An experimental investigation on mass transfer in presence of chemical reactions on a graphite cylinder in crossflow

In connection with analyses of hypothetical massive air ingress accidents in HTGR ($\underline{H}$igh $\underline{T}$emperature $\underline{G}$as-Cooled $\underline{R}$eactor), in which it is assumed that the air is transported through the hot region of graphite core support posts, experiments on mass transfer and in-pore diffusion with homogeneous and heterogeneous chemical reactions were performed on a graphite cylinder in crossflow. Two BLMR ($\underline{B}$oundary $\underline{L}$ayer $\underline{M}$ass transfer controlled $\underline{R}$egime) runs and two runs in an intermediate regime between BLMR and IPDR ($\underline{I}$n-$\underline{P}$ore-$\underline{D}$iffusion controlled $\underline{R}$egime) were executed at atmospheric pressures, Reynolds numbers ranging from 533 to 2490, and cylinder temperatures from 848°C to 1120°C. The nuclear grade graphite cylinder having a diameter of 100 mm and a porosity of 21.2 % was corroded in a nitrogen gas flow containing approximately 5 % oxygen. Mean and local mass transfer coefficients and corrosion rates were obtained to examine the influences of the chemical reactions on the mass transfer. As a result it can be concluded that the chemical reactions and small changes in shape do not significantly influence the mass transfer under conditions to be expected in HTGR air ingress accidents and that thus the analogy between heat and mass transfer can be used for safety calculations