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Simple Prediction Method for Condensation Heat Transfer Inside a Micro-Fin Tube.

pdf icon Simple Prediction Method for Condensation Heat Transfer Inside a Micro-Fin Tube. (1861 K)
Donati, F. M.; Kedzierski, M. A.

NISTIR 6417; 38 p. November 1999.

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Order number: PB2000-101399


heat transfer; in-tube condensation; kinetic theory; enthalpy-based method; correlation


This study examines an alternative method for modeling in-tube condensation heat transfer. The method's fundamental premise is that the heat flux is directly proportional to the difference between the enthalpy of the vapor at saturated free stream conditions and the enthalpy of the condensed subcooled liquid at the wall. The proportionality coefficient is a pseudo condensation mass velocity. The traditional method for modeling in-tube condensation uses Newton's law of cooling, which defines the heat flux to be directly proportional to the temperature difference rather than the enthalpy difference. Kraay and Rite have used an enthalpy-based expression for the condensation heat flux where the condensation mass velocity was derived from kinetic theory. The present research demonstrates that the kinetic theory approach does not yield realistic results. Consequently, this study presents an alternate energy balance approach is subsequently used to solve for an enthalpy based condensation heat flux. The method reveals that the heat transfer process depends strongly on the derivative of the vapor quality with respect to the distance along the tube axis. Based on this derivation, a correlation is presented that is simpler than those derived from traditional methods. The temperature difference between the free stream vapor and the liquid at the wall does not appear in the correlation.