Pressure-concentration Isotherms Research Articles

Analytical and experimental evaluation of LaNi5-xMx, where M = Fe, Mn, and Al hydrides for hydrogen compression applications

Metal Hydride Hydrogen Compressors (MHHC) will play a vital role in the hydrogen economy in the coming times. Developing a more efficient and optimized MHHC requires revisiting the existing materials and selecting the best-suited material. The current work compares LaNi5-xMx, where M = Fe, Mn, and Al hydrides, through a thermodynamic evaluation of the compressor's performance. The operating conditions have been chosen as 20 to 40 °C for absorption and 80 to 140 °C for desorption to provide a baseline for comparing the materials. The performance parameters include thermal efficiency, pressure ratio, and throughput (i.e. mass of hydrogen delivered per 100 g of hydride (wt.%)). The Pressure Concentration Isotherms (PCIs) are taken from the published literature, and the equilibrium pressures at the desired temperature conditions are calculated from the van't Hoff equation. LaNi4.8Al0.2 gives good performance throughout the studied temperature and pressure range. The throughput of LaNi4.8Al0.2 drops from 1.4 wt.% to around 1 wt.% at high absorption temperatures. A separate experimental study of LaNi4.8Al0.2 is documented where it is used in a prototype of MHHC, and its performance parameters are compared with the thermodynamic analysis. The reaction kinetics, throughput, pressure ratio, and efficiency are reported. A pressure ratio of 4.2 is achieved with an efficiency of 5.2 % at 3 bar supply pressure, and absorption and desorption temperatures of 30 and 140 °C, respectively.

Thermodynamic analysis of La and Mm based metal hydride pairs for solar energy-driven cold storage applications

Cold storage plays a vital role in many applications such as agricultural and food processing units. Metal hydride-based sorption cold storage systems are environmentally friendly as they use hydrogen. In the present study, La and Mm metal hydrides based cooling system is proposed for cold storage application which can work using solar energy. Ten metal hydride (AB5) pairs were selected for the thermodynamic analysis of the cold storage module. The minimum cooling temperature and maximum heat source temperature required for each pair are calculated. Hydrogen storage and thermodynamic properties of La0.95Ce0.05Ni5, La0.85Ce0.15Ni5, and MmNi4.5Al0.5 are obtained by measuring pressure concentration isotherms at different temperatures. The effect of source temperature and cooling temperature on COP, Exergy COP, and specific cooling load (SCL) are studied. MmNi4.6Fe0.4/MmNi4.6Al0.4 pair has attained a theoretical maximum COP and exergy COP of 0.784 and 0.89 respectively at a heat source temperature of 60 °C and cooling temperature of 2 °C. However, at higher heat source temperature La0.95Ce0.05Ni5/MmNi4.5Fe0.5 has better performance than MmNi4.6Fe0.4/MmNi4.6Al0.4. In addition, the effect of cooling load on the size of the system for cold storage of 10 kg apples is also studied. For cold storage of 10 kg apples at 2 ℃, La0.95Ce0.05Ni5/ LaNi4.7Al0.3 has the best performance with a COP of 0.693 and minimum total weight of 18.35 kg.

Development of a Two‐Stage Hydrogen‐Based Thermochemical Energy Storage System

Both energy conservation and the use of renewable resources are necessary due to the global increase in energy demand. A useful technique for energy storage, when renewable energy sources are available, is a thermochemical energy storage system that relies on the interaction of gases with solids. From this vantage point, hydrogen offers a sustainable and regenerative response to this pressing issue. In line with that, herein, the operation of a novel two‐stage hydrogen‐based thermochemical energy storage system (TS‐H‐TCES) is proposed to attain a higher energy density and is analyzed with the help of the thermodynamic cycle. The proposed system operates at 298, 373, 403, and 423 K as atmospheric temperature (Tatm), waste heat input temperature (Tm), storage temperature (Ts), and upgraded/enhanced heat output temperature (Th), respectively. For the given operating temperature, the thermodynamic performance of TS‐H‐TCES is evaluated using experimentally measured pressure–concentration isotherms of LaNi4.7Al0.3, LaNi4.6Al0.4, and MmNi4.6Al0.4. The maximum coefficient of performance, second law efficiency (ηII), and thermal energy storage density are found to be 0.67, 0.70, and 220.98 kJ kg−1, respectively. The impact of operating temperatures on system performance is also investigated, which is important in choosing the best temperature range for a certain application.

