New theoretical models of evaporation heat transfer in horizontal microfin tubes

A stratified flow model and an annular flow model of evaporation heat transfer in horizontal microfin tubes have been proposed. In the stratified flow model, the contributions of thin film evaporation and nucleate boiling in the groove above the stratified liquid level were predicted by a previously reported numerical analysis and a newly developed correlation, respectively. The contributions of nucleate boiling and forced convection in the stratified liquid region were predicted by the new correlation and the Carnavos correlation, respectively. In the annular flow model, the contributions of nucleate boiling and forced convection were predicted by the new correlation and the Carnavos correlation in which the equivalent Reynolds number was introduced, respectively. The flow pattern transition curve between the stratified-wavy flow and the annular flow proposed by Kattan et al. was introduced to predict the heat transfer coefficient in the intermediate region by use of the two theoretical models. The predictions of the heat transfer coefficient compared well with available experimental data for ten tubes and four refrigerants.