Two-passage heat-exchanger tube

Heat exchange – Non-communicating coaxial enclosures – Helical conduit means

Reexamination Certificate

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Details

C165S154000, C165S169000

Reexamination Certificate

active

06220344

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a two-passage heat-exchanger tube. More particularly this invention concerns such a tube forming at least two separate passages through which fluids at different temperatures can flow for heat exchange between them.
BACKGROUND OF THE INVENTION
A heat-exchanger tube forming a pair of passages one of which extends helically is used in many different applications as described in German patent application 45,544, German patents 31,764 of Hocking and 804,502 of Sommer as well as in U.S. Pat. No. 3,566,615 of Roeder and U.S. Pat. No. 3,777,343 of D'Onofrio. A standard such system has an inner tube wall formed with a radially outwardly projecting helical ridge and an outer tube wall formed with a radially inwardly projecting helical ridge. The two tube walls are assembled together so the two ridges fit in direct contact with each other and create a helical passage. An outer passage can be provided around the two joined walls by fitting them with play in an outer pipe, and an inner pipe can be run coaxially through the inner wall to form an inner chamber. One fluid is flowed through the helical passage and another in the same direction or countercurrent through the outer and/or inner passage.
Such a heat-exchanger tube is fairly hard to manufacture. The inner and outer tube walls must be made to very exacting tolerances so that when they are fitted together the outer surface of the outwardly projecting ridge snugly engages the inner surface of the inwardly projecting ridge. Even with very accurate construction, assembling the system is quite difficult. Furthermore after some use, adhesions on the tube walls often make it impossible to pull the inner and outer walls apart for cleaning.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide an improved heat-exchanger tube assembly.
Another object is the provision of such an improved heat-exchanger tube assembly which overcomes the above-given disadvantages, that is which is of simple construction and which is easy to assemble and disassemble.
SUMMARY OF THE INVENTION
A heat-exchanger tube has according to the invention an inner tube wall centered on an axis, formed with an outwardly projecting helical ridge having a helical outer surface, and forming an outwardly open helical groove delimited by the ridge and an outer tube wall centered on an axis, formed with an inwardly projecting helical ridge of the same hand as the inner-tube ridge, having a helical inner surface, and forming an inwardly open helical groove delimited by the outer-tube ridge. The inner tube is coaxially received in the outer tube with the grooves together forming a helical passage having a plurality of turns and the surfaces radially confronting and spaced from each other to form an axial passage for fluid communication between adjacent turns of the helical passage. A fluid is fed to one end of the helical passage and withdrawn from an opposite end with flow of the fluid helically along the helical passage and axially through the axial passage.
It has surprisingly been found that leaving a space between the inner-ridge outer surface and the outer-ridge inner surface does not appreciably affect the heat-exchange efficiency of the tube according to the invention. The bulk of the flow is still helical with the axial leakage having little effect on overall residence time of the fluid between the tube walls. On the other hand the spacing of the inner and outer ridge surfaces makes it much easier to manufacture the two tube walls, since if they are a tiny bit too big or small they will still fit together, and makes it very easy to assemble and disassemble the tube according to the invention.
The helical passage in accordance with the invention has a flow cross section that is substantially greater than a flow cross section of the axial passage. This is typically done by making the grooves axially longer (that is wider) than the ridges and making the helical passage substantially deeper measured radially than the space between the ridge surfaces. The grooves are of generally rectangular section and the surfaces extend parallel to the respective axes.
According to the invention an inner pipe spaced radially coaxially inside the inner wall therewith an inner passage, and an outer pipe spaced radially coaxially outside the outer wall forms therewith an outer passage. The inner and outer pipes can be cylindrical or helically corrugated.
Since with the system of this invention the loose fit makes it difficult to determine if the inner-tube ridge is radially aligned with the outer-tube ridge, the inner and outer tubes are formed with markings that are aligned axially when the inner-tube ridge is radially aligned with the outer-tube ridge. These markings can be bumps.


REFERENCES:
patent: 1005441 (1911-10-01), Lovekin
patent: 3332446 (1967-07-01), Mann
patent: 3566615 (1971-03-01), Roeder
patent: 3777343 (1973-12-01), D'Onofrio
patent: 4086959 (1978-05-01), Habdas
patent: 4351389 (1982-09-01), Guarneschelli
patent: 4924838 (1990-05-01), McCandless
patent: 5148861 (1992-09-01), Colvin et al.
patent: 5690167 (1997-11-01), Rieger
patent: 5799726 (1998-09-01), Frank
patent: 670481 (1966-01-01), None
patent: 203201 (1908-10-01), None
patent: 455 44 (1950-10-01), None
patent: 804 502 (1951-04-01), None
patent: 3320956 (1984-12-01), None
patent: 317 64 (1985-01-01), None
patent: 295 00 063 U (1996-02-01), None
patent: 1158943 (1958-06-01), None
patent: 394643 (1931-09-01), None

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