Comprehensive Performance Evaluation of Phase Change Materials Using Multi-Attribute Decision Making Method: TOPSIS

An experimental and numerical study on phase change material melting rate enhancement for a horizontal semi-circular shell and tube thermal energy storage system

Review of passive PCM latent heat thermal energy storage systems towards buildings’ energy efficiency

A novel correlation for the direct determination of the discharging time of plate-based latent heat thermal energy storage systems

Performance study of a novel funnel shaped shell and tube latent heat thermal energy storage system

Solid–liquid phase transitions in phase change materials (PCM) usually exhibit a complex dynamics, which critically determines the performance of latent heat thermal energy storage systems (LHTES). Experimental approaches enabling to track the dynamics of the entire PCM solid–liquid phase transition are thus crucial to provide relevant data for PCM material development and to validate PCM-models used to design efficient LHTES. In this work, we show how in-situ dynamic X-ray computed tomography (XCT) can be used to track the dynamics of the solid–liquid phase transition in PCMs. The method based on time-lapse XCT is illustrated based on data collected for two PCMs (ice/water and calcium chloride hexahydrate) during melting and solidification processes, respectively. Key enabler of the method is the density difference between solid and liquid PCM, which facilitates a clear identification of the solid and liquid PCM phases and, thus, tracking their spatial evolution in time. Analysis of the transient liquid fraction curves reveals a volumetric melting rate of 0.55 (% vol)/min for ice with a total melting time of 165 min, whereas calcium chloride hexahydrate undergoes a partial solidification at −0.30 (% vol)/min, with an overall volumetric shrinkage of 12.7 %. Furthermore, an image-based approach to quantify the time-dependent liquid volume fraction curve from the sequences of XCT imaging data, is presented. The extracted liquid volume fraction curves capture the entire dynamics of the solid–liquid phase transition and can either be directly inserted in the mass and energy balance equations of currently existing PCM models to predict LHTES performance or used for PCM-models validation.

While solar thermal power plants are increasingly gaining attention and have demonstrated their applications, extending electricity generation after the sunset using phase change material (PCM) still remains a grand challenge. Most of the organic PCMs are known to possess high energy density per unit volume, but low thermal conductivity, that necessitates the use of thermal conductivity enhancers (TCEs) to augment heat transfer within PCM. In this paper, thermal performance and optimization of shell and tube heat exchanger-based latent heat thermal energy storage system (LHTES) using fins as TCE for medium temperature (<300 °C) organic Rankine cycle (ORC)-based solar thermal plant are presented. A commercial grade organic PCM, A164 with melting temperature of 168.7 °C is filled in the shell side and heat transfer fluid (HTF), Hytherm 600 flows through the tubes. A three-dimensional numerical model using enthalpy technique is developed to study the solidification of PCM, with and without fin. Further, the effect of geometrical parameters of fin, such as fin thickness, fin height, and number of fin on the thermal performance of LHTES, is studied. It is found that fin thickness and number of fin play significant role on the solidification process of PCM. Finally, the optimum design of the fin geometry is determined by maximizing the combined objective of HTF outlet temperature and solid fraction of PCM at the end of the discharging period. The latent heat thermal storage system with 24 fins, each of 1 mm thickness and 7 mm height, is found to be the optimum design for the given set of operating parameters.

Latent heat thermal energy storage (LHTES) systems are essential for efficient thermal energy storage. However, these devices are often constrained by long charging and short discharging periods. This study presents a novel triplex‐tube LHTES design incorporating a copper helical coil positioned between two concentric stainless‐steel shells. Stearic acid was used as the phase change material and water as the HTF, with two separate flow paths provided for charging and discharging. During charging, HTF is circulated through the outer shell at a higher mass flow rate to increase energy input and accelerate the charging process. During discharging, HTF flows through the inner helical copper coil at a reduced mass flow rate, increasing its residence time by 97.54%. This enhances the uniformity index and extends the discharge duration by 26.8% compared to a conventional concentric triplex‐tube design. Additionally, the discharge efficiency increases to 87.5% due to a 31.4% rise in heat‐transfer area and higher thermal conductivity of copper compared to stainless steel.

A review of materials, heat transfer and phase change problem formulation for latent heat thermal energy storage systems (LHTESS)

Numerical study and multilayer perceptron-based prediction of melting process in the latent heat thermal energy storage system with a finned elliptical inner cylinder

Numerical simulations are performed to analyze the thermal characteristics of a latent heat thermal energy storage system with phase change material embedded in highly conductive porous media. A network of finned heat pipes is also employed to enhance the heat transfer within the system. ANSYS-FLUENT 19.0 is used to create a transient multiphase computational model to simulate the thermal behavior of the storage unit. Copper foam is the porous medium used to enhance the heat transfer and is impregnated with the phase change material, potassium nitrate (KNO3). The effects of the porosity of the metal foam and the quantity of heat pipes on the thermal characteristics of storage unit have been investigated. The results indicated that increasing the quantity of the embedded heat pipes leads to drastic acceleration of both charging and discharging process. Impregnating the copper foam with potassium nitrate phase change material significantly affects the total charging and discharging times of the storage unit. It was shown that the porosity of the metal foam plays a key role in the thermal behavior of the system during the charging and discharging processes.

Numerical analysis of latent heat thermal energy storage using encapsulated phase change material for solar thermal power plant

Improving the charging performance of latent heat thermal energy storage systems using triply periodic minimal surface (TPMS) structures

Purpose This study aims to address the low thermal conductivity and suboptimal performance of phase change materials (PCMs) by examining the impact of geometric adjustments on their melting rate. Design/methodology/approach A two-dimensional numerical model was created to investigate the effect of different positions and angular inclinations of the inside heating surface (IHS) on the melting rate of PCM within a latent heat thermal energy storage system. The model analysed the IHS at the centre and below the centre at various positions (10, 20, 30 and 40 mm) and inclinations (0°, 15°, 30°, 45°, 60°, 75° and 90°). Findings The 90° inclination (vertical) significantly reduced the melting time by 75% compared to the 0° inclination (horizontal). The best melting performance was recorded with the IHS positioned 20 mm below the centre. At a 30° inclination, the maximum reduction in melting time was observed with the IHS at 30 and 40 mm placements. The system demonstrated the highest energy storage capacity of 307.72 kJ/kg at a 75° inclination with the IHS positioned 10 mm laterally, and the lowest capacity of 255.02 kJ/kg at a 0° inclination with the IHS at a 30 mm lateral position. Practical implications To address the deficient part of PCM like low thermal conductivity and below level performance characteristics, a structural (geometrical) adjustment was developed to study the effect on the melting rate of PCM without any cost addition. Using the computational model, an optimised thermal energy storage system is developed that can play a pivotal role in improving the applicability of thermal energy storage systems. Originality/value This research is novel in simultaneously investigating the numerical characteristics of PCM melting behaviour with different lateral positions and angular orientations of the IHS. A unique design modification was introduced, using a 2D numerical model and simulations to explore the effects under isothermal conditions.

Experimental and numerical characterization of natural convection in a vertical shell-and-tube latent thermal energy storage system

Thermal performance of cascaded latent heat thermal energy storage units constructed based on solid-liquid interface information