Device for indirect heating by radiation in the form of a radiant housing

Abstract

The present disclosure relates to a device for indirect heating by radiation in the form of a radiant housing having two front walls and two side walls and comprising at least one heat source, said radiant housing having front walls joining one another such that the housing has a lenticular shape in cross-section.

Claims

1. A furnace for the heat treatment of products or parts comprising: at least one device for indirect heating by radiation that includes a radiant housing having two front walls and two side walls and comprising at least one heat source, said radiant housing having front walls joining one another such that the housing has, in cross-section, a lenticular shape having a chord C, wherein said front walls come together at least at one end of said chord C of said lenticular shape while forming an edge or a slight flat in that location, wherein said at least one device for indirect heating by radiation includes first and second devices for indirect heating by radiation, each of said first and second devices having a center and a lenticular shape having a main curve radius R, the two centers of said first and second devices being separated by a pitch P, each main curve radius R of each of said first and second devices being such that a ratio between R and P is greater than 0.5.

2. The furnace according to claim 1, wherein said at least one device comprises at least one inner element for channeling gas flow or stiffening.

3. The device according to claim 2, wherein said at least one inner element is a structure for stiffening.

4. The furnace according to claim 2, wherein said at least one inner element is formed as a plate.

5. The furnace according to claim 1, wherein said front walls of said housing are profiled with corrugations with any shape or with indentations with any shape.

6. The furnace according to claim 1, wherein said at least one device comprises an inner or outer heat recuperator.

7. The furnace according to claim 6, wherein said inner or outer recuperator is a regenerative heat exchanger.

8. The furnace according to claim 1, wherein the products or parts are generally made from metal or ceramic.

9. The furnace according to claim 6, wherein said at least one heat source is a combustion heat source.

10. A method of using a furnace, the method comprising: treating a product or part with at least one device for indirect heating by radiation, said at least one device including a radiant housing having two front walls and two side walls and comprising at least one heat source, said radiant housing having front walls joining one another such that the housing has, in cross-section, a lenticular shape having a chord C, wherein said front walls come together at least at one end of said chord C of said lenticular shape while forming an edge or a slight flat in that location, wherein said furnace comprises two said devices, each having a center and a lenticular shape having a main curve radius R, the two centers of said two devices being separated by a pitch P, each main curve radius R of each of said two devices being such that a ratio between R and P is greater than 0.5.

11. The method according to claim 10, wherein the product or part includes a bar, a tube, or a strip of metal or ceramic.

Description

DESCRIPTION OF THE DRAWINGS

(1) Other features, details and advantages of the invention will emerge from the following description, provided non-limitingly and in reference to the appended drawings.

(2) FIG. 1 is a diagrammatic perspective illustration of a representative heating device according to an aspect of the invention.

(3) FIG. 2 is a diagrammatic front view of a representative heating device according to an aspect of the invention.

(4) FIG. 3 is a diagrammatic cross-sectional illustration along axis (as illustrated in FIG. 2) of the heating device.

(5) FIG. 4 is a diagrammatic illustration of one particular furnace comprising heating devices.

(6) FIG. 5 is a diagrammatic illustration of two heating devices that are placed above one another, as is for example the case in a furnace (like that shown in FIG. 4).

(7) FIG. 6 is a diagrammatic illustration of another heating device according to an aspect of the invention.

(8) In the figures, identical or similar elements bear the same references.

DETAILED DESCRIPTION

(9) FIG. 1 shows a perspective view of the heating device 1 according to the invention. As illustrated, the heating device 1 assumes the form of a housing with a lenticular (biconvex) shape in its cross-section. This housing is made up of two substantially convex front walls 2, coming together in their upper part and their lower part, i.e., each of the ends of the chord C of the lenticular shape, forming an edge 3, 3 at that location. A location 4, for a heat source, passes through a side wall 5 of the heating device 1, and a second side wall (not visible) closes the end of the housing opposite the side wall 5 receiving the location 4 for a heat source. This second side wall is connected to an attachment and/or fastening means 6 of the housing when it is placed in a furnace.

