Long-term Thermal Storage Research Articles

Scattered Co-anchored MoS2 synergistically boosting photothermal capture and storage of phase change materials

Pristine phase change materials (PCMs) suffer from inherent deficiencies of poor solar absorption and photothermal conversion. Herein, we proposed a strategy of co-incorporation of zero-dimensional (0D) metal nanoparticles and two-dimensional (2D) photothermal materials in PCMs for efficient capture and conversion of solar energy into thermal energy. Highly scattered Co-anchored MoS2 nanoflower cluster serving as photon and phonon triggers was prepared by in-situ hydrothermal growth of ZIF67 polyhedron on 2D MoS2 and subsequent high-temperature carbonization. After encapsulating thermal storage unit (paraffin wax), the obtained composite PCMs integrated high-performance photothermal conversion and thermal energy storage capability. Benefiting from the synergistic enhancement of 0D Co nanoparticles with localized surface plasmon resonance effect, carbon layer with the conjugation effect and 2D MoS2 with strong solar absorption, composite PCMs exhibited a high photothermal conversion efficiency of 95.19%. Additionally, the resulting composite PCMs also demonstrated long-term thermal storage stability and durable structural stability after 300 thermal cycles. The proposed collaborative co-incorporation strategy provides some innovative references for developing next-generation photothermal PCMs in solar energy utilization.

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

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

Integrating thermal energy storage and microwave absorption in phase change material-encapsulated core-sheath MoS2@CNTs

Developing advanced nanocomposite integrating solar-driven thermal energy storage and thermal management functional microwave absorption can facilitate the cutting-edge application of phase change materials (PCMs). To conquer this goal, herein, two-dimensional MoS2 nanosheets are grown in situ on the surface of one-dimensional CNTs to prepare core-sheath MoS2@CNTs for the encapsulation of paraffin wax (PW). Benefiting from the synergistic enhancement photothermal effect of MoS2 and CNTs, MoS2@CNTs is capable of efficiently trapping photons and quickly transporting phonons, thus yielding a high solar-thermal energy conversion and storage efficiency of 94.97%. Meanwhile, PW/MoS2@CNTs composite PCMs exhibit a high phase change enthalpy of 101.60 J/g and excellent long-term thermal storage durability after undergoing multiple heating–cooling cycles. More attractively, PW/MoS2@CNTs composite PCMs realize thermal management functional microwave absorption in heat-related electronic application scenarios, which is superior to the single microwave absorption of traditional materials. The minimum reflection loss (RL) for PW/MoS2@CNTs is −28 dB at 12.91 GHz with a 2.0 mm thickness. This functional integration design provides some insightful references on developing advanced microwave absorbing composite PCMs, holding great potential towards high-efficiency solar energy utilization and thermally managed microwave absorption fields.

Copper–Alumina Capsules for High-Temperature Thermal Energy Storage

High corrosivity, leakage, and oxidation of metallic phase-change materials (PCMs) have limited their applications in high-temperature thermal energy storage (TES) systems, regardless of their favorable benefits for high-temperature TES applications of over 1000 °C. To overcome these major challenges, this work presents a facile paraffin sacrificial layer approach for directly encapsulating copper (Cu) sphere PCMs with the alumina (Al2O3) shell, considering a buffer inner cavity. The cavity is formed by the decomposition of the paraffin layer through a pre-sintered process. It plays a key role in accommodating the volume expansion of the Cu core, thereby preventing the breakage of the shell and the leakage of the liquid PCM. A series of macrocapsules with different sizes (9.5–21 mm) containing the Cu core, cavity, and Al2O3 shell are successfully produced using the paraffin sacrificial layer method and deploying a two-step heat treatment. The experimental results show that the Al2O3 shell possesses a good structure, which can prevent the leakage of the Cu core. The Al2O3 shell also has strong compatibility with the Cu core without any chemical reaction between two materials. In a temperature range of 1000–1100 °C, the calculated mass and volume energy storage densities of the PCM macrocapsule with 21 mm outer diameter are found to be 222 kJ/kg and 745 J/cm3, which are 1.83 and 1.76 times, respectively, higher than those for the Al2O3 ceramic. After thermal cycle tests, the encapsulated Cu PCM shows superior shape stability, chemical stability, and thermal durability, which can be applied in long-term thermal storage systems for high-temperature TES systems.

