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This study investigates the airflow and thermal management of a compact electric energy storage system by using computational fluid dynamic (CFD) simulation. A porous medium model for predicting the flow resistance performance of the battery modules in a battery cabinet is developed. By studying the influence of rack shapes, the effects of heat exchanger arrangements and other parameters on the airflow and battery thermal distribution are analyzed. When applying a larger bottom air channel, the inlet flow uniformity of each battery cabin in the cabinet increases by 5%. Meanwhile, temperature standard deviation decreases by 0.18 while raising the flow rate from 3 m/s to 8 m/s, indicating better temperature uniformity in the battery cabin. When the charge–discharge ratio reaches 0.5 C, the temperature deviation of the entire cabinet significantly increases, reaching 8 K. Furthermore, a rack-level thermal management scheme is proposed to effectively reduce the thermal deviation of the container electric energy storage system and improve the overall temperature uniformity. Results reveal that the rack-level thermal management of the wavy cabinet in the electric storage container can effectively improve the thermal uniformity of the distributed battery cabin, and the overall thermal deviation is controlled within 1.0 K. [ABSTRACT FROM AUTHOR]

The present paper numerically investigates the air-cooling thermal management in a large space energy storage container in which packs of high-power density batteries are installed. The validated porous media model is applied for simplification and the airflow distribution in the overhead duct, vertical ducts, side-in and front-out battery packs and hot-aisle channel are analyzed. The mechanism of airflow reorganizing by perforated deflectors is demonstrated and the influence of the angle and position are recognized by using orthogonal method. Then, perforated deflectors with various porosities are utilized to improve the airflow uniformity in vertical ducts. Result shows the pressure loss caused by perforated deflectors is not sensitive. When applying deflectors in the overhead duct, the airflow can be reorganized to achieve more uniform distribution and hot-spot elimination. The standard deviation of the volumetric flowrate σ flo is used to reflect the flowrate uniformity, which can be reduced to 0.003, indicating 98.24% reduction in comparison to the initial case without perforated deflectors. When applying the optimized layout into a practical asymmetrically distributed energy storage container, the maximum temperature at the battery rack inlet is reduced by 8.31 °C and 5.13 °C on the long-flow side and short-flow side, respectively. [ABSTRACT FROM AUTHOR]

Salt-hydrate based thermochemical energy storage is currently a momentous technique utilized for long-term energy storage due to the reversible gas-solid reaction under low-temperature. Among available salt candidates, LiOH·H 2 O is a promising thermochemical material owing to its high heat storage density of 1400 kJ/kg and low charging temperature. The expanded graphite (EG) is selected as a host matrix owing to its excellent thermal conductivity and abundant microstructure, which can promote the heat and mass transfer. This work focuses on the thermochemical performances of the form-stable LiOH·H 2 O/EG composite sorbents. Five samples were being synthesized with EG contents of 0, 5, 8, 12 and 15 wt%. These porous sorbents are characterized to understand the microstructure and thermophysical properties. Considering the comprehensive effect of thermal conductivity and storage density, as well as the adsorption kinetics, the 8 wt% EG-doped sample is the most favourable sorbent, which possesses the thermal conductivity of 6.92 W/(m K) and energy density of 1120 kJ/kg. The cyclability results also reveal the energy capacity of this composite maintains ∼90% of the original after ten consecutive heat charging (dehydration) and discharging (hydration), suggesting good stability. Additionally, the active energy of 2.58 × 109 s−1 and pre-exponential factor of 59.5 kJ/mol for the sorbent is derived. Finally, the thermal power of 123 W and thermal efficiency of 83.6% are achieved for the storage unit in simulation. All these results further confirmed the feasibility of the developed composite sorbent in low-grade heat storage. Image 1 • The TCMs based on LiOH·H 2 O with EG doping are developed. • The 8 wt% EG doped composite shows superior sorption property. • Over 90% of the original storage density is maintained after 10 cycles. • The active energy of 2.58×109 s−1 and pre-exponential factor of 59.5 kJ/mol are derived. • The thermal efficiency for heat charging is 83.6%. [ABSTRACT FROM AUTHOR]

