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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]

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]