Thermal Storage Characteristics Research Articles

Influence characteristic and improvement mechanism of thermal storage performance of Packed-bed thermocline tank based on high-temperature molten salt

Chloride salts and carbonates thermal energy storage (TES) have great application potential in high-temperature concentrated solar power (CSP) plants. However, their thermal storage characteristics, performance improvement mechanism and economic feasibility of application in high-temperature conditions are not clear. In this study, a transient, two-dimensional and axisymmetric model is developed for packed-bed thermocline tanks. The effects of six commonly solid fillers on thermal storage performance of NaCl-KCl-MgCl2 salt and Na2CO3-K2CO3-Li2CO3 salt at an operation temperature of 450–800 °C are simulated. The suggestions for optimizing fillers are provided combined with thermal and economic performance. Results show that high volume heat capacity and low thermal conductivity of fillers play important roles in deferring migration and weakening diffusion of thermocline, thus promoting thermal storage capacity and efficiency of tanks. Concrete and cast iron are suitable fillers for chloride salts and carbonates TES. The concrete tank is suitable for systems with strict cost control and low TES requirements. The iron tank is suitable for systems with high TES and low cost control requirements, which significantly increases effective thermal storage capacity of chloride salts by 222.1 % and considerably reduces TES cost of carbonates by 41.1 %. The results can be beneficial for high-temperature TES system of CSP plants.

Geothermal Resource Assessment and Development Recommendations for the Huangliu Formation in the Central Depression of the Yinggehai Basin

As a renewable resource, geothermal energy plays an increasingly important role in global and regional energy structures. Influenced by regional tectonic activities, multi-stage thermal evolution, and continuous subsidence, the subsurface temperatures in the Yinggehai Basin has been consistently rising, resulting in the formation of multiple geothermal reservoirs. The Neogene Huangliu Formation, with its high geothermal gradients, suitable burial depths, considerable thickness, and wide distribution, provides excellent geological conditions for substantial geothermal resources. However, the thermal storage characteristics and geothermal resources of this formation have not been fully assessed, limiting their effective development. This study systematically collected and analyzed drilling, geological, and geophysical data to examine these reservoirs’ geometric structures, thermal properties, and physical characteristics. Further, we quantitatively evaluated the geothermal resource potential of the Huangliu Formation and its respective reservoirs through volumetric estimation and Monte Carlo simulations, pointing zones with high geothermal prospects and formulating targeted development strategies. The findings indicate: (1) The Yinggehai Basin exhibits an average geothermal gradient of 39.4 ± 4.7 °C/km and an average terrestrial heat flow of 77.4 ± 19.1 mW/m2, demonstrating a favorable geothermal background; (2) The central depression of the Huangliu Formation harbors considerable geothermal resource potential, with an average reservoir temperature of 140.9 °C, and a total geothermal resource quantified at approximately 2.75 × 1020 J, equivalent to 93.95 × 108 tec. Monte Carlo projections estimate the maximum potential resource at about 3.10 × 1020 J, approximately 105.9 ×108 tec. (3) Additionally, the R14 and R23 reservoirs have been identified as possessing the highest potential for geothermal resource development. The study also proposes a comprehensive utilization model that integrates offshore geothermal power generation with multiple applications. These findings provide a method for the evaluation of geothermal resources in the Yinggehai Basin and lay a foundation for the sustainable development of resources.

Thermal storage and loss characteristics of underground water pits of solar district heating systems in Xizang Plateau, China

Large-scale thermal storage systems are crucial for solar district heating systems. Currently, there is less engineering guidance on the heat loss patterns of underground water pits, especially in the special climatic conditions of the Xizang Plateau. Therefore, this study analyzes the heat transfer characteristics of underground water pits in the plateau climate. A cylindrical underground water pit model is constructed, and the heat loss law of underground water pits of the heating season and seasonal heat storage is investigated under multiyear operation. The results show that the heat loss rate of the underground water pit with seasonal heat storage is 0.8 % higher than that of the heating season heat storage for the same volume. The difference in heat loss between the two heat storage modes is small. The heat loss from the top, sides and bottom of an underground water pit accounted for 34.2 %, 36 % and 29.8 % of the heat loss in the first year, respectively. The percentages of heat loss from each surface after ten years of operation were 46.7 %, 36.6 %, and 16.7 %. In addition, the functions of storage volume and heat loss per unit volume of the first year in Xizang were fitted. The relationship equation between heat loss per unit volume of the first year and the annual heat loss per unit volume in the nth year was obtained. This study provides support for the heat loss of underground water pits that operate continuously for many years.

