Heat and Mass Transfer in Countercurrent Flow of Air and Water Film in a Rectangular Vertical Duct

Abstract

Experiments were carried out concerning heat and mass transfer between falling water film and upward air flow in a rectangular vertical duct with a large aspect ratio under the various conditions of rate of flow, water temperature and humidity. The behaviour of the falling water films, e.g., the film thickness and the wave inception, was also examined. The results represented in terms of teh Nusselt number and Sherwood number can be explained using the Reynolds Number based on the mean air velocity relative to the water surface regardless of the water flow rate. When the water temperature at the entrance is varied from 20 to 50°C, the Nusselt number increases, while the Sherwood number decreases in spite of an increases in the rate of evapotation. When saturated humid air is supplied, the Nusselt number is larger and the Sherwood number is slightly smaller compared with air having a relative humidity of 65 per cent.