This work presents a numerical investigation of the integration of conventional parallel air-cooling battery system with multi-phase change materials (PCMs) to improve the cooling effectiveness at low power consumption (P c) rate. The study considers various cells partitioning of the PCMs on nine different parallel air-cooled battery packs. The impact of PCMs pattern schemes, inclination angle of the manifold, and air inlet velocity are analysed by employing finite volume technique coupled with an enthalpy-porosity method. Compared with a typical parallel air-cooling system, despite 90% reduction in the air inlet velocity, the integrated system successfully lowers the maximum temperature (T max) by 12.0 K and improves uniformity of temperature distribution based on standard deviation (SDV) of temperature field by 43.9%. Subsequently, inclining the air inlet manifold to an angle close to vertical leads to a poor cooling performance. Also, a proper pattern of PCMs cells partitioning having a trapezoidal cell shape at the top and bottom, and a parallelogram cell shape at the midsection exhibits a better heat dissipation performance. Moreover, compared to the module with highest inlet velocity of 1.5 m/s, reducing the inlet velocity by 66.7% still controls T max at 313.13 K which is well below the critical limit, and decreases the P c by 65.8%. • A comprehensive analysis of integrated traditional parallel air-cooled BTMS is presented. • Thermal performance of the modified battery module based on patterns of PCMs cell partitioning, inclination angle of manifolds, and low airflow rate was investigated. • The effect of various evaluation parameters on thermal behavior are presented. • The cooling effectiveness is remarkably improved. • The optimal pattern of multi-PCMs cells partitioning is obtained. [ABSTRACT FROM AUTHOR]

Due to the prominent advantages of high energy density and long-term energy conservation ability, salt hydrate-based gas-solid thermochemical energy storage (TCES) is a promising technology for effectively employing low-grade energy such as industrial waste heat and minimising fossil fuel-based sources depletion. As an innovative thermal energy storage technology that has drawn great attention from scholars in recent years, it still remains in the stage of a laboratory-scale investigation. This study establishes a reasonable classification of salt hydrates-based TCES systems, discusses the properties and performance regulation strategies of materials, types of reactors, applications, heat and mass transfer process, reaction mechanisms, and also provides critical comments and outlooks on this adsorption TCES technology. It is comprehensively elaborated and evaluated in the following steps. (i) The development of various thermochemical materials (TCMs), including pure salts, mixtures of salt hydrates, and composite TCMs of salt/matrix, is summarised and assessed in detail from the perspectives of thermochemical performances such as ESD and cyclability. (ii) The progress of the conceptual design of the reactor and prototype used for vapour/salt gas-solid reaction are presented and analysed. (iii) The existing theoretical models ranging from the views of microcosmic molecular dynamics to macrocosmic reaction kinetics are discussed. (iv) Additionally, the existing challenges regarding salt hydrate-based TCES technology are identified, and the prospects are also provided. This review enables researchers to timely grasp the latest advancements and thus may provide some rewarding insights for future investigations of salt hydrate-based gas-solid TCES and facilitate scholars to achieve better improvements. • Salt hydrate-based sorption technology is the potential for heat storage. • The composite thermochemical materials need to be further developed. • The optimisation includes three levels: material, reactor, and system. • Mechanism, model, and performance control strategy need to be further studied. • Challenges and prospects of this technology are identified. [ABSTRACT FROM AUTHOR]

Perovskite Solar Cell (PSC) have recently emerged as exciting new candidates of Photovatics (PVs) for solar-to-electrical energy conversion. Nevertheless, one huge obstacle to its commercialization is how to improve its tolerance to operation at elevated temperatures. To address this issue, Composite Phase Change Material (CPCM) incorporated with a porous skeleton structure is proposed to integrate with PVs. In this structure, an important theoretical problem is that the temperature dependence of PV and the temperature control behavior of CPCMs interact with each other (bidirectional relationship). In this work, a pore-scale lattice Boltzmann phase change model is established to describe the dynamic thermal behavior of CPCMs and explore the roles of the bidirectional relationship between PVs and CPCMs, the change of power conversion efficiency influenced by temperature variation and glass transmissivity is discussed by comparing the overall liquid fraction of CPCMs, and the average temperature and power conversion efficiency of PVs. Furthermore, the situation of time-varying solar irradiation is discussed to mimic real application conditions. Results indicate that the neglecting temperature dependency of PVs leads to underestimation of PV surface temperatures and overestimation of power conversion efficiencies, while glass transmissivity provides reverse effects. These phenomena not only happen in constant solar irradiation but also in varying solar irradiation, calling for increasing attention to designing PV/CPCMs for varying heat flux conditions. The findings of this work establish a comprehensive manner toward integrated design of CPCMs for PV thermal control. • The roles of the bidirectional relationship between PVs and CPCMs are discussed. • Neglecting temperature dependency endows an overestimation of PV efficiency. • The highest temperature is underestimated if simplifying the variable heat flux to constant heat flux. • The temperature dependency of a PV has a slight influence on phase change. [ABSTRACT FROM AUTHOR]

