A method for determining the heat and mass transfer efficiency in a film cooling tower with intensified fill packs

Abstract

A modified method of transfer units is developed for a countercurrent film cooling tower with a structured tubular packing with surface intensifiers in order to determine the thermal efficiency of the gas and liquid phases and the temperature of the cooled water at the output. The approach of presenting the number of transfer units, taking into account additional terms with reverse mixing coefficients is applied to indirectly consider the hydrodynamic structure of flows and a decrease in the heat and mass transfer efficiency, compared with the ideal displacement model. An experimental installation with a layout (column) of a Plexiglass cooling tower with a diameter of 200 mm and a height of 2 m is described. Experimental data for water cooling in a structured packing block in the form of a vertical bundle of tightly packed polyethylene pipes with a diameter of 0.05 m with an annular discretely structured surface roughness are presented. Generalized calculated empirical expressions for the drag of dry and irrigated pipes, as well as the dependence of the volumetric mass transfer coefficient on air velocity at different irrigation densities, are obtained. The parameters of expression of the modified number of transfer units are identified based on experimental data on thermal efficiency in the gas phase. As a result, the dependence of the thermal efficiency in the gas phase on the pressure and design characteristics of the structured packing is obtained taking into account the reverse mixing of the flows. Reverse mixing is shown to reduce thermal efficiency by 8 – 15 %, which must be taken into account in the calculations of film cooling towers. The calculation results for the SK-400 industrial cooling tower using the presented expressions are provided and the agreement of the thermal efficiency of the cooling tower with the calculation according to the proposed method is shown.