Investigation of the process of thermal runaway in nickel–cadmium accumulators

It has been established experimentally that during thermal runaway a great amount of hydrogen is given off from nickel–cadmium accumulator KSX-25. Through the thermal decomposition of nickel–cadmium accumulator electrodes, it has been shown that hydrogen had been present in the electrodes before the onset of thermal runaway. Through an analysis of the energy balance of thermal runaway, it has been shown that it is not an external source of current that causes thermal runaway, but rather a powerful internal exothermic reaction.     

Ammonia thermal decomposition on quartz and stainless steel walls

Ammonia has been proposed as a promising solution for hydrogen carriers as well as clean fuels. However, the reaction kinetics is still not robust in many engineering applications, where the deviation is mainly caused by the surface reactions of ammonia on the wall. To examine the ammonia surface reaction on engineering materials, in the present study, the thermal decomposition of ammonia is systematically investigated in uniformly heated quartz/SUS304 tubular flow reactors with the prescribed heating length. A decrease in the inner diameter of the quartz tubular reactor leads to an increase in the ammonia thermal decomposition rate, showing that the thermal decomposition reaction occurs even on quartz surfaces, which is usually believed to be inert. The thermal decomposition on the SUS304 reactor surface starts from as low as 700 K, indicating it is much more reactive than the quartz surface. One-step surface reaction models of ammonia for quartz/SUS304 surfaces are proposed, with which the reaction rates are estimated based on the experimental data. The inner surface of the SUS304 tubular reactor after the thermal decomposition experiments is examined by X-ray photoelectron spectroscopy. The formation of iron nitride on SUS304, which in turn facilitates ammonia thermal decomposition, reveals the positive feedback between ammonia decomposition and nitriding. Moreover, the present one-step surface reaction on stainless steel has been validated by measuring ammonia distributions in the preheat zone of NH₃/O₂/N₂ premixed flame impinging on a stainless steel plate through a two-photon absorption laser-induced fluorescence (TALIF) technique.     

Large scale synthesis of nickel oxide/multiwalled carbon nanotube composites by direct thermal decomposition and their lithium storage properties

A large scale direct thermal decomposition method has been developed to prepare NiO/MWCNT nanocomposites. The as-prepared NiO nanoparticles are uniformly coated onto the surface of MWCNTs. The well crystallized NiO/MWCNT composites show superior electrochemical performance in Li ion batteries. The lithium storage capacity maintains at ∼800 mAh g⁻¹ after 50 discharge/charge cycles, which is much larger than those reported for NiO and its composites. Therefore, the NiO/MWCNT composites have significant potentials for application in energy storage devices. The direct thermal decomposition method is a versatile route for preparing carbon nanotube-inorganic hybrid electrode materials for lithium ion batteries.     

An operational high temperature thermal energy storage system using magnesium iron hydride

Metal hydrides have been demonstrated as energy storage materials for thermal battery applications. This is due to the high energy density associated with the reversible thermochemical reaction between metals and hydrogen. Magnesium iron hydride (Mg₂FeH₆) is one such material that has been identified as a thermal energy storage material due to its reversible hydrogenation reaction at temperatures between 400 and 600 °C. This study demonstates an automated thermal battery prototype containing 900 g of Mg₂FeH₆ as the thermal energy storage material with pressurised water acting as the heat transfer fluid to charge and discharge the battery. The operating conditions of the system were optimised by assessing the ideal operating temperature, flow rate of the heat transfer fluid, and hydrogen pressures. Overall, excellent cyclic energy storage reversibility was demonstrated between 410 and 450 °C with a maximum energy capacity of 1650 kJ which is 87% of the theoretical value (1890 kJ).     

Study of kinetics and thermal decomposition of ammonia borane in presence of silicon nanoparticles

Ammonia borane (AB, NH₃BH₃) is a promising material by virtue of its high gravimetric hydrogen storage capacity of 19.6 wt%. Hydrogen release from AB initiates at around 100 °C and as such is compatible to meet the present-day requirements of a PEM fuel cell. The thermal decomposition of AB is a complex process involving several reactions. Major issues include poor reaction kinetics, leading to delayed commencement of hydrogen generation i.e. long induction period, and the small amount of hydrogen released at optimal temperature. In the current paper the thermal decomposition of AB is studied at different temperatures. Further the effect of Si nanoparticles on the induction period and kinetics as well as the gas release reaction is studied in detail using different characterization techniques. It was found that the induction period reduced and the amount of gas released increased as a result of Si nanoparticle addition. This was facilitated by a reduction in the activation energy of decomposition and improved kinetics with the addition of silicon nanoparticles.     

