Performance evaluation of an indirect–direct evaporative cooler using aluminum oxide-based nanofluid

Indoor comfort has become a necessity in recent times with the advancement of science and technology. The usage of direct type air coolers increases the humidity of the closed room, and this increase in humidity is unfavorable. The present work deals with the study related to the combination of direct and indirect type air cooler to increase the performance. A set of mild steel plates have been arranged to form a cross flow heat exchanger to exchange the heat between cold nanofluid and warm air forms the indirect heat exchanger. Al2O3-based nanoparticles have been blended with pure water and used in indirect air coolers. Celdek pad 7090 is used as the cooling pad in the direct type of air cooling. Experiments are performed by varying the flow rates of water from 1 to 4 lpm, by varying the air velocities from 3 to 6 ms−1, and by varying the concentration of nanoparticles in the water from 0 to 0.2.5%. Performance parameters such as change in temperature, change in Relative humidity (RH), cooling efficiency and coefficient of performance (COP) are determined. It was found that by adding the nanoparticles, the performance of the cooler has been enhanced. Chane in dry bulb temperature (ΔDBT), cooling efficiency increased by 13.1%, 14% as compared to the indirect method without using the nanoparticles and 39.2% and 21% as compared to the only direct type. Similarly, ΔRH reduced by 27% when compared to only direct evaporative cooler. 3 LPM showed the best performance with the highest humidification efficiency and COP of 96% and 5.9, respectively. When the air velocity is increased from 3 to 6 ms−1, energy consumption increases by 49%. Combination of indirect–direct techniques with the use of nanofluid has shown the potential of greater reduction in the exit DBT with simultaneously without appreciably increasing the exit RH.