Experimental analysis of a multistage direct-indirect evaporative cooler using a straight heat pipe

•The performance of a multistage direct–indirect evaporative cooler using a heat pipe is evaluated.•Heat pipe module can increase the performance of the direct evaporative cooler.•Three arrangements of combined heat pipes and evaporative coolers were conducted in this research. Mechanical vapour compression air conditioning has advantages and drawbacks. The compressor used in this system increases energy consumption. In addition, the refrigerant used in this system harms the environment and contribute to ozone layer depletion. However, keeping a building at a comfortable temperature is still necessary and cannot be neglected. An evaporative cooler can be an alternative for overcoming this drawback because evaporative coolers are environment-friendly and have low operation costs. However, the evaporative cooler disadvantageous for producing air with a high relative humidity. The objective of this experiment is to evaluate the performance of a multistage direct–indirect evaporative cooler using a heat pipe in terms of saturation efficiency, the output air humidity, and sump water consumption. In this experiment, heat pipes are used as a pre-cooler in the first stage and for indirect cooling in the third stage. Tests are performed under different inlet temperatures ranging from 36 to 45 °C and an air flow rate ranging from 0.4 to 1.4 m/s. Thermocouple and humidity sensors are used to obtain the temperature and relative humidity values, respectively. The largest decrease in temperature is obtained when evaporation occurs during the first stage heat pipe at a 0.8 m/s air flow rate and 45 °C. The saturation efficiency and the output humidity are calculated and evaluated. The experiment shows that the first and second stages together can increase the saturation efficiency, but this process also increases the relative humidity of the outlet air and consumes more water than a single stage does. All three stages together produce a smaller decrease in temperature and relative humidity.