Potential of hydrogen and thermal storage in the long-term transition of the power sector: A case study of China

Hydrogen and thermal storage can reduce cost of long-term and large-scale energy storage with high efficiency and low or even zero carbon emissions. Their potential in the low-carbon transition pathway of an energy system with rapid growth of energy demand, large shifting of energy supply structure and limited investment budget remains unclear. A long-term power generation planning model is proposed in this paper, featuring detailed technical and economic characteristics of hydrogen and thermal storage. The power supply system of China is selected as a case study, due to its urgent need for low-carbon transition and complex spatial characteristics. Results show that the application of hydrogen and thermal storage can benefit the development of volatile renewable power generation technologies, facilitate the transition towards zero or even negative carbon emissions while simultaneously reducing power supply costs. Hydrogen is expected to be mainly produced in spring and consumed in summer while heat is expected to be primarily generated in autumn and consumed in winter. Shifting from thermal storage to hydrogen storage might happen around 2050 in accordance to the low-carbon transition progress.

Two-stage optimization model for day-ahead scheduling of electricity- heat microgrids with solid electric thermal storage considering heat flexibility

Traditional electricity-heat microgrid (EHM) is limited in flexibility due to real-time balancing between the supply and demand of electric and heat system. The heat flexibility (HF) can be released by thermal inertia and heat storage characteristics of district heating systems (DHS) and heat storage units, and it can be used to increase the electric power flexibility (EF) of EHM. In this paper, the quantitative relationship between HF and EF is investigated, and a two-stage optimization model for day-ahead scheduling of EHM with solid electric thermal storage (SETS) is established. Firstly, the electric-heat flexibility conversion coefficient (EHFC) is developed to decide the allocation of HF among different electricity-heat coupling units, such as CHP and SETS, and EF supply model of EHM based on HF is built. Secondly, a two-stage optimization model is proposed for day-ahead scheduling of EHM to improve EF and economy of EHM by optimizing the heating power and HF's allocation. Thirdly, the equivalent energy storage of the DHS is quantitatively analyzed, providing a reference for planning and operating of EHM's flexibility resource. Finally, the case study shows that by considering HF and deploying SETS, the total cost can be reduced by 18.8 % and 22.6 %, respectively.

Performance analysis of solar thermal storage systems with packed bed utilizing form-stable phase change materials and heat pump integration

Solar energy, a pivotal renewable resource, faces operational challenges due to its intermittent and unstable power output. Thermal energy storage systems emerge as a promising solution, with phase change materials (PCMs) packed beds attracting attention for their compactness and stable temperature transitions. This paper details a laboratory-scale solar thermal storage PCM packed bed integrated with a heat pump, utilizing a novel form-stable PCM. A numerical model was established to assess the thermal storage characteristics and heat extraction performance of the solar PCM packed bed coupled with a heat pump. Simulation results show that increasing solar irradiance significantly reduces storage duration, achieving full thermal storage in 3.4 h at 900 W/m2 irradiance. Optimal starting times were identified as 9:00 a.m. or 11:00 a.m., with later starts resulting in incomplete storage due to the PCM not reaching its phase change temperature. Additionally, packed bed parameters influenced storage conditions; increasing the paraffin content in the PCM extended the phase change duration, while graphene nanoparticles slightly reduced it. Lower porosity (0.49) beds, with higher PCM content, reached 70 °C quicker than higher porosity (0.61) beds due to higher pressure drops promoting more uniform flow and temperature distribution. During heat extraction, coupling the heat pump at 2 liters/min achieved temperatures below 45 °C in 4.1 h, while at 6 liters/min, the time reduced to 1.6 h, demonstrating adaptability to different extraction rates. These findings provide insight into the thermal performance of solar PCM packed beds coupled with heat pumps, contributing to efficient and stable thermal utilization of solar energy.

