Experimental work was performed to determine local Nusselt numbers in the region beyond an abrupt expansion in a circular channel. Three expansion geometries, ratios of upstream-to-downstream diameter of 0.43, 0.54, and 0.82, were tested with air as the working fluid. Data are shown for Reynolds numbers from 4000 to 50,000–90,000 depending on geometry. Selected comparisons with previously published data for air and water are included.