Phase Change Material Temperature Research Articles

Influence of Carboxymethyl Cellulose as a Thickening Agent for Glauber's Salt-Based Low Temperature PCM.

This work is focused on a novel, promising low temperature phase change material (PCM), based on the eutectic Glauber's salt composition. To allow phase transition within the refrigeration range of temperatures of +5 °C to +12 °C, combined with a high repeatability of melting-freezing processes, and minimized subcooling, the application of three variants of sodium carboxymethyl cellulose (Na-CMC) with distinct molecular weights (700,000, 250,000, and 90,000) is considered. The primary objective is to optimize the stabilization of this eutectic PCM formulation, while maintaining the desired enthalpy level. Preparation methods are refined to ensure repeatability in mixing components, thereby optimizing performance and stability. Additionally, the influence of Na-CMC molecular weight on stabilization is examined through differential scanning calorimetry (DSC), T-history, and rheology tests. The PCM formulation of interest builds upon prior research in which borax, ammonium chloride, and potassium chloride were used as additives to sodium sulfate decahydrate (Glauber's salt), prioritizing environmentally responsible materials. The results reveal that CMC with molecular weights of 250 kg/mol and 90 kg/mol effectively stabilize the PCM without phase separation issues, slowing crystallization kinetics. Conversely, CMC of 700 kg/mol proved ineffective due to the disruption of gel formation at its low gel point, hindering higher concentrations. Calculations of ionic concentration indicate higher Na ion content in PCM stabilized with 90 kg/mol CMC, suggesting increased ionic interactions and gel strength. A tradeoff is discovered between the faster crystallization in lower molecular weight CMC and the higher concentration required, which increases the amount of inert material that does not participate in the phase transition. After thermal cycling, the best formulation had a latent heat of 130 J/g with no supercooling, demonstrating excellent performance. This work advances PCM's reliability as a thermal energy storage solution for diverse applications and highlights the complex relationship between Na-CMC molecular weight and PCM stabilization.

Predicting the performance of a photovoltaic unit via machine learning methods in the existence of finned thermal storage unit

The process of cooling the photovoltaic (PV) cells is essential since increasing solar cell temperatures reduces electrical effectiveness. One suggested method to reduce cell temperature is employing PCM (phase change material) mixed with nanomaterial. Thermoelectric modules between the layers are also recommended to increase electrical efficiency. By taking advantage of machine learning predictive algorithms, the objective is to forecast the effectiveness of a PV unit equipped with finned thermal storage unit in existence of nanomaterials, while maintaining an appropriate accuracy based on two evaluation metrics throughout prediction. According to the data analytics of the simulation, the selected models used to achieve this goal are linear regression, polynomial regression, lasso regression, and an Auto-Regressive Integrated Moving Average (ARIMA) model. These models were then examined employing the root mean squared error (RMSE) and mean absolute percentage error (MAPE) across three cases, namely plain mode, mode with fins, and plain mode with the effect of gravity. The test RMSE and MAPE of these models across the above-mentioned cases were then calculated for comparison purposes, where the best-performing model for predicting both PCM temperature and melting fraction (MF) was ARIMA, with an average RMSE of 0.11, and an average MAPE of 0.0003 for predicting PCM temperature and an average RMSE of 0.003, and an average MAPE of 0.0034 for predicting MF across all cases. The ARIMA model was then used to predict the MF, PCM temperature, and PV temperature of the last case, namely mode with fins and the effect of gravity. Finally, this model was also used to predict the time at which the PCMs are completely melted in all modes, as well as to predict PV temperature. The total electrical efficiency of the mode with fins and the effect of gravity were calculated using the predicted PV temperature, yielding a result of 13.993 %.

