초임계 영역내 CO2 냉각 열전달과 압력강하 분석

Abstract

The Condensation heat transfer coefficients of R-22 and R-134a were measured in smooth horizontal copper tubes with inner diameters of 1.77, 3.36 and 5.35 mm, respectively. The experiments were conducted in a closed loop, which was driven by a magnetic gear pump. They were performed for the following ranges of variables: mass flux (200 to 500 kg/m2·s), saturation temperature 30 ℃ and quality (0 to 1.0).The main results obtained are as follows : Condensation heat transfer coefficients in the small diameter tubes (ID ＜ 7 mm) were observed to be strongly affected by inner diameter change and to differ from those in the large diameter tubes. The heat transfer coefficients in the small diameter tubes were 20 ∼ 40 % higher than those in the large diameter tubes as the inner diameter of the tube was reduced. Also, it was very difficult to apply some well-known previous predictions (Cavallini-Zecchin's, Haraguchi's and Dobson's correlation) to small diameter tubes. Based on an analogy between heat and mass transfer, the new correlation is proposed to predict the experimental data more accurately.