Investigation on dynamic behaviour of condensation heat transfer in indirective evaporative cooler

Indirect evaporative cooling is a rapidly developing air-handling technology and has great application potentials for energy recovery in hot and humid regions. The condensation in dry channels of an indirect evaporative cooler (IEC) occurs when the dew point temperature of outdoor air is high. However, the dynamic heat transfer performance of an IEC during the process of condensation evolution was rarely discussed. This paper aims to experimentally investigate the dynamic behaviour of primary air condensation and its effects on the convective and total heat transfer rate of an IEC. A transparent cover plate is placed outside an aluminium heat exchanger plate to visualize the evolution process of droplets retained on the surface. The droplets' falling frequency was recorded and the accumulated condensate mass was correlated based on an analytical method taking into account the contact angle and droplet volume. Results showed that the dynamic dehumidification performance can pose great influences on the convective heat transfer in IEC. The gradually diminished dropwise regions and increase of filmwise regions deteriorate the wet-bulb effectiveness of IEC by 14.8%. The convective heat flux keeps decreasing with the accumulation of condensate retention until a dynamic equilibrium is achieved between the retained and falling droplets.