Laminarization of strongly heated gas flows in a concentric annular tube

This paper aims to clarify the laminarization phenomena of strongly heated gas flows within concentic annular tubes by means of both experimental and numerical procedures. In the first part, the annular flow is heated from the inner wall only, the outer wall being thermally insulated. Although a certain reduction in heat transfer coefficient is observed in the experiment, corresponding numerical results indicate that there still remains a certain amount of turbulent kinetic energy in the flow field. Therefore, the conclusion on whether observed heat transfer reduction is due to laminarization or not is deferred for a while, and the attention is turned to the case in which the flow is heated from both walls. A remarkable reduction is observed in heat transfer coefficient and corresponding numerical results also indicate that the turbulent energy of this case is uniformly attenuated so that it is concluded that the reduction is certainly due to laminarization. Following these results, some discussions are developed on the criteria of occurrence of laminarization for the annular flows