Simple Prediction Method for Condensation Heat Transfer Inside a Micro-Fin Tube.
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
Keywords:
heat transfer; in-tube condensation; kinetic theory;
enthalpy-based method; correlation
Abstract:
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.
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National Institute of Standards and Technology
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