Thermal Energy Storage Performance Research Articles

Insights into effect of lignocellulosic biomass framework types on bio-based shape stable composite phase change materials

The utilization of biomass waste as framework materials to inhibit the leakage of phase change material (PCMs) has gained widespread attention. In this work, three new kinds of shape stable composite phase change materials (sscPCMs) were prepared which combined with stearic acid (SA) and peanut shell powders (PSP), poplar wood powders (PWP), and corn straw powders (CSP), respectively. The influence of lignocellulosic biomass types on the thermal energy storage performance of sscPCMs was studied by comparing three types of sscPCMs. The research results indicated that SA/CSP exhibited superior properties in terms of load capacity and thermal energy storage performance. According to leakage experiments the load capacity of SA/PSP, SA/PWP and SA/CSP was 31.67 %, 44.69 %, and 50.09 %, respectively. The phase change latent heat of SA/PSP, SA/PWP, and SA/CSP was 55.78, 84.27 and 98.47 J/g, respectively. In addition, the relationship between biomass component content and load rates was studied. The results showed that there was a positive correlation between the loading rates of SA and the ratio of holocellulose (cellulose + hemicellulose) to lignin. The results provided a promising approach for the selection of lignocellulosic biomass framework materials.

Machine-learning-assisted long-term G functions for bidirectional aquifer thermal energy storage system operation

Optimization of aquifer thermal energy storage (ATES) performance in a building system is an important topic for maximizing the seasonal offset between energy demand and supply and minimizing the building's primary energy consumption. To evaluate ATES performance with bidirectional operation, this study develops an analytical solution-based model to simulate the spatiotemporal thermal response in an aquifer. The model consists of three temperature response functions, similar to the G functions in borehole thermal energy storage (BTES), to estimate the transient temperature profile in the aquifer during seasonally varying injection and extraction of hot/cold water. Applying machine learning (ML) based data classification and regression techniques to the results of a series of finite element (FE) benchmark simulations of typical ATES configurations, model input parameters are linked to the subsurface thermal, hydrogeological, and ATES operational properties. Compared to the benchmark simulation results, the errors of the proposed model in estimating the annual energy storage and locating the thermally affected area are about 3 % and 1 %, respectively. The model was applied to a previous short-term case study, and the error in the transient production temperature estimation is about 1 %. The long-term heat recovery ratio estimated from the model also compares well to those calculated from the previous study and the validated numerical model. Because of its fast computation, the proposed model can be coupled with the individual building system simulation and used for preliminary ATES design, and this will allow for greater exploration of ATES operational space and, therefore, better choices of ATES operating conditions. The proposed model can also be coupled with the district heating and cooling network simulation for computationally efficient city-scale long-term ATES potential assessment.

Modeling of heat and solute transport in a fracture-matrix mine thermal energy storage system and energy storage performance evaluation

Repurposing groundwater-filled mine cavities for thermal energy storage has demonstrated promising potential to buffer the imbalance of energy supply and demand. Fractured formations are widespread in old mines due to previous excavation activities, which dominates the performance and efficiency of the mine thermal energy storage (MTES) system. Therefore, understanding the mechanisms of fluid flow, heat, and solute transport in fractured reservoirs in the MTES system is essential for its application and the assessment of environmental impact. In this study, fluid flow, heat, and solute transport in a 3D fracture-matrix MTES system are modeled simultaneously based on site-specific data in Freiberg, Germany. The simulations are conducted with a coupled Hydro-Thermo-Component process newly developed in the open-source software OpenGeoSys (OGS). To stabilize the simulation in the fracture-matrix hybrid system, a flux-corrected transport scheme is specifically implemented and applied in the model. Thus, heat and mass exchange between the embedded fractures and the matrix in the formation of MTES can be accurately simulated on the basis of the conforming mesh. In a hypothetical short-term scenario of a 15-day heating and cooling cycle of the MTES operation, the solute is transported faster than the heat in the fractured formation, indicating that disturbance of mineral compositions in the original mine water can affect a larger region than heat. The embedded fracture network in the surrounding formation is also found to increase the thermal energy storage capacity by 44%, while decreasing the recovery ratio by 14% compared to those of the unfractured formation. More energy will be transported and stored in the more fractured formation from heated mine water, but less energy can be recovered. The behavior of the MTES system strongly depends on local geology and hydraulic conditions and therefore needs to be evaluated in a site- and application-specific manner. This study provides preliminary insights into the performance and efficiency, as well as the environmental impact of the MTES operation in the short term.