Novel temperature-driven technique to characterize hydrogen sorption properties under vacuum conditions: Method development, experimental setup, and demonstration on the AB5-type metal hydride LaNi4.1Al0.52Mn0.38

In this study, a modified temperature-controlled sorption characterization technique based on a Sieverts’ apparatus is presented. The main characteristic of the developed method is the hydrogen mass being constant in the system over individual measurement runs while the thermochemical reaction is controlled by the sample temperature. This allows the sorption properties to be measured in vacuum – even down to high vacuum - without the need for large capturing volumes provided. The method itself, the correspondingly built test rig as well as the measurement procedure are discussed in detail. Sources of uncertainty are discussed and evaluated.By performing reference measurements of the absorption and desorption equilibria of the AB5-type alloy LaNi4.1Al0.52Mn0.38, the method is validated and the corresponding results are demonstrated for the first time. Extensive measurements are performed and complete pressure-composition-isotherms are presented along with repeat measurements series to confirm the results of the novel technique. The obtained PCI data are compared with pressure-concentration isotherms from the literature to validate the measurement method and system. The primary equilibrium data in this work are in very good agreement with both the repeat measurements and the comparison with literature data. It can be shown that the method as well as the experimental design are valid and capable of providing accurate measurements of hydrogen sorption behavior.

Thermochemical energy storage using coupled metal hydride beds of Mg-LaNi5 composites and LaNi5 based hydrides for concentrated solar power plants

• A MHTES system is proposed for CSP plant application. • Energy storage and recovery temperatures are estimated. • PCIs of Mg based composites and LaNi 5 based alloys are measured. • Reaction enthalpy and entropy are evaluated using van’t Hoff equation. • The performance of the MHTES system is analyzed thermodynamically. • The effect of operating temperatures on the performance of the MHTES is studied. Thermochemical energy storage based on coupled hydride beds is an attractive option for Concentrated Solar Power plant applications due to its efficient long term and high energy storage density. In the coupled system, a high temperature metal hydride (HTMH) bed is coupled with a low temperature metal hydride (LTMH) bed. In the present study, Mg-LaNi 5 composite hydrides are taken as HTMHs due to their high absorption capacity and high reaction enthalpy, and LaNi 5 based alloys are taken as LTMHs as these hydrides are ideal for hydrogen storage at ambient conditions. The thermodynamic properties such as reaction enthalpy and entropy are evaluated by measuring Pressure Concentration Isotherms of Mg- x wt% LaNi 5 ( x =20 and 30) composites, LaNi 4.7 Al 0.3 and LaNi 4.6 Al 0.4 . A new methodology for storing and recovering thermal energy together with upgradation of the quality of energy is established. Methodology to determine the minimum energy storage temperature and maximum energy recovery temperature is proposed. The quality of the thermal energy will be improved by increase in delivery temperature. Thermodynamic analysis is performed using measured properties to evaluate the performance parameters such as heat upgradation, coefficient of performance (COP), and energy storage density (ESD). Maximum COP and ESD of 0.705 and 418.841 kJ/kg, respectively is obtained for hydride pair Mg-5wt% LaNi 5 -La 0.8 Ce 0.2 Ni 5 . Maximum degree of upgradation of 34°C is obtained using the hydride pair Mg-20wt% LaNi 5 -LaNi 4.7 Al 0.3 . The effects of variation of heat source temperature, regeneration temperature and ambient temperature on the performance of the MHTES is studied. It is observed that the regeneration temperature is a significant parameter that influences the performance of the MHTES.

