Thermal-hydraulic experimental study of louvered fin-and-flat-tube heat exchanger under wet conditions with variation of inlet humidity ratio

Abstract

An experimental study for air-side thermal-hydraulic performance of louvered fin-and-flat-tube heat exchanger under dehumidifying conditions has been performed. The louvered fin studied, used for an automotive evaporator, is geometrically defined by a flow depth of 47 mm, a high louver angle of 50° and a louver pitch of 1.1 mm. The test was conducted for frontal air velocity ranging from 1.1 to 4.5 m/s. The heat exchanger was tested first in dry condition, working as a heater. In wet conditions, the cooling coil was tested for three air inlet temperatures, Ta, and for various inlet relative humidity, RH, organized as follows: Ta = 30 °C (RH = 40 to 70%), Ta = 35 °C (RH = 30 to 60%), and Ta = 40 °C (RH = 20 to 60%); which correspond to a variation of the inlet humidity ratio from 9.2 to 27.7 gwater/kgdry-air. It was found that, for all inlet conditions, the wet friction factor is higher than that for dry surface (up to 43%). Concerning the heat transfer performance, at low Reynolds number, the sensible Colburn ‘j’ factor is insensitive to the surface conditions. However, as Re number increases, the sensible wet j factor decreases (up to 23%) compared to the dry one. This degradation is more and more pronounced as the inlet humidity ratio increases.