ИСТИНА

Predicting evaporation rates from hot or cool water tanks is important for various industrial applications. Evaporation rate determines the liquid mass losses from water storage basins. Evaporation also plays an important role in energy consumption of indoors swimming pool facilities. It determines the cooling effect in air-conditioning systems. A number of empirical correlations relating evaporation rate to vapour pressure or absolute humidity difference have been proposed, beginning from Carrier’s correlation in 1918 [1]. However, they are valid only for the range of parameters (reservoir size, temperature difference, humidity) covered in concrete experiment. Analytical correlation was proposed by Shah [2], but it does not account for temperature difference between water and air. CFD calculations using commercial software were also performed by several groups [3], making use of empirical correlations to specify the mass flux at the interface. The present paper’s objective is to derive numerical model for direct computation of evaporation rate based on simple physical considerations. No heat or mass flux is specified at the boundary. Instead, they are calculated from local parameters of the medium using physical boundary conditions. 2D-simulations are performed and the calculated evaporation rate is compared to known empirical correlations. New correlation is proposed taking into account both the effects of thermal and concentration-induced convection. Possible evaporation rate dependence on the pool size is discussed. It is shown that evaporation has cellular nature, it proceeds with localized chaotic bursts which can be observed experimentally. Geophysical problem of explaining the temperature difference and profile near the surface of water reservoir [4] is also considered. It is shown that numerical model allows finding out the temperature difference by solving non-stationary CFD problem. Numerical results are verified by experimental investigation using Background Oriented Schlieren method. Good agreement is found indicating that temperature difference is explained by evaporation. REFERENCES [1] W.H. Carrier, “The temperature of evaporation”, ASHVE Trans., Vol. 24, pp. 25-50, (1918). [2] M.M. Shah, “Prediction of evaporation from occupied indoor swimming pools”, Energy & Buildings, Vol. 35, pp. 707-713, (2003). [3] S.J.K. Bukhari and M.H. Kamran Siddiqui, “Characteristics of air and water velocity fields during natural convection”, Heat Mass Transfer, Vol. 43, pp. 415-425, (2007). [4] Y.Y. Plaksina, V.N. Aksenov, E.G. Andreev, “Study of cool and warm surface skin formation in laboratory conditions”, Moscow Univ. Phys. Bulletin, Vol. 64, pp. 355-357, (2009).