Preparation and Thermal Shock Resistance of Mullite Ceramics for High Temperature Solar Thermal Storage

Mullite thermal storage ceramics were prepared by low-cost calcined bauxite and kaolin.The phase composition,microstructure,high temperature resistance and thermophysical properties were characterized by modern testing techniques.The experimental results indicate that sample A3(bauxite/kaolin ratio of 5:5)sintered at 1620℃has the optimum comprehensive properties,with bulk density of 2.83 g·cm^(-3)and bending strength of 155.44 MPa.After 30 thermal shocks(1000℃-room temperature,air cooling),the bending strength of sample A3 increases to 166.15 MPa with an enhancement rate of 6.89%,the corresponding thermal conductivity and specific heat capacity are 3.54 W·(m·K)^(-1)and 1.39 kJ·(kg·K)^(-1)at 800℃,and the thermal storage density is 1096 kJ·kg^(-1)(25-800 mullite ceramics;sintering properties;high-temperature thermal storage;thermal shock resistance).Mullite forms a dense and continuous interlaced network microstructure,which endows the samples high thermal storage density and high bending strength,but the decrease of bauxite/kaolin ratio leads to the decrease of mullite content,which reduces the properties of the samples.

Effect of MnO2 on Properties of SiC-mullite Composite Ceramics for Solar Sensible Thermal Storage

For improving the properties of SiC-mullite composite ceramics used for solar sensible thermal storage, MnO2 was introduced as sintering additive when preparing. The composite ceramics were synthesized by using SiC, andalusite, a-Al2O3 as the starting materials with non-contact graphite-buried sintering method. Phase composition and microstructure of the composites were investigated by XRD and SEM, and the effect of MnOz on the properties of SiC composites was studied. Results indicated that samples SM1 with 0.2 wt% MnO2 addition achieved the optimum properties： bending strength of 70.96 MPa, heat capacity of 1.02 J.（g.K）-1, thermal conductivity of 9.05 W-（m.K）-1. Proper addition of MnO2 was found to weaken the volume effect of the composites and improve the thermal shock resistance with an increased rate of 27.84% for bending strength after 30 cycles of thermal shock （air cooling from 1 100 ℃ to RT）. Key words： SiC-mullite composite ceramics; MnO2; solar sensible thermal storage; non-contact graphite-buried sintering; thermal shock resistance

Cold Thermal Storage and Peak Load Reduction for Office Buildings in Saudi Arabia

This paper the chilled water and involves the investigations of ice cold thermal storage technologies along with the associated operating strategies for the air conditioning （AC） systems of the typical office buildings in Saudi Arabia, so as to reduce the electricity energy consumption during the peak load periods. In Saudi Arabia, the extensive use of AC for indoor cooling in offices composes a large proportion of the annual peak electricity demand. The very high temperatures over long summer periods, extending tYom May to October, and the low cost of energy are the key factors in the wide and extensive use of air conditioners in the kingdom. This intense cooling load adds up to the requirement increase in the capacity of power plants, which makes them under utilized during the oil：peak periods. Thermal energy storage techniques are one of the effective demand-side energy management methods. Systems with cold storage shifts all or part of the electricity requirement from peak hours to off-peak hours to reduce demand charges and/or take advantage of off-peak rates. The investigations reveal that the cold thermal energy storage techniques are effective from both technical and economic perspectives in the reduction of energy consumption in the buildings during peak periods.

Numerical simulation and experimental verification of solar seasonal soil thermal storage

To analyze the characteristics of solar seasonal soil thermal storage in a solar-ground coupled heat pump system (SGCHPS) in severe cold area,the software FLUENT was used to establish the three-dimensional unsteady state fluid-solid coupling mathematical model of multi-well ground heat exchanger (MWGHE).The User-Defined Functions (UDF) of solar collector and plate heat exchanger were written and dynamically loaded into the model of MWGHE as the boundary conditions.In this way,the dynamic simulation of solar seasonal soil thermal storage was realized.The comparison of simulative and experimental results showed that the overall variation trend of simulative and experimental values achieves a good agreement with time;the relative errors of simulated parameters are all in the allowable range.Therefore,it can be obtained that the models established can be applied in the investigation of performance of solar seasonal soil thermal storage.At the same time,it provides a theoretical basis for the study of heating in SGCHPS and soil heat balance analysis after long-time thermal storage and extraction.

