Heat exchange – With coated – roughened or polished surface
Reexamination Certificate
1997-03-26
2001-10-30
Flanigan, Allen (Department: 3743)
Heat exchange
With coated, roughened or polished surface
C165S184000
Reexamination Certificate
active
06308775
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to an exchanger tube for a heat exchanger. More particularly, the invention relates to an exchanger tube of the type having a structured inner surface formed from ribs running at an angle with respect to the longitudinal tube axis and having inclined flanks and channels that are limited laterally by the ribs and troughs. These channels extend transversely through the ribs and also have inclined flanks, which extend at an angle with respect to the longitudinal tube axis.
An exchanger tube of this general type is described in EP 0 692 694 A2 (the corresponding U.S. Pat. No. 5,458,191 is incorporated herein by reference). In this case, both the ribs and the channels that are limited laterally by the ribs each have a trapezoidal cross section. The flanks of the ribs are planar, the transitions from the flanks to the channel beds are sharp-edged. Sharp-edged transitions are also present between the flanks and the level top sides of the ribs. The rib cross-sectional volume is dimensioned to be approximately one-half that of the channels. The parallel ribs extend at a 90° angle with respect to the longitudinal tube axis. All of the ribs have the same radial height.
The troughs extending transversely through the ribs likewise run at a 90° angle with respect to the longitudinal tube axis. The trough flanks are arched convexly. The transitions from the flanks to the level beds of the troughs, and to the level top sides of the rib regions between two adjacent troughs of a rib, are sharp-edged. The depth of the troughs is dimensioned to be less than the radial extension of the ribs. All of the troughs are of identical depth. In producing the troughs, the material formed from the ribs is shaped into the channels on the end face of the troughs.
The preferred method of producing the known exchanger tube is first to perform a rolling process to create the structure on one side of a metal band that will later be the inside surface, then shape the metal band into a slit tube with the surface structure on the inside, and then weld the slit edges together.
Because of the flat top sides and the level flanks of the ribs, in practical use the exchanger tube can be subject to the formation of condensate films that are difficult to remove and that retard condensation. Hence, blocking layers having thermally-insulating properties can form, leaving only a few edges available for developing steam bubbles for evaporation.
There remains a need for a heat exchanger tube having an inside surface structure with which a clearly more intensive channel flow-through can be assured, and which combines the advantages of uniformly good evaporation or condensation performance and a reduced rib weight.
SUMMARY OF THE INVENTION
The present invention addresses this need by providing an exchanger type having a structured inner surface that is formed of primary and secondary ribs running at an acute angle with respect to the longitudinal tube axis. The ribs have inclined flanks, and further serve to laterally delimit channels separating the rows of ribs from one another. A series of troughs is also provided. These troughs extend transversely through the ribs and have inclined flanks, which extend at an angle with respect to the longitudinal tube axis. Rows of these ribs are offset from one another by intermediately disposed secondary ribs. The primary ribs have a greater radial extent or height than the secondary ribs.
Because every other one of the primary and secondary ribs following one another in the circumferential direction now has a radial extension (height) that differs from the radial height of the adjacent secondary or primary rib, alternating high primary ribs and low secondary ribs are formed. This reduces the flow speed in the channels by only an insignificant amount. Nevertheless, more violent turbulence can arise at appropriate locations in the channels, ultimately intensifying the transfer of heat from the flowing fluid to the tube wall. Internal testing has revealed that the alternating heights of the primary and secondary ribs result in a marked increase in heat exchange performance.
In one embodiment, all of the primary ribs possess the same radial height, as do all of the secondary ribs. In other words, all of the primary ribs are of the same height, and all of the secondary ribs are of the same height.
Both the primary ribs and the secondary ribs to extend at the same angle with respect to the longitudinal tube axis. In another embodiment, the primary and secondary ribs extend at different angles with respect to the longitudinal tube axis.
Testing has shown that primary ribs should run at an angle ≧20° but ≦90° with respect to the longitudinal tube axis. The primary ribs preferably extend at an angle between 20° and 40° with respect to the longitudinal tube axis.
Also with regard to the course of the secondary ribs, internal testing indicates that the secondary ribs should optimally extend at an angle ≧20°, but ≦90° with respect to the longitudinal tube axis. In this case, the secondary ribs also preferably run at an angle between about 20° and 40° with respect to the longitudinal tube axis.
Both the primary ribs and the secondary ribs have rounded summits and planar flanks. This is of particular advantage for when an exchanger tube is inserted, for example, into the lamellae of a heat exchanger, particularly through widening by means of a tool moved through the exchanger tube, the rounded summits of the primary and secondary ribs are only insignificantly flattened. This measure effectively combats the formation of hard-to-remove condensate films.
The flanks of the primary ribs transition into the beds of the channels by way of rounded chamfers. Similarly, the flanks of the secondary ribs transition into the beds of the channels via rounded chamfers. These features also contribute substantially to the optimization of heat exchange between the fluid flowing in the exchanger tube and the wall of the exchanger tube.
A narrow rib contour can be used. Accordingly, the flank angle of the primary and secondary ribs is 20° and 40°, preferably 25°.
The invention recognizes that, when the primary ribs extend at an appropriate angle with respect to the longitudinal tube axis and alternate with lower secondary ribs that follow one another in the circumferential direction, the ratio of the spacing of the center longitudinal planes of two adjacent primary ribs to the radial extension of the secondary ribs is of special significance. This ratio is 15:1 to 8:1, preferably 10:1. In this connection, it has proven to be particularly useful to dimension the spacing of the center longitudinal planes of two adjacent primary ribs to be between approximately 0.8 mm and 2.0 mm.
The radial extension of the primary ribs advantageously measures between approximately 0.15 mm and 0.40 mm.
The flow relationships in the channels between the primary and secondary ribs are further improved by the dimensioning of the ratio of the radial extension of the primary ribs to that of the secondary ribs to be approximately 3:1.
The cross-section-related surface ratio of the primary ribs relative to the secondary ribs is also important in attaining especially good heat transfer. Therefore, the surface ratio of the primary to secondary ribs is approximately 15:1 to 5:1, preferably 8:1 to 6:1.
As explained above, the secondary ribs can extend at the same angle with respect to the longitudinal tube axis as the primary ribs. If, however, the secondary ribs do not extend at the same angle with respect to the longitudinal tube axis as the primary ribs, it is advantageous for the spacing between adjacent secondary ribs to be a maximum of 10 mm.
At least the beds of the channels are roughened. It is also within the scope of the invention to roughen all of the primary and secondary rib surfaces, as with a degree of microroughness. This type of roughness is especially noticeable during condensation and evaporation of refrigerants if the exchanger tube is incorporated into a correspo
Flanigan Allen
Kenyon & Kenyon
KM Europa Metal AG
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