Numerical Estimation of the Heat and Mass Transfer Efficiency Considering Nonuniformity in Water and Air Distribution

Abstract

Using a system of differential equations of heat and mass transfer written in a cylindrical coordinate system with volumetric interphase sources of heat and mass transfer, a mathematical model of heat and mass transfer in film blocks of cooling tower irrigators has been developed. Expressions describing the interphase sources of heat and mass transfer and correlations for calculation of their parameters are presented. The parameters of the sources, i.e., the coefficients of heat and mass transfer, are related with the hydraulic resistance of irrigator blocks and can be calculated with both uniform and nonuniform distribution of air and water. The calculated volumetric coefficients of mass transfer were calculated and compared with the experimental data for regular mesh packing made of polyethylene and sheet-type metal packing. The numerical solution of the system of differential equations yielded the distribution of water, air, and air humidity content along the height of a packing block. The thermal efficiency of water cooling was calculated. It agrees satisfactory with the experimental data for spraying blocks made of polyethylene mesh. The causes of nonuniform distribution of phases among the packing blocks, which decreased the thermal efficiency of the cooling tower, were examined. The numerical investigations revealed that nonuniform air supply has the most significant influence decreasing the thermal efficiency of water cooling by as much as 35% or more compared with uniform phase distribution. The presented mathematical model can be used for estimating the cooling capacity of existing cooling towers at thermal power stations (TPSs) and industrial plants as well as in upgrading or developing high-efficient spraying blocks for film-type apparatuses.