Numerical study of heat transfer characteristics of phase change materials reinforced with porous media based on hybrid mesh

To address the drawbacks of inadequate energy density as well as utilization effectiveness in solar energy utilization, phase change energy storage offers a possible option. However, the low thermal conductivity of traditional phase change materials (PCMs) restricts the extent to which solar energy utilization can be enhanced. In this paper, the impact of the metal foam (MF) on the solid–liquid interface, the flow field, the enhancement heat transfer mechanism during the paraffin wax (PX) melting process and thermal storage characteristics was analyzed. Besides, a three-dimensional mathematical model of MF-PX using the hybrid mesh technique was established and software ANSYS-FLUENT was used for simulation. The results indicated that, the hybrid mesh exhibited a reduction of 52.75 % in mesh count compared to the unstructured mesh, resulting in 45 % reduction in computational time. Moreover, the hybrid mesh also showcased improved mesh quality that the unstructured mesh was mainly distributed in the range of 0.48–0.6, while within the range of 0.84–1.0 for the hybrid mesh. More important, the maximum relative error between experimental and simulation was 8.67 %, indicating that the model can make a reasonable prediction. With the proportions of MF increased from 0.11 % to 0.43 %, both the Rayleigh number (Ra) and its amplification decreased. At 800 s, the Ra decreased from 1.76E+07 to 1.20E+07, while the amplification of the Ra was reduced from 1.88E+07 to 1.30E+07. In addition, the natural convection proportions of CMF decreased from 96.31 % to 80.65 %. These observations indicated that natural convection was the primary heat transfer mechanism, and the conduction was enhanced by the increasing proportion of MF. Finally, in terms of heat storage characteristics, the heat storage capacity and heat storage rate of the composite PCM slightly decreased. The heat storage values decreased from 19.30 kJ to 18.66 kJ. Similarly, the heat storage rates decreased from 19.86 J/s to 18.81 J/s.

Numerical study on thermal storage and exothermic characteristics of subway station fresh air shaft surrounding rock

Subway stations are typically equipped with fresh air shafts to introduce outdoor air, while the surrounding rock and air channels form a vertical earth-air heat exchanger (VEAHE). This study is the first to analyze the year-round thermal storage and exothermic characteristics of the surrounding rock. A numerical model was developed, incorporating ground surface heat transfer and axial heat transfer within the rock. The simulation results aligned well with field test data. This model was then utilized to explore the thermal storage and release properties of the surrounding rock. The findings revealed that both z-directional and r-directional annual temperature wave affect the enclosing rock. The monthly average natural energy efficiency (NEE) and storage efficiency (SE) were determined to be 10.75% and 17.47%, respectively. Notably, the shallow rock exhibited the highest NEE but the lowest SE. The energy used for fresh air pre-treatment derives not only from the rock's current annual cycle but also from previously stored energy. Lastly, λsr and c were identified as major influencers of NEE, while λsr, c, and the burial depth of the shaft collectively impact the air pre-treatment process in the shaft. The findings contribute to further understanding of the thermal process in VEAHE systems.

Thermal performance study of a solar-coupled phase changes thermal energy storage system for ORC power generation

The current solar organic Rankine cycle power generation (ORC) system cannot run smoothly under the design conditions due to the shortcomings of solar fluctuations, and thermal energy storage (TES) can effectively buffer the fluctuations of solar energy. Cascaded heat storage (CLTES) has been shown to be more suitable for solar heat storage than single-stage heat storage (LTES). The main objective of this study is to analyze the thermal storage characteristics of thermal storage systems under real-time solar energy fluctuations, and to improve the thermal storage efficiency and total thermal storage capacity of solar phase change thermal storage systems in distributed scenarios. The current research on solar CLTES system needs to focus on the heat storage characteristics under the actual solar fluctuations to provide guidance for the design and practical operation of CLTES system. Analyzing the effect of solar fluctuations on thermal storage performance is the focus of solar thermal storage research, which can provide guidance for the design and actual operation of CLTES systems. However, the current research on solar CLTES system lacks the analysis of thermal storage characteristics under typical solar energy fluctuations. Therefore, a simplified two-dimensional enthalpy-dynamic model of heat transfer for shell-and-tube latent heat storage system is developed in this paper to simulate the heat storage characteristics of single-stage and cascade heat accumulators containing different phase change materials (PCMs) at a fixed temperature of the heat source, and the heat storage performance of the system is simulated based on the solar fluctuations of typical four seasons. Finally, based on the shortcomings of large-capacity thermal storage, a dual-tank recirculation thermal storage model is proposed and the thermal storage characteristics of the improved recirculation model are analyzed. The results show that the optimized cycle heat storage mode can bring about a minimum of 10 % and a maximum of 17.2 % thermal efficiency improvement. On a typical summer day with the most abundant solar energy resources, four times of complete phase change heat storage and one incomplete phase change heat storage were completed (melting fraction = 81.83 %), and on a typical winter day with the least solar energy resources, two times of complete phase change heat storage and one incomplete phase change heat storage were completed (melting fraction = 75.81 %). The maximum difference of heat storage between them is 45.38 %.

