Abstract: An internally grooved heat transfer tube for a cross fin tube type heat exchanger of a refrigerating air-conditioning water supply apparatus using a high-pressure refrigerant, wherein an intra-tubular heat transfer rate is improved while maintaining a sufficient strength for pressure resistance. A heat transfer tube formed of copper or copper alloy has internal fins between internal grooves. In the tube, t/D is not smaller than 0.041 and not greater than 0.146, d2/A is not smaller than 0.75 and not greater than 1.5, where D [mm] is an outside diameter of the tube, t [mm] is a groove bottom thickness, d [mm] is a depth of each groove, and A [mm2] is a cross sectional area of each groove. N/Di is not smaller than 8 and not greater than 24 where N is a number of grooves, and Di is a maximum inside diameter corresponding to an inside diameter of the tube.

Abstract: An internally grooved heat transfer tube for a cross fin tube type heat exchanger of a refrigerating air-conditioning water supply apparatus using a high-pressure refrigerant, wherein an intra-tubular heat transfer rate is improved while maintaining a sufficient strength for pressure resistance. A heat transfer tube formed of copper or copper alloy has internal fins between internal grooves. In the tube, t/D is not smaller than 0.041 and not greater than 0.146, d2/A is not smaller than 0.75 and not greater than 1.5, where D [mm] is an outside diameter of the tube, t [mm] is a groove bottom thickness, d [mm] is a depth of each groove, and A [mm2] is a cross sectional area of each groove. N/Di is not smaller than 8 and not greater than 24 where N is a number of grooves, and Di is a maximum inside diameter corresponding to an inside diameter of the tube.

Abstract: A method of manufacturing a cross fin tube and a cross fin type heat exchanger including the cross fin tube obtained in accordance with the manufacturing method. A tube-expanding plug has cutout-forming protuberances which are formed on an outer circumferential surface thereof with a number of 60-160 per circumference such that the cutout-forming protuberances extend in a direction which intersects primary grooves which are previously formed on an inner circumferential surface of a heat transfer tube, and at the same time when the heat transfer tube and plate fins are fixed integrally to each other in accordance with the mechanically tube-expanding operation, secondary grooves which are cross grooves with respect to the primary grooves are formed to have a depth (d2) which is held in a range of 10-40% of a depth (d1) of the primary grooves.