High Heat Release Research Articles

Optimization design of ultra-fine supplementary cementitious materials ultra-high performance concrete mix proportion based on orthogonal experiment

Traditional ultra-high performance concrete has problems such as high viscosity, high early-age autogenous shrinkage, and high heat release during early hydration. In recent years, with the development of ultra-fine grinding technology, ultra-fine supplementary cementitious materials (USCMs) have received widespread attention, which have higher pozzolanic activity than traditional supplementary cementitious materials. This study investigated the effects of water-binder ratio, silica fume content, and ultra-fine supplementary cementitious materials (USCMs) content on the workability, mechanical properties, and early-age autogenous shrinkage of ultra-high performance concrete (UHPC) based on orthogonal experiments. In orthogonal experiments, multiple factors and levels were introduced, and a combination of range analysis, variance analysis, and multi-factor interaction analysis were combined to determine the optimization level range of each factor. The results showed that the water-binder ratio had the greatest impact on the fluidity, compressive strength, and autogenous shrinkage of UHPC; The content of silica fume had the greatest impact on the flexural strength of UHPC. Compared with the control group, USCMs can significantly improve the workability and rheological properties of UHPC, reduce early hydration heat release, and inhibit the autogenous shrinkage of UHPC.

Flexibility, malleability, and high mechanical strength phase change composite films for solar-thermal and electro-thermal energy storage

Phase change materials (PCMs) are widely used in a range of energy storage applications due to high latent heat absorption and release capacities during phase change processes. There is still a lot to be done to resolve the inherent leakage, stiffness problems, and poor solar-thermal and electrical-thermal conversion capacities of PCMs to functionalize them. Here, a novel solid-solid phase change material (IGPCM) is created using block copolymerization. The IGPCM has a tunable enthalpy (from 58.16 to 99.60 J g−1) by adjusting the molecular weight of the PEG. The obtained IGPCM10K has high toughness (479.1 MJ/m3), excellent bending and malleability. Since IGPCM10K suffers from poor thermal conductivity, photo responsiveness, and electro-thermal conversion, carbon nanotubes (CNT) can be added to our IGPCM10K in a simple way to improve these issues. The thermal conductivity of IGPCM10K-CNT-3 is improved by 55.6 % compared to IGPCM10K. The photothermal conversion efficiency is 84.9 % at 300 mW/cm2. The electrothermal conversion efficiency is 82.3 % at 12 A. The prepared flexible PCM composites have super toughness, high enthalpy, excellent thermal conductivity, and photo-thermal and electro-thermal conversion capabilities, which will show great potential in future applications.

Bacterial cellulose-based Janus energy storage phase change composite aerogel for efficient interfacial solar vapor generation

Interfacial solar evaporation systems based on Janus structures exhibit potential application prospects in terms of salt tolerance. However, intermittent and unstable light conditions limited the evaporation rate and water production performance of the evaporators. The introduction of energy storage phase change (ESPC) composite materials into the interface solar evaporators can effectively solve this problem. In this work, bacterial cellulose (BC) is selected as the matrix material, sodium alginate (SA) and multi-walled carbon nanotubes (MWCNTs) are added as functional fillers, and porous composite aerogels are prepared using direct freeze-drying. On this basis, Janus porous composite aerogel (J-BCS/CNT) with ESPC function is further constructed by depositing paraffin onto the upper layer of the aerogel through a unilateral vacuum impregnation method. The aerogel exhibits strong photothermal conversion capabilities and excellent thermal management properties. The addition of appropriate amount of MWCNTs enables it to obtain high latent heat storage and release functions, providing energy for operation in dark conditions. Under the solar irradiation of 1.5 kW m−2, J-BCS/CNT40% aerogel exhibits a high evaporation rate of 1.95 kg m−2h−1 in pure water and 0.67 kg m−2h−1 under dark conditions. The salt evaporation resistance test shows that the aerogel has excellent purification capabilities in high-concentration salt water (20 wt%) solutions. More importantly, the long-term energy storage-release tests of J-BCS/CNT in 3.5 wt% saline water indicate that the aerogel reveals excellent sustainability and latent heat release functions.

