Medium Temperature Phase Change Material Research Articles

A novel microencapsulated medium-temperature phase change material employing dicarboxylic acid for thermal energy storage

Microencapsulation enhances the performance of phase change materials (PCMs). However, the existing research on microencapsulation of dicarboxylic acids (DAs) is inadequate, with only one study dedicated to the development of microcapsules containing a low DA content and a shell that decomposes at low temperatures. In this study, glutaric acid (GA), as a representation of DA, was successfully microencapsulated with an enhanced encapsulation ratio. The results obtained by scanning electron microscopy (SEM) revealed a uniform spherical core–shell structure of the microencapsulated GA (MEGA). Fourier transform infrared spectroscopy (FT-IR) an X-ray diffractometer (XRD) analysis confirmed the absence of any chemical reaction between the core and shell materials. Additionally, differential scanning calorimetry (DSC) results demonstrated excellent heat storage. Notably, MEGA exhibited a thermal reliability index of 94.4 % after 200 accelerated thermal cycles. Thermogravimetry analyzer (TGA) results showed good thermal stability of MEGA. The dispersion stability and thermal conductivity of MEGA suspensions displayed significant enhancements compared to those of GA suspensions. Furthermore, compared with the base fluid, the MEGA suspensions with 1.0 wt%, 5.0 wt% and 10.0 wt% demonstrated reduced pumping power requirements by 16.9%, 54.6% and 70.0%, respectively. These findings suggest that MEGA holds promising prospects for applications in the medium temperature energy storage field.

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 %.

Effect of blending of medium-temperature phase change material on the bitumen storage heat

This study aims to investigate the feasibility of using D-Mannitol as a phase-change material (PCM) to increase the energy storage capacity and improve the thermomechanical characteristics of the modified bitumen. D-mannitol (Dm) was incorporated into Bitumen (Bm) using a high-speed shearing method. The results showed that the integration of PCM enhanced the physical characteristics of the basic bitumen, with the modified bitumen having a melting point close to that of D-mannitol (Tm = 164 °C). The D-mannitol was found to crystallize during cooling, indicating that it can store or release heat in the latent form. The specific heat capacity of the modified bitumen was proven to increase gradually as the PCM content (2, 4, and 8 wt%) increased. The maximum temperature regulation effect of the modified bitumen was observed when the PCM content reached 8 wt%, resulting in a temperature reduction of up to 9 °C. This study provides a basis for the utilization of D-Mannitol as a form of energy storage in bitumen-based pavement applications.

Characterization by differential scanning calorimetry of thermal storage properties of organic PCMs with operating temperature of 150 °C

The involvement of Phase Change Materials (PCMs) in energy storage systems leads to more sustainable and efficient use of energy. Medium operating temperature (melting point 100–400 °C) find various applications in industrial waste heat recovery and hybrid compressed air - thermal energy storage systems. However, there is still a lack of detailed knowledge in terms of their thermal storage properties that hinders them from being more integrated in industry. In this study, thermal properties such as melting point, enthalpy and heat capacity of three medium temperature PCMs were characterized using Differential Scanning Calorimetry (DSC). The enthalpy-temperature graph for each PCM is presented that contains key information on sensible and latent heat contribution in the total energy storage. The selected organic PCMs are adipic acid with two different purities 99%, 99.5%, and its chemical equivalent PureTemp151® with a melting point of (150.5 ± 0.5 °C) and a latent heat of (230 ± 10 J/g). Furthermore, the effect of heating rate and sample mass in DSC procedures on transition temperatures and enthalpy were evaluated. Finally, thermal performance of PCMs was quantified through 150 cycles of melting and solidification. The tested PCMs show a significant storage capacity and good thermal stability with less than 10 % enthalpy loss.

Thermal performance investigation of a novel medium-temperature pilot-scale latent heat storage system at different charging and discharging temperatures

