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Vapor Flow Effect on Falling Film Evaporation of R134a Outside Horizontal Tube Bundle

DOI: 10.1615/IHTC15.evp.008581
pages 2315-2328

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

Ya-Ling He
Key Laboratory of Thermo-Fluid Science and Engineering of Ministry of Education, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China

Guannan Xi
Nantong University

Wen-Quan Tao
Key Laboratory of Thermo-Fluid Science and Engineering of MOE, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China


KEY WORDS: Boiling and evaporation, Air conditioning and refrigeration, Falling film evaporation, Boiling heat transfer, Refrigerant, Tube bundle

Abstract

Vapor flow effect on falling film evaporation of refrigerant R134a outside horizontal tube bundle is investigated experimentally. The test space is a cube with a rectangular cross section of 0.575m (length) × 38.8mm (width). The tested tube is designed for enhancing pool boiling, which has an external fin density of 45fpi (fins per inch), and an outside diameter of 19.05mm. The transverse narrowest bundle clearance is 3.25mm where the vapor velocity can be adjusted in the range of 0 to 3.1m/s. R134a vapor is distributed uniformly from the bottom of tube array to the test section. The liquid falling film flow rate ranges from 0.07 to 0.2kg/m????s. Experiment is firstly conducted at saturation temperature of 6????without the effect of the additional vapor flow at the heat flux of 20, 60, 100 and 180kW/m2 (for the first tube row). Vapor effect experiment was carried out at three heat fluxes 20, 40 and 60kW/m2. For the falling film flow rate of 0.07 kg/m????s and heat flux of 40kW/m2, it is found that at the vapor velocity less than 0.5 m/s, vapor velocity has no significant effect on the falling film evaporation heat transfer. In addition, it is found that the vapor velocity effect is also dependent on the falling film flow rate: within the variation range of vapor velocity tested the variation patterns of the eight tubes are different at different flow rate.

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