Experimental Study on the Thermal Behavior Characteristics of the Oxidative Spontaneous Combustion Process of Fischer–Tropsch Wax Residue

Coal-to-liquid technology is a key technology to ensuring national energy security, with the Fischer–Tropsch synthesis process at its core. However, in actual production, Fischer–Tropsch wax residue exhibits the characteristics of spontaneous combustion due to heat accumulation, posing a fire hazard when exposed to air for extended periods. This significantly threatens the safe production operations of coal-to-liquid chemical enterprises. This study primarily focuses on the experimental investigation of the oxidative spontaneous combustion process of three typical types of wax residues produced during Fischer–Tropsch synthesis. Differential Scanning Calorimetry (DSC) was used to test the thermal flow curves of the three wax residue samples. Kinetic analysis was performed using the Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods to calculate their apparent activation energy. This study analyzed the thermal behavior characteristics, exothermic properties, and kinetic parameters of three typical wax residue samples, exploring the ease of reaction between wax residues and oxygen and their tendency for spontaneous combustion. The results indicate that Wax Residue 1 is rich in low-carbon chain alkanes and olefins, Wax Residue 2 contains relatively fewer low-carbon chain alkanes and olefins, while Wax Residue 3 primarily consists of high-carbon chain alkanes and olefins. This leads to different thermal behavior characteristics among the three typical wax residue samples, with Wax Residue 1 having the lowest heat release and average apparent activation energy and Wax Residue 3 having the highest heat release and average apparent activation energy. These findings suggest that Wax Residue 1 has a higher tendency for spontaneous combustion. This research provides a scientific basis for the safety management of the coal chemical industry, and further exploration into the storage and handling methods of wax residues could reduce fire risks in the future.

Microstructure and energy release properties of W-Zr-Al energetic structural material fabricated by explosive consolidation

Multi-element intermetallic energetic structural materials (ESMs) as a new typical ESMs characterized by their high heat release properties and strength, which could be applied as reactive fragment, reactive shell and reactive shaped charge. Al-based ESMs had been extensively studied due to their excellent mechanical properties and high energy release characteristics. But, the low density of Al-based ESMs hindered its application. However, the need for higher density and energy release persists. In this work, the nearly fully dense W-Zr-Al ESMs with a molar ratio of 1.9:1:1 was fabricated successfully by explosive consolidation. The density reached 10.12 g/cm3 (97.5 % of the theoretical maximum density). Microstructure of the specimen was characterized by X-ray diffractometer (XRD), optical microscopy (OM), scanning electron microscope (SEM), energy dispersive spectrometry (EDS) and transmission electron microscope (TEM). The heat treatment was used to further improve the performance of the specimen and the mechanical properties of quasi-static compression was investigated before and after heat treatment. The reaction activity and process of W-Zr-Al ESMs was discussed by differential scanning calorimetry (DSC). Besides, the impact-induced energy release tests were carried out to evaluate the reactive characteristics of the W-Zr-Al ESMs. The results indicated that high-density, good-strength and high energy release unreacted W-Zr-Al energetic materials were fabricated successfully by explosive consolidation.

Effect of H[formula omitted] addition on NH[formula omitted] flame structure and dynamics in a mixing layer

Hydrogen addition has been widely used to improve the combustion performance of low-reactivity fuels such as NH3. In this study, a series of two-dimensional NH3/H2 flames in mixing layers were investigated numerically. The aim is to assess and interpret the effects of H2 addition on the structure and dynamics of ammonia flames. Detailed chemistry and transport models were considered in the simulations. It was shown that for pure hydrogen or ammonia flames, a classical tribrachial structure was observed. The non-premixed branch in the tribrachial flame of NH3 combustion features high heat release rate (HRR), while the two premixed branches are weak. The mixture fraction corresponding to the maximum HRR of NH3 combustion is significantly lower than the stoichiometric mixture fraction. When blending ammonia with hydrogen, a tetrabrachial flame structure consisting of two premixed branches and two non-premixed branches was observed, where one non-premixed branch corresponds to the reaction of NH3, while the other is formed due to the reaction of H2. It was suggested that the formation of the tetrabrachial flame is related to the preferential diffusion of hydrogen. After decreasing artificially the diffusivity of hydrogen to suppress the preferential diffusion effect, the flame exhibits only three branches with the merging of the two non-premixed branches. By analyzing the flame dynamics at the leading edge, it was found that the flame speed (Sd∗) is negatively correlated with the flame stretch (κ) and scalar dissipation rate (χ), with Sd∗ decreasing almost linearly with κ or χ, consistent with previous studies of methane and hydrogen flames. As the H2 concentration is increased, the values of Sd∗ increase due to the enhanced reactivity.

