Performance of an indirect evaporative cooler (IEC) made of PET/cellulose composite sheet as wetting media

Abstract

Indirect evaporative cooler (IEC) is commonly made of plate-type aluminum. However, because aluminum is a rather expensive material, and has a problem of white rust with water, continuous efforts have been made to replace the aluminum. In this study, a cross-flow IEC, where PET/cellulose corrugated sheet (50/50% by mass) was used as a wet channel was devised, and the performance was compared with those of exiting aluminum and PET IEC. Results showed that the wet and the dry surface heat transfer coefficients were approximately the same for the composite IEC, probably because of the superb wetting characteristics of the PET/cellulose wet channel. For PET and the aluminum IEC, wet surface heat transfer coefficients were significantly lower than those of the dry surface. The dry portions of the total surface area were estimated to be 43–63% for the aluminum IEC, and 65–80% for PET IEC. Wet bulb effectivenesses of the composite IEC (38.5–51.4%) were approximately the same as those of the aluminum IEC (41.9–47.5%), which were significantly higher than those of PET IEC (29.0–37.4%). On the other hand, the pressure drops of the PET/cellulose channel were 92–105% higher than those of the aluminum channel due to the difference in the channel configuration. A hypothetical plate-type IEC having the composite membrane was devised, and it was shown that the material change may increase the wet bulb effectiveness by 44%.