This paper reports an investigation of the critical heat flux (CHF) in the subcooled flow boiling regime. Hardened copper tube is heated on one side of its external rectangular section like for fusion reactor plasma facing components. It is cooled by a subcooled water flowing in a circular channel equipped with an inserted twisted tape. During experiments, CHF is detected by means of an infrared camera picture. Experimental results corresponding to various thermal hydraulic conditions are reasonably well predicted by a correlation deduced from the sublayer dryout model proposed by Celata et al. This new correlation also applies to classical situations of parallel flow with axisymmetrical heating.