Energy characteristics of the vapor-gas shell formation stage during electrolyte-plasma treatment

The article presents the results on energy characteristics and the thermophysical state in the vapor-gas shell formation stage during electrolyte-plasma treatment. The vapor-gas shell formation stage is characterized by intense heating of the anode layer, a transition to undeveloped bubble boiling with high heat release capacity, boiling crisis emergence, and by a transition to the film mode with low heat release capacity. At the same time, a traditional electrochemical process occurs on the anode, which is accompanied by dissolving the surface layer. Dependences characterizing the influence of electrolyte-plasma treatment parameters on the specific power and specific energy of the vapor-gas shell formation stage are established. The obtained results allow optimizing the parameters of new effective processes of electrolyte-plasma treatment in controlled pulse modes, at which both electrochemical (vapor-gas shell formation) and electrolyte-plasma stages are realized within one pulse of millisecond duration.

Study on organic carbon in medium-low mature shale oil reservoirs rich in type II kerogen: Oxidation behavior, thermal effect, and kinetics

In-situ combustion technology (ISC) was a potential technology for efficient development of medium–low maturity shale oil reservoirs. Clarifying the exothermic behavior of organic carbon oxidation will be beneficial for better control of ISC processes. In this work, the organic carbon composition, type II kerogen and residual oil, were separated and extracted from the shale samples of typical medium–low maturity shale oil reservoirs in the Ordos Basin, China. The synchronous thermal analyzer and mass spectrometry (STA-MS), Fourier transform infrared spectroscopy (FTIR), and ROCK-EVAL VI were used to study the products, heat release, and functional group changes of type II kerogen, residual oil, and shale during the oxidation process. The results indicated that the oxidation heat release of shale mainly came from the oxidation reaction between its residual oil and type II kerogen, but the oxidation heat release range of shale was relatively lagging compared to the single residual oil or type II kerogen affected by rock debris. Secondly, under atmospheric pressure, the type II kerogen experiences obviously higher heat release than residual oil and heavy oil, indicating its superior potential of in-situ heat release. In addition, the major productions that CO, H2O, SO2, and CO2 were quantitatively characterized, with CO2 having the highest production of 882.25 mg/g. Furthermore, combined with the molecular weight, an oxidation reaction equation of type II kerogen was constructed. Finally, the oxidation kinetics parameters of type II kerogen, residual oil, and shale were determined using Friedman and Ozawa-Flynn-Wall (OFW) models. It was found that the activation energy of shale was higher than II kerogen and residual in low temperature oxidation (LTO) and fuel deposition (FD) stages. This may be due to the joint reaction between kerogen and residual oil, thus exacerbating the challenge of shale in-situ ignition. However, due to the catalytic effect of rock debris, the activation energy of shale was lower than LTO in high temperature oxidation (HTO) stage, indicating that once fuel deposition was completed, organic carbon will undergo stable combustion. This study has theoretical guidance for the numerical simulation research of ISC development technology of maturity-low shale oil reservoirs.

Comparative study on the influence of chemical reaction mechanisms on turbulent jet flame

Abstract This paper focus on the influence of chemical reaction mechanisms on the simulation of turbulent jet flame of 11 different chemical reaction mechanisms. These mechanisms are mainly selected from GRI series and their reduced mechanisms, and their reaction kinetics were analyzed. This paper uses LES-TPDF method to simulate Sandia Flame D turbulent jet flame and then analyze the difference of time-averaged temperature, heat release rate and species concentration results in different mechanisms. The results show that the kinetic performance of different chemical mechanisms is very different. The ignition delay time of JL4, SMOOKE and z42 mechanisms are either overestimated or underestimated due to the omission of multi-carbon species and other important species. The differences of the LES results in different mechanisms increase along the axis. The differences near the fuel inlet are mainly due to the difference of kinetic performance, while the difference away from the fuel inlet is more due to the different species and elementary reactions involved in different chemical reaction mechanisms. For all chemical mechanisms, there is a tendency that the more species used in the chemical reaction, the more concentrated the region of high heat release rate, the shorter the flame length, and the higher the maximum temperature throughout the field.

