Experimental Studies of Heat Transfer for Air-Water Mist Flow Impinging on an Isothermal Plate

Abstract

Experimental studies of heat transfer enhancement have been made for a laminar air–water mist flow impinging on an isothermal plate. Heat transfer data for various mass flow rate of water, wall temperature and air–water mist flow velocity have been obtained. The mechanism of heat transfer enhancement can be separated into two parts: (1) An enhancement function Ø 1 , pertaining to water droplets that mix with air stream in the flow field; and (2) another enhancement function Ø 2 , representing water droplets which separate from the mainstream because of inertia, impacting on the heated wall and then evaporating. The sum of Ø 1 and Ø 2 is related to the ratio of the average Nusselt number of the present two–phase flow with that for one phase flow in the formml: Nu/Nu 0 = 1 + ∅ 1 + ∅ 2 Experimental results of Nu/Nu 0 at different wall temperatures presented in this paper vary from 1 to 20. The wall temperature is practically uniform for each test, ranging from 60 C to 110 C. The water flow rate per unit cross–sectional area changes from 0.038 to 0.092 (kg/m 2 s). The air–water mist velocity ranges from 4.7 to 18.0 m/s. The average sizes of the water droplets are 16 and 21 μm that are obtained from two nozzles.