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Summary: In the present study, the performance of H2‐metal hydrides‐based (HSRS) and CO2‐adsorbent‐based refrigeration systems (CSRS) are investigated and compared. The pair of metal hydrides (MH) used for HSRS is La0.9Ce0.1Ni5‐LaNi4.7Al0.3 whereas, for CSRS, it is Activated Carbon – Pore Expanded Mesoporous Silica (PEMS) adsorbents. The above pairs are chosen due to their suitability toward the sorption refrigeration system, which results from the screening of different pairs. The performances of these systems are investigated through the thermodynamic simulation as well as computational fluid dynamics (CFD) approach. The thermodynamic cycles of both the systems are analyzed for the operating temperatures of 0°C (Tr; refrigeration), 25°C (Ta; heat sink), and 100°C (Ts; heat source). Upon thermodynamic simulation, the refrigeration output, coefficient of performance (COP), specific refrigeration power, and second law efficiency are observed as 87.04 kJ, 0.91, 24.17 W/kg, and 41.6% for HSRS whereas, it is 49.32 kJ, 0.72, 20.55 W/kg, and 33.1% for CSRS, respectively, using 0.5 kg of each alloy. The CFD simulation results in the behavior of absorbent/adsorbent beds concerning temperature and gas mass variations. The minimum bed temperature is observed to be −31°C in HSRS, which is lower than that of CSRS (i.e., ‐9°C). The overall cycle time is predicted to be 3600 seconds for HSRS and 2400 seconds for CSRS. The shorter cycle time in CSRS is due to the high‐pressure differential between coupled beds during reactions and higher reaction rates of adsorbent materials than metal hydrides. Though CSRS possessed shorter cycle time, HSRS is found to be more suitable for refrigeration application due to better thermodynamic performance, in the given operating temperature range. Besides, the influence of variations in operating temperatures on the system performance is investigated and obtained the optimum temperature range of Tr = 5°C, Ta = 20°C, and Ts = 95°C. Finally, the thermodynamic performances of HSRS, CSRS, and CO2‐based vapor adsorption refrigeration system (CO2 VARS) are compared and observed that HSRS possessed better refrigeration performance among three. [ABSTRACT FROM AUTHOR]

Summary: In this study, La0.9Ce0.1Ni5 alloy is characterised to investigate the performance of a single‐stage thermally driven sorption hydrogen compressor (TDSHC). The pressure‐concentration isotherm (PCI) properties of La0.9Ce0.1Ni5 alloy are measured through Sievert's Apparatus, and the thermodynamic properties are estimated by constructing van't Hoff plots at different temperature ranges between 20°C and 140°C. The effects of an increase in operating temperature on hydrogen storage capacity as well as on thermodynamic properties and the corresponding effects on TDSHC performance are studied. It is observed that the hydrogen storage capacity decreased, whereas reaction enthalpy increased, with an increase in operating temperature. It is also observed that the equilibrium pressure increased dramatically with an operating temperature; therefore, this alloy is employed, in this study, for the development of TDSHC. The proposed TDSHC operates at the supply temperature and pressure of 20°C and 15 bar, respectively, in which the compressed hydrogen is delivered at 40°C, 60°C, 80°C, 100°C, 120°C and 140°C with a maximum pressure output of 270 bar. The measured PCI and thermodynamic data are employed to investigate the thermodynamic performance of TDSHC which results in the maximum compressor work of 10.13 W and the maximum cycle efficiency of 27.57% with an average heat input of 35 ± 3 W. The increase in discharge temperature on system performance are observed to increase in compressor work and efficiency due to the increase in discharge pressure, whereas the effect on heat input is not significant due to the reduction in hydrogen discharge amount. Also, the behaviour of metal hydride (MH) bed is predicted through the finite volume method in terms of variations in MH bed temperature and hydrogen transmission. The numerical investigation is carried out by solving the required energy equations and are validated with experimental data. The numerical investigation results into minimum cycle time of 2700 seconds for the operation of TDSHC. It is also observed that the increase in discharge temperature increases the reaction kinetics and hydrogen mass fraction. [ABSTRACT FROM AUTHOR]

