LASER HOLOGRAPHIC-INTERFEROMETRY STUDY OF DEVELOPING HEAT-TRANSFER INA DUCT WITH A DETACHED RIB ARRAY

Laser holographic interferometry measurements of temperature distribut ions are presented for a developing rectangular duct with a detached s quare-rib array and an abrupt-contraction inlet. The Reynolds number b ased on the duct hydraulic diameter and bulk mean velocity extended fr om 5.0 x 10(3) to 5.0 x 10(4). The ratios of rib pitch to height, rib to duct height, and detached distance to rib height were 10, 0.13 and 0.58, respectively. Isotherm contours and local and average Nusselt nu mber distributions were used to document the heat transfer characteris tics. The complementary pressure loss measurements allowed thermal per formance comparison between detached-ribbed, attached-ribbed and smoot h ducts to be made. It was found that thermal performance was better i n the detached-ribbed duct flows than in the attached-ribbed duct flow s. The entry length effect was 5.3-10.6% in terms of length-mean Nusse lt number ratio for the detached-ribbed duct flows. Further, semi-empi rical correlations for heat transfer and friction in the fully develop ed region and length mean Nusselt number ratio were developed.