Fuel Temperature Effects on Combustion Stability of a High-Pressure Liquid-Fueled Swirl Flame

The influence of fuel temperature on combustion instabilities is investigated in a liquid-fueled, piloted swirl flame at 1.0 MPa. Fuels used for this study include Jet A and a Fischer–Tropsch-based synthetic paraffinic fuel (Shell GTL GS190). Simultaneous OH* chemiluminescence, particle image velocimetry, and Mie scattering measurements are performed in an optically accessible combustion chamber at 10 kHz for fuel temperatures ranging from 294 to 525 K. At ambient fuel temperature, a self-excited longitudinal instability is observed at 825 Hz. A higher instability amplitude is observed for Jet A compared to GS190 at all fuel temperatures. Analysis of the chemiluminescence images shows axial flame fluctuations at the instability frequency that are coupled to oscillations in fuel droplet consumption. Lower fuel temperatures lead to unburnt fuel accumulation in low-velocity regions of the flame, and consumption during the acoustic compression wave arrival results in high heat release magnitude that amplifies acoustic perturbations. Spatial correlations of the axial velocity and heat release fluctuation highlight the flame shear layers as predominant regions driving the global dynamics. Increased fuel temperature results in higher droplet evaporation rates in these regions, which promotes more uniform fuel deposition and subsequent burning over the thermoacoustic cycle, attenuating the instability.

Investigation of [formula omitted] formation in non-premixed, swirl-stabilised, wet hydrogen/air gas turbine combustor

In line with the Paris Agreement and the United Nations Sustainable Development Goals, the use of fossil fuels is to be phased out in the coming decades. Fossil-free hydrogen is a promising candidate for decarbonising the energy sector. However, hydrogen combustion is known to produce undesirable emissions such as nitrogen oxides (NOx) and calls for mitigation measures such as steam-diluted hydrogen combustion, which is known to reduce the NOx emissions. This study focuses on improving the understanding of NOx formation in a swirl-stabilised, steam-diluted, non-premixed hydrogen/air combustion using high-fidelity large eddy simulation (LES) and zero-dimensional (0D) perfectly stirred reactors (PSR). The LES results are used to identify four salient points in the domain where the NOx chemistry is analysed in detail. These points are chosen in the main flame, flame tail, post-flame and central recirculation regions. Note, the high heat release rate (HRR) region is referred to as the main flame while the flame tail denotes the low-HRR and V-shaped flame region adjacent to the main flame. Based on the LES data at these chosen points, the contribution of the major NO production pathways such as the Zeldovich mechanism, extended Zeldovich mechanism, N2O route and the NNH route are studied and reveal different rates of production of NO (i.e. ROPNO). Also, the role of individual reactions in NO production and consumption is investigated. Furthermore, reaction pathway diagrams illustrating the chemical pathways leading to NO are visualised. The sensitivity of NO to each reaction is also reported. These analyses provide insights into the NO chemical pathways observed at the salient points across the domain. The dominance of the Zeldovich mechanism remains but is much less compared to that in dry hydrogen combustion as its contribution to ROPNO is less than 20% at all the points considered. However, the extended Zeldovich mechanism is significant at all the points. The NNH route is observed to be important in the flame regions. The major NNH reaction contributing to ROPNO in the flame regions is NNH+O⇌NH+NO. Furthermore, the complex NO chemistry at all the identified points is presented in great detail using the above-mentioned analyses and illustrations. This work highlights the possibility of combining a high-fidelity simulation and a simple 0D ideal reactor to decipher the nuances of NO chemical pathways in a practical swirl-stabilised gas turbine combustor and provide new understanding for assisting engineers in designing clean burners.