(10) FIG. 2 is a side view showing the same elements as those illustrated in FIG. 1, where the inner elements 7 are shown for channeling the flow of gas and/or reinforcing in the form of plates.

(11) FIG. 3 is a sectional view along axis (as illustrated in FIG. 2) of the heating device 1 assuming the form of a housing that is lenticular in its cross-section, this lenticular shape having a sagitta F and a chord C. This housing is made up of two substantially convex front walls 2, coming together in their upper part and their lower part, i.e., each of the ends of the chord C of the lenticular shape, forming an edge 3, 3 at that location. The heating device 1 receives a location 4 for a heat source, said location 4 having a circular section in the illustrated embodiment.

(12) During operation, when a burner present in the location 4 is supplied with a combustible product and a combustive, a flame develops in the heating device 1, i.e., in the housing, centrally according to the illustrated embodiment. When the inner elements 7 for channeling the flow of gas and/or for reinforcing are present, they also make up a screen between this central flame and the parts adjacent to the center of the housing and make it possible to channel the flow of gas related to the combustion.

(13) FIG. 4 is a diagrammatic illustration of one particular furnace 8 comprising a plurality of heating devices 1, 1 according to the invention. According to the illustrated embodiment, a metal strip 9 travels in the furnace while being driven by return and transport rollers 10. The strip 9 is thus heated on both of its faces by each of the heating devices 1, 1 while passing in front of the front faces 2, 2 of the latter. Due to the biconvex lenticular shape of the heating device 1, 1 according to the invention, the metal strip 9 is subject to homogenous heating along its entire travel in the furnace 8, the mutual radiations between successive housings 1, 1 being significantly minimized. This biconvex lenticular shape of the heating devices according to the invention makes it possible, as indicated above, to optimize the view factor values both between the radiant elements (housings) and an element to be treated as well as between successive radiant elements (housings).

(14) FIG. 5 is a diagrammatic illustration of two heating devices 1, 1 that are placed above one another, as is for example the housing in a furnace 8 according to the invention. As can be seen, when two successive housings 1, 1 are placed above one another, only the edges 3, 3 face one another, which greatly minimizes the mutual radiations between these same housings 1, 1 and optimizes the view factors of each of the heating devices 1, 1.

(15) Furthermore, it has been determined that preferably, the housing 1, 1 has, in cross-section, a lens shape (lenticular shape) whereof the main curve radius R is such that the ratio between this main curve radius R and the pitch P defined between two successive housings 1, 1 is greater than 0.5.

(16) FIG. 6 is a diagrammatic illustration of another heating device according to an aspect of the invention having a lenticular shape inasmuch as the housing 1 has front walls each made up of three facets f.sub.1, f.sub.1, f.sub.1/f.sub.2, f.sub.2, f.sub.2, these walls coming together such that the housing has, in cross-section, a lenticular shape according to the invention having a chord C. More particularly, the front walls come together at each of the ends of the chord C of the housing 1 as shown in FIG. 6, forming an edge (3, 3) in that location. This makes it possible to significantly minimize the mutual radiations between housings and optimize the view factors of the heating device according to the invention. Of course, the heating device shown in FIG. 6 is only an illustration, and another heating device could have a high number of facets globally forming a front wall with a lenticular shape in cross-section.

EXAMPLES

Example 1: Comparison of the Power Per Cubic Meter of Volume of the Combustion Space for Different Types of Radiant Elements

(17) Comparisons have been done in order to determine the power per cubic meter of volume and square meter of flame passage section of a heating device of the present disclosure relative to the traditional radiant tubes described above, as well as relative to the radiant cartridge described in document EP 1,203,921. The results obtained are shown in the table below.