Central electric thermal storage (ETS) feasibility for residential applications: Part 2. Techno‐economic study

This techno‐economic feasibility study was performed to evaluate the viability of central electric thermal storage (ETS) systems for the residential sector. Numerical models have been used to study the effect of a number of parameters on the annual heating cost and unit storage capacity. The considered parameters were the type of central ETS heating system, the proposed rate electricity structure and the storage strategy. The viability of thermal storage systems is determined using a simple payback criteria. The results show that the implementation of thermal storage in the Montreal area is economically viable only if hourly based differential rates are in effect. Simple rules for the design of central ETS heating units were also developed. Copyright © 2001 John Wiley & Sons, Ltd.     

Effect of pressure and sample type on decomposition of ammonium perchlorate

Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and high pressure DSC (HP-DSC) have been used to study the thermal decomposition of ammonium perchlorate samples in the form of 2-mm monocrystals, 265- and 3-μm powders, and pellets pressed at 4 and 7 tons. HP-DSC runs have been performed to determine the effect of pressure on decomposition. TGA and DSC techniques have been employed to examine the effect of sample type on the kinetics of the process. The effects have been evaluated as changes in the temperature, reaction heat, and rate of decomposition. Isoconversional kinetic analysis has been carried out to detect changes in the effective activation energy of the process. These measurements and calculations show sublimation and decomposition for ammonium perchlorate to be highly dependent on sample preparation and applied pressure. This calculation finds that the activation energy for the early stages of sublimation/decomposition for all samples starts at ∼120 kJ mol⁻¹, which is followed by a dramatic drop to ∼60 kJ mol⁻¹ at 20% mass loss. The activation energy for the later stages of sublimation/decomposition varies with sample type ranging from ∼95 to 145 kJ mol⁻¹.     

The catalytic thermal decomposition of water and the production of hydrogen

Experiments have been carried out on the Pt and Ir catalyzed thermal decomposition of water. The dissociation is very rapid indeed, yielding appreciable quantities of hydrogen and oxygen at approx. 1300–1400°C. The great speed of this catalytic decomposition compensates for the small degrees of thermal decomposition in this temperature range.Two prototypes for large scale thermal hydrogen production are proposed on the basis of the experiments on the catalytic decomposition of water. These have been described and characterized in detail. A reasonable number of these prototypes can replace 1 year's supply of natural gas by hydrogen in the U.S.A. Economic aspects have also been considered.     

Kinetic analysis of the thermal decomposition of Polygonum lapathifolium

The optimal reaction model for analysis of thermal decomposition of various types of biomasses is currently under debate. Four established models for the kinetic analysis of Polygonum lapathifolium were employed in this study: double extrapolation method, Flynn–Wall–Ozawa method (FWO), distributed activation energy model (DAEM), and global kinetic model. The values of activation energy and frequency factor calculated by global kinetic model are much lower than that of the other three methods. Moreover, it has been demonstrated that the activation energy analyzed by FWO method and DAEM is widely distributed and is not directly related to the heating rates, which are more objective than double extrapolation method and global kinetic model.     

Modeling thermal response of polymer composite hydrogen cylinders subjected to external fires

With the anticipated introduction of hydrogen fuel cell vehicles to the market, there is an increasing need to address the fire resistance of hydrogen cylinders for onboard storage. Sufficient fire resistance is essential to ensure safe evacuation in the event of car fire accidents. The authors have developed a Finite Element (FE) model for predicting the thermal response of composite hydrogen cylinders within the frame of the open source FE code Elmer. The model accounts for the decomposition of the polymer matrix and effects of volatile gas transport in the composite. Model comparison with experimental data has been conducted using a classical one-dimensional test case of polymer composite subjected to fire. The validated model was then used to analyze a type-4 hydrogen cylinder subjected to an engulfing external propane fire, mimicking a published cylinder fire experiment. The external flame is modelled and simulated using the open source code FireFOAM. A simplified failure criteria based on internal pressure increase is subsequently used to determine the cylinder fire resistance.     

