A STUDY ON THE EFFECT OF ROUGHNESS ON PAN EVAPORATION

Abstract

The present work is based on the extensive investigation of evaporation from circular and rectangular evaporation pans for smooth as well as rough flow condition for different relative roughness heights introduced in the path of approach flow to pan. Experimental setup to measure the evaporation rates, temperature, humidity and velocity is designed and fabricated. Data have been collected for mass transfer for smooth and roughened flow conditions. Experimental set-up for mass transfer has been validated by collecting data pertaining to evaporation for conventional smooth flow. The uncertainty analysis as proposed by Kline and McClintock [1953] was carried out for the selection of instruments used. The uncertainty analysis of all the experimental data has been carried out. Based on the analysis of the errors in the experimental measurements using different instruments, the uncertainty in the calculated values of Sherwood number have been estimated to lie in the range of ± 1.1%, and ± 10.6%. Experimentation was carried out for circular and rectangular evaporation pans for smooth and rough flow conditions using different values of relative roughness height to collect the mass transfer data. The data has been presented in the form of evaporation rates and Sherwood number as function of roughness and flow parameters to bring out the effect of these parameters on the enhancement in mass transfer in terms of roughness parameters and Reynolds number. The experimental data have also been used to develop dimensional and dimensionless correlations to predict evaporation rates and Sherwood number for circular and rectangular evaporation pans. The evaporation rate and Sherwood number for circular and rectangular pan shape has been compared and it has been found that the shape has negligible effect. Substantial enhancement of evaporation rate and Sherwood number has been observed as a result of roughness elements in the path of the incoming air.