A method of roughening the surface of cylinders by media-blasting with micron scale particles was tested for heat transfer enhancement and pressure drop characteristics with an air flow over a range of Reynolds numbers from 200 to 7000. It was found that the surface treatment had an adverse effect on the rate of convective heat transfer over a range of Reynolds numbers. However, over the same range, the surface pressure drop was unaffected by the surface treatment.

The pressure data likely indicates that the stream turbulence of the oncoming air flow was high enough to cause the critical Reynolds number to drop to the lower end of the Reynolds number range and nullify any positive effects that a roughened surface might have. Lower Nusselt numbers for the blasted wires suggest that for flows with high free-stream turbulence intensity a roughened surface decreases heat transfer. This decrease is possibly caused by earlier turbulent boundary layer separation on the rough surface due to the fact that the flows are all in the trans-critical flow regime at every Reynolds number tested.