Analysis of condensation and evaporation heat transfer inside 3-D enhanced tubes

Abstract

An experimental investigation was conducted to evaluate heat transfer performance of several enhanced surface tubes during in-tube evaporation and condensation of R410A; results were then compared to the results of a smooth tube. Tubes considered in this evaluation included: smooth; herringbone and helix micro-grooves; herringbone-dimple and hydrophobic; all the tubes evaluated have the same external diameter of 12.7 mm. Experimental condensation and evaporation results were acquired at saturation temperatures of 318 K and 279 K, respectively. The mass velocities varied in the range of 40–230 kg m−2 s−1; vapor quality decreased from 0.8 to 0.2 for condensation and 0.2 to 0.8 for evaporation. Moreover, heat fluxes increased with mass velocity. Condensation heat transfer coefficients (HTCs) are enhanced by 40%–73%, with the dimpled herringbone-finned tube (EHT-HB/D) exhibiting the highest HTC among five tested tubes. The herringbone grooves can help lift the accumulated condensate along the circumference in addition to producing the drainage effects; dimples produce condensate turbulence and the droplet entrainment. For the evaporation, hydrophobic herringbone tube (EHT-HB/HY) provides the best thermal performance; its HTCs are 4%–46% larger than those of the smooth tube. This enhancement may be attributed to the expanded heat transfer area and the increased nucleation sites.