Search

Molten salt has been widely used in latent heat thermal energy storage (LHTES) system, which can be incorporated into hybrid photovoltaic/thermal solar system to accommodate the built environment. Solar salt (60 wt.% NaNO3 and 40 wt.% KNO3) was employed as the phase change materials (PCMs) in this study, and both aluminum oxide (Al2O3) nanopowder and metal foam were used to improve the properties of pure solar salt. The synthesis of the salt/metal foam composites seeded with Al2O3 nanopowder were performed with the two-step and impregnation methods, and the composite PCMs were characterized morphologically and thermally. Then pure solar salt, the salt/2 wt.% Al2O3 nanopowder and salt/copper foam composite seeded with 2 wt.% Al2O3 nanopowder were encapsulated in a pilot test rig, respectively, where a heater of 380.0 W was located in the center of the LHTES unit. The charging and discharging processes of the LHTES unit were conducted extensively, whereas the heating temperatures were controlled at 240 °C, 260 °C and 280 °C respectively. Temperature evolutions at radial, angular and axial positions were recorded, and the time-durations and volumetric mean powers during the charging and discharging processes were obtained and calculated subsequently. The results show that physical bonding between Al2O3 nanopowder and nitrate molecule has been formed from the morphological pictures together with XRD and FTIR curves. Slight changes are found between the melting/freezing phase change temperatures of the salt/metal foam composites seeded with Al2O3 nanopowder and those of pure solar salt, and the specific heats of the salt/Al2O3 nanopowder composite slightly increase with the addition of Al2O3 nanopowder. The time-duration of the charging process for the salt/copper foam composite seeded with Al2O3 nanopowder at the heating temperature of 240 °C can be reduced by about 74.0%, compared to that of pure solar salt, indicating that the heat transfer characteristics of the LHTES unit encapsulated with the salt/copper foam composite seeded with Al2O3 nanopowder can be enhanced significantly. Consequently, the mean volumetric powers of the charging process were distinctly enhanced, e.g., the volumetric mean power of heat storage can reach 110.76 kW/m3, compared to 31.94 kW/m3 of pure solar salt. However, the additive has little effect on the volumetric mean power of heat retrieval because of the domination of natural air cooling.

Energy pile is a kind of economic and efficient geothermal utilization technology that the ground heat exchanger (GHE) used in ground source heat pump (GSHP) is embedded into building pile foundation to realize heat exchange with surrounding soil. Adding phase change material (PCM) into the energy pile can not only reduce the temperature variation and thermal deformation range of energy pile, but also improve its energy storage and heat transfer performance. In this work, phase change concrete energy pile (PCCEP) is proposed by using PCM as a part of backfill material of energy pile. A three-dimensional numerical model is developed to find the influences of thermal properties of PCCEP on its thermo-mechanical behaviour. According to the model, the influences of thermal conductivity, phase change latent heat (PCLE) and phase change temperature (PCT) on the thermal performance and mechanical characteristics of PCCEP are numerically investigated. It can be seen that for improving heat transfer performance of PCCEP, the thermal conductivity should be increased, but from the perspective of reducing change of pile displacement, axial force and side friction resistance, the thermal conductivity should be reduced. Under heat release mode, lower PCT and larger PCLE contribute to the improvement of thermal performance of PCCEP, and accordingly the rise range of pile temperature, pile displacement change and pile thermal stress can all be reduced. The experimental validation on the model shows that the simulation values of pile wall middle temperature(PWMT) and pile top displacement are agreed well with the corresponding experimental results, the real-time relative error of PWMT and pile top displacement are respectively within 5.1 and 12%.

The use of nano phase change material in thermal energy storage applications appears promising, but the often-poor performance and the lack of understanding of the heat transfer mechanisms interconnectedness remains a challenge and hinders their widespread integration. The existing numerical work has unveiled numerous impediments in predicting the actual melting behaviour. They rarely combine the effects of conduction enhancement, convection degradation, and latent heat reduction, due to inaccurate characterization of the thermophysical properties and the limitations of their model assumptions. In the present study, an enhanced numerical approach was developed to investigate the melting performance of xGnP-octadecane filled in a vertical cylindrical enclosure at different weight concentrations. The model results for the pure phase change material were compared and validated against the experimental data. The progression of the melting front, temperature probes, energy storage capacity and heat transfer rate of the nano phase change material were thoroughly evaluated. The current numerical observations demonstrate that the addition of nanoparticles improves, up to a critical concentration of 0.5wt%, the melting rate. The results showed that by adding 0.5wt% of xGnP in the base phase change material (octadecane), the melting rate decreases by 9.7% and the heat storage rate increases by 12.6%. However, at higher loadings, the heat transfer rate is deteriorated due to worsening of other thermophysical properties provoking the prevalence of viscous forces over natural convection and latent capacity. The system overall efficacy was found to be dependent on the net effects of relative changes of all thermophysical properties with nanoparticle concentration and temperature in the solid, so called mushy, and liquid zones. Finally, when characterizing nano phase change material, the thermal conductivity cannot be considered alone as a criterion for nano phase change material selection. A high thermal conductivity is needed for maximum heat absorption in thermal transport applications. Nevertheless, low viscosity, high latent heat and specific heat capacities are also essential to ensure a better thermal energy storage efficiency in terms of capacity and heat extraction/release rate.

This paper introduces a kind of open cycle absorption heat wet flue gas heat recovery system, which use CaCl2 as the working medium. The system will use the wet heat recovery method and combined with an efficient heat pump system for flue gas as a heat source generator. Through direct contact with the solution in the absorber, the flue gas is going to carry out gas, liquid heat transfer between heat exchanger, realization of sensible heat and latent heat step by step. As the key part of the system, absorber is established by one-dimensional steady-state heat transfer and mass transfer model. This paper uses the finite difference method to model the discrete numerical methods, and analyzes the characteristics of heat and mass transfer in the absorber. We obtain the concentration curves of the three kinds of working medium's temperature and flow along the height direction. We also analyze the influence of CaCl2 solution parameters changes on the absorption process, parsing the reason of the temperature change by analyzing the three working medium's energy flow trend. We found that the temperature change of flue gas is non-monotonic, which decreases gradually in the range of absorption tower height 0–0.9 m, and then increases gradually. The reason for this change is that sensible heat exchange and latent heat exchange exist between flue gas and solution. Although such a change has an impact on the efficiency of the system, it prevents the "white smoke" from condensing in the air, which effectively protects the environment. Compared with conventional LiBr absorption heat pump, the system constructed in this paper has certain advantages in latent heat recovery, flue gas heat energy utilization, energy conservation and emission reduction and economy.

