LOCAL AND AVERAGE TRANSPORT-COEFFICIENTS FOR THE TURBULENT-FLOW IN INTERNALLY RIBBED TUBES

Heat transfer coefficients and pressure drop data were determined experimentally for the turbulent flow in circular ducts equipped with internal transverse ribs, that is, ribs normal to the flow. Both fully developed and entrance region results were obtained. Also, both local and per-cycle average heat transfer results were determined. The naphthalene sublimation technique was employed in the experiments. The effects of rib height, rib spacing, and Reynolds number were investigated. The friction factor is shown to increase with rib height and to decrease with rib spacing in the range investigated. The local heat transfer results revealed, for most cases investigated, that the film coefficient in a cycle increases in the axial direction up to a maximum value. Then it decreases mildly up to a local minimum, increasing from this axial position to the end of the cycle.