Experimental and theoretical investigation of internal two-stage evaporative cooler

• A new type of evaporative cooler is introduced and given a distinctive name.
• This type of system involves two stages with no external sources involved.
• The saturation efficiency of this type cannot be higher than 1.
• Relative Humidity of the supply air is higher than that of the direct evaporative cooler.

The internal two-stage evaporative cooler is studied by experimentally comparing its performance with direct evaporative cooler and theoretically with direct and external two-stage evaporative coolers. The results show that the efficiency of the internal two-stage evaporative cooler is higher than that of direct evaporative cooler but it cannot be raised over 100%. It was also shown that the efficiency of the internal evaporative cooler type is less sensitive to air speed than direct type. The efficiency of the direct evaporative cooler increases by 12%, and the internal evaporative cooler increases only by 5% when fan speed switches from high to low value. The results also show that the supply air of the internal evaporative cooler has higher humidity content than direct evaporative cooler which makes it a good humidifier in cold storages where humidly close to saturation is required.