EFFECT OF PERMEABLE RIBS ON HEAT-TRANSFER AND FRICTION IN A RECTANGULAR CHANNEL

Heat transfer and friction characteristics in a rectangular channel wi th perforated ribs arranged in-line on two opposite walls are investig ated experimentally. Five perforated rib open-area ratios (0, 10, 22, 38, and 44 percent) and three rib pitch-to-height ratios (10, 15, and 20) are examined The Reynolds number ranges from 5000 to 50,000. The r ib height-to-channel hydraulic diameter ratio and the channel aspect P atio are 0.081 and 4, respectively Laser holographic interferometry is employed not only to measure the heat transfer coefficients of the ri bbed wall but also to determine the rib apparent permeability. It is f ound that ribs with appropriately high open-area ratio and high Reynol ds number are permeable, and the critical Reynolds number for evidence of flow permeability decreases with increasing rib open-area ratio. R esults of local heat transfer coefficients further show that the perme able ribs have an advantage of obviating hot spots. Moreover, the duct with permeable ribs gives a higher thermal performance than that with solid ribs.