Evaluation of the effect of the plate conductivity on the wet-bulb effectiveness of a cross-flow indirect evaporative cooler: a CFD analysis

In air-to-air Indirect Evaporative Cooling (IEC) systems, heat transfer between adjacent channels is usually achieved by means of water evaporation. This mechanism, which allows to cool down the primary air stream without increasing its humidity ratio, can be promoted by improving the plate wettability, pre-mixing air and water droplets before they enter the secondary air channels, increasing the water flow rate, and reducing the conductive resistance of the plates. The latter aspect is usually neglected, and an evaluation of the effect of the plate conductivity on the performance of IEC systems has not been found in literature. Therefore, in this work, a preliminary evaluation of this property is conducted, using a Computational Fluid Dynamics (CFD) model, which was experimentally validated in a previous work. In particular, a cross-flow IEC recuperator having plates with 0.15 mm thickness was chosen as a case study, and five different plate conductivities, ranging from 0.015 to 150 W/(m·K), were investigated under two different operating conditions, in order to assess their effect on the wet-bulb effectiveness of the cooler. The results showed that the wet-bulb effectiveness remains essentially unchanged for conductivities above 0.15 W/(m·K), while a reduction of about 6% occurs at 0.015 W/(m·K). This behavior indicates that, for thin-plate recuperators, conduction through the plates does not generally represent the limiting factor of the heat transfer process.