Research on creating the indoor thermal environment of the solar greenhouse based on the solar thermal storage and release characteristics of its north wall

Improving the solar thermal storage capacity of the north wall of the solar greenhouse can effectively enhance the indoor thermal environment during the night-time in winter. However, the indoor thermal environment is also influenced by the interaction between the spatial parameters of the solar greenhouse and outdoor meteorological conditions. Additionally, the heat storage and release performance of the north wall are dynamically affected by changes in the indoor thermal environment. This complicates the quantitative assessment of the impact of solar active–passive heat storage methods applied to north walls on the indoor thermal environment. Therefore, in this study, we develop a mathematical model that considers simplified calculations of the solar greenhouse’s spatial parameters and the design method of an active–passive ventilation wall with latent heat storage, which was proposed in the early stage, for evaluating the impact of the solar thermal storage and release characteristics of the north wall on the indoor thermal environment of the solar greenhouse. This model is validated against measured data from the experimental solar greenhouse with high accuracy. Using this model, we analyze the quantitative reinforcement effects of a phase change composite wallboard and a solar collector system on the solar energy utilization of the north walls and its effects on the indoor thermal environment. Compared to ordinary solar greenhouses in Wuzhong, the application of a GH-20 composite phase change thermal storage wallboard to improve the passive solar energy utilization of the north wall can increase the solar energy contribution rate by 90.9%. Furthermore, integrating a multi-surface solar air collector with double-receiver tubes on the phase change composite wall can increase the solar energy contribution rate by 95.4%. Also, the experimental results reveal that the solar active–passive heat storage methods applied to the north wall can enhance the indoor thermal environment during night-time and increase cucumber yield by more than 10% in winter. This study provides a method reference for optimizing the active–passive solar thermal utilization of the solar greenhouse.

HEAT TRANSFER IN A FORM-STABLE DIRECT-CONTACT LATENT THERMAL ENERGY STORAGE UNIT

This study investigated various aspects of thermal storage concept, including material characterization and analysis of form-stable, unencapsulated phase-change materials (PCM) that underwent solid-solid phase transition and was in direct contact with the working fluid. The study focused on temperature range between 100-140°C (212-284°F). Mathematical heat transfer models were developed to examine the operating characteristics of the thermal energy storage unit, identify key parameters influencing storage, and conducted parametric studies. Both single-phase and phase-change working fluids were considered in the models. Experiments were conducted using a packed bed of PCM pellets and a single-phase working fluid (tri-ethylene glycol) to evaluate and demonstrate the heat storage concept during charging and discharging. The experimental results aligned well with the heat transfer models, validating their accuracy. Parametric studies explored a wide range of parameters not feasible in laboratory experiments, shedding light on charging, discharging, and thermal storage characteristics. These models facilitated the development and implementation of optimization algorithms for packed bed latent heat storage units. The findings indicated that form-stable latent heat units utilizing commercially available polymers undergoing solid-solid phase transition can serve as long-term stable thermal storage candidates for use with several single-phase working fluids as well as two-phase steam.

