Numerical investigation on synthetical performances of fluid flow and heat transfer of semiattached rib-channels

Although the conventional internal ribs or turbulators can significantly improve the performances of the convective heat transfer within a channel, the added ribs can also cause two demerits, a larger friction factor and some lower heat transfer areas (LHTA) than that in the corresponding smooth channel, especially behind fully attached (solid-type) ribs and at the corners formed by bottom and side walls. This paper presents a novel design of the ribbed channel, which is here called semiattached rib-design. The ribs are perforated at the rib corners to form two rectangular holes, so a portion of the fluid can pass through the holes. The characteristics of the semiattached rib-design are numerically investigated by the commercial software Fluent 6.3 in a Reynolds number range from 104 to 2.5 × 104. Five different structures of the rib (width ratios of channel to hole) and two positions (transverse rib and 45° angled ribs) are analyzed. The numerical results show that the semiattached rib-design can significantly improve local heat transfer and fluid flow performances; the semiattached ribs with 45° angle of attack can even achieve a higher efficiency of synthetical heat transfer than that of the fully attached and detached rib-channels, at the same time eliminate the LHTA; although the average Nusselt number over a pitch in the transverse ribbed channel is lower than that of fully attached and detached rib-channels, this semiattached ribs can also fully eliminate the LHTA.