Design of a CO2 heat pump drier with dynamic modelling tools

Drying is an energy and time intensive process which thermal energy demand is mostly provided by fossil resources. Especially in the food processing industry it is important to increase the energy efficiency of drying processes in terms of organic products and sustainability. The potential of using a heat pump with R744 (CO2) as a working media to provide the thermal energy was investigated for typical food drying temperature of 50 °C at a relative humidity of 20 %. A dynamic heat pumpassisted dryer model has been developed and validated. The model was created with respect to heat transfer, pressure loss and flow requirements. The simulated results showed that a closed-loop heat pump assisted drying process has the potential to reduce the energy demand by around 80 % compared to conventional open-loop drying processes with fossil resources as energy source. Furthermore, the implementation of a bypass in the air cycle was examined to further enhance the energy efficiency of the system