Effect of divergence ratio on heat transfer and friction factor in the ribbed rectangular channel

The local heat transfer and pressure drop of turbulent flows developed in stationary ribbed rectangular divergent channels are experimentally investigated. The rectangular divergent channels with a one sided ribbed surface only have inclination angles of 0.72A degrees and 1.43A degrees. The ribbed wall is manufactured with a fixed rib height (e) of 10 mm and rib spacing (p) to height (e) ratio of 10. The measurement was conducted within a Reynolds number range of 15,000 to 89,000. The local heat transfer characteristics of the rectangular divergent channels are quite different from those of the square straight channels because of the streamwise flow deceleration. The thermal performances of the ribbed rectangular divergent channels are compared with those of the ribbed square straight channels under three constraints: identical mass flow rate, identical pumping power, and identical pressure drop. The comparison shows that between the two channels D1 (D (ho) /D (hi) = 1.16) and D2 (D (ho) /D (hi) = 1.49), the divergent channel D2 (D (ho) /D (hi) = 1.49) has the higher thermal performance at identical mass flow rate, and the divergent channel D1 (D (ho) /D (hi) = 1.16) has the higher thermal performance under the constraints of identical pumping power and static pressure drop.