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Abstract: In this paper, the operating feasibility of a single-stage metal based hydride heat pump (SS-MHHP) working on the principle of crossed van't Hoff line concept is presented. The performance of the system is predicted by solving the unsteady, two-dimensional mathematical model in an annular cylindrical configuration employing two different hydride alloy pairs, namely, V0.846Ti0.104Fe0.05/Fe0.9Mn0.1Ti and V0.855Ti0.095Fe0.05/MmNi4.7Al0.3 (regeneration alloy/refrigeration alloy). The influences of heat source (T H ) and refrigeration (T C ) temperatures on the amount of hydrogen transferred between the paired reactors, coefficient of performance (COP) and specific cooling power (SCP) of the crossed van't Hoff SS-MHHP system are studied. Within the selected ranges of operating temperatures, the COP of the crossed van't Hoff SS-MHHP is about 60% higher than the conventional single-stage MHHP. The optimum operating temperatures of V0.846Ti0.104Fe0.05/Fe0.9Mn0.1Ti and V0.855Ti0.095Fe0.05/MmNi4.7Al0.3 combinations are found to be 373/303/291 K and 400/303/283 K (heat source/heat sink/refrigeration temperatures), respectively. At the optimum operating temperatures, the COP and SCP of the V0.846Ti0.104Fe0.05/Fe0.9Mn0.1Ti and V0.855Ti0.095Fe0.05/MmNi4.7Al0.3 combinations are 0.89 and 30.8 W/kg of total mass and 0.86 and 30.3 W/kg of total mass, respectively. [Copyright &y& Elsevier]

Abstract: In this paper a two-dimensional model of an annular cylindrical reactor filled with metal hydride suitable for hydrogen storage is presented. Comparison of the computed bed temperatures with published experimental data shows a reasonably good agreement except for the initial period. Effects of hydrogen pressure and external fluid temperatures on heat transfer and entropy generation are obtained. Results show that the time required for hydrogen charging and discharging is higher when the thermal capacity of the reactor wall is considered. The time required for absorption and desorption can be reduced significantly by varying the hydrogen gas pressure and external fluid temperatures. However, along with reduction in time the entropy generated during hydrogen storage and discharge increases significantly. Results also show that for the given input conditions, heat transfer between the external fluid and hydride bed is the main source of entropy generation. [Copyright &y& Elsevier]

Abstract: The metal hydride heat transformer shows great potential for the low-grade heat recovery. However, the heat output is variable, and these dynamics have to be taken into account in realistic applications. In this paper, a new index called true temperature boost is introduced together with conventional indices to assess the performance of the heat transformer system. Detailed analyses are carried out using a mathematical model that authors developed, investigating effects of key design and operating factors on the system’s performance. The amount of hydrogen transferred between coupled reactors is found to be crucial to obtain a high coefficient of performance, while specific heating power is very sensitive to the cycle time. On the true temperature boost, the driving force of reaction and the heat transfer conditions exert the most significant effects. [Copyright &y& Elsevier]

Abstract: This paper describes the design, fabrication and performance evaluation of a high efficiency, compact heater that uses the catalytic oxidation of hydrogen to provide heat to a hydrogen storage system. The heater was designed to transfer up to 30kW of heat from the catalytic reaction to the hydrogen storage system via a recirculating heat transfer fluid. The catalytic heater consists of three main parts: 1) the reactor, 2) the gas heat recuperator, and 3) oil and gas flow distribution manifolds. The reactor and recuperator are integrated, compact, finned-plate heat exchangers to maximize heat transfer efficiency and minimize mass and volume. Detailed, three-dimensional, multi-physics computational models were used to design and optimize the system. At full power the heater was able to catalytically combust a 10% hydrogen/air mixture flowing at over 80 cubic feet per minute and transfer 30kW of heat to a 30 gallon per minute flow of oil over a temperature range from 100°C to 220°C. The total efficiency of the catalytic heater, defined as the heat transferred to the oil divided by the inlet hydrogen chemical energy, was determined to exceed the design goal of 80% for oil temperatures from 60°C to 165°C. [Copyright &y& Elsevier]

Abstract: This paper presents both a dynamic model and experimental results of a single-stage metal hydride cooling system working with alloys LmNi4.91Sn0.15 (hot reaction bed) and Ti0.99Zr0.01V0.43Fe0.09Cr0.05Mn1.5 (cold reaction bed). The system can work under regeneration temperatures ranging between 100 °C and 140 °C. Firstly, the model and experimental set-up are presented, and secondly, the key parameters of the cooling system are analyzed by carrying out a sensitivity analysis. A comparison between the actual and static P–C curves provides important information on the operating conditions of the reaction beds. Finally, an optimized system is proposed based on the optimization of the operation and on a more suitable selection of the alloys. [Copyright &y& Elsevier]

Abstract: This work was prompted by the publication of Puls''s recent papers claiming that the Dutton–Puls model is valid enough to explain the stress and temperature dependences of the crack growth rate (CGR) in zirconium alloys. The first version of the Dutton–Puls model shows that the CGR has positive dependences on the concentration difference ΔC, hydrogen diffusivity D H, and the yield strength, and a negative dependence on the applied stress intensity factor K I, which is one of its critical defects. Thus, the Dutton–Puls model claiming that the temperature dependence of CGR is determined by D H C H turns out to be incorrect. Given that ΔC is independent of the stress, it is evident that the driving force for DHC is ΔC, not the stress gradient, corroborating the validity of Kim''s model. Furthermore, the predicted activation energy for CGR in a cold-worked Zr–2.5Nb tube disagrees with the measured one for the Zr–2.5Nb tube, showing that the Dutton–Puls model is too defective to explain the temperature dependence of CGR. It is demonstrated that the revised Dutton–Puls model also cannot explain the yield stress dependence of CGR. [Copyright &y& Elsevier]