Currently most food products are cooled and frozen in air-blast cold storage to prolong storage time. The airflow field distribution in storage has a great impact on the process of food freezing and energy cost by that. In this paper, a transient model of food freezing considering airflow field was developed to simulation the temperature profile of air and food products during freezing process. A lumped parameter model was used to predict the temperature and moisture profile of air, which connected all other components together, such as air coolers, food products, envelop enclosure and refrigeration system. A finite difference method was employed to model the heat transfer inside food products during freezing, where the mass transfer was neglected as the food products were wrapped with polystyrene films. Unit load factor method was applied to calculate the sensible heat refrigeration capacity and thus the total capacity of air coolers. The simulation was conducted on a large cold storage filled with large quantities of packaged food products. Results show that there are great differences in airflow field distribution at different locations in cold storage, which lead to spacial differences in freezing time required. Inappropriate set point of freezing time prolongs freezing process unnecessarily and leads to extra energy consumption. Operational mode of air coolers has a great impact on the total energy consumption, as they consume energy themselves and release equivalent heat into storage simultaneously.
Review on application and research of trans-critical CO2 refrigeration system in food freezing and cold storage