Design and Fabrication of Ultrathin Nanoporous Donor-Acceptor Copolymer-Based Organic Field-Effect Transistors for Enhanced VOC Sensing Performance.

The development of organic field-effect transistor (OFET) chemical sensors with high sensing performance and good air stability has remained a persistent challenge, thereby hindering their practical application. Herein, an OFET sensor based on a donor-acceptor copolymer is shown to provide high responsivity, sensitivity, and selectivity toward polar volatile organic compounds, as well as good air stability. In detail, a polymer blend of N-alkyl-diketopyrrolo-pyrrole-dithienylthieno[3,2-b]thiophene (DPP-DTT) and polystyrene is coated onto an FET substrate via shearing-assisted phase separation (SAPS) combined with selective solvent etching to fabricate the DPP-DTT-based OFET device having an ultrathin nanoporous structure suitable for gas sensing applications. This is achieved via optimization of the film morphology by varying the shear rate to adjust the dynamic balance between the shear and capillary forces to obtain an ultrathin thickness (∼8 nm) and nanopore size (80 nm) that are favorable for the efficient diffusion and interaction of analytes with the active layer. In particular, the sensor presents high responsivities toward methanol (∼70%), acetone (∼51.3%), ethanol (∼39%), and isopropyl alcohol (IPA) (∼29.8%), along with fast response and recovery times of ∼80 and 234 s, respectively. Moreover, the average sensitivity was determined to be 5.75%/ppm from the linear plot of the responsivity against the methanol concentration in the range of 1-100 ppm. Importantly, the device also exhibits excellent long-term (30-day) air and thermal storage stability, thereby demonstrating its high potential for practical applications.

Enhancing flexibility for climate change using seasonal energy storage (aquifer thermal energy storage) in distributed energy systems

Long-term energy storage is expected to play a vital role in the deep decarbonization of building energy sectors, while enhancing the flexibility of buildings to withstand future climate variations. However, it is challenging to design distributed multi-energy systems (DMES) while taking into account the uncertainties introduced by climate change, since stochastic optimization of such systems is difficult. The present study introduces a stochastic optimization model to address this bottleneck, taking into account DMES including aquifer thermal energy storage (ATES) as the long-term thermal storage. For the first time, a novel optimization algorithm links ATES with the DMES optimization model with the support of a simplified geotechnical model. Subsequently, a case study was conducted, focusing on a residential district in Chicago where the impact of future climate condition, energy demand, and solar and wind energy potentials were evaluated using Weather Research and Forecasting (WRF) data (up to 2080) and the EnergyPlus model. The study revealed that ATES is an attractive way to improve the renewable energy penetration level and minimize the dependence on fossil fuels with reasonable support from the grid to assist the fluctuations in both demand and generation. Furthermore, ATES notably reduces fuel consumption and dependence while greatly enhancing the flexibility of the energy system to withstand fluctuations in demand and renewable energy generation brought by future climate variations. These qualities will make ATES an important part of distributed energy systems, even though it is not currently the lowest cost alternative due to lack of technology maturity. The design platform introduced in the present study can be used to design DMES enhancing flexibility to accommodate future climate variations.