Influence of fin shape design on thermal efficiency of phase change material-based thermal energy storage unit

The present numerical study treats the impact of fin shape design on the thermal efficiency of phase change material (PCM)-based thermal energy storage (TES) unit, focusing on the same surface area occupied by fins. Comparing two different finned TES units equipped with rectangular and triangular fin shapes, respectively, showed significant enhancements in PCM melting activity. Comparative analysis demonstrated that triangular fin shape lowers PCM melting time by 12.64% for equivalent fin numbers, and by 15.38% for equal fin lengths due to the enlargement of the heat transfer area provided by the triangular shape. Further examination of fins with triangular shape in terms of spacing and length, under fixed thickness and size parameters, revealed significant reduction in melting time with increasing fins length. Notably, 50.75% decrease in melting time was achieved by decreasing the number of fins to 20 while increasing fin length to 10 mm. Moreover, maintaining a heat transfer fluid (HTF) temperature 20 K higher than the melting PCM temperature maximizes TES thermal efficiency. These outcomes emphasize the importance of optimizing fin shape design for enhancing heat transfer without affecting the energy storage capacity of TES systems, with potential applications in building thermal management.

Design, analysis, and testing of a prototype-scale latent heat thermal energy storage (LTES) system

A parametric analysis was performed to design a prototype-scale latent heat thermal energy storage (LTES) system using commercial grade hexahydrate calcium chloride as phase change material (PCM) in a staggered tube array configuration, placed horizontally. The study involved numerical analysis of melting and solidification processes of the PCM within the tube array, considering transient two-dimensional Navier-Stokes equations and a Realizable k-ɛ turbulence model to predict fluid flow and heat transfer. The enthalpy-porosity technique was used to model PCM melting and solidification. The study included a comparison between numerically predicted and experimentally obtained air temperatures at the tube array outlet, as well as PCM temperatures. This comparison revealed an excellent level of agreement. Additionally, the study compared the pressure drop within the array and the average peripheral heat transfer coefficient calculated from the numerical results to the well-established Zukauskas correlation. The resulting design successfully met the predefined performance criteria: achieving a cooling effect of 4 °C for a four-hour duration while maintaining a pressure drop of <100 Pa. The proposed prototype-scale tube array design can be efficiently cooled down and PCM frozen overnight. The energy storage density of the system falls within the range of 22 to 27 kWh/m3.

Assessing performance of an external compound parabolic concentrator solar collector with cascaded latent heat thermal storage

AbstractThis study presents quantitative results of charging experiments conducted on cascaded thermal energy storage system (CTESS) integrated with external compound parabolic concentrator solar collector (XCPCSC). Increasing mass flow rate in 2‐stage CTESS integrated with XCPCSC resulted in a 30% reduction in initiation time of phase change materials (PCMs) during charging, with a higher mass flow rate of 0.025 kg/s. However, due to disparate melting point temperatures of PCMs, phase transition in the two‐stage CTESS did not occur simultaneously, leading to poor heat transfer rates within the CTESS. To address this, study extended number of phases from two to three, resulting in a 1.5‐fold increase in rate of heat transfer compared to 2‐stage PCM system. The simultaneous melting processes at various stages in the CTESS maximized energy absorption, leading to a 25% increase in system efficiency. Notably, the values of energy stored efficiency and over‐all efficiency reached their peak values of 95% and 60%, respectively, between t = 12.00 h and t = 13.00 h. This time period also saw a significant increase in collector efficiency to 72%. These quantitative findings highlight importance of mass flow rate and PCM arrangement in achieving efficient heat transfer and system performance in a CTESS integrated with XCPCSC.

Experimental and numerical study on the thermal performance of earthbag-wall units incorporated with phase change materials

The demand for temporary housing for refugees and displaced communities has led to the development of earthbag buildings. While these structures are affordable and sustainable, they often struggle with thermal discomfort in extreme climates. This study aims to examine the integration of phase change materials (PCM) into earthbag walls to improve thermal performance. The research involved incorporating paraffin wax and microencapsulated PCM into scaled-down earthbag walls, with their performance evaluated in a controlled environment. The results were validated against a numerical simulation model developed in EnergyPlus. The study revealed significant thermal improvements with PCM integration. Wall-2, with paraffin wax A31, demonstrated a surface temperature reduction of up to 1.9 °C, while Wall-3, with microencapsulation Inertek26, showed a decrease of 2.4 °C compared to the reference wall. A parametric analysis highlighted the importance of PCM layer thickness. Specifically, Wall-2 with a 6 cm paraffin wax layer achieved a maximum reduction of 4.0 °C compared to the base case. The study identified the transition temperature of PCM as a critical factor in thermal performance, with paraffin wax A31 emerging as the optimal choice. Placing the PCM layer on the interior surface of the wall was more effective than exterior placement. Overall, PCM integration in earthbag walls offers a promising solution to enhance thermal comfort in temporary housing, addressing the critical needs of refugees and displaced communities. This research fills existing gaps in thermal comfort in temporary housing and demonstrates the potential of PCM as an innovative passive design strategy.

