Heat exchange surface with porous coating and subsurface cavities

• US 4,359,086 A
• Filed: 05/18/1981
• Issued: 11/16/1982
• Est. Priority Date: 05/18/1981
• Status: Expired due to Fees

• Current Assignee: American Standard Companies Incorporated (Ideal Standard International Topco SCA)
• Original Assignee: Trane Company (Trane Technologies plc)
• Inventors: Sanborn, Duane F., Ware, Chester D., Holman, John L. M.
• Primary Examiner(s): Richter, Sheldon J.
• Application Number:
  US06/264,519
• Time in Patent Office: 547 Days
• Field of Search: 165/DIG. 10, 62/527, 165/133
• US Class Current: 165/133
• CPC Class Codes: F28F 1/12 the means being only outside the tubular element
• CPC Class Codes: F28F 13/187 especially adapted for evaporator surfaces or condenser surfaces, e.g. with nucleation sites
• CPC Class Codes: Y10S 165/907 Porous

Abstract

A heat exchange surface having nucleate boiling cavities defined by subsurface cavities in combination with a thin porous coating. A preferred embodiment of the heat exchange surface includes a plurality of helical fins formed on the outer surface of a metallic tube, the tips of which are deformed by rolling to define gaps opening into fin cavities between adjacent fins. A porous open-celled coating flame-sprayed on the deformed portion of the fins substantially bridges these gaps, except at random open points caused by the inherent porosity of the coating. These openings in the porous coating in combination with the fin cavities provide nucleate boiling sites which promote efficient heat transfer for boiling a liquid.

Claims

1. A heat exchange surface comprising means for vaporizing a liquid, said means including continuous subsurface cavities formed in a metallic surface, said cavities being generally abridged where they are open onto the exterior of the metallic surface, by a porous open-celled coating deposited thereon, except at random points at which the cavities are directly open to the liquid said porous coating providing nucleate boiling cavities by its open-cell structure and its random open points in combination with the subsurface cavities, and thereby adapted to provide improved efficiency in boiling the liquid which is in fluid communication with the subsurface cavities.

8. The heat exchange surface of claim 1, 3, or 4 wherein the average thickness of the porous coating is at least 5 mils.

9. The heat exchange surface of claim 1, 3, or 4 wherein said porous open-celled coating comprises oxidized metallic particles flame-sprayed onto the metallic surface.

2. A heat exchange surface comprising:

a metallic surface having a plurality of generally parallel fins formed thereon, the tips of said fins being deformed to generally define a gap between adjacent fins opening into a fin cavity at the root portions thereof;

a porous, open-celled coating deposited on the deformed portion of the fins, substantially bridging the gap between adjacent fins except at random open points caused by the inherent porosity of the coating, said porous coating in combination with the fin cavities, providing nucleate boiling cavities, and thereby adapted to provide improved efficiency in boiling a liquid.

3. The heat exchange surface of claim 2 wherein the fin tips are flattened or split into a generally "T"-shaped configuration, with the gaps being defined between the flattened or split portions of adjacent fins.

4. The heat exchange surface of claim 2 wherein the fin tips are turned over toward the side portions of adjacent fins, with the gaps being defined between the turned-over tips and sides of adjacent fins.

5. The heat exchange surface of claim 3 or 4 wherein the average gap width, as measured between adjacent fins, is within the range of 1 to 8 mils.

6. The heat exchange surface of claim 3 or 4 wherein the metallic surface is the external surface of a metal tube.

7. The heat exchange surface of claim 6 wherein the fins form a helical spiral around the tube.

10. The heat exchange surface of claim 5 wherein the metallic particles are aluminum or aluminum containing alloy.