Experimental investigation and numerical modelling of a compact wet air-to-air plate heat exchanger

Abstract

Air-to-air plate heat exchangers are widely used for domestic and industrial scale HVAC applications. The wide use of plate heat exchangers makes their control and optimisation critical for improving overall system performance. The application of plate heat exchangers has recently been demonstrated in domestic scale dehumidifier and heat pump clothes dryer systems. In the case of the domestic dehumidifier, the plate heat exchanger, referred to as an evaporator economizer, reduces the sensible load of moist air, and raises the drying efficiency of the system. However, they have shown to contribute to the latent cooling process also. There is little information regarding control and optimisation of air-to-air plate heat exchangers operating under wet operating conditions typical of domestic scale dehumidification and heat pump clothes drying.In this work, a plate heat exchanger was designed and constructed to experimentally investigate several different conditions for optimizing the moisture extraction rate for application of a plate heat exchanger as an energy recovery device. The test configurations include varied tilt angle, thermal effectiveness control, varied duct aspect ratio and varied air volume flow rate and moist air conditions that are applicable to domestic scale dehumidification systems. The research findings show that a modest tilt angle of up to −20°, relative to a reference setting of the hot-side face area being parallel to the horizontal, the pressure drop can be reduced by 33% with a corresponding decrease in the moisture extraction rate of 8%. Furthermore, a study of different ducting configurations shows that deactivating cold-side ducts, while fixing the active hot-side, allows for a greater range of hot-side temperature difference control, while maintaining a relatively high MER compared with deactivating hot-side ducts while keeping the active cold-side ducts fixed.The experimental data obtained in this work has been used to extend the validity of a recently developed numerical model for a wet air-to-air plate heat exchanger expanding its working range of hot-side and cold-side moist air inlet conditions, airflow conditions and ducting configurations and duct aspect ratios. This model provides for a quantitative approach when engineering emerging advanced domestic scale dehumidification and heat pump clothes drying systems.