[Display omitted] • Binary lithium-based salt hydrates hierarchical inclusion in the matrix. • Temperature lift is over 20℃ accompanied by high energy density. • Energy capacity decreases with the discharging temperature. • Over 95% of the original energy capacity is maintained after 20 cycles. Considering the eminent benefits of high energy storage density (ESD) and long-term energy storage ability with ignorable heat losses, thermochemical energy storage (TCES) in salt hydrates is a potential technology to bridge the gap between supply and demand for renewables in domestic heating. The development of thermochemical material is currently the primary concern. In this work, the composite sorbents consisting of expanded graphite (EG) and varying mass ratios of LiOH and LiCl are synthesised and characterised, and the thermochemical behaviours such as sorption kinetics and sorption isotherms are also investigated. The results suggest the salts are uniformly dispersed in the EG matrix in the form of hierarchical micro-nano scale particles, and the salt contents of samples are over 60 wt%, which in favour of the enhancements of vapour sorption property and ESD. By regulating the mass ratio of LiOH and LiCl, the composite sorbents (LiOC@EG) can achieve thermal upgrade with different temperature requirements, i.e., 35–45℃ for space heating and 45–55℃ for domestic hot water (DHW) production, accompanied by high volumetric ESD (over 200 kWh/m3) benefiting from the reaction enthalpy. Besides that, the effects of regenerative temperature and vapour pressure on the water uptake and ESD of the sorbent are revealed. The cyclability results indicate that more than 95% and 96% of the original ESDs are retained after 20 dehydration-hydration cycles for the samples of LiO2C1@EG and LiO3C1@EG, suggesting good stability of the composites. The developed composite sorbents provide new insights into the fields of long-term energy storage and heat upgrade with high energy density. [ABSTRACT FROM AUTHOR]

The present study aims to improve the thermo-chemical conversion behaviours, including reactive transport processes and output performances of an open thermochemical energy storage (TCES) unit. The local thermal non-equilibrium (LTNE) model and the effect of non-uniform porosity are adopted and considered to better elucidate the conversion processes. Cascading the reaction sub-units filled with different thermochemical materials (TCMs), i.e., zeolite, salt hydrate-based composite sorbent, and pure salt of SrBr 2 ·6H 2 O, to form an integrated storage bed ameliorates the output performance. The numerical results indicate that the maximum temperature difference ranging from 3.5 to 4.9 °C between heat transfer fluid and solid reactants exists during desorption, and the realistic non-uniform porosity facilitates the reactant conversion near the wall compared to the uniform porosity assumption. The cascaded scheme promotes the charging and discharging processes compared to the cases filled with sole TCM, the time required for charging this 10.8 kWh storage model is 16 h. Increasing the charging temperature from 100 °C to 145 °C, the charging time reduced to 6.5 h, saving 59.4%. Boosting the inlet velocity of airflow also accelerates the charging rate. The cascaded storage unit significantly stabilises the output temperature during discharging, warming up the airflow from 20 °C to 35 °C for 24 h with a tiny temperature fluctuation. Airflow with higher relative humidity facilitates hydration but shortens the stable period. Overall power and thermal efficiency of the "thermal accumulator" in charging are 598 W and 92.8%, 164 W and 92.4% in discharging, with a total COP of 0.71. The satisfying performances suggest that the cascaded TCES unit may provide a strategy and reference in the design and promotion of the low-grade energy storage system. [Display omitted] • Local thermal non-equilibrium model is adopted. • Inhomogeneous porosity is considered. • Cascaded heat storage materials stabilise output temperature. • Numerical system storage capacity and COP are 10.8 kWh and 0.71. [ABSTRACT FROM AUTHOR]