Experimental and simulated evaluation of inverse model for shallow underground thermal storage

This study employs an inverse grey-box (IGB) modeling approach, which combines measured data and the physics of systems to predict the performance of shallow underground thermal energy storage (UTES) with top and side insulation. A simplified IGB model of the shallow UTES was developed using thermal network analysis. Experimental studies were conducted for shallow vertical and horizontal UTES configurations. Detailed models representing the field experiments were developed using the TRNSYS simulation tool and calibrated with the measured data from the experimental setup. The 4 Resistance 2 Capacitance (4R2C) IGB model was trained and tested in MATLAB using field experimental data and the data from the calibrated TRNSYS model. In comparing experimental data with the TRNSYS model for UTES, the prediction of outlet water temperature showed good agreement, with root mean square error (RMSE) and coefficient of variation of RMSE (CVRMSE) values of 0.94 °C and 3.16 % for vertical, and 0.99 °C and 2.97 % for horizontal configurations. The IGB model also aligned well with the experimental data, showing CVRMSE of 7.91 % and 3.17 % for vertical and horizontal systems, respectively. Sensitivity analysis revealed that model performance improves with longer training durations and closer testing times to training periods. However, a convergence point of 20 weeks of training data was achieved for making long-term performance predictions.

Performance evaluation and optimization of compact tube-fin latent heat storage system in phase change nanoemulsion discharge mode

The low thermal conductivity of phase change materials (PCMs) and the reduced heat transfer temperature difference along a tube both limit the thermal performance of latent heat thermal energy storage (LHTES). Herein, a compact tube-fin LHTES system based on phase change nanoemulsions was developed and the heat transfer process of nanoemulsion and PCM was numerically investigated. The effects of the heat transfer structure of the heat exchanger and the thermophysical parameters of the heat transfer fluid (HTF) on the cold energy discharge performance of the system were quantified. The optimized model reduced the discharge time by 24.4 % in nanoemulsion mode relative to water. Heat transfer improvement on the PCM side could be achieved by decreasing the fin spacing and tube spacing and by increasing the fin thickness. Such improvement reinforced the heat transfer enhancement of the nanoemulsion. The heat transfer mechanism was explained by the temperature distributions of the HTF and PCM along the tube. The phase-change thermostatic properties of the nanoemulsion and PCM contributed to the formation of dual-phase-change coupled heat transfer (i.e., the heat transfer process when the fluid inside the tube and the PCM filled outside the tube undergo a simultaneous phase change) within the LHTES, increasing the heat transfer temperature difference and the magnitude of the driving force. Increasing the phase change temperature difference accelerated the onset of dual-phase-change heat transfer, while increasing the PCM content prolonged the process. Briefly, this study provided operational and design assistance for LHTES systems in nanoemulsion mode with the intention to accelerate heat transfer rates.

Encapsulation effectiveness and thermal energy storage performance of aluminum-graphite composite phase change materials subjected to oxide coating

The utilization of metals as phase change materials (PCMs) in high-temperature latent heat storage technology holds promising prospects, especially when integrated with concentrated solar power (CSP) systems, as it enables higher working temperatures for CSP and enhances power generation cycle efficiency. However, the practical application of metal-based phase change processes faces challenges such as liquid leakage and high-temperature corrosion, which impede their widespread implementation. In this study, aluminum (Al) is employed as the PCM, while expanded graphite (EG) is used as the matrix material. Composite PCMs with embedded structures were synthesized using powder metallurgy techniques. Notably, an oxidation pre-treatment process was employed to create an oxide layer on the surface of Al particles, thereby improving the encapsulation performance and thermal properties of the composite PCM. By increasing the oxidation pre-treatment temperature to 1100°C, the maximum encapsulation ratio was enhanced from 50 wt% to 80 wt%, and the latent heat energy storage density increased from 101.0 J/g to 188.2 J/g. Moreover, the composite PCM subjected to oxidation pre-treatment at temperatures of 670°C and above maintained a stable structure, chemical composition, and energy storage density after 50 thermal cycles. Within the temperature range of 600–700°C, the total energy storage density of the composite PCM reached 284.5 J/g. These results indicate that the oxidation pre-treatment is a promising technology in high-temperature energy storage technology.