Thermodynamic analysis of a metal hydride hydrogen compressor with aluminium substituted LaNi5 hydrides

The operating conditions of a Metal Hydride Hydrogen Compressor (MHHC) is often dictated by the hydride used to build it. This research focuses on finding the appropriate operating conditions for MHHC to get the ideal throughput and efficiency using aluminium based hydrides. For this, hydrogen absorption and desorption characteristics of LaNi5-xAlx (where x is 0, 0.2 and 0.4) hydrides were studied for estimating the suitability of these materials for developing hydrogen compressor. From the Pressure Concentration Isotherms (PCIs) and van't Hoff plot, an estimate of the reversible hydrogen weight percent attainable, equilibrium pressure and absorption and desorption temperature range were collected and the effect of aluminium concentration on these properties was studied. Further thermodynamic analysis was made by calculating the performance parameters like thermal efficiency, isentropic work required, theoretical heat supplied and pressure ratio by varying the operating conditions like supply pressure (3–5 bar), absorption temperatures (20–40 °C), and desorption temperature (80–140 °C). It is observed that the higher aluminium content in the hydride allows the hydrogen compressor to be operated at a lower supply pressure. Whereas lower aluminium content in hydrides give higher thermal efficiency and discharge pressure for a particular desorption temperature, while requiring a higher supply pressure to perform efficiently. The maximum thermal efficiency within the studied operating conditions was found to be 0.24 for LaNi5 at 3 bar supply pressure, 30 °C absorption and 140 °C desorption temperature with a pressure ratio of 8.97.

Performance investigation of the hydrogen-based energy storage system employing high-pressure metal hydride pair

ABSTRACT The performance of hydrogen-based energy storage (HBES) systems is anticipated using a finite volume technique and thermal analysis with TiCrMn-MmNi4.15Fe0.85 as a linked metal hydride (MH) pair, obtained through screening. To understand the behavior of the materials during reactions, a set of governing equations is solved using the computational fluid dynamics (CFD) technique. The pressure concentration isotherms (PCIs) are predicted through numerical code and are used for numerical analysis. The performance of the HBES system is evaluated at the operating temperatures of 423 K, 403 K, 373 K, and 298 K as output, storage, regeneration, and ambient temperatures, respectively. The current HBES system has energy storage (ES) density of 136.74 kJ/kg and a coefficient of performance of 0.47. The total operation duration is obtained as 36 min, and it consists of two hydrogen exchange and two heat transfer processes.

Thermodynamic characterization of Mg‐50 wt% LaNi5 composite hydride for thermochemical energy storage application

AbstractIn the present work, composite material, Mg‐50 wt% LaNi5, is thermodynamically characterized for thermochemical energy storage application, and its mechanism of hydrogen absorption is studied by using Johnson‐Mehl‐Avrami (JMA) equation. Pressure concentration isotherms (PCI) of the composite during hydrogen absorption and desorption are measured at 250°C, 300°C, 350°C, and 375°C. The enthalpy of absorption and enthalpy of desorption are calculated as 62.082 and 66.009 kJ/mol H2. Absorption kinetics is measured at 250°C, 300°C, and 350°C with hydrogen supply pressures of 10, 20, and 30 bar. The activation energies are calculated at different supply pressures using Arrhenius equation. Based on activation energy, the rate‐limiting steps are identified. A thermochemical energy storage method is proposed based on equilibrium pressure‐temperature relation obtained during absorption and desorption. The amount of thermochemical energy stored and recovered per kg of the composite is calculated based on reaction enthalpies and hydrogen concentration. The maximum theoretical thermochemical energy stored and recovered at a temperature of 350°C is calculated as 1452.198 and 1365.804 kJ/kg respectively. The maximum theoretical energy storage efficiency is estimated as 0.94. Hence, the composite, Mg‐50 wt% LaNi5, can be used as thermochemical energy storage material in the temperature range of 250°C‐350°C with a thermochemical energy storage capacity of 0.403 kWh/kg composite.

