STUDY OF HEAT TRANSFER AUGMENTATION IN A HIGH-TEMPERATURE FIELD BY A RADIATION PROMOTER GENERATING A SECONDARY FLOW

Abstract

Characteristics of flow and heat transfer have been investigated for a circular pipe in which a pair of twisted tapes were inserted to enhance the convective and radiative heat transfer. From the measurement of the three-dimensional velocity field, it was clarified that a secondary flow was induced by the present promoter, heat transfer performance was enhanced about three times compared with that of a smooth pipe, and a remarkable increase of the local heat transfer rate was observed near the impinging region of the secondary flow. The performance of the present promoter was evaluated based on the total surface area for heat transfer under the same conditions of flow rate, pressure loss, and heat load. It was found that, at room temperature, the total heat transfer area could be reduced to about 30% less than for a smooth pipe. In the case of high temperature, above 450°C, the heat transfer rate was further increased 50% due to the effect of radiation between the pipe watt and the promoter. By using a vertical pipe and the promoter, the flow characteristic with solid particles was investigated, where the particles were sustained in the flow due to the promoter.