(18) TABLE-US-00001 Shape Combustion space Surface of the Burner Diameter/ Sec- Vol- power Power radiant power.sup.1 Dimension tion ume density density element [kW] [mm] [m.sup.2] [m.sup.3] [kW/m.sup.2] [kW/m.sup.3] 4 strands 174 203 0.0324 0.243 5,370 716 (W) 3 strands 140 247 0.0479 0.203 2,923 690 (double P) Cartridge 130 104 740 0.0770 0.139 1,690 935 EP 1,203,921 Lenticular 174 .sup.350.sup.2 0.0962 0.598 1,808 290 .sup.1connected power .sup.2equivalent diameter at the center of the lenticular housing

(19) As one can see, with the housing having a biconvex lenticular shape in its cross-section, the power per cubic meter of volume of the combustion area is significantly reduced relative to that observed with the radiant tubes and the radiant cartridge of the state of the art. This results in a significant improvement to the homogeneity of the temperature of the flame, and therefore of the radiating walls. Heating by significantly more homogenous radiation is thus obtained with a heating device disclosed herein.

Example 2: Comparisons of the View Factor Values for Radiant Housings with a Lenticular Shape and an Elliptical Shape

(20) Comparisons have been done in order to determine the view factor values for radiant housings with a lenticular shape or an elliptical shape having either the same perimeter or the same surface area. In order to perform these comparisons, in each of the housings, the distance (pitch) between two lenticular housings or between two successive elliptical housings has been set at 1444 mm (see table below).

(21) As mentioned above, to be able to compare the computed view factor values, the following were considered:

(22) an elliptical radiant housing whereof the perimeter, in cross-section, is identical to that of a given lenticular housing, and

(23) an elliptical radiant housing whereof the surface area, in cross-section, is identical to that of a given lenticular housing.

(24) The view factor values were computed using the crossed strings method well known by those skilled in the art.

(25) The table below shows the results obtained by computation:

(26) TABLE-US-00002 Elliptical radiant housing: Elliptical radiant housing: surface area, in cross- perimeter, in cross-section, section, identical to that of identical to that of the the lenticular radiant Lenticular radiant housing lenticular radiant housing housing Sagitta: 177 mm Small half-axis: 177 mm Small half-axis: 177 mm Cord: 1303 mm Large half-axis: 636.7 mm Large half-axis: 561 mm Vertical (pitch): 1440 mm Vertical (pitch): 1440 mm Vertical (pitch): 1440 mm Surface area: 312,001 mm.sup.2 Surface area: 354,023 mm.sup.2 Surface area: 312,001 mm.sup.2 Half-perimeter: 1366.2 mm Half-perimeter: 1366.2 mm Half-perimeter: 1239.3 mm Housing-housing view Housing-housing view Housing-housing view factor: 0.0384 factor: 0.0478 factor: 0.0419

(27) As can be seen from these comparisons, for a same distance between successive radiant housings (1440 mm) having a same perimeter (2732.4 mm) or a same surface area (312,001 mm.sup.2), a lower view factor value between successive radiant housings (0.0384) is observed for radiant housings with a lenticular shape according to an aspect of the invention compared to elliptical radiant housings (view factor of 0.0478 for a same perimeter as that of the lenticular housing and view factor of 0.0419 for a same surface area as that of the lenticular housing).

(28) An optimized view (shape) factor is therefore obtained with a heating device according to one or more embodiments of the invention, which allows a significant reduction in the mutual radiations between successive housings. Consequently, with a lenticular radiant housing, the view factor between successive radiant elements (radiant housings) is optimized when that view factor should indeed be minimized, i.e., when the total heat flow emitted from a surface (S.sub.1) of a first radiant housing and arriving on a surface (S.sub.2) of a second radiant housing should be minimized.

(29) It is clearly understood that the present invention is in no way limited to the embodiments described above, and that changes may be made thereto without going beyond the scope of the appended claims.