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Thermal performance of a metal hydride reactor for hydrogen storage with cooling/heating by natural convection

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Energy Storage and Saving 2023年第4期2卷 597-607页

作者： Konstantin Borisovich Minko Maksim Nashchekin Department of Engineering Thermophysics Moscow Power Engineering Institute(MPEI)National Research UniversityMoscow111250Russia

Metal hydride(MH)systems can be used for storage in stationary facilities of hydrogen with a high volume density at temperatures and pressures close to ambient ones.Recently,the possibility of using passive heating/cooling systems or regenerative heat exchangers has been studied to improve the energy efficiency of MH systems for hydrogen storage without the need for forced circulation of a heating/cooling fluid.natural convection of air may be used to passively remove/add heat as required for proper operation of a MH reactor.Under these conditions,the MH reactor can operate at a constant ambient air temperature and be driven by a difference in pressure between the source and the consumer of hydrogen.Since operation of MH systems with natural convective heating/cooling has not been systematically investigated as yet,a tubular MH reactor based on this principle is examined in this paper.Two-thirds of the internal volume ofø25.4×1 mm tube is occupied by a composition of LaNi5 and aluminium foam(one linear metre contains 1.1 kg of LaNi5 with a hydrogen capacity of 153 NL H2).Annular fins are used to increase heat transfer to air.Detailed and simplified mathematical models of the systems of this class are proposed and validated.It is shown that acceptable hydrogen charging/discharging rates in such systems are achieved with proper selection of fining characteristics.Charging from a hydrogen source at a pressure of 10 atm and an ambient air temperature of 10 to 30℃ takes 15 min.A reactor with a length of 1 m can desorb almost all stored hydrogen at a minimum outlet pressure of 0.45 bar to feed 30-300 W fuel cells.

关键词： Metal hydride Hydrogen storage natural convection Annular fins CFD Numerical simulation Optimization

natural convection flow in a vertical annulus with time-periodic thermal boundary conditions

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Propulsion and Power Research 2019年第1期8卷 47-55页

作者： Basant K.Jha Michael O.Oni Department of Mathematics.Ahmadu Bello University Zaria.Nigeria

This paper presents an analytical solution for natural convection flow in a vertical annulus due to time-periodic heating of annulus surfaces.Closed-form expressions for velocity,temperature,skin-friction,mass flow rate and rate of heat transfer which is expressed as Nusselt number are obtained by solving the present mathematical model after separating into steady component and periodic regime.The effects of pertinent parameters such as Strouhal number(St),Prandtl number(Pr)and radius ratio(λ)are shown with the aid of contour and line graphs.Results indicate that the role of Strouhal number and Prandtl number is to decrease fluid velocity,temperature and skin-friction.Furthermore,increase in Strouhal number increases the temperature phase-lag.

关键词： natural convection Fully developed flow Time-periodic heating Vertical annulus Strouhal number

natural convection gas pendulum and its application in accelerometer and tilt sensor

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Progress in natural Science:Materials International 2005年第9期15卷 857-860页

作者： ZHANG Fuxue(Research Center of Sensor Technology, Beijing Information Technology Institute, Beijing 100101, China) Research Center of Sensor Technology Beijing Information Technology Institute Beijing 100101 China

It is discovered that the natural convection gas has the pendulum characteristic, which leads to the introduction of the new concept of gas pendulum. In this paper, the buoyancy lift of natural convection gas is analyzed in a hermetic chamber, and the relationship between the buoyancy lift and the change of temperature is formulated. The experimental results show that the gas pendulum, similar to the solid pendulum and liquid pendulum, can be utilized to sense the acceleration and the tilt angle.

关键词： natural convection accelerometer tilt sensor.

natural convection of MHD over a Vertical Wavy Surface in Presence of Porous Media

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Journal of Applied Mathematics and Physics 2022年第11期10卷 3288-3300页

作者： Rasha Adel Department of Mathematics Faculty of Science Helwan University Cairo Egypt

This paper shows the natural convective heat transfer in porous media over the vertical wavy surface and it assumes that the fluid is viscous and in-compressible. This model shows the effects of the inverse of Darcy number. The dimensional partial differential equations are converted into a dimensionless form. The non-linear system of equations is obtained and these equations are solved numerically by the finite difference method. The results are obtained for inverse Darcy number, magnetic parameter, Prandtl number, amplitude of surface, parameter of heat generation and parameter of thermal conductivity, and their effects on the velocity, temperature of the fluid and Nusselt number.

