Measurement of heat and mass transfer from a body in air–water mist flow

Abstract

Principle By suspending a small quantity of water droplets in a gas stream, convective cooling of heated bodies is remarkably improved in comparison with singlephase gas cooling. Object This experiment demonstrates how convective heat transfer can be enhanced due to the evaporation of a thin water film, maintained on a heated surface by continuous impingement of water droplets, and the sensible-heat cooling by droplet impingement. The enhancement of heat transfer is governed by the temperatures of the air–water mist and a heated body, air-stream velocity, water-to-air mass flow ratio, size and spatial distribution of water droplets, wet-area fraction of the body surface, and so on. Apparatus The outlines of the air–water mist flow tunnels to be used for the heattransfer experiments are illustrated in Figs. 15.1 and 15.2. Figure 15.1 shows a test tunnel of the open type for horizontal air–water mist flow; 5 Fig. 15.2 shows a test tunnel of the circulation type for vertical air–water mist flow. 2 In the test tunnel shown in Fig. 15.1, pressurized water is sprayed through ten hollow-cone spray nozzles which are arranged in a circle around the centerline of the spray chamber. The additional use of a flat spray nozzle is recommended to humidify and saturate the carrier air. It is better to locate these nozzles sufficiently upstream so that drops larger than the desired ones may settle out of the mist in the low-velocity spray chamber.