Mitigating supercooling in microencapsulated phase change materials by incorporating compatible polyethylene wax as a nucleating agent

Microencapsulated phase change materials (MicroPCMs) have been investigated as thermal storage materials for decades, due to their benefits in storage container protection and PCM leakage prevention. For improved thermal storage properties, the elimination of supercooling, where the micro-sized PCMs crystallize at temperatures significantly below their designated melting point, or over a broad temperature range, has been targeted in many researches. However, most successful methods either compromise the protective shell or reduce the storage enthalpy. In this work, a relatively high-melting-point polyethylene wax (PE-W) that exhibits good compatibility with PCM n-octadecane (n-Oct) was introduced to mitigate the supercooling. MicroPCMs containing n-Oct core materials incorporated with PE-W, were prepared using emulsion polymerization, resulting in cross-linked shell poly(methyl methacrylate-co-allyl methacrylate) denoted as P(MMA-co-AMA). The MicroPCMs with PE-W present consistent sizes ranging from 1 to 5.5 μm, maintained a regular spherical shape, and retained uniform morphologies. The quantity incorporated is exceptionally minimal, constituting merely 2.5 ‰, owing to the effective dispersion, which arises from their intrinsic compatibility. The addition of PE-W nucleating agent significantly reduced the degree of supercooling from 8.0 °C for reference MicroPCM to 1.7 °C for MicroPCM with PE-W. Additionally, the enthalpy associated with heterogeneous nucleation saw a substantial increase, rising from 0% in the reference MicroPCM to 58% in that containing PE-W. The heat resistance of MicroPCM encapsulated by P(MMA-co-AMA) has been greatly improved by 90 °C. The endurance of the MicroPCM highlights the remarkable durability and the sustained effectiveness of PE-W in eliminating supercooling over 100 heating and cooling cycles. Furthermore, in a thermal load scenario, the MicroPCM demonstrated exceptional thermal storage and protective characteristics. The outstanding thermal energy storage properties make them promising candidates for use in textiles, preservation, and transportation applications.

Thermal storage characteristics of microencapsulated phase change material coatings in low-energy rural prefabricated building walls

ABSTRACT Prefabricated buildings in rural areas of China waste a large amount of energy due to poor thermal insulation. Phase change materials (PCMs) are able to stabilize room temperature by latent heat absorption and release during the phase change process. This study incorporated PCMs in the form of microcapsules into the interior wall coatings of prefabricated buildings, and by taking advantage of PCMs’ energy storage capacity, the thermal storage characteristics of PCM-coated bricks were investigated. The results show that microencapsulated phase change material(MPCM) coatings for prefabricated walls exhibit excellent thermal stability properties and effectively reduce the heat flux of prefabricated walls, with coatings having a MPCM mass fraction of 15% and a thickness of 5 mm providing the highest overall benefits. By fitting the numerical simulation results with experimental data, a novel multifunctional passive solar phase change heat collection and storage wall system was developed. This study innovatively combines energy storage materials with interior wall coatings in prefabricated walls of modular buildings investigating how it enhances the thermal stability of the external insulation walls and effectively reduces the reliance on heating equipment for auxiliary heating in rural residences. This essay aims to provide feasible recommendations for optimizing the dual-stage energy-saving and carbon reduction goals in both the construction and operation of rural areas.

Application of graded phase change materials for solar energy inter-seasonal storage heating and thermal storage characteristics

Abstract In this paper, firstly, the heat transfer characteristics of the stepped phase change accumulator are studied, and the location of the solid-liquid phase interface is determined by the phase fraction in a fixed grid scheme, while the phase change heat transfer process is simulated using Fluent. Secondly, for the phase change heat transfer problem, the enthalpy-porosity method in the Solidification/Melting model is used to treat the solid-liquid mixed paste region of the phase interface as a porous media region, and the evaluation system is constructed in terms of heat storage and discharge efficiency, heat storage, and heat recovery efficiency. Then the mathematical model, boundary conditions and solution parameters of the stepped phase change heat accumulator are set, and the data analysis of the effect of the pool height-to-diameter ratio on the heat storage in the solar inter-seasonal storage heating system is carried out by using ANSYSCFD software. The results show that the heat storage of the system also shows an overall increasing trend with the increase of the pool height-to-diameter ratio, and the heat storage of the system increases faster when the height-to-diameter ratio increases from 0.2 to 1.0 in sequence, and the heat storage of the system increases less when the height-to-diameter ratio changes between 0.9 and 1.8, and basically tends to be stable. This study realizes the graded heat storage and graded heat use of solar energy, which is useful for the research of solar heat supply and heat storage.

