Correlations and Theory for Microchannel Condensation

In recent years several correlations have been proposed for calculating the heat-transfer coefficient during condensation in circular and non-circular channels of typical dimension around 1 mm where surface tension effects are important and correlations for larger diameter channels are inappropriate. A wholly theoretical approach applicable to annular flow has also been proposed. The correlations are all based on data for R134a, while the theory is applicable to any fluid. In this paper comparisons are made between the correlations for R134a and ammonia; plots based on theory are also included. Fair agreement is seen between all calculation methods for R134a but wide differences are seen for ammonia indicating that the correlations, based only on one fluid, do not capture the fluid property dependence accurately.