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Causes of the Apparent Heat Transfer Degradation for Refrigerant Mixtures.

pdf icon Causes of the Apparent Heat Transfer Degradation for Refrigerant Mixtures. (6028 K)
Kedzierski, M. A.; Kim, J. H.; Didion, D. A.

HTD-Vol. 197;

American Society of Mechanical Engineers. Two-Phase Flow and Heat Tranfers, 1992. National Heat Transfer Conference, 28th. HTD-Vol. 197. August 9-12, 1992, San Diego, CA, ASME, New York, Kim, J. H.; Nelson, R. A.; Hashemi, A., Editor(s)(s), 149-158 pp, 1992.


Department of Energy, Washington, DC


refrigerants; heat transfer; degradation; evaporation; temperature distributions; mixing


This paper presents an investigation into the causes of the apparent heat transfer degradation associated with horizontal-annular flow evaporation of refrigerant mixtures. The apparent heat transfer degradation is the difference between the measured heat transfer coefficient and the heat transfer coefficient that would be obtained from a linear interpolation of the single component values. The degradation is apparent since the linearly interpolated values have no physical basis. For horizontal-annular flow evaporation, most of the heat transfer degradation is a consequence of the use of the locally uniform equilibrium temperature in the measurement and calculation of the heat transfer coefficient. In reality, both circumferential and radial compostion gradients can exist within the liquid film which cause temperature distributions that deviate significantly from a uniform saturation temperature. If the actual liquid-vapor interface temperatures (local vapor temperatures) were used in the calculation of the measured heat trransfer coefficient for the impose heat flux condition, most of the apparent degradation would not exist. The remainder of the heat transfer degradation is due to nonlinear mixtgure property effects. Previously published measured heat transfer coefficients for three mixtures were investigated. The focus of the study was to determine the magnitude and the cause of the individual components of the heat transfer degradation of the studied mixture.