INVESTIGATION AND DEVELOPMENT OF CONDENSATION HEAT TRANSFER CORRELATIONS FOR STRAIGHT AND HELICALLY COILED TUBES

摘要

This paper introduces a set of developed condensation heat transfer correlations used in both straight and helically coiled tube systems. A literature search found that there are no applicable heat transfer correlations for two-phase flow in a helically coiled tube. As such, a study was first undertaken on condensation heat transfer in a straight tube. The investigation into condensation heat transfer for a fluid flowing in a straight tube began with a review of existing correlations. It is assumed that the annular flow is the dominant flow pattern over most of the condensing length of the tube. Depending upon the experimental methods and the theoretical and/or numerical approach, the results obtained by using the (existing) correlations show some degree of inconsistency over the ranges of parameters. Thus, it is not a simple matter to select a proper condensation heat transfer correlation for a straight tube system. This resulted in the development of generalized correlations for specific fluids such as water and R134a by employing least-squared property curves in terms of parameters such as Reynolds number based on the liquid, vapor quality and reduced pressure for each fluid considered. As a consequence, a number of plausible condensation heat transfer correlations in a coiled tube for specific fluids mentioned above are proposed employing the two-phase fluid flow Coiling Influence Factor (CIF_(TP)) for heat transfer obtained by using the Coiling Influence Factor for liquid and vapor (CIF_1 and CIF_v) respectively along with a vapor quality as a weighting parameter.