Photothermal properties and performance of hybrid carbon-paraffin/water emulsions

Solar thermal energy has attracted renewed research interest for its excellent energy efficiency among different types of solar technologies. However, the limiting factor of them all is the intermittent nature of solar radiation. To overcome this drawback, it is possible to store absorbed light in form of heat using emulsions with phase-change materials (PCMs) dispersed in solar nanofluids by combining the advantage of solar thermal storage characteristics of PCMs and the higher light absorption capacity of solar nanofluids. In this study, paraffin/water and hybrid carbon-paraffin/water emulsions with 5 wt% paraffin wax RT44HC as PCM are proposed. Low-cost emulsions with proven colloidal stability were successfully produced, with and without small amounts of oxidized carbon black nanoparticles (0.01 wt%) dispersed in the emulsion. Thermal energy storage capacity improved up to 16 %, while maintaining good thermal conductivity properties. Optical properties were evaluated by means of a spectrophotometer with an integrating sphere, including both spectral absorptance and reflectance of the samples. Two experimental setups were developed with concentrated light, to evaluate the photothermal conversion efficiency under simulated and natural sunlight. The improvement of the light to heat conversion properties provided by the oxidized carbon black nanoparticles was confirmed, with PTE values of 1.5- and 2.7-fold better than the base fluid (water) using a solar simulator and natural sunlight, respectively.

Rheological and phase behaviour of paraffin wax/bitumen blends with thermal storage characteristics

This paper analyses the thermomechanical properties, heat storage characteristics and compatibility of bitumen blends with a paraffin wax, having a melting point around 60 °C, as phase change material. To that end, temperature sweeps in the linear viscoelastic range, technological properties, Modulated Differential Scanning Calorimetry (MDSC), and cross-polarised optical microscopy observations were carried out on blends and pure compounds. The obtained results reveal a partial compatibility between the compounds and the development of a multiphasic microstructure, where the paraffin-rich or bitumen-rich domains form the continuous phase depending on the concentration, with the phase inversion around 20 wt% wax. Below this threshold concentration, the disperse paraffin-rich phase acts as filler that reinforces the continuous bitumen matrix until it reaches the melting transition. Above the critical concentration for the phase inversion, the continuous paraffin-rich phase controls the rheological response. However, both phases retain their own identity and show their individual transitions and relaxations. Despite the partial compatibility, a high degree of crystallinity is found, especially for high paraffin contents, which would result in a significant capacity to store thermal energy, for applications such as solar thermal collection or thermoregulation materials for buildings, etc.

Optimal control method of active distribution network considering soft open point and thermostatically controlled loads under distributed photovoltaic access

To achieve the flexible operation of the active distribution network (ADN), an optimal control method for the ADN considering the soft open point (SOP) and thermostatically controlled loads under distributed photovoltaic (PV) access is proposed. First, the mathematical model of the SOP and thermostatically controlled loads are constructed based on the flexibility of the SOP and the thermal storage characteristic of thermostatically controlled loads, respectively. Then, the mathematical model of the ADN considering the SOP and thermostatically controlled loads are further constructed. The optimal control of the ADN is realized by adjusting the transmission power of the SOP and the switching state of the electric water heater. Finally, the optimal operation analysis of the SOP and thermostatically controlled loads under various control methods is carried out, and the impact of the SOP and thermostatically controlled loads on the economic and secure operation of the ADN is further investigated. The results show that the proposed method taps the demand response potential of thermostatically controlled loads while satisfying the water consumption habits of different customers, and utilizes the network reconfiguration with the SOP to further improve the security and economy of the ADN operation.

Melting Characteristics of Hybrid Nano Enhanced Phase Change Material in a Finned Circular Tube

