Thermal performance evaluation of water-based gel packs and insulating covers: A case study on raw milk preservation for local transport

Abstract

• A cooling system with water-based gel packs and UV-reflective covers was proposed. • The system reduced product temperatures by 10–13 °C within an hour. • This temperature reduction slowed the Escherichia coli growth rates by 1.1–1.3 times. • A simplified heat transfer model was developed and showed an RMSE < 3.0 °C. Maintaining the quality and safety of raw milk during transportation to collection centers poses significant challenges for small-scale producers, especially in regions with limited access to advanced refrigeration systems. This study proposes a cost-effective cooling system utilizing water-based phase change material (PCM) gel packs and UV-reflective covers. The thermal performance was evaluated using a tank filled with water, both with and without PCM, under constant and variable ambient temperature conditions. Results demonstrated that the tanks with PCM achieved a temperature reduction of 10–13 °C within an hour. Comparative analysis revealed similar thermal behaviors for milk and water, enabling the extrapolation of results. A simplified heat transfer model based on energy balance was developed to predict product temperature changes under different operational conditions. Some input parameters were adjusted using experimental data, and the model was subsequently validated against separate experimental datasets, showing reasonable accuracy (RMSE < 3.0 °C). The model could be used for application under comparable conditions. Furthermore, milk quality preservation was assessed through the enumeration of Escherichia coli and total coliforms in milk stored in tanks with and without PCM, as well as through predictive microbiological modeling. Both measured and predicted results suggested a moderate reduction in E. coli growth rates (1.1–1.3 times slower) in the tank with PCM, depending on initial microbial load. Based on these findings, the proposed system offers an effective and economical solution for small milk producers, enhancing cold-chain management and reducing spoilage.