Heat exchange – With coated – roughened or polished surface
Utility Patent
1996-05-28
2001-01-02
Atkinson, Christopher (Department: 3743)
Heat exchange
With coated, roughened or polished surface
C165S184000, C165S181000
Utility Patent
active
06167950
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to heat transfer tubes of the type used in shell and tube type heat exchangers. More particularly, the invention relates to a tube for use in an application such as a condenser for an air conditioning system.
A shell and tube type heat exchanger has a plurality of tubes contained within a shell. The tubes are usually arranged to provide a multiplicity of parallel flow paths for one of two fluids between which it is desired to exchange heat. The tubes are immersed in a second fluid that flows through the heat exchanger shell. Heat passes from the one fluid to the other fluid by through the walls of the tube. In one typical application, an air conditioning system condenser, a cooling fluid, usually water, flows through the tubes of the condenser. Refrigerant flows through the condenser shell, entering as a gas and leaving as a liquid. The heat transfer characteristics of the individual tubes largely determine the overall heat transfer capability of such a heat exchanger.
There are a number of generally known methods of improving the efficiency of heat transfer in a heat transfer tube. One of these is to increase the heat transfer area of the tube. In a condensing application, heat transfer performance is improved by maximizing the amount of tube surface area that is in contact with the fluid.
One of the most common methods employed to increase the heat transfer area of a heat exchanger tube is by placing fins on the outer surface of the tube. Fins can be made separately and attached to the outer surface of the tube or the wall of the tube can be worked by some process to form fins on the outer tube surface.
Beside the increased heat transfer area, a finned tube offers improved condensing heat transfer performance over a tube having a smooth outer surface for another reason. The condensing refrigerant forms a continuous film of liquid refrigerant on the outer surface of a smooth tube. The presence of the film reduces the heat transfer rate across the tube wall. Resistance to heat transfer across the film increases with film thickness. The film thickness on the fins is generally lower than on the main portion of the tube surface due to surface tension effects, thus lowering the heat transfer resistance through the fins.
It is possible, however, to attain even greater improvement in condensing heat transfer performance from a heat transfer tube as compared to a tube having a simple fin enhancement. Such a tube is described and claimed in U.S. Pat. No. 5,203,404, issued Apr. 20, 1993 to Chiang, et al. (the '404 tube), the assignee of which is the same entity as the assignee of the present invention.
SUMMARY OF THE INVENTION
The present invention is a heat transfer tube having one or more fin convolutions formed on its external surface. Notches extend at an oblique angle across the fin convolutions at intervals about the circumference of the tube.
The notches in the fin further increase the outer surface area of the tube as compared to a conventional finned tube. In addition, the configuration of the finned surface between the notches promote drainage of refrigerant from the fin. In most applications, the tubes in a shell and tube type air conditioning condenser run horizontally or nearly so. With horizontal tubes, the notched fin configuration promotes drainage of condensing refrigerant from the fins into the grooves between fins on the upper portion of the tube surface and also promotes drainage of condensed refrigerant off the tube on the lower portion of the tube surface.
The density of notches in the fin convolutions on the tube of the present invention is relatively high when compared to the same parameters in a prior art tube such as the '404 tube. The external surface area is therefore even larger. Furthermore, the increased number of notches per convolution revolution results in a fin surface between the notches that is spiked or “sharper” than prior art tubes such as the '404 tube, a configuration that even more strongly promotes drainage of condensed refrigerant from the tube.
Manufacture of a notched fin tube can be easily and economically accomplished by adding an additional notching disk to the tool gang of a finning machine of the type that forms fins on the outer surface of a tube by rolling the tube wall between an internal mandrel and external finning disks.
REFERENCES:
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patent: 4733698 (1988-03-01), Sato
patent: 5186252 (1993-02-01), Nishizawa et al.
patent: 5203404 (1993-04-01), Chiang et al.
patent: 5332034 (1994-07-01), Chaing et al.
patent: 5458191 (1995-10-01), Chiang et al.
patent: 0101760 (1979-08-01), None
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patent: 0087036 (1989-03-01), None
patent: 0165875 (1990-06-01), None
patent: 3234302 (1991-10-01), None
Chiang Robert H. L.
Gaffaney Daniel
Gupte Neelkanth S.
Liu Xin
Spencer Steven J.
Atkinson Christopher
Carrier Corporation
Habelt William W.
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