Research on Operation of Electrothermal Integrated Energy System Including Heat Pump and Thermal Storage Units Based on Capacity Planning

In view of the Three North areas existing wind power absorption and environment pollution problems,the previous scholars have improved the wind abandon problem by adding electrothermal coupling equipment or optimizing power grid operation.In this paper,an electrothermal integrated energy system including heat pump and thermal storage units was proposed.The scheduling model was based on the load data and the output characteristics of power units,each power unit capacity was programmed without constraints,and the proposed scheduling model was compared with the traditional combined heat and power scheduling model.Results showed that the investment and pollutant discharge of the system was reduced respectively.Wind power was fully absorbed.Compared with the traditional thermal power unit,the proportion of the output was significantly decreased by the proposed model.The proposed system could provide a new prospect for wind power absorption and environment protection.

Performance analysis of thermal storage unit with possible nano enhanced phase change material in building cooling applications

The heat transfer performance of the phase change materials used in free cooling and air conditioning applications is low,due to the poor thermal conductivity of the materials.The recent phenomenal advancement in nano technology provides an opportunity for an appreciable enhancement in the thermal conductivity of the phase change materials.In order to explore the possibilities of using nano technology for various applications,a detailed parametric study is carried out,to analyse the heat transfer enhancement potential with the thermal conductivity of the conventional phase change materials and nano enhanced phase change materials under various flow conditions of the heat transfer fluid.Initially,the theoretical equation,used to determine the time for outward cylindrical solidification of the phase change material,is validated with the experimental results.It is inferred from the parametric studies,that for paraffinic phase change materials with air as the heat transfer fluid,the first step should be to increase the heat transfer coefficient to the maximum extent,before making any attempt to increase the thermal conductivity of the phase change materials,with the addition of nano particles.When water is used as the phase change material,the addition of nano particles is recommended to achieve better heat transfer,when a liquid is used as the heat transfer fluid.

More than Color:Pigments with Thermal Storage Capacity;Processing and Degradation Behavior

A standard ultramarine pigment was used to produce phase change material composites, by adsorbing n-hexadecane paraffin around the pigment surface with the aim of obtaining a pigment providing thermal storage capacity apart from color. Vacuum impregnation method was employed optimizing the process variables to maximize the latent heat of the hexadecane/pigment composite. In addition to the process optimization, the stability of the composite having the maximum latent heat was investigated. The hexadecane/pigment composite providing the highest latent heat has a Latent heat of fusion of 44 J/g (around a 20%wt. hexadecane adsorbed in the pigment). Durability of the material was tested by thermo-diffractometric measurements. The results indicate slow reduction of the area intensity up to 6.5% after the 100 cycles.

Microstructure and Characterization of Capric-stearic Acid/Modified Expanded Vermiculite Thermal Storage Composites

In order to improve the thermal storage capacity of expanded vermiculite（EV） based formstable composite PCM（FS-PCM） via organic modification of EV, first, EV was modified with a sodium stearate（Na St） as surface modifier, and organic EV（OEV） with hydrophobicity and higher adsorption capacity for fatty acid was obtained. A novel capric-stearic acid eutectic（CA-SA）/OEV FS-PCM with high thermal storage capacity was then developed. OEV and CA-SA/OEV were characterized by scanning electron microscopy（SEM）, X-ray diffraction（XRD）, Fourier transform infrared spectroscopy（FTIR）, differential scanning calorimetry（DSC）, thermal gravimetry（TG）, and thermal cycling test. Results showed that OEV has obvious hydrophobicity and a higher adsorption capacity for fatty acid. Its adsorption ratio has increased by 48.71% compared with that of EV. CA-SA/OEV possesses high thermal storage density（112.52 J/g）, suitable melting temperature（20.49 ℃）, good chemical compatibility, excellent thermal stability and reliability, indicating great application potential for building energy efficiency. Moreover, organic modification of inorganic matrix may offer novel options for improving its adsorption capacity for organic PCMs and increasing heat storage capacity of corresponding FS-PCMs.

