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ACRC Contract Report 49PDF


Title:Condensation of CO2 at Low Temperature inside Horizontal Microfinned Tubes
Author(s):Zilly, J.; Jang, J.; Hrnjak, P.S.
Subject(s):heat exchangers
micro-fin tubes
pressure drop
Abstract:Enhanced tubes have been commonly used in heat exchangers for 30 years. Modern micro-fin tubes play a significant role in high-efficiency refrigerators and air conditioners with their significantly enhanced heat transfer coefficients and low pressure loss characteristics. Experimental data for condensation exist for commonly used refrigerants but not for CO2 at low temperatures. This study investigates inner heat transfer coefficient and pressure drop during condensation of CO2 inside micro-fin tubes at low temperatures. A test rig has been build to measure heat transfer coefficients in horizontal condenser pipes and adiabatic horizontal and vertical pressure drop at low temperatures. Heat transfer coefficients and pressure drop are measured at different mass flux, qualities, saturation and wall temperatures. Correlations for commonly used refrigerants and higher condensation temperatures are used to predict measured data for CO2 at low temperatures. Results for microfin tubes with new geometric parameters are compared to smooth tube data. Main results are the fact that the heat transfer coefficients of the investigated micro-fin tube are less dependent on mass flux as heat transfer coefficients of smooth tubes. It was found that lower saturation temperature results in higher heat transfer coefficients and pressure drop for the micro-fin tube similar to the smooth tube. Heat transfer coefficients for micro-fin tubes are not dependent on the temperature difference between saturation temperature and inner wall temperature. The experimental data for both the smooth and the micro-fin tube were over predicted by correlations. Enhancement factors show that micro-fin tubes increase heat transfer coefficients most for low mass flux and high qualities. At that conditions heat transfer coefficients for the micro-fin tube are 3 times higher than for the smooth tube. Penalty factors indicate that the increase in pressure drop is highest for low mass flux and low qualities. At that conditions penalty factors are 1.9 decreasing to 1.2 for high qualities. Further research will be done on other geometrical parameters including different tube diameters for micro-fun tubes
Issue Date:2003-03
Publisher:Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report:Air Conditioning and Refrigeration Center CR-49
Genre:Technical Report
Date Available in IDEALS:2009-08-06

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