Comparative investigations on dynamic characteristics of basic ORC and cascaded LTES-ORC under transient heat sources

Abstract

In order to overcome the thermal power fluctuations of transient heat sources and improve the safety performance of organic Rankine cycles (ORC), a novel combined system that latent thermal energy storage (LTES) using phase change material (PCM) is integrated into an ORC is proposed in this study. In the proposed system, LTES and evaporator have a cascaded configuration where the transient heat source first flows through LTES and then flows into the evaporator, with the fluctuating amplitude largely buffered. To validate the superiorities of the proposed cascaded LTES-ORC system, effects of PCM thermophysical properties including thermal conductivity and melting temperature are evaluated on the dynamic performance of LTES-ORC system, and they are comprehensively compared with that of basic ORC system under step-change and cyclic heat sources. Results indicate that proposed LTES-ORC system achieves significantly smaller fluctuating range of evaporating pressure and superheat degree than basic ORC system under both step-change and cyclic heat sources. Especially, LTES-ORC system has a larger maximum allowable fluctuating limitation range of heat sources and improves the safety performance under fluctuating heat source. In detail, under small-period fluctuating heat sources, LTES-ORC system can bear 15%–20% higher fluctuating amplitude ratio than basic ORC system under the same period of heat source. When the period is within the range of 600–3600 s, about 33%–42% higher fluctuating amplitude ratio can be resisted by LTES-ORC system. In addition, a correlation is proposed and validated to fast predict the maximum allowable fluctuation limitation for LTES-ORC system.