Keeping harvested tomatoes cool is difficult in off-grid tropical regions, where high ambient temperatures accelerate deterioration but reliable electricity may not be available. Solar-powered refrigeration can provide daytime cooling, but maintaining low temperatures after sunset commonly requires electrochemical batteries. This study instead investigates whether phase change material (PCM) can store cooling thermally and provide a battery-free alternative for small-scale cold storage.
The researchers developed a coupled refrigeration and thermal-storage simulation framework. COCO modeled the propane R-290 vapor-compression refrigeration cycle, while FEATool Multiphysics modeled transient heat transfer and solid-liquid phase change within the PCM and tomato storage chamber. The combined simulations showed that PCM storage can buffer the chamber against temperature changes and substantially extend cooling into periods without solar input, supporting the feasibility of battery-free operation under the simulated tropical conditions.
The modeled system combines a photovoltaic (PV) array, a direct-current compressor refrigeration cycle, an insulated tomato chamber, and PCM modules arranged around the storage space. During periods of solar input, the refrigeration system cools both the chamber and PCM, storing cooling capacity through sensible and latent heat effects. When solar input is unavailable, the PCM absorbs heat as it changes phase and helps maintain the chamber temperature. FEATool represented this transient thermal behavior with an enthalpy-based phase-change formulation, accounting for sensible energy, latent energy, liquid fraction, and heat conduction between the PCM and chamber. The model also included environmental heat gain and the thermal load associated with the stored tomatoes.
The FEATool solution resolved how the PCM temperature field and phase state evolved through charging and discharge. The reported simulations show the PCM undergoing almost complete phase change, with liquid fraction varying from 0.05 to 0.95 and discharge lasting about 17 to 19 hours. Temperature-field results also show heat transfer between the central tomato chamber and the surrounding PCM layer. At the complete-system level, adding PCM reduced the average chamber temperature from 16.5 °C to 6 °C and reduced temperature fluctuations from ±2.8 °C to ±0.6 °C. Cooling autonomy increased from 3 hours without PCM to 17 hours with PCM, demonstrating how the thermal storage modeled in FEATool bridges the gap between daytime solar refrigeration and nighttime cooling demand.
FEATool formed the thermal-storage part of a broader COCO-FEATool workflow. COCO supplied the refrigeration-cycle performance, including a simulated R-290 cooling capacity of 1371 W at 693 W compressor power and a coefficient of performance (COP) of 2.0. The transient FEATool results supplied the PCM and chamber behavior needed to evaluate how that cooling was stored and released over time. Within the resulting energy balance, the paper reports that PCM storage accounted for approximately 43.6% of the total refrigeration duty. Parametric analysis further showed that cooling autonomy was particularly sensitive to tomato load, PCM latent capacity, and insulation performance, making these important variables for subsequent system design and scaling.
The coupled numerical framework was checked using several independent procedures. Refrigeration-cycle results were compared with thermodynamic benchmarks, the PCM phase-change behavior was compared with published melting data, and grid refinement was used to test numerical convergence. The reported mesh-independence test produced a temperature change below 0.4%, while the global energy-balance residual remained below 3%. These checks support the numerical consistency of the model, but the authors also identify an important limitation: validation was based on literature data and energy balances rather than a full field-scale experiment. The study additionally considered a specific PCM volume and chamber configuration, so other storage sizes, geometries, and PCM types would require further investigation.
In this work, FEATool Multiphysics provided the transient thermal model within a larger solar-refrigeration workflow, resolving the PCM and chamber temperature field, heat conduction, and enthalpy-based solid-liquid phase change. This allowed the researchers to connect thermal-storage behavior with the system-level refrigeration model and quantify how PCM buffering affected chamber stability and cooling autonomy. Related FEATool examples include Transient Heat Diffusion in a Rod for time-dependent conduction, Heat Conduction with Tabulated Thermal Conductivity for temperature-dependent material properties, and Cooling Analysis of a Battery Pack Module for transient cooling in a multi-domain thermal system.
References
- Osodeke Onovughe Sylvester, Joseph.O. Oyekhale, Oreko Benjamin Ufuoma. Transient Energy-Exergy Analysis of a Battery-Free Solar–Phase Change Material Tomato Preservation System under Tropical Conditions, SSRN preprint, 2026.