Energetic and Exergetic Investigations of an Integrated Heat Pump System for Drying Applications

Abstract

The main aim of this study is to conduct energetic and exergetic investigations of a dual stage heat pump for drying applications in order to evaluate the performance of the overall system. The integrated system consists of two processes, namely a drying unit and a dual stage heat pump. In the heat pump process, R-134A is used as the thermodynamic fluid and the drying unit is used to reduce the moisture content of the air. There are two evaporators used in the dual stage heat pump process: the first evaporator works at high pressures and the second evaporator works at lower pressures. The second evaporator provides supplementary cooling and drying effect for the air used in the drying unit. In the integrated system, there are two sub-coolers which provide additional heating to R-134A after the condenser. In this study, the energy and exergy efficiencies and exergy destruction rates of the overall integrated system, and each component and subprocess are calculated and discussed in detail. Exergetic performance of each component and subprocess are further investigated to identify where the highest exergy destructions occur in order to minimize irreversibilities within the integrated system and hence enhance the overall exergetic efficiency of the integrated system. The impact of environmental conditions on exergetic efficiency and exergy destruction is investigated via parametric studies. In addition, the coefficient of performance COP of the whole system and the effect of operating conditions are examined. The highest energy and exergy efficiencies occur when the drying unit’s inlet air mass flow rate is 0.5 kg/s and the environmental pressure and temperature are at 101 kPa and 298K which are 62% and 35%, respectively. The overall integrated system has a COP of around 3.8.

Keywords

• energy
• exergy
• efficiency
• heat pump
• drying
• sustainability