Large-capacity medium-temperature latent heat storage (LHS) systems have the potential to be extensively utilized for waste heat recovery and peak load shifting. However, the phase change behavior and mechanism of medium-temperature phase change materials (PCMs) in shell-and-tube LHS systems, as well as the impact of charging and discharging temperatures on the thermal performance, are still unclear. To address these issues and verify the reliability of the cylindrical pilot-scale LHS system, this article designed and constructed a novel cylindrical medium-temperature (up to 300 °C) LHS system with a large capacity (approximately 1 GJ) equipped with spiral and H-shaped fins. The research focused on investigating the impact of various charging and discharging temperatures on the thermal behavior of the LHS system to adapt different temperature scenarios in waste heat recovery while also analyzing the coupling effect of heat conduction and natural convection during charging and discharging and depicting the PCM liquidus based on thermocouple data. The experimental findings indicated that increasing the charging temperature could effectively shorten the charging duration, with a decrease from 5.99 h at 280 °C to 4.00 h at 300 °C, representing a reduction of 33.22%. In contrast, the impact of decreasing the discharging temperature on the discharging duration was less significant than that of increasing the charging temperature. Besides, the differences in heat transfer mechanisms between the charging and discharging processes were analyzed. In the charging process, the heat transfer was initially dominated by heat conduction, followed by natural convection. Conversely, heat conduction predominantly governed the heat transfer process in the discharging process. The heat transfer process dominated by heat conduction would increase the non-uniformity of PCM temperature on the horizontal plane, while the heat transfer process dominated by natural convection would alleviate this non-uniformity. Moreover, the accumulative stored energy under the charging temperature of 290 °C was 952.37 MJ, while the released energy under the discharging temperature of 160 °C was 648.72 MJ, which was approximately 10–200 times greater than those documented in existing studies.

MXene/d-Mannitol aerogel phase change material composites for medium-temperature energy storage and solar-thermal conversion

Accelerate the development of medium-temperature phase change materials (PCMs) with high enthalpy of phase change and light absorption capability is very important for medium-temperature energy storage and solar thermal utilization. However, low energy conversion capacity and easy leakage limit the practical application of PCMs. To improve these properties of materials, a MXene/DM aerogel composite phase change material was prepared by self-assembly followed by freeze-drying of d-mannitol (DM) and MXene nanosheets using a simple solution blending method. The MXene/DM containing 20 wt% MXene has a high enthalpy (Hm) of phase change (202.7 J/g) with phase change temperature (Tm) of 153.3 °C, and still has good shape stability at 170 °C without leakage. In addition, MXene/DM has strong absorption ability in UV–Vis-NIR regions, with significant solar-thermal conversion efficiency of 88.1 %. The results indicate that the MXene/DM aerogel have comprehensive performance and have promising applications in medium-temperature thermal storage and photothermal conversion.

Experimental study on a pilot-scale medium-temperature latent heat storage system with various fins

In this article, a pilot-scale latent heat storage system loaded with 5674.7 kg medium-temperature phase change material (PCM), having four groups of tubes embedded with various fins (longitudinal, H-shaped, spiral, and without fins), was designed and built. During the charging process, the smooth tube had the highest outlet temperature, followed by the tubes with longitudinal, H-shaped, and spiral fins, indicating that the spiral fins had the best heat transfer performance while the smooth's was the worst. The temperature difference in the vertical direction of the thermal energy storage unit was more significant than that in the horizontal direction. Besides, the thermal insulation performance test indicated that the temperature of PCM in the upper part decreased more slowly than that in the lower part due to the charging of the latent heat system being conducted from top to down. Moreover, after charging for 6.5 h, the accumulative energy and the mean power of the tubes with longitudinal, H-shaped, spiral, and without fins were 500.67, 541.57, 567.35, 432.56 MJ, 21.39, 23.14, 24.24, and 18.48 kW, respectively. The calculated charging efficiency of the latent heat storage system was 66.48%.

Energizing organic phase change materials using silver nanoparticles for thermal energy storage

Medium temperature phase change materials (PCMs) are of great interest for thermal devices due to their energy storage capability. In the current study, organic PCMs with silver nanoparticles are experimentally investigated and energized to improve the energy storage ability. Organic PCM composites with silver metal nanoparticles of 20–40 nm in size at different concentrations of 0.2 %, 0.4 %, 0.6 %, 0.8 % and 1.0 % were prepared and characterized to explore the thermophysical properties. Scanning electron microscopy observations provides a higher magnification level to ensure the presence of Ag nanoparticles in the PCM matrix. Optical investigation confirms that the permeability of PCM with Ag nanoparticle decreases from 22.7 % to 15.9 % at a concentration of 0.8 %, which increases the absorptivity; this phenomenon is due to the dark colour of the silver nanoparticle. Thermal conductivity of Ag dispersed composite improved the thermal conductivity of the base material PCM from 0.218 W/mK to 0.44 W/mK with a mass fraction of 0.8 % of nanoparticles, resulting in an improvement of 101 %, which can be attributed to the well-developed thermal networks with the PCM matrix. The latent heat of the composite PCM differs by 1 % from the base PCM, which is important for effective energy storage due to better intermolecular attraction. The Ag dispersed composites were also thermally stable up to a temperature of 220 °C and their thermal stability was slightly improved by the nanoparticles. Composite PCM samples with better thermal conductivity were tested for 500 thermal cycles and its chemical stability and thermal properties were equated with PCM. In addition, a numerical heat transfer analysis is performed under varied heat sources (60 °C, 70 °C & 80 °C) to compare the thermal performance between PCM and the synthesized nano PCM. In correspondence to the experimental characterization and numerical investigation the silver nanoparticle dispersed PCM exhibits outstanding energy storage & release routine, ensuring the beneficial usage of developed composite PCM in TES applications like battery thermal management and solar photovoltaic thermal systems.