The outstanding advantages of methanol such as low pollutant emissions of nitrogen oxides (NOx) and carbon monoxide (CO) make it a promising clean-burning fuel. Despite, the latent heat of vaporization of methanol is 3.70 times that of gasoline, the low heating value of methanol is one of the most critical barriers to its effective utilization in industrial applications. Thus, the methanol burner needs to be effectively designed to determine the desired combustion characteristics and the optimal design of this type of clean burner. Hence, this study presents a computational fluid dynamic analysis on the combustion characteristics of a methanol swirling burner with two layers of swirling blades. A particular focus of this study is emphasized on the effects of different swirling blade angles (45°+45°, 60°+60°, and 45°+60°) and various equivalence ratios (0.5, 0.75, 1.0, 1.25, and 1.75) on the combustion characteristics and pollutants formation of the swirl burner. The velocity and temperature profiles, combustion characteristics, and concentrations of major combustion species are analyzed in detail. The results show that the blade angle arrangement of 45°+60° exhibits the best combustion characteristics in comparison with the other blade angle arrangements. It is also found that the BA3 with an equivalent ratio in the range of 1.0~1.25 shows the best performance in the emissions of NOx and CO compared with other combinations of swirling blade arrangements and equivalence ratios. More specifically, the optimal equivalence ratio ranges from 1.0 to 1.25 at which the NOx and CO emissions are measured to be 27.0 and 11.0 mg/m3, respectively.

Contamination and waste heat are major issues in water pollution. Aiming at efficient synchronous recovery wastewater and waste heat, we designed a novel CaCO3-based phase-change microcapsule system with an n-docosane core and a CaCO3/Fe3O4 composite shell. The system was fabricated through an emulsion-templated in situ precipitation approach in a structure-directing mode, resulting in a controllable morphology for the resultant microcapsules, varying from a peanut hull through ellipsoid to dumbbell shapes. The system has a significantly enlarged specific surface area of approximately 55 m2·g−1 with the CaCO3 phase transition from vaterite to calcite. As a result, the microcapsule system exhibits improved adsorption capacities of 497.6 and 79.1 mg/g for Pb2+ and Rhodamine B removal, respectively, from wastewater. Moreover, increase in the specific surface area of the microcapsule system with a sufficient latent heat capacity of approximately 130 J·g−1 also resulted in an enhanced heat energy-storage capability and thermal conductance for waste-heat recovery. The microcapsule system also exhibits a good leakage-prevention capability and good multicycle reusability owing to the tight magnetic CaCO3/Fe3O4 composite shell. This study provides a promising approach for developing CaCO3-based phase-change microcapsules with enhanced thermal energy storage and adsorption capabilities for efficient synchronous recovery of wastewater and waste heat.

Due to the rapid exploitation of fossil fuels, energy sources are becoming nonrenewable, and there is a need to develop other technologies to provide a clean supply of energy. The heat is stored in the thermal storage unit utilizing phase change materials in one of two ways: sensible heat or latent heat. When the temperature of phase change materials rises, energy stored in the perceptible form in the materials rises as well. While latent heat is stored during phase change of materials during the charging process and retrieved during phase change discharging at a virtually constant temperature during the discharging process. Latent heat has a large capacity to store a large amount of thermal energy per unit space. The use of phase change material (PCM) can be found in a variety of fields, including: • Improving the efficiency of photovoltaic cell. • Thermal storage of solar energy. • Waste heat recovery. • Engine cooling. • Building cooling to store energy during peak time and retrieving during requirement. The main drawback of PCM is its low thermal conductivity, which can be increased by incorporating fins and adding nanoparticles (to enhance heat transfer) in PCM. Our task in this study was to evaluate literature and develop applications for PCM, as well as to reduce PCM charging and discharging by boosting the rate of heat transfer.

Experimental work has been undertaken to improve the thermal conductivity of the Phase Change Material (PCM), Paraffin Wax (PW) by adding Alumina and Copper particles in increased mass fractions to elevate thermal energy storage efficiency. Composite PCMs of PW-Alumina and PW-Copper with 5%,10% and 15% mass fractions were prepared by sonication. Morphology of microstructures of PW and composite PCMs were examined using Scanning Electron Microscope (SEM). Thermophysical properties were measured using Standard testing methods. Latent heat and Specific heat were recorded with Differential Scanning Calorimeter (DSC). Thermal conductivity was tested using Two Slab Guarded Hot Plate apparatus. The results showed an improvement in thermal conductivity and latent heat of the composite PCMs. The enhancement ratio of thermal conductivity was 10% and 80% for PW-Alumina and PW-Copper composite PCMs respectively at 15 wt%.

Considering the significant threat of heat to electronic equipment and the heat dissipation problems existing in powerful systems, thermal management materials are in high demand. In conjunction with the increasing desire of dissipating heat and stabilizing temperature, high thermal conductivity and phase change latent heat are attracting more attention when designing thermal management material. This work proposes a strategy to combine phase change matrix and thermally conductive filler using freeze casting. The highest thermal conductivity reaches 23.1 W m-1 K-1 accompanied by 62 J g-1 phase change latent heat. Meanwhile, replacing ice with organic phase change material in freeze casting can result in an aligned structure. This discovery will pave a novel way for introducing thermal latent heat without abandoning the aligned structure.

Electric Vehicles (EVs) owing to their relatively low emissions and noise pollution are the most suitable alternatives for conventional vehicles. Lithium-ion batteries which are widely used in Electric Vehicles are meant to operate within a strict temperature range of 20 °C–50 °C Battery Thermal Management Systems (BTMS) plays a vital role in maintaining this temperature range, improving performance, service life and safety of the battery. Conventionally, there are two categories of BTMS, namely active cooling and passive cooling. Owing to the drawbacks such as power consumption and design complexities involved in active cooling, passive cooling techniques are increasingly gaining popularity. Passive cooling using Phase Change Materials (PCMs) are excellent candidates for BTMS application. PCMs have high latent heat and can absorb a large quantity of heat generated from the battery, with minimal change in temperature. Two PCMs (n-Docosane and Sodium Thiosulfate Pentahydrate) were chosen based on their properties such as melting temperature, Latent heat, Specific heat, Thermal Conductivity, Dynamic Viscosity and Density. This article also provides a methodology to optimize the usage of PCM for BTMS applications. While excess usage of PCM will add to the battery’s weight and also lead to ineffective use of PCM, using insufficient amount of PCM might lead to uncontrolled rise in cell temperature. This objective can be achieved by observing the trends of two specific output parameters – Mean Cell Temperature and Liquid Fraction derived from computational methods.