With the increasingly energy consumption and environmental degradation, the recovery of low-grade industrial waste heat and the development and utilisation of renewables have become urgent needs. At present, the recovery of waste heat is mainly at high temperature, and the recovery rate of waste heat at medium and low temperatures is low. Adsorption thermochemical energy storage (TCES) is a pivotal technology applied for long-term thermal energy storage based on the reversible gas-solid reaction at mid-to low-temperature. LiOH·H 2 O is a potential thermochemical material (TCM) candidate because of the high energy storage density (ESD). In this paper, the expanded graphite (EG) is used as supporting matrix to impregnate LiOH to further improve its heat and mass transfer. The water vapour adsorption properties such as sorption capacity and sorption isotherms of the consolidated composite sorbents with EG contents of 0, 5, 8, 12, and 15 wt% were tested. It was found that the samples with 5% and 8% wt% EG have superior sorption capacity and kinetics at various relative humidities (RHs), and the maximum water uptake substantially decreased with increasing temperature. The cyclability results showed 90% and 92% of the original ESDs are retained after 12 cycles for the samples with 8% and 15% wt% EG, suggesting good stability of composite sorbent. The ad/desorption isobars processes also proved the existence of the sorption hysteresis loop, and this phenomenon is more obvious at low pressure. The data fitting results revealed that the kinetics coefficient of the promising composite sorbent containing 8 wt% EG is 0.01671 s – 1 at 30 °C with 58% RH. Compared with the sensible or latent energy storage, the heating temperature produced from the sorbent is adjustable for different purposes. Considering the low emissions and pollution of LiOH-based heat production compared to the coal-fire system, i.e., 1262 kg pollutants are theoretically reduced for a household per year, it is a clean alternative for the residential heat supply. Image 1 • Sorption capacity of a mixture is 32% higher compared to pure salt at 58% relative humidity. • Over 90% of the original storage density is maintained after 12 cycles. • The adsorption hysteresis loop is more obvious at low pressure. • Sorption kinetics coefficient 0.01671 s – 1 at 30 °C with 58% relative humidity. • 1262 kg/y emissions of pollutants avoided for a household. [ABSTRACT FROM AUTHOR]

Adsorption thermochemical energy storage (TCES) is currently a momentous technique utilised for long-term energy storage due to the reversible gas-solid reaction under low-temperature. A novel 3D heat storage reactor, including two shaped columnar sorbent reactive beds is proposed. The heat charging (dehydration) and discharging (hydration) processes under different operating conditions are numerically investigated. The roughly uniform temperature and conversion degree evolutions of the bed during reaction suggest a good heat and mass transferability of the porous shaped sorbent bed. For reference cases, the time required to finish the dehydration and hydration processes are 328 and 748 min; the decreased condensation temperature and increased evaporation temperature promote dehydration and hydration kinetics. The charging power and thermal efficiency increase firstly and decline later till the end of dehydration, the final values are 212 W and 91.1%; while discharging power and efficiency decrease with the advancement of conversion degree, with thermal power and thermal efficiency of 93 W and 87.5%. Moreover, the overall thermal coefficient of performance of 80.9% and exergy coefficient of performance of 27.7% are achieved; and the coefficients of performance can be further optimised at specific charging temperature and flow rate of heat transfer fluid (HTF). All these satisfying performances of this model preliminarily confirm its feasibility in TCES. • A 3D closed thermochemical energy storage model is proposed. • Pressure effect in dehydration and hydration kinetics is investigated. • The average charging power is 212 W for this reactor model. • Overall COP th and COP ex are 80.9% and 27.7%. • Specific charging temperature and flow rate of the heating medium further enhanced COP. [ABSTRACT FROM AUTHOR]