A LES study on the instantaneous H2 jet-ignited combustion characteristics of H2/NH3 mixtures

This paper presents a Large Eddy Simulation (LES) study investigating jet flame ignition characteristics to achieve stable ammonia combustion for novel applications in gaseous ammonia/hydrogen-fueled engines with an active prechamber. The study investigated three cases with initial global equivalence ratios of 0.6, 0.8, and 1.0. Two main ignition modes were proposed, and five stages of coupled flame propagation processes were identified. The oscillation of supersonic hydrogen jet flame was investigated. The modes of flame-vortex interaction including vortex ring formation, along with the mechanism of highly reactive zone formation, were proposed. The effects of reactivity and turbulence transition on piloted ammonia flame were investigated to attain stable ammonia combustion and achieve a high heat release rate. The results showed that oscillations in the jet flame were strengthened at low global equivalence ratios with high hydrogen mass ratios. Enhancing propagation of initial and secondary vortex rings broadened highly reactive zones. Vorticity dissipated more rapidly at low equivalence ratios, leading to a stratified structure and enhanced piloted spherical flame. The Unsteady Flamelet Ignition Prediction (UFIP) sub-model of combustion was verified for the piloted ammonia flame, enabling a more comprehensive discussion of flame propagation tendencies.

The Dispersion and Hydration Improvement of Silica Fume in UHPC by Carboxylic Agents.

Silica fume (SF) is an essential component in ultra-high-performance concrete (UHPC) to compact the matrix, but the nucleus effect also causes rapid hydration, which results in high heat release and large shrinkage. In this paper, the carboxylic agents, including polyacrylic acid and polycarboxylate superplasticizer, were used to surface modify SF to adjust the activity to mitigate hydration at an early time and to promote continuous hydration for a long period. The surface and dispersion properties of modified SF (MSF), as well as the strength and pore structure of UHPC, were studied, and the stability of the modification was also investigated. The results demonstrated that, after treatment, the carboxylic groups were grafted on the SF surface, the dispersion of SF was improved due to the increased negative pentanal of the particle surface and the steric hindrance effect, the early hydration was delayed about 3-5 h, and the hydration heat release was also mitigated. The compressive strength of UHPC with MSF reached a maximum of 138.7 MPa at 3 days, which decreased about 3.7% more than the plain group, while flexural strength varied insignificantly. More pores and cracks were observed in the matrix with MSF, and the hydration degree was promoted with MSF addition. The grafted group on SF fell off under an alkali environment after 1 h.

Simulation of lithium-ion battery thermal runaway considering active material volume fraction effect

The multi-physics solver BatteryFOAM couples with the side reaction model for thermal runaway (TR) simulations, including the electrolyte decomposition (E) and solid electrolyte interface layer decomposition (SEI), and the reaction of the electrolyte with graphite intercalated lithium (NE-E) and the reaction of positive electrode active material with the electrolyte (PE-E). This solver is used to study the lithium-ion battery (LIB) TR at different conditions. The published experimental results are used to validate the effectiveness and practicability of BatteryFOAM in predicting the temperature under constat high temperature. We also discuss the reactant concentration, reaction rate, and heat release rate during the LIB TR. The influences of the external factor of the equal equivalent heat transfer (h) on the battery TR is considered, and the sequence in which the battery reaches the critical temperature rising rate (RTR, 60 K/min) and the separator failure temperature (Tsep) is predicted. The results demonstrate that overall the exothermic reaction peaks arise sequentially from SEI decomposition, PE-E reaction, NE-E reaction, and electrolyte decomposition, and NE-E reaction has three exothermic peaks induced by other three side reactions. PE-E reaction contributes more heat for fuse energy to trigger TR, but the NE-E reaction and electrolyte decomposition mainly accounts for the runaway energy. In addition, increasing SEI and electrolyte decomposition intensity is found no effect on the TR temperature. Besides, the rapid reaching to RTR is caused by the high heat release rate of positive electrode active material with electrolyte. Results further show that reducing the fNE−E within 5.0 % will significantly reduce TR risk.

