TUBE FOR HEAT EXCHANGER

PROBLEM TO BE SOLVED: To enhance heat exchanging efficiency significantly by inserting a spiral member into a tubular member, making a plurality of grooves in the outer circumference of the spiral member at an interval and setting the depth of the groove equal to a specified multiple of the diameter at the spiral member or less. SOLUTION: A spiral member is inserted into a tubular member. The spiral member is formed by twisting a long planar member 25 of stainless steel. A plurality of grooves 27 are made in the outer circumference of the planar member 25 at an interval of L. The cut 27 has square shape and the depth X thereof is equal to 0.1 times of the diameter D of the planar member 25 or less. Total area of all grooves 27 is set in the range of 0.5-4% of the area S of the planar member 25. When the spiral member is inserted, current velocity of fluid, e.g. EGR gas, is increased and the diameter of the fluid is decreased. Furthermore, fluid flow is disturbed in the vicinity of the inner surface of the pipe member by means of the grooves 27 thus enhancing the thermal conductivity.