INTERNALLY GROOVED HEAT TRANSFER TUBE FOR HIGH-PRESSURE REFRIGERANT

摘要

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 whose typical example is a carbon dioxide gas, wherein an intra-tubular heat transfer rate is improved while maintaining a sufficiently high degree of strength for pressure resistance. In a heat transfer tube (10) formed of copper or a copper alloy and having internal grooves (12) and internal fins (14) which have a prescribed height and each of which is formed between adjacent two of the internal grooves, t/D ranges from not smaller than 0.041 to not greater than 0.146 and d 2 /A ranges from not smaller than 0.75 to not greater than 1.5 where an outside diameter of the tube is represented as D [mm], a groove bottom thickness which is a wall thickness of the tube at a portion thereof corresponding to each groove is represented as t [mm], a depth of each groove is represented as d [mm], and a cross sectional area of each groove taken in a cross sectional plane perpendicular to the axis of the tube is represented as A [mm 2 ], and N/Di ranges from not smaller than 8 to not greater than 24 where a number of the grooves is represented as N and a maximum inside diameter which corresponds to an inside diameter of the tube formed by connecting bottoms of the grooves is represented as Di.