Thermal performance of a novel high-temperature sensible heat thermal storage steam generation system using solid graphite as material

Abstract

In this paper, a prototype of high-temperature sensible heat thermal storage system for direct steam generation was presented. The structure of solid graphite blocks with embed tube was applied to improve the efficient density of thermal storage. And a net thermal storage capacity of 1.038 GJ was achieved for the module with a total mass of 1480 kg solid graphite under the working temperature range of 250–600 °C. Meanwhile, a novel series-parallel tube structure was applied for discharging power regulation. A two-stage working strategy was found to be efficient for confining discharging power fluctuated in a certain range instead of monotonously decreasing. Further, three mass flow rates from 106 kg/h to 175 kg/h were performed to investigate thermal performance of the thermal storage system. The results show that the effect of mass flow rate on discharging power and heat transfer coefficient seems to be tiny due to the major thermal resistance is resulted from contact thermal resistance. The extension of working tube in stage II has improve the development of two-phase flow, which finally results in a higher heat transfer coefficient. The flow distribution in parallel tube has a significant effect on the local discharging characteristics and the two-phase flow development in tube. The manifold header for stage transition has not only enhanced the heat transfer in the second half tube by mixing effect but also redistributed the flow rate in parallel tubes.