Thermodynamic study of a heat storage device in an organic Rankine cycle system with a non-fluctuating heat source

Abstract This study aims to examine the influence of heat storage devices (HSD) in organic Rankine cycle (ORC) systems which are powered by stable heat sources. Unlike the conventional approach which relies on fluctuating heat sources, this study proposes the use of constant heat sources in ORC systems. Three positions of the HSD in the ORC system were studied in comparison with an ORC system without an HSD. The results show that thermal storage helps to compensate for energy losses and to stabilize the cycle, thereby improving overall energy efficiency. Although these devices do not provide significant gains under high superheat conditions, they remain essential for optimizing efficiency when other parameters are adjusted. Specifically, the thermal efficiency of the ORC system increases with the inlet temperature, ranging from 3.8% to 7.9%, while thermal storage contributes additional gains of 1%, 2%, and 3% for positions (a), (b), and (c), respectively. The R245fa fluid offers the best performance, with a maximum efficiency difference of 1.08% in the absence of thermal storage. With this thermal storage, efficiency increases from 0.87% to 1.52% for position (a), while the gains for positions (b) and (c) remain more modest, at 0.19% and 0.09%, respectively. Thus, although thermal storage is not always effective under all superheat conditions, it plays a key role in optimizing thermal energy recovery and improving ORC system performance.