Biochar-infused cellulose foams with PEG-based phase change materials for enhanced thermal energy storage and photothermal performance.

Energy performance of seasonal thermal energy storage in underground backfilled stopes of coal mines

Optimizing the thermal energy storage performance of shallow aquifers based on gray correlation analysis and multi-objective optimization

Fossil fuels like coal, oil, and natural gas currently dominate global energy production but release significant amounts of CO2 and other greenhouse gases, contributing to global warming and climate change. To address these environmental concerns, alternative methods of energy production and storage must be explored. This study investigates the thermal performance of latent heat thermal energy storage (LHTES) using phase-change materials (PCMs) in a horizontal cylinder. The experimental setup consists of a copper tube, 650 mm in length, with an inner diameter of 25 mm and a thickness of 2 mm, enclosed by a 600 mm acrylic tube with a diameter of 45 mm and thickness of 5 mm, and insulated to minimize heat loss. The temperature distribution was monitored along the axial direction during charging and discharging processes. These findings suggest that the proposed method can enhance the efficiency and performance of thermal energy storage systems, making them more suitable for practical applications in renewable energy storage.

Thermal energy storage plays an important role in energy conservation and reducing CO2 emissions. Thermal energy storage involves sensible heat storage, latent heat storage and thermochemical heat storage. Compared with sensible heat storage, latent heat storage and thermochemical heat storage benefits of their high energy storage densities, which helps to reduce the initial cost of the construction of heat storage systems. However, the thermal conductivities of the phase change and thermochemical reaction materials are usually lower than 1 W m - 1 K - 1, which impedes the development and further applications of the corresponding energy storage systems. Porous materials, e.g. metal foams and expanded graphite, combining with other materials to form composites is an effective method for heat transfer enhancement. In this paper, the feasibility of using metal foams to enhance the heat transfer characteristics of heat storage materials in thermal energy storage systems was assessed. Heat transfer in solid/liquid phase change and thermochemical reaction of porous materials (metal foams and expanded graphite) was investigated. Organic commercial paraffin wax and inorganic calcium chloride hydrate were employed as the low-temperature materials, whereas sodium nitrate was used as the high- temperature materials in the experiment. Heat transfer characteristics of these PCMs embedded with open-cell metal foams and expanded graphite were studied. Composites of paraffin and expanded graphite with a graphite mass ratio of 3%, 6%, and 9% were prepared. The heat transfer performances of these composites were tested and compared with the results using metal foams. It is shown that heat transfer can be enhanced by adding these porous materials. Metal foams have better heat transfer performance due to their continuous inter-connected structures than expanded graphite. However, porous materials can suppress the effects of natural convection in liquid zone, particularly for PCMs with low viscosities, thereby leading to different heat transfer performances at different regimes (solid, solid/liquid, and liquid regions). This implies that porous materials do not always enhance heat transfer in every regime; thereby an optimal metal foam structure or expanded graphite fraction can be developed using PCMs for the overal thermal energy storage performance. For thermochemical heat storage systems, the feasibility of using metal foams to enhance the heat transfer capability of heat storage materials was assessed. Reversible reaction MgH2↔Mg+H2 was used as thermochemical heat storage reaction. The effective thermal conductivities of metal foams with various porosities (0.88–0.98) were estimated with Boomsma & Poulikakos model. A two dimensional mathematical model for the Mg/MgH2 system was estabilished to study the transient heat and mass transfer process. Heat release characteristics of chemical reaction in fixed beds with/without metal foams were compared to illustrate the effects of metal foams. Various factors influencing the reaction time for fixed reaction beds with metal foams were analyzed. The results show that metal foams shorten the reaction time and increase the output power by decreasing the average temperatures of the fixed beds. After adding metal foams with a porosity of 0.92, a 40% reduction of the reaction time and 60% promotion of the exothermic power can be achieved. The parametric study shows that there exists an optimal porosity of metal foams for the highest output power under a certain reaction condition. The cooling fluid temperature and hydrogen pressure are confirmed to have a more significant impact on the reaction rate when metal foams are embeded in fixed beds. In general, as heat transfer is coupled to phase change and chemical reaction processes in latent heat storage and thermochemical heat storage, the effects of porous materials on these heat storage systems are complex. The porous materials need to be carefully selected in order to optimizing the performance of heat storage systems.

Combined effects of nanoparticles and ultrasonic field on thermal energy storage performance of phase change materials with metal foam

The objective of this study was to experimentally establish thermal energy storage (TES) performance using a technical grade paraffin wax as a phase change material (PCM) in a vertical concentric pipe-in-pipe latent heat storage system. The melting and solidification temperature range of the paraffin was found as 38°C–43°C and 36°C–42°C, respectively. These values were well in agreement with the values measured by differential scanning calorimetry (DSC) analysis. The inlet temperature and mass flow rate of the heat transfer fluid (HTF) were selected as experimental parameters. The radial and axial temperature distributions were determined during the heat charging and discharging processes of the PCM. The temporal temperature data showed that the relevant experimental parameters were more effective on the melting time than on the solidification time due to increased natural convection during the melting process. Furthermore, heat fraction during the charging and discharging processes of the PCM were established. Experimental results indicated that the heat charging fraction was affected by change in the relevant experimental parameters more during the heat charging than discharging processes of the PCM. Finally, it was concluded from the results that the investigated technical grade paraffin wax encapsulated in the annulus of the two vertical cylindrical pipes had good thermal energy storage performance and it is a suitable latent heat storage material for passive solar thermal energy storage applications.

