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 &amp; Sons, Ltd. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Vinod Kumar Sharma

Department of Thermal and Energy Engineering

School of Mechanical Engineering

Vellore Campus

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

International Journal of Energy Research

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. © 2019 John Wiley & Sons Ltd

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

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. © 2019 Elsevier Ltd

Applied Thermal Engineering

Studies on thermodynamic performance of three stage sorption heat transformer

The hydrogen absorption and desorption pressure-concentration isotherms (PCI) of La0.9Ce0.1Ni5 and LaNi4.6Al0.4 alloys are measured by static and dynamic method. The hydrogen absorption and desorption kinetics of the alloys also measured. The measured properties are used to study the performance of hydrogen based solid sorption heat transformer (MHHT). The thermodynamic simulation of MHHT is conducted using statically and dynamically measured PCI and thermodynamic properties. Due to variation in statically and dynamically measured metal hydride properties, significant variations in coefficient of performance (COP) and heat transformation capacity of MHHT are observed. In case of thermodynamic analysis using dynamically measured properties the heat transformation capacity and COP are decreased by 42.6% and 22.2% respectively, compared to statically measured data. This is due to the decrease in amount of hydrogen transmission and pressure differential between paired metal hydride reactors, and increase in reaction enthalpies. Later, the actual thermodynamic cycle for MHHT is constructed by considering the variation in pressure during hydrogen transfer processes between the metal hydride reactors. © 2017 Elsevier Masson SAS

International Journal of Thermal Sciences

Thermodynamic simulation of hydrogen based solid sorption heat transformer

Pressure-concentration isotherms (PCIs) of LaNi4.6Al0.4 metal hydride are measured using a Sievert's Apparatus at different temperatures to study the phenomenon of the formation of metal hydrides. PCI properties (plateau pressures, plateau slope, hysteresis, etc.) and thermodynamic properties (reaction enthalpy and entropy) of LaNi4.6Al0.4 metal hydride are calculated. To understand the effects of measurement parameters on PCI and thermodynamic properties the experimental conditions are varied. During the PCI measurements, the available pressure differences between supply volume and reactor volume are varied from 1 bar to 4 bar, then effects of the pressure interval (pressure difference) during each step of the absorption/desorption PCI measurement on the hydrogen storage capacity, equilibrium pressure, plateau slope, metal hydride bed temperature and hysteresis are studied. All of these properties showed a significant variation with pressure intervals. Later, to study the effect on thermodynamic properties, van't Hoff plots are constructed for wide temperature range and reaction enthalpies are calculated for different temperature points. The effect of the temperature range on the enthalpy of formation is observed to be dependent on the experimental temperature range. © 2017 Elsevier Ltd. All rights reserved.

Journal	Data powered by TypesetInternational Journal of Energy Research
Publisher	Data powered by TypesetWiley
ISSN	0363-907X
Open Access	0