Thermal Energy Storage Process Research Articles

Simulation of Magnetic Field Effects on Heat and Mass Transfer in a Porous Spline Half‐Cylinder Using ANN and ISPH Approaches

ABSTRACTThis study utilizes Artificial Neural Networks (ANNs) and Incompressible Smoothed Particle Hydrodynamics (ISPH) simulations to explore the effects of magnetic fields on heat and mass transfer in a porous spline half‐cylinder filled with Nano‐Encapsulated Phase Change Material (NEPCM). Simulations were conducted over a range of physical parameters: buoyancy ratio () from −2 to 2, Darcy number () from 10−5 to 10−2, Hartmann number () from 0 to 50, Rayleigh number (Ra) from 103 to 106, and fusion temperature from 0.05 to 0.9. The results demonstrate that increasing the Ha reduces heat transfer efficiency by up to 15%, as the magnetic field stabilizes fluid flow and enhances conduction. Conversely, increasing the Ra improves heat transfer efficiency by approximately 25% due to enhanced convection and mixing. The buoyancy ratio significantly influences fluid flow, with higher values favoring concentration‐driven buoyancy, while lower values enhance temperature‐driven convection. The Da affects permeability, with higher values promoting convective heat transfer and dynamic flow, whereas lower values result in stable, conductive heat transfer. Fusion temperature impacts phase change behavior, affecting heat capacity and flow dynamics through latent heat absorption. These insights underscore the critical role of optimizing these parameters to enhance performance in applications such as thermal energy storage and industrial processes involving phase change materials.

Experimental and analytical study on continuous frozen/melting processes of latent thermal energy storage driven by bubble flow

It is emphasized direct contact method that introduced to the frozen/melting processes has a high value of development due to the role for mitigating thermal stratification, reducing phase separation and enhancing heat transfer efficiency. However, the absence of fixed solid heat transfer walls can lead to discontinuous switch and difficult-to-control problem during frozen/melting processes. In this paper, the latent thermal energy storage device driven by bubble flow is experimentally investigated. With the usage of low melting point paraffin and the pattern of free expansion in a cabinet, continuous switch between the frozen and the melting process can be realized. Phase change processes, temperatures, heat transfer efficiency, volume change and pressure drops are measured and analyzed. A dynamic analytical model to describe the processes is also developed based on the ε - NTU method. The results show that the heat transfer efficiency can reach to 0.8 at least in all the experimental cases. Moreover, this study records the pressure difference of the gas flow, predicts the required input mechanical work and analyses the volumetric heat transfer coefficient, which help to reveal feasibility of the device.

A Review on the Nanofluids-PCMs Integrated Solutions for Solar Thermal Heat Transfer Enhancement Purposes

The current review offers a critical survey on published studies concerning the simultaneous use of PCMs and nanofluids for solar thermal energy storage and conversion processes. Also, the main thermophysical properties of PCMs and nanofluids are discussed in detail. On one hand, the properties of these types of nanofluids are analyzed, as well as those of the general types of nanofluids, like the thermal conductivity and latent heat capacity. On the other hand, there are specific characteristics of PCMs like, for instance, the phase-change duration and the phase-change temperature. Moreover, the main improvement techniques in order for PCMs and nanofluids to be used in solar thermal applications are described in detail, including the inclusion of highly thermal conductive nanoparticles and other nanostructures in nano-enhanced PCMs and PCMs with extended surfaces, among others. Regarding those improvement techniques, it was found that, for instance, nanofluids can enhance the thermal conductivity of the base fluids by up to 100%. In addition, it was also reported that the simultaneous use of PCMs and nanofluids enhances the overall, thermal, and electrical efficiencies of solar thermal energy storage systems and photovoltaic-nano-enhanced PCM systems. Finally, the main limitations and guidelines are summarized for future research in the technological and research fields of nanofluids and PCMs.