Latent heat thermal energy storage was widely used to solve the problem of the intermittency in time and space for solar energy systems. To improve the energy storage efficiency, metal fins were typically further added to the shell side to increase thermal conductivity of phase change materials (PCMs). However, the positive effect of metal fins on enhancing heat transfer has not been fully utilized. In this paper, a novel design on angled fins was proposed to improve the thermal transport for PCMs in a shell-and-tube thermal storage unit. A numerical model was built and verified by comparing with experimental observations on the melting front evolution and temperature history. Bending angles for fins ranging from 0° to 75° were designed upwardly and downwardly and quantified on the melting front shape and location, melting time, and temperature field. Results demonstrated that melting rates were improved for the angled-fin cases other than cases with large bending angles. The case with a 10° downward angle exhibited as much as 55.41% reduction in full melting time. Simultaneously, the temperature uniformity can be improved by 20.00%. The novel design strategy on fin angles engendered a promising solution to enhancing thermal storage for emerging engineering applications.

In the concentrating solar power generation (CSP), the latent heat thermal energy storage system (LHTES) is under the constraint of the outlet threshold temperatures, which caused lower effective utilization rate (Uma) of the phase change material (PCM). The objective of the present work is to improve the performance of the shell-and-tube LHTES which is under the constraint of the outlet threshold temperatures in charging and discharging processes. In this study, a transient, two-dimensional, and axisymmetric model of a shell-and-tube LHTES is established. Based on the model prediction, first, the sensitivity analysis of the geometry parameters to the performance of the LHTES shows that with the increase of the specific surface area and the porosity, the Uma monotonically increases, but the investment cost for LHTES per unit of stored heat (cTES) has a minimum value. Then based on the influence of the number and filling thickness of cascaded PCMs, a design criterion of the cascaded PCMs distribution is proposed for the shell-and-tube LHTES constrained by the outlet threshold temperatures, and the effectiveness of this design criteria is verified. Based on the proposed design criterion, the Uma of the optimal shell-and-tube LHTES with 5-cascaded PCMs can reach 77.6%, which is 3.1 times larger than that of a non-cascaded LHTES. Its cTES is only about 2/5 of a non-cascaded LHTES. The results of optimizing the geometry parameters of the TES device and the distribution of cascaded PCMs can be beneficial to the shell-and-tube LHTES which is under the constraint of outlet threshold temperatures in the real utilization of CSP.

Cryoablation is the most commonly used type of cryosurgery. Today, this treatment is insufficiently automated and therefore less accurate than alternative technologies that significantly limits and gradually reduces the scope of its application. However, from low temperature engineering point of view cryosurgery has the untapped potential of the improving its accuracy. In this paper three major methodological problems of cryosurgical equipment and procedure improving are considered: the impact on target isotherm location (1) of the soft biotissue moisture content solidification latent heat variation, (2) of the cryoprobe constructions and operating at maximum cooling power including the fluid cryogen features and the accuracy of boundary condition replacing a cryoprobe and (3) target isotherm fixation approach by modifying the cryoprobe operating mode. The numerical results showed that the target isotherm location depends insignificantly on different moisture content of soft biotissue, then it is not a limiting factor for cryoexposure prediction. Also numerical results showed that the theoretically minimum temperature of cryoprobe surface significantly overestimates their movement, this leads to a significant difference between the experimental and simulation results. The typical shape and movement of cryonecrosis isotherm at refined maximum cryoprobe cooling power for two typical constructions of cryoprobes and two cryogens are presented. The novel algorithm of modifying the cryoprobe operation mode for controlled precision cryosurgery is proposed and validated. All this complements the previously obtained data and shows the prospects for performing precision cryosurgery. The total average uncertainty of target isotherm location during the studied preliminary predicting stage of temperature field movement (virtual cryoablation) is estimated no more than ±0.41 mm. This information is expected to be useful for improving the quality of cryosurgery planning algorithms (e.g. for tumor treatment).

The economic and industrial development of any nation depends on energy. To fulfil the future energy requirements, it is very necessary to switch over the renewable energy sources for energy generation. Among all the renewable energy sources solar energy can effectively convertible to the other forms of energy but the major drawback is that it is only available during the day time and if it needs to be utilised during the night-time, the only option is to store it during the day time when it is abundantly available. Several techniques have been introduced for the storage of solar thermal energy and there are three basic ways to store the solar thermal energy i.e. in the form of sensible heat, latent heat and thermochemical heat. The main objective of the present work is to compare different energy storage techniques which resulted that a metal hydride based thermochemical energy storage (MH-TCES) system is more suitable. In addition, it enlightens on the selection of working materials for MH-TCES.

In this study, a dual-source solar-heat pump latent heat thermal energy storage system for hot-water supply was proposed to take advantage of renewable energy sources. An experimental setup mainly consisting of a solar heat collector with a gross area of 2 m2 and an air-source heat pump with a maximum capacity of 2 kW was established to evaluate the adaptability of the phase-change material to the solar-heat pump and the feasibility of the heating system. A comparative study was carried out to investigate the effects of the operation modes on the system thermal performance and explore optimal operating parameters. Compared to the single heating mode, the overall efficiency of the system was enhanced by about 57.5% under the combined heating mode due to the introduction of solar energy. The coefficient of performance of the heat pump significantly increased from 2.09 to 2.60 when the flow rate increased from 0.010 L/s to 0.038 L/s. However, an increase in the flow rate could not significantly improve the overall efficiency of the entire heating system due to the higher power consumption of the pump. The storage unit exhibits a great storage density of about 211.13 MJ/m3 with a volume saving rate of 21%.

