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Supercritical Gas Cooling and Near-Critical-Pressure Condensation of Refrigerant Blends in Microchannels

A study of heat transfer and pressure drop in zero ozone-depletion-potential (ODP) ‎refrigerant blends in small diameter tubes was conducted. The azeotropic refrigerant ‎blend R410A (equal parts of R32 and R125 by mass) has zero ODP and has properties ‎similar to R22, and is therefore of interest for vapor compression cycles in high-‎temperature-lift space-conditioning and water heating applications. Smaller tubes lead to ‎higher heat transfer coefficients and are better suited for high operating pressures.‎ Heat transfer coefficients and pressure drops for R410A were determined experimentally ‎during condensation across the entire vapor-liquid dome at 0.8, 0.9xPcritical and gas ‎cooling at 1.0, 1.1, 1.2xPcritical in three different round tubes (D = 3.05, 1.52, 0.76 mm) ‎over a mass flux range of 200 < G < 800 kg/m2-s. A thermal amplification technique was ‎used to accurately determine the heat duty for condensation in small quality increments ‎or supercritical cooling across small temperature changes while ensuring low ‎uncertainties in the refrigerant heat transfer coefficients. ‎ The data from this study were used in conjunction with data obtained under similar ‎operating conditions for refrigerants R404A and R410A in tubes of diameter 6.22 and ‎‎9.40 mm to develop models to predict heat transfer and pressure drop in tubes with ‎diameters ranging from 0.76 to 9.40 mm during condensation. Similarly, in the ‎supercritical states, heat transfer and pressure drop models were developed to account for ‎the sharp variations in the thermophysical properties near the critical point.‎ The physical understanding and models resulting from this investigation provide the ‎information necessary for designing and optimizing new components that utilize R410A ‎for air-conditioning and heat pumping applications.‎

Identiferoai:union.ndltd.org:GATECH/oai:smartech.gatech.edu:1853/14503
Date14 December 2006
CreatorsAndresen, Ulf Christian
PublisherGeorgia Institute of Technology
Source SetsGeorgia Tech Electronic Thesis and Dissertation Archive
Detected LanguageEnglish
TypeDissertation

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