Wojciech Zalewski

Mathematical model of heat and mass transfer processes in evaporative fluid coolers

Abstract In this paper heat and mass transfer processes in evaporative fluid coolers are discussed. A new mathematical model of evaporative fluid cooling with countercurrent air flow is presented. The model consists of four ordinary differential equations with their boundary conditions and some associated algebraic equations. A method of adjusting the model to geometrical arrangement which is used in bare-tube heat exchangers is proposed. The study presents a comparison of the results computed using an analytical model with the experimental results of the evaporative water cooler test. A good agreement between the calculated and experimental values is achieved. The correction function of mass transfer coefficient introduced into the analytical model improves this agreement.

Optimization of evaporative fluid coolers

Abstract In the paper the optimization of geometrical and operating parameters for evaporative fluid coolers has been presented. The algorithm of optimizational calculations contains: • the mathematical model of heat and mass transfer in evaporative fluid coolers; • model of operating costs based, among others, on the Zalewski–Gryglaszewski relations developed by the authors for evaluation of air pressure drops in the heat exchanger; • model of evaporative heat exchangers production costs. Optimization problem formulated for non-linear objective functions with inequality and equality constraints has been solved using Schittkowskis method based on quadratic programming. Two optimization problems have been considered. A solution to the first problem consists in the design of a heat exchanger with such geometrical parameters which ensure its maximum heat capacity at minimal total costs. A result to the second optimization problem are such thermal and flow parameters which will ensure minimum operating costs.The results of optimization calculations presented in the paper are accompanied by their experimental verification.