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Comparison of Thermal Performance between annular fins and Longitudinal fins in Latent Heat Storage Unit

Journal of Thermal Science 2023年第3期32卷 1227-1238页

作者： ZHU Yuxi QIU Yan School of Energy and Power Engineering Shandong UniversityJi'nan 250061China

As a simple and effective method of heat transfer enhancement,fins are widely used in latent heat storage systems.However,the choice of annular fins and longitudinal fins has always been controversial.In this paper,the melting process of phase change material(PCM)in annular fins and longitudinal fins latent heat storage units with the same volume is numerically simulated.To ensure the same thermal penetration,three-dimensional spaces occupied with fins are specially controlled to be the same.Combined with finned structures,the effects of natural convection(NC),placement mode and heat transfer fluid(HTF)inlet direction on the melting process are studied.The results show that the melting time in annular finned structure is always 10%less than that in longitudinal finned structure,which demonstrates the superior of the annular fins in the latent heat storage unit.The melting time is the shortest in vertical unit with annular fins and HTF inlet at the bottom.Additionally,the correlation formulas of the liquid fraction are proposed in the vertical unit with HTF inlet at the bottom.

关键词： latent heat storage annular fins longitudinal fins natural convection

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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

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