Experimental Analysis of the Microconvective Heat Transfer in the Laminar and Transition Regions

This article details experiments to determine the Nusselt number for laminar and tran- sitional liquid flows (water and FC-72) through rough stainless-steel microtubes of 440-, 15 280-, and 146-m inner diameter. Under laminar conditions, the average Nusselt number approaches the fully developed value for uniformly heated tubes as Reynolds decreases. For higher Reynolds, the region of thermal development increases the average convective heat transfer coefficient, which becomes a function of the Reynolds and Prandlt numbers and of the inner diameter-to-heated-length ratio. The effect of roughness is negligible in 20 the laminar regime. Under transition, the average Nusselt steeply increases with Reynolds, more than for conventional pipes.