A novel cascade latent heat thermal energy storage system consisting of erythritol and paraffin wax for deep recovery of medium-temperature industrial waste heat

Recovering medium-temperature (e.g., 150–180 °C) industrial waste heat through latent heat thermal energy storage (LHTES) can effectively attenuate the consumption of fossil fuels. However, the LHTES system containing a single medium-temperature phase change material (PCM), e.g., erythritol, cannot absorb the part of heat below the PCM's melting point (∼118 °C) during the charging process. Meanwhile, a single low-temperature PCM, e.g., paraffin wax, is unable to supply a significant amount of heat at temperatures higher than its melting point upon discharging. Therefore, a cascade LHTES system combining one erythritol unit and two paraffin wax units (melting point of ∼60 °C) was proposed to deeply recover the waste heat during charging and increase the heat supply temperature during discharging. Through prototype testing, the performance of such a cascade system was examined under various working conditions. It was shown that the cascade system could improve the efficiency of the waste heat recovery from 15.8% to 63.4% under the charging condition of 100 L/h and 160 °C, as compared to a single-stage erythritol-based system. The average heat supply temperature of the cascade system was also increased from 37 °C (at a constant flow rate) to 53.6 °C via an active discharging strategy (by tuning the flow rate). This highly efficient cascade LHTES system has great potential for recovery of medium-temperature waste heat towards a decarbonized future of space heating for buildings.

Thermal Characterization of Medium-Temperature Phase Change Materials (PCMs) for Thermal Energy Storage Using the T-History Method.

To reduce energy consumption and increase energy efficiency in the building sector, thermal energy storage with phase change materials (PCMs) is used. The knowledge of the thermophysical properties and the characteristics of PCMs (like their enthalpy changes and the distribution of stored energy over a specified temperature range) is essential for proper selection of the PCM and optimal design of the latent thermal energy store (LHTES). This paper presents experimental tests of the thermophysical properties of three medium-temperature PCMs: OM65, OM55, RT55, which can be used in domestic hot water installations and heating systems. Self-made test chambers with temperature control using Peltier cells were used to perform measurements according to the T-history method. In this way the temperature range of the phase transition, latent heat, specific heat capacity, enthalpy and the distributions of stored energy of the three PCMs were determined. The paper also presents measurements of the thermal conductivity of these PCMs in liquid and solid state using a self-made pipe Poensgen apparatus. The presented experimental tests results are in good agreement with the manufacturers’ data and the results of other researchers obtained with the use of specialized instruments. The presented research results are intended to help designers in the selection of the right PCM for the future LHTES co-working with renewable energy systems, waste heat recovery systems and building heating systems.

Selection Principles and Investigation of Substances for Synthesis of Composite Medium-Temperature Phase Change Materials for Space Heating and Domestic Hot Water

The types of heat accumulation and the types of heat-accumulating materials are considered. It is shown that the most promising as heat-accumulating materials for heating and hot water are the salts hydrates. Based on the conducted factor analysis, a number of criteria are excluded from further consideration, which significantly reduces the list of criteria considered for selecting phase change materials (PCM) and simplifies further work on the selection of the most promising materials. There were selected from over 160 salt hydrates as PCM for the future of composite synthesis for the heating and hot water the Na (CH3COO) •3H2O, Ba (OH)2•8H2O, Mg (NO3)2 •6H2O and Zn (NO3)2•6H2O.

Thermophysical Properties of a Novel Nanoencapsulated Phase Change Material

Thermophysical properties are important parameters that influence the performance of phase change materials (PCMs) and heat transfer fluids. Micro/nanoencapsulation is an effective technique for preventing leakage and enhancing thermophysical properties of PCMs. In the present study, novel d-mannitol nanocapsules with inorganic shells were synthesized as a medium-temperature PCM. The nanocapsulation was confirmed by scanning electronic microscopy. The specific heat and thermal diffusivity of the nanocapsules and their suspension with heat transfer oil as base fluid were measured by a differential scanning calorimeter and light flash apparatus. The thermal conductivity of the nanocapsule suspension was measured using a hot-disk thermal constants analyzer. The viscosity of the nanocapsule suspension was measured by a rotational rheometer. The results show that the thermal conductivity and thermal diffusivity of the nanocapsules were enhanced compared to the bulk of the PCM due to the inorganic shell. The specific heat, thermal conductivity, and viscosity of the nanocapsule suspension were increased compared to the base fluid. The potential of the nanocapsule suspension as a heat storage and transfer fluid was evaluated.

