An engine bleed air system of an aircraft, comprising a heat exchanger which comprises a rectangular core with a rectangular outlet section, a cylindrical outlet duct and a transition area between the rectangular outlet section of the rectangular core and the cylindrical outlet duct, and at least a downstream system, further comprising a flow deflector located at least in the cylindrical outlet duct, such that the outlet flow characteristics homogeneity are improved and a particular flow deflection and distribution of the outlet flow is achieved, avoiding the damage of the at least one downstream system. The invention also provides a method for homogenizing the temperature of the outlet flow of a heat exchanger outlet in an engine bleed air system of an aircraft.