Heat transfer and friction in a high aspect ratio rectangular channel with angled and intersecting ribs

Forced convection heat transfer in a high aspect ratio (5:1) rectangular channel with 45 deg angled ribs has been investigated. The ribs are periodically positioned on one wall of the channel, heated at uniform heat flux over each inter-rib region. In the pursuit of heat transfer enhancement, longitudinal ribs (termed intersecting ribs), oriented parallel to the mainstream, have been added to the angled ribs. Friction and heat transfer characteristics were determined for two values (10000 and 20000) of the Reynolds number. Liquid crystal thermography was employed as diagnostic tool in heat transfer experiments. The study was supplemented with CFD numerical calculations using the RNG k-ε turbulence model. Local and regionally averaged heat transfer and flow characteristics of the tested rib configurations have been presented and compared. Both experimental and numerical results were able to capture the effect produced by the intersecting ribs on vortices and their ability to locally increase the heat transfer coefficient and promote its more uniform distribution. If the standard angled rib configuration is assumed to be the reference condition, the thermal performance based on the same pumping power is increased in the case of the insertion of one intersecting rib, while two intersecting ribs are unable to provide further enhancements.