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International Heat Transfer Conference 16

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

COMPARATIVE STUDY ON THE POOL BOILING AND FALLING FILM EVAPORATION OF REFRIGERANT R134A OUTSIDE THE SAME TUBES

Wentao Ji
Key Laboratory of Thermo-Fluid Science and Engineering of MOE, Xi'an Jiaotong University, 28 Xian Ning West Road, Xi'an 710049, China

Chuang-Yao Zhao
Key Laboratory of Thermo-Fluid Science and Engineering, MOE, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi, 710049, People's Republic of China

Er-Tao Zhao
Key Laboratory of Thermo-Fluid Science and Engineering of MOE, Xi'an Jiaotong University, Xi'an 10049, China

Zeng-Yao Li
Key Laboratory of Thermo-Fluid and Science and Engineering, Ministry of Education School of Energy and Power Engineering, Xi'an Jiaotong University No. 28 West Xianning Road, Xi'an, Shaanxi, 710049, China

Wen-Quan Tao
State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science & Engineering, Tongji University, Shanghai 200092, China; Key Laboratory of Thermo-Fluid Science and Engineering of MOE, School of Energy and Power Engineering, Xian Jiaotong University, Xian 710049, China

DOI: 10.1615/IHTC16.bae.022117
pages 851-858


KEY WORDS: Boiling and evaporation, Heat transfer enhancement, Falling film evaporation, Pool boiling, Refrigerant, Tube bundle

Abstract

Pool boiling and falling film evaporation of R134a outside a typical reentrant enhanced tube was investigated with an experimental approach. Experimental data from literature with other refrigerants were also compared. The saturate temperature was 11°C. It was found that the overall heat transfer coefficients for the enhanced tube was up to 3 times higher than smooth tube for the water velocity from 0.8 to 3.5m/s. Falling film evaporation heat transfer coefficients increased by a factor of 2.5 to 4. The pool boiling yielded a slightly higher heat transfer coefficient at higher heat flux for the enhanced tube. The dependence of falling film evaporation heat transfer coefficient on the heat flux was also not different from pool boiling for the same tube. Although the bubbles in pool boiling were pushed up by buoyancy and in falling film evaporating were driven by the flow of films, the transmission of energy were both dominated by the phase change heat transfer. The contributions of forced convection to falling film evaporation heat transfer coefficient seems to be weak compared with phase change heat transfer.

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