Abstract: One heat transfer tube for an absorption refrigerating machine of the present invention has a plurality of grooves formed on the circumferential surface of a tube at uniformly angular intervals to extend continuously or discontinuously in the length direction of the tube, wherein the width and/or depth of each groove gently varies in the length direction of the groove, and the height of each ridge between the mutually adjacent grooves gently varies from the axial tube center in the length direction of the ridge. Another heat transfer tube of the present invention has a large number of concave portions formed in rows on the circumferential surface of the tube at predetermined angular intervals and each having a gently down-grade surface extending in the tube length direction to gradually get closer to the axial tube center and a gently up-grade surface extending continuously from the down-grade surface in the tube length direction to gradually become more distant from the axial tube center.

Abstract: According to the invention, there is provided a heat transmission tube having a tube body, first grooves formed at a predetermined pitch therebetween on an outer surface of the tube body continuously along a circumferential direction, the first grooves open to an outside, and having an opening portion, a width of which is narrower than that of a bottom portion thereof, and second grooves formed at a predetermined pitch therebetween on the outer surface of tube body continuously along an axial direction, the second grooves having a depth shallower than that of the first grooves, and connecting opening portions of the adjacent first grooves to each other, wherein a projecting member is provided on a bottom surface of each of the first grooves so as to connect a side wall of each of the first grooves to another is brought into contact with the tube body. This heat transmission tube exhibits a high and stable heat transmissibility in both high and low heat flux cases.