Thermochemical energy storage (TCES) based on hydrated salts is gaining popularity because it can provide high storage capacity at low costs. It is critical to improving heat storage efficiency and capacity due to technical challenges such as low thermal conductivity of thermochemical materials (TCMs) and poor mass transfer. The reversible reaction of strontium bromide monohydrate (SrBr 2 ·H 2 O) and water vapor forming strontium bromide hexahydrate (SrBr 2 ·6H 2 O) for TCES is used in numerical simulation, aiming to investigate the discharging performance of a double-pipe closed TCES reactor considering the influences of fin layouts (radial and longitudinal fins) by evaluating several indicators such as the reaction time and outlet temperature. The results show that the use of fins can improve the exothermic process. The discharging time of the reactor with upward L-shaped fins is reduced by 8.6% for radial fins and by 8.9% for the reactor with four longitudinal fins. The addition of fins expands the heat transfer area and makes the hydration rate of TCM around fins significantly higher than other parts. The Taguchi method is adopted to optimize the structure parameters of case 7 as it has the highest heat transfer amount of heat transfer fluid (HTF), and the optimal combination (A (fin number) = 4, B (fin extension length) = 20 mm, C (fin thickness) = 2 mm) increases the peak value of average outlet temperature by 1.47% and the heat exchange efficiency by 4.7% compared with case 7. • Hydration of SrBr 2 ·H 2 O in a closed TCES reactor is investigated in bed scale. • Adding fins increases average outlet temperature and heat transfer efficiency. • Effective heat transfer of reactor with radial fins is slightly higher than that of reactor with longitudinal fins. • The optimal structure parameter combination of the reactor is obtained by the Taguchi method. [ABSTRACT FROM AUTHOR]

Abstract Phase change materials used in thermal energy storage systems are critical for energy utilization. Organic phase change materials have received considerable attention both for applications and research due to their favorable properties, such as large latent heat, low cost, stability, nontoxicity, and corrosion resistance. Because of the inherently low thermal conductivity, there has been a lot of research on various combinations of organic phase change materials with high conductivity materials. Carbon nanotubes, graphene and porous carbon have excellent properties, such as ultrahigh surface area and high thermal conductivity, which have become the preferred materials for thermal properties enhancement. Benefit from the varied dimensional spaces for retaining materials, these carbon-based materials can act as excellent confinement for phase change materials to form shape stabilized, phase change tunable, and thermally enhanced phase change composites. In this paper, a review about recent advancement and challenges for organic phase change materials confined in different types of carbon-based materials is presented, associated with some relevant theories trying to understand the mechanism of heat transfer and phase change in micro/nano confinement. Some promising applications in thermal management and energy conversion that have great potential for more explorations are also introduced. Highlights • Carbon-based materials are suitable for infiltrating organic phase change materials. • The thermal properties of organic phase change materials can be improved effectively. • The challenges and perspectives of organic phase change materials are proposed. [ABSTRACT FROM AUTHOR]

• Thermal performance of multilayered PCM(s) thermocline TES tank is analyzed. • A numerical model is used for the thermal evaluation of thermocline configurations. • A parametric study of PCM melting temperature and heat of fusion is performed. • Results indicated the optimal values of melting temperature and latent heat for MLSPCM(s). The current paper presents two parametric studies (inverse Stefan number and dimensionless temperature difference) to optimize the values of latent heat and melting temperature of multilayered phase change materials (MLPCM(s)) in thermocline tank for concentrating solar power (CSP) plants. Spherical capsules filled with PCM(s) of different thermo-physical properties are used to fill the bed region, and the molten salt is used as heat transfer fluid (HTF). The numerical model that has been developed uses the Dispersion-Concentric (D-C) equations. By using MATLAB, the governing equations are solved and validated against the experimental results. The results show that in the optimal configuration of the case (B), the values of InvSte number and dimensionless temperature (θ m) are equal to 1.2 and 0.8 for the top PCM layer, respectively; 0.75 and 0.55 for the middle PCM layer, respectively; and 0.65 and 0.3 for the bottom PCM layer, respectively. Moreover, it is also found that to obtain the best design and distribution of temperature for a thermocline tank consisting of three layers of PCM, the top PCM layer should melts by Δ T = 55.4 °C below the HTF charging inlet temperature, the PCM layer at the bottom should solidifies by Δ T = 83.1 °C above HTF discharging inlet temperature. [ABSTRACT FROM AUTHOR]