To overcome the leakage of phase change materials (PCMs) above melting temperature, PCMs are commonly encapsuled by chemically crosslinked networks, which bring the issues of reparability, reprocess-ability and recyclability making for the environment pollution and resource waste. Herein, a reversible aromatic disulfide is adopted to form dynamic epoxy networks which not only encapsulate polyethylene glycol (PEG) as the shape-stabilized PCMs (SSPCMs) but also address the issues about the un-recyclability of traditional SSPCMs. The PEG was well encapsulated and uniformly dispersed in disulfide-based epoxy due to the elaborate molecular design. The obtained SSPCMs (named EXAP2) shows typical solid–solid phase transitions characteristic and thermal reliability with high latent heat value of 82.7 J/g. Besides, the EXAP2 exhibit dynamic performance and can be reprocessed by hot press via the disulfide bonds exchange reaction above topology freezing temperature (Tv). And the reprocessed EXAP2 exhibits close phase change properties with the original sample, implying the reprocessing does not affect the crystalline structure and encapsuling capability of disulfide crosslinked networks. This strategy prove a significant way for fabricating the novel SSPCM with recyclability, reprocessability and reliability.

Heat storage efficiency is required to maximize the potential of combined heat and power generation or renewable energy sources for heating. Using a phase change material (PCM) could be an attractive choice in several instances. Commercially available paraffin-based PCM was investigated using T-history method with sufficient agreement with the data from the manufacturer. The introduced LHTES with cylindrical capsules is simple and scalable in capacity, charging/discharging time, and temperature level. The overall stored energy density is 9% higher than the previously proposed design of similar design complexity. The discharging process of the designed latent heat thermal energy storage (LHTES) was evaluated for two different flow rates. The PCM inside the capsules and heat transfer fluid (HTF) temperature, as well as the HTF flow rate, were measured. The lumped parameter numerical model was developed and validated successfully. The advantage of the proposed model is its computational simplicity, and thus the possibility to use it in simulations of a whole heat distribution network. The so-called state of charge (SoC), which plays a crucial role in successful heat storage management, is a part of the evaluation of both experimental and computational data.

Corrosion is regarded as one of great challenges for the application of salts-based phase change materials. To address such problem, a novel skeleton of modified diatomite-based porous ceramic was used to load NaNO3 salt and develop shape-stabilized NaNO3. Particularly, thermophysical properties of composites with skeletons of unmodified and modified diatomite-based porous ceramics (UM-DC and M-DC4) were analyzed. The results showed that these two skeletons effectively prevented NaNO3 from leakage and were chemically compatible with NaNO3. Shape-stabilization of NaNO3 using porous ceramic hardly changed phase transition temperature, but decreased latent heat and enhanced thermal stability. M-DC4 possessed a capacity to load 58.67 wt% salt, nearly 10 wt% higher than other porous ceramics. Compared with NaNO3/UM-DC, NaNO3/M-DC4 performed a higher thermal energy storage density and efficiency of 382.92 J/g and 58.71%, respectively, within 130–330 °C. Importantly, NaNO3/M-DC4 exhibited much better cycling stability during 500 thermal cycles, benefited by the improved micro-flow of molten salt in M-DC4; while NaNO3/UM-DC appeared crack after 100 thermal cycles. Accordingly, the novel skeleton could greatly enhance thermophysical properties of shape-stabilized NaNO3. Such composites could be easily integrated into solar thermal energy storage system. This work proposed a new strategy for the application of salts-based phase change materials.

Nowadays, thermal conductivity as a key parameter affecting the thermal performance of PCM has attracted much attention. However, the thermal performance evaluation of ultra-high thermal conductivity PCM is scarce, especially in field of building energy conservation. Therefore, we traversed the range of thermal conductivity that can be prepared at present and within the expected time frame, which is 0.08–49.28 W ⋅ m − 1 K − 1 . In addition, a novel index, Utilization Rate of Latent Heat (URLH), was proposed to evaluate matching degree between PCM and a certain application background in buildings, so as to explore the reason of poor energy-saving effect of PCM under some application backgrounds. We found that the thermal conductivity of PCM is not the higher the better in buildings, in other words, a turning point appears. The optimal thermal conductivity is about 0.6 W ⋅ m − 1 K − 1 and when the value is lower than 0.3 W ⋅ m − 1 K − 1 , URLH is equal to 0 in the cases of Shanghai. Therefore, we recommend PCM researchers to evaluate the URLH before using PCM to avoid the ineffective use of materials. Through the analysis of URLH, researchers can know the specific parameters that affect the thermal performance of PCM and obtain the way to optimize them.

Circumventing ice formation is critical to successful cryopreservation by vitrification of large organs. While ice formation during the cooling part of the cryogenic protocol is dictated by the evolving thermal conditions, ice formation during the rewarming part of the cryogenic protocol is also dependent on the history of cooling and storage conditions. Furthermore, while the exothermic effect of ice crystallization during cooling tends to adversely slow down the desired high cooling rates to ensure ice-free preservation, the same effect under some conditions tends to assist acceleration of rewarming during recovery of the specimen from cryogenic storage when limited crystallization does occur. The current study proposes a computational framework to study the thermal effects of crystallization during recovery from cryogenic storage, using a semi-empirical approach to account for the relationship between latent heat effects and the rewarming rate. This study adds another layer of computational capabilities to a recent study investigating similar effects during cooling. Results of this study demonstrate that the thermal effects of crystallization on the local cooling and rewarming rates cannot be neglected. It further explains how crystallization during rewarming helps in increasing the rewarming rate and, thereby, affects rewarming-phase crystallization. Counterintuitively, this study suggests that the fastest possible rewarming rate at the outer surface of the domain in an inwards rewarming problem is not always advantageous, while the proposed computational tool is essential to find an intermediate optimal rate.

This study aims to analyze the effect of fin geometry on the thermal performance of longitudinally finned-tube horizontal latent heat thermal energy storage (LHTES) systems. The longitudinal fins with different fin heights, thickness, and numbers were applied in the horizontal shell-and-tube LHTES system and the paraffin was packed in the annulus. The melting fronts, average temperature, and velocity profiles of Phase Change Material (PCM) were graphically illustrated and compared for charging processes. It was found that the incorporation of longitudinal fins in a small quantity (2.85% of total volume) could reduce the complete melting time by 34% in comparison to the bare-tube configuration. Melting characteristics were compared using average liquid fraction, average PCM temperature, and stored energy. It was recommended that the fin height should not exceed half of the annulus gap. The optimum fin volume was identified by comparing the enhancement ratio for examined configurations. Furthermore, for the same fin volume configurations, this study evaluated (i) whether a large number of short fins are beneficial or a smaller number of long fins and (ii) whether thick short fins are beneficial or thin long fins? Comparison results showed that a small number of long fins were more beneficial than that of more short fins and the melting characteristics of thin long fins were superior to that of the thick short fins. Finally, the optimum fin configuration was justified, and the priority sequence was suggested for the design of longitudinally finned-tube energy storage systems.

