US2529545A - Finned tubing - Google Patents

Description

Nov. 14, 1950 c, EDWARDS 2,529,545

FINNED TUBING Filed Oct. 14, 1948 FIG. 3

IN V EN TOR.

Patented Nov. 14, 1950 FINNED TUBING 7 Ray 0. Edwards, Glen Rock, N. J.

Application October 14, 1948, Serial No. 54,369

Claims.

This invention concerns improvements in a certain type of metallic heat-transfer device known as finned tubing. This device consists essentially of a metallic tube, conduit or channel, through which a heat-transfer fluid may flow, and contiguously or integrally attached thereto. a series of uniformly spaced, thin, metallic sheets or fins, usually mounted on said tube in parallel array and positioned at an appreciable angle, customarily from 45 to 90 relative to the axis of said tube. These fins serve to enlarge the metallic surface available for the transfer of heat between the attached tube and the solid or fluid medium surrounding the tube and fins, and thus efiecting an enormous increase in the amount of heat transferable per lineal foot "of the tube.

Such devices find widespread application in refrigerating and heating systems where the finned tubes are customarily arranged in banks or stacks in order to conserve space and lower costs. This minimum space requirement is particularly important in many commercial applications such as domestic refrigerators and the so called baseboard convectors. For such purposes, the replacement of the earlier bare tube, or coil of tubing, by a tubing with fins attached has accomplished a disproportionately large increase in the amount of heat transferable per lineal foot of tube and per unit volume of space occupied by the stack of such tubes in comparison with the somewhat increased space requirement for the finned tubing itself, so that a great net saving is achieved in the space, or volume or stack required for a given amount of heat tran fer. This has made possible the commercial success of devices such as the abovementioned baseboard convectors which consist of one or more finned tubes mounted in place of the conventional baseboards of building interiors, or stair-risers, etc. Heat is obtained therefrom by the circulation of hot water, hot air or steam through the tubes and effecting heat transfer, via the tube and fins, with the surrounding air. Despite the comparatively insignificant volume of the unit, its heating efilciency is adequate to replace the conventional radiators, thereby increasing the fioor area of the room involved and enhancing its appearance.

In the utilization of finned tubing, however, it has been found that the amount of heat transferred per lineal inch of tube does not increase continuously with an increasing number of fin per lineal inch. To the contrary, this quantity of heat attains a maximum and then decreases markedly as the linear density of fins along the tube is further increased. Thus for example, in the baseboard convectors previously mentioned, it has been found that for a stack height of ten inches, a maximum of about four to five fins per lineal inch of tube constitutes the optimum arrangement with respect to efliciency. Thus while it is mechanically possible to increase the number of fins per inch considerably beyond this value, no useful purpose is served in so doing, and indeed a marked decrease in the heat-exchange capacity of the stack may result. Thus a. considerable loss in potentially useful space is imposed on the system by this limitation on the linear fin density and a sacrifice in the uniformity of the heatexchange is likewise. encountered with such a sparse distribution of fins along the tube.

I have now discovered a unique finned tube construction which effects a marked improvement in the amount of heat exchanged per lineal foot for any given stack depth which is shown in the acrompanying drawings, wherein;

Figure 1 is a side elevation of the improved finned tube constructed in accordance with my invention.

Figure 2 is an end view of the tube.

Figure 3 is a top view or elevation of the tube taken at right angles to the view shown in Figure 1 0f the drawings.

My device comprises a finned tube structure including a metallic tube i having a spiral fin tube wrapped thereon and bonded thereto in any suitable manner as is usual in the manufacture of fin tubes of this type. A portion of the periphery of the fin tube is bent over or "1ipped as shown at 3, at an angle to the surface of the fin and preferably the lips 3 are based on a line lying in a plane approximately parallel to the axis of the tube. The lips 3 may be all on the same sides of successive fins or they may be arranged so that each fin tube bears 2 lips based on two lines lying in the plane of each fin with the two base lines in two planes on opposite sides of the axis of the tube and approximately parallel to each other and to this axis of the tube.

