inlet header 26 because of the swirling motion imparted to the flow of refrigerant within the inlet header 26 the refrigerant flowing to the individual microchannels 13 is uniformly distributed so as to obtain maximum efficiency from the heat exchanger it should be noted that the inlet header 26 may be of a progressively diminishing size to reflect a reduction in the refrigerant mass flow rate toward a remote end of the inlet header 26 once again the inlet header 26 may have enhancement elements such as surface indentations or internal fins to further promote the mixing process referring now to fig4 an alternative embodiment is shown wherein an insert 28 is placed within the inlet opening 14 as shown rather than within the internal cavity 16 of the inlet manifold 11 the insert 21 is preferably suspended in a coaxial relationship with the inlet opening 14 by way of brazing or the like to the sides of the inlet opening 14 the insert 28 may be closed so as to allow the refrigerant to flow around the outer surfaces thereof so as to impart a swirling motion to the refrigerant entering the internal cavity 16 of the inlet manifold 11 alternatively the spiral insert 28 may be opened at its ends such that the refrigerant may pass through the internal confines thereof as it flows through the length of the insert 28 and enters the internal cavity 16 it may also be so constructed as to pass the refrigerant both through the internal structure and the outer surface of the insert 28 as it enters the internal cavity 16 in all cases the swirling motion imparted to the refrigerant as it enters the.