Salt gradient solar pond as a thermal energy storage system: A review from current gaps to future prospects

A Salt Gradient Solar Pond (SGSP) is an artificial pond or natural lake, able to collect and store the incident solar energy, characterizing by a specific vertical gradient of salt concentration. SGSPs have been studied for many years for its long-term thermal storage capacity, simplicity and low cost. This review presents an overview of the studies on the topic, presenting the achievements obtained and highlighting, for the first time on the SGSP reviews, the limiting factors where improvements are needed. In this sense, attenuation of solar radiation approaches, different numerical models developed and aspects affecting the SGSP performance are dealt with. The choice of the geometrical shape and the thickness of the zones is the first step in the design phase. The salt, in function of type and concentration, affects the stability of the pond. The heat extraction modality is crucial for the overall efficiency and a wide description of the position of the heat extraction and the cross-section shape of the tubes is provided. Then, over the last years, different enhancing methods have been proposed, such as floating rings, gels, porous and phase change materials, to maximize the performance and to reduce the heat losses with the environment. At the end, the key points on which further research should focus are discussed.

Implementation of a Model Predictive Control Strategy to Regulate Temperature Inside Plug-Flow Solar Reactor With Countercurrent Flow

Abstract Solar-driven thermochemical energy storage systems are proven to be promising energy carriers (solar fuels) to utilize solar energy by using reactive solid-state pellets. However, the production of solar fuel requires a quasi-steady-state process temperature, which represents the main challenge due to the transient nature of solar power. In this work, an adaptive model predictive controller (MPC) is presented to regulate the temperature inside a tubular solar reactor to produce solid-state solar fuel for long-term thermal storage systems. The solar reactor system consists of a vertical tube heated circumferentially over a segment of its length by concentrated solar power, and the reactive pellets (MgMn2O4) are fed from the top end and flow downwards through the heated tube. A countercurrent flowing gas supplied from the lower end interacts with flowing pellets to reduce it thermochemically at a temperature range of 1000—1500 °C. A low-order physical model was developed to simulate the dynamics of the solar reactor including the reaction kinetics, and the proposed model was validated numerically by using a 7-kW electric furnace. The numerical model then was utilized to design the MPC controller, where the control system consists of an MPC code linked to an adaptive system identification code that updates system parameters online to ensure system robustness against external disturbances (sudden change in the flow inside the reactor), model mismatches, and uncertainty. The MPC controller parameters are tuned to enhance the system performance with minimum steady-state error and overshoot. The controller is tested to track different temperature ranges between 500 °C and 1400 °C with different particles/gas mass flowrates and ramping temperature profiles. Results show that the MPC controller successfully regulated the reactor temperature within ± 1 °C of its setpoint and maintained robust performance with minimum input effort when subjected to sudden changes in the amount of flowing media and the presence of chemical reaction.

A data-driven approach to low-enthalpy shallow geothermal energy extraction: A case study on indoor heating for precision agriculture applications

Shallow geothermal energy systems utilize the upper layers of the ground to provide space heating and cooling, with a relatively high efficiency. The research presented aims to assess the potential harnessing of this source and applying it for indoor conditioning of a precision agriculture facility. An experimental phase was conducted to measure the temperature of the ground at 0.75 m, 1.5 m, 2.25 m, and 3.0 m. Field testing was performed employing two probes; one uncovered and a second insulated with a polyethylene sheet, to evaluate the effect soil water content variations exert over the soil temperature. It was found that, given the high permeability and good drainage of the soil material, water content is not statistically significant, ruling out the presence of microconvective phenomena within the interstices of the undisturbed earth. Based on the temperature profile obtained, achievable heat extraction capacity was computed by modelling a buried pipe system. A parametrization was conducted showing that, of all the involved factors, pipe depth, pitch and their interaction, are the ones that contribute the most to the heat output variability. The computed available heat flow was used to simulate the performance of a geothermal heat pumping system for greenhouse heating based on real operation data, provided by the owners. The results show that, shallower layers of the ground, can provide adequate solutions for immediate thermal needs; a 5-pipe, 100m-length ground loop at 0.75 m, could provide 90% of the total thermal demand, whilst an 11-pipe, 200m-length loop, at 1.5 m depth, reaches 84% of the same demand, with a variability reduction in availability of 10% to 20% depending on the severity of surface conditions. However, for deeper layers, i.e., 2.25 m and 3.0 m, respective maximum heat output amounts to 43% and 49% of the total thermal demand. Nonetheless, these configurations yield the most stable and constant heat flow of the lot, making them particularly suitable for preheating/subcooling processes or even long-term thermal storage. Despite not fulfilling the total thermal demand of the greenhouse, these setups are more than capable of providing support to on-site conditioning devices; requiring a lower upkeep and yielding a higher efficiency, which would reduce overall production costs. Furthermore, from the conducted data analysis, it was found that controlling the agronomic values, associated to indoor agriculture, facilitates the physical aspect of greenhouse energy management, paving the way to more optimized thermal solutions, tailored to different sets of operation conditions.