CO 2 hydrate is a potential cold thermal energy storage material with latent heat of 500 kJ/kg, however, the dissociation principle of CO 2 hydrate is different from that of solid-liquid phase change materials and therefore, exploring the dissociation mechanism of CO 2 hydrate is of great significance for efficient cold storage. In this paper, a new lattice Boltzmann model is proposed, considering dissociation kinetics, two phase flow, heat transfer, latent heat, surface reaction, thermal buoyancy and variable parameter depended with temperature. The necessity of the temperature consideration related with latent heat and buoyancy is clarified. For the combined effect of depressurization decomposition and thermal decomposition of CO 2 hydrate dissociation, depressurization decomposition diminishes as time increases and initial pressure increases and thermal decomposition enhances as hot wall temperature increases. The fully dissociated Fo is 0.544, 0.514, 0.604, 0.628, showing a first decreasing and then increasing trend while initial pressure increases from 0 to 0.002, 0.004, 0.006 lu. As hot wall temperature increases from 8, 10, 12–14 °C, the fully dissociated Fo is 0.566, 0.544, 0.473 and 0.419 respectively. This new lattice Boltzmann model is of significance in providing guidance for the future cold thermal energy storage system application by using CO 2 hydrate. • A lattice Boltzmann model with thermal buoyancy consideration is developed for the dissociation process of CO 2 hydrate. • The dissociation tendency of CO 2 hydrate is revealed when coupling depressurization and thermal decomposition. • Increasing initial environmental pressure reduces the dissociation rate, but prolongs the fully dissociated time. • Increasing hot wall temperature apparently accelerates the heat transfer and dissociation performance. [ABSTRACT FROM AUTHOR]

Because of the low charging temperature, salt hydrate-based adsorption thermochemical energy storage (TCES) is currently a significant technology that promises long-term energy storage. A corrugated-shaped heat storage unit (HSU) in which embedding porous metal bracket is proposed in this work to enhance heat transfer between the thermochemical material (TCM) wrapped inside and the heat fluid transfer (HTF) in the external corrugated channel. The thermo-chemical conversion behaviours, including reactive transport processes during dehydration (charging) and hydration (discharging), as well as the influence of parameters, are comprehensively investigated. The numerical results indicate that increasing the HTF temperature facilitates the charging process while the discharging can be promoted by decreasing reaction bed temperature. The time required to complete charging and discharging for the reference cases is 2990 s and 5700 s. For both charging and discharging powers of reactive bed, the values dramatically surge in a short time and then gradually decrease, with the maximum powers of 2638 W and 1866 W, respectively. Boosting evaporation temperature (water vapour pressure) accelerates hydration while the effect of condensation temperature on dehydration is insignificant. The reaction period can be further shortened by heightening the thermal conductivity of TCM, and the porosity also has a distinct influence on the reaction. Compared to the storage unit of a straight external channel without a metal bracket inside, this heat storage module saves 34% and 23% in charging and discharging times. The results of this work provide insights into the prediction and improvement of thermochemical conversion behaviours. • A corrugated heat storage unit with porous metal support is proposed for heat storage. • Parametric studies for energy charging and discharging are performed. • Higher temperature facilitates dehydration while lower temperature promotes hydration. • The maximum thermal power is 2638 W when the charging temperature is 110 °C. • Energy charging and discharging times are saved by 34% and 23%. [ABSTRACT FROM AUTHOR]