Thermal investigation and parametric analysis of cascaded latent heat storage system enhanced by porous media

Cascaded latent heat storage (CLHS) has become a promising solution to the recovery and utilization of thermal energy. Many studies optimized the inlet temperature and velocity of heat transfer fluid to improve the heat transfer rate for the charging process of CLHS systems with pure phase change materials (PCMs), but the effect is not significant, mainly because the thermal resistance of the system comes from the PCMs side due to the low thermal conductivity of pure PCMs. Porous media composite phase change materials (CPCMs) have been shown to have promising prospects in a single PCM system, but no research precedent has been found for the application of porous media CPCM in the CLHS system. Besides, when CPCMs are encapsulated in the cavities of the CLHS system instead of pure PCMs, the difference in the degree of impact between the porosity of a porous media and boundary conditions on the thermal performance of a CLHS system is still unclear. The purpose of this article is to significantly improve the heat transfer rate by applying the CPCM to the CLHS system and to comprehensively compare the impact of porosity and HTF inlet boundary conditions on the charging/discharging time and energy/exergy charged/discharged rates of a CLHS system with CPCMs through two sensitivity analysis methods. When the porosity reduces from 0.97 to 0.92, the charging time and the discharging time decrease by 74.50 % and 73.39 % respectively; the average energy charge rate and average exergy charge rate increase by about 4.11 times; the average energy and exergy discharge rates increase by 5.76 times and 5.8 times respectively. Sensitivity analysis shows that the porosity of a porous media is the most important factor affecting the charging and discharging rates of a CLHS system, but its impact on energy and exergy charge/discharge rates is not monotonic. The effect of the inlet temperature and velocity of the HTF on a CLHS system is complex, and simply changing a single variable may not be effective in optimizing thermal performance parameters. This study provides a comprehensive performance enhancement strategy for the thermal energy storage and utilization processes of CLHS systems, which have great potential in fields such as solar energy collection, waste heat recovery, and building heating.

Nanofluids as a Waste Heat Recovery Medium: A Critical Review and Guidelines for Future Research and Use

The thermal energy storage and conversion process possesses high energy losses in the form of waste heat. The losses associated with energy conversion achieve almost 90% of the worldwide energy supply, and approximately half of these losses are waste heat. Hence, waste heat recovery approaches intend to recuperate that large amount of wasted heat from chimneys, vehicles, and solar energy systems, among others. The novel class of thermal fluids designated by nanofluids has a high potential to be employed in waste heat recovery. It has already been demonstrated that nanofluids enhance energy recovery efficiency by more than 20%. Also, the use of nanofluids can improve the energy capacity of steelworks systems by around three times. In general, nanofluids can improve efficiency and reduce exergy destruction and carbon emissions in devices like heat exchangers. The current work summarizes the application of nanofluids in waste heat recovery and discusses the involved feasibility factors. Also, the critical survey of more than one hundred scientific papers enabled the overview of the environmental aspects of the nanofluid’s waste heat recovery. Finally, it discusses the main limitations and prospects of the use of nanofluids in waste heat recovery processes.

Physicochemical Properties of N,N-Diethylethanolammonium Chloride/Ethylene Glycol-Based Deep Eutectic Solvent for Replacement of Ionic Liquid

Abstract Ionic liquids (ILs) that are used in the market nowadays have high complexity of processing, high viscosity, and high toxicity in comparison to deep eutectic solvent (DES). Deep eutectic solvent is typically used in thermal energy storage, separation and extraction process or electrochemistry field. This study focuses on determining the physicochemical properties of DES, which are thermal conductivity, viscosity, and surface tension. DES was prepared by mixing hydrogen-bond donor (HBD) compounds (ethylene glycol) and hydrogen-bond acceptor (HBA) compounds (N,N-diethylethanolammonium chloride) at different molar compositions. The data show that the molar ratio HBA:HBD of 1:2 resulted in optimized values of thermal conductivity (0.218 W/mK), low viscosity (38.1 cP), and high surface tension (54 mN/m). Most notably, DES is capable of sustaining in a liquid phase at ambient condition (25 °C) for more than 30 days. Fourier transform infrared spectrum did not indicate any presence of a new peak. This established that only delocalization of ions occurred, and hence, chemical transformations did not take place during mixing. The data obtained showed that the newly synthesized solvent (DES) possess better result than the ILs. Therefore, DES can be proposed to replace the dependency on ILs.

