Passive cooling of two phase change materials installed in series

Abstract

Portable transport passive-type refrigeration systems keep products in specific temperature ranges for several days without electricity. Phase change material (PCM) is often combined with insulation panels to form an insulated box.This paper presents the effect of utilizing multiple PCMs with different melting temperatures and heat capacities on product storage and product temperature abuse. Two PCMs with different transition temperatures were thermally coupled, forming a cascade passive refrigeration system. The primary PCM (water) had the largest storage capacity. At the same time, the secondary PCM acted as a thermal buffer to prevent the temperature abuse, namely freezing, of the product carried inside the box.Modifications were made to an existing state-of-the-art refrigerated transport box to install PCM-based passive refrigeration systems that extended the refrigeration performance while maintaining the same envelope and interior volume. Experiments were conducted at ambient temperatures of 20 °C, 35 °C, and 42 °C while the temperature inside the container remained below 6 ℃ for several days. Effective thermal resistance values for the insulated refrigerated transport box and between the PCMs and the product inside the box were determined experimentally. A semiempirical numerical thermal model was developed to predict the duration, and the average error between the predicted duration and the data was 9.7 %. Correlations from the literature were also compared to estimate the transport box performance for various configurations, and the results indicated that such correlations estimated the storage duration satisfactorily only for simple configurations of the insulated box.