Laminarization of strongly heated annular gas flows

This paper aims to clarify the laminarization phenomena of strongly heated gas flows within concentric annular tubes. In the first place, the authors' former experimental results, in which annular flows were strongly heated exclusively from the inner side of the annulus, are examined by means of a κ-ε model that was previously modified by the authors so as to reproduce the laminarization of strongly heated circular tube flows. Numerical results indicate a certain amount of turbulent kinetic energy remains in the flow field so that the observed heat transfer reduction is judged not to be due to laminarization, and the attention is turned to the case in which the flow is heated from both sides. A remarkable reduction in heat transfer is observed in both numerical and experimental results, and the corresponding turbulent kinetic energy is found to be uniformly attenuated over the whole tube cross section so that it is concluded that the reduction is certainly due to laminarization. Following the results, some discussions are developed on the occurrence criteria of laminarization of the annular flows, and the obtained criteria are in fairly good agreement with the experimental results by Ogawa et al. (author)