Boiling Heat Transfer of R-134a Flowing in Horizontal Small-Diameter Tubes

2007 ◽  
Author(s):  
Shizuo Saitoh ◽  
Hirofumi Daiguji ◽  
Eiji Hihara
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Small Diameter ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Tube Diameter ◽  
Local Heat Transfer Coefficient ◽  
R 134A

The boiling heat transfer of refrigerant R-134a flow in horizontal small-diameter tubes with inner diameter of 0.51, 1.12, 2.0 and 3.1 mm was experimentally investigated. Local heat transfer coefficient and pressure drop were measured at a heat flux ranging from 5 to 39 kW/m2, mass flux from 100 to 450 kg/m2s, inlet vapor quality from 0 to 0.2, and evaporating pressure of 0.49 MPa, 3.0 and 3.7 MPa. Results showed that the local heat transfer coefficient tends to decrease at lower vapor quality with the decrease in tube diameter. The effect of heat flux on local heat transfer coefficient becomes significant with the decrease in tube diameter, while the effect of mass flux is weak especially for small diameter tube. With decreasing tube diameter, the flow inside it approached homogeneous flow, and the contribution of forced convective evaporation to the boiling heat transfer decreases. With the increase in pressure near the critical pressure (3.0 to 3.7 MPa), the heat transfer coefficient increased, and the effect of mass flux on the heat transfer coefficient became weak. These results implied that the nucleate boiling was dominant under high pressure conditions. A modified Chen-type correlation taking into account the effect of tube diameter was proposed for the prediction of boiling heat transfer of R-134a in horizontal tube. The effect of tube diameter on flow boiling heat transfer coefficient was characterized by the Weber number in gas phase. Comparison with experimental results showed that this correlation could be applied to a wide range of tube diameters (0.5 to 11 mm) and pressure conditions (reduced pressure from 0.1 to 0.9).

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.

Local and Average Heat Transfer Characteristics for a Disk Situated Perpendicular to a Uniform Flow

1985 ◽  
Vol 107 (2) ◽  
pp. 321-326 ◽  
Author(s):  
E. M. Sparrow ◽  
G. T. Geiger
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Stagnation Point ◽  
Radial Distance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Average Heat ◽  
Radial Profiles

Wind tunnel experiments were performed to determine both the average heat transfer coefficient and the radial distribution of the local heat transfer coefficient for a circular disk facing a uniform oncoming flow. The experiments covered the range of Reynolds numbers Re from 5000 to 50,000 and were performed using the naphthalene sublimation technique. To complement the experiments, an analysis incorporating both potential flow theory and boundary layer theory was used to predict the stagnation point heat transfer. The measured average Nusselt numbers definitively resolved a deep disparity between information from the literature and yielded the correlation Nu = 1.05 Pr0.36 Re1/2. The radial distributions of the local heat transfer coefficient were found to be congruent when they were normalized by Re1/2. Furthermore, the radial profiles showed that the local coefficient takes on its minimum value at the stagnation point and increases with increasing radial distance from the center of the disk. At the outer edge of the disk, the coefficient is more than twice as large as that at the stagnation point. The theoretical predictions of the stagnation point heat transfer exceeded the experimental values by about 6 percent. This overprediction is similar to that which occurs for cylinders and spheres in crossflow.

Heat Transfer to the Turbulent Separated Flow of Air Downstream of a Step in the Surface of a Plate

1964 ◽  
Vol 86 (2) ◽  
pp. 259-264 ◽  
Author(s):  
R. A. Seban
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Separated Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Suction Or Injection ◽  
Turbulent Separated Flow

Experiments on a system in which separation of a turbulent boundary layer occurred at a downward step in the surface of a plate and reattached on the plate downstream of the step have produced additional results for the local heat-transfer coefficient and for the velocity and temperature distribution in the separated and reattached regions of the flow. In neither region was there found the kind of similarity near the wall that characterizes flows that are dominated by the friction at the wall, so that even this first element of the usual rationalization of the heat transfer is unavailable for the interpretation of the results. The effect of suction or injection through a slot at the base of the step is also indicated and this demonstrates relatively small effects on both the pressure distribution and the local heat-transfer coefficient.

scholarly journals Studies of Full-Coverage Film Cooling: Part 2 — Measurement of Local Heat Transfer Coefficient

1981 ◽  
Author(s):  
M. Kumada ◽  
M. Hirata ◽  
N. Kasagi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flux Ratio ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Stanton Number ◽  
Temperature Ratio ◽  
Full Coverage

The local heat transfer coefficient of full-coverage film-cooled wall has been measured by using the law of analogy to mass transfer. For this experiment, the technique of sublimation of naphthalene was used. The geometric shape of FCFC plate and the experimental condition were the same as those in Part 1. From these experiments, the effects of the mass flux ratio and non-dimensional injection wall temperature ratio on the local Stanton number are made clear and it is confirmed experimentally that the local Stanton number is a linear function of non-dimensional temperature ratio as expected from the analysis. Furthermore, the local heat transfer coefficient on the backside surface has been obtained and a technique for the improvement of cooling effectiveness is discussed.

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