Resonant enhancement of grazing incidence neutron scattering for the characterization of thin films

We use signal enhancement in a quantum resonator for the characterization of a thin layer of vanadium hydride using neutron reflectometry and demonstrate that pressure-concentration isotherms and expansion coefficients can be extracted from the measurement of totally externally reflected neutrons only. Moreover, a consistent data analysis of the attenuation cross section allows us to detect and quantify off-specular and small angle scattering. As our experiments are effective direct beam measurements, combined with resonant signal enhancement, counting times become considerably reduced. This allows us to overcome the challenges resulting from the comparatively low brilliance of neutron beams for grazing incidence scattering experiments. Further, we discuss the potential of resonant enhancement to increase any scattering, which is of particular interest for grazing incidence small angle neutron scattering and spectroscopy.

Performance investigation of a two-stage sorption hydrogen compressor

Metal hydrides (MH) are widely investigated for several thermodynamic applications; sorption hydrogen compressor (SHC) is one among them. In this study, the thermodynamic performance and heat – mass transfer behaviour of a two-stage sorption hydrogen compressor (TSSHC) are investigated with the employment of La0·9Ce0·1Ni5 and MmNi4.8Al0.2 alloys in series. The hydrogen supply and the discharge temperatures are chosen as 20 °C and 80 °C, respectively. The thermodynamic performance data, i.e. compressor work and efficiency, are evaluated using the experimentally measured pressure-concentration-isotherm (PCI) and thermodynamic properties. In contrast, the heat and mass transfer behaviour is predicted by solving governing equations through the finite volume method (FVM). The numerical model is validated with experimental PCIs, and the results are in close agreement. The predicted cycle time is 75 min, comprising hydrogen supply, sensible heating and cooling, and hydrogen delivery. The TSSHC possessed a compression ratio of 9.5 and a cycle efficiency of 11.4% in which the hydrogen supply pressure is 9 bar using 0.5 kg of each alloy. Later, the influence of mass transfer on overall compressor work, heat input and efficiency is also presented.

Innovative method to estimate state of charge of the hydride hydrogen tank: application of fuel cell electric vehicles

ABSTRACT Significant attention has been paid to metal hydrides (MH) as an environmentally friendly and safe way to store hydrogen. This technology has considerable potential for the application of embedded hydrogen storage in fuel cell electric vehicles, but its widespread application faces a major problem in terms of estimating the remaining hydrogen amount in the tank. In this work, a new method is proposed for estimating the state of charge (SoC) of the hydrogen hydride tank (HHT) by application of piezoelectric material. The idea is to cover the entire inner wall of the metal-hydride tank with a layer of piezoelectric material. During the process of hydrogen absorption, the pressure inside the tank increases, resulting in an increase in the mechanical stress applied to the piezoelectric layer, thus generating a voltage. This effect can therefore be used as an effective means of estimating the amount of hydrogen absorbed. The COMSOL Multiphysics software was used to implement the model and solve the differential equation of energy, mass, and moment. The simulation results showed that the voltage evolution as a function of hydrogen concentration follows the same behavior as the variation of the Pressure Concentration Isotherm (PCI).

Hydrogen desorption from alloys Mg–Cu(–KCl): Cu catalysis in detail

Effect of chemical composition of Mg-xCu based alloys (x = 9.94–58.00 wt %) modified by KCl upon their hydrogen storage performance was studied. Kinetic curves and pressure-concentration isotherms were measured in the ranges up to 60 bar and 388 °C, respectively. It was observed that desorption rate dc/dt is not significantly influenced by the composition. Unknown Cu-rich phase was detected that has shown a catalytic effect on desorption from a mixture with other phases. Activation energy of hydrogen desorption decreased with increasing x from 180 kJ/mol down to 98 kJ/mol. Average hydride dissociation enthalpy, ΔH, for the lowest plateau was 75 kJ/mol which is equal to literature value for pure Mg. Slightly lover average value, 67 kJ/mol was obtained for the second plateau and ΔH for the third one decreased from 70 kJ/mol for the lowest to 49 kJ/mol for the highest x.