Graft phase change materials (GPCMs) networks with pendent side chains of phase change component trend to simultaneously enhance the encapsulation fraction and latent heat efficiency, leading to ultrahigh latent heat, compared to backbone phase change materials (BPCMs) networks with skeleton chains of phase change component. Herein, the GPCMs networks containing graft polyethylene glycol (PEG)-based side chains were synthesized via a facile high efficiency esterification approach between hydroxyl and anhydride as well as between resulting carboxyl and aziridine ring. The GPCMs had much higher normalized latent heat (from 122.6 kJ/g to 157.6 kJ/g) and latent heat efficiency (from 0.76 to 0.93) than BPCMs (from 79.3 kJ/g to 130.6 kJ/g and from 0.49 to 0.77) networks counterparts with various molecular weight (from 2 kDa to 20 kDa) of used PEGs. Also, GPCMs could reach experimental latent heat of 155 J/g with ultrahigh PEG weight fraction of 98.8% and high latent heat efficiency of 0.93 resulting from the promoted crystallization, while GPCMs showed good solid-solid phase change behavior, high thermal reliability and stability, which could not be realized in conventional BPCMs. The synergetic enhancement of PEG weight fraction and latent heat efficiency in GPCMs is due to the decreased non-PEG components and the existence of free molecular end of PEGs in GPCMs. The efficient strategy of constructing graft side chains of PEGs can enable an obvious increase in both PEG weight fraction and latent heat efficiency in solid-solid PCMs network, further leading to a significant increase in latent heat.

The current work investigates the performance of charging and discharging cycles of phase-changing material encapsulated inside spherical balls required for latent heat thermal energy storage of wa...

In order to solve the phase separation problem of Na2S2O3·5H2O–CH3COONa·3H2O PCM (phase change material), sodium carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), xanthan gum (XG), sodium polyacrylate (PAAS) and polyacrylamide (PAM) were selected as additives. The effects of different proportions of the above thickeners on the supercooling degree, phase separation, phase change temperature and latent heat of Na2S2O3·5H2O–CH3COONa·3H2O system were studied by using the cooling curve and DSC, so as to screen the best thickener for eutectic PCM. The experimental results show that CMC, XG and PAAS can eliminate the phase separation of Na2S2O3·5H2O–CH3COONa·3H2O. Among them, the optimal ratio of CMC, XG and PAAS is 3 mass%, 3 mass% and 1 mass%, respectively. From the perspective of heat storage performance, PAAS is the optimal thickener for Na2S2O3·5H2O–CH3COONa·3H2O. The phase change temperature is 40.5 °C. The subcooling degree is about 14.7 °C, and the latent heat is about 221 J g−1. The melting time is 15 min. Only PAAS can make Na2S2O3·5H2O–CH3COONa·3H2O eutectic PCM completely exothermic at room temperature, which can not only play the role of thickener to eliminate phase separation, but also is a nucleating agent. After 100 melting-solidification cycles, the change rate of latent heat value was only 5%, and the change rate of phase transition temperature was less than 1%. Considering heat storage performance and cyclic stability, PAAS is the optimal thickener for Na2S2O3·5H2O–CH3COONa·3H2O PCM.

In the present contribution, the authors investigate the peculiarity of Phase Changing Material for accumulating heat in the region equivalent to the hilly area by creating its atmosphere, having 20˚C DBT and 18˚C WBT. A water cooler is used in 5*7 feet bathroom to conceive the above-intimated temperature, measured by a sling psychrometer. In particular, in this study, trials are carried out in the LHTES tank where water is charged from ambient temperature to 55˚C with the aid of an Immersion water heater rod of 1000W,230V thereby liquifying PCM and then discharging to ambient temperature. Two Orientations namely, Circular and Cross are appropriated into the study, where Circular Orientation poses better results articulating the charging in an hour and discharging in 25 long hours, whereas Crossed Orientation represents charging in an hour and discharging in 23 hours. The volume of PCM and the net heat transfer surface have been kept constant in both cases, to compare them in the same operative conditions. The reason for the detour is manifested.

Nanocapsules with poly(methyl methacrylate e-co-methacrylamid) wall and n-dodecanol and 1-tetradecanol cores were fabricated using emulsion polymerization processes which were defined as one-stage and two-stage. The energy storage capacity of the encapsulated n-dodecanol was in the range of 155 to 159 j/g while the tetradenanol capsules could store energy in the range of 166 to 175 j/g. The wall of the capsules exposed to two-stage decomposition, and the thermal degradation temperature of the nanocapsules prepared using the two-stage process increased. It was concluded that thermal and chemical resistance of the nanocapsules could be improved slightly using two-stage emulsion polymerization method. In the study, the nanocapsules were applied to the chemically modified cotton fabrics using pad-dry-cure method. The homogeneous distribution of the nanocapsules on the fabric surface and their durability after repeated 20 times washings were confirmed by SEM images. The washing durable thermo-regulating property of the fabrics was revealed by T-history test.

Thermal energy storage (TES) associated with phase change materials (PCMs) is an effective way to conserve the waste heat and convert other energy sources for storage and reuse in the form of latent heat. With the superiorities of high energy storage density and low or negligible supercooling, organic PCMs have been extensively investigated as an advanced TES technique, whereas their inherent leakage and low thermal conductivity greatly hinder their applications. Integrating functional component with organic PCMs is considered as a promising route to fabricate phase change composites for energy conversion and storage. In this chapter, recent advances in solid–liquid and solid–solid polymeric phase change composites with improved shape stability and thermal conductivity are presented. We put emphasis on the processing technologies covering micro/nanoencapsulation, physical blending and porous supporting scaffold, and emerging applications involving energy conversion, thermal management, smart textile, and shape memory devices. Finally, the limitations and future innovations of the high‐performance polymeric phase change composites are discussed.