Numerical investigation of a thermal energy storage system based on the serpentine tube reactor

Thermochemical heat storage (TCHS) technology is widely concerned for its high energy storage density (ESD) and long-term storage of energy in the form of chemical energy for long-term thermal storage applications. TCHS with hydrated salt as the thermochemical material (TCM) has low regeneration temperature, clean reaction products, and appropriate heat release temperature, which is suitable for the application of medium and low temperature applications. A 3D numerical model is developed to simulate and understand the hydration (heat discharging) process of the serpentine tube reactor filled with hydrate of K2CO3. The coupled multiphysics includes fluid flow, heat and mass transfer, and chemical reaction process. Variations of hydration characteristics, such as temperature and conversion, are discussed in detail. The heat discharging processes at different vapor pressure (1200 Pa–1600 Pa) and different inlet flow rates (0.5–5 m/s) of heat transfer fluid (HTF) are investigated. It is found that higher vapor pressure can significantly increase output temperature, and a higher HTF inlet flow rate can improve overall heat exchange performance. By increasing the vapor pressure from 1200 Pa to 1600 Pa, the maximum outlet temperature lift could be significantly increased by 7.9 %. However, pipe shape has little effect on enhancing the performance of the reactor.

Supercooled sugar alcohols stabilized by alkali hydroxides for long-term room-temperature phase change solar-thermal energy storage

Seasonal thermal energy storage within organic phase change materials (PCMs) offers a promising way to solve intermittency of renewable energy, but the charged PCMs tend to undergo spontaneous crystallization and lose the stored latent heat to cold environment during storage. Herein, we report introduction of alkali hydroxides into sugar alcohols to increase the activation energy barrier for liquid-to-solid phase transition and stabilize the supercooling state, thereby realizing long-term phase change thermal energy storage. Owing to increased intermolecular hydrogen bonding interaction, the charged composites can maintain the supercooled state and conserve latent heat (∼200 J/g) during storage at room temperature or extremely cold temperatures for months. Further compounding with polydopamine organic pigments, the composites demonstrate high solar absorptance (∼91.6 %) and thus enable seasonable storage of solar-thermal energy as latent heat at room temperature. The stored heat can be readily released through adding seed crystals or applying mechanical deformation, which triggers cold crystallization of the supercooled composites and releases latent heat within a suitable temperature range of 40–60 °C. Such phase change composites not only eliminate complicated thermal insulation engineering required in conventional long-term thermal storage processes, but also unlock diverse application opportunities for thermal energy systems.

Experimental investigation on space heating performances of supercooled thermal storage units with sodium acetate trihydrate

Supercooled salt hydrates could be applied for long-term solar thermal storage and then be activated to release the stored latent heat on demand. To realize this strategy, the space heating performances with supercooled storage units need to be clarified. Experiments were performed on two heating modes using thermal storage units filled with supercooled liquid sodium acetate trihydrate (SAT), i.e. the capillary-mat floor water heating and direct heat release to the room air, respectively. The results show that, with the terminal of capillary-mat radiant floor, the maximum supply water temperature reaches 35 °C within 0.3 h and the room temperature increases from initial 20.3 °C to the maximum 25.8 °C within 2.8 h. The room temperature could be kept above 24.8 °C after the system runs for 12 h. Also, the temperature difference between the 0.5 m and 1.5 m height levels in the room space is within 0.2 °C. While the thermal storage units directly release heat to the room air with the same mass of SAT, the room temperature could rise up to 27.2 °C within 1.1 h which is higher than that of the capillary-mat terminal even in shorter period. However, the room temperature drops quickly and is about 20.9 °C after 12 h, and the maximum temperature difference between the heights of 0.5 m and 1.5 m in the room is 2.4 °C. Although the combination of supercooled liquid SAT and the capillary-mat radiant floor terminal has delayed heating rate into the room space, it presents less temperature swing and lower vertical temperature gradient, thus not only meets the room temperature requirement, but also has better thermal comfort. The results provide guidance for application of supercooled liquid PCMs for solar thermal storage in space heating systems.

