Internal heat exchanger double-tube structure of air conditioning system having alternative refrigerant applied thereto

An internal heat exchanger double-tube structure of an air conditioning system having an alternative refrigerant applied thereto for heat exchange between a low-temperature low-pressure refrigerant discharged from an evaporator and a high-temperature high-pressure refrigerant discharged from a condenser, the double-tube structure comprising:

• an inner pipe having a channel through which the low-temperature low-pressure refrigerant discharged from the evaporator flows;
• and
• an outer pipe surrounding the inner pipe and having a channel through which high-temperature high-pressure refrigerant flows,
• wherein the inner pipe has a spiral groove forming a channel on an outer side thereof,
• wherein a recessed groove is formed on an outer surface of the spiral groove for generating a vortex, the recessed groove comprising:
• a single center portion protruded radially outward and formed along a direction of the spiral groove;
• and
• a left and a right slope inclined from the single center portion to left and right edges of the spiral groove,
• wherein each of the left and the right slopes has a groove shape and one of the left and the right slopes has a greater groove shape than the other,
• wherein an entire outer surface of the single center portion and the left and the right slopes is directly exposed to an inner surface of the outer pipe.