HEAT TRANSFER TUBE HAVING INTERNAL RIDGES, AND METHOD OF MAKING SAME

摘要

"IMPROVED HEAT TRANSFER TUBE HAVING INTERNAL RIDGES, AND METHOD OF MAKING SAME" Improved heat transfer tube and method of making same has mechanical enhancements which can individually improve either the inner or outer surfaces or which can cooperate to increase the overall efficiency of the tube. The internal enhancement, which is useful on either boiling or condensing tubes, comprises a plurality of closely spaced helical ridges which provide increased surface area and are positioned at an angle which gives them a tendency to swirl the liquid. The external enhancement, which is applicable to boiling tubes, is provided by successive cross-grooving and rolling operations performed after finning. The finning operation, in a preferred embodiment for nucleate boiling, produces fins while the cross-grooving and rolling operation deforms the tips of the fins and causes the surface of the tube to have the general appearance of a grid of generally rectangular flattenedblocks which are wider than the fins and separated by narrow openings between the fins and narrow grooves normal thereto. The roots of the fins and the cavities or channels formed therein under the flattened fin tips are of much greater width than the surface openings so -that the vapor bubbles can travel outwardly through the cavity and to and through the narrow openings. The cavities and narrow openings and the grooves all cooperate as part of a flow and pumping system so that the vapor bubbles can readily be carried away from the tube and so that fresh liquid can circulate to the nucleation sites. The rolling operation is performed in a manner such that the cavities produced will be both larger and smaller than the optimum minimum pore size for nucleate boiling of a particular fluid under a particular set of operating conditions.