Condensation characteristics of flows in newly developed three-dimensional enhanced heat transfer tubes

Abstract

Condensation heat transfer characteristics were studied experimentally in order to evaluate the heat transfer performance of horizontal copper heat transfer tubes (smooth and enhanced). Using R410A and R32 as refrigerants, condensation heat transfer experiments were carried out for a saturation temperature of 45 °C; inlet vapor quality of the tube was 0.8 and outlet quality was 0.2; refrigerant mass flow rate range was in the range from 68 to 371 kg/(m2·s). Single-phase heat balance verification found that the heat loss is less than 6 %, with the deviation between single-phase experimental results and various correlations being less than 15 %. The condensation heat transfer coefficient increases with an increase in mass flow; as the mass flow rate increases, the turbulence of the liquid flow increases and the liquid film becomes thinner; thermal resistance is reduced and the heat transfer coefficient (HTC) increases. Experimental results determined that the performance factor ratio (enhanced tube/smooth tube) of the three-dimensional surfaces investigated here are greater than 1. Tubeside heat transfer enhancement factor (EF) of the HB/D tube is the highest (max 1.76); its performance is closely related to increasing fluid turbulence and improving drainage. Performance factor (PF) of the HB/D tube (max 1.38) is the highest for most of the flowrates. All this indicates excellent thermal performance. Flow model-based analysis was performed in order to develop a correlation for the condensation heat transfer coefficient and the pressure drop for the enhanced surface tubes. Both prediction models accurately predicted all data points within a limited margin of error.