The development of phase change materials (PCMs) is hampered by issues like leakage, poor thermal conductivity, and poor light absorption. In this study, we innovatively combined modified melamine foam (MF) and graphene nanoparticle (GNP) to address these defects of PCMs in the solar-thermal energy system. The MF was modified to endow the solar-thermal energy conversion ability and superhydrophobic interface characteristics due to the polypyrrole (PPy) by the in-situ polymerization and the polymerized octadecylsiloxane (PODS) layer coating on the sponge skeleton. The composite PCMs consisting of the modified MF, paraffin wax (PW), and GNP were fabricated and exhibited good leakproof ability, high thermal conductivity, and excellent solar-thermal energy conversion capability. Results showed that due to the effects of the PPy and the PODS on the sponge skeleton structure, MF@PPy-PODS/PW composite PCMs showed a decrease in the mass loss ratio to less than 0.34% and an increase in the thermal conductivity of 0.33 W/m·K and the solar-thermal storage efficiency of 75.68%. Besides, adding GNP with higher concentrations impacted positively on the thermal conductivity and the solar-thermal energy conversion ability but negatively on the phase change enthalpies. MF@PPy-PODS/GNP3/PW composite PCMs increased the thermal conductivity to 0.59 W/m·K and the solar-thermal storage efficiency to 79.36% while decreasing the phase change enthalpy to 130.61 J/g. Furthermore, a thermoelectric conversion system driven by solar energy was developed to show the potential of composite PCMs for cleaner energy production. The open-circuit voltages of the MF@PPy-PODS/GNP3/PW composite PCMs achieved 0.78 and 0.91 V at 2 and 4 Sun, respectively. The open-circuit voltages remained for a period of time and slowly dropped without the simulated solar light irradiation. This study provided a potential strategy for the optimal performance of composite PCMs and their application in solar thermal systems. • PCMs composited with modified melamine foam and graphene nanoparticle were prepared. • Composite PCMs showed good leakproof ability and high thermal conductivity. • Solar-thermal storage efficiency of composite PCMs achieved 79.36%. • Open-circuit voltage in solar-driven thermoelectric conversion system was improved. [ABSTRACT FROM AUTHOR]

Abstract: Solar thermal energy storage is important to the daily extended operation and cost reduction of a concentrated solar thermal power plant. To provide industrial engineers with an effective tool for sizing a thermocline heat storage tank, this paper used dimensionless heat transfer governing equations for fluid and solid filler material and studied all scenarios of energy charge and discharge processes. It has been found that what can be provided through the analysis is a series of well-configured general charts bearing curves of energy storage effectiveness against four dimensionless parameters grouped up from the storage tank dimensions, properties of the fluid and filler material, and operational conditions (such as mass flow rate of fluid and energy charge and discharge periods). As the curves in the charts are generalized, they are applicable to general thermocline heat storage systems. Engineers can conveniently look up the charts to design and calibrate the dimensions of thermocline solar thermal storage tanks and operational conditions, without doing complicated modeling and computations. It is of great significance that the generalized charts will serve as tools for thermal energy storage system design and calibration in energy industry. [Copyright &y& Elsevier]

Photovoltaics, as a direct technology to convert sunlight into electricity, possess significant potential to deal with ever-increasing environmental problems and the desire to reduce the use of fossil fuels. Thermal stability of photovoltaics is of major concern when considering large-scale commercialization under conditions in which device degradation by high temperature operation is possible. Phase change materials (PCMs) are highly promising for thermal management of such devices due to their high latent heat and inherent heat transfer properties. However, a great challenge in applying PCMs to photovoltaics is in achieving high energy density while maintaining high power density, especially with different orientations of the photovoltaics. In this work, the dynamic heat transfer characteristics of a composite PCM with embedded metal foam are systematically studied by a pore-scale lattice Boltzmann model. It is found that the melting rate of composite PCMs dramatically decreases at late-stage melting, leaving a region of solid PCM ("dead zone") for a long time. To address this issue, we propose a special, nonuniform structure for the composite PCM that has a different porosity in the dead zone than elsewhere. The melting rate, energy density, and power density of the composite PCM can be significantly enhanced by tailoring the porosity of the composite metal foam. For instance, at a Fourier number of 0.30, the energy density of a case with a dead zone porosity of 0.80 is 6.8% higher than that with a dead zone porosity of 0.95. This work provides an effective strategy toward applying PCMs for thermal management of photovoltaics and paves a way toward optimizing energy storage capabilities of PCMs under various working conditions. [ABSTRACT FROM AUTHOR]