关键词： natural convection Magnetohydrodynamics (MHD) Porous Media Wavy Surface

natural convection of Temperature-Sensitive Magnetic Fluids in Porous Media

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Advances in Applied Mathematics and Mechanics 2011年第1期3卷 121-130页

作者： Valentin Roussellet Xiaodong Niu Hiroshi Yamaguchi Frederic Magoules Applied Mathematics and Systems Laboratory Ecole Centrale Paris92295 Chatenay-MalabryFrance Department of Mechanical Engineering Doshisha UniversityKyoto 610-0321Japan

In this article,natural convection of a temperature-sensitive magnetic fluid in a porous media is studied numerically by using lattice Boltzmann method.Results show that the heat transfer decreases when the ball numbers increase.When the magnetic field is increased,the heat transfer is enhanced;however the average wall Nusselt number increases at small ball numbers but decreases at large ball numbers due to the induced flow being more likely confined near the bottom walls with a high number of obstacles.

关键词： Temperature sensitive magnetic fluid natural convection porous media lattice Boltzmann method

natural convection Heat Transfer in a Porous Cavity with Sinusoidal Temperature Distribution Using Cu/Water Nanofluid: Double MRT Lattice Boltzmann Method

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Communications in Computational Physics 2021年第1期29卷 292-318页

作者： Hasan Sajjadi Amin Amiri Delouei Rasul Mohebbi Mohsen Izadi Sauro Succi Department of Mechanical Engineering Faculty of EngineeringUniversity of BojnordBojnordIran School of Engineering Damghan UniversityDamghanIran Mechanical Engineering Department Faculty of EngineeringLorestan UniversityKhorramabadIran Center for Life Nanoscience Italian Institute of TechnologyViale Regina Margherita 29500161RomaItaly Physics Department Harvard University29 Oxford StreetCambridgeMA 02138USA

In this study,natural convection flow in a porous cavity with sinusoidal temperature distribution has been analyzed by a new double multi relaxation time(MRT)Lattice Boltzmann method(LBM).We consider a copper/water nanofluid filling a porous cavity.For simulating the temperature and flow fields,D2Q5 and D2Q9 lattices are utilized respectively,and the effects of different Darcy numbers(Da)(0.001-0.1)and various Rayleigh numbers(Ra)(10^(3)-10^(5))for porosity(ε)between 0.4 and 0.9 have been considered.Phase deviation(θ)changed from 0 toπand the volume fraction of nanoparticles(∅)varied from 0 to 6%.The present results show a good agreement with the previous works,thus confirming the reliability the new numerical method proposed in this paper.It is indicated that the heat transfer rate increases at increasing Darcy number,porosity,Rayleigh number,the volume fraction of nanoparticles and phase deviation.However,the most sensitive parameter is the Rayleigh number.The maximum Nusselt deviation is 10%,32%and 33%for Ra=10^(3),10^(4) and 10^(5),respectively,withε=0.4 toε=0.9.It can be concluded that the effect of Darcy number on the heat transfer rate increases at increasing Rayleigh number,yielding a maximum enhancement of the average Nusselt number around 12%and 61%for Ra=10^(3) and Ra=10^(5),respectively.

关键词： Porous media double multi relaxation time-lattice Boltzmann method nanofluid natural convection sinusoidal temperature distribution

Numerical Analysis on Charging Performance of the Macro-Encapsulating Combined Sensible-Latent Heat Storage System with Structural Parameters

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Journal of Thermal Science 2024年第3期33卷 1026-1036页

作者： WANG Wei PAN Zhenfei WANG Jingfu WU Yuting MA Chongfang Key Laboratory of Enhanced Heat Transfer and Energy Conservation Ministry of EducationCollege of Energy and Power EngineeringBeijing University of TechnologyBeijing100124China Key Laboratory of Heat Transfer and Energy Conversion Beijing MunicipalityCollege of Energy and Power EngineeringBeijing University of TechnologyBeijing100124China

