Economic upgradation and optimal use of multi-cell crossflow evaporative water cooling tower through modular performance appraisal

Abstract

A novel numerical-cum-experimental technique is presented for modular performance evaluation of multi-cell crossflow evaporative water cooling tower of single-flow design, that determines fill characteristic for individual cell half with total system in operation. Fill characteristic is a single composite nondimensional parameter, involving dimensions of the cell half, configuration of the packing and water flow rate through it; representing overall potential of the fill to cool water and is a sole function of mass flow ratio of water to air for a given system. It diminishes with use mainly due to packing damage and its prevailing value represents the departure from design state at any instant of time. The result of deterioration manifests as increase in overall temperature of the cooled water ensuing from the tower. Since, in general, different cell halves undergo varied level of degradation and because fill characteristic for individual cell half is available; packing for all the cell halves need not be replaced simultaneously, which otherwise is a common practice for obtaining lower temperature of cooled water from the tower, as it entails a huge expenditure. It is possible to achieve significant lowering of overall exit cooled water temperature from the total system at a much reduced cost by undertaking packing replacement only for some selected cell halves at a given time, beginning with the worst affected cell half and then taking up the immediately better one, and so on. It is further feasible to obtain lower value of overall cooled water temperature from the existing tower system, with or without partial upgradation, by passing larger quantity of hot water through such cell halves which are less damaged and smaller quantity through those which are degraded more, thus requiring no extra expenditure. The proposed scheme of modular performance appraisal and the benefits resulting from sequential fill upgradation and that due to selective hot water flow distribution are displayed through an example for a typical cooling tower of single-flow design having 12 cells by considering deteriorated state of six different fills.