Investigation on a Reduction in Thermal Load at the Main Cooler in a Refrigerated Dryer.

The refrigerated dryer mentioned in this paper is one of types of air purifiers, and is one of the popular types of compressed air dryers. The refrigerated dryer consists of a precool-reheater, main cooler, and refrigerator. In the precool-reheater, the cold humid air delivered from the main cooler is heated by the hot air delivered from the after-cooler, and changes into dry air, the relative humidity of which is fairly low. In the main cooler, the slightly hot humid air delivered from the cooling process in the precool-reheater is cooled further by the cooling medium in the refrigerator to the minimum temperature, which means a dew point of compressed air, and changes into cold and saturated humid air. The main cooler requires external energy to cool the compressed air, but the precool-reheater does not. For this reason, to miniaturize a refrigerated dryer, it is very important to reduce the thermal load in the main cooler. In this paper, the reduction in the thermal load in the main cooler is estimated with the power-saving factor that means the ratio of heating rate in the precool-reheater to one in the dryer, which is investigated theoretically and experimentally. As a result, the effect of the thermal conductance of the precool-reheater on the power-saving factor is clarified, considering compressed air temperatures at the main locations in the dryer. In addition, a proper guide for the design of a refrigerated dryer is derived, paying attention to the relationship not only between thermal conductances of an after-cooler and a refrigerated dryer but also between ones of a precool-reheater and main cooler.