Flow Boiling Inside a Single Circular Minichannel: Measurement of Local Heat Transfer Coefficient

2007 ◽  
Author(s):  
Alberto Cavallini ◽  
Stefano Bortolin ◽  
Davide Del Col ◽  
Marko Matkovic ◽  
Luisa Rossetto
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Experimental Apparatus ◽  
Boiling Process

This paper describes a new experimental apparatus for the measurement of the local heat transfer coefficient during flow boiling inside a 0.96 mm internal diameter single round cross section minichannel and reports preliminary heat transfer data taken during flow boiling of R134a. As a peculiar characteristic of the present technique, the heat transfer coefficient is not measured by imposing the heat flux; instead, the boiling process is governed by controlling the inlet temperature of the heating secondary fluid. This paper also presents a methodology to determine the critical conditions during the flow boiling process when no heat flux is imposed.

Local Heat Transfer Coefficient During Condensation in a 0.8 mm Diameter Pipe

2006 ◽  
Author(s):  
Alberto Cavallini ◽  
Davide Del Col ◽  
Marko Matkovic ◽  
Luisa Rossetto
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Operating Conditions ◽  
Local Heat Transfer Coefficient ◽  
Wide Range ◽  
The Heat Transfer Coefficient

The first preliminary tests carried on a new experimental rig for measurement of the local heat transfer coefficient inside a circular 0.8 mm diameter minichannel are presented in this paper. The heat transfer coefficient is measured during condensation of R134a and is obtained from the measurement of the heat flux and the direct gauge of the saturation and wall temperatures. The heat flux is derived from the water temperature profile along the channel, in order to get local values for the heat transfer coefficient. The test section has been designed so as to reduce thermal disturbances and experimental uncertainty. A brief insight into the design and the construction of the test rig is reported in the paper. The apparatus has been designed for experimental tests both in condensation and vaporization, in a wide range of operating conditions and for a wide selection of refrigerants.

Flow Boiling in Minichannels Under Normal, Hyper and Microgravity: Frictional Pressure Loss and Flow Patterns

2007 ◽  
Author(s):  
D. Brutin ◽  
S. Luciani ◽  
O. Rahli ◽  
Ch. LeNiliot ◽  
L. Tadrist
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Pressure Loss ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Flow Patterns ◽  
Local Heat Transfer Coefficient ◽  
Parabolic Flights

We present in this paper, flow boiling results obtained during parabolic flights campaigns. The experimental aim is to obtain the local heat transfer coefficient and the influence of gravity on HFE-7100 flow boiling in minichannels. The hydraulic diameter investigated is: 0.84 mm. The influence of hypergravity and microgravity solely on the frictional pressure loss is evidenced in this paper, and explained using the flow patterns.

Modeling Bubble Growth in Micro-Channel Cooling Systems

2007 ◽  
Author(s):  
Joshua L. Nickerson ◽  
Martin Cerza ◽  
Sonia M. F. Garcia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Conduction Equation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

The solution of the heat conduction equation in the liquid layer beneath a moving bubble’s base and the resulting local heat transfer coefficient are presented. An analytical model was constructed using separation of variables to solve the heat conduction equation for the thermal profile in the liquid film beneath the base of a bubble moving through a microchannel at a given velocity. Differentiating the resulting liquid thermal profile and applying the standard definition for the local heat transfer coefficient resulted in a solution for local heat transfer coefficient as a function of bubble length. Analysis included varying pertinent parameters such as film thickness beneath the bubble base, wall heat flux, and superheated temperature in the microchannel. Water and FC-72 were analyzed as prospective coolant fluids. Analytical data revealed that as the superheated temperature in the microchannel increases, local heat transfer coefficients increase and arrive at a higher steady-state value. Increasing wall heat flux achieved the same result, while increasing film thickness resulted in lower heat transfer coefficients. The model indicated that water had superior performance as a coolant, provided the dielectric fluid (FC-72) is not mandated.