Numerical investigation of the non-Newtonian power-law fluid with convective boundary conditions in a non-Darcy porous medium

The boundary layer nanofluid flow over a horizontal plate embedded in a non-Darcy porous medium is investigated in this study. Non-Newtonian power-law fluid is considered the base fluid. The nanofluid model incorporated the effects of Brownian motion and thermophoresis. A mixed convective boundary condition that is more useful, in practice, is employed at the surface instead of Dirichlet or Neumann boundary conditions. The flow and convective heat transfer has engineering and industrial applications such as the thermal design of industrial equipment dealing with molten plastics and polymeric liquids and applications in nuclear plants and thermal energy storage processes. The main aim of this study is to use the spectral quasi-linearization method to study the effects of non-Newtonian nanofluid flow over a horizontal surface for a porous medium. The objective is to explore both the accuracy and the convergence of the method through the evaluation of residual errors and error norms and to investigate the impact of specific parameters on flow behavior and heat transfer characteristics. The velocity profile increases for higher values of the power law index and mixed convection parameter. The influence of the number of active variables on dimensionless temperature profiles increases for different values of the Biot number.

Component-based modeling of ground-coupled seasonal thermal energy storages

Seasonal thermal energy storages are considered a central element of modern, innovative energy systems and help to harmonize fluctuating energy sources. Furthermore, they allow for an improved coupling between the electricity and heating sectors. Despite recent improvements of planning processes and enhanced models, significant discrepancies between projected and measured heat losses were revealed. Additional shortcomings of available tools relate to limitations in specifying geometry, internal design, or physical processes. Addressing these drawbacks, this study employs a revised, alternative approach by using a flexible, component-based, model (“STORE”). It allows variable flexible parameterizations to study diverse design scenarios. After introducing relevant seasonal thermal energy storage components, processes and mechanisms, datasets, and evaluation techniques, a plausibility test is presented that applies a common thermal energy storage model for benchmarking. In a test study, the re-use of a circa 1,000 m3 large swimming pool is simulated. STORE is used to investigate performance trends caused by different designs (e.g., insulation thicknesses, materials at individual interfaces). For the plausibility test, the results show a high degree of coverage and good applicability. Further, the results of the test study show a storage efficiency of 12.4% for an uninsulated base case, which can be improved to 69.5% in case of the most complex, highly insulated configuration. Critical trends are revealed, covering reduced peak capacity levels (26.5 to 23.5 MWh) and raised average filling temperatures (39.1 to 45.2 °C). Improved long-term behavior involves reduced environmental impacts due to reduced heating of the ambient soil (+7.9 K compared to +14.1 K after 2 years). General conclusions reveal that an optimal design should initially focus on an external cover of soil and top insulation. However, evaluations should base on multiple parameters depending on the target criteria. This is where the present model is highly useful. The capability of STORE to rapidly analyze a plethora of scenarios proves its high applicability for optimizing the planning processes of seasonal thermal energy storage projects.

A State of the Art Review on Sensible and Latent Heat Thermal Energy Storage Processes in Porous Media: Mesoscopic Simulation