Thermal performance investigation of a single medium temperature phase change microcapsule used for wind power absorption and heat storage system

Phase change microcapsules have a wide application in the heat storage system. The medium temperature heat storage systems such as medium temperature solar thermal plants, waste heat recovery systems and wind power absorption systems. In order to analyse the effects of configuration parameters and materials on phase change heat transfer process in a single medium temperature microcapsule, an enthalpy-transforming model was applied to trace the location of the solid-liquid interface and obtain the liquid fraction at different time in the melting process. Based on this model, the effects of particle size, the effects of wall thickness, the effects of wall materials and different medium temperature phase change materials were analyzed. The numerical results show that the larger particle size has a longer melting time, the melting time of 50 μm particle size and 250 μm particle size is 0.036 s and 2.48 s, respectively. In addition, the melting time of microcapsules with different wall thicknesses from the 1μm to 9μm is the same i.e., 0.14 s. Therefore, the wall thickness has little effect on the melting time of microcapsules. Besides, the microcapsule with the erythritol as inner material and the polystyrene as wall material has the longest melting time. Furthermore, the thermal conductivity of the wall materials is the main factor affecting the melting time. Moreover, the product of latent heat and density of phase change material is the main factor of the melting time.

Thermal energy storage and thermodynamic properties of (E)-3-m-tolylbut-2-enoic acid as a medium temperature phase change material

ABSTRACTPhase change materials (PCMs) that can store and release heat energy over the temperature range from 363 to 393 K are crucial for solar absorption cooling, and it is worthy to seek new solid-liquid PCMs candidates that melt and crystallize in this temperature range. In this paper, (E)-3-m-tolylbut-2-enoic acid (mTBEA) was applied as a PCM candidate. Its thermal energy storage properties and thermal stability were systematically investigated. The results showed that mTBEA melted at 382.9 ± 0.5 K and crystallized at about 364 K, with a melting enthalpy (ΔfusH) of 138.4 ± 6.9 J g−1 and showed good long-term cyclic stability and thermal stability. The supercooling of mTBEA was stabilized at about 20 K, indicating that the conservation condition of melted mTBEA could be simple. In addition, the melted mTBEA could release all the absorbed thermal energy upon crystallizing. Besides, mTBEA exhibited good thermal stability for it to be applied as PCM. Hence, mTBEA is a promising PCM candidate for solar absorption cooling. Furthermore, the heat capacity of mTBEA was measured by modulated temperature differential scanning calorimetry (MTDSC) over the temperature range from 198.15 to 431.15 K, and the molar thermodynamic functions, [HT-H298.15]m and [ST-S298.15]m, were calculated based on the fitted molar heat capacity data.

Characterization of medium-temperature phase change materials for solar thermal energy storage using temperature history method

In this work, thermal properties of five phase change materials (PCMs) with medium phase change temperature including mannitol, sebacic acid (SA), SA/expanded graphite (EG) composite, LiNO3-KCl eutectic salt and LiNO3-KCl/EG composite, were characterized using temperature history (T-history) method with improved accuracy. The studies on mannitol showed that although the T-history method could yield a supercooling degree which was lower than that from differential scanning calorimetry (DSC) determination, the severe supercooling and great latent heat loss during mannitol's solidification were still the problems which hindered the use of this material. As for the rest materials, slight or no supercooling phenomena were observed and the obtained phase change temperatures were well matched to literature data. The latent heat measurements of these four materials proved a proportional relationship between the PCM/EG composite's latent heat and PCM's mass fraction. However, the latent heat values determined by T-history were higher than the DSC results. Therefore, repeated studies were still required to further evaluate the latent heat storage densities of these materials. The results in this work could play key roles in design, simulation and modification of latent thermal energy storage (LTES) systems based on these medium-temperature PCMs for solar heat applications.

