A modified logarithmic mean enthalpy difference (LMED) method for evaluating the total heat transfer rate of a wet cooling coil under both unit and non-unit Lewis Factors

Abstract The logarithmic mean enthalpy difference, (LMED) method has been extensively used in evaluating the thermal performance of an air cooling coil under wet condition. The LMED method has been developed based on the assumption of unit Lewis Factor, i.e., Le 2/3  = 1. However, a number of previous studies have suggested that the Lewis Factor can actually deviate from being 1. Consequently, errors can be resulted in when calculating the total heat transfer rate of a wet cooling coil using the LMED method. Therefore, a modified LMED (m-LMED) method has been developed for calculating the total heat transfer rate under both unit and non-unit Lewis Factors and is reported in this paper. This m-LMED method has been validated by comparing its prediction of the total heat transfer rate to that from numerically solving the fundamental governing equations of heat and mass transfer of a wet cooling coil. The m-LMED method can therefore replace the LMED method for calculating the total heat transfer rate of a wet cooling coil under both unit and non-unit Lewis Factors.

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