Sharing renewable energies, reducing energy consumption and optimizing energy management in an attempt to limit environmental problems (air pollution, global warming, acid rain, etc.) has today become a genuine concern of scientific engineering research. Furthermore, with the drastic growth of requirements in building and industrial worldwide sectors, the need for proper techniques that allow enhancement in the thermal performance of systems is increasingly being addressed. It is worth noting that using sensible and latent heat storage materials (SHSMs and phase change materials (PCMs)) for thermal energy storage mechanisms can meet requirements such as thermal comfort in buildings when selected correctly. However, as the operating temperature changes, a series of complex technical issues arise, such as heat transfer issues, leaks, corrosion, subcooling, supercooling, etc. This paper reviews the most recent research advances in the area of sensible and latent heat storage through the porous media as potential technology while providing useful information for researchers and engineers in the energy storage domain. To this end, the state and challenges of PCMs incorporation methods are drawn up, and an updated database of various research is provided while discussing the conclusions concerning the sensible and latent heat storage in porous media, their scopes of application and impact on energy consumption. In the light of this non-exhaustive review, it turns out that the adoption of porous matrices improves the thermal performance of systems, mitigates energy consumption and drops CO2 emissions while ensuring thermal comfort within buildings. In addition, at the representative elementary volume (REV) and pore scales, the lattice Boltzmann method (LBM) is examined as an alternative method to the commonly used, traditional numerical methods. These two approaches are compared based on results available in the literature. Through these means, their ability to handle latent and sensible heat storage process in a porous medium is demonstrated. To sum up, to be more complete, perspectives of sensible and latent energy storage technologies are covered.

Thermal Energy Storage Characteristics of Paraffin in Solar Water Heating Systems with Flat Plate Collectors

Indonesia is a tropical country with a relatively stable intensity of solar radiation throughout the year, ranging from 10 to 12 hours a day, and averaging 4.8 kWh/m²/day. This great potential can be used for heating water for bathing. Water heating technology based on solar collectors is now widely available in the commercial market. Additionally, thermal energy storage from solar radiation is performed using sensible heat and requires a large volume. Assuming that the water is not used until the afternoon, then the heated water is stored in the tube. A phase change material (PCM) was used in several studies to maximize thermal energy storage (TES) from solar radiation. Also, PCM uses latent heat to absorb and release heat. This is adjusted to the water temperature produced from the solar collector, which attains 70°C. Hence, the potential PCM used is solid paraffin, which is widely available in the market with melting temperatures of 40° to50°C. The study was conducted on a solar water heating system using an 80 cm x 50 cm flat plate collector, and thermal energy storage using paraffin wax. Meanwhile, the heat exchanger used a tube with a diameter of 1 inch arranged in series with a pipe length of 50 cm and 36 rods. The mass of paraffin used was 15 kg or 17.7 liters. Furthermore, the test was performed with variations in the flow rate of water, namely: 2, 3, and 4 lpm, and solar radiation of: 997.5 W/m², 1183 W/m², and 1399.8 W/m². From the results, the thermal energy storage process in PCM paraffin with an amount of 15 kg, took 3.2 hours with a total stored energy of 3.6 MJ. Moreover, solar radiation of 1,399.8 W/m² was used as an energy source and water with a flow rate of 4 lpm as a medium heat transfer. Therefore, this radiation has a very significant effect on the heat transfer process to the PCM, while the flow rate with a value of 2 to 4 lpm does not have.

Experimental and numerical investigations of solar charging performances of 3D porous skeleton based latent heat storage devices

Volumetric-absorption-based solar charging via phase change processes is an emerging technology to harvest solar energy, however, how pore-scale radiation transport interacts with latent heat thermal energy storage processes is still vague. In this paper, volumetric-absorption-based solar charging processes at pore scale are investigated by experiments and numerical simulations based on Monte Carlo ray tracing coupled with the Finite Volume Method. The solar radiation transport, temperature distribution, liquid fraction, and solar thermal energy storage efficiency are systematically evaluated under different radiation intensities and skeleton thermal conductivities. Compared to the traditional surface-absorption-based mode, solar thermal energy storage efficiency of the volumetric-absorption mode is enhanced by 94% due to presence of multi-region heat sources. The solar thermal energy storage efficiency reaches a peak value of 54.09% at a radiation intensity of 10 kW·m−2. That is because low radiation intensities increase the melting time while too high intensities lead to large temperature nonuniformity, leading to high heat losses for both scenarios. Increasing the skeleton thermal conductivity can continuously improve the efficiency by reducing temperature nonuniformity, but further enhancement becomes marginal for thermal conductivity over 90 W·m−1·K−1. This work paves the way for the design and deployment of efficient integrated solar thermal conversion and latent heat storage systems.