Micron-sized aluminum particle combustion under elevated gas condition: Equivalence ratio effect

Micron-sized aluminum (Al) particle combustion under elevated gas condition is critical for improving energetic material performance, impacting propulsion and explosives technology. This study utilizes Eulerian-Lagrangian method to investigate Al particle combustion dynamics, encompassing both heterogeneous reaction (HTR) and homogeneous reaction (HMR). It focuses on the critical role of the equivalence ratio in single Al particle combustion, highlighting the interplay between HTR and HMR, aiming to optimize energy release and emission control. Our study identifies four stages in the combustion of a single Al particle, where the highest heat release is attributed to HTR, succeeded by HMR, and the minimal from unburned Al vapor. We observe a decline in the total heat release rate with an increasing equivalence ratio, primarily due to the differential impacts of heterogeneous and homogeneous reactions. The thermal-runaway stage in HTR is governed by the particle temperature, while the subsequent decaying stage is influenced by either the diminishing effective Al droplet diameter or the availability of oxygen, contingent upon the fuel conditions. Utilizing Cantera software to analyze HMR allows us to elucidate the thermal effects of elementary reactions and the key reaction pathways. These findings underscore the complex interactions between Al particles and the surrounding gas, providing insights into optimizing the conditions for Al-containing reaction systems.

PTFE-modified Al through bridging approach to enhance combustion reaction and energetic performance

Aluminum/Polytetrafluoroethylene (Al/PTFE) composites have attracted a great deal of attention due to their remarkable energy density and wide range of applications. Unfortunately, the inert oxide layer (Al2O3) on the surface of Al and the interfacial contact area between PTFE and Al seriously impact the combustion reaction kinetics and energy output efficiency. Here, an approach is utilized to significantly enhance the interfacial contact area between Al and PTFE through F2601 serving as the bridging agent. The ignition, combustion reaction, and energetic performance (pressure and combustion heat) can be adjusted by varying the particle size of Al and PTFE content. The energy release efficiency of bridging Al/PTFE has been improved significantly as PTFE content increases and the particle size of Al decreases. The bridging Al/PTFE with 10 μm Al and nano Al exhibit a bright and wide flame, and a fierce flame propagation process, as well as much high pressure output (167.73 kPa and 199.92 kPa) and heat release (11879 J/g and 12322 J/g). Furthermore, the critical mass ratio (approximately 88/12) of bridging Al/PTFE for self-sustained combustion has been obtained for the first time. The improvement of energy output performance is attributed to the interfacial contact between PTFE and Al and the reaction of fluorine and Al2O3 resulted from bridging Al/PTFE through F2601. The prepared bridging Al/PTFE with high energy output characteristics holds great potential in solid propellants, reactive materials, and other high-energy fuels.

Startup characteristics of a water loop heat pipe with dual heat sources for battery thermal management system in electric vehicle

Abstract The usage of electric vehicles has significantly reduced emissions of greenhouse gases and other pollutants. However, the high heat release generated by the electric vehicle batteries poses a challenge. To solve this problem, scientists have created a passive cooling thermal management system specifically for electric vehicle based on heat pipes, particularly loop heat pipes. A battery pack often consists of several battery modules, which results in multiple heat sources being dispersed according to their power capacity. Startup behavior of loop heat pipe has been investigated extensively in the literature. However, most of the studies use only one heat source. This paper aims to fill the research gap, particularly when the system is implemented in dual heat sources managed by only one evaporator. To achieve the research objectives, a custom loop heat pipe was constructed. This cooling system’s design is briefly described. The evaporator is made of copper, deionized water was selected as the working fluid because of its high merit number, which indicates strong performance as a heat pipe working fluid and the stainless-steel wire mesh serves as the porous wick. Battery simulator was built using aluminum material and a cartridge heater to mimic the heat produced by the battery. Two case studies were done. First, only one battery simulator was used. Second, two battery simulators were placed on both sides of the evaporator. A type-K thermocouple attached to the NI DAQ 9214 module was used to measure the temperature while the electric heat load varied between 10 W and 50 W. The study investigated the interaction between the heat load distribution and the startup behavior of the loop heat pipe. Startup behavior is crucial for the performance of the loop heat pipe. Based on the experimental results, the loop heat pipe demonstrates outstanding startup performance. It can effectively initiate operation even at a minimal heat load as low as 30 W for the first and second case study. The findings of the study indicate that the dual heat source arrangement effectively mitigates overshoot temperatures and enhances heat transfer performance by increasing the contact area.

