الملخص
.The most efficient equipment in which heat rejection processes may be realized is the cooling towers, evaporative fluid coolers and evaporative condensers. This class of heat rejection devices is defined as evaporative heat exchangers. The mathematical models of these heat exchangers are developed and validated against the experimental data available in the literature, using Engineering Equation Solver (EES) software, where the maximum error encountered is 6.5%. These devices basically consist of three zones; namely, spray zone, packing/tube-bundle and rain zone. The spray and rain zones are often neglected even though in large cooling towers, a significant portion of the total heat that is rejected may occur in these zones. Therefore, the heat and mass transfer contribution of the spray and rain zones in cooling towers is discussed as well. A parametric study is performed to evaluate the effect of fouling (which is the deposition of unwanted material on heat transfer equipment), atmospheric pressure and mass flow rate ratio on typical performance parameters such as effectiveness for rating calculations while volume/surface area for design calculations. Also, a sensitivity analysis is carried out to evaluate the response of the above parameters to various input variables such as inlet wet-bulb temperature, inlet process fluid temperature and outlet water temperature. Second-law analyses based on exergy analyses are studied as well to investigate the variation in second-law efficiency of these heat exchangers under different operating conditions. Furthermore, the rate of water evaporation under a wide range of operating conditions is also presented
