Experimental study of the characteristic of frosting on low-temperature air cooler

Abstract

In order to find out the influencing factors of frosting on air coolers, the experiments were conducted for air coolers under frosting, and the frost layer thicknesses under various operating conditions were measured with the aid of microphotography. Experimental results show that the frosting process for air coolers is significantly influenced by those parameters including the fin spacing, coating material over fin surface, air relative humidity, evaporating temperature and air flow rate. It is found out that the smaller the fin spacing is, the earlier frosting occurs and the faster the frost grows. The frosting can be delayed by coating the hydrophilic material over fin surfaces; however, the frost quantity is not obviously affected. Under the condition of large air relative humidity, the frost growth rate increases, and the increasing tendency drops off when the relative humidity is larger than 80%. The starting time of frosting may not be obviously influenced. The lower the evaporating temperature is, the larger the frost growth rate. As the evaporating temperature decreases, the initial morphology of frost layer varies from large and flat shape to needle-shape or column-shape due to the increasing of temperature difference. The occurrence of the frosting is delayed by increasing the air flow rate and the increasing of frost layer thickness can also be delayed due the melting of frost, but the frosting rate is not sensitive to the air flow rate.