For combined sensible-latent heat storage system(CSLHS)(termed as the hybrid configuration),macro encapsulation can effectively solve the leakage problem of PCMs.However,due to the poor thermal conductivity of PCMs,the charging performance of the hybrid configuration slightly increases compared to the solid structure(with only sensible materials).Meanwhile,the natural convection in the PCMs zone could improve the charging performance.So,how to improve natural convection intensity is a key issue for the CSLHS by macro encapsulating.It is found that adding fins can significantly enhance natural convection and accelerate the melting of PCM.In this paper,we proposed the hybrid configuration with fins built-in by macro encapsulation,and analyzed its charging performance with different fin structural parameters in the PCM zone by CFD simulation.In the case,the sensible heat storage material is high-temperature concrete and the PCM is a low-melting-point mixed molten salt.We analyzed the effects of fin number,fin length and fin thickness on the charging performance of the hybrid configuration respectively.From the result,the charging performance increases with the fin number,but the increase rate gradually decreases.When the fin number is 6,the charging performance increases by 20.18%compared to the situation without fin.The charging performance increases gradually with the fin length.Compared with the hybrid configuration without fin,for each 10 mm increase in fin length,its charging performances increase by 4.09%,5.26%,7.02%,8.77%,11.70%,and 15.79%,respectively.Different from number and length of fins,the effect of thickness on the charging performance is very small.When the fin thickness increased from 1 mm to 4 mm,the charging performance only increased by 2.3%.It indicates that the main reason for the improving the charging performance is to increase the natural convection intensity by dividing the PCM zone through fins.These results show that the charging performance of the CSLHS with macro encapsulation can be im

关键词： macro-encapsulation hybrid configuration natural convection structural parameter charging performance

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natural convection IN AN INFINITE SQUARE UNDER LOW-GRAVITY CONDITIONS

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Applied Mathematics and Mechanics(English Edition) 1992年第5期13卷 461-466页

作者：马云丽 Institute of Mechanics Academia Sinica Beijing

In order to study natural convection effects on fluid flows under low-gravity in space, we have expanded variables into a power series of Grashof number by using perturbation theory to reduce the Navier-Stokes equations to the Poisson equation for temperature T and biharmonic equation for stream function φ . Suppose that a square infinite closed cylinder horizontally imposes a specified temperature of linear distribution on the boundaries, we investigate the two dimensional steady flows in detail. The results for stream function φ, velocity u and temperature T are gained. The analysis of the influences of some parameters such as Grashof number G r and Prandtl number Pron the fluid motion lead to several interesting conclusions. At last, we make a comparison between two results, one from approximate equations, the other from the original version. It shows that the approximate theory correctly simplifies the physical problem, so that we can expect the theory will be applied to unsteady or three-dimensional cases in the future.

关键词： low-gravity natural convection Grashof number

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Simulation on scrap melting behavior and carbon diffusion under natural convection

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International Journal of Minerals,Metallurgy and Materials 2021年第3期28卷 380-389页

作者： Ming Gao Jin-tao Gao Yan-ling Zhang Shu-feng Yang State Key Laboratory of Advanced Metallurgy University of Science and Technology BeijingBeijing 100083China School of Metallurgical and Ecological Engineering University of Science and Technology BeijingBeijing 100083China

A 3D model applying temperature-and carbon concentration-dependent material properties was developed to describe the scrap melting behavior and carbon diffusion under natural convection.Simulated results agreed reasonably well with experimental ones.Scrap melting was subdivided into four stages:formation of a solidified layer,rapid melting of the solidified layer,carburization,and carburization+normal melting.The carburization stage could not be ignored at low temperature because the carburization time for the sample investigated was 214 s at 1573 K compared to 12 s at 1723 K.The thickness of the boundary layer with significant concentration difference at 1573 K increased from 130μm at 5 s to 140μm at 60 s.The maximum velocity caused by natural convection decreased from 0.029 m·s^(−1)at 5 s to 0.009 m·s^(−1)at 634 s because the differences in temperature and density between the molten metal and scrap decreased with time.

关键词： scrap melting natural convection carbon diffusion numerical simulation electron probe micro-analyzer

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