Characterisation of La0.9Ce0.1Ni5 alloy for the development of single‐stage thermally driven sorption hydrogen compressor

SummaryIn 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.

Influence of effective thermal conductivity on hydrogen sorption in Mg-LaNi4.6Al0.4 composite hydride beds for thermal energy storage

Thermochemical energy storage using metal hydrides is well known. Appreciable quantities of heat energy interactions involved in the hydrogenation and dehydrogenation processes of metal hydride make the metal hydrides suitable for the storage of thermal energy. This paper discusses the synthesis, Pressure Concentration Isotherm (PCI) characterization and estimation of thermal properties of Mg + 50 wt% LaNi4.6Al0.4 composite hydride suitable for thermal energy storage. Maximum theoretical energy density of 918 kJ/kg can be achieved in the temperature range of 150–200 °C. Low values (0.1–1 W/mK) of effective thermal conductivity (ETC) of metal hydride beds is responsible for poor heat and mass transfer characteristics of metal hydride beds. The ETC of Mg + 50 wt% LaNi4.6Al0.4 composite hydride bed was augmented by fabricating two types of pellets. The sorption kinetic measurements were performed for three different configurations of metal hydride beds, one with powder composite hydride and remaining with two different types of pellets. Enhancement in ETC improved the heat and mass transfer characteristics of the composite metal hydride bed.

MEASUREMENT OF THE ABSORPTION-BASED HYDROGEN STORAGE CAPACITY OF Ti0.95Zr0.05Cr0.8Mn0.8V0.2Ni0.2 ALLOY

The article describes potential application of the BCC alloy Ti0.95Zr0.05Cr0.8Mn0.8V0.2Ni0.2 in the hydrogen absorption process. It deals with the measurements of the PCI (Pressure Concentration Isotherm) characteristics applying the volumetric method. With regard to the fact that it is an indirect measurement method, the thermodynamic description was analysed in details and subsequently used to identify the weight capacity of the stored hydrogen. The article presents a detailed description of the procedure for measuring the free volume of the measuring equipment using helium which is able to penetrate into pores and apertures with the size of only a few nanometres but does not participate in the absorption into the intermetallic structure of the alloy. The hydrogen absorption into the tested alloy was initiated by repeatedly performed activation of the alloy surface. The final section of the article presents the examination of the cyclic stability of the absorption-desorption cycle within the repeated monitoring of the maximum weight capacity of the stored hydrogen.

Comparison of ammonia sorption properties and thermodynamic performance of adsorption‐based thermal energy storage system for MnCl2, CaCl2, and their composites

AbstractIn this work, composite adsorbent materials are prepared using metal halide salts and expanded natural graphite (ENG). Ammonia adsorption and desorption pressure concentration isotherms of composite adsorbents are experimentally measured. The van't Hoff plots are constructed to calculate the enthalpy of a reaction during adsorption and desorption. The average value of adsorption enthalpies (∆Had) for MnCl2 + ENG and CaCl2 + ENG are 55.821 and 33.434 kJ mol−1, respectively, and average values of desorption enthalpies (∆Hdes) are 73.817 and 73.016 kJ mol−1, respectively. Comparison of ammonia sorption properties of composites and their corresponding plain salts is done. Thermodynamic analysis of adsorption thermal energy storage (ATES) system) showed that maximum gravimetric energy storage density for MnCl2 + ENG based system is 1394.83 kJ kg−1 (158.85 kWh m−3) at energy storage and ambient temperatures of 172°C and 35°C, respectively. The same for CaCl2 + ENG based system is 1350.86 kJ kg−1 (165.85 kWh m−3) at storage and ambient temperatures of 92°C and 35°C, respectively. Volumetric energy storage density is higher for CaCl2 + ENG based ATES system since it has higher density. Thermodynamic performance of composite‐based systems is compared with plain salts (MnCl2‐CaCl2) based thermal energy storage system.