A Study of Aquifer Thermal Energy Storage:Numerical Simulation of Thermal Storage Experiments in Shanghai

This paper proposes a 3-D convection-heat dispersion model for a confined aquifer. The governing equation of the model contains not only the traditional convection and conduction terms, but also a heat dispersion term which has often been overlooked in many similar researches. The model is used to describe a series of aquifer thermal energy storage experiments conducted at the Shanghai experimental site, including single-well injection, double-well injection/production and multiple-well injection/prodution tests. The simulated temperatures agree very well with the field data (relative error: 2.8%-4.5%). A detailed description of the model is given, followed by a detailed comparison of simulated and measured temperature distributions.

Performance analysis of a photovoltaic/thermal system with lunar regolith-based thermal storage for the lunar base

Powering a moon base,especially keeping it warm during the long lunar night,is a big challenge.This paper introduces a photovoltaic/thermal(PV/T)system incorporating regolith thermal storage to solve the challenge of power and heat provision for the lunar base simultaneously.The vacuum of space around the moon helps this system by reducing heat loss.During the moon's daytime,the system not only generates electricity but also captures heat.This stored heat in the regolith is then used at night,reducing the amount of equipment we need to send from Earth.The spectrally selective PV/T panels are designed to absorb a wide range of sunlight(0.3–2.5μm)while minimizing heat loss in the infrared range(3–30μm).Simulation results of the hybrid solar energy system indicate the average value of the overall efficiency is 45.9%,which relatively elevates 56.1%compared to the PV system.The launch mass of the proposed PV/T system is only 8.4%of a traditional photovoltaic-lithium battery system with the same amount of energy storage.And the total specific energy of the proposed system is 7.3 kWh kg^(-1),while that of the photovoltaic-lithium battery system is about 0.3 kWh kg^(-1).In summary,this study proposes an alternative combined heat and electricity supply system for the lunar base,which can greatly reduce the launch mass and free up load for other scientific research equipment.

Self‑Assembly of Binderless MXene Aerogel for Multiple‑Scenario and Responsive Phase Change Composites with Ultrahigh Thermal Energy Storage Density and Exceptional Electromagnetic Interference Shielding

The severe dependence of traditional phase change materials(PCMs)on the temperature-response and lattice deficiencies in versatility cannot satisfy demand for using such materials in complex application scenarios.Here,we introduced metal ions to induce the self-assembly of MXene nanosheets and achieve their ordered arrangement by combining suction filtration and rapid freezing.Subsequently,a series of MXene/K^(+)/paraffin wax(PW)phase change composites(PCCs)were obtained via vacuum impregnation in molten PW.The prepared MXene-based PCCs showed versatile applications from macroscale technologies,successfully transforming solar,electric,and magnetic energy into thermal energy stored as latent heat in the PCCs.Moreover,due to the absence of binder in the MXene-based aerogel,MK3@PW exhibits a prime solar-thermal conversion efficiency(98.4%).Notably,MK3@PW can further convert the collected heat energy into electric energy through thermoelectric equipment and realize favorable solar-thermal-electric conversion(producing 206 mV of voltage with light radiation intensity of 200 mw cm^(−2)).An excellent Joule heat performance(reaching 105℃with an input voltage of 2.5 V)and responsive magnetic-thermal conversion behavior(a charging time of 11.8 s can achieve a thermal insulation effect of 285 s)for contactless thermotherapy were also demonstrated by the MK3@PW.Specifically,as a result of the ordered arrangement of MXene nanosheet self-assembly induced by potassium ions,MK3@PW PCC exhibits a higher electromagnetic shielding efficiency value(57.7 dB)than pure MXene aerogel/PW PCC(29.8 dB)with the same MXene mass.This work presents an opportunity for the multi-scene response and practical application of PCMs that satisfy demand of next-generation multifunctional PCCs.

