Experimental study of an energy efficient hybrid system for surface drying
Rapid surface drying is an important and energy intensive process in food and beverage packaging industry. Usually these products are dried at low dew-point temperatures (DPT) −10 to −20 °C and low dry ball temperatures (DBT) 20–30 °C for product quality optimization. The conveyor moves at very high speeds and it is necessary to expose as much of the drying surface to the drying effect in a shortest time possible. Re-condensation is a big problem in these systems and a good drying system is that preserves the quality of the product and is energy efficient. This paper presents a feasibility study to obtain the design parameters of a hybrid dryer suited for rapid drying applications. Drying process of a re-circulation heat pump is integrated with rotary dehumidifier (desiccant wheel) system. The system employed a refrigerant circuit in conjunction with a heat reactivated desiccant wheel to provide efficient drying capability and supply low DPT conditions. To increase the economic practicality of such a hybrid system, the combined system utilises the heat dissipated by the condenser in regenerating the desiccant wheel. The study shows that the proposed hybrid system can deliver supply air at much lower DPT compared to the single refrigerant circuit and a desiccant wheel. By operating the combined system in tandem, greater amount of dehumidification could be realised due to the improved ratio of latent to total load at the hybrid. Up to 60% heat energy can be saved in rapid surface drying applications by using the proposed hybrid system.