Kay Wittig

This work is devoted to the three‐dimensional, direct modeling of porosity and specific surface development during the gasification of a char particle. The model was developed for heterogeneous reactions occurring inside a char particle in a kinetically controlled regime. The main goal of this work is to analyze the impact of different pore size distributions on the particle carbon conversion rate. In particular, it is shown that under certain conditions the outer particle surface can influence the specific surface area. In this context the possible adaptation of the parameter ψ from the random pore model (RPM) developed by Bhatia and Perlmutter is explained. The results of simulations are compared against the RPM and discussed. Additionally, based on the results of simulations, the physics behind several input parameters used by the RPM are explored. Finally, the possible fragmentation of a chemically reacting char particle during its gasification in dependence of instantaneous porosity was investigated numerically. It was shown that the earliest fragmentation occurs at a carbon conversion of about 0.5–0.6 due to the disaggregation of the pore walls. The results are discussed and compared implicitly with data published in the literature. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1638–1647, 2017

This work is devoted to a numerical investigation into heat and fluid flow past a particle of a cubical shape. Additionally, it is a continuation of the recent publication by Richter and Nikrityuk (Int. J. Heat Mass Transfer, vol. 55, no. 4, pp. 1343-1354, 2012a), where the authors performed numerical calculations of drag forces and heat transfer coefficients for nonspherical particles in laminar flows with an angle of attack of zero. In this work we focus on the influence of the angle of attack on flow past a cubical particle. Due to the asymmetric flow, three-dimensional calculations were carried out based on the immersed boundary (IB) method in continuous forcing mode; see the review by Mittal and Iaccarino (Ann. Rev. Fluid Mech., vol. 37, pp. 239-261, 2005). In order to substantiate the results, additional calculations were made based on a so-called conventional computational fluid dynamics (CFD) solver using body-fitted meshes. Based on the present analysis of numerical results obtained for a cubical particle, new correlations for both the drag coefficient (c(D)) and the Nusselt number (Nu) were developed. In addition to the Prandtl and Reynolds numbers, both correlations incorporate the angle of attack. A significant influence of the particle orientation on the characteristics c(D) and Nu was observed. The accuracy of the closures developed for c(D) and Nu is discussed, comparing the relations developed with published models.