Enhancement of refrigerant-side condensation heat transfer performance of additively-manufactured air-cooled heat exchangers

Abstract

This report presents both experimental findings to validate the efficacy of heat transfer enhancement techniques of a novel air-cooled heat exchanger, as well as simulation findings to evaluate the heat transfer performance of a novel micro-channel design. On the experimental front, experiments were conducted on a novel air-cooled heat exchanger which was manufactured using selective laser melting (SLM). It consisted of porous P-cell lattice structures on the air-side, and triangular multiport channels on the refrigerant-side. The two-phase performance of the refrigerant-side multiport channels was characterised. Two mass fluxes, 45 kg/m2 ⋅ s and 80 kg/m2 ⋅ s were conducted to investigate the heat transfer coefficient and pressure drop values against the average vapour quality of the micro-channel. For the heat transfer coefficient, while the overall range of values obtained were in line with literature, the trend of an increasing heat transfer coefficient with an increase in average vapour quality was not observed. For the pressure drop of the refrigerant, the higher mass flux of 80 kg/m2 ⋅ s showed a higher pressure drop than that of the lower mass flux of 45 kg/m2 ⋅ s. On the numerical front, a new micro-channel was designed, consisting of a cross-finned and twisted tube setup. These enhancement methods were predicted to improve heat transfer performance through inducing turbulence as well as increased surface area-to-volume ratio. Three-dimensional two-phase simulations were conducted, using ANSYS Fluent, on this design, as well as a simple circular tube to validate the simulation setup. The simulation results were largely not in agreement with those found in the literatures, rendering the results to be highly unreliable.