Heat Transfer 1970/2. [antikvár]

T-HE MEASUREMENT AND CALCULATION OF LAMINAH MASS, HEAT AND MOMENTUM BOUNDARY LAYERS ABOVE A FLAT WET PLATE WITH AIR PROPERTIES VARYING WITH TEMPERATURE AJVD HUMIDITYP.E. Doe, B.E. B.Sc., MIE Aust. Lecturer in Mechanical Engineering, University of Tasmania, Hobart, Tasmania, Australia.AbstractVelocity, temperature and humidity were measured in a laminar mass transfer boundary layer above a flat wet plate. The appropriate boundary layer equations are solved for conditions approximating those of the experiment. Variations of fluid properties with temperature and humidity are included. The method can be extended to include certain functional forms of the pressure gradient, A comparison between the theory and experiment indicates that wall corrections, similar to those applied in hot wire anemometry are applicable to thermocouple psychrometer measurements close to an evaporating surfaceINTRODUCTIONIn recent years there has been a revival of attention to the detail of mass transfer processes. El-Wakil et al. (Ref. l), using a method of interferoraetry. Doe (Ref, 2) with thermocouple psychrometers, Lai and Hidy (Ref, 3) with an aluminium oxide hygrometer, and Wasan et alo (Ref, 4.) have measured mass concentration profiles in boundary layers. Spalding (Ref, 5) has made an extensive theoretical study of the laminar mass transfer boundaiy layer.One of the reasons for this interest is the hope that attention to the detail of mass transfer boundary layers will lead to improvements in the design and efficiency of equipment employing mass transfer processes, in the same way that attention to the detail of velocity boundary layers has contributed greatly to aerodynamics.This paper describes the measurement of a laminar mass transfer boundary layer and the development and solution of a theoretical model of the process. The solutions of the theoretical model are compared with the measurements and from this comparison comes a measure of the applicability of the model and an indication of possible refinements to the humidity measurements by way of corrections for the proximity to a solid boundaiy,2, Measurement2,1 Generation of the laminar mass transfer boundary laver All measurements were carried out in an open ended wind tunnel. The working section was of square section, 0,23m X 0,23in and 1 m long. The top surface of a 50% porosity sintered bronze plate, 0.l5m wide X 0.6lm long and C.Olm thick was flush with the bottom of the working section. Water supply to the plate was by gravity feed to a reservoir below the plate.Humidity and temperatiire of the air outside the boundary layer were measured with wet and dry bulb thermometers in the working section and a sling psychrometer at the tunnel entrance. The temperature of the wet plate was found from a copper-constantan thermocouple peened into the plate, Velocities of the bulk air flow in the tunnel were measured with a vane anemometer which was calibrated against the hot wire anemometer used for boundary layer velocity measurements,FC 1.1