To address the problem of heat removal by phase change material (PCM) wall at nighttime in the summer season, a new cooling wall that makes use of the high latent heats of PCMs, the high heat conductivities of micro-channel heat pipes (MHPs), and the passive cooling of sky radiative cooling (RC) is introduced, and is named the MHP-RC-PCM wall. In this study, preliminary experiments were first conducted to determine the emissivity of the radiative plate and the properties of PCMs (paraffin, RT28HC). Next, numerical models of the MHP-RC-PCM wall were established to simulate the thermal behavior, and the model was validated with the experimental results. The parameters that affect the thermal behavior of the MHP-RC-PCM wall, including the phase transition temperature, latent heat of the PCM, number of MHPs, and year-round thermal behavior were investigated. The results showed that the phase transition temperature (Tm) of the PCM had a significant influence on the interior surface temperature, liquid fraction and cooling load reduction ratio of the MHP-RC-PCM wall, whereas the PCM latent heat had little effect. The cooling load reduction ratio was approximately 4% for Tm = 31 °C, which was higher than that for Tm = 26 °C. In addition, it was determined that the year-round energy-saving of the MHP-RC-PCM wall were approximately 18.2% greater than that of the Brick wall with the same thickness, and 0.4% higher than that of PCM wall in Guangzhou City, China.

The use of solar thermal technologies has shown great prospects towards solar energy conversion into more useful forms of energy and has increasingly expanded solar thermal technology applications. However, the inability to properly store the excess solar energies during peak hours and demands have limited many of their applications. The integration of thermal energy storage (TES) systems with thermal technologies have increased the solar thermal technology performance but the poor thermal characteristics exhibited by phase change materials (PCM) limited the system overall performance. The enhancement of PCM properties by nonadditive have shown increased material performance in TES application and thereby extending the use of solar thermal technology application. Given this narrative and identifies literature gaps, the present study investigated experimentally the enhancement of paraffin PCM using nonadditive metallic of different types and concentrations and analysed their thermal behaviours. The results showed that Cu/paraffin PCM nanocomposites had good thermal reliability in proposed applications even after 150 thermal cycles under different temperatures. Moreover, thermal conductivity was improved significantly as an enhancement of 39% was reported when adding 2.5% of Cu nanoparticles. While specific heat and thermal diffusivity has been enhanced by 16% and 9%, respectively compared to pure paraffin. The obtained results were compared with different theoretical models such as Maxwell mode, Hamilton Crossover model, Jeffery model, and Bruggeman model. The calculated values show a good agreement with experimental ones. As a result, the prepared Cu/Paraffin nanocomposite PCM shows significant promise in thermal energy storage application due to its favourable phase change temperature, comparatively large latent heat, enhanced thermal conductivity and high thermal reliability and conversion. The proposed nanocomposite PCM can be used in many applications such as building materials to reduce interior temperature swings, enhance thermal comfort, and conserve electricity consumption.

Although renewable energy systems have become an interesting global issue, it is not continuous either daily or seasonally. Latent heat energy storage (LHES) is one of the suitable solutions for this problem. LHES becomes a basic element in renewable energy systems. LHES compensate for the energy lack when these systems are at low production conditions. The present work considered a shell and tube LHES for numerical investigation of the tube rotation influence on the melting process. The simulation and calculations were carried out using ANSYS Fluent software. Paraffin wax represents the phase change material (PCM) in this work, while water was selected to be the heat transfer fluid (HTF). The calculations were carried out for 9 rpm tube rotation case as well as the stationary case. The results show a slight increase in the liquid content of phase change material PCM due to tube rotation. The enhancement percentage in liquid content was 3.5% for 6 hrs charging process. The heat transfer in the axial direction was small relative to that in the radial direction.

Being a novel energy storage medium, ice slurry has the advantage of good fluidity, high latent heat and heat transfer efficiency, which has a broad application prospect. In this work, the ice making characteristics of different types of additives (MgCl2, ethylene glycol and magnetic iron oxide nanoparticles) in a binary ice system by vacuum flash evaporation under the action of solid adsorption were experimentally investigated. Subcooling, flash rate, ice packing factor, latent heat and thermal conductivity were measured to evaluate the performance of ice production. The results showed that 0.075% wt of iron oxide nanoparticles and 1% wt of MgCl2 are more suitable to be used as additives for binary ice preparation than ethylene glycol, with the former outperforming the latter. Under optimal conditions, compared with pure water for ice making, the subcooling degree of iron oxide nanofluid was reduced by 55.80%, and the thermal conductivity and ice packing factor were increased by 98.80% and 54.22%, respectively. The subcooling degree of the MgCl2 solution was reduced by 37.52% and the ice packing factor was improved by 59.51%. Meanwhile, DSC tests showed that the latent heat of the nanofluid was almost independent of the nanoparticle concentration. However, the increase of MgCl2 solution would cause the decrease of latent heat. In addition, high concentrations of additives can inhibit ice crystal nucleation and growth, but a certain concentration of additives facilitates ice crystal refinement in vacuum ice making process, which is conducive to the transportation of ice slurry.

A 3D finite-element thermal model has been developed to estimate weld geometry and analyze thermal gradients and cooling rates in pulsed laser welding of Inconel 718 superalloy. Since Inconel 718 superalloy is sensitive to hot cracking, the extent of hot crack sensitive areas including heat affected zone, mushy zone and partially melted zone is very important in the investigation of weldability for this alloy. Because the welding process is very fast and the welding width is very thin, the numerical modeling approach can be very helpful to overcome the difficulties and limitations of experimental procedure. In this study, a finite element model is presented to simulate the process of pulsed laser welding of Inconel 718 and to predict the temperature distribution and shape of the weld pool and finally to estimate the extent of the hot cracking sensitive regions. Heat source was modeled by the combination of conical Gaussian and ellipsoid Goldak. Then, the results of numerical model were compared to the experimental results at preheat temperatures of 308, 393, 473 Kelvin. The proposed numerical model exhibits good agreements with the experimental results including the internal and external weld pool geometries and the extent of the hot cracking susceptible regions. Furthermore, detailed pulsed temperature distribution and thermal cycle containing solidification latent heat are obtained. Accordingly, this pulsed temperature history is correlated to the internal and external geometry of pulsed solidified weld pool.

Using an infrared camera, we measured the latent heat of the first order phase transition in lead scandium tantalate at different applied electric fields. The entropy change value of 3.4 J kg−1 K−1 is consistent with differential scanning calorimetry measurements. The advantage of such an approach stems from the possibility to obtain both adiabatic temperature change and latent heat of the phase transition material only with an infrared camera or a thermocouple. This may prove useful for a systemic characterization of first order electrocaloric materials.

