HTCs) of five refrigerants of differing vapour pressures are measured on a horizontal, smooth copper surface of 9.53×9.53 mm. The tested refrigerants are R123, R152a, R134a, R22, and R32 and HTCs are taken from 10 kW/m2 to the critical heat flux (CHF) of each refrigerant. Wall and fluid temperatures are measured directly by thermocouples located underneath the test surface and in the liquid pool, respectively. Test results show that nucleate pool boiling HTCs of halogenated refrigerants increase as the heat flux and vapour pressure increase. This typical trend is maintained even at high heat fluxes above 200 kW/m2. Zuber's prediction equation for CHF is quite accurate showing a maximum deviation of 21 per cent for all refrigerants tested. For all refrigerants, Stephan and Abdelsalam's well-known correlation underpredicted nucleate boiling HTC data up to the CHF with an average deviation of 21.3 per cent, while Cooper's correlation overpredicted the data with an average deviation of 14.2 per cent. On the other hand, Gorenflo's and Jung et al.'s correlations showed 5.8 and 6.4 per cent deviations, respectively, in the entire nucleate boiling range up to the CHF.

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