Summary Hydrogen is considered as a viable alternative fuel source for many domains. The main challenge in hydrogen technology is its storage. The most efficient form of storing hydrogen by volume is to adopt solid‐state storage. This is achieved by gas‐solid interaction using metal hydrides (MH). But, to achieve the full storing potential of MH, the heat management of the reactor is the critical factor. MHs having inferior thermal conductivity prove a challenge and thus, several kinds of research have gone into developing efficient MH reactors with features trying to enhance the heat transfer rate. In the view of this, in the present work, an MH reactor is designed and numerically (finite volume method) analyzed its heat transfer characteristics during hydrogenation and dehydrogenation of La0.9Ce0.1Ni5 at 293 K. Besides, to achieve improved heat transfer rates, new internal copper fins, and external water jackets are provided. The objective of the present work is to achieve high heat transfer rates with minimum reduction in MH mass within the reactor. Also, a parametric study is carried out to identify the optimized fin design by varying number fins, fin height, and fin thickness, which results in the optimum fin structure of 12 numbers, 12 mm, and 2 mm, respectively. The CFD simulation of MH reactor with and without fins results in improved heat transfer rates and reaction kinetics with internal copper fins. The maximum temperature rise during absorption is reduced by 22.3 K, and during desorption, the drop in bed temperature is reduced by 6.8 K, using optimized copper fins. The obtained results are compared with previous work and observed that the implementation of internal copper fins with external water cooling provides better heat transfer. The proposed reactor + fin arrangement can be efficiently used for the development of MH based thermodynamic devices. [ABSTRACT FROM AUTHOR]

Summary: The requirement of simultaneous heating and cooling effects at different zones of a building demands for the development of an energy‐efficient air‐conditioning system for heating and cooling outputs. In order to fulfil this requirement, a novel multistage hydrogen‐alloy–based sorption heat pump (H‐A SHP) for space air‐conditioning is proposed in the present work. The proposed system produces multiple cooling and heating outputs at 20°C and 45°C, respectively, with single heat input at 160°C. A set of MmNi5, La0.8Ce0.2Ni5, MmNi4.4Al0.6, and LaNi4.6Al0.4 metal hydrides (MHs) is chosen to operate at the above‐mentioned temperature range with hydrogen as working fluid. The proposed system can completely eliminate the requirement of conventional compressor because it operates using waste heat, and useful outputs (cooling‐heating) result from reaction enthalpies (MH + H2 interaction). The thermodynamic and heat‐hydrogen transfer analyses of H‐A SHP are carried out through finite volume approach, in which heat and mass transfer equations are solved to foresee the variations in MH bed temperature, hydrogen concentration, and heat interactions during cycle operation as well as the amount of cooling and heating outputs delivered to the air‐conditioning space. The numerical code is validated with experimental pressure‐concentration isotherms (PCIs) measured through Sievert's apparatus. The maximum heat exchange during the cooling and heating processes, at a particular instant of time, is observed as 257.5 and 286.1 W with cooling temperature of 10°C and heating temperature of 53°C, respectively. The thermodynamic performance is estimated as 178.5 kJ of cooling effect, 265.5 kJ of upgraded heat with overall coefficient of performance (COP) of 6.8, and overall specific alloy output of 396.5 W/0.34 kg of alloy. [ABSTRACT FROM AUTHOR]

This short review discusses the classification, pressure concentration isotherm (PCI) characterisation and applications of metal hydrides. Special attention is paid to describe the design criterion and fabrication of Sievert's apparatus and PCI characterisation methods of metal hydrides. Different classes of metal hydrides and their properties are broadly discussed. Also, some of the important applications of metal hydrides are presented. The absorption and desorption PCIs of four Lanthanum based alloys namely La0.9Ce0.1Ni5, La0.8Ce0.2Ni5, LaNi4.7Al0.3 and LaNi4.6Al0.4 are measured using volumetric method in the temperature range of 20 to 80 °C. Later, different PCI simulation models are compared, and Zhou's model is used to simulate the experimentally measured PCIs at different temperatures. It is found that the simulation results are in good agreement with the experimentally measured results. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Pairs of low-temperature (La0.9Ce0.1Ni5 and La0.8Ce0.2Ni5) and high-temperature (LaNi4.7Al0.3 and LaNi4.6Al0.4) LaNi5 hydrides were used for thermodynamic analysis of metal hydride-based solid sorption refrigeration system (SSRS). In general, static pressure-concentration isotherm (PCI) properties were considered for the thermodynamic analysis of solid sorption thermodynamic cycles. But, the hydrogen transfer processes involved in the thermodynamic cycle are dynamic in nature. Therefore, in the present study, the dynamic PCIs of these metal hydrides were measured at different temperatures and compared with their static PCIs. Significant variation in PCI and thermodynamic properties were observed in dynamic conditions compared with static conditions. Later, the performance of SSRS was determined by using static and dynamic PCI properties. Refrigeration effect and coefficient of performance of SSRS decreased by 60% and 35% respectively, when dynamic (at 80 mi/min) PCI data were considered. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]