Air source heat pump system for drying biomaterial

摘要

Need for a more economic method of drying biomaterial, from paper to fruit, in South Africa has for long been sought. This paper explains research into an advanced air source heat pump drying (ASHPD) system, designed, manufactured and installed for drying South African fruit and taking into account local climactic conditions. The effect of ambient temperature and condenser fan speed on the coefficient of performance (COP) of the heat pump (HP) was evaluated, also the influence of drying temperature and air velocity analysed. Using banana slices (the sample fruit selected for this study) results indicated the moisture content of bananas produced in Mpumalanga Province averaged 75.5±1.5% on a wet basis. The COP of the HP was found to be significantly high — an average 4.7. The influence of the evaporator temperature on the COP was important since it assisted in temperature control during the drying process. It was also observed the COP increased with an increase in room temperature. Drying process results indicated for drying South African bananas a possible optimal drying temperature range was 30–40 °C with 1.5 m/s drying air velocity. Generally, the study demonstrated an ASHPD system was suitable for use in South African climatic conditions. Now South Africa has an opportunity to continue research and to design applications for this green and efficient drying technology — especially for drying biomaterial. This could reduce high energy consumption, something all of South Africa is striving towards.