Journal of Enhanced Heat Transfer Theory and Application in High Performance Heat and Mass Transfer

ISSN for PRINT: 1065-5131

For Online Access

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2001, Volume8

Issue 6

65 pages

Issue price - $138.00

Zhiping Lin
Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing, People's Republic of China

Tongze Ma
Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing, People's Republic of China

Zhengfang Zhang
Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing, People's Republic of China

Lichun Zhang
Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing, People's Republic of China

The investigation of saturated boiling heat transfer was performed from different surfaces in narrow space formed by two concentric tubes with two open ends at atmospheric pressure. The boiling liquid was ethanol and distilled water. The 300-mm-long outer tubes whose inner surfaces acted as boiling surfaces were heated. The inner surfaces of the heated tubes were plain surfaces, surfaces with axial rectangular grooves, and sintered porous surfaces, respectively. The stainless steel tubes with different diameter were inserted into the heated tubes. The gap sizes between the two tubes were 0.41∼12.35 mm for the plain outer tubes, 0.71∼12.65 mm for the grooved tubes, and 0.5∼15.5 mm for the sintered porous tubes. Experimental results show that for the plain tubes, with the inserted inner tubes, the boiling heat transfer coefficients increase with a decrease in gap size. The Bond number has important effects on boiling heat transfer. The boiling critical heat flux was found to decrease with decreasing gap size. For the grooved tubes, with inserted tubes, the variation of the boiling heat transfer coefficient with decrease of gap size is the same as that for the plain tubes, with inserted tubes; but the enhancement of the grooved surfaces on boiling in narrow spaces is better than that of the plain tube. The grooved surfaces can also augment the critical heat flux. Sintered porous surfaces, in pool boiling, can enhance boiling heat transfer, but the boiling heat transfer from these surfaces is affected little by the gap size. The experimental results also show that the local boiling heat transfer coefficients vary with the height of the heated tubes.

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