Heat exchange – With coated – roughened or polished surface
Reexamination Certificate
1994-07-07
2001-01-16
Atkinson, Christopher (Department: 3743)
Heat exchange
With coated, roughened or polished surface
C165S184000, C165S181000, C165S179000
Reexamination Certificate
active
06173762
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat exchanger tube for a falling film evaporator suitable to employ in the falling film evaporator of an absorption refrigeration machine and so forth.
2. Description of the Related Art
In a falling film evaporator employed in absorption water cooling and heating appliance and so forth, a refrigerant flows down along the outer peripheral surface of a heat exchanger tube for performing heat exchanging with a media to be cooled, such as water, flowing through the tube, for cooling the medium. The refrigerant contacting with the heat exchanger tube spreads on the surface of the heat exchanger tube with wetting the latter and evaporates under low pressure to remove heat from a heat transmission surface of the heat exchanger tube to cool the water as the medium to be cooled, in the tube. Upon evaporation of the refrigerant spread on the surface of the heat exchanger tube, vaporization heat is removed from the heat transmission surface so that the water or so forth in the tube can be efficiently cooled. Therefore, in order to attain high performance heat exchanger tube, it is necessary to increase the contact area between the refrigerant and the heat exchanger tube (namely, the area of the heat transmission surface) as great as possible.
Increasing of the contact area between the refrigerant and the heat exchanger tube may be achieved by increasing the surface area of the heat exchanger tube and by enhancing refrigerant spreading ability in spreading of the cooling water with wetting the surface of the heat exchanger tube. As the conventional heat exchanger tube with the increased surface area, there are a flute tube which has grooves formed on the external surface of the tube along the tube axis, and a low fin tube which is provided with collar-like or spiral fin or fins on the external surface of the tube. On the other hand, as the heat exchanger tube having an improved refrigerant wetting and spreading ability, there is a surface treated tube having a smoothed external surface and a surface treated tube having the external surface treated by wire brush polishing. Also, as the heat exchanger tube which can achieve both of the increased external surface area and improved refrigerant wetting and spreading ability, there is proposed a high performance heat exchanger tube, in which cut-outs are formed in the fins arranged on the external surface of the tube in alignment in the tube axis direction (Shuichi Takada “
RecentAbsorption Refrigeration Machine and Heat Pump
(3)”, March, 1989).
However, above-mentioned conventional heat exchanger tubes encounter the following problems. Namely, in the case of the surface treated tube with smoothed or polished external surface, when the refrigerant drops on the surface of the tube, the refrigerant may widely spread with wetting the external surface of the tube in the area near the drop point. However, the refrigerant has a tendency to converge toward the tube axis direction as flowing down along the external surface of the heat exchanger tube to lower wetting and spreading ability. In case of the flute tube, since the refrigerant flows in the tube axis direction along the grooves to achieve higher wetting and spreading ability in comparison with the above-mentioned surface treated tube. However, at ridge portions between the adjacent grooves, no wetting and spreading ability can be obtained. Therefore, the heat transmission area of the whole heat exchanger tube cannot be satisfactorily large. On the other hand, in the case of low fin tube, while the surface area of the external surface of the tube can be increased by the presence of fins arranged on the outer periphery of the tube, the wetting and spreading ability of the refrigerant inherently becomes small since motion of the refrigerant in the tube axis direction is blocked by the fins. Furthermore, though the high performance heat exchanger tube, in which cut-outs are formed in the fins, can achieve certain level of gain in improving the heat exchanging performance, it does not achieve the satisfactorily level of gain of the heat exchanging performance, yet. In the recent years, needs for further higher performance of absorption type water cooling and heating appliance. In order to satisfy such needs, it is strongly desired to have a further improved performance of the high performance heat exchanger tube.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a heat exchanger tube for a falling film evaporator which holds high refrigerant wetting and spreading ability and has increased heat transmission area to provide improved heat transmission performance superior to the conventional heat exchanger tubes.
In order to accomplish the above-mentioned and other objects, a heat exchanger tube, according to the present invention, has fins extending transversely or in oblique to the tube axis direction, on the external surface. Groove portions extending along the fins are formed on the tip end portion of respective fins. In addition, a plurality of cut-outs are formed on the tip end portion of the fins at a predetermined pitch in the circumferential direction of the tube, in alignment in the transverse direction to the fin extending direction.
When a refrigerant, such as water, is dropped on the heat exchanger tube constructed as set forth above, the refrigerant droplets are captured by the fins on the heat exchanger tube and thus flows in circumferential direction along the groove. In addition, the refrigerant further flows in axial direction of the heat exchanger tube along the aligned cut-outs. The refrigerant past through the cut-outs finally enters into bottom portion defined between the fins to flow from the upper side to the lower side of the tube. As set forth above, in the heat transmission tube, according to the present invention, since the refrigerant can be propagated through the grooves formed on the tip end portion of the fins, the cut-outs transversely formed at a predetermined pitch on the tip end portion of the fins in axial and circumferential direction of the tube. Therefore, the refrigerant flowing on the external surface of the heat exchanger tube will never cause local concentration of the refrigerant in propagation on the tube surface. Accordingly, the heat exchanger tube according to the present invention can achieve large contact area between the refrigerant and the heat exchanger tube, permits effective use of the increased surface area of the tube by formation of the fins, and whereby achieves excellent heat transmission performance.
Here, in the preferred construction, 905 to 1102 of fins are required for 1 m of axial length of the heat exchanger tube. In either case where the number of fins per 1 m of axial length of tube is less than 905 or greater than 1102, the refrigerant wetting and spreading ability is potentially lowered to cause degradation of the heat transmission performance. Therefore, the preferred range of density of the fins is 905 to 1102 fins per 1 m of axial length of the heat exchanger tube.
On the other hand, the preferred height of the fin is in a range of 0. 2 mm to 0.8 mm. In either case where the height of the fin is less than 0.2 mm or greater than 0.8 mm, the wetting and spreading ability of the refrigerant can be lowered. Therefore, 0.2 mm to 0.8 mm of height is required for the fins in the heat exchanger tube according to the invention.
Also, when an angle defined by both side peripheries of the groove is less than 70° or greater than 150°, the wetting and spreading ability of the refrigerant is lowered. Therefore, the preferred range of angle defined by the opposing peripheral walls of the grove is in a range of 70° to 150°.
Furthermore, the preferred pitch of the cut-outs in the circumferential direction of the tube is 0.5 mm to 1.00 mm. When the circumferential pitch of the cut-outs is smaller than 0.5 mm, difficulty should be encountered in formation of the cut-outs. On the other hand, when the circumferential pit
Furukawa Masahiro
Higo Tomio
Ishida Seiji
Izumi Masashi
Uchida Tetsuo
Atkinson Christopher
Kabushiki Kaisha Kobe Seiko Sho
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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