RIRDC - Research Compendium 1993

Rural Industries
Research & Development Corporation

Research Compendium 1993 - 1994

Research Project

DEVELOPMENT AND APPLICATION OF HEAT PUMP DRYERS

Objectives

To develop optimum processing parameters for an advanced heat pump dryer to produce low-cost, high-quality dried products.
To evaluate the energy/cost savings and the quality advantages of products dried by the heat pump system as compared to products dried by conventional methods.
To investigate the use of the low cost, low temperature drying that these pumps offer to dry-heat susceptible products.
To inform and demonstrate to relevant industries the application and advantages of the heat pump technology.

Background

Heat pump drying is a new technology for the food industry. It utilises a refrigeration system to dehumidify and reheat the drying air, normally in a closed recirculation system.

In principle, air from the product is cooled to below its dew point by passing it over the evaporator of the system, condensing water from the air stream. The air then passes over the condenser, reheating it before it is returned to the drying chamber to complete the cycle. The system recovers the latent heat of evaporation from the water in the air stream, and so is highly energy efficient. It also enables effective drying at lower temperature, offering quality advantages with many food products.

Research

An advanced heat pump dryer was fitted with instruments to allow measurement of temperature and humidity throughout the cycle. Product weight during drying could also be monitored. A range of food materials were dried using the system, and assessed including fruits (eg. mango, pineapple, apple, banana, strawberry), vegetables (eg. onion, mushroom, broccoli, carrot, capsicum, tomato), macadamia nuts, ginger, herbs (basil, parsley), scallops, prawns, beche-de-mer, meats, and biscuits.

Only limited trials were carried out for most of these products, at the request of growers or processors interested in commencing production. Ginger, mangoes, and mushrooms were studied in greater detail. The effects of parameters such as air velocity, temperature, and product size were evaluated.

Outcome

The research contributed significantly to the efforts of a larger team working in this area. Commercial processors have now installed heat pump dryers for the processing of products including macadamia nuts, peanuts, biscuits, mangoes, bananas, leather, tomatoes, carrots, and beche-de-mer. The team was awarded the 1993 National Energy Award (Industry Category) and the 1994 Food Innovation Award (presented by the Australian Institute of Food Science and Technology) for their work.

Implications

While a large range of products were tested briefly, there is still a lack of detailed information on drying characteristics or the heat pump system.

RIRDC Project No: DAQ-98A

RESEARCHERS: Dr Bandu Wijesinghe Mr Gordon Young

ORGANISATIONS: International Food Dept of Food Science

Institute of Qld Technology

19 Hercules Street University of Qld

HAMILTON QLD 4007 LAWES QLD 4343

PHONE: 07 268 8573 074 601 385

FAX: 07 268 4798 074 601 171