Numerical Simulation of Heat Pipe-Assisted Latent Heat Thermal Energy Storage Unit for Dish-Stirling Systems

Abstract

A two-dimensional numerical model is developed to simulate the transient response of a heat pipe-assisted latent heat thermal energy storage (LHTES) unit integrated with dish-Stirling solar power generation systems. The unit consists of a container which houses a phase change material (PCM) and two sets of interlaced input and output heat pipes (HPs) embedded in the PCM. The LHTES unit is exposed to time-varying concentrated solar irradiance. A three-stage operating scenario is investigated that includes: (i) charging only, (ii) simultaneous charging and discharging, and (iii) discharging only. In general, it was found that the PCM damps the temporal variations of the input solar irradiance, and provides relatively smooth thermal power to the engine over a time period that can extend to after-sunset hours. Heat pipe spacing was identified as a key parameter to control the dynamic response of the unit. The system with the greatest (smallest) heat pipe spacing was found to have the greatest (smallest) temperature drops across the LHTES, as well as the maximum (minimum) amount of PCM melting and solidification. Exergy analyses were also performed, and it was found that the exergy efficiencies of all the systems considered were greater than 97%, with the maximum exergy efficiency associated with the system having the minimum heat pipe spacing.

Numerical study of finned heat pipe-assisted thermal energy storage system with high temperature phase change material

“…Recently, Shabgard et al [45] developed a two-dimensional model to study a HP-assisted LHTES system with sodium chloride (NaCl, T m = 800°C) PCM. They used a conduction-controlled model for melting in which the effect of natural convection within the molten PCM was neglected.…”

Heat pipe heat exchangers and heat sinks: Opportunities, challenges, applications, analysis, and state of the art

“…In another study by Shabgard et al [70], a PCM-HPHX was considered for use in a Dish-Stirling system, in which the PCM serves as a thermal buffer to accommodate interruptions in the solar irradiation of a single dish due to cloud passage. The PCM-HPHX consisted of a PCM enclosure in which two separate sets of HPs, one for charging and another for discharging, were utilized to transfer energy collected by the solar dish to provide a nearly isothermal input for a Stirling engine.…”

Metallic Phase Change Material Thermal Storage for Dish Stirling

“…The simplicity of this design contrasts trough and tower high-temperature storage systems which need further development to provide a high-temperature thermodynamic cycle and receiver, as well as high-concentration optics suitable to limit collection losses. The phase change material, due to high thermal throughput, must be a metallic storage media in order to achieve a goal of 95% exergy efficiency [2,4]. The metallic-based options provide sufficient thermal conductivity that can reduce the number of heat pipe tubes used by about an order of magnitude compared to salt PCM options.…”