Mass transfer coeficient for the prediction of volatile organic compound evaporation rate from water basin : Effect of wind speed

Recently, volatile organic compound (VOC) evaporation from open water basin such as an equalization basin in wasterwater treatment plant has been recognized as an important source of air polution. The amount of VOC evaporation from open water basin can be predicted by using the two-film theory that requires two mass transfer coefficients includint kG and kL. This paper studies the effect of wind speed over sater surface on the gas-film (kG) and the liquid-film (kL) mass transfer coefficient. A series of volatile organic compounds evaporation experiments were performed in a wind tunnel-water tank system in which the wind speed above the water surface can be easily controlled. The wind speeds were varied from 0 to 4.8 m/s. The water and the air temperature were constant at 25?1 and 28?1 OC, respectively.The kG and kL for various wind speeds were determined from unsteady state volatilization of methanol and toluene from water, respectively. The results indicated that kG increased lineraly with wind speed over the entire range while the relationship between kL and wind speed fell into two regimes with a break at the wind speed of 2.58 m/s. The mass transfer coefficient correlations (kG and kL) were developed from the experimental data and validated by comparing the predicted value of KOL, and the evaporation flux (Nvoc), which were predicted from kG and kL correlations, against the experimental data from evaporation of accetone and chloroform from water. The predicted value of KOL and NVOC provided good agreement with the experimental data.