Preparation and Performance of Inorganic Hydrated Salt-Based Composite Materials for Temperature and Humidity Regulation

In this work, it was first proposed to combine hydrated salt phase change materials (PCMs) with humidity control materials to prepare the temperature and humidity control material. The composite PCM was prepared by absorbing Na2HPO4·12H2O with colloidal silicon dioxide, and diatomite was selected as the humidity control material. The humidity performance tests found that diatomite had good moisture absorption/desorption capacity and excellent moisture buffering capacity. The supercooling degree tests showed that Na2SiO3·9H2O as nucleating agent effectively reduced the supercooling degree, and the addition of deionized water improved the water loss problem of composite PCMs. The DSC tests showed that the enthalpy and melting temperature of composite PCMs were 153.1 J/g and 28.9°C, respectively. By placing the temperature and humidity control material in different humidity, it was found that the moisture content of diatomite affected the thermal properties of composite PCMs. Diatomite could not only transfer moisture to hydrated salts but also absorb moisture from hydrated salt. The application performance tests of the temperature and humidity control material in the room model showed that it could simultaneously regulate indoor temperature and humidity. Overall, this temperature and humidity control material was more suitable for environments with high relative humidity such as greenhouses.

Optimal Design and Simulation Analysis of Phase Change Material Composite Self-Insulating Block in a Typical Cold Region City of China in Summer

Background:: Incorporating PCMs (Phase Change Materials) into the building envelope can achieve the purpose of regulating heat transfer and enhancing indoor comfort. In recent years, lots of patents for new phase change concretes have been proposed and applied to the envelope. Objective:: This study aimed to explore the optimum phase change temperature and installation position of PCM by optimizing different concrete blocks to improve the thermal behavior of concrete compound self-insulating blocks. Methods:: Firstly, based on the existing patents, five new types of phase change self-insulating blocks were proposed. The thermal insulation performance of different blocks was tested using ANSYS simulation. Then, the feasibility of using EnergyPlus to simulate the thermal environment of the room was verified by taking a summer south-facing room in Hohhot City as a research object. Finally, 13 phase-change block types containing 4 phase-change temperatures and 3 PCM installation locations were designed for further testing. Results:: A three-row staggered perforated block was selected, and the heat transmission coefficient of the masonry wall was 0.437 W/(m2·K). The optimal phase change temperatures of outdoor, medium- temperature, high-temperature, and low-temperature periods in summer, were 24.0 oC, 30.0 oC, and 28.0 oC, respectively. The optimal phase change temperature in the whole summer was 26.0~ 28.0 oC, and the best phase transition layer location was the inner hole of the block. Conclusion:: The PCM mounting position has a greater effect on room temperature than the PCM phase change temperature. The study results are of great significance for stabilizing room temperature and building energy conservation.

Enhancing sustainability with waste hemp-shive and phase change material: Novel gypsum-based composites with advanced thermal energy storage properties

