Causes of the Apparent Heat Transfer Degradation for Refrigerant Mixtures.
Causes of the Apparent Heat Transfer Degradation for
Kedzierski, M. A.; Kim, J. H.; Didion, D. A.
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.
Sponsor: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.