Optimization Study on the Supercritical R744 in a Coaxial Tube under Water-cooling Conditions
Today there is a raising interest in industrial and scientific fields, aiming at natural refrigerants,among which R744 (CO2) is a unique and promising substitute for synthetic fluids. CO2, in particular, is seen as one of the best fluids for a heat pump water heater (HPWH) application system. A great many theoretical and experimental studies were conducted by foreign and domestic researchers. But studies on heat transfer enhancement are scare in open literature. Under the design conditions-the inlet dry (wet) bulb air temperature of 16℃(12℃), the evaporation temperature of 7℃, the inlet hot water temperature of 17℃, the outlet hot water temperature of 65℃, the compressor power at 750W-CO2 heat transfer coefficient is found to be 3-4 times more than that of water coefficient for a one-tube-in-a-tube coaxial gas cooler.Based on a steady state simulation model using engineering equation solver(EES), inner tube with external micro-fin effectively enhanced water coefficient, thus the coaxial gas cooler has 35％ increase in heat weight ratio. For more tubes in a tube, three tubes in a tube show the best characteristics. The wall thickness of copper tube is also discussed.The conventional tube made of copper can sustain high pressure without any problems in the short-term test or operation, but for the long time safe application, the tube should be thickened. In china, nowadays, no small diameters (less than 16-18mm) with external micro-fin are available in market, thus the results of optimization design are expected to offer useful guidelines for CO2 external micro-fin tube design and its development.
Zhang X P Fan X W Wang F K Shen H G Zheng H F
School of Environmental Science & Engineering,Donghua University,Shanghai 201620,China;Henan Institu Energy and Environmental Engineering Research Center,Zhongyuan Institute of Technology,Zhengzhou 450 School of Environmental Science & Engineering,Donghua University,Shanghai 201620,P.R.China
国际会议
上海
英文
137-141
2008-04-05（万方平台首次上网日期，不代表论文的发表时间）