4.57 mm 세관 열교환기 내 이산화탄소의 증발열전달 특성

Abstract

The evaporation heat transfer coefficient of CO₂(R-744) in a horizontal tube was investigated experimentally. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and evaporator(test section). The test section consists of a smooth, horizontal stainless steel tube of inner diameter of 4.57 ㎜. The experiments were conducted at mass flux of 200 to 500 ㎏/㎡s, saturation temperature of -5 to 5℃, and heat flux of 10 to 40 ㎾/㎡. The test results showed the heat transfer of CO₂ has a greater effect on nucleate boiling more than convective boiling. Mass flux of CO₂ does not affect nucleate boiling too much. In comparison with test results and existing correlations, the best fit of the present experimental data is obtained with the correlation of Jung et al. But existing correlations failed to predict the evaporation heat transfer coefficient of CO₂, therefore, it is necessary to develope reliable and accurate predictions determining the evaporation heat transfer coefficient of CO₂ in a horizontal tube.