Thermal stratification significantly affects the performance of thermal energy storage (TES) systems, especially in domestic hot water (DHW) applications. While stratification in sensible heat storage is well studied, its optimization in phase change material (PCM)‐based systems has received less attention. This article examines the effects of heat transfer fluid (HTF) inlet temperature and flow rate on stratification and energy performance in a PCM‐based TES tank. Experiments are conducted at flow rates of 200, 300, and 400 LPH with inlet temperatures of 70 and 75 °C. Higher inlet temperatures reduce PCM charging time by 31.03%, 36.00%, and 36.84% for the respective flow rates. Stratification, measured by the MIX number, improves with higher flow rates and temperatures, as shown by lower values. Elevated HTF temperatures increase the temperature gradient, enhancing sensible heating and raising average storage temperature during PCM melting. The Richardson number rose initially but declined rapidly as melting reduced the thermal gradient. After melting, charging efficiency decreases due to weakened stratification. These findings emphasize the importance of controlling HTF operating conditions to enhance stratification and TES efficiency, supporting the development of advanced control strategies and designs for PCM‐based TES in DHW and renewable energy applications.

A comparison of the field performance of thermal energy storage (TES) and conventional chiller systems

Experimental investigation of the thermal performance of a helical coil latent heat thermal energy storage for solar energy applications

Numerical investigation on the effect of fin design on the melting of phase change material in a horizontal shell and tube thermal energy storage

The construction and maintenance of building stock is responsible for approximately 36% of all CO2 emissions in the European Union. One of the possibilities of how to achieve high energy-efficient and decarbonized building stock is the integration of renewable energy sources (RES) in building energy systems that contain efficient energy storage capacity. Phase Change Materials (PCMs) are latent heat storage media with a high potential of integration in building structures and technical systems. Their solid-liquid transition is specifically utilized for thermal energy storage in building applications. The typically quite old example is the use of ice that serves as long-term storage of cold. Large pieces of ice cut in winter were stored in heavily insulated spaces and prepared for cooling of food or beverages in summer. In the contemporary use of the principle, the PCMs for building applications and tested in this study must have a melting range close to the desired temperature in the occupied rooms. As the PCMs need to be encapsulated, several types of metal containers have been developed and tested for their thermal conductivity and resistance to mechanical damage, which enhances the performance of these so-called latent heat thermal energy storage (LHTES) systems. Long-term compatibility of metals with PCMs depends, i.e., on the elimination of an undesirable interaction between the metal and the specific PCM. Heat storage medium must be reliably sealed in a metal container, especially if the LHTES is integrated into systems where PCM leaks can negatively affect human health (e.g., domestic hot water tanks). The aim of this study is to evaluate the interactions between the selected commercially available organic (Linpar 17 and 1820) and inorganic (Rubitherm SP22 and SP25) PCMs and metals widely used for PCM encapsulation (aluminum, brass, carbon steel, and copper). The evaluation is based on the calculation of the corrosion rate (CR), and the gravimetric method is used for the determination of the weight variations of the metal samples. The results show good compatibility for all metals with organic PCMs, which is demonstrated by a mass loss as low as 2.1 mg in case of carbon steel immersed in Linpar 1820 for 12 weeks. The exposure of metals to organic PCMs also did not cause any visual changes on the surface except for darker stains, and tarnishing occurred on the copper samples. More pronounced changes were observed in metal samples immersed in inorganic PCMs. The highest CR values were calculated for carbon steel exposed to inorganic PCM Rubitherm SP25 (up to 13.897 mg·cm−2·year−1). The conclusion of the study is that aluminum is the most suitable container material for the tested PCMs as it shows the lowest mass loss and minimal visual changes on the surface after prolonged exposure to the selected PCMs.

In this study, the effect of the thermal conductivity of phase change material (PCM) on the performance of thermal energy storage has been analyzed numerically. A horizontal concentric shell-and-tube latent heat thermal energy storage system (LHTESS) has been performed during the solidification process. Two types of paraffin wax with different melting temperatures and thermal conductivity were used as a PCM on the shell side, case1=0.265W/m.K and case2=0.311 W/m.K. Water has been used as heat transfer fluid (HTF) flow through in tube side. Ansys fluent has been used to analyze the model by taking into account phase change by the enthalpy method used to deal with phase transition. The numerical simulation assumptions were three-dimensional, transient, and laminar flow was used. The result for the PCMs of performance, temperature distribution, and liquid fraction during the discharge process were compared to each other. Furthermore, the Nusselt number was analyzed. The result showed that the increase in thermal conductivity of PCM reduces the time of the solidification process by 20%. The performance of LHTESS for case 2 is 63.2%, whereas for case1 is 54.6%.

Heat transfer enhancement of charging and discharging of phase change materials and size optimization of a latent thermal energy storage system for solar cold storage application

Titanium dioxide/graphene oxide synergetic reinforced composite phase change materials with excellent thermal energy storage and photo-thermal performances

Effect of phase change material tubes inclination angel on the performance of indirect hybrid thermal energy storage system: An experimental approach