Experimental and numerical investigation of the temperature and humidity distribution inside the channels for a regenerative indirect evaporative cooler

•A 400 mm wet surface length is sufficient for saturated evaporation.•Evaporative process tends to dynamic equilibrium when relative humidity above 95%.•Over 5 °C temperature difference means the need for sensible heat transfer strengthen.•Sensible heat transfer after evaporative needs to be strengthened in dry environment. This paper presents a simulation study of a regenerative indirect evaporative cooler combined with a series of experimental tests. A research prototype was employed to collect the air state signals in the channels with built-in high-precision temperature and humidity sensors on a test platform which helped to maintain the required environment. A validated numerical model was developed to simulate the impacts of air velocity, working air ratio and testing environment parameter on the distribution of temperature and relative humidity inside the channels. Results show that the upstream of the secondary air approaches saturation rapidly, and the evaporation process reaches dynamic equilibrium when the relative humidity of the secondary air comes to 95%. Under most working conditions, a 400 mm wet pathway can meet the performance requirements for an evaporative cooler. The low velocity allows a shorter distance for the secondary air to approach saturation while the lower product air temperature can be obtained. The working air ratio has little impact on the temperature and humid parameters. When the temperature difference between the primary air and the secondary air is higher than 5 °C, the potential for sensible heat exchange becomes more significant. In the dry environment, the regenerative indirect evaporative cooler should reserve a longer wet surface length, and high temperature difference exist between primary air and secondary air. The sensible heat transfer needs to be strengthened to fully utilize the potential of evaporative cooler.