FROZEN PRODUCTS STABILISATION BY PHASE CHANGE MATERIAL

摘要

The study presented here aims at finding the ideal method to achieve optimal product quality by using thermal energy storage devices in the case of frozen products storage. These products are usually sensitive to temperature levels and temperature fluctuations. However, reducing storage temperature leads to energy consumption increases. Moreover, temperature peaks are one of the main quality decay causes (e.g. ice crystal growth in frozen food). It is therefore interesting to try to reduce temperature fluctuations. Unsteady-state models were developed to simulate the heat transfer in the refrigeration plant, warehouse, phase change material (PCM), and product. Temperature levels and fluctuations were fed into the product quality model to evaluate its evolution. Results are shown for ice crystal growth in long term ice-cream storage. Various PCM solutions were compared which enabled the optimisation of the on-off control strategy, keeping the same setpoint and adjusting the deadband. In most cases, they helped reduce temperature fluctuations. When PCM was placed in the walls or in the ceiling, the reduction was not very large. The best results were achieved when PCM was put either in an additional heat exchanger placed after the evaporator, in a storage tank (indirect cooling), or in the product packaging. The first solution increases the pressure drop, and thus, the fan pumping power. The second solution also increases energy consumption due to the need of a pump for the secondary refrigerant. The third solution has the advantage of no additional energy consumption and offers an additional protection during transport.