Long-Term Thermal Cycling Test and Heat-Charging Kinetics of Fe-Substituted Mn2O3 for Next-Generation Concentrated Solar Power Using Thermochemical Energy Storage at High Temperatures

We studied the performance in terms of the long-term cyclic thermal storage and heat-charging kinetics of Fe-substituted manganese oxide for use in thermochemical energy storage at temperatures exceeding 550 °C in a next-generation concentrated solar power system in which a gas stream containing oxygen is used for reversible thermochemical processes. The Fe-substituted Mn2O3 was evaluated from the viewpoint of its microstructural characteristics, thermodynamic phase transitions, and long-term cycling stability. A kinetic analysis of the heat-charging mode was performed at different heating rates to formulate the kinetic equation and describe the reaction mechanism by determining the appropriate reaction model. Finally, the kinetics data for the sample obtained after the long-term cycling test were compared and evaluated with those of the as-prepared sample and kinetic literature data tested under different conditions. For the long-term cycled sample, the Avrami–Erofeev reaction model (An) with n = 2 describes the behavior of the first part of the charging mode, whereas the contracting area (R2) reaction model best fits the last half of the charging mode. For the as-prepared sample, except for the early stage of the charging mode (fractional conversion < 0.2), the contracting volume (R3) reaction model fits the charging mode over a fractional conversion range of 0.2–1.0 and the first-order (F1) reaction model fits in the fractional conversion range of 0.4–1.0. The predicted kinetic equations for both the samples were in good agreement with the experimental kinetic data.

Investigation of Combined Heating and Cooling Systems with Short- and Long-Term Storages

Modern buildings in cold climates, like Norway, may have simultaneous heating and cooling demands. For these buildings, integrated heating and cooling systems with heat pumps, as well as short-term and long-term thermal storage, are promising solutions. Furthermore, combining this integrated system with renewables aids in the transition to future sustainable building energy systems. However, cost-effectively designing and operating such a complicated system is challenging and rarely addressed. Therefore, this research proposed an integrated heating and cooling system that incorporated a short-term water tank and a long-term borehole thermal storage. Meanwhile, three operating modes: heating, cooling, and free cooling were defined based on different heating and cooling load conditions. A detailed system model was developed in MATLAB using heat pump manufacture data as well as simulated and measured building loads. Following that, sensitivity studies were performed to investigate the impacts of ground properties, thermal storage size, setpoint temperature, heat pump characteristics, and load conditions. The findings identified the crucial factors that influence the system’s overall energy efficiency and the functioning of the key system components. Particularly, it revealed that low cooling to heating ratios caused an imbalance in charging and discharging, further reducing the ground temperature and degrading the heat pump’s performance.

Ambient loop district heating and cooling networks with integrated mobility, power and interseasonal storage

