A numerical investigation has been performed to determine the effect on heat transfer in the laminar regime of introducing a single protrusion in a rectangular channel. The geometry consists of a three dimensional channel 10 mm high, 40 mm wide and 290 mm long in which a spherical protrusion was placed 90 mm from the inlet on the centreline of one of the wide sides. The print diameter of the obstacle was equal to the height of the channel and it protruded 2.2 mm above the surfaces. A commercial code, ANSYS-CFX11.0 was used for all simulations. The resultant very complex flow and thermal fields in the channel are discussed in detail. The presence of the protrusion results in an enhancement in the total heat transfer rate of 7% above that of a channel lined with flat plates only. This is a worthwhile increase since it is brought about by a pressure increase of only 1%.