This study addresses the rising demand for sustainable construction by introducing composite materials from natural and renewable resources: gypsum, hemp, and phase change materials (PCMs). These materials cater to the growing preference for eco-friendly building solutions. Incorporating hemp enhances sustainability while integrating PCMs into the porous hemp structure ensures adequate thermal energy storage and release without leakage. Firstly, the agricultural waste hemp shives and lauryl alcohol (LA) PCM were mixed to create shape-stabilized hemp/PCM composites. The highest PCM ratio was determined in shape-stabilized composites exhibiting non-leakage properties, which was 45 wt %. These composites were then incorporated into gypsum materials at loadings of 7.5 %, 15 %, 22.5 %, and 35 wt % to produce the final composites. Morphological, thermal, and chemical characteristics of shape-stabilized composites were examined using SEM, TGA, and DSC, while the solar thermoregulation tests assessed the gypsum matrix composites. The phase change temperature of PCM was determined as 20.24 °C with a melting enthalpy value of 224.4 J/g. The hemp/PCM shape-stabilized composites demonstrated an impressive melting enthalpy value of 100.2 J/g, with only a slight reduction to 99.5 J/g after 750 test cycles. When the ambient temperature exceeded 50 °C, the central temperature of the cabins containing PCM composites was found to be at least 4 °C cooler than those containing only gypsum. Conversely, when the ambient temperature dropped to around 20 °C, it was observed that the central temperature of the cabins with PCM composites was approximately 2 °C warmer than those with only gypsum. This study introduces a novel approach to creating environmentally friendly gypsum/hemp/PCM composites for thermal energy storage systems.

Energy and exergy analysis of a laboratory-scale latent heat thermal energy storage (LTES) using salt-hydrate in a staggered tube arrangement

The energy and exergy analyses were performed for a laboratory-scale latent heat thermal energy storage (LTES) using hexahydrate calcium chloride (CC6) as phase change material (PCM) in a staggered tube array configuration, placed horizontally. The PCM melting and solidification process within the tube array was investigated by performing a numerical analysis using transient two-dimensional Navier-Stokes equations and Realizable k-ɛ turbulence model to predict flow and heat transfer. The enthalpy-porosity technique was applied to model PCM melting and solidification. The accuracy of the numerical model was validated against experimentally obtained data where the numerically predicted and measured air temperature at the tube array outlet and PCM temperatures were compared. Additionally, the pressure drop in the array and the average peripheral heat transfer coefficient calculated from the numerical results were compared to the well-known Zukauskas correlation (Zu). The results show that the melting and solidification process of PCM in the tubes of the array is asymmetric in nature, with the PCM melting taking slightly longer compared to the solidification process. It was also observed that the energy quantity was higher compared to the exergy quantity, as exergy considers entropy generation and accounts for irreversibility within the system.

Investigation of numerical phase transition of nano-enhanced SiC/paraffin wax PCM in solar-assisted water desalination system

Adding nanoparticles in phase change material (PCM) is a new trend for enhancing their thermal energy-storing ability as well as thermal conductivity. From this point of view, a numerical study is carried out to examine the addition of silicon carbide nanoparticles in paraffin wax PCM, used as heat energy storing material in a semi-cylindrical solar water desalination system. The PCM temperature is maintained at 52 °C and the semi-cylindrical tubular section has a wall temperature of 85 °C. The top plane section of the tubular solar collector is made up of graphite material. A semi-circular cross-section is selected for numerical analysis. A finite volume solver is used for solving thermal and fluid flow governing equations. A pressure staggering option algorithm is applied for pressure–velocity coupling. The temporal parameters like temperature, velocity contours, melting fraction, enthalpy, and entropy of nano silicon embedded paraffin wax PCM are widely discussed. The results clearly show that the phase transition of solid PCM to fluid PCM is greatly influenced by nanoparticle addition and enhances the rate of heat transfer. Initially for the first 60 min the melting fraction and temperature of PCM remain uniform as the time step increases above 60 min the behavior of PCM changes abruptly which clearly indicates the random distribution of nanoparticles within the PCM. A critical time and temperature limit exists for nanoparticles-based PCM beyond which, the thermal efficiency of the solar water desalination system gets influenced.