This paper describes a heat pump investigation for GreenSCIES (GS), a fifth Generation district heating and cooling (5DHC) network in Islington, London. The paper describes the GreenSCIES concept integrating Mobility, Power and Heat into a Smart Local Energy System (SLES). At the heart of the system is an ultra-low temperature ambient loop network, which permits bi-directional flow within the pipes to allow energy exchange between heating and cooling customers at different times and in different locations, depending on where demand is at any given time. An existing data centre provides the primary source of waste heat for the scheme. Heat pumps in distributed energy centres are utilised to amplify the temperature of the ambient loop to deliver heat in connected buildings. The energy centres integrate heat pumps with building-mounted solar photovoltaic (PV) systems and electric vehicle (EV) charging points. The paper provides an overview of the integrated SLES concept, focussing on the heat pump selection and the short and long-term thermal storage options designed for the scheme. The results show that even the smaller constructible ‘New River’ scheme will save 5,000 tons of CO2e annually. This will tend to 100% as the grid decarbonise further. Therefore, the GS SLES concept applied to urban areas could deliver significant carbon emission savings in the UK and elsewhere. Practical application: Project GreenSCIES, is a detailed design study to develop a Smart, Local Energy System (SLES) for a large community in the London Borough of Islington. Our consortium have developed an innovative SLES concept, centred around a fifth generation district heating and cooling network. The GS ambient loop systems have negligible losses and much greater efficiencies than traditional district heat networks. As recognised by the UK Government’s Heat and Buildings Strategy, ambient loop systems should be considered where large-scale neighbourhood regeneration occurs. The proposed SLES concept applied to wider urban areas could deliver significant carbon emission savings in the UK.

A 100 Gbaud On-off-Keying Silicon-Polymer Hybrid Modulator Operating at up to 110°C

We demonstrate 100-Gbaud on-off-keying (OOK) transmission driven at a low voltage using an electro-optic (EO) polymer modulator combined with a silicon Mach-Zehnder interferometer waveguide. Various types of organic- and polymer-based modulators have been reported to perform efficient EO modulation and high-speed data transmission at over 100 Gbaud. However, there are critical concerns regarding the practical application of polymer devices in terms of environmental stability. In particular, long-term thermal storage and stability during operation require improvements before EO polymer modulators can be applied in practical systems. We have developed an EO polymer with enhanced thermophysical stability and used it to fabricate an efficient EO polymer modulator. In this study we extend our earlier work on high-speed EO polymer modulators by performing fiber-link 100-Gbaud OOK transmission at various operating temperatures. A thermal stability test revealed that the EO polymer modulator can survive high-temperature exposure up to 110°C. Error-free signal transmissions over a distance of 2.0 km was successfully demonstrated with a driving voltage of 1.9 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> and a bit error rate below the 7% overhead forward error correction threshold. The driving voltage, bandwidth, bit error rate, and fiber-link performance of the device are presented.

A novel modified LiCl solution for three-phase absorption thermal energy storage and its thermal and physical properties

• A novel LiCl solution for three-phase absorption thermal energy storage is proposed. • The energy storage density of the solution is enhanced by adding two types of additives. • The LiCl crystal slurry overcomes the fluidity problem caused by crystallization. • Thermal and physical properties of the modified solution are measured by experiments. Absorption thermal energy storage (TES) is gaining increasing attention due to its large energy storage density (ESD), mobility and long-term thermal storage capability. Expanding the working concentration difference of a solution can significantly enhance its ESD; however, this may result in crystallization, influencing fluidity and blocking flow channels in a TES device. Furthermore, bulky crystals are difficult to dissolve during energy discharge. In this paper, a novel modified LiCl solution is proposed for three-phase absorption TES, which allows the growth of fine crystals and the formation of well suspended slurry. For the first time, two types of additives with competing mechanism are introduced into the solution: ethylene glycol as a crystallization inhibitor and SiO 2 nanoparticles (SNPs) as a nucleating agent. Compared with traditional working fluids, the proposed solution has a larger ESD and good fluidity. The expanded concentration difference is determined by experiments on solubility and suspension. The optimal mass ratio of the LiCl solution, ethylene glycol and SiO 2 nanoparticles are obtained considering both ESD and fluidity. Heat and cold storage density using this novel LiCl crystal slurry can be enhanced by 24.8% and 156.0% respectively. Measurements on thermal and physical properties including vapor pressure, density and viscosity are also carried out.

