Abstract An improved nucleate boiling surface can be obtained on a metal heat transfer tube or other form of heat transfer member by knurling or otherwise deforming a smooth surfaced member to notch and partially work harden its surface and then subjecting the knurled portion to a finning operation. The method results in small splits or ruptures of a controlled geometry and depth being produced in the tip area of the fins which become nucleation sites for boiling enhancement. Preferably, the knurling rolls are mounted on the same arbors as the finning disks so that a tube is progressively knurled and then finned in a single pass through the apparatus. If desired, the tube can also be internally ridged as it is being externally finned.
A process for improving the heat transfer capability of a metal heat transfer surface comprising the steps of: Knurling at least a portion of said heat transfer surface and then subjecting said knurled portion to a finning operation.
Claim 2
Dependent Claim
38 words
A process for improving the heat transfer capability of a metal heat transfer surface comprising the steps of: Knurling at least a portion of said heat transfer surface and then subjecting said knurled portion to a finning operation.
Claim 3
Dependent Claim
71 words
A process in accordance with claim 1 wherein said knurling step produces a controlled pattern of work hardened regions on the surface which, when subjected to additional metal working by the finning operation, result in splits of controlled depth and orientation in the outer portions of the fins, said splits being sufficiently small to serve as nucleate boiling sites when said heat exchange surface is in contact with a boiling liquid.
Claim 4
Dependent Claim
16 words
A process in accordance with claim 2 wherein said heat transfer surface is on a tube.
Claim 5
Dependent Claim
43 words
A process in accordance with claim 3 wherein the controlled pattern of work hardened regions comprises a pattern of grooves produced by said knurling step which are diagonally arranged relative to the tube axis and generally transverse to the plane of each fin.
Claim 6
Dependent Claim
19 words
A process in accordance with claim 1 wherein said tube is subjected to said knurling and finning operations simultaneously.