Review on storage materials and thermal performance enhancement techniques for high temperature phase change thermal storage systems

Designing a cost-effective phase change thermal storage system involves two challenging aspects: one is to select a suitable storage material and the other is to increase the heat transfer between the storage material and the heat transfer fluid as the performance of the system is limited by the poor thermal conductivity of the latent heat storage material. When used for storing energy in concentrated solar thermal power plants, the solar field operation temperature will determine the PCM melting temperature selection. This paper reviews concentrated solar thermal power plants that are currently operating and under construction. It also reviews phase change materials with melting temperatures above 300 °C, which potentially can be used as energy storage media in these plants. In addition, various techniques employed to enhance the thermal performance of high temperature phase change thermal storage systems have been reviewed and discussed. This review aims to provide the necessary information for further research in the development of cost-effective high temperature phase change thermal storage systems.     

Current status of ground source heat pumps and underground thermal energy storage in Europe

Geothermal Heat Pumps, or Ground Coupled Heat Pumps (GCHP), are systems combining a heat pump with a ground heat exchanger (closed loop systems), or fed by ground water from a well (open loop systems). They use the earth as a heat source when operating in heating mode, with a fluid (usually water or a water–antifreeze mixture) as the medium that transfers the heat from the earth to the evaporator of the heat pump, thus utilising geothermal energy. In cooling mode, they use the earth as a heat sink. With Borehole Heat Exchangers (BHE), geothermal heat pumps can offer both heating and cooling at virtually any location, with great flexibility to meet any demands. More than 20 years of R&D focusing on BHE in Europe has resulted in a well-established concept of sustainability for this technology, as well as sound design and installation criteria. Recent developments are the Thermal Response Test, which allows in-situ-determination of ground thermal properties for design purposes, and thermally enhanced grouting materials to reduce borehole thermal resistance. For cooling purposes, but also for the storage of solar or waste heat, the concept of underground thermal energy storage (UTES) could prove successful. Systems can be either open (aquifer storage) or can use BHE (borehole storage). Whereas cold storage is already established on the market, heat storage, and, in particular, high temperature heat storage (> 50 °C) is still in the demonstration phase. Despite the fact that geothermal heat pumps have been in use for over 50 years now (the first were in the USA), market penetration of this technology is still in its infancy, with fossil fuels dominating the space heating market and air-to-air heat pumps that of space cooling. In Germany, Switzerland, Austria, Sweden, Denmark, Norway, France and the USA, large numbers of geothermal heat pumps are already operational, and installation guidelines, quality control and contractor certification are now major issues of debate.     

Integrated design of hydrogen production and thermal energy storage functions of Al-Bi-Cu composite powders

In recent years, the hydrolysis of Al-based composite powders to produce hydrogen has become a hot topic in the field of hydrogen energy research. However, the hydrogen generation products of Al-based alloys have not been reasonably utilized. For this purpose, this study proposed a novel research idea to achieve the integrated design of hydrogen production and thermal energy storage functions of Al-based composite powders. Specifically, Al-Bi-Cu composite powders with stable hydrogen production were taken as research objects. The hydrogen was obtained by the reaction of Al-Bi-Cu alloy powders with H₂O for different reaction times, and then the hydrogen generation products were directly sintered at high temperature to obtain Al-Cu alloy based composite phase change thermal energy storage materials. The results indicated that at 50 °C, the hydrogen yield of Al-Bi-Cu alloy powders in 100min, 200min and 400min are 319.9 mL/g, 428.5 mL/g and 665.8 mL/g, respectively. Importantly, the Al-Cu alloy based composite phase change thermal energy storage materials prepared by the hydrogen generation products exhibited an adjustable phase change temperature (577.3 °C ∼ 598.2 °C), high thermal energy storage density (44.1J/g ∼ 153.5J/g), good thermal cycling stability and structural stability.     

Microstructure,surface properties and hydrating behaviour of Mg–C composites prepared by ball milling with benzene

Mg–graphite composites, suitable for hydrogen storage, have been synthesized by ball milling metallic Mg with different amounts of graphite and benzene. The microstructure and the surface chemical composition have been characterized in order to explain the kinetics of reaction with hydrogen. The presence of benzene in the milled blends induces a finer powder particle size, helps to preserve the structural integrity of the graphite crystals and results to be necessary for a complete transformation of the milled powder to the hydride phase by thermal reaction with hydrogen gas. On the other hand, it induces a more pronounced reaction of the milled Mg–C composites with the air. The transport properties of the resulting surface contamination layer appear to control the kinetics of thermal decomposition of the MgH₂ phase, so that the addition of benzene induces a higher reaction temperature owing to a larger thickness of the surface compound.     

