수평원관 내 CO₂,R-22 및 R-134a 의 증발열전달 특성에 관한 실험적 연구

윤린; 김용찬; 황준현; 최영돈

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Evaporation heat transfer coefficients of carbon dioxide(CO₂), R-22, and R-134a in a horizontal smooth tube were measured and analyzed as a function of heat flux, mass flux, and evaporating temperature. The experiments were carried out by varying heat flux from 10 to 20 ㎾/m², mass flux from 170 to 340 kg/m²s, and saturation temperatures of 5 and 10°C. It was found that the heat transfer coefficient of CO₂ decreased with a rise of quality due to an earlier liquid-film dryout as compared to R-22 and R-134a. Averaged heat transfer coefficients of CO₂ were 22-63% higher than those of R-22 and R-134a at all test conditions. The effects of mass flux and heat flux on averaged heat transfer coefficients were much greater in CO₂ than in R-22 and R-134a. When comparing CO₂ test results with the correlations in the literature, the existing models yielded large deviations at medium and high qualities. Therefore, a generalized correlation for CO₂evaporation heat transfer needs to be developed by including the effects of dryout phenomenon.