|Publication number||US2122504 A|
|Publication date||Jul 5, 1938|
|Filing date||May 2, 1936|
|Priority date||May 2, 1936|
|Publication number||US 2122504 A, US 2122504A, US-A-2122504, US2122504 A, US2122504A|
|Original Assignee||Lee Wilson|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (8), Classifications (8)|
|External Links: USPTO, USPTO Assignment, Espacenet|
July 5, .1938. L. WILSON HEATING APPARATUS Filed May 2, 1936 Patented July 5, 1938 UNITED STATES PATENT OFFICE 2 Claims.
This invention relates to the art of heating and, particularly to indirect heating, e. g., that which is effected by passing hot fluids through a conduit and by radiation from the latter to the point or v 5 object to be heated.
that this problem is general and the applicability of the present invention is correspondingly broad. While the invention will be described with particular reference to furnaces or annealing covers, this is merely by way of illustration and does not constitute a limitation upon the scope of the invention.
When it is attempted to heat a space or an object by passing hot fluids through a radiating tube or conduit, the natural result is that the temperature of the tube wall decreases progressively therealong from the point at which the hot gases are supplied thereto or generated therein. In other words, the hot fluids, such as combustion gases, cool gradually as they 'give up heat to the tube. In many cases, however, it is desired that the temperature of the tube remain substantially constant throughout its entire length, instead of presenting a so-called hot spot at the point of admission or generation of the-heating fluid, and a progressively decreasing temperature from that point toward the discharge end of the tube. This problem is particularly acute. in the process of annealing steel sheets in stacks, since the characteristics of the finished product depend largely on the temperatures to .which they are heated during the annealing.
I have invented an apparatus whereby it is pos- 40 sible to obtain a greater uniformity in the temperatures at various'points along the length of a radiant tube, even though the hot fluid supplying heat thereto is introduced or generated in a relatively confined space and-transmitted therealong, gradually losing heat to the tube. In accordance with my invention, I restrict the flow of heat radially through the tube wall to varying degrees, the restriction being greatest adjacent the point of introduction or generation ofthe hotfluids, and decreasing gradually along the length of the tube from thatpoint toward the discharge end. I thus counteract the natural tendency for the tube to radiate the, greater portion of the heat from the zone of its length traversed by the gases while at their highest temperature, the restrictive effect being tapered 01!, along the length of the tube, to permit greater heat radiation from points at which the gases traversing the tube are somewhat cooled from their original temperature.
My invention, in one embodiment, takes the 5 form of a plurality of; thickening bands disposed about the radiant tube at varying intervals. The bands are closest together at the points of introduction or generation of the hot fluid, the spacing therebetween increasing gradually toward the 1 discharge end of the tube. The thickening bands provide relatively short zones of' increased thickness and thereby restrict transmission of heat radially of the tube wall.
For a complete understanding of the invention 15 reference is made to the accompanying drawing illustrating several forms which the apparatus of my invention may take.
In the drawing:
Figure 1 is a view partly in section and partly in 20 elevation showing a radiant tube with thickening bands applied externally thereof;
' Fig. 2 is a view similar to Fig. 1 showing a modifled form;
Fig. 3 is a view similarto Fig. 1 showing .thick- 25 ening bands disposed interiorly of the tube; and
Fig. 4 is an axial section through a heating tube showing thickening bands as illustrated in Fig.
,2 disposed interiorly of the radiant tube.
Referring now in detail to the drawing, aheat- 30 ing tube I0 is provided at the end of a burner ll. Fuel and air for combustion are delivered to the burner, by any known means (not shown). The resulting combustion evolves considerable quantitles of hot gases in a relatively'short portion of 35 the tube length just beyond the burner. As the gases expand because of the heat generated, they flow along the tube toward the discharge end thereof indicated generally at II. The fuel and air for combustion, of course, must be delivered 40 under a pressure greater than that created in the tube by the expansion of ,the combustion gases.
Thickening bands I! are disposed at intervals along the length of the tube III. In Fig. 1 these bands are simply annular rings and may be of any desired shape or material and secured to the tubes in any convenient manner. The dimension of the bands axially of the tube III is preferably 50 several times (i. e., two or three times) the dimension thereof radially oi the tube. The bands II provide relatively short zones of increased thickness. This increased thickness, together with the film of air or gas between the bands and the 55 tube, causes a reduction in the flow of heat radially of the tube wall, as compared to the rate of flow through the portions of the wall not covered by the bands.
The. spacing between the bands increases in proportion to the distance along the tube from the burner II. As the hot gases travel along the tube and are cooled as a result of giving up heat thereto, a greater proportion of tube surface uncovered by the thickening bands is provided to permit transmission of about the same amount of heat per unit length as in the tube sections nearer the burner. The temperature of the tube at all points therealong is thus maintained substantially constant. At the discharge end, the entire surface of the tube may be left uncovered.
By this arrangement, I limit the amount of heat transmitted through the tube walls for radiation therefrom adjacent the burner where the mines the temperatures of the tube at various points along its length. v
Figure 2 shows a slight modification in which the tube 10 is provided with a helical wrapping of strip, wire, rod or the like, indicated generally at l4.' The turns of the wrapping are spaced more closely adjacent the burner II and at points remote therefrom, the spacing between turns increasing, gradually almost in proportion to the distance from the burner. The result produced by the structure shown in'Fig. 2 is substantially the same as that of the arrangement of Fig. 1,
about the only difference being that the successive turns of the wrapping form helical bands which,
. instead of being independent, are connected each to its neighbors.
. Figure 3 illustrates a heating tube similar to that of Fig. 1 except that the thickening bands I! are disposed interiorly of the tube instead of exteriorly.
Figure 4 likewise shows a tube similar to that of Fig. 2 except that the helical wrapping I4 is disposed inside the tube.
- It will be apparent from the foregoing description that the invention makes it possible to attain' a substantially uniform external temperature along all points of the heating tube despite the fact that the heating gases are hottest adjacent the burner and cooled progressively as they flow therefrom along the tube. By properly spacing the thickening bands, a considerable range of average external tube temperatures may be obtained. The invention utilizes the principle that the average temperature along the outside of the tube is dependent upon the heat transmitting characteristics of the wall section at various points therealong.
While I have illustrated and described herein but pneembodiment of the invention with certain modifications, it will be recognized that changes in the construction described may be made, within the scope of the appended claims,
without departing from the spirit of the. invention. In the claims, the term bands is to be defined as including both the separate bands of Figures 1 and 3 and the successive turns of a helix as shown in Figures 2 and 4.
1. In a heat exchange apparatus, a tube of substantially -uniform.diameter and wall thickness adapted to be heated by the passage of fluid therethrough, and thickening bands extending around the tube in spaced relation longitudinally thereof, the spacing between adjacent bands varying along the length of the tube, and the dimension of said bands axially of the tube being several times their dimension radially of the tube.
2. In a heat, exchange apparatus, a tube of substantially uniform diameter and wall thickness adapted to be heated by the passage of fluid therethrough, and thickening bands extending around the tube in spaced relation longitudinally thereof, the spacing between adjacent bands varying, along the length of the tube, the bands having a width greater than their thickness and disposed fiatwise on the tube.
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|U.S. Classification||165/184, 165/146, 122/155.4, 126/91.00A, 138/38|