Manufacturing process for tube-in-tube internal heat exchanger

A method of forming a bend in a tube arrangement, the method comprising the steps of:

• providing a tube arrangement including an inner tube disposed within an outer tube;
• providing a bending die having a concave groove formed therein, the concave groove including a curved portion extending around a peripheral surface of the bending die, the curved portion of the concave groove having at least one ridge projecting therefrom;
• locating at least a portion of the tube arrangement within the concave groove of the bending die;
• applying force to the tube arrangement in a direction toward the concave groove of the bending die to cause the tube arrangement to bend around the curved portion of the concave groove;
• and
• deforming the outer tube of the tube arrangement, the deforming step including forming at least one groove in an exterior surface of the outer tube having a shape conforming to a shape of the at least one ridge projecting from the curved portion of the concave groove, wherein the at least one groove formed in the exterior surface of the outer tube causes at least one projection to be formed on an interior surface of the outer tube, wherein the at least one projection contacts an exterior surface of the inner tube.