Thermal energy storage performance of biaxial voided RCC roof slab integrated with macroencapsulated PCM for passive cooling of buildings

Building space heating and cooling power consumption is growing due to population and economic growth. Integrating phase change materials (PCMs) into various building envelope components is being explored to enhance thermal energy storage capacities. Specifically, roofs exposed to direct sunlight significantly promote thermal energy transfer to the interior, increasing the space heating and cooling requirements. In this study, thermal energy storage performance of a biaxial voided roof slab integrated with PCM is experimentally investigated under ambient conditions and compared with a normal reinforced concrete (RCC) without PCM. PCM selection, characterization, and metal void former development are performed, followed by macroencapsulation and integration into the roof slab. Thermal performance measures are evaluated, including temperature profile, heat flux, thermal load, time lag, and decrement factor. Financial viability indicators such as electricity cost savings, payback period, and CO2 emissions savings are also assessed. The results show PCM integrated biaxial voided roof slab reduces interior temperature by upto 7.2 °C during sunny hours, heat transfer to the interior by upto 60.6 %, and thermal load by upto 54 %. In addition, considering heating and cooling, it offers an average daily saving of 0.06 USD/kWh/m2 and a payback period of about 5.7 years. Further, it gives CO2 emissions savings of upto 13.7, 12.3, and 4.3 kgCO2/kWh for lignite-, coal-, and natural gas-fired power plants. Furthermore, its mean time lag is 4.2 h, with a decrement factor of 0.75 compared to 3.9 h and 0.85 for the normal RCC unit. The study makes significant contribution to knowledge by providing a unique, simple yet highly effective PCM macroencapsulation integration technique for roof slabs and insights into its thermal performance under the hot weather conditions.

Melting and Solidification Characteristics of PCM in Oscillated Bundled-Tube Thermal Energy Storage System

Phase change material (PCM) based thermal energy storage (TES) is an important solution to the waste of heat and intermittency of new energy sources. However, the thermal conductivity of most PCMs is low, which severely affects the thermal energy storage performance. Oscillation of the tube bundles in a TES unit can intensify the convection of liquid PCM and, therefore, enhance heat transfer. However, the energy storage performance of bundled-tube TES systems in response to oscillation at different amplitudes and frequencies has not been well understood yet, and the optimum time to apply the oscillation during phase transition remains unexplored. To address this issue, this present study was carried out. First, the melting behaviour of PCM with oscillation starting at different times was investigated. Then, the influences of oscillation frequency and amplitude on the melting performance were explored. Finally, the solidification behaviour of PCM with oscillation starting at different times was examined. Results show that the oscillation can accelerate the phase transition process by enhancing convective heat transfer. Compared to the case without oscillation, the complete melting and solidification times are reduced by 8.2 and 6.7% for the case with oscillation starting at 200 s, respectively. The effect of oscillation frequency on the melting enhancement is negligible, while the oscillation amplitude has an important effect on the melting enhancement.

Energy storage, thermal-hydraulic, and thermodynamic characteristics of a latent thermal energy storage system with 180-degree bifurcated fractal fins

The low thermal conductivity of organic phase change materials limits the performance of latent thermal energy storage (TES) systems. Inspired by fractal theory, this study proposes an innovative 180° fractal fin for enhancing the thermal performance of latent TES systems. The effects of length ratios (l) and fractal levels (N) are numerically investigated employing the enthalpy-porosity method. Compared with traditional rectangular fins, the results indicate that the 180° fractal fins reduce the integral average value of the maximum velocity by 2.24%–48.51%, which indicates the suppression of natural convection by the latter. Increasing l and N result in a general increase in melting time. Compared to the TES systems without fins and with rectangular fins, the 180° fractal fins can respectively reduce melting time by up to 88.79% and 28.00%, increase integral average Nusselt number by up to 7.30 times and 34.21%, and enhance energy storage power by a maximum of 8.55 times and 38.71%. Moreover, flow viscous entropy generation can be neglected compared to thermal entropy generation. In contrast to rectangular fins, the employment of fractal fins leads to a maximum reduction of 90.06% and 99.10% in total frictional entropy generation and thermal entropy generation, respectively.

