Potential of Phase Change Material (PCM) as a thermal energy source for uninterrupted on-farm agricultural food processing

This research addresses the critical challenge of unreliable thermal backup solutions encountered by small-scale farmers who rely on decentralised solar food processing systems. Since these systems depend on solar energy, an inherently intermittent source, a reliable thermal backup is essential to ensure continuous and effective operation. To achieve this, the study explores the possibility of expanding the use of phase change materials (PCMs) for thermal energy storage in such systems, which offers a more efficient and compact alternative to conventional sensible heat-based systems such as biomass boilers and thermal oils In this context, a standalone PCM-based thermal backup system was designed to support a variety of food processing units operating below 100 °C, with a particular focus on milk pasteurisation. The system features a Scheffler concentrator and a PCM tank with an unconventional shell-and-tube configuration, in which the PCM is housed inside the tubes while the heat transfer fluid (HTF) circulates around them. This reverse design enhances the adaptability of the system for different applications. Performance testing revealed that the system’s thermal behaviour was strongly influenced by solar irradiance and HTF flow rates. Higher solar irradiance and lower HTF flow rates resulted in greater energy storage. Under field operating conditions, the system captured and released enough thermal energy to pasteurised 5 kg of milk. To assess not just the quantity but the quality of energy stored, an exergy analysis was performed, identifying mechanical irreversibility as a major factor affecting overall system performance leading to an unconventional combination of HTF flow and irradiance conditions to achieve maximum exergetic efficiency. The flexibility of the system was tested by integrating it with an existing decentralised pasteurisation unit, which was achieve with only minor modifications. A mathematical model, developed in Python, was used to predict system behaviour under different operational scenarios and to optimise key parameters such as flow rates and suitable heat exchanger type. The model shows flow rate changes in milk pasteurisation tank are more effective and identified a plate-type heat exchanger to be a better option, owing to its compactness and superior ability to reduce pasteurisation time. In conclusion, this research presents a robust and versatile PCM-based thermal backup system capable of ensuring reliable operation for a wide range of decentralised food processing applications, regardless of solar availability. Its compact structure, design adaptability and scalability potential make it a highly promising solution for sustainable, on-farm food processing.