The Effects of Gap Position in Discrete Ribs on Local Heat/Mass Transfer in a Square Duct

Local heat/mass transfer measurements are conducted to investigate the effects of rib arrangements and gap positions on the discrete rib. The combined effects of the gap flows of the discrete ribs and secondary flows are examined in order to promote uniformity of heat/mass transfer distributions, as well as to augment heat/mass transfer. A square channel with rectangular ribs is used for the stationary duct test. The rib-to-rib pitch to the rib height ratio is 8, and the rib attack angle is 60°. The gap width is the same as the rib width, and two gap positions, which are upstream and downstream gaps, are examined with parallel and cross rib arrangements. A naphthalene sublimation method is used to measure local heat/mass transfer coefficients. With the angled discrete ribs, the heat transfer on the surface is enhanced and the uniformity of the heat transfer coefficients is promoted because the gap flow promotes local turbulence and flow mixing near the ribbed surface, while the rib-induced secondary flow is maintained in a duct. The discrete rib arrangements with downstream gaps show better cooling performance than continuous rib or discrete rib arrangements with upstream gaps.