Temporal numerical analysis of beeswax PCM melting in a cube geometry subjected to a constant wall temperature condition

The ability of phase change materials (PCM) to store thermal energy has gained wide application area, like battery thermal management, solar water desalination and many other. The melting process of beeswax phase change material within the cube geometry with constant wall temperature (65 °C) boundary condition has been investigated using solidification and melting model. The fluid flow and heat transfer governing equations are solved using second order finite volume scheme. A PRESTO algorithm is applied for pressure-velocity coupling. The convergence criteria of 10−10 have been selected for energy equation, while 10−8 is selected for both momentum and continuity equations. The results like percentage variation along length-height and height-width plane for transient liquid fraction and temperature has been plotted, along with velocity streamlines within the cube geometry. From the obtained results it is concluded that the melting fraction and temperature of beeswax PCM is different in different planes and the major factors which affect the complete melting process is wall temperature, and the geometry. A difference of more than 0.1 °C in temperature has been recorded between mid-length-height and height-width plane while a difference of more than 2% in liquid fraction of PCM is observed. Even the uniformity of temperature and liquid fraction is notably influenced and vary along length, height, and width of cube geometry. Thus, it is concluded that melting process of PCM may affect the ability to store and release the heat energy which further affect the performance parameters of applied physical system.

An experimental method of determination and validation of latent thermal energy storage dynamic characteristic by effective enthalpy

The paper draws attention to the problems of evaluating stored heat capacity in a latent heat thermal energy storage (LHTES) that operates with unsteady inlet temperature conditions. These problems are studied for custom-built LHTES designed to be charged/discharged at varying heat transfer rates in a chilled water system. The LHTES incorporates a typical fin and tube heat exchanger and commercially available ATP 20 phase change material (PCM). For the designed storage construction, the ratio of heat transfer area to PCM volume is 354 m2/m3, and the ratio of PCM volume to the total volume (compactness factor) is 0.87. The LHTES thermal characteristics were investigated on a test stand using inlet temperature inputs changing linearly at 1, 2 or 3 K/h. During each test, a complete phase transition in the PCM was ensured. Based on LHTES inlet and outlet temperature profiles, enthalpy distributions versus outlet temperature were evaluated. The experiments proved that these distributions are not a material property as they depend on the geometric characteristics of the LHTES and charging/discharging rates. However, they can describe the thermal behaviour of the PCM filling the LHTES and include the influence of a non-uniform temperature distribution inside the LHTES on the PCM hysteresis and temperature range of the complete melting/solidification. These effects can be modelled by the proposed function of effective enthalpy. The effective enthalpy allows for relatively simple monitoring of phase transition progression in the LHTES based solely on the parameters measurable outside the storage.

Thermal Properties and Characterization of n-Decanol-Capric Acid/Expanded Graphite/Boron Nitride for Thermal Energy Storage

To find a low temperature phase change material (PCM) that can be applied to the middle constant temperature chamber of the three chamber refrigerator, this study proposes a binary eutectic PCM of n-decanol and capric acid as a base liquid, expanded graphite as a support material, and boron nitride as a thermal conductivity enhanced particle to modify the material. The composite PCM with suitable phase change temperature and high phase change latent heat is prepared by the solution blending method. The leakage rate experiment determines the maximum adsorption ratio of expanded graphite to be 92 %. The chemical structure, microstructure and thermodynamic properties are characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, scanning electron microscopy, thermal conductivity analyzer and thermogravimetric analyzer. The results show that the n-decanol and capric acid binary eutectic PCM is fully wrapped in the porous structure of expanded graphite, and boron nitride thermal conductivity enhanced particles are well adsorbed on the surface and pores of expanded graphite. The n-decanol and capric acid phase change material, boron nitride thermal conductivity enhanced particles and expanded graphite support material are only physically combined and no chemical reaction occurred. The phase change temperature of CPCM-2 with 3 % boron nitride thermal conductivity enhanced particles is -3.68 °C, the phase change latent heat is 129.2 J/g, and the thermal conductivity is 0.75 W/m·K. It has good thermal stability and reliability in the application temperature range.

