The Effect of PCM Materials on the Performance of Cold Storage Mini Containers

Abstract

The global spatial distribution of fresh produce cultivation does not align with population centers, necessitating robust long-distance transportation. Maintaining the quality of perishables is challenging, as ambient conditions often fluctuate outside the optimal temperature and relative humidity ranges. Mini refrigerated containers are one solution to this problem. In these containers, cold air is blown to maintain the desired environmental conditions. To enhance the capabilities and performance of these containers, adding phase change materials (PCMs) to their walls is studied. A lumped-capacitance approach is used to analyze the energy balances for the produce, the air, and the PCM. These energy/mass balances are ordinary differential equations coupled to each other, making it possible to model the heat transfer between them. The study simulations use tomatoes as an example of the produce to be kept at the desired conditions. The energy balance equations take into consideration the respiratory heat generation from the produce, the evaporative cooling due to the vapor pressure deficit between the air and the produce, and the convective heat transfer between the air, the produce, and the PCM. In the energy balance of the air, advection of incoming and outgoing air is taken into account. The latent heat of PCM is modeled over a temperature range of 2℃ using an effective specific heat capacity method, in which the latent heat is treated as specific heat capacity. Two different scenarios are examined. The first one is cooling down produce from ambient temperature to a desired temperature, while the other is of pre-cooled produce at 9 ℃ that is heated by ambient conditions, with no cooling air being blown inside the container. The results show that PCM addition helps with faster cooling, with a difference of over 1.9 hours, and an almost 24.8 hours slower rise in temperature for the pre-cooled i produce. The system sensitivity was tested by comparing two different PCMs across various input parameters. Achieving a full phase change is critical for the system to provide any thermal benefit. Additionally, air velocity has a significant impact on performance, though its influence only becomes dominant once a specific threshold is surpassed.