Enhanced properties of stone coal-based composite phase change materials for thermal energy storage

Phase change materials (PCMs) can be incorporated with low-cost minerals to synthesize composites for thermal energy storage in building applications.Stone coal (SC) after vanadium extraction treatment shows potential for secondary utilization in composite preparation.We prepared SC-based composite PCMs with SC as a matrix,stearic acid (SA) as a PCM,and expanded graphite (EG) as an additive.The combined roasting and acid leaching treatment of raw SC was conducted to understand the effect of vanadium extraction on promoting loading capacity.Results showed that the combined treatment of roasting at 900℃ and leaching increased the SC loading of the composite by 6.2%by improving the specific surface area.The loading capacity and thermal conductivity of the composite obviously increased by 127%and 48.19%,respectively,due to the contribution of 3wt% EG.These data were supported by the high load of 66.69%and thermal conductivity of 0.59 W·m^(-1)·K-1of the designed composite.The obtained composite exhibited a phase change temperature of 52.17℃,melting latent heat of 121.5 J·g^(-1),and good chemical compatibility.The SC-based composite has prospects in building applications exploiting the secondary utilization of minerals.

Vertically aligned montmorillonite aerogel-encapsulated polyethylene glycol with directional heat transfer paths for efficient solar thermal energy harvesting and storage

The conversion and storage of photothermal energy using phase change materials(PCMs)represent an optimal approach for harnessing clean and sustainable solar energy.Herein,we encapsulated polyethylene glycol(PEG)in montmorillonite aerogels(3D-Mt)through vacuum impregnation to prepare 3D-Mt/PEG composite PCMs.When used as a support matrix,3D-Mt can effectively prevent PEG leakage and act as a flame-retardant barrier to reduce the flammability of PEG.Simultaneously,3D-Mt/PEG demonstrates outstanding shape retention,increased thermal energy storage density,and commendable thermal and chemical stability.The phase transition enthalpy of 3D-Mt/PEG can reach 167.53 J/g and remains stable even after 50 heating-cooling cycles.Furthermore,the vertical sheet-like structure of 3D-Mt establishes directional heat transport channels,facilitating efficient phonon transfer.This configuration results in highly anisotropic thermal conductivities that ensure swift thermal responses and efficient heat conduction.This study addresses the shortcomings of PCMs,including the issues of leakage and inadequate flame retardancy.It achieves the development and design of 3D-Mt/PEG with ultrahigh strength,superior flame retardancy,and directional heat transfer.Therefore,this work offers a design strategy for the preparation of high-performance composite PCMs.The 3D-Mt/PEG with vertically aligned and well-ordered array structure developed in this research shows great potential for thermal management and photothermal conversion applications.

Thermo-hydro-mechanical (THM) coupled simulation of the land subsidence due to aquifer thermal energy storage (ATES) system in soft soils