The Modification of Thermal Conductivity of Phase Change Material Using Nano Metal-Oxide Particles

The phase change materials (PCM) based cooling system have gained recent popularity with PV module temperature (TPV) reduction. PCM is an effective thermal energy storage material with the activation of latent heat capacity. Its low heat conductivity has been discovered in several studies. In this study, PCM is chosen to mix with nanoparticles to enhance its thermal conductivity and performance. For an ambient temperature of 38, it is suggested that the melting temperature (Tmelt) of PCM should be between 41 and 44 °C. Nanoparticle composited PCM (nc-PCM) are generated by mixing lauric acid (LA) with three different types of nanoparticles, including aluminum oxide (Al2O3), copper oxide (CuO), and magnesium oxide (MgO) in the following proportions: 100:0, 99:1, 98:2, 94:6, 92:8 and 90:10. It has been shown that the melting points (Tmelt) of the studied nc-PCMs are between 41.18 and 42.47 °C and thermal conductivity increases. According to the findings, the best balance between latent heat of fusion and thermal conductivity should be at 6% nanoparticle. Finally, it is expected that employing these three nc-PCM to reduce the PV module's temperature will enhance PV efficiency.

Study of Thermal Management of Li‐Ion Batteries with an Encapsulated Phase‐Change Material and Internal Liquid Channels

ANSYS Fluent is used to simulate battery thermal management (BTM). A new concept design of cooling techniques with encapsulated phase‐change material (PCM) and internal coolant channels is proposed. In this study, the passive mode of cooling (MODEL‐A: without internal cooling) and proposed design incorporating with internal liquid channels (MODEL‐B, MODEL‐C, MODEL‐D, MODEL‐E, and MODEL‐F) are considered. The upper section of the chamber is the starting point for the melting progression, which then moves toward the downward lower section of the chamber. Two design concept cooling techniques are used: straight and spiral coolant channels. At the point 15 mm, the PCM gets initiated melting at 1000 s for MODEL‐A (no coolant channels), and only a heating up of PCM is observed for MODEL‐B and MODEL‐C. Faster initiation of melting period over and above 35 mm position and at higher position point 55 mm, which reaches a liquidus temperature 328.6 K at below 2000 and 1000 s, respectively. MODEL‐D, MODEL‐E, and MODEL‐F show the PCM temperature reduction across the axial length due to the presence of coolant channels. The spiral channels can maintain the liquid fraction for longer periods, which allows liquid to contribute to the sustainability of a longer‐lasting thermal storage system.

Research on the thermal behavior of medium-temperature phase change materials and factors influencing the thermal performance based on a vertical shell-and-tube latent heat storage system

Medium-and-high temperature latent heat storage systems have been developed to address challenges related to exhaust heat utilization and energy peak regulation in the field of energy engineering. However, there is still a lack of understanding regarding the thermal behavior of medium-and-high temperature phase change materials within heat exchangers and the factors influencing the system's thermal characteristics. Therefore, this study designed and constructed a new medium-temperature (300 °C) latent heat storage system with spiral-finned heat exchanger tubes. It uses 260 kg of medium-temperature phase change material for 68.3 MJ energy storage over 2 h. The system's response to variations in the inlet temperature and flow rate of the heat transfer fluid is investigated using thermocouples and visualization windows and provides recommendations for operating parameters. Results show natural convection as the primary heat transfer mechanism in the charging process, leading to temperature stratification in the tank (the upper has a higher temperature than the lower part). In contrast, heat conduction dominates heat transfer during discharging, resulting in a more uniform temperature distribution in vertical latent heat storage systems. Besides, inlet parameters significantly influence the system. Increasing storage temperature by 20 °C or flow rate by 20 L/min reduces storage time by 33.5 % and 54.0 %, respectively. In contrast, during the exothermic stage, heat conduction dominates with a more uniform temperature distribution. Optimal conditions are found at 280–150 °C, 15 L/min, achieving an input of 84 MJ and output of 50.25 MJ over 200 min, with a cycle efficiency of approximately 59.82 %.

Experimental study on the melting heat transfer characteristics of a phase change material under mechanical agitation