In this study, the melting characteristics of hybrid nano-enhanced phase change material in a finned circular tube were studied by using the Finite volume method. This setup of circular tubes with a phase change material is used as cooling systems in automotive industries, air-conditioning, refrigerators, and other applications of cooling systems. There is a need for enhancing the specific heat capacity of this system to ensure that the system works even at high temperatures. As the current problem includes many design parameters and boundary constraints, the finite volume method has been performed to obtain a detailed report and data to examine the deformation of the hybrid nanoparticles and heat transfer rate on the corresponding surface. The current paper reviews and focuses mainly on the high-temperature PCM. And the suitable PCM has been selected based on its limitations and properties. To ensure the increased specific heat capacity, a salt-based phase change material, i.e., a mixture of NaNO3-KNO3 (60:40 ratio) binary salt. This PCM could hold a temperature up to 334◦C before melting to change its phase. In addition to spherical-shaped nanoparticles of silica (SiO2) in this binary salt, it tends to have a significant potential for enhancing the thermal storage characteristics of the NaNO3-KNO3 binary salt. On an extended surface, Finns are used on the peripheral of the circular tube to increase the surface area, which leads to an increase in frictional resistance resulting in a reduced airflow rate in the vicinity of the finned surface. From case studies, it has been found that the optimum fork-shaped fin array with two branches gives higher heat dissipation than the optimum rectangular fin. In the majority of the cases, the optimum fork-shaped fin array gives a 59.9% higher heat transfer rate compared to the rectangular fin array. Thus, the melting characteristics of the hybrid of NaNO3- KNO3 with nanoparticles of silica are studied when placed in a circular tube containing fork-shaped fins.

Synergistic enhancement of heat transfer and thermal storage characteristics of shell and tube heat exchanger with hybrid nanoparticles for solar energy utilization

Incorporating phase change material and nanoparticle into shell and tube heat exchangers is a common strategy to achieve thermal storage for solar energy utilization. However, the heat transfer and thermal storage characteristics of shell and tube heat exchangers with hybrid nanoparticles are limited. In this paper, twenty representative cases for three kinds of nanoparticles (Al2O3, TiO2, and CuO) and three sets of nanoparticle combination types (mono Nano-PCM, binary Nano-PCM, and ternary Nano-PCM) are considered. The effects of nanoparticle combination types and nanoparticle volume ratios on heat transfer and thermal storage characteristics of shell and tube heat exchangers are analyzed. The results show that the average melting rate of shell and tube heat exchangers with hybrid Nano-PCM is higher than mono Nano-PCM, which is enhanced by 2.3% with binary Nano-PCM and 5.2% with ternary Nano-PCM, respectively. The average energy storage and average energy storage rate of ternary Nano-PCM are the highest, followed by binary Nano-PCM and mono Nano-PCM, respectively. The maximum energy storage increment and enhanced average storage rate of shell and tube heat exchangers with ternary Nano-PCM are 1.13 kJ and 1.7%, compared to mono Nano-PCM. However, the average energy storage density of shell and tube heat exchangers with ternary Nano-PCM is the lowest with the maximum reduction rate of 20.22% compared to pure PCM. The results confirm that optimizing the configuration of hybrid nanoparticles can enhance the efficiency of solar thermal utilization.

Synthesis and Characterization of Titania–MXene-Based Phase Change Material for Sustainable Thermal Energy Storage

PLUCISE A82 (PW82) is considered one of the best phase change materials as it is economical, commercially viable, and eco-friendly. Unless there is a great need to optimize the number of parameters to investigate encapsulated PCMs with good performance, for the effective and practical applications of organic phase change materials, it is required to enhance their thermal conductivity. In this study, efforts were made to increase the thermal properties of phase change materials by seeding different nanoparticles. The direct synthesis method, in which the mixing of nanoparticles in paraffin wax (PW82) takes place, is used for the production of NEPCM. Differential scanning calorimeter and heat conduction experiments were used to evaluate the effect of variable concentration of nano-encapsulation on thermal storage and heat conduction characteristics of nano-enhanced PCM. The thermal storage feasibility was also determined. In this study, titania (TiO2), Ti3C2/MXene was mixed in PW82 in 0.1, 0.2, and 0.3 wt.%. The investigation was also carried out for hybrid nano-enhanced PCM in a hybrid combination of (TiO2), and Ti3C2 (MXene) in PW82, used in wt.% concentration of 0.1, 0.2, and 0.3. Doping of titania and MXene improves the specific heat capacity of PCM. For doping of 0.3 wt.% of TiO2–Ti3C2 in PCM, the specific heat is improved to 41.3%. A maximum increment in thermal conductivity of 15.6% is found for doping of TiO2–Ti3C2 0.3 wt.%. The dissociation temperature of this prepared nano-enhanced PCM increases by ~6% for 0.3 wt.% weight fraction. Therefore, this study demonstrates that the doping of TiO2 and Ti3C2 with PW82 to form a new class of NEPCMs has significant scope to enhance the thermal storage capacity of organic paraffin.