Heat- and mass-transfer characteristics of a cooling and dehumidifying coil and the effect of upstream turbulence on them

Abstract

This paper presents an experimental investigation and study of the performance of a cooling and dehumidifying coil and the effect of variation of upstream turbulence (generated by introducing commercially available screens of various mesh sizes in the upstream) on its performance. The experimental set up consists of a closed circuit air-conditioning tunnel in which velocity, temperature and humidity of air approaching the coil could be varied. The test coil chosen is a commercial evaporator of a 1.5 ton window model air-conditioner. The experiments are conducted for the following ranges of operating parameters: dry bulb temperature, 20–48°C; wet bulb temperature, 20–36°C; sensible heat to latent heat ratio, 0.4–15; Reynolds number based on evaporator tube diameter and approach air velocity, 650–2400; turbulence level, in percentage, 2.2–6.5; turbulent Reynolds number based on evaporator tube diameter and approach air velocity, 15–150. The heat-transfer coefficient based on enthalpy potential is presented in dimensionless form as a function of sensible to latent heat ratio, Reynolds number and turbulence (also turbulent Reynolds number). In the ranges of parameters considered the results indicate that the upstream turbulence does not have any significant effect on the heat-transfer coefficient for the evaporator coil. In view of this the following correlation, embracing the entire experimental data, is presented for the heat-transfer coefficient: j e = 0.0627 Syl −0.02 Re −0.498.