Thermal Retention of Sodium Nitrate PCM in Organic Rankine Cycle–Stirling Engine under Continuous Night Shift Mechanical Loading.
This study evaluated the thermal retention performance of sodium nitrate (NaNO₃) phase change material (PCM) and its influence on the mechanical output of a hybrid ORC–Stirling system under sustained night-shift loading for small-scale industrial energy conversion in Delta State, Nigeria. In the study, two major parameters were considered: PCM thermal retention effect on the stability of power at the shaft and how it affects the consistency of torque under continuous mechanical loading. Data of PCM temperature, shaft power and torque were simulated at constant intervals of night-shift and examined by multidimensional visualizations using MATLAB. Findings revealed that NaNO3 PCM exhibited superior thermal stability between 260- 300 oC, as it occupied about 65% of the recorded intervals and this corresponded to stable shaft power of about 58 kW and average torque of 108 Nm over a small number of peaks and valleys. Positive correlations between PCM thermal stability and mechanical output were found to be strong, and this confirms that thermal buffering reduced transient losses in power during long-term loading. The results showed that ORC-Stirling systems enhanced by NaNO3 PCM have the capacity to maintain the provision of mechanical power to the night-shift industrial process. To this end, it was recommended that PCM-integrated ORC-Stirling systems should be employed by small-scale industrial operators, the Manufacturers Association of Nigeria (Delta State Chapter) should assist in creating awareness and collaborative buying, and the tertiary institutions should create training and pilot programs to facilitate the long-term implementation. Such measures will make the adoption of ORC-Stirling for small scale industrial purpose more mechanically relevant and reliable, decrease the downtime and develop sustainable decentralized industrial power solutions.
Keywords: ORC–Stirling system; Sodium nitrate PCM; Thermal retention; Shaft power stability; Small-scale industrial energy