Aquifer thermal energy storage(ATES)system has received attention for heating or cooling buildings.However,it is well known that land subsidence becomes a major environmental concern for ATES projects.Yet,the effect of temperature on land subsidence has received practically no attention in the past.This paper presents a thermo-hydro-mechanical(THM)coupled numerical study on an ATES system in Shanghai,China.Four water wells were installed for seasonal heating and cooling of an agriculture greenhouse.The target aquifer at a depth of 74e104.5 m consisted of alternating layers of sand and silty sand and was covered with clay.Groundwater level,temperature,and land subsidence data from 2015 to 2017 were collected using field monitoring instruments.Constrained by data,we constructed a field scale three-dimensional(3D)model using TOUGH(Transport of Unsaturated Groundwater and Heat)and FLAC3D(Fast Lagrangian Analysis of Continua)equipped with a thermo-elastoplastic constitutive model.The effectiveness of the numerical model was validated by field data.The model was used to reproduce groundwater flow,heat transfer,and mechanical responses in porous media over three years and capture the thermo-and pressure-induced land subsidence.The results show that the maximum thermoinduced land subsidence accounts for about 60%of the total subsidence.The thermo-induced subsidence is slightly greater in winter than that in summer,and more pronounced near the cold well area than the hot well area.This study provides some valuable guidelines for controlling land subsidence caused by ATES systems installed in soft soils.

Development status and prospect of underground thermal energy storage technology

Underground Thermal Energy Storage(UTES)store unstable and non-continuous energy underground,releasing stable heat energy on demand.This effectively improve energy utilization and optimize energy allocation.As UTES technology advances,accommodating greater depth,higher temperature and multi-energy complementarity,new research challenges emerge.This paper comprehensively provides a systematic summary of the current research status of UTES.It categorized different types of UTES systems,analyzes the applicability of key technologies of UTES,and evaluate their economic and environmental benefits.Moreover,this paper identifies existing issues with UTES,such as injection blockage,wellbore scaling and corrosion,seepage and heat transfer in cracks,etc.It suggests deepening the research on blockage formation mechanism and plugging prevention technology,improving the study of anticorrosive materials and water treatment technology,and enhancing the investigation of reservoir fracture network characterization technology and seepage heat transfer.These recommendations serve as valuable references for promoting the high-quality development of UTES.

Advanced solid-solid phase change thermal storage material

The practicality of conventional solid-liquid phase change materials(PCMs)is adversely restricted by liquid phase leakage,large volume expansion,shape instability,and severe corrosion in high-temperature thermal management systems.This highlight presents the latest development to resolve these challenges by designing ultrahigh-performance high-temperature Ni-Mn-Ti solid-solid PCMs using martensitic phase transition strategy,offering a new paradigm to develop advanced wide-temperature high-temperature metallic solid-solid phase change thermal storage materials.

Soft Open Point Planning in Renewable-dominated Distribution Grids with Building Thermal Storage

With an increasing integration of intermittent distributed energy resources(DERs),the consequent voltage excursion and thermal overloading issues limit the self-sufficiency of distribution networks(DNs).The concept of soft open point(SOP)has been proposed as a promising solution to improve the hosting capacity of DNs.In this paper,considering the ability of building thermal storage(BTS)to increase the penetration of renewable energy in DNs,we provide an optimal planning framework for SOP and DER.The optimal planning model is aimed at minimizing the investment and operational costs while respecting various constraints,including the self-sufficiency requirement of the DN,SOP,building thermal storage capacity and DER operations,etc.A steady-state SOP model is formulated and linearized to be incorporated into the planning framework.To make full use of the BTS flexibility provided by ubiquitous buildings,a differential equation model for building thermal dynamics is formulated.A hybrid stochastic/robust optimization approach is adopted to depict the uncertainties in renewable energy and market prices.IEEE 33-bus feeder and a realistic DN in the metropolitan area of Caracas are tested to validate the effectiveness of the proposed framework and method.Case studies show that SOP/BTS plays a complementary and coordinated coupling role in the thermo-electric system,thereby effectively improving the hosting capacity and self-sufficiency of DNs.

