Experimental investigation of heat transfer coefficient of R134a during condensation in vertical downward flow at high mass flux in a smooth tube
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Author list: Dalkilic A.S., Laohalertdecha S., Wongwises S.
Publisher: Elsevier
Publication year: 2009
Journal: International Communications in Heat and Mass Transfer (0735-1933)
Volume number: 36
Issue number: 10
Start page: 1036
End page: 1043
Number of pages: 8
ISSN: 0735-1933
eISSN: 1879-0178
Languages: English-Great Britain (EN-GB)
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Abstract
The two-phase heat transfer coefficients of pure HFC-134a condensing inside a smooth tube-in-tube heat exchanger are experimentally investigated. The test section is a 0.5 m long double tube with refrigerant flowing in the inner tube and cooling water flowing in the annulus. The inner tube is constructed from smooth copper tubing of 9.52 mm outer diameter and 8.1 mm inner diameter. The test runs are performed at average saturation condensing temperatures between 40-50 ฐC. The mass fluxes are between 260 and 515 kg m- 2s- 1 and the heat fluxes are between 11.3 and 55.3 kW m- 2. The quality of the refrigerant in the test section is calculated using the temperature and pressure obtained from the experiment. The average heat transfer coefficient of the refrigerant is determined by applying an energy balance based on the energy transferred from the test section. The effects of heat flux, mass flux and condensation temperature on the heat transfer coefficients are also discussed. Eleven well-known correlations for annular flow are compared to each other using a large amount of data obtained from various experimental conditions. A new correlation for the condensation heat transfer coefficient is proposed for practical applications. ฉ 2009 Elsevier Ltd. All rights reserved.
Keywords
Refrigerant
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