Phase change materials (PCMs) are extensively employed for the thermal management of electronic devices, but their low thermal conductivity often results in slow heat absorption and release in practical applications. Existing improvement measures primarily focus on enhancing heat conduction, while research from the perspective of convection is scarce. Therefore, an experimental study on the melting heat transfer characteristics of n-docosane under mechanical agitation (0–1600 RPM) was conducted at 4.7–34 kW/m2. Upon agitation, the heating wall temperature (Tw) rapidly decreases, while the PCM temperature, heat transfer coefficient and Nusselt number significantly increase, and their variation amplitude is positively correlated with the rotation speed. This can be attributed to enhanced liquid PCM convection and accelerated solid PCM melting. At 8.5 kW/m2, the Tw at 1600 RPM is approximately 27 °C lower than that at 0 RPM, leading to a fourfold increase in the Nusselt number. Tw decreases with increasing rotation diameter, especially at lower rotation speeds. From 30 to 50 mm, the temperature decreases by approximately 13 and 10 °C at 800 and 1600 RPM, respectively. Tw changes slightly with increasing rotation height. Agitation can reduce the increase in Tw caused by a higher heat flux. Agitation can quadruple the upper limit of heat flux from 8.5 to 34 kW/m2 while maintaining consistent thermal control requirements. The power consumption of agitation increases as the rotation speed and diameter increase, peaking at 10.1 W. Moreover, after considering the minimum start-up time, Tw, and power consumption, the optimal configuration is determined: a rotation height of 10 mm and a rotation diameter of 40 mm for 1600 RPM and 50 mm for 800 RPM. These findings hold significant implications for PCM-based thermal management, particularly in terms of incorporating active convection enhancement.

Accelerated charging dynamics in shell-and-multi-tube latent heat storage systems for building applications

Thermal energy storage (TES) is an emerging technique to store the surplus energy generated during periods of excess supply and utilise it when demand arises. Phase change material (PCM) stands out as a highly efficient TES system. Enhancing heat transfer during phase change is a major challenge in creating effective PCM-based TES systems. This study focuses on enhancing the melting performance of a shell-and-tube latent heat thermal energy storage (LHTES) system. This improvement is achieved by conducting an extensive parametric study involving various geometric factors including tube position from the bottom, vertical tube spacing, tube diameter, different heat exchanger shell aspect ratios, PCM temperature, tube temperature, and PCM type. A three-dimensional model is simplified to a two-dimensional geometry for numerical simulation. The results indicate that the PCM melting time decreased by 20.6 % and 4.4 % with a 20 mm vertical tube distance compared to 15 mm and 25 mm. Among the considered scenarios, the configuration with a doubled number of tubes in width consistently exhibits a higher melt fraction throughout the entire duration. Regarding the aspect ratio, the square-shaped system demonstrates both quicker melting times and a higher energy storage rate. When comparing PCM types, it is evident that RT 35 exhibits a 3.2 % higher heat storage rate and a 44.7 % shorter melting time compared to RT 35 HC.

Carbonated balsa-based shape-stable phase change materials with photothermal conversion and application in greenhouse

Greenhouse enables to promote plant yield through creating optimal environment. Efficient solar energy conversion and storage is a promising strategy to address energy shortage issue of greenhouse in winter. This paper prepares form-stable composite phase change materials (PCMs) to store solar energy efficiently. Lightweight and porous balsa wood subjected to high-temperature carbonization is designed to simultaneously solve the liquid leakage, enhance the thermal conductivity, and improve the photothermal conversion and thermal energy storage of PCM. OP44E and SEBS are utilized as PCM and thickener, followed by vacuum impregnation into the carbonized balsa wood (CW). Results indicate that carbon content of CW increases with the augment of carbonization temperature. Shaping effects of CW and SEBS endow composite PCMs to have highest adsorption rate of 92.7 wt% with enthalpy over 190 J/g. Composite PCMs reveal reliable thermal properties and thermal stability below 100 °C. Composite PCMs have photothermal conversion larger than 88 % under a xenon lamp radiation. Temperature of PCMs on the shallow layer is higher owing to its photothermal conversion capacity. Greenhouse test indicates that CW/OP44E/SEBS greenhouse gains higher PCM temperature of 71.5 °C at 70 min, compared to 40.3 °C in empty and OP44E/SEBS cases. CW/OP44E/SEBS greenhouse maintaining indoor temperature over 20 °C lasts 15.3 min longer than empty and OP44E/SEBS greenhouses. In addition, form-stable composite PCMs featured with excellent thermal stability and photothermal conversion are capable of maintaining stable indoor temperature of greenhouse, indicating potential in the field of agricultural building temperature regulation.