Thermal energy storage by the chemical reaction augmentation of heat transfer and thermal decomposition in the CaO/Ca(OH)2 powder

The present paper is concerned with the utilization of a thermal decomposition reaction, Ca(OH)₂CaO + H₂O, for energy storage. One of the important problems in this case is how to heat up and decompose the powder of Ca(OH)₂ effectively, where the thermal conduction is poor.In this study, the effect of copper plates, which are placed in the powder of Ca(OH)₂ as heat-transfer fins, is investigated experimentally and numerically. The results show that the Cu-plates are very effective for heat transfer and the thermal decomposition, and that the optimum configuration of the Cu-plate is 5–10 cm in height and 0.5–1 cm in interval for the condition of this study.     

A method of testing for rating thermal storage devices based on thermal performance

This paper describes a proposed test method for determining the “effective capacity” and heat loss characteristics of thermal storage devices. The prescribed series of tests should provide useful data for the rating of thermal storage devices based on thermal performance. The apparatuses and major components used in the tests have been prescribed so a liquid or air can be used as the transfer fluid. The series of tests to be conducted consist of one steady-state test to determine the heat loss characteristics and eight transient tests to determine the “effective capacity” for both heat storage and heat removal. During the transient tests, the entering fluid temperature is changed in a step-wise manner and amount of energy either stored or removed over a specified test time is determined. Sample experimental data are given in the paper to demonstrate the concept of the transient tests.     

Numerical study on hydrogen and thermal storage performance of a sandwich reaction bed filled with metal hydride and thermochemical material

Hydrogen storage and release process of metal hydride (MH) accompany with large amount of reaction heat. The thermal management is very important to improve the comprehensive performance of hydrogen storage unit. In present paper, thermochemical material (TCM) is used to storage and release the reaction heat, and a new sandwich configuration reaction bed of MH-TCM system was proposed and its superior hydrogen and thermal storage performance were numerically validated. Firstly, the optimum TCM distribution with a volume ratio (TCM in inner layer to total) of 0.4 was derived for the sandwich bed. Then, comparisons between the sandwich reaction bed and the traditional reaction bed were performed. The results show that the sandwich MH-TCM system has faster heat transfer and reaction rate due to its larger heat transfer area and smaller thermal resistance, which results in the hydrogen storage time is shortened by 61.1%. The heat transfer in the reaction beds have significant effects on performance of MH-TCM systems. Increasing the thermal conductivity of the reaction beds can further reduce the hydrogen storage time. Moreover, improving the hydrogen inflation pressure can result in higher equilibrium temperature, which is beneficial for the enhancing heat transfer and hydrogen absorption rates.     

A review on thermal energy storage systems in solar air heaters

The drying needs of agricultural, industrial process heat requirements and for space heating, solar energy is one of the prime sources which is renewable and pollution free. As the solar energy is inconsistent and nature dependent, more often there is a mismatch between the solar thermal energy availability and requirement. This drawback could be addressed to an extent with the help of thermal energy storage systems combined with solar air heaters. This review article focuses on solar air heaters with integrated and separate thermal energy storage systems as well as greenhouses with thermal storage units. A comprehensive study was carried out in solar thermal storage units consisting of sensible heat storage materials and latent heat storage materials. As the phase change heat storage materials offer many advantages over the sensible heat storage materials, the researchers are more interested in this system. The charging and discharging characteristics of thermal storage materials with various operational parameters have been reported. All the possible solar air heater applications with storage units have also been discussed.     

Phase-structural transformation of erbium trihydride studied by thermal desorption spectroscopy

Thermal desorption behaviours of erbium trihydride (ErH₃) powders were studied using simultaneous thermogravimetry and thermal desorption spectroscopy (TG-TDS) method. The crystal structures and chemical compositions of the samples were investigated by X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. Two-peak structures were observed in the hydrogen desorption spectra and the corresponding activation energies were determined to be 160.7 and 212.3 kJ/mol, respectively. The phase transformation sequences during thermal desorption process were established by combining the changing trends in the temperature/hydrogen content with the Er–H phase diagram. It was established that the low-temperature and high-temperature peaks were related to the β + γ → β and α + β → α phase transformation steps, respectively. The origins of the observed TDS peaks and shoulders were attributed to the equilibrium hydrogen pressures of the phase regions that the decomposition reaction passed through.