Polyhedral array heat transfer tube

Details Polyhedral array heat transfer tube Polyhedral array heat transfer tube

1998-11-02

2001-02-06

Lazarus, Ira S. (Department: 3743)

Heat exchange

With coated, roughened or polished surface

C165S181000, C165S182000

Reexamination Certificate

active

06182743

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to tubes used in heat exchangers and more particularly, the invention relates to a heat exchanger tube having an internal surface that is capable of enhancing the heat transfer performance of the tube.
BACKGROUND OF THE INVENTION
The heat transfer performance of a tube having surface enhancements is known by those skilled in the art to be superior to a plain walled tube. Surface enhancements have been applied to both internal and external tube surfaces, including ribs, fins, coatings, and inserts, and the like. All enhancement designs attempt to increase the heat transfer surface area of the tube. Most designs also attempt to encourage turbulence in the fluid flowing through or over the tube in order to promote fluid mixing and break up the boundary layer at the surface of the tube.
A large percentage of air conditioning and refrigeration, as well as engine cooling, heat exchangers are of the plate fin and tube type. In such heat exchangers, the tubes are externally enhanced by use of plate fins affixed to the exterior of the tubes. The heat exchanger tubes also frequently have internal heat transfer enhancements in the form of modifications to the interior surface of the tube.
In a significant proportion of the total length of the tubing in a typical plate fin and tube air conditioning and refrigeration heat exchanger, the refrigerant exists in both liquid and vapor states. Below certain flow rates and because of the variation in density, the liquid refrigerant flows along the bottom of the tube and the vaporous refrigerant flows along the top. Heat transfer performance of the tube is improved if there is improved intermixing between the fluids in the two states, e.g., by promoting drainage of liquid from the upper region of the tube in a condensing application or encouraging liquid to flow up the tube in a wall by capillary action in evaporating application.
It is also desirable that the same type of tubing be used in all of the heat exchangers of a system. Accordingly, the heat transfer tube must perform satisfactorily in both condensing and evaporating applications.
In order to reduce the manufacturing costs of the heat exchangers, it is also desirable to reduce the weight of the heat transfer tube while maintaining performance.
Accordingly, what is needed is a heat transfer tube that provides suitable performance for both condensing and evaporating applications and that offers practical and economical features to end users.
SUMMARY OF THE INVENTION
The heat exchanger tube of the present invention meets the above-described needs by providing a tube with features that enhance the heat transfer performance such that, at equal weight, the tube provides heat transfer performance superior to the prior art tubes and, at a reduced weight, the tube provides heat transfer performance equal to the prior art tubes and pressure drop performance that is superior to the prior art tubes.
The heat exchanger tube of the present invention has an internal surface that is configured to enhance the heat transfer performance of the tube. The internal enhancement has a plurality of polyhedrons extending from the inner wall of the tubing in a preferred embodiment. In a preferred embodiment the polyhedrons are arranged in rows that are substantially parallel to the longitudinal axis of the tubes. However, the rows may be offset from the longitudinal axis up to approximately 40 degrees. The polyhedrons have first and second planar faces that are disposed substantially parallel to the polyhedral axis. The polyhedrons have third and fourth faces disposed at an angle oblique to the longitudinal axis of the tube. The resulting surface increases the internal surface area of the tube and thus increases the heat transfer performance of the tube. In addition, the polyhedrons promote flow conditions within the tube that also promote heat transfer.
The tube of the present invention is adaptable to manufacturing from a copper or copper alloy strip by roll embossing the enhancement pattern on one surface on the strip for roll forming and seam welding the strip into tubing. Such a manufacturing process is capable of rapidly and economically producing complicated, internally enhanced heat transfer tubing.


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