THEORETICAL EVALUATION OF NEW PHASE DELAY METHODS FOR MEASURING LOCAL HEAT TRANSFER COEFFICIENTS

1999 ◽  
Vol 23 (3-4) ◽  
pp. 361-376 ◽  
Author(s):  
W. Turnbull ◽  
P. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Phase Delay ◽  
Driving Frequency ◽  
One Dimensional

A one-dimensional analytical solution has been derived for unsteady heat conduction within a semi infinite body, of high thermal resistance, that is subject to a surface heat flux that varies periodically with time. The heat flux is assumed to be generated within a thin isothermal coating. The model predicts that a phase delay will develop between the heat flux and the coating thermal response. This phase delay is independent upon the material properties of the substrate and coating, on the heat flux driving frequency, and on the local heat transfer, coefficient. With the exception of this last quantity the other parameters are known a priori, hence if the phase delay can be measured experimentally it can then be used to determine the local heat transfer coefficient. Absolute values of the local coating temperature and local heat flux are not required. Hence calibration of the devices for measuring these quantities should not be required. In contrast to the overall surface temperature, it is predicted that the phase delay angle will attain a steady-state value within a few heat flux cycles, thus reducing the time required obtaining a measurement. Furthermore, the one-dimensional mathematical model that has been developed reduces to those used in previous experimentally validated techniques, when appropriate constants in the boundary condition are used.

Boiling in Microchannels with Refrigerant Mixtures

2010 ◽  
Vol 34-35 ◽  
pp. 576-581
Author(s):  
Zi Cheng Hu ◽  
Hu Gen Ma ◽  
Xin Nan Song ◽  
Qian Wang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Refrigerant Mixtures

Experiments were conducted to investigate the saturated flow boiling heat transfer characteristics in single micro tube using environmentally acceptable refrigerant mixtures R32 and R134a. Local heat transfer coefficient was measured and boiling heat transfer mechanisms were discussed for a range of heat flux (3-65 kW/m2) , mass flux (860-4816 kg/m2•s) and quality (0-0.9). These characteristics indicated that the local heat transfer coefficient was greatly dependent of heat flux and independent of mass flux and quality in the nucleate boiling regime, which was oppsite to that in forced convection regime, and deterioration of boiling heat transfer occurred in the local dry-out regime. In addition, a correlation for nucleate dominant boiling in micro tube was developed ,which included the effects of heat flux and fluid property and showed some success with the data of this study within a 20% random error band.

Experimental and Numerical Analyses of R134a Flow Boiling Heat Transfer Characteristics in an Evaporator Tube of Refrigeration System

2019 ◽  
Vol 27 (03) ◽  
pp. 1950024
Author(s):  
Zahraa Kareem Yasser ◽  
Ahmed J. Hamad
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Refrigeration System ◽  
Heat Transfer Characteristics

The heat transfer characteristics of R134a flow boiling in a horizontal tube of an evaporator section for a refrigeration system of 310-W capacity are investigated experimentally and numerically. The experimental work was conducted using an evaporator tube test section of inner diameter 5.8[Formula: see text]mm and length 600[Formula: see text]mm. The ranges of investigated experimental data for heat flux, mass flux, saturation temperature and vapor quality were 13.8–36.6[Formula: see text]kW/m2, 52–105[Formula: see text]kg/m2[Formula: see text][Formula: see text][Formula: see text]s, [Formula: see text]–[Formula: see text]C and 0.2–1, respectively. Numerical analysis was based on two-phase flow turbulent model and this model was solved using the Ansys-18 code. The results showed that the effects of heat flux, mass velocity and saturation temperature on local heat transfer coefficient and pressure drop were greater compared to that of the refrigerant vapor quality. The enhancements in local heat transfer coefficient due to the increase in heat flux, mass and saturation temperature were 38%, 57% and 64%, respectively, within the prescribed test conditions. The influence of mass flux variation on pressure drop along the evaporator channel was higher in the range of 27% compared to the heat flux effect. The average deviations between experimental and numerical results of heat transfer coefficient and pressure gradient were 14% and 17%, respectively, while the same between the experimental and predicted results were 16% and 33%, respectively.

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