A review of flow pattern-based predictive correlations during refrigerant condensation in horizontally smooth and enhanced tubes

A state-of-the-art review of recent work on flow pattern-based predictive correlations during refrigerant condensation in horizontally smooth and enhanced tubes is presented. The review focuses primarily on correlations for heat transfer coefficient and pressure drop during flow condensation that ignored flow regime effects and treated flows as either annular or non-stratified flow, or as stratified flow. This resulted in correlations of poor accuracy and limited validity and reliability. Current heat transfer coefficient, pressure drop, and void fraction models are based on the local flow pattern, resulting in deviations of around 20% from experimental data. There are, however, several inconsistencies and anomalies regarding these models that are addressed in this paper. A generalized solution methodology for two-phase flow problems still remains an elusive goal, mainly because gas-liquid flow systems combine the complexities of turbulence with those of deformable vapor-liquid interfaces. The paper focuses on the state-of-the-art research in the field of enhanced heat transfer, and proposes future research areas to help pave the way for the development of a unified and accurate two-phase flow model.