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A recent paper titled "A continuous hydrogen absorption/desorption model for metal hydride reactor coupled with PCM as heat management and its application in the fuel cell power system", published in the International Journal of Hydrogen Energy, describes the desorption kinetics modification without which the authors of this paper was unable to obtain experimental dependencies in the simulation during desorption. According to the opinion of the author of this commentary, modification of the kinetics is not required, and experimental results can be obtained using the standard kinetics by replacing the inlet/outlet boundary condition with a better one. [ABSTRACT FROM AUTHOR]

• A model was developed for forced convection condensation in the presence of air. • Condensation influences the mixture flow only through the boundary condition. • The proposed model was verified using published experimental data. • The tube bundle case was viewed as more closely reflecting industrial devices. This paper presents a description and the results of verification of an unsteady model for forced convection condensation on a smooth single horizontal tube in the presence of noncondensables. The external flow is described by the two-dimensional (2D) unsteady Navier–Stokes equations for a laminar regime or by the unsteady Reynolds-averaged Navier–Stokes (URANS) equations for a turbulent regime, and the condensate film is considered using a one-dimensional model. Details of the numerical implementation of the developed algorithm are described. The available literature data were employed to verify the proposed model for forced convection condensation for an arbitrary flow direction of vapour with and without noncondensables. The numerical results are in good agreement with the published experimental data. In the proposed model, condensation influences the air-vapour mixture flow only through the boundary condition; therefore, this model can be easily implemented using different computational fluid dynamics (CFD) codes (in this work, an "in-house" CFD code ANES) for modelling more complex configurations, like tube bundles. Results for condensation on five tubes in a tube bundle are also presented in this work. The influence of mutual irrigation of pipes by drops coming off was also approximated. [ABSTRACT FROM AUTHOR]

In the present comment, the results of recently published by Li Shu and Yonglin Ju "Numerical Study on the Condensation Characteristics of Various Refrigerants Outside a Horizontal Plain Tube at Low Temperatures" in International Journal of Thermal Sciences 2022 are discussed. It is shown that one of the conclusions of the work that "at low saturation temperatures, the periodic-averaged heat transfer coefficient in the numerical simulation is lower than that calculated with Nusselt's equation, especially at large wall subcooling", is not supported by the results of simulation performed by the author of this comment. [ABSTRACT FROM AUTHOR]

Abstract This work presents a hybrid model for the simulation of heat and mass transfer in metal hydride (MH) reactors. The model combines "lumped" approach based on mass and energy conservation for the gas phase with detailed consideration of the heat and mass exchange processes in the solid. The developed calculation procedure was realised numerically and integrated in a combined model of a two-stage MH hydrogen compressor (MHHC). Experimental validation based on the data available in the literature, the results of testing two types of MH reactors for H 2 compression, as well as a small-scale two-stage MHHC, demonstrated the qualitative and quantitative agreement of calculated and experimentally measured dependencies. Highlights • Simplified hybrid model for simulation of heat and mass transfer in MH reactors. • The model was implemented for the simulation of MHHC. • The model realistically predicts the H2 charging/discharging dynamics. • Test results of multi-stage MHHC can be used for verification of other models. • Improvement of charging dynamics due to copper foam is demonstrated. [ABSTRACT FROM AUTHOR]

The present paper describes a numerical study of heat and mass transfer processes in a metal hydride reactor for hydrogen purification with aluminium foam. A numerical simulation was done with the help of the mathematical model, which had been used previously for a numerical simulation of heat and mass transfer processes in different types of metal hydride reactors during sorption/desorption processes. The results illustrate that the major factors that reduce the rate of sorption, and consequently the efficiency of the system, are increasing the temperature of the reactor and the pressure drop, which is due to filtering the mixture through a metal hydride bed with low permeability. It is shown that the use of aluminium foam allows us to realise a more effective system for hydrogen purification from impurities, compared to a case without aluminium foam, while the volumetric capacity of the system is reduced slightly (9%). Increasing pressure at the reactor inlet also increases the efficiency of the system. [ABSTRACT FROM AUTHOR]

A novel method is proposed to increase the effective thermal conductivity of a metal-hydride (MH) bed by incorporating highly conductive inclusions into it in the form of metal rods made from various materials. The volume fraction of the inclusions, which had a diameter of 0.5 mm and length of 5 mm, ranged from 0.01 to 0.1. The structure of the composite beds was modelled by a specially developed algorithm. The results of the numerical simulation revealed that the effective thermal conductivity of the composite beds increased by 1.44–2.93 times when the volume fraction of the inclusions was 0.1. To estimate the effectiveness of the proposed method, a case study of hydrogen purification from a hydrogen–nitrogen mixture was performed for the cylindrical flow-through MH reactor, with two MH bed types: without inclusions (base case) and with inclusions (volume fraction of 0.1). The alloy fraction saturated by hydrogen and the mass of absorbed hydrogen higher for an equivalent reactor size notwithstanding a 10% reduction in the alloy mass. Moreover, the hydrogen losses were comparable to those of the base case. At hydrogen breakthrough, the fraction of hydride saturated by hydrogen increased from 61.5% to 81%, and the amount of hydrogen absorbed increased by 18.7%. The described method for enhancing the heat- and mass-transfer in MH beds enables the purification of a significantly larger volume of hydrogen with an equivalent number of sorption/desorption cycles. • The dynamics of metal hydride (MH) hydrogen purification system is investigated. • The composite MH bed with rods made from highly conductive material was used. • The effective thermal conductivity of composite MH bed was simulated. • The alloy fraction saturated by hydrogen increases from 61.5% to 81%. • The cycle time before hydrogen breakthrough increases by 18.7%. [ABSTRACT FROM AUTHOR]

• The turbulent flows under the influence of body forces were investigated. • The transverse magnetic field and buoyancy were considered to be body forces. • The flows in a vertical pipe and a square channel were considered. • Four subgrid scale models for LES were verified. • The effect on the friction and heat transfer of body forces was investigated. The main purpose of this work was to assess the performance of subgrid stress models for large eddy simulation (LES) of the flow and heat transfer of a conductive liquid simulating a molten salt (Pr = 4.1) in a square duct under the influence of a transverse magnetic field and an upward flow of air in a vertical heated pipe under a strong influence of buoyancy. An analysis of these problems is important when choosing the most appropriate subgrid-scale LES model for calculating the flows of an electrically conductive liquid under the combined influence of a magnetic field and buoyancy forces. Four subgrid-scale (SGS) models were verified: the Smagorinsky model with damping function (SMP), a coherent structure model (CSM), a WALE model and a hybrid model based on the equation for turbulent kinetic energy (KDES). For magnetohydrodynamic (MHD) flow in the duct, computations were performed in a domain with periodic inlet-exit boundaries and in a domain corresponding to the entrance region of a duct with a transverse magnetic field. Mixed convection of the air in the vertical heated pipe was simulated only in the domain with periodic boundaries. The results are compared with available data of direct numerical simulations (DNS). For MHD flow in the duct, the best predictions of DNS data for the average and fluctuating velocity components at Ha = 21.2 and Re = 5602 were obtained with the CSM and WALE models. The skin-friction and heat transfer coefficients are well known to have a minimum as Ha increases due to turbulence suppression by the magnetic field. The SMP and KDES models predict a minimum at H a dip ≈ 22 , whereas the CSM and WALE models predict a minimum at H a dip ≈ 30 for Re = 5602. The DNS data marked these values as the lower and upper boundaries of the complete turbulence suppression region for the same Reynolds number. For mixed convection of the air upward flows in a circular heated pipe at Re = 5300 , the CSM and WALE models showed weaker suppression of turbulence due to buoyancy forces when compared to the DNS results. The results of calculations of skin-friction and heat transfer coefficients performed with the help of the SMP and KDES models are much more coincident with the DNS data. [ABSTRACT FROM AUTHOR]