TWO-PHASE FLOW REGIMES AND EVAPORATIVE HEAT TRANSFER IN INTERNALLY-GROOVED TUBES

The limited accuracy and parametric range of two-phase heat transfer correlations for internally-grooved tubes have impeded the widespread application of this most promising technology. The success of regime-based analyses and correlations in providing improved predictive accuracy for heat transfer coefficients in smooth tubes has motivated this effort to explore the relationship between two-phase flow regimes and heat transfer rates in internally-grooved tubes. Following a brief introduction to the geometries and manufacturing techniques of internally-grooved tubes and a description of the state-of-the-art smooth tube flow regime maps, fundamental studies of thermofluid performance in internally-grooved tubes are reviewed and analyzed to demonstrate the relationship between flow regime and evaporative heat transfer rates. Then, the current state of two-phase flow regime maps and heat transfer coefficient correlations for internally-grooved tubes are summarized. Finally, recommendations for future internally-grooved tube research directions are given. The majority of the studies herein deal with halogenated fluids in conventional-sized tubes at standard temperature and pressure. However, studies of small diameter tubes, as well as alternative refrigerants and reduced pressure, are also considered.