| Title |
Evaporative Heat Transfer Characteristics of Carbon Dioxide in a Horizontal Tube |
| Keywords |
Evaporation ; 증발 ; Heat transfer coefficient ; 열전달계수 ; Supercritical cycle ; 초월임계 사이클 |
| Abstract |
The evaporative heat transfer coefficient of CO2(R-744) in a horizontal tube was investigated experimentally. The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. 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 7.75mm. The experiments were conducted at mass flux of 200 to 500 kg/m2s, saturation temperature of －5 to 5℃, and heat flux of 10 to 40kW/m2. 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, and the effect of mass flux on evaporative heat transfer of CO2 is much smaller than that of refrigerant R-22 and R-134a. In comparison with test results and existing correlations, correlations failed to predict the evaporative heat transfer coefficient of CO2, therefore, it is necessary to develope reliable and accurate predictions determining the evaporative heat transfer coefficient of CO2 in a horizontal tube. |