Packed beds with methane steam reforming reaction (MSR) can be used as thermochemical storage devices. The packing configuration can have a significant effect on the flow distribution which will further influence the heat/mass transfer, dispersion and reaction characteristics. In the present paper, the hydraulic, dispersion, heat/mass transfer and the MSR reaction properties are investigated in packed beds with the simple-cubic (SC) packing, the body-centered cubic (BCC) packing and face-centered cubic (FCC) packing forms. ANSYS FLUENT integrated with user defined scalars (UDS) and user defined functions (UDF) are used to perform the simulations. Results show that firstly, the residence time distribution (RTD) can be used to evaluate the dispersion property in packed beds where a narrower RTD curve reflects a more uniform velocity distribution with less dispersion. Secondly it is found that, regions with backflow are not beneficial for heat/mass transfer and chemical reactions from two aspects. One is that the heat transfer between the main fluid and the particle surfaces is weak and low temperature of the particles will reduce the reaction rates. The other is that the poor species transport will prevent the reactant to flow into the reaction region and the products cannot be taken away by the main flow timely, which will have a negative effect on the reaction. Thirdly, it is revealed that, the dimensionless variation of the residence time distribution (DVRTD) can reflect the heat/mass transfer and reaction performances, where a smaller DVRTD corresponds to better heat/mass transfer and higher reaction rates. [ABSTRACT FROM AUTHOR]

Clean energy storage is of vital importance for cleaner production and environmental protection. This present study focuses on the promotion of clean energy storage efficiency in the widely used shell and tube latent heat thermal energy storage unit. The enhancing effects of fin inside the tube on the charging time and energy storage rate are studied. Numerical investigations are performed through the enthalpy based lattice Boltzmann method couple with curved boundary. Three kinds of configurations for one-fin and two-fin are investigated. Results indicated that fin position can effectively impact the enhancing effects. For one-fin, the maximum difference of the enhanced ratio for different fin positions is 15.17% when R a = 107, while it is 7.52% for two-fin. The optimal fin position varies with different Ra , but with appropriate approximation, it can be concluded that one-fin on the bottom and two-fin on the vertical direction are the optimal fin position for one-fin and two-fin cases. In addition, one long fin shows better enhancing effects than two short fins. Under the same fin length, the average enhanced ratio for one long fin is 41.82%, while it is only 27.03% for two short fins. These results can provide guidance for the fin configuration in the shell and tube latent heat thermal energy storage unit to achieve higher energy storage efficiency. Since this unit is widely used in various clean energy storage systems, the results would also be beneficial for various industrial applications of clean energy storage and utilization. • The characteristics of energy storage process with fins inside tube are obtained. • The different enhancing effects caused by fin position can be as high as 15.17%. • One-fin on bottom and two-fin on vertical direction are the optimal fin position. • The average enhanced ratio for one long fin is 14.79% higher than two short fins. • The charging efficiency can be enhanced by 40% with proper fin configuration. [ABSTRACT FROM AUTHOR]

• A new simplified enthalpy based lattice Boltzmann model is proposed. • Heat source location can determine the charging and energy storage efficiency. • The exact optimal heat source location can be replaced by a small optimal region. • The optimal region decreases with the increase of Rayleigh and Prandtl numbers. • A map is provided to indicate the optimal region under varied conditions. The present study aims to fill the knowledge gap in the partially heated energy storage process by finding the optimal heat source location. A new simplified enthalpy based lattice Boltzmann method is proposed for the present work. The new model follows the predictor–corrector step, while the traditional model follows the collision-streaming step. Compared to the traditional model, this new model has the same accuracy, but it has advantages on virtual memory saving and physical boundary treatment due to its unique structure. Besides, in the partially heated energy storage process, the heat source location can pose significant impact on the charging efficiency and the energy storage rate. The optimal heat source location is where the maximum charging efficiency and energy storage rate are achieved. Results indicate that, a small region with the length of 0.1 l can be deemed as the optimal region for the heat source location, for that the charging time and the energy storage rate at various locations inside that region are almost the same. The optimal region decreases with the increase of Rayleigh and Prandtl numbers. In addition, the optimal regions for some specific heat source lengths and Rayleigh numbers are obtained. Based on these results, a map is provided to indicate the variations of the optimal region. According to this map, the optimal heat source locations for more varied conditions can be estimated through the heat source length and the Rayleigh number, which would be quite useful and significant for the thermal design in various engineering applications. [ABSTRACT FROM AUTHOR]