Exergetic and performance analyses of two‐layered packed bed latent heat thermal energy storage system

Abstract

Summary In concentrating solar power (CSP) plant, a novel method involving the use of thermocline can be employed to augment the capability of the thermal energy storage system (TES). The rate of thermocline degradation can be reduced by packing encapsulated phase change material (PCM) in the TES. The thermal performance of the packed bed latent heat thermal energy storage system (PBTES) can be further enhanced by employing different diameters of PCM capsules arranged in multiple layers. In this paper, the thermal and exergetic performance of single‐layered and two‐layered PBTES is evaluated for varying mass flow rate, PCM capsule diameter and bed height of larger PCM capsules using a dynamic model based on simplified energy balance equations for PCM and heat transfer fluid (HTF). The single‐layered PBTES has a lower TES latent charging rate than the two‐layered PBTES. The charging efficiency and charging time of two‐layered PBTES are increased by 15.85% and 16.85%, respectively for reducing the HTF mass flow rate by 14.29%. A higher stratification number can be achieved by using a two‐layered PBTES instead of a single‐layered PBTES filled with the corresponding larger diameter PCM capsules. The second law efficiency of the two‐layered PBTES is found to be less than that of the single‐layered PBTES. A decrease in the bed height of larger PCM capsules decreases the exergetic efficiency of the two‐layered PBTES by 3.27%. The findings from this study can be used in further designing and optimising the multi‐layered PBTES.

A Review on the Performance Indicators and Influencing Factors for the Thermocline Thermal Energy Storage Systems

“…Thus, an optimal flow rate could exist for the given structure and working temperature, due to the competition between mixing and thermal diffusion. Additionally, several previous articles investigated the thermal performance of TES systems with sensible solid fillers [35,[47][48][49][50][51][52][53][54][55], which reached the contrary conclusions. On the one hand, the increasing flow rate has been found to decrease the discharging efficiency, since the incoming flow at a high flow rate can penetrate far away along the centerline of the tanks [48][49][50].…”

Performance analysis of a packed bed latent heat thermal energy storage with cylindrical‐shaped encapsulation

“…The stratification number and charging efficiency are improved with an increase in the bed height. Saha and Das 28 compared a two‐layered packed bed TES system with a single‐layered packed bed TES system on the basis of based charging efficiency and the second law efficiency. The charging rate of a two‐layered packed bed TES system was found higher as compared to the single‐layer PBTES system.…”

A comprehensive investigation of the mathematical models for a packed bed latent heat thermal energy storage system

“…The PCM filling ratio of the PBTES system decreases due to the interspace between the PCM capsules, but an appropriate reduction of PCM filling ratio is still considered acceptable to achieve better performance. Therefore, the PBTES system using PCM capsules has been widely applied 7‐9 . In the PBTES system, there is a temperature gradient of heat transfer fluid (HTF), that is, thermocline, along the flow direction of HTF which is due to the convective heat transfer between PCM capsules and HTF.…”

“…Therefore, the PBTES system using PCM capsules has been widely applied. [7][8][9] In the PBTES system, there is a temperature gradient of heat transfer fluid (HTF), that is, thermocline, along the flow direction of HTF which is due to the convective heat transfer between PCM capsules and HTF. This phenomenon results in a "dead zone" and the thermal energy of the HTF cannot be fully utilized.…”