HEAT TRANSFER IN A DUCT IN REGIONS OF SEPARATED FLOW
Measurements of heat-transfer coefficients in pipes were made in regions of separated flow using circumferential grooves, ribs and sudden enlargements. Heat fluxes were kept low with Re = 20 000 to 250 000 and air as the working fluid. In all the tests a development length, usually heated uniformly, preceded the irregularity causing separation. Other tests were performed with small isolated heated areas downstream of a rib. Wall shear stress in the reattachment zone downstream of an enlargement was studied visually using oil drops.
A peak in the heat-transfer coefficient occurs downstream of the irregularity and it is evident that this increase is determined by the length of separation and to a lesser extent by turbulence.