Studies on the Enhancement of Forced Connective Heat Transfer in Three-Dimensional Rib-Roughened Tubes : 2nd Report, Staggered Arrangement

Abstract

The enhancement of heat transfer inside a tube by means of three dimensional ribs of a regular triangle shape arranged in-line was discussed in the 1st report. Thus, the rib pitch along the tube circumference and the rib height for excellent thermal performance was found. In this report, the same experiment was performed by changing the arrangement of the ribs to the staggered manner. Furthermore, in order to make clear the mechanism of high·thermal performance, a few experiments on the flow field by means of a hot-wire anemometer and of flow-visualization (oil-film method) were performed. The results obtained show that (1) the average heat transfer coefficient, N_um in the staggered arrangement decreases futher than that in the in-line arrangement under n=6(N : rib number), but N_um is independent of the differences in rib arrangement above N=6. (2) Finally, the thermal performance in the staggered arrangement is less than that in the in-line arrangement. (3) these chracteristics depend on the behavior of three-dimensional reattachment flow downstream of the rib. A strong three dimensional reattachment flow occurs in the case of a small number of ribs in the in-line arrangement, in which interference to the flow field by adjacent ribs does not occur.