Research Paper Optimal design of a regenerative heat and mass exchanger for indirect evaporative cooling Farbod Fakhrabadi ⇑ , Farshad Kowsary School of Mechanical Engineering, Faculty of Engineering, University of Tehran, Tehran, Iran highlights  Cooling performance of a regenerative heat and mass exchanger (RHMX) is optimized.  Room cooling capacity is considered to evaluate the cooling performance of a RHMX.  Product flow rate and working-to- product flow ratio are adapted as design variables.  Effects of climatic and design conditions on the cooling performance are discussed. graphical abstract article info Article history: Received 27 November 2015 Accepted 23 March 2016 Available online 12 April 2016 Keywords: Optimal design Regenerative heat and mass exchanger Indirect evaporative cooling abstract This article presents the optimal design of a regenerative heat and mass exchanger (RHMX) for indirect evaporative cooling. The room cooling capacity which is the product of the supply air mass flow rate, specific heat of the supply air and the difference between the supply air temperature and the comfort temperature, was considered as a criterion to evaluate the cooling performance of the RHMX. The air con- ditions throughout the RHMX were obtained by a heat and mass transfer model. The model was validated by comparing the modeled results with the existing experimental data. The simplified conjugate gradient method was used as an optimizer to obtain the optimal performance, and to adjust the design variables, i.e. product air flow rate and working-to-product air flow ratio. The effects of the exchanger’s parameters as well as the inlet air condition on the performance of the optimized RHMX and on the values of the design variables were discussed. It was concluded that the working-to-product air flow ratio is around 0.4 under various climatic and design conditions. Moreover, the channel length and the channel height should be selected between 0.4–0.6 m and 0.004–0.006 m, respectively, to have a high RCC with an acceptable fan power. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Evaporative cooling is a sustainable, energy-efficient and cost- effective air conditioning method for comfort cooling in buildings. Evaporative cooling is classified into two main categories, direct evaporative cooling and indirect evaporative cooling. In direct evaporative cooling (see Fig. 1(a)), the air is in direct contact with liquid water. The heat and mass transfer between the air and water reduces the air’s dry bulb temperature, and raises its humidity. In indirect evaporative cooling (see Fig. 1(b)), a wet surface heat and mass exchanger with alternating dry and wet passages is used. The product (supply) air stream is sensibly cooled through the dry passages without humidity rise. Simultaneously, the working air stream is humidified in the adjacent wet passages where the heat of the product air is absorbed due to the evaporation of water. The minimum temperature that can be reached by both direct and indirect evaporative cooling is limited to the wet bulb http://dx.doi.org/10.1016/j.applthermaleng.2016.03.115 1359-4311/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: ffakhrabadi@ut.ac.ir (F. Fakhrabadi). Applied Thermal Engineering 102 (2016) 1384–1394 Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng