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Combustion of iron powder is a promising option for clean and sustainable generation of heat and power. However, a fundamental understanding of the flame propagation mode is missing, especially under strong convection effects. In part I of this work, we analyzed the modes of flame propagation under weak convection effects and estimated the discreteness parameter as a ratio of the particle burn time to the conduction timescale. We found that both, the selection of temperature at which thermal properties are evaluated, and the selected length scale, are critical for a reliable prediction of the transitional particle spacing indicating the transition from the continuous to the discrete mode. In this paper, we extend our previous work by studying the effect of convection on inter-particle heat and mass transfer using boundary layer resolved numerical simulations. It is shown that for increasing convection, iron flames transition from the continuous to the discrete mode at higher particle distances. Taking into account both diffusion and convection-dominated heat transfer, an extension for the scaling of transitional particle spacing of part I is proposed. Furthermore, since iron flames could experience varying ranges of particle distances at different velocities in a practical flame, a regime diagram is constructed which is based on the Péclet number and the particle spacing with a boundary separating the two modes of flame propagation. The regime diagram offers orientation for simulations of large-scale flames using Euler–Lagrange methods where boundary layers around the particles are not resolved. [ABSTRACT FROM AUTHOR]

• Algorithm for PLIC-based interfacial area concentration on 3D non-orthogonal grids. • Thermal phase change model with geometrical basis and free of empirical input. • Oscillating behavior of GOX jet plume in LOX crossflow is reproduced in simulation. • Imbalance between the mass transfer rate and the supply causes the oscillation. • Methodology developed is verified by the Stefan problem and the bubble experiment. In order to enhance the physical basis of the mass transfer model in numerical simulation of gas-liquid direct contact condensation and improve the fidelity, a set of methods and models are developed. Based on the concept of the piecewise-linear interface calculation (PLIC), an interface reconstruction algorithm is proposed to calculate the interfacial area concentration in three-dimensional non-orthogonal structured grids. The actual interface in the cell is replaced by a plane, whose position is determined iteratively to satisfy the local volume fraction and orientation of the actual interface. The area of the polygonal cut by the plane is taken as the interfacial area in the cell. The proposed algorithm is validated by calculating the surface area of a series of basic geometries. Obvious superiority of the proposed algorithm over the traditional models (gradient model and algebraic model) is seen. Then, the reconstructed area is used to determine the interfacial area concentration in the thermal phase change model. The process is implemented by ANSYS Fluent user-defined functions. The Stefan problem and steam bubble condensation experiment are used to test the performance of the developed methods and models. The simulation results agree well with the theoretical and experimental results with the quantitative relative errors no more than 4.3 % and 15 %, respectively. The oxygen jets condensation experiments are also used as test cases. The primary dominant frequencies predicted by the simulations are 163.01 Hz and 131.65 Hz, which agree well with the 139.72 Hz and 125.75 Hz in the experiments. The relative errors are only 17 % and 4.7 %. The unstable flow pattern of oxygen jet in liquid oxygen crossflow is explained based on the dynamic characteristics of turbulence, heat and mass transfer. The periodic variation of mass transfer rate is considered as the cause of condensation oscillation. The method for calculating the interfacial area proposed in this paper can serve as an optional and practical improvement to the numerical simulation of direct contact condensation. [ABSTRACT FROM AUTHOR]

• A Reference-Standard-Volume optimization method is proposed to improve CESPB. • The best aspect ratio of CESPB is 2–4 considering efficiencies and pressure drop. • The volume multiple is given at 1.1 with the highest exergy efficiency of 63.72 %. • The thermal and exergy efficiencies are increased by 2.03 % and 3.65 %, respectively. Cryogenic liquids (e.g., liquid air, liquid hydrogen, liquid carbon dioxide) have gained popularity in electricity storage due to their high energy density, no geographical constraints, and environmental friendliness. The cryogenic energy storage packed bed (CESPB) is widely employed as a cold recovery device to enhance the round-trip efficiency of cryogenic energy storage systems. Nonetheless, the cycle efficiencies of CESPB remain relatively low, with limited research investigating efficient methods for determining the design parameters. To address this, a novel optimization method named as the Reference-Standard-Volume (RSV) approach is introduced to enhance the thermodynamic performance of CESPB. In this paper, the complete optimization process of CESPB is illustrated, presenting the optimization outcomes in the view of heat and mass transfer. The findings reveal that a larger aspect ratio leads to the higher efficiencies but increased pressure drops. An optimal aspect ratio of 3 and a volume multiple of 1.1 is identified, achieving the highest exergy efficiency of 63.72 %. Meanwhile, increasing charging/discharging time enhances heat transfer in CESPB, however, it leads to an increase in external cold dissipation, which gives an optimal charging/discharging time of 3/3 h. By implementing the RSV optimization method, the percentage increase of discharging efficiency, thermal efficiency, and exergy efficiency of CESPB is 2.08 %, 2.03 %, and 3.65 %, respectively. These research outcomes offer valuable reference and guidance for future CESPB design and research. [ABSTRACT FROM AUTHOR]

The packing is the core heat transfer unit in the cooling tower. To improve the heat and mass transfer performance of the counterflow wet cooling tower, a new double S-wave structure packing is proposed in this paper, and its performance in heat-mass exchange is investigated using a combination of numerical simulation and experiment. The flow heat transfer performance of the double S-wave packing with different sheet spacing, tilt angle and inlet area is studied by numerical simulation, and the law of different structural parameters affecting the packing is derived to determine its optimal structure. The thermal and resistance performance of double S-wave packing and conventional double-folded packing under different working conditions were studied in comparison with each other by building an experimental bench. The results show that the cooling efficiency of double S-wave packing is 13.74% higher and the pressure drop is 3.58% lower than that of double-folded packing. The research results can provide important guidance and reference for engineering practice. [ABSTRACT FROM AUTHOR]

Spray cooling is an efficient cooling technology with high heat dissipation, and has been extensively utilized in various industry areas. The interaction mechanism between the spray droplet and environmental space with high pressure and temperature is extremely complex, especially with non-condensable gas. In this paper, a pseudopotential multicomponent multiphase lattice Boltzmann model for droplet migration with non-condensable gas in high temperature and pressure was proposed. The mechanism of transfer characteristics for droplet in steam were studied. It is found that the mass transfer of droplet is controlled by density and condensation, droplet growth is mainly impacted by density at initial stage, and in later period, the growth is greatly weakened by the condensation suppression of non-condensable gas. The calculated results show that when Fo > 0.4, mass transfer is significantly decreased. Heat transfer is also affected by non-condensable gas, and 2% gas declines the droplet heat transfer rate by about 10%. It is also found that the mass transfer rate is approximately linearly associated with the ratio of non-condensable gas content inside and outside the droplet. The results can be used for development of spray cooling model, and have positive guiding significance for optimizing spray cooling system. • A heat and mass transfer model of droplet and steam with non-condensable is established. • The mechanism of transfer characteristics for droplet in steam were studied. • The mass transfer of droplet is controlled by density and condensation in different stage. • The mass transfer rate is approximately linearly associated with the ratio of non-condensable gas content. [ABSTRACT FROM AUTHOR]

• The process of melting-reconsolidation of the frost layer is considered. • Improvement of the existing Eulerian multiphase flow model of frost formation. • The whole process of frost layer growth under prolonged periods of time was studied. • Changes of ice-phase volume fraction and melt-reconsolidation region with time are discussed. Frost growth is a complex heat and mass transfer process, which involves the vapor-liquid-solid three-phase interconversion problem, and the investigation of the frost growth process helps to understand the mechanism of frost growth. In this paper, frost model is considered, taking into account the role of the frost layer melting-reconsolidation. The aim is to improve the existing Eulerian multiphase flow model. Using the improved frost model, the whole process of the frost layer growth is simulated. In addition, an investigation is presented dealing with, the frost layer growth in various stages of the ice phase volume fraction and melting-reconsolidation area, considering the change and the proportion of the situation. The results showed that the volume fraction of the ice phase increased with time. Additionally, the melting-reconsolidation process starts from the front area of the frost layer surface and then gradually spreads to the whole surface. Moreover, it is shown that the proportion of the melting area increases and then decreases with time before attaining a constant value. On the other hand, the proportion of the solidifying area increases with time and finally tends to 0. [ABSTRACT FROM AUTHOR]

This review paper presents an overview of transpired solar collectors (TSCs) - a clean energy technology that has gained considerable attention due to its potential to minimise building energy demand and contribute to achieving net zero emissions. The review is mainly focused on scrutinising the disparities in heat and mass transfer mechanisms, specifically the impact of homogeneous and inhomogeneous suction flow distributions on the TSC, encompassing performance improvement methods, performance assessment, and optimisation strategies for TSCs. The inconsistency between the theoretical and real-world performance of TSCs was observed, attributed to the high turbulence wind with non-uniform speed distribution and suction flow interactions with the main flow in the plenum. Corrugations on the absorber improved thermal performance but increased wind heat loss on the exterior surface, which could be mitigated by adding glazing to corrugated TSCs. The review highlighted the flexibility of integrating TSCs with other technologies, including coupling with separate phase change material (PCM) thermal energy storage units, which outperformed those placing the PCM plate into the plenum. Moreover, integrating TSCs with desiccant wheel cooling systems showed some interesting results in terms of cost and payback period, while integration with heat pump systems could reduce electricity consumption, but it was not recommended in cold climates. Exergetic analysis has been frequently used to determine thermodynamic losses of TSCs and it could provide a more accurate performance assessment when integrating TSCs with power generation systems. The review identified several research gaps in related study fields and provided recommendations, encompassing dimensionless analysis of the relationships between wind effect and heat transfer of TSC absorbers, the development of convective heat transfer correlations for TSC's absorber, and the exploration of cost-effective design and optimisation strategies for hybrid TSCs. • Heat and mass transfer mechanisms of transpired solar collectors (TSCs) were analysed. • TSCs can be integrated with different energy technologies to improve flexibility. • Various designs of TSC systems and their main design parameters were discussed. • It provides some insights into developing convective heat transfer correlations. [ABSTRACT FROM AUTHOR]

To improve the water production of the disc solar still (SS), this paper proposed a new type of membrane distillation enhanced SS by installing an air-gap membrane module vertically inside the SS, and its technical feasibility was confirmed by experiments. An unsteady heat and mass transfer mathematical model of the new SS was also constructed. MATLAB was used to program and solve it, realizing the theoretical prediction of the operation and output characteristics of the new SS, and revealing the change rule and interaction mechanism between the operation parameters and water production. Tests have shown that it is feasible to install membrane modules vertically to increase water production in the SS. The hourly water production per unit area of membrane distillation is at least 3.7 times higher than that of the disc distillation, and the addition of the membrane module can enhance the water production of the SS during the weak period of water production, and realize the continuous water production day and night. The hydrophobic membrane area of 0.08 m2, which is less than one-eleventh of the disc evaporation area, can increase the SS's daily water production by 7.6% to 3457.8 g. The efficiency is 33.4%, which is about 10.2% higher than that of SS. • A new type of solar still called a membrane distillation enhanced disc solar still was designed. • The air gap membrane module was installed inside the disc solar still and was vertically mounted. • An unsteady heat and mass transfer mathematical model of the new solar still was constructed. • Theoretical prediction of the operational characteristics of the device was realized. • The change rule and interaction mechanism between the operating parameters and water production of the device were revealed. [ABSTRACT FROM AUTHOR]

• Heat and mass transfer model of pyrolysis gases in a confined space was developed. • Growth rates of pyrolysis product concentrations were determined. • Synergistic effects were identified for different fire hazard sources. • Role of ventilation in the growth of pyrolysis gases concentrations was defined. • Correlation of room sizes with concentrations of pyrolysis gases was established. Numerical research findings are presented on the patterns of spread of thermal decomposition products of wood-based materials in confined spaces isolated from the external environment. Based on the experimental data, a physical problem statement was formulated and a mathematical model of heat and mass transfer was developed for rooms with the most typical sources of fire hazard. The experimental and numerical research findings were obtained for the conditions corresponding to compartments isolated from the external environment (e.g., rooms at dedicated facilities, like ships, small and medium-sized rooms) and to underventilated rooms. The performed experiments and calculations revealed satisfactory agreement in the findings and demonstrated the validity of the proposed model of heat and mass transfer. Wood was used as the main material in fires. A comparative analysis was also carried out for paper of different quality. The modeling was performed for the most frequent causes of fires: careless handling of fire, unsafe operation of heating equipment and electrical short circuits. The rates of growth of thermal decomposition product concentrations were determined for different distances from the material. The impact of a number of factors on the characteristics under study was determined. These are the fire and room sizes, fire cause, supply and exhaust ventilation. The data were extrapolated to the conditions corresponding to business, warehouse and residential premises. [Display omitted] [ABSTRACT FROM AUTHOR]

Numerical prediction of melt pool morphology and temperature distribution of thermomechanical processes (welding, additive manufacturing) plays an important role in understanding the relationships between process parameters and the quality of manufactured parts. The heat conduction models are limited in their predictability because the transport phenomena relevant to the melt pool dynamic are ignored. In contrast, the multiphysics model allows consideration of the heat transfer, free surface evolution, and transport phenomena in the melt pool, leading to more accurate predictions. However, the computational cost of multiphysics models makes them impractical for part-scale simulations. In this paper, a local moving thermal-fluid framework based on the finite element method is presented, which allows solving the thermal-fluid problem only in the small moving zone containing the melt pool and the heat transfer problem in the rest part. Therefore, this new proposed moving thermal-fluid (MTF) framework is predictive as well as the full thermal-fluid model, while it is much more efficient than a full thermal-fluid model since there are much fewer degrees of freedom (DOF) to solve. Finally, numerical validation tests in welding and additive manufacturing simulations highlight its computational efficiency and high-fidelity, and a relative error of less than 2.6% was observed in predicting melting pool dimensions compared to full thermal-fluid model. In the part-scale simulation of laser welding benchmark, the MTF model takes only 62 h in place of about three weeks required by a full thermal-fluid model. • A computational efficient local moving thermal-fluid framework is proposed. • The thermal-fluid problem is solved only in the small zone containing the melt pool. • The new model is applied for modeling welding and additive manufacturing processes. • The accuracy and efficiency of new approach is verified against numerical references. [ABSTRACT FROM AUTHOR]

• A correct formulation of average Nusselt number for the case of linearly heated wall is derived. • Thermal balance analysis provides the verification of the correct formulation. • Comparison of the existing and the correct formulation is included. The comment below addresses an inaccurate formulation in the calculation of the Nusselt number for linear heating as presented in the paper titled "Steady natural convection flows in a square cavity with linearly heated side wall(s)" by M. Sathiyamoorthy, T. Basak, S. Roy, and I. Pop, Int. J. Heat Mass Transfer 50 (2007) 766–775. Consequently, this analysis provides a mathematical reformulation for the local and mean Nusselt numbers of a linearly heated side wall. It regenerates a few quantitative results for a specific case solely intended for comparative purposes. [ABSTRACT FROM AUTHOR]

• RBF-DG was a novel prediction for absorption process in falling film and membrane based absorbers. • RBF-DG method provided excellent solutions. • Comparison with analytical solutions and experiments provided good agreements. • It becomes possible to predict accurately the absorption rate of falling film and membrane. The present investigation is intended to develop an understanding of how the vapor pressure and inlet temperature of the solution affect the absorption rate, which is helpful for the design of absorption heat pump systems. Many conjugated heat and mass transfer processes in falling film and membrane during lithium bromide (LiBr) absorption have not been well addressed. This paper proposes combining the meshless Radial Basis Function (RBF) and Discontinuous Galerkin (DG) methods to solve the conjugated heat and mass transfer in falling film and membrane-based absorption problems. The derivatives in the transverse direction are discretized using the RBF method. Owing to the parabolic nature of the governing equations, the DG methods can be used to discretize the derivatives in the streamwise direction. The efficacy of the proposed method is shown by comparing its results with analytical solutions and experimental data available in the literature. Furthermore, the proposed method is used to evaluate the analytical solutions of the heat and mass transfer problem in a membrane-based absorber. The previous published works simplified the problem to obtain the analytical solutions by providing the mean temperature and concentration values as the boundary conditions at the membrane-solution interface. The comparison of the RBF-DG method and the analytical solutions reveals that there are minor changes in temperature and local concentration values along the streamwise direction, but the profiles and trends are relatively similar across the film. A comparison of mass absorption rate calculations shows that RBF-DG and analytical solutions are compatible. The advantage of the numerical method is that various types of boundary conditions can be handled easily without any simplifications. Moreover, the numerical results of the proposed method are compared with experimental data, and they present good agreement. As a results, the absorption rate of falling film and membrane becomes capable of being accurately predicted. [ABSTRACT FROM AUTHOR]