Effect of local mechanical oscillation on the performance of PCM thermal energy storage with various unit configurations

The low thermal conductivity of phase change materials is an essential restriction to their usage in thermal energy storage units. In this research, applying local oscillation by an oscillator on the portion of a side wall of RT35 enclosure is presented as a novel method to enhance the charging rate. The finite volume method is conducted for the numerical study on the effect of different configuration parameters including enclosure aspect ratios in the range of 1: 6, 1:2, 1:1, and 2:1, various oscillator lengths of 5, 10, 15, and 20 mm, as well as different oscillation frequencies of 10, 100 and 1000 Hz on the melting performance. Results indicate that applying local oscillation enhances the melting rate by more than 50 % as compared to without using oscillator because of enhancing convection heat transfer originating from vorticity intensification. The improvement of required time for melting the PCM is 91.55 %, 54.66 %, 67.7 % and 71.4 % for aspect ratios of 1:6, 1:2, 1:1 and 2:1, respectively.Results show that the melting performance is enhanced as the length of the oscillator increases. The required time for complete melting is obtained equal to 24, 26, 28, and 33 min at the oscillator length of 20, 15, 10, and 5 mm, respectively. The finding on the effect of oscillation frequency reveals that the liquid fraction, mean temperature, and heat flux at a specified time of melting process becomes higher as the oscillation frequency increases with significant enhancement of vorticity around the oscillator. At the frequency of 1000 Hz, the required time for melting is reduced by 9.5 % and 20.8 % as compared to frequencies of 100 Hz and 10 Hz, respectively. Other results also indicate that the higher Nusselt number is obtained for a higher enclosure aspect ratio.

Simultaneous impregnation and microencapsulation of CaCl2 using silica gel and methyl cellulose for thermal energy storage applications

Thermal energy storage utilizing the adsorption of moisture from air is a promising energy storage technology due to its high energy density and minimum heat losses. Salt hydrates and salt hydrate composites, such as calcium chloride (CaCl2) and CaCl2-based composites, have shown favourable energy storage properties in this area of research. However, these materials have shown issues with stability due to swelling and deliquescence. In this work, CaCl2 was stabilized using three methods: impregnation into silica gel, encapsulation in methyl cellulose, and both impregnation and encapsulation stabilization techniques used simultaneously. Therefore, three CaCl2-based composites were synthesized. For the first composite, silica gel was impregnated with CaCl2. For the second composite, CaCl2 was encapsulated by methyl cellulose. For the third composite, silica gel was impregnated with CaCl2 and the CaCl2 was encapsulated with methyl cellulose. These samples were structurally characterized using scanning electron microscopy as well as Brunauer-Emmett-Teller (BET) to determine surface area, pore size distribution and nitrogen adsorption isotherms at 77 K. Water vapour adsorption isotherms were also determined at 25 °C for different relative humidities by dynamic vapor sorption (DVS). Similarly, LiCl-based composites were also synthesized and examined in this work, but issues of deliquescence, swelling, and agglomeration made the materials impractical to work with. To determine the prepared materials’ thermal energy storage performance, 2–6 g of each sample was tested in a lab-scale apparatus. This process uses the exothermic adsorption of moisture from ambient air in an open thermal energy storage system. The CaCl2 impregnated silica gel that was encapsulated in methyl cellulose showed reasonably high stability and energy storage performance after 3 hydration and dehydration cycles with minimum agglomeration. An energy storage density of 241 kWh/m3 (0.87 GJ/m3) and specific energy of 630 Wh/kg (2268 kJ/kg) was achieved with this material for 90% inlet relative humidity after a regeneration at 90 °C.

