Similarity analysis and comparative study on the performance of counter-flow dew point evaporative coolers with experimental validation

摘要

This paper entails a comparative study on the performance of counter-flow dew point evaporative coolers with two different configurations (type A and type B). Type A refers to the flow configuration where the supply air flows parallel to the water film, while type B refers to the flow configuration where the supply air flows counter to the water film. Both cooler types, when compared with a conventional indirect evaporative cooler, have better potential of lowering the product air temperature below its wet bulb temperature approaching the dew point temperature. A two-dimensional computational fluid dynamics model based on the continuity, momentum, energy and diffusion equations is firstly formulated and then employed to simulate the heat and mass transfer processes. The model, when validated with experimental date, shows a maximum discrepancy of 6.0%. A similarity analysis is then performed to structure the original governing equations of the model into dimensionless forms so as to evolve a fundamental platform that allows key dimensionless parameters to be determined. By regulating these key dimensionless parameters, distributions of the dew point and wet bulb effectiveness and the dimensionless product temperature are plotted via numerical simulation method. Additionally, key simulated data are regressed to obtain the empirical correlation of the dimensionless product air temperature. The key findings that emerged from the present study include: (1) the key dimensionless parameters that are essential to evaluate the performance of the counter-flow dew point evaporative cooler are supply air Reynolds number, water Reynolds number, working air to supply air mass flow rate ratio, water inlet dimensionless temperature, channel length to half width of dry channel ratio and half width of wet channel to half width of dry channel ratio; (2) comparatively, type B configuration has a higher cooling effectiveness and lower product temperature than type A configuration; and (3) the developed dimensionless product air temperature correlation for type B adhered closely to simulated results.