Heat transfer and friction in a low-aspect-ratio rectangular channel with staggered perforated ribs on two opposite walls

Experiments are conducted to study the turbulent heat transfer and friction in a low-aspect-ratio rectangular channel in which two opposite walls are roughened by perforated ribs. The perforated ribs are arranged in a staggered manner. Effects of perforated rib open-area ratio (beta = 10, 22, 38, 44, and 50 percent), rib pitch-to-height ratio (PR = 5, 10, 15, and 20), rib height-to-channel hydraulic diameter ratio (H/De = 0.063 and 0.081), rib alignment (staggered and symmetric), and Reynolds number (10,000 less than or equal to Re less than or equal to 50,000) are examined. It is found that approximately the same heat transfer enhancement and pressure drop penalty are obtained between symmetric and staggered rib arrangements. A permeability criterion is proposed by tracing heat transfer coefficient distributions, which compares well with previous flow-visualization results. Results also show that ribs with beta = 44 percent give the best thermal performance under either the constant friction power or the constant flow rate constraint. Roughness functions for friction and heat transfer are further developed in terms of rib and flow parameters.