ABSTRACT
The term air-side of heat pumps concern evaporators, condensers, and blowers. In heat pump dryers, the air-cooled condensers are finned-tube coils, where unmixed fluids move roughly perpendicular to each other. The refrigerant-to-air condensers, most common in heat pump-assisted drying applications, are fin-and-tube heat exchangers that reject heat from the refrigerant circulating inside horizontal tubes to the outside air. The refrigerant-to-air condensers can be located outside or inside the drying chambers, and oriented vertically or horizontally. Air-cooled heat exchangers with in-tube condensation of refrigerants are widely used in industrial heat pump-assisted drying systems. As a consequence, the condensing heat transfer coefficients vary throughout the horizontal condensing tubes. Based on the energy balance of the refrigerant condenser, its steady-state thermal capacity can be calculated from the refrigerant-side enthalpy change and flow rate, or from the air-side mass flow rate, specific heat and temperature change.
