| In the refrigeration and air conditioning field, the research of alternative refrigerants has been recognized as one of the urgent issues to ease the ozone depletion and global warming. For the excellent environmental performance (ODP=0, GWP=12), small charge amount, and good commonality with the existing systems, fluoroethane (HFC-161) is another potential substitute for R22and R502. For any alternative refrigerant, the in-tube heat transfer characteristic is rather necessary for comprehensively analyzing its actual performance and the application potential. So far, research on the heat transfer of HFC-161has not been conducted at home and abroad, and the related data and reference models are limited in open literatures. To fill in this blank and supply reference for designing more compact and effective heat exchangers, study on the heat transfer characteristics of this potential refrigerant is definitely necessary.Based on this work, the optimization of operating conditions and the enhancement in working efficiency of the actual refrigeration systems would be achieved, and the application process of HFC-161would be promoted.Starting from the fundamental problem of the heat transfer characteristics of HFC-161and applying the experimental methods, the in-tube boiling heat transfer coefficients and pressure drop data were obtained in this work. Furthermore, effect of working conditions on the boiling heat transfer was analyzed theoretically, comparison on the heat transfer and pressure drop performance between HFC-161and the traditional refrigerant R22was carried out, and new correlations for predicting heat transfer of HFC-161flow boiling inside tubes were developed.The main contents and conclusions are as follows:1. The experimental apparatus for the boiling heat transfer of refrigerant inside tubes was built up, and its reliability was validated by the early experiment on R22.2. The boiling heat transfer characteristics of HFC-161in a9mm I.D. horizontal smooth tube were investigated. Heat transfer coefficients and pressure drop data were measured at the saturation temperature range of510℃,the heat flux range of15～25kW/m2, and the mass flux range of100-200kg/m2-s, a predicting model for HFC-161boiling inside smooth tubes was developed. Results showed that:1) the local heat transfer coefficients increased with the vapor quality and up to the maximum value when the quality rose to about0.5-0.7, then "dry-out" occurred and the heat transfer coefficients decreased with the increasing vapor quality;2) the heat transfer coefficients increased with the mass flux and the heat flux, and decreased with the saturation temperature;3) The pressure drop decreased with the saturation temperature, increased strongly with the mass flux and increased mildly with the imposed heat flux;4) The Gungor-Winterton correlation, Mathurcorrelation and Liu-Winterton correlation had better agreements with the experimental data than other exiting correlations;5) The developed correlation covered88.6%of the experimental heat transfer coefficients within the deviation range of-18%～+18%, with a mean deviation of+3.4%, an absolute mean deviation of6.4%and a maximum deviation of-19.0%.3. The boiling. heat transfer characteristics of HFC-161in a7mm O.D. horizontal micro-fin tube were investigated. Heat transfer coefficients and pressure drop data were measured at the saturation temperature range of-5～8℃, the heat flux range of28.15～49.29kW/m2, and the mass flux range of100～250kg/m2·s, a predicting model for HFC-161boiling inside micro-fin tubes was developed. Results showed that:1) the heat transfer coefficients increased firstly and then decreased with the vapor quality,"dry-out" occurred at x>0.8, independent of the working conditions;2) The effect of working conditions on the boiling heat transfer in the micro-fin tube was similar to that in the smooth tube, excepting the saturation temperature;3) the variation of pressure drop with the working conditions were amost the same as that in the smooth tube;4) the Cavallini correlation and Yun correlation agreed much better with the experimental data than other exiting correlations;5) The developed correlation covered89.1%of the experimental heat transfer coefficients within the deviation range of-10%～+10%, with a mean deviation of+1.6%, an absolute mean deviation of5.6%and a maximum deviation of+48.6%;4. The boiling heat transfer characteristics of HFC-161were compared with those of R22at the same test conditions. Results showed that:1) in the smooth tube, HFC-161had much higher (25%-32%) heat transfer coefficients than R22, especially in the high quality region, and the frictional pressure drop of HFC-161was about20%lower than that of R22;2) in the micro-fin tube, the heat transfer coefficients and frictional pressure drop of HFC-161were5%～40%higher and18%lower than those of R22, respectively. Generally. HFC-161has better heat transfer performance and lower pressure drop than R22. |
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