Performance and economic analysis of a molten salt furnace thermal energy storage and peaking system coupled with thermal power units for iron and steel gas waste heat recovery

A new peaking system utilizing a molten salt furnace energy storage system coupled with a blast furnace gas thermal power unit in a steel mill is proposed, which stores excess blast furnace gas thermal energy in molten salt and releases the thermal energy for power generation during peak power demand. The heating efficiency of 74.57% is experimentally verified by building a molten salt furnace, and a 135 MW blast furnace gas thermal power unit is simulated using modeling to explore the energy storage and peak shifting performance and economic feasibility of the system. The results show that during the charging phase, the system can recover up to 9.361 t/h of standard coal, increasing the low valley regulation ratio to 20.31% with the increase of extraction rate. During the discharging phase, the system can provide an additional 17.42 MW of generating power, with a peak modulation ratio of 12.90%. The exergy losses from the combustion process dominates the overall system exergy losses with a maximum of 21.00 MW, followed by the exergy from the turbine, which occupies 18.42% of the input energy. The cycle efficiency of the system is up to 63.54%, and the molten salt temperature has a more significant impact on the system performance than the molten salt flow rate. The economic feasibility analysis yields a peaking capacity cost of $74.28/kWh for the modified system. The system will complete 100% recovery of the investment cost in 4.90 years, and thereafter, the annual profit is more than $3.71 Million. The peaking hours and regional electricity price are the main factors affecting the system. The effect of critical factors on the payback years of the system was further explored, and the payback years remains within 8 years only when the molten salt temperature is above 500 °C and the molten salt flow rate exceeds 400 t/h.

Solar to thermal energy storage performance of composite phase change material supported by copper foam loaded with graphite and boron nitride

Phase Change Materials (PCM) have emerged as one of the potential candidates for solar Thermal Energy Storage (TES) because of their high energy density, low volume change, and easy availability in varying temperature ranges. However, PCM suffers from a few critical drawbacks such as leakage during phase transformation, low thermal conductivity, and poor photothermal energy conversion performance. In this study, shape-stable composite PCM loaded with varying percentages of Graphite (GR) and Boron Nitride (BN) were prepared. Copper foam of 96 PPI was used as 3-dimensional skeleton support to provide shape stability to the eutectic mixture of Lauric Acid (LA)-Myristic Acid (MA). Shape stable composite PCM CF/LA-MA/GR with 0 %, 5 %, 15 %, 25 %, and 35 % of GR and CF/LA-MA/BN with 0 %, 5 %, 15 %, 25 %, and 35 % of BN were prepared and characterized for thermal, physical, and photothermal energy conversion performance. A maximum loading percentage of 67 % of LA-MA in CF without leakage was obtained. The PCM composites show excellent thermal stability at elevated temperatures and suitable TES parameters for solar thermal storage applications. Among all the prepared samples, CF/LA-MA/GR35% shows a maximum rise of 76.1 % in heating rate and 81.2 % in photothermal energy conversion efficiency in comparison with CF/LA-MA/GR0%. In addition, CF/LA-MA/GR35% shows a maximum of 1.08 W/m-K of thermal conductivity at a melting enthalpy of 95.36 J/g. The shape-stable composite PCM shows a stable physical structure along with good surface morphology.

Magnetically triggered heat release from hydrate salt composite microchannels for low-temperature battery thermal management

While active thermal managements for Li-ion battery (LIB) consume a large amount of energy, passive one based on phase change material (PCM) fails to release thermal energy for heating as required. Thus, intelligent heat storage and release is urgently needed for utilizing PCM as passive thermal management. Herein, porous boron nitride/polyvinyl alcohol (BN/PVA) skeleton with highly ordered microchannels was fabricated to impregnate hydrate salt sodium acetate trihydrate (SAT) solution forming shape-stable SAT@BN/PVA composite with efficient thermal energy storage performance. Disturbance from magnetic trigger in the hydrate salt composite microchannels promotes nucleation and solidification, thus initiates heat release as required and remotely. Meanwhile, anisotropic heat transfer from the highly ordered microchannels can effectively enhance heat release velocity and efficiency. The magnetic triggered process is studied theoretically and experimentally, and optimized to release heat in 25 s with efficiency up to 99%. Consequently, heat release can improve temperature by 10 °C when battery pack stops working at −20 °C and enhance discharge capacity by 75% during cold-start. This research provides a new method for intelligent thermal management of LIB working in cold environment.

