Heat exchange – With coated – roughened or polished surface
Reexamination Certificate
1998-12-04
2001-01-23
Lazarus, Ira S. (Department: 3743)
Heat exchange
With coated, roughened or polished surface
C165S183000, C165S184000
Reexamination Certificate
active
06176301
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to heat transfer tubes, and more particularly to a heat transfer tube having an internal surface which enhances the liquid-vapor two-phase flow heat transfer performance of the tube.
BACKGROUND OF THE INVENTION
In order to obtain increased two-phase flow heat transfer performance, heat transfer tubes have been provided with surface enhancements on their inner surfaces. The higher heat transfer performance of an internally enhanced tube as compared to a smooth tube can be utilized to reduce the size of heat exchangers which, in turn, provides the advantages of increased energy efficiency, reduced noise levels, and cost reductions in air conditioning and refrigeration equipment.
An early form of internally enhanced tube was the helical type which can be characterized as numerous continuous fins extending spirally along the tube axis. An example of such a helical tube is disclosed in U.S. Pat. No. 4,658,892. The fins typically are formed by an extrusion process and are substantially trapezoidal in cross-sectional shape with the larger end at the junction of the fin and the tube wall. This tube improves refrigerant evaporation heat transfer up to about two times that of the performance of a corresponding smooth tube. It also has one and one-half to two times the performance of the smooth tube in condensation. On the other hand, refrigerant flow pressure drop, which is not desired, is increased only about 30% to 50% in both evaporation and condensation.
Thereafter an axial internally enhanced tube was developed, which is a variation of the helical internally enhanced tube, with the helical angle of the fins being 0 degrees. This tube typically has more fins than the helical type and has more surface area. The axial internally enhanced tube has two-phase flow heat transfer performance similar to that of the helical tube in most practical flow rates, but provides significantly lower refrigerant pressure drop.
Crosshatch internally enhanced tubing is available currently in the air conditioning and refrigeration industry. It employs the axial or helical tube as its first enhancement and a cross notch of the continuous fins as the second enhancement to provide a relatively more complicated surface structure. Instead of continuous fins, like those in the helical and axial internally enhanced tubes, small segments of fins are provided on the tube inner surface. The crosshatch internally enhanced tube significantly increases condensation performance, i.e. about 35 percent, while providing a similar evaporation performance compared with the helical tube. The pressure drop of the crosshatch tube is slightly higher than that of the helical tube and significantly higher than that of the axial tube. Examples of crosshatch internally enhanced tubing are shown and described in U.S. Pat. Nos. 5,332,034 and 5,458,191.
SUMMARY OF THE INVENTION
It is known in the field of evaporation heat transfer that certain types of cavities on a heat transfer surface enhance evaporation so that the rate of heat transfer increases. This common knowledge was obtained from applications of pool boiling, in which the involvement of fluid flow is minimal. Thus, such knowledge leaves open the question of what will happen to a boiling liquid that has significant flow movement associated with it. It is therefore an objective of the present invention to answer the foregoing question and to provide tubes with improved flow evaporation heat transfer. As a result of the present invention, it is determined that surface cavities do help to enhance flow evaporation (boiling), and a cavity based enhanced heat transfer tube is developed.
The heat exchanger tube of the present invention has an internal surface that is formed to enhance the heat transfer performance of the tube, and in particular enhanced flow evaporation heat transfer. The internal enhancement has a plurality of polyhedrons extending from the inner wall of the tubing. The polyhedrons are arranged in polyhedral rows that are either substantially parallel to or disposed at an angle to the longitudinal axis of the tube. The polyhedrons have first and second planar faces that are disposed substantially parallel to the polyhedral rows. The polyhedrons have third and fourth faces disposed at an angle oblique to the direction of the polyhedral rows. The four faces of each polyhedron meet a fifth face spaced outwardly from the inner wall of the tubing. A single polyhedron has crack-like cavities on at least two of its faces, preferably three, which are not in the same geometrical plane and which cavities enhance flow evaporation heat transfer.
In order to achieve the foregoing surface enhancement, in accordance with the present invention, (1) a plurality of generally parallel first grooves are formed on the inner surface of the tube or what is to become the inner surface of the tube, (2) a plurality of generally parallel second fins extending at an angle relative to the first grooves of between about 2 and about 10 degrees and are formed in the inner surface, and (3) a pattern of generally parallel cuts are impressed into the second fins to extend cross-wise thereto. The formation of the second fins devolves the first grooves into the pattern of crack-like cavities. These continuous crack-like cavities are cut further into segments by the third enhancement step. The final surface has a dense array of polyhedrons having crack-like cavities on at least two surfaces of a single polyhedron, forming three-dimensional crack-like cavities that enhance flow evaporation heat transfer.
The prior art does not teach or suggest heat transfer tubing having an inner surface enhanced by polyhedrons having crack-like cavities on at least two surfaces which are not in the same geometrical plane and which cavities enhance flow evaporation heat transfer. U.S. Pat. No. 5,052,476 discloses a heat transfer tube having an inner surface in which are formed (1) U-shaped primary grooves which are parallel to one another and extending at an angle to the longitudinal direction of the heat transfer tube, and (2) V-shaped secondary grooves which are parallel to each other and which extend at an angle and intersecting with the primary grooves. As a result, pear shaped grooves are formed at the intersections of the primary and secondary grooves whose inner opening dimension is smaller than the dimension of the bottom of the pear-shaped groove. After the tube is formed, it may be expanded to narrow the opening of the secondary grooves and thereby introduce additional narrowing of the opening of the pear-shaped grooves located along the primary grooves. However, no crack-like cavities are formed.
U.S. Pat. No. 5,259,448 and the corresponding E.P. patent 0,522,985 disclose a heat transfer tube wherein (1) primary trapezoidal-shaped grooves are roll-formed parallel to one another on a metal strip surface (which will become the inner surface of the tube) and said to be desirably oriented less than 30 degrees from the tube axis, wherein (2) secondary trapezoidal-shaped grooves are roll-formed on the strip surface independent of the primary grooves and at the same angle, thereby inclining side faces of each primary groove closely toward the bottom face thereof, and forming a pair of sharp cuts between each of the side faces and the bottom face symmetrically, the strip then being rolled into a tube and the side edges joined to form a complete tube. After the strip is formed into a tube, an enlarging plug having a smooth periphery surface is inserted and drawn through the tube so that the heads of protruding portions between the main grooves are flattened. The cracks extend continuously only long the grooves or fins.
The above and other objects, features, and advantages of the present invention will be apparent to one of ordinary skill in the art to which this invention pertains from the following detailed description of the preferred embodiments thereof when taken in conjunction with the accompanying drawings wherein the same reference numerals or ch
Bennett Donald L.
Tang Liangyou
Duong Tho
Hodgson Russ Andrews Woods & Goodyear LLP
Lazarus Ira S.
Outokumpu Copper Franklin, Inc.
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