Abstract: The present invention has the object of increasing the heat exchanging performance of heat transfer tubes having grooved inner surfaces. In order to achieve this object, the heat transfer tubes having grooved inner surfaces according to the present invention have fins which are formed consecutively in a circumferential direction on the inner surface of a metallic tube. The inner surface of the metallic tube is divided into regions R1.about.R4 in the circumferential direction. The inclination angle .alpha. with respect to the axis of the heat transfer tube of the fins 2 in odd-numbered regions when counting from one of the regions is 10.about.25.degree., and the inclination angle .beta. with respect to the axis of the heat transfer tube of the fins 2 in even-numbered regions when counting from the region is -10.about.-25.degree.. The pitch of the fins 2 is 0.3.about.0.4 mm, the height of the fins from the inner circumferential surface of the metallic tube is 0.15.about.0.

Abstract: The present invention has the object of increasing the heat exchanging performance of heat transfer tubes having grooved inner surfaces. In order to achieve this object, the heat transfer tubes having grooved inner surfaces according to the present invention have fins which are formed consecutively in a circumferential direction on the inner surface of a metallic tube. The inner surface of the metallic tube is divided into regions R1.about.R4 in the circumferential direction. The inclination angle .alpha. with respect to the axis of the heat transfer tube of the fins 2 in odd-numbered regions when counting from one of the regions is 10.degree..about.25.degree., and the inclination angle .beta. with respect to the axis of the heat transfer tube of the fins 2 in even-numbered regions when counting from the region is -10.degree..about.-25.degree.. The pitch of the fins 2 is 0.3.about.0.4 mm, the height of the fins from the inner circumferential surface of the metallic tube is 0.15.about.0.