Preparation and performance of solid thermal energy storage materials based on low-grade pyrophyllite minerals

The new sensible thermal energy storage materials were prepared by the sintering method with low-grade pyrophyllite mineral powders as main raw materials, Suzhou clay as the sintering aid and sulfite liquors as the binder. Further, the performance of sensible thermal energy storage under different size distributions and sintering temperatures was investigated and analyzed. The results show that the optimum particle size distribution is 50:15:35, the bulk density, thermal conductivity, and specific heat capacity are the largest values, which are 1.97 g cm−3, 0.87 W m−1 K−1 and 0.63 kJ kg−1 K−1, respectively. Other properties including porosity, water absorption, flexural and compressive strength and so on are optimal under this size distribution. When the sintering temperature is 1200 °C, the material has a good thermal conductivity of 0.89 W m−1 K−1 and a high bulk density of 2.05 g cm−3. Meanwhile, the sample with the used temperature from 50 to 900 °C has the best thermal energy storage capacity of 306.29 kWh·m−3.

Preparation and thermal properties of zeolite/MgSO4 composite sorption material for heat storage

Thermochemical sorption heat storage based on salt hydrates offers the potential advantages such as high energy density, negligible heat loss, small volume change and flexible working modes. Magnesium sulphate (MgSO4) is a high energy density hydrated salt available for the thermochemical sorption heat storage. In this work, different types of zeolites (including 3A, 5A and 13X zeolites) have been selected as mass-transfer-enhancing and structural stabilizing materials, and a series of zeolite/MgSO4 composites have been fabricated. To investigate the thermal energy storage performance of zeolite/MgSO4 composites, the properties of the composites, such as micro-morphology, pore structure, chemical composition and sorption-desorption behavior, have been characterized and analyzed. Results indicated that the mass transfer performance of the composite materials is significantly better than that of the pure zeolites. As the mass fraction of MgSO4 in the composite sorbents increases, the specific surface area and porosity of the composite sorbent decreases, and the sorption performance has been enhanced. Compared with 3A zeolite-based and 5A zeolite-based composites, 13X zeolite/MgSO4 composite materials show the best heat storage performance. At the condition of 25 °C and 60% RH, the 13XM20 has the highest sorption capacity of 0.21 g/g, which is 24% higher than that of pure zeolite 13X. Accordingly, the maximum heat storage density is 438.4 kJ/kg, which exhibits the superior heat storage performance among of the hydrated salt sorbents. The potential of 13X zeolite/MgSO4 as sorption heat storage material in efficient utilization of solar heat and low-grade industrial waste heat has been revealed.

High value utilization of waste peanut shell: Prepared novel shape stable composite phase change materials with high thermal conductivity

To address the leakage and low thermal conductivity issues of phase change materials (PCMs), this study aims to prepare high thermal conductivity shape stable composite phase change materials (sscPCMs) using waste peanut shell. Employing pyrolysis technology, waste peanut shell has been successfully converted into high-performance framework materials. In addition, it also compared the thermal energy storage performance of shape stable composite stearic acid/peanut shell biochar (ss-cSA/PSC) with that of shape stable composite stearic acid/peanut shell (ss-cSA/PS). Excitingly, the thermal energy storage performance of ss-cSA/PSC has been significantly improved. Specifically, the thermal conductivity of ss-cSA/PSC reached 0.527 W/(m·K), which is 3.2 times higher than that of pure SA and 2.4 times higher than that of ss-cSA/PS. In addition, the phase change latent heat of ss-cSA/PSC can reach 70.59 J/g, which is 27.2% higher than that of ss-cSA/PS. The high thermal conductivity and phase change latent heat highlighted its significant superiority in the field of thermal energy storage. Furthermore, ss-cSA/PS and ss-cSA/PSC have been characterized by SEM, FTIR, XRD, and TGA. The results indicated that both two kinds of sscPCMs have excellent chemical compatibility, thermal reliability, and thermal stability. In summary, PSC is an economical, environmentally friendly, and sustainable framework material which used to prevent the leakage of PCMs and improve the thermal performance.