Experimental and theoretical investigation of an innovative composite nanofluid for solar energy photothermal conversion and storage

Molten salts play a key role in the heat transfer and thermal energy storage processes of concentrated solar power plants. A novel composite material was prepared in this work by adding micron-sized magnesium particles into Li2CO3-Na2CO3-K2CO3 molten salt, the heat transfer and thermal energy storage properties of the composites were studied experimentally. A stable composite nanofluid can be obtained, and a thermal conductivity of 0.728 W/(m·K) at 973 K with an enhancement of 31% is achieved for the Mg/molten carbonate nanofluid. And the strengthening mechanism of thermal conductivity was revealed by using ab-initio molecular dynamics method. It is found that the main bonding interactions exist between Mg and O atoms at the surface of Mg particles. A compressed ion layer with a more compact and ordered ionic structure is formed around Mg particles, and the Brownian motions of Mg particles lead to the micro-convections of carbonate ions around them. These factors are helpful to the enhancement of thermal conduction with the improved probability and frequency of ion collisions. This work can provide a guidance for further studies and applications on metal/molten salt composites with enhanced heat transfer and thermal energy storage capacity.

Partial charging/discharging of bio-based latent heat energy storage enhanced with metal foam sheets

Due to the intermittent/volatile nature of renewable energy resources, they may periodically fail to provide enough energy to complete the charging/discharging processes of Latent Heat Thermal Energy Storage (LHTES) systems. However, only a limited understanding is available for the implications of partial charging/discharging. To address this knowledge gap, the present study numerically analysed the performance of a circular LHTES under partial charging/discharging modes. Three sheets of aluminium foam (all spaced equally at 120°) were added to enhance the thermal response of the storage. Sixteen different storage configurations were studied and revealed that the angle of the right-most metal foam sheet (θ) and their thickness (wmf) considerably affect the charging/discharging process. According to the proposed capacity-based and time-based charging/discharging powers, it was found that the configuration with maximum complete charging power (case no.7, θ=π/6 and wmf=7 mm) does not necessarily exhibit the best performance during partial charging mode. Instead, case no.7 has up to 6% lower charging power than the other cases when partially charged. Finally, it was revealed that a Y-shaped design can achieve optimal performance if it is charged in the upright orientation, but rotated 60° (i.e., to a ⅄-shaped orientation) to maximise the discharging process.

Artificial Neural Network Simulation of Energetic Performance for Sorption Thermal Energy Storage Reactors

Sorption thermal heat storage is a promising solution to improve the development of renewable energies and to promote a rational use of energy both for industry and households. These systems store thermal energy through physico-chemical sorption/desorption reactions that are also termed hydration/dehydration. Their introduction to the market requires to assess their energy performances, usually analysed by numerical simulation of the overall system. To address this, physical models are commonly developed and used. However, simulation based on such models are time-consuming which does not allow their use for yearly simulations. Artificial neural network (ANN)-based models, which are known for their computational efficiency, may overcome this issue. Therefore, the main objective of this study is to investigate the use of an ANN model to simulate a sorption heat storage system, instead of using a physical model. The neural network is trained using experimental results in order to evaluate this approach on actual systems. By using a recurrent neural network (RNN) and the Deep Learning Toolbox in MATLAB, a good accuracy is reached, and the predicted results are close to the experimental results. The root mean squared error for the prediction of the temperature difference during the thermal energy storage process is less than 3K for both hydration and dehydration, the maximal temperature difference being, respectively, about 90K and 40K.

