LOW-TEMPERATURE THERMAL ENERGY HARVESTING USING SOLID/LIQUID PHASE CHANGE MATERIALS

摘要

This paper presents the design, fabrication, and analysis of a prototype system that demonstrates the use of a solid/liquid phase change material (PCM), namely pentadecane (C_(15)H_(32)), to harvest thermal energy associated with relatively low temperature and small temperature variation (e.g., 1°C to 20°C). The fundamental idea is to utilize the volume expansion of the PCM in the melting process to pressurize a hydraulic fluid, which is then released to drive a direct current (DC) water turbine generator. The prototype features the use of a tube system to store degassed and encapsulated PCM packages, therefore can be easily scaled to meet different energy output requirements. The performance of the prototype is assessed through measurements of the peak pressure of the hydraulic fluid and the produced power profile. The dependence of the electrical energy output on external load resistance is investigated within the range of 25 Ohm to 250 Ohm. Further, a thermomechanical model is developed to characterize the energy conversion process. Specifically, the thermodynamic behavior of PCM and hydraulic fluid is modeled with the Tait equation of state. The structural mechanics is modeled using the linear elasticity theory. The peak pressure predicted by the model agrees reasonably well with the experimental measurement, with a discrepancy of 3.40%. Finally, a series of numerical parameter studies are conducted to investigate the effects of the structural stiffness and the volume fraction of the PCM, indicating possible methods to improve the thermal efficiency and the specific energy output of the prototype system.