Thermal storage properties of Mg with synergistic effect of LaNi and TiH_(2)

The effect of LaNi and Ti on thermal storage properties of MgH_(2)was investigated.The thermal storage performances of Mg are significantly improved by adding LaNi and Ti.The pressure-composition-temperature(PCT)curves indicate that the formation enthalpy for Mg-15 wt%Ti-5 wt%LaNi sample is 73.00 kJ·mol^(-1),which approaches to the theoretical values of pure MgH_(2).The isothermal measurement indicates that,for the Mg-15wt%Ti-5 wt%LaNi,the first absorption reaction fraction within 2 min is 93.77%,increasing by 0.32%,0.24%and0.08%compared with those for Mg,Mg-5 wt%LaNi and Mg-15 wt%Ti,respectively.The first desorption reaction fraction within 2 min is 73.18%,increasing by 55.91%,9.79%and 8.12%compared with those for Mg,Mg-5wt%LaNi and Mg-15 wt%Ti,respectively.Moreover,Mg-15 wt%Ti-5 wt%LaNi has the best cyclic stability in all the samples.The thermal storage performances of Mg by adding both LaNi and Ti are improved mainly ascribed to synergistic effect of in situ formed La_(4)H_(12.19),Mg_(2)NiH_(4),H_(0.3)Mg_(2)Ni and TiH_(2)particles during cyclic process.The above analysis demonstrates that Mg-15 wt%Ti-5wt%LaNi is suitable for using as a heat storage material.

Thermal storage properties of Mg-LaNi using as a solar heat storage material

The effect of LaNi on thermal storage properties of MgH2 prepared by ball milling under hydrogen atmosphere was investigated.The thermal storage properties,cyclic property and thermal storage mechanism were studied by pres sure-composition-temperature(PC T),X-ray diffraction(XRD)and transmission electron microscopy(TEM).The Van't Hoff curve indicates that the formation enthalpy of Mg-16 wt%LaNi is 74.62 kJ·mol^(-1),which approaches to the theoretical values of MgH2.The isothermal measurement indicates that Mg-16 wt%LaNi can absorb 6.263 wt%H_(2)within 30 min at 390℃for the first absorption,the absorption reaction fraction within2 min is over 90.00%,and the desorption reaction fraction within 2 min is 72.63%,increasing by 55.36%compared with that of Mg.Mg-16 wt%LaNi has better cyclic stability than that of Mg,only decreasing by 0.609 wt%after 80cycles.The enhancement in thermal storage performances of Mg by adding LaNi is mainly ascribed to the formed Mg_(2)NiH_(4),H_(0.3)Mg_(2)Ni and La_(4)H_(12.19)during the cyclic process which act as catalysts and inhibit the growth of Mg.The above results prove that Mg-16 wt%LaNi is suitable for use as a heat storage material.

Spatiotemporal phase change materials for thermal energy long-term storage and controllable release

Phase change materials(PCMs)have attracted much attention in the field of solar thermal utilization recently,due to their outstanding thermal energy storage performance.However,PCMs usually release their stored latent heat spontaneously as the temperature below the phase transition temperature,rendering thermal energy storage and release uncontrollable,thus hindering their practical application in time and space.Herein,we developed erythritol/sodium carboxymethylcellulose/tetrasodium ethylenediaminetetraacetate(ERY/CMC/EDTA-4Na)composite PCMs with novel spatiotemporal thermal energy storage properties,defined as spatiotemporal PCMs(STPCMs),which exhibit the capacity of thermal energy long-term storage and controllable release.Our results show that the composite PCMs are unable to lose latent heat due to spontaneous crystallization during cooling,but can controllably release thermal energy through cold crystallization during reheating.The cold-crystallization temperature and enthalpy of composite PCMs can be adjusted by proportional addition of EDTA-4Na to the composite.When the mass fractions of CMC and EDTA-4Na are both 10%,the composite PCMs can exhibit the optical coldcrystallization temperature of 51.7℃ and enthalpy of 178.1 J/g.The supercooled composite PCMs without latent heat release can be maintained at room temperature(10-25℃)for up to more than two months,and subsequently the stored latent heat can be controllably released by means of thermal triggering or heterogeneous nucleation.Our findings provide novel insights into the design and construction of new PCMs with spatiotemporal performance of thermal energy long-term storage and controllable release,and consequently open a new door for the development of advanced solar thermal utilization techniques on the basis of STPCMs.