A variable cross-section annular fins type metal hydride reactor for improving the phenomenon of inhomogeneous reaction in the thermal energy storage processes

Metal hydride (MH) has been of great interest as one of the potential thermochemical heat storage materials. Previous studies have revealed that with the progress of the reaction, the inhomogeneous reaction will gradually appear in the metal hydride heat storage reactor (MHHSR), which will lead to the decrease of the heat output capacity of the reactor. In this study, an innovative MHHSR with a variable cross-section annular fin (VCSAF) structure is proposed. The thermal coupling model between the powder bed and VCSAF is established. It is found that the VCSAF can effectively resolve the inhomogeneous reaction phenomenon in the reaction process by adjusting the inclination angle between outer profile of VCSAF and outer edge of bed (θfin). At the same time, the influence of different fin structures parameters is analyzed on the uniformity of the reactor based on sensitivity analysis. The width of the largest fin (Lfin,max) is the main factor affecting the uniformity in comparison with fin thickness (hfin), fin spacing (Δh). With the increase of Lfin,max, Δh and hfin, exergy output (Ex,out) changes from 266.12 kJ to 249.65 kJ, 222.64 kJ to 282.99 kJ, and 264.01 kJ to 255.82 kJ, respectively, gravimetric exergy-output power of reactor (GEOPR) changes from 41.96 W kg−1 to 48.22 W kg−1, 49.88 W kg−1 to 42.41 W kg−1, and 43.11 W kg−1 to 47.40 W kg−1, respectively, and gravimetric efficient exergy-output (GEEO) remains unchanged. Besides, the simulation results of four different designs: no fin (NF), same cross-section fin (SCSF), longitudinal fin (LF) and VCSAF are compared to assess their performance. Compared to NF, SCSF and LF, VCSAF has a more uniform heat transfer effect and better performance. Finally, the performance improvement of the enlarged VCSAF reactor is analyzed. With the increase of length (L), the platform end time difference between the SCSF and VCSAF and between LF and VCSAF (Δt1 and Δt2) increases from 800 s to 2800 s and 2250 s to 4800 s, respectively. Compared with NF, the growth rates of Ex,out, exergy efficiency (ηEx), GEEO and GEOPR for VCSAF change from 4.04% to 16.07%, 6.79% to 14.42%, 10.60% to 22.22%, and 31.74% to 6.81%, respectively. Compared with SCSF, the growth rates of Ex,out, ηEx, GEEO and GEOPR change from 12.41% to 26.23%, 9.74% to 17.97%, 12.54% to 26.01%, and 5.00% to 2.18%, respectively. Compared with LF, the growth rates of Ex,out, ηEx, GEEO and GEOPR change from 14.52% to 34.02%, 10.12% to 20.18%, 13.53% to 27.99%, and 7.70% to 5.56%, respectively. The VCSAF structure has an excellent performance in eliminating inhomogeneous reaction. With the enlargement of the reactor, the heat output capacity has been improved obviously, which has an important guiding significance for the engineering application of the MH high-temperature heat storage technology.

Effect of graphene nanoparticles on charging and discharging processes of latent thermal energy storage using horizontal cylinders

In this paper, thermal charging and discharging processes of a phase change material (PCM) dispersed with graphene nanoplatelets (GN) are investigated in a horizontal cylinder for thermal energy storage. The heat transfer and phase change processes are modeled using the enthalpy-porosity method. The momentum and energy equations are solved using a commercial code. The numerical simulations are validated by comparison with experimental and numerical data of the literature. The results showed that GN concentrations (i.e. ϕ = 0, 0.5 and 1 wt% GN) expedite the charging time while a slight reduction in melting time is obtained for ϕ = 3 wt%. The solidification time reduced by up to 50% whereas the thermal storage capacity declined by up to 14%. These results can help designing efficient thermal energy storage systems.

Estimation of the pressure oscillation in geyser process occurring in cryogenic fluid pipeline

Geyser is a complex two-phase flow instability phenomenon that may lead to safety issues in many energy fields. However, the understanding and studies of geyser physics are still limited. In the present paper, the evolution of thermal oscillation and energy storage process during geyser is visualized. Different kinds of geyser with particular pressure oscillation regimes are analyzed. A new dimensionless parameter of maximum energy storage ability (Ae) is proposed to quantitatively characterize geyser's occurrence and intensity. The effects of Ae on the oscillation of thermal parameters in geyser are analyzed. And then a transition boundary of weak and strong geyser is divided based on a critical Ae value. It is found that the energy storage inside the pipe is an essential mechanism for the geyser occurrence. With more energy is stored inside the pipe, both the geyser occurrence possibility and intensity increase. Moreover, the amount of energy storage inside the pipe and the pressure oscillation regimes could be predicted by Ae integrating multiple fundamental parameters. More energy could be stored in the pipe and released in the eruption process as Ae increasing, and it eventually facilitates the occurrence of geyser or enhances an existing geyser. The Ae also has a critical transition boundary value between 3 and 4 reflecting geyser from weak to strong regime. When Ae exceeds 4, a strong geyser with a harmful pressure peak might occur.