Identifying the Long-Term Thermal Storage Stability of SBS-Polymer-Modified Asphalt, including Physical Indexes, Rheological Properties, and Micro-Structures Characteristics

The thermal storage stability of styrene–butadiene–styrene tri-block copolymer modified bitumen (SBSPMB) is the key to avoid performance attenuation during storage and transportation in pavement engineering. However, existing evaluation index softening point difference within 48 h (ΔSP48) cannot effectively distinguish this attenuation of SBSPMB. Thus, conventional physical indexes, rheological properties, and micro-structure characteristics of SBSPMB during a 10-day storage were investigated in this research. Results showed that during long-term thermal storage under 163 °C for 10 days, penetration, ductility, softening point, recovery rate (R%), and anti-rutting factor (G*/sinδ) were decayed with storage time increasing. This outcome was ascribed to the phase separation of SBS, which mainly occurred after a 4-day storage. However, ΔSP48 after a 6-day storage met the specification requirements (i.e., below 2.5 °C). Thus, the attenuation degree of asphalt performance in field storage was not effectively characterized by ΔSP48 alone. Results from network strength (I) and SBS swelling degree tests revealed that the primary cause was SBS degradation and base asphalt aging. Moreover, conventional indexes, including penetration, ductility, and softening point, were used to build a prediction model for rheological properties after long-term storage using partial least squares regression model, which can effectively predict I, R, Jnr, G*/sinδ, and SBS amount. Correlation coefficient is above 0.8. G*/sinδ and I at the top and bottom storage locations had high coefficient with SBS amount. Thus, phase separation of SBSPMB should be evaluated during thermal storage.

Study on long-term thermochemical thermal storage performance based on SrBr2-expanded vermiculite composite materials

Strontium bromide hexahydrate (SrBr2·6H2O) is one of the most promising storage materials of thermochemical energy storage for space heating. In this study, four different SrBr2/expanded vermiculite composites (SrBr2/EVMs) were prepared by the impregnation method. After that, the micro and macro-structural characteristics of those composites were characterized by Scanning Electron Microscopy (SEM) and X-ray Energy Dispersive Analysis (EDX). Moreover, the composites’ dynamical desorption behaviors were tested by Thermo Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Meanwhile, the composites’ dynamical adsorption behaviors were investigated in a constant temperature and humidity chamber. Lastly and most importantly, the kinetic models for the adsorption and desorption processes of SrBr2·6H2O were first deduced based on the above experimental data. The results showed that the carrying capacity of SrBr2/EVM composite linearly increased with the concentration of SrBr2 solution. And the composite can likely achieve a higher water uptake amount and better adsorption performance than pure salt. However, the composite loaded with more salt would deliquesce at high humidity and reduce the adsorption performance. It was found that SrBr2·6H2O in the composite could be well desorbed and achieve a reaction enthalpy as high as 644.9 J/g. The developed conversion rate function can reasonably predict the hydration reaction of SrBr2. Besides, six different kinetic equations of the solid-state decomposition were established to calculate the desorption reaction. The findings are useful to the design and operation of the thermochemical energy storage system with SrBr2·6H2O.

Sizing and performance analyses of a combined heating and cooling system with the integration of short- and long-term storages

Technological advancements in the utilization of renewable energy sources have unveiled potentials for increasing building energy efficiency. Integrating heat pump-based energy systems with thermal storages is a suitable option to meet the thermal requirements of modern buildings and exploiting the available renewable energy sources. However, how to size the main components of a heat pump-based energy system with the integration of short- and long-term storages is not yet well explored. Therefore, this study focused on the design and performance analyses of an integrated heating and cooling system consist of a heat pump, borehole long-term thermal storage, and hot water tank short-term thermal. Heat pump models were introduced as parametric models based on the producer data. The dynamic thermal model of the energy system was developed and analysed in MATLAB. Different combinations of heating and cooling loads were tested. Integration of cooling and heating systems was discussed through different operation strategies and challenges were addressed. The results of the parametric analysis identified the key parameters affecting the design of components and efficiency of the system. Moreover, the results showed that lower cooling to heating load ratio leads to an excessive reduction of the ground temperature and overall efficiency over the long-term operation.