As shown in Figures 1 and 3 of the drawings, the maximum width of the lips 3 is approximately equal to the distance between adjacent fins, slight clearance s ace being left as shown at I. This facilitates the intensified draft provided by the channeling hereinafter more specifically referred to. For maximum efllciency each fin should bear at least one such lip 3 positioned so that the break or baseline of the lip joining two points 'on the periphery of the fin is of approximately equal length on each fin, and the breaks all ly- 3 ing in a plane approximately parallel to the axis of the tube. Thus in my construction, the series sequence of lips 3 forms a new and additional heat-exchange surface preferably parallel to the axis of the tube, which actually decreases the volume of space occupied by the tube, particularly in respect to the depth of the column of fluid being heated or cooled by the fins, this distance being customarily designated as stack depth. Hence my lipped fin construction not only increases the amount of heat exchangeable per lineal foot of tube for a given stack depth by utilizing a part of the heretofore empty space between the fins, but more important, it increases the amount of heat exchangeable per lineal foot for any given stack depth. This decrease in the required stack depth per unit of heat transferred achieves a very important saving in space, particularly in the abovementioned baseboard convectors, where it is highly desirable that the convector unit protrude into the room as little as possible beyond the wall-line.

Moreover, as is well-known, the temperature in conventional finned tubes alters continuously across the fins along a path from the tube to the edge of the fin. By employing my lipped-fin construction. this temperature gradient is appreciably lessened and a more uniform source of heat is obtained.

A further improvement is achieved with my construction when the tube is mounted in such a way as to bring the plane of the lips parallel or inclined to the direction in which a heat transfer fluid is circulating among and over the fins or the finned tube bank. In such a case, the lips and the wall of the tube cooperate to induce a channelling shown at G, i. e. an intensified draft or fluid motion through the fins, thereby increasing the so-called "stack effect which becomes very pronounced in a bank or other ordered array .of such tubes with all of the fin lips mounted in parallel or preferably coplanar relation.

This stack effect can be further intensified by adding a second lip to each fin, on the opposite side from and parallel to the first lip. This construction, which is illustrated by the accompanying drawings, is much preferred, not only because of this heightened stack efl'ect, but even more because of the still greater increase in the heat exchange attainable per lineal foot for a given stack depth, which incidentally effects still further economies in space requirements. Moreover. a further decrease in the undesirable temperature gradient in the unit is likewise achieved.

My type of finned tubes can be constructed tween adjacent fins.

from conventional metals, or which copper, aluminum and steel are preferred. The tube cross-section and the fin may both enJoy a variety o1. shapes, including square, rectangular, circular, elliptical and streamline. The relative areas of the fin and the tube cram-section, as well as the number of fins per lineal inch of the tube are determined by the thermodynamic requirements and the physical and economic aspects of the installation employing the finned tube.

I claim as my invention:

1. An improved heat exchange device consisting of a spiral wrapped finned metallic tube in which each fin bear a lip based on a line lying inthe plane of each fin, all of the said base lines lie in a plane approximately parallel to the axis of the tube, said lips being on the same side of successive fins.

2. An improved heat exchange device consisting of a spiral wrapped finned metallic tube in which each fin bears two lips based on two lines lying in the plane of each fin, said base lines lie in two planes on opposite sides of the axis of the tube and approximately parallel to each other and to the axis of the tube.

3. An improved heat exchange device consisting of a spiral wrapped finned metallic tube, a lip formed on each fin and extending transversely of the normal plane of the fin and based on a line lying in the plane of each fin, all of said lips being on the same side of successive fins.

4. An improved heat exchange device as claimed in claim 1 wherein the maximum width of said lips is approximately equal to the distance between adjacent fins.

5. An improved heat exchange device as claimed in claim 2 wherein the maximum width of said lips is approximately equal to the distance be- RAY c. EDWARDS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,707,564 Otis et a1. Apr. 2, 1929 1,758,684 Blackmore May 13, 1930 1,874,940 Dwyer Aug. 30, 1932 1,907,036 Belleau May 2, 1933 FOREIGN PATENTS Number Country Date 519,798 Great Britain Apr. 5, 1940

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