Engineers at the Food Refrigeration and Processing Engineering Research Centre (FRPERC) at the University of Bristol said that they are currently testing and optimising air cycle refrigeration equipment for food processing that requires a linked need for the cooking and cooling of product.
Lead researcher Alan Foster told FoodProductionDaily.com that until now it has been difficult to link the processes because the heat generated by direct expansion refrigeration systems – the most common form of refrigeration employed in the food industry - is not at a high enough temperature to be useful in cooking.
However, he claims that air cycle refrigeration can generate large quantities of reasonably high grade heat (above 230°C), while at the same time producing air at very low temperatures (-100°C).
Product quality
The very low temperatures of the combined air cycle system allow rapid cooling and freezing, potentially improving quality, reducing weight loss, residence time and factory footprint for the process, continued Foster.
“We have achieved [in testing] a minimum temperature at the outlet of the turbine of -114°C and a maximum temperature at the outlet of the bootstrap compressor of 221°C for no load conditions.
“This equates to process temperatures of -64°C in the cooling tunnel and 150°C in the heating tunnel,” he explained.
Green benefits
According to Foster, the downside of air cycle refrigeration is its energy inefficiency compared to vapour compression systems; however, he stressed that air offers important advantages over other refrigerants:
“If it leaks it has a zero ozone depletion and global warming potential and is non-toxic and non-flammable. The system is far less susceptible to leakage than vapour compression systems and is therefore more reliable.
“If the leakiness of a vapour compression plant is taken into account the total equivalent warming impact (TEWI) of air cycle can compare favourably with many vapour compression systems,” added Foster.
FRPERC describes itself as a multi-disciplinary R&D team of researchers, scientists, engineers and technologists that aims to improve the efficiency of food manufacturing processes.