CALCULATION OF CLOSED WET COOLING TOWERS USING MODIFIED Ε-NTU APPROACHES

Abstract

Two modified ε-NTU approaches developed for air-to-air indirect contact evaporative coolers have been adapted for calculation of heat/mass transfer in the closed wet cooling towers. These approaches use the analogy between the heat and mass transfer and the linearization of the direct or inverse correlations of moist air enthalpy on the temperature of the wet bulb. The results of calculation based on the modified ε-NTU approaches were compared with the data obtained by the traditional method, using the average logarithmic temperature and concentration differences. The comparison was carried out in terms of heat transfer efficiency according to the temperature of the wet bulb, this temperature is the theoretical limit of the outlet water temperature for this type of heat and mass exchange equipment of the indirect evaporative type. Calculations showed that both ε-NTU approaches demonstrate almost identical results, the possible inconsistency between them may be related to the inaccuracy of linearization. These data agree well with the data of the calculations, which are based on application of the average logarithmic difference of the flow parameters and the empirical dependencies of the heat and mass transfer coefficients. A small discrepancy (up to 7%) occurs with a small flow rate of working water. Bibl. 15, Fig. 5