Experimental heat transfer data for single-phase water flow in the annuli with corrugated inner tubes are presented. In the annuli with parallel flow, ten different annular arrangements are considered. For water flow rate in 1,700<Re<13,000 regime, data for Nusselt numbers are presented. The results show significant effects of both the pitch to trough height ratio (P/e) and the radius ratio (${gamma}$$^$*/). As P/e becomes closer to 8 in the range below the radius ratio (${gamma}$$^$*/) of 0.5, Nusselt numbers increase. However, Nusselt numbers decrease in the range above the radius ratio (${gamma}$$^$*/) of 0.5 because flow reattachment position becomes farther in the narrower clearance.