TURBULENT-FLOW HEAT-TRANSFER AND FRICTION IN A RECTANGULAR CHANNEL WITH VARYING NUMBERS OF RIBBED WALLS

All experimental study of wall heat transfer and friction characterist ics of a fully developed turbulent air flow in a rectangular channel w ith transverse ribs on one, two, and four walls is reported. Tests wer e performed for Reynolds numbers ranging from 10,000 to 80,000. The pi tch-to-rib height ratio, P/e, was kept at 8 and rib height-to-channel hydraulic diameter ratio, e/D-h, was kept at 0.0625. The channel lengt h-to-hydraulic diameter ratio, L/D-h, was 15. The heat transfer coeffi cient and friction factor values were enhanced with the increase in th e number of ribbed walls. The friction roughness function, R(e(+)), wa s almost constant over the entire range of tests performed and was wit hin comparable limits of the previously published data. The heat trans fer roughness function, G(e(+)), decreased with additional ribbed wall s and compared well with previous work in this area. Friction data obt ained experimentally for the case with four ribbed walls compared well with the values predicted by the assumed theoretical relationship use d in the present study and past publications. Results of this investig ation could be used in various applications of internal channel turbul ent flows involving different numbers of roughened walls.