ON THE EFFECT OF WATER EVAPORATION ON COOLING EFFICIENCY IN COOLING TOWERS

The paper introduces the results of theoretical study of cooling water droplets as they move in a stream of cold air under conditions characteristic of high-capacity tower cooling towers and the results of a numerical analysis of temperature distributions along the droplet radius. Due to the large temperature differences and significant speeds in the system under consideration, the temperature distribution inside the droplets is assumed to vary along the radius. The increase in air humidity in the near-wall area due to water evaporation is taken into account. The resulting system of nonstationary partial differential equations is solved by the finite difference method using an implicit four-point difference scheme. The solution of the problem with a moving boundary was carried out by the method of catching the front into a node of a spatial grid. To solve nonlinear equations, the iteration method was used. The aim of the work is a numerical evaluation of convective and evaporative cooling contribution to formation of the temperature field of water droplets under conditions typical of modern cooling towers. The analysis was carried out for two characteristic values of the ambient air temperature corresponding to the summer and winter periods of the year. The analysis of the effect of cooling droplets due to water evaporation and thermal conductivity was performed. The temperature distribution over the radius is obtained for different values of the characteristic sizes of droplets. It is shown that the change in radius for the entire range of characteristic sizes of droplets during their flight is less than 0,73 % and does not have a significant effect on the amount of water cooling in the cooling tower. It is established that the absorption of heat by evaporation plays an important role in formation of temperature distribution in the droplets of circulating water at the outlet of the cooling towers. It is shown that at negative ambient temperatures, excessive crushing of droplets is impractical.