Three-dimensional oscillating heat pipes with novel structure for latent heat thermal energy storage application

Latent heat thermal energy storage (LHTES) has been considered as a good approach to alleviate energy source shortage and reduce environment pollution. As a high effective heat transfer device, heat pipes have been utilized in the LHTES unit to assist the melting and solidification of phase change material (PCM). To improve the thermal performance of the LHTES unit, three-dimensional oscillating heat pipes (3D-OHPs) with novel structures have been designed and manufactured in the current work. Thermal performance of 3D-OHPs with different turns and filling ratios under different cooling air velocities and inclination angles was experimentally tested. Then, a LHTES unit based on the 3D-OHP was built and tested, the charge and discharge performance was compared with that of another LHTES unit assisted by a conventional heat pipe (CHP). Composite PCMs with different thermal conductivity were utilized in the LHTES units. The results showed that the 3D-OHP could operate well to assist thermal energy storage process of the LHTES unit, especially when the thermal conductivity of PCM was low. Compared with the CHP LHTES unit, the 3D-OHP LHTES unit showed about 32% increase in charging efficiency. During the discharge process, the 3D-OHP LHTES unit had a better temperature uniformity because of the novel structure of 3D-OHP, which was helpful for avoiding potential heat accumulation.

Carbonation Reaction of Lithium Hydroxide during Low Temperature Thermal Energy Storage Process

In order to apply lithium hydroxide (LiOH) as a low temperature chemical heat storage material, the carbonation reaction of LiOH and the prevention method are focused in this research. The carbonation of raw LiOH at storage and hydration condition is experimentally investigated. The results show that the carbonation reaction of LiOH with carbon dioxide (CO₂) is confirmed during the hydration reaction. The carbonation of LiOH can be easily carried out with CO₂ at room temperature and humidity. LiOH can be carbonated at a humidity range of 10% to 20%, a normal humidity region that air can easily be reached. Furthermore, the carbonation reaction rate has not nearly affected by the increase of reaction temperature. An improved storage method by storing LiOH at a low humidity less than 1.0% can be effectively prevented the carbonation of LiOH. The hydration reaction ratio of LiOH at the improved storage method shows a better result compared to the ordinary storage method. Therefore, the humidity should be carefully controlled during the storage of LiOH before hydration and dehydration reaction when apply LiOH as a low heat chemical storage material.

Model-based optimal design of phase change ionic liquids for efficient thermal energy storage

The selection of phase change material (PCM) plays an important role in developing high-efficient thermal energy storage (TES) processes. Ionic liquids (ILs) or organic salts are thermally stable, non-volatile, and non-flammable. Importantly, researchers have proved that some ILs possess higher latent heat of fusion than conventional PCMs. Despite these attractive characteristics, yet surprisingly, little research has been performed to the systematic selection or structural design of ILs for TES. Besides, most of the existing work is only focused on the latent heat when selecting PCMs. However, one should note that other properties such as heat capacity and thermal conductivity could affect the TES performance as well. In this work, we propose a computer-aided molecular design (CAMD) based method to systematically design IL PCMs for a practical TES process. The effects of different IL properties are simultaneously captured in the IL property models and TES process models. Optimal ILs holding a best compromise of all the properties are identified through the solution of a formulated CAMD problem where the TES performance of the process is maximized. [MPyEtOH][TfO] is found to be the best material and excitingly, the identified top nine ILs all show a higher TES performance than the traditional PCM paraffin wax at 10 h thermal charging time.