Development of snow removal system using embedded pipes inside road with solar thermal energy collector and packed bed latent heat thermal energy storage

To enhance winter safety for drivers and pedestrians, this study developed and assessed an efficient snow removal system. Utilizing a packed bed latent heat thermal energy storage system with a solar thermal energy collector and phase change material (PCM), the research demonstrated performance over sensible thermal energy storage, offering increased storage capacity, isothermal characteristics, and efficient charging and discharging processes. In this study, a packed bed PCM container was proposed for the improved heat transfer performance of latent heat thermal energy storage (LHTES). The heat and fluid flow inside LHTES was numerically and experimentally analyzed for the optimization. The snow removal system comprised solar thermal energy collectors, a packed bed LHTES, and concrete pavement. As a results, the phase change material temperature increases from 30 °C to 75 °C during a 27-hour charging process, accumulating 58 MJ of thermal energy. The system's snow removal effectiveness was validated in an experiment, affirming the efficient transfer of stored heat to melt 10 cm-thick snow at −5 to 13 °C. Notably, no snow accumulation occurred on the concrete pavement surface.

Enhancing the performance of thermal energy storage by adding nano-particles with paraffin phase change materials

Abstract Phase change materials (PCMs) are now being extensively used in thermal energy storage (TES) applications. Numerous researchers conducted experiments using various circumstances and materials to optimize storage performance. A study was conducted to compare the numerical research of the melting process of paraffin wax using a hybrid nano-integrated paraffin PCM with graphene oxide (GO) and single-walled carbon nanotubes (SWCNTs) in a TES unit. Hence, this research focuses on a sustainable TES system using hybrid nanomaterials (PCM + GO, PCM + SWCNTs, PCM + GO + SWCNT) with varying concentrations of nanoparticles. The objective is to improve the thermal characteristics of PCMs. The main aim of this study is to examine the numerical analysis of the system inside a TES that has a rectangular form. The numerical experiments were conducted using the finite-volume solver Ansys Fluent. The obtained findings show the thermophysical characteristics fluctuations with respect to the solid volume fractions, liquid fraction, temperature, and velocity inside the TES system. Implementing an effective heat transfer mechanism from the point of capture to storage and later consumption necessitates the employment of a heat transfer fluid. The inclusion of SWCNT particles at a concentration of just 10% has been seen to expedite the melting phenomenon. Furthermore, incorporating GO in conjunction with SWCNT alleviates this phenomenon, resulting in a melting behavior that resembles that of unadulterated paraffin. Additionally, the introduction of just 1% GO, combined with SWCNT, leads to a rapid alteration in surface heat transfer coefficient compared to the scenario with single SWCNT and paraffin. These insights hold practical relevance for the development of TES systems in various applications.

Thermal performance and analysis of high-temperature aquifer thermal energy storage based on a practical project

Geothermal heating technology based on high-temperature aquifer thermal energy storage (HT-ATES) is one of important development directions of geothermal multi-energy complementary and integrated energy system. In present article, thermal performance of HT-ATES based on a practical project is first proposed, and a long-term cycle of HT-ATES is constructed and verified. The heating up storage and isothermal heat storage of HT-ATES are experimentally conducted. The different standing time schemes causing mutation of the heat storage mechanism have been implemented to identify the optimal scheme. And then the outlet water temperature, heat storage efficiency is further calculated and analyzed under the same and different conditions of heat storage capacity. Compared with original heat production, the outlet water temperature is promoted and the single well heat storage efficiency can reach >80 % after 9 years of heat storage. The heat storage flow rate decreases or the heat storage temperature increases can prevent heat dissipation to the surroundings, so that obtaining high outlet water temperature and heat storage efficiency under the persistent annual heat storage capacity. Results also show that the outlet water temperature and heat storage efficiency are promoted when the heat storage temperature increases and heat storage flow rate decreases.