Experimental Study of the Effects of Rib Angle and Discretization on Heat Transfer and Friction in an Asymmetrically Heated Rectangular Duct

Abstract

The paper presents results of an experimental investigation of heat transfer and friction in a high-aspect-ratio rectangular duct with repeated rectangular cross-section ribs on one broad wall in v-discrete and discontinuous patterns at different angles. The ribs have been arranged in both v-up and v-down patterns. The flow and thermal boundary conditions correspond closely to those of solar air heater ducts. Over the range of the Reynolds number studied, the Stanton number and friction factor values for the roughened ducts are 1.56-2.21 and 1.65-2.93 times of the values for the smooth duct, respectively. Thermal performance comparison of different rib patterns, based on equal pumping power for roughened and smooth ducts, shows that 60° v-discrete ribs with a relative roughness length of 6 gives 4-18%, 14-27%, and about 3-5% better performance than the 45° v-discrete ribs, discontinuous ribs, and 60° discrete ribs with a relative roughness length of 3, respectively. The performance of the v-down arrangement of ribs is better than v-up arrangement for all cases studied. The friction factor and heat-transfer coefficient correlations have been developed for the most preferred type of roughness.