Turbulent Heat Transfer and Friction in a Square Channel With Discrete Rib Turbulators

Abstract

Experiments study the turbulent heat transfer and friction for fully developed flow of air in a square channel with discrete rib turbulators. The discrete ribs are staggered on two opposite walls of the channel in alternate rows of three and two ribs. Nine rib configurations are examined: transverse ribs with an angle of attack (α) of 90 deg, discrete ribs with α = 90 deg, parallel arrays of discrete ribs with α = 45 deg and −45 deg on alternate rows, and parallel and crossed arrays of discrete ribs with α = 60, 45, and 30 deg. The rib height-to-hydraulic diameter ratio and the rib pitch-to-height ratio are 0.0625 and 10, respectively. The Reynolds number ranges from 10,000 to 80,000. Results show that the average Stanton number in the 90 deg discrete rib case is about 10 to 15 percent higher than that in the 90 deg transverse rib case. Turning the discrete ribs on the oppsite walls 60, 45, or 30 deg in the same direction with respect to the main flow increases the average Stanton number 10 to 20 percent over that in the 90 deg discrete rib case. Parallel oblique discrete ribs with α = 60, 45, and 30 deg have comparable performances and have higher overall heat transfer per unit pumping power than 90 deg discrete ribs. Crossed oblique discrete ribs perform poorly compared with 90 deg discrete ribs and are not recommended.