Study on the lower head failure in severe accidents Part II: Thermal-mechanical coupling behavior analysis on CAP1400 reactor lower head

Under severe accident conditions with core meltdown, large amounts of molten material relocate to the lower head at high temperatures. Significant thermal and mechanical loads may lead to failure of the reactor pressure vessel (RPV) lower head, spreading radioactive fission products. Lower head failure time and location are crucial for accident mitigation and consequence assessment. This study developed a thermodynamic failure analysis model for the lower head by investigating material failure mechanisms, coupling this into an Integrated Severe Accident Analysis code (ISAA), and conducting experimental validation and applied research. Part I mainly introduces the thermodynamic analysis module development, validation against OLHF experiments, and preliminary failure criteria analysis. Results indicate the model accurately predicts lower head failure behavior, and Larson-Miller life fraction and Hedl-Dorn parameter criteria accurately assess lower head integrity. Part II presents applied research after validation and preliminary analysis. Using the improved ISAA, melt pool behavior and lower head thermal–mechanical response were analyzed for a CAP1400 small break loss-of-coolant accident (SBLOCA), assuming multiple safety system failures. Results indicate the bottom of the lower head melt pool didn’t form a hard shell due to high heat release rate, only an oxide shell layer around the second layer. Decay heat from melt pool components cannot be dissipated, leading to lower head failure. Further External Reactor Vessel Cooling (ERVC) heat transfer model analysis and research are needed in ISAA. The two developed mechanical analysis models predict material failure at high temperatures, and the timing and location of lower head failure are consistent, at approximately 16,000 s at 25.38°±5.47° on the lower head. The predicted failure mode is similar to Part I validation, indicating both Larson-Miller life fraction and Hedl-Dorn parameter criteria provide consistent lower head integrity judgments.

Development of Macro-Encapsulated Phase-Change Material Using Composite of NaCl-Al2O3 with Characteristics of Self-Standing

Developing thermal storage materials is crucial for the efficient recovery of thermal energy. Salt-based phase-change materials have been widely studied. Despite their high thermal storage density and low cost, they still face issues such as low thermal conductivity and easy leaks. Therefore, a new type of NaCl-Al2O3@SiC@Al2O3 macrocapsule was developed to address these drawbacks, and it exhibited excellent rapid heat storage and release capabilities and was extremely stable, significantly reducing the risk of leakage at high temperatures for industrial waste heat recovery and in concentrated solar power systems above 800 °C. Thermal storage macrocapsules consisted of a double-layer encapsulation of silicon carbide and alumina and a self-standing core of NaCl-Al2O3. After enduring over 1000 h at a high temperature of 850 °C, the encapsulated phase-change material exhibited an extremely low weight loss rate of less than 5% compared with NaCl@Al2O3 and NaCl-Al2O3@Al2O3 macrocapsules, for which the weight loss rate was reduced by 25% and 10%, respectively, proving their excellent leakage prevention. The SiC powder layer, serving as an intermediate coating, further prevented leakage, while the use of Al2O3 ceramics for encapsulation enhanced the overall mechanical strength. It was innovatively discovered that the Al2O3 particles formed a network structure around the molten NaCl, playing an important role in maintaining the shape and preventing leakage of the composite thermal storage phase-change material. Furthermore, the addition of Al2O3 significantly enhanced the rapid heat storage and release rate of NaCl-Al2O3 compared to pure NaCl. This encapsulated phase-change material demonstrated outstanding durability and rapid heat storage and release performance, offering an innovative approach to the application of salt phase-change materials in the field of high temperature rapid heat storage and release and encapsulating NaCl as a high-temperature thermal storage material in a packed bed system. Compared with conventional salt-based phase-change materials, the developed product is expected to significantly improve the reliability and thermal efficiency of thermal storage systems.

The application of UHPC on the monolithic part of the Štvanice footbridge

The use of UHPC with fibers is becoming an increasingly common topic in the world. This material is used for its superior mechanical and physical properties and long service life. However, the production cost is high, hence UHPC is used for special applications or for smaller prefabricated parts. This paper focuses on UHPC application for the construction of the Štvanice Footbridge, Prague, the Czech Republic. A monolithic part of the structure was made of UHPC from fresh transport concrete, which was produced by Skanska Transbeton. The special feature is that about 126m3 of fresh concrete was industrially prepared. This concrete achieved the properties of SCC and the final 28 day compressive strength was 120MPa with tensile strength of 18.6 MPa. Due to high hydration heat release rate, an internal water cooling system was designed and sucessfully appled using water from Vltava River.