Thermodynamic and heat‐hydrogen transfer analyses of novel multistage hydrogen‐alloy sorption heat pump

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.

Performance investigation of novel multi stage multi effect sorption thermodynamic system for heating and cooling applications

Performance of novel multi stage multi effect sorption thermodynamic system for heating and cooling applications (MSTS-HCA) is investigated using finite volume method (FVM) with a metal hydride pair of La0.9Ce0.1Ni5, MmNi4.4Al0.6, LaNi4.7Al0.3 and MmNi3.7Co0.7Mn0.3Al0.3. Numerical code is generated to solve governing equations to determine the transferable amount of hydrogen, bed temperature variation and heat loads between paired reactors. The numerical code is validated with experimental pressure concentration isotherms (PCIs) of these metal hydrides measured at operating temperatures of 20 ℃, 45 ℃, 140 ℃ and 180 ℃, using Sievert’s apparatus. The slope and hysteresis factors are identified from PCI validation results which are needed for further performance investigation. Upon performance investigation through finite volume method and thermodynamic analysis, it is observed that the novel MSTS-HC can able to produce 424 kJ cooling output with cooling capacity of 0.29 kW, 412 kJ high temperature heat output with heating capacity of 0.22 kW and 729 kJ low temperature heat output with pumping capacity of 0.41 kW at a total low grade heat input of 530 kJ with overall COP and specific alloy output of 2.98 and 622 W/340 g of metal hydride, respectively. In addition, the detailed flow chart demonstrating the steps involved in performance analysis of novel MSTS-HCA through computation fluid dynamics (CFD) simulation is presented.

Numerical optimization of a plate reactor for a metal hydride open cooling system

Open cooling systems based on metal hydrides (MH) are promising as they are purely driven by the on-board available compression work of the compressed hydrogen in a fuel cell vehicle. In this study, the plate reactor is numerically optimized for fast reaction dynamics leading to an increased power density. Experimental results for the thermodynamic characterization of the applied Hydralloy C2 (Ti0.98Zr0.02V0.41Fe0.09Cr0.05Mn1.46) in the temperature range of 0–50 °C and a mathematical expression for the pressure–concentration isotherms are presented. The model is validated with data from the experimental literature for different cooling temperatures (15–25 °C) and electrical fuel cell powers (4–6 kW). As the reactor alternately passes through two temperature levels in its continuous operation, the effects of thermal losses are evaluated in detail. The optimum thickness for the MH bed is close to the channel thickness of a commercially available reactor. A further increase of the cooling power can be obtained by reducing the distance of the hydrogen gas transport, porosity of the MH bed, and fuel cell backpressure.

Studies on thermodynamic performance of three stage sorption heat transformer

In the present study, a novel four alloys three-stage hydrogen based sorption heat transformer (4A – HSHT) is proposed to achieve higher heating output and efficiency with wide range of operating temperatures. The 4A – HSHT system can able to produce multiple heating outputs compared to conventional single stage metal hydride heat transformer (MHHT) with higher COP. The screening of metal hydrides is carried out to identify the best suited working pair for 4A – HSHT which results in the pair of La0.9Ce0.1Ni5 – MmNi4.4Al0.6 – LaNi4.7Al0.3 – MmNi3.7Co0.7Mn0.3Al0.3 hydrides for operating temperature range of 180 °C for heating output, 140 °C for heat supply and 45 °C for heat sink. The thermodynamic performance of 4A – HSHT is investigated using experimentally measured pressure concentration isotherm (PCI) and thermodynamic properties of chosen metal hydrides. The thermodynamic performance i.e. COP, specific heat output and heating capacity are estimated as 0.75, 81.8 W/kg and 0.9 kW, respectively for 2.75 kg of each alloy with 64 min of cycle time followed by the discussion on effects of heating output temperature on COP and specific heat output. The detailed flow chart demonstrating the methodology of material selection and thermodynamic simulation is presented. In addition, the various issues related to the implementation of practical devices based on metal hydride sorption systems are discussed including recent developments.