Medium-temperature phase-change materials thermal characterization by the T-History method and differential scanning calorimetry

ABSTRACTThis paper presents a thermal characterization of salt mixtures applying the T-History method (THM) and the differential scanning calorimetry (DSC) techniques. By using water as a standard substance, the original THM was developed to analyze materials with melting points under 100°C. This is the first research that proposes to replace water by glycerin to characterize medium-melting-temperature phase-change materials (PCMs) (140–220°C). Moreover, the DSC technique was used to validate and compare the results obtained with the THM for each mixture. For instance, the system compound of 40% KNO3–60% NaNO3 was studied, and the enthalpy of fusion determined by THM and DSC differs by 2.1% between each method. The results given by the two methods for all mixtures showed that both techniques are complementary and present satisfactory agreement with the specialized literature.

Preparation of microencapsulated medium temperature phase change material of Tris(hydroxymethyl)methyl aminomethane@SiO2 with excellent cycling performance

Abstract Polyalcohol is one of the important medium temperature phase change materials (PCMs) for thermal energy storage, in which liquid-free solid–solid PCMs are more promising although sublimation can hardly be avoided when crystals transform to the “plastic phase”. We reported here the preparation of encapsulated Tris(hydroxymethyl)methyl aminomethane (Tris) with the SiO2 shell by sol–gel process. Through the hydrolysis and polycondensation of the bicomponent silicon precursors mixed with tetraethoxysilane (TEOS) and 3-aminopropyl triethoxysilane (APTS) of proper ratio, Tris@SiO2 microcapsules with excellent sealing property can be obtained, which prevent the leakage of Tris outside the capsules. Besides, silica encapsulation doubles the thermal conductivity of the PCMs to 0.478 W/(m K). The DSC measurement shows that the Tris@SiO2 capsule owns a reversible phase change in the range of 110–155 °C, which will stabilize at about 146 J/g during 70 times of thermal cycling. The Tris@SiO2 capsules have good potential for medium temperature thermal energy storage applications.

Experimental investigation on melting heat transfer characteristics of lauric acid in a rectangular thermal storage unit

This paper presents an experimental effort to visualize temperature field and melt front evolution during solid–liquid phase change process. The study is focused on the melting of lauric acid in a rectangular thermal storage unit heated from one side. Thermophysical properties of lauric acid are determined and found to be desirable for application as a medium temperature phase change material (PCM). Image processing of photographs together with recorded temperatures are used to calculate the melt fractions, temporal heat storage and heat transfer characteristics, including the average Nusselt number on the hot wall as well as the local heat transfer rates on the melt front. Moreover, solid–liquid interface morphology and temperature field are employed to infer dominant heat transfer mechanisms and time-dependent flow structures during different stages of the melting process. Results indicate that during the initial stage of melting, heat conduction is the dominant mode of heat transfer, followed by transition from conduction to convection regime and convection dominated heat transfer at later times. Approaching the end of the melting process, bulk temperature of the liquid PCM increases and stratified temperature field appears at upper part of the enclosure which reveals depression of the convection currents.

A comparison of heat transfer enhancement in a medium temperature thermal energy storage heat exchanger using fins

An experimental energy storage system has been designed using a horizontal concentric tube heat exchanger incorporating a medium temperature phase change material (PCM) Erythritol, with a melting point of 117.7 °C. Three experimental configurations, a control system with no heat transfer enhancement and systems augmented with circular and longitudinal fins have been studied. The results presented compare the system heat transfer characteristics using isotherm plots and temperature–time curves. The system with longitudinal fins gave the best performance with increased thermal response during charging and reduced subcooling in the melt during discharging. The experimentally measured data for the control, circular finned and longitudinal finned systems have been shown to vindicate the assumption of axissymmetry (direction parallel to the heat transfer fluid flow) using temperature gradients in the axial, radial and angular directions in the double pipe PCM system.

Heat transfer enhancement in medium temperature thermal energy storage system using a multitube heat transfer array

An experimental energy storage system has been designed using an horizontal shell and tube heat exchanger incorporating a medium temperature phase change material (PCM) with a melting point of 117.7 °C. Two experimental configurations consisting of a control unit with one heat transfer tube and a multitube unit with four heat transfer tubes were studied. The thermal characteristics in the systems have been analysed using isothermal contour plots and temperature time curves. Temperature gradients along the three directions of the shell and tube systems; axial, radial and angular directions have been analysed and compared. The phase change in the multitube system was dominated by the effect of convective heat transfer compared to conductive heat transfer in the control system. The temperature gradient in the PCM during phase change was greatest in the radial direction for both the control and multitube systems. The temperature gradients recorded in the axial direction for the control and multitube systems during the change of phase were respectively 2.5 and 3.5% that of the radial direction, indicating essentially a two-dimensional heat transfer in the PCM. The onset of natural convection through the formation of multiple convective cells in the multitube system significantly altered the shape of the solid liquid interface fluid flow and indicates the requirement for an in-depth study of multitube arrangements.