The glass system 22SiO2- 23Bi2O3-37B2O3-13TiO2 $$-(5-x)$$ LiF- $$x$$ BaO $$, (0\le x\le 5) \text{m}\text{o}\text{l}.\text{\%}$$ . was fabricated using melt-quenching techniques. X-ray diffraction and ultrasonic techniques were used to characterize the glasses. X-ray diffraction patterns were used to prove that fabricated glasses are amorphous. The impacts of incorporating BaO on the composition dependence of the elastic characteristics of fabricated samples were explained. Density of the manufacture glasses increment, and molar volume reduced. The elastic moduli were investigated experimentally then compared using theoretical arguments. Makishima – Mazinize model were used to determine the elastic moduli theoretically for fabricated samples. Elastic moduli increase with BaO, and experimental and theoretical elastic moduli are in good agreement. Deviation values between elastic moduli (both experimentally and theoretically) were estimated. All the experimental variations values of elastic moduli of fabricated glasses were increment as BaO increased. Latent heat of melting, diffusion constant, and Gruneisen factor have been used to link the mechanical and thermodynamic characteristics of manufactured glass.

The experimental thermal characterization during charging and discharging of a prototype compact latent heat thermal energy storage system (LHTESS) with an embedded horizontally oriented finned mul...

The development of high-performance form stable phase change materials (FSPCMs) with higher optical absorbance and phase change enthalpy is of great significance to building energy conservation. A kind of Ti3C2/pectin aerogels was prepared by self-assembly of pectin and MXene nanosheet (Ti3C2) by solution blending method. These aerogels were directly dipped in the molten dodecylamine (DDA) as the phase change material. The results show that the PCM composites with 3 wt% Ti3C2 have a phase change temperature of 25.47 °C (at which the human body feels comfortable), latent heat of phase change of 218.8 kJ kg−1, and thermal conductivity of 0.1817 W/(m K). The prepared FSPCMs have the characteristics of suitable phase change temperature, high latent heat, good melting/freezing cycle reliability, strong mechanical properties, significant photothermal energy conversion capacity (more than 92%), and good thermal insulation performance. Therefore, the corresponding pectin-based composites with better light absorption and mechanical properties are expected to have broad application prospects in energy conversion and building energy conservation.

Efficient thermal management is crucial for enhancing the performance and reliability of electronic devices. In this regard, flow boiling with microchannels promises high heat dissipation capability for a nominal temperature budget as it inherently takes advantage of high latent heat of vaporization along with high surface-area-to-volume ratio. However, the promise of high heat dissipation in flow boiling microchannels is limited by two-phase flow instabilities which cause large-amplitude temperature and pressure fluctuations. The current state-of-the-art thermal management techniques for enhancing heat transfer during flow boiling in microchannels operate in steady-state condition and provide sufficient continuous cooling to address the peak thermal loads. While such approaches can manage the thermal challenge, they result in significant cooling overdesign. To eliminate the overdesign, we introduce an adaptive vapor venting strategy which continuously adjusts to the varying vapor generation across different heat fluxes to completely mitigate two-phase fluctuations. Our results demonstrate that significant transient temperature fluctuations (±5 °C) in the conventional microchannels were completely eliminated with the incorporation of the adaptive vapor venting (within the experimental uncertainty). Furthermore, our results show that this strategy has the capability to handle transience and accordingly avoid the need for cooling overdesign.

The hydrated salt disodium hydrogen phosphate dodecahydrate (DHPD, Na2HPO4·12H2O) has a suitable phase transition temperature and high latent heat of phase transition. Still there are problems such as supercooling, phase separation, and low thermal conductivity. In this paper, DHPD, sodium carboxymethyl cellulose (CMC), aluminum oxide (Al2O3), and poly(vinylpyrrolidone) (PVP) are used to configure DHPD-CAP to suppress supercooling and phase separation successfully. Multiwalled carbon nanotubes (MWCNTs) are used to stabilize DHPD-CAP phase-change materials and improve the thermal conductivity of pure DHPD. Further studies show only a physical interaction between MWCNTs and DHPD, and no new phases are generated. The addition of MWCNTs can also promote the nucleation of the DHPD-CAP composite, and the corresponding latent heat of phase change shows a trend of increasing and then decreasing with the increase of MWCNT content. Compared with DHPD after one cycle, the latent heat of DHPD-CAP/MWCNT4 increases by 36.19%. With the addition of MWCNTs, the thermal stability of the composites is improved compared to pure DHPD. The DHPD-CAP/MWCNT4 composite has good stability after many cycles.

The solution absorption system has great potential for recovery of water and latent heat from industrial gas. However, few investigations have been conducted on the synergistic removal of SO2 and the treatment of the associated precipitation when the method is applied for flue gas from coal-fired power plants. To solve this problem, a falling-film reaction platform was established and the CaCl2 solution was chosen as the liquid desiccant. The effects of solution temperature and concentration, solution pH, O2 content and catalyst concentration on the efficiency of SO2 removal were investigated. The solubility of the CaSO4·2H2O precipitates in the CaCl2 solution was measured. The results revealed that the precipitated component was influenced by the O2 content. The decrease in solution pH was responsible for the decrease in the efficiency of SO2 removal. The highest SO2 removal efficiency of 95.6% was obtained during the operation of solution circulation in this experiment. In addition, the solubility test showed that a higher temperature, a lower concentration and the addition of Ca(OH)2 were conducive to reducing the solubility of the CaSO4·2H2O precipitate in CaCl2 solution.

Well-integrated thermal energy storage units can enhance flexibility and profitability for a cogeneration system by enabling its decoupling of electricity and heat production. In the present study, novel latent heat thermal energy storage technologies are numerically investigated on their thermal and economic performance to evaluate their implementation at an existing combined cycle power plant. Three commercially available storage designs are analyzed: one shell-and-tube heat exchanger design based on planar spiral coils, and two types of advanced macro-encapsulated designs with capsules resembling ellipsoid and slab in shape, respectively. For the spiral coil design, three-dimensional flow velocity and temperature fields are simulated with finite volume method to predict the transient storage heat transfer process, including the effect of secondary flow induced by centrifugal forces. For the macro-encapsulated designs, effective heat transfer coefficients between heat transfer fluid (HTF) and phase change material (PCM) are inferred from scaled-down storage prototyping and testing. A one-dimensional two-phase packed bed model was developed based on the apparent heat capacity-based enthalpy method to numerically study the heat transfer in macro-encapsulated PCM. With an operating temperature range of 46–72 °C and a HTF supplying flowrate range of 4.2–8.4 m3/h defined by the cogeneration strategy, thermal power and accumulated storage capacity are calculated and compared for the first three hours of charge and the first hour of discharge for the three designs. The effect from increasing the HTF flowrate to accelerate charging/discharging processes is indicated by the simulation results. Performance comparison among the three designs shows that the slab capsule design exhibits the highest accumulated storage capacity (710 kWh) and state of charge (40%) after three hours of charge, though it has a lower theoretical total storage capacity (1760 kWh) than the spiral coil design (1830 kWh). The ellipsoid capsule design shows a slightly lower accumulated storage capacity (700 kWh) than the slab design for 3-hr charge and an equivalent accumulated storage capacity/depth of discharge (250 kWh/14%) as the latter. Furthermore, the storage power cost of the slab capsule design is the lowest, by 6–12% lower than the spiral coil design and by 2–3% lower than the ellipsoid capsule design. However, with the highest design flowrate of 8.4 m3/h, the low state of charge (below 40%) after three hours and the low depth of discharge (below 14%) after one hour indicate that redesigning the heat transfer boundary conditions and the configurations of the three units are necessary to meet desirable storage performance in cogeneration applications.

In joining of aluminum alloy to hot-dip galvanized (GI) steel by arc welding-brazing process, evaporation of zinc (Zn) layer and formation of brittle Fe Al intermetallic compound (IMC) layer can affect the joint quality both thermally and metallurgically. At this point, the alternate current pulse gas metal arc welding (AC pulse GMAW) process is an excellent joining method because of its relatively low heat input to the base metal by controlling the electrode negative polarity (EN) ratio in its current waveform. In this study, a numerical analysis of joining 1.2 mm-thick GI steel to 1.2 mm-thick AA5052 aluminum alloy in the lap configuration using AC pulse GMAW was conducted to determine the effect of the EN ratio and Zn evaporation on joint quality. Based on the finite element method (FEM) 3D heat transfer model, the heat conduction analysis and the estimation of the IMC layer growth at the joint interface were carried out. The calculated results were validated with the corresponding experimental results and demonstrated a fair agreement. The results indicated that the temperature-dependent Zn mass evaporation and the increased EN ratio decrease the heat input to the joint interface. In particular, the heat loss caused by Zn evaporation with its latent heat restricts the growth of the brittle Fe Al IMC layer, which follows a function of temperature variation per unit length and time, by decreasing the heat from the arc to the joint interface. A 7.83 μm-thick IMC layer was obtained at a welding current of 55 A with an EN ratio of 20%, and a sound dissimilar material joint was achieved.

The applications of salts-based phase change materials (PCMs) are greatly restricted by their corrosion to containers and low thermal conductivity. To address these issues, a modified diatomite-based porous ceramic (MDPC) was prepared to shape-stabilize KNO3 salt in this paper. Particularly, effects of graphite content on the pore structure of diatomite-based porous ceramic (DPC) and MDPC on the thermophysical properties of shape-stabilized KNO3 were investigated. The results showed that 30 wt% graphite increased apparent porosity of DPC up to 67.21% and enlarged average pore diameter from 0.71 to 3.58 μm, while weakened its compressive strength from 19.12 to 5.51 MPa. The MDPC effectively prevented leakage of molten KNO3 to avoid its corrosion problem, and possessed an excellent chemical compatibility with KNO3 salt. Additionally, the MDPC hardly changed phase transition temperature of shape-stabilized KNO3, while increased latent heat of composites from 51.70 to 60.21 J/g due to its higher apparent porosity. The MDPC was also shown to enhance thermal conductivity of shape-stabilized KNO3 from 1.16 to 1.52 W/(m·K) at 25 °C, which was attributed to that the MDPC with a larger pore size was more easily infiltrated by molten salt, contributing to a lower apparent porosity of composites. Compared with pure KNO3, thermal conductivity and thermal stability of shape-stabilized KNO3 were seen to be significantly improved by 238% and 60 °C, respectively. This work therefore solved two key challenges for the application of KNO3 salt, and proposed an effective way to improve thermophysical properties of such heat storage material.

The use of phase changing materials (PCMs) for energy storage has been in the focus of scientific research for a while, primarily focusing on building cooling/heating applications due to favourable melting temperature ranges. In this paper we simulated the suitability of encapsulated Paraffin Wax on a small scale in a low temperature thermal energy storage system using COMSOL Multiphysics. Heat absorption and heating dynamics were analysed for different inlet designs and velocities, and the thermal gradient was evaluated across the tank geometry in a number of charging scenarios. Results show that paraffin wax proves to be a good storage medium based on its fast charging and good latent heat absorption. The study found that although an addition of a second inlet to the system yields higher final temperatures and improves the heat transfer rate, it does so minimally and therefore is not notably beneficial. Both designs follow the same heating dynamics independently on the final temperatures. Lastly, higher or lower velocities benefit the system based on the design.

The latent heat thermal energy storage unit (LHTESU) strengthened by metal foam can effectively store solar energy and realize the sustainable utilization of solar energy. In this paper, the metal foam with a two-dimensional (radial and circumferential direction) porosity gradient is proposed for the problem of slow melting rate and non-uniform melting in the horizontal shell-and-tube LHTESU. The non-uniform index and thermal energy storage rate are introduced to evaluate different metal foam structures. Under the same amount of metal foam, the influence of one-dimensional and two-dimensional graded structures is numerically studied. The results show that circumferential graded structure can alleviate the non-uniform melting problem. Compared with the uniform structure, the non-uniformity index decreases by 36.63% and the thermal energy storage rate is increased by 38.60%. In addition, the optimum circumferential porosity gradient also increases with the increase of Ra*. The strengthening effect of the circumferential and radial graded structures is also compared. It can be found that with the increase of porosity gradient, the strengthening effect of the circumferential graded structure increases gradually and that of radial graded structure first increases and then decreases. When the circumferential graded structure is combined with the radial graded structure, the two-dimensional porosity gradient structure can further improve the thermal performance of LHTESU. Compared with the uniform structure, the thermal energy storage rate can be increased by 47.40%.