US3305011A

US3305011A - Radiant panel for two media with offset return bends

Info

Publication number: US3305011A
Application number: US536918A
Authority: US
Inventors: Jr Horace L Smith
Original assignee: Hupp Corp
Current assignee: Hupp Corp
Priority date: 1963-11-14
Filing date: 1966-03-23
Publication date: 1967-02-21
Anticipated expiration: 1984-02-21

Description

Feb. 21, 1967 H. L. SMITH, JR

RADIANT PANEL FOR TWO MEDIA WITH OFFSET RETURN BENDS Original Filed Nov. 14, 1963 4 Sheets-Sheet l 750F 655F 576F 533F INVENTOR 110M015 L. SMITH JR.

M ATT%NEYS BY- WWW Feb. 21, 1967 H. L. SMITH, JR 3,305,011

RADIANT PANEL FOR TWO MEDIA WITH OFFSET RETURN BENDS Original Filed Nov. 14, 1963 4 Sheets-Sheet 2 INVENTOR HORACE L. SMITH JR Feb. 21, 1967 H. L. SMITH, JR 3,305,011

RADIANT PANEL FOR TWO MEDIA W ITH OFFSET RETURN BENDS Original Filed Nov. 14, 1963 4 Sheets-Sheet 5 INVENTOR HORACE L. SMITH JR ATTORzEYS Feb. 21, 1967 H. 1.. SMITH, JR

RADIANT PANEL FOR TWO MEDIA WITH OFFSET RETURN BENDS 4 Sheets-Sheet 4 Original Filed Nov. 14, 1963 INVENTOR HORACE LSMI TH JR.

ATTONEYS United States Patent WITH This application is a division of United States application Number 323,848 filed November 14, 1963, now Patent No. 3,262,494 granted July 26, 1966, for Heat Exchangers.

This invention relates to heat exchangers and, more particularly, to heat exchange units of the tubular type and to systems employing such units.

Tubular heat exchangers of various kinds are well known. One kind of tubular heat exchanger (hereinafter referred to by the appellation radiator) consists of a planar array of intercomrnunicating, parallel flow passages for-med, for example, by metal tubes. Hot water or steam is circulated through the tubes, heating them to a temperature at which the tubes will emit substantial quantities of radiant energy.

Such radiators are used for many different purposes such as, for example, to dry continuously moving webs of sheet material. In this and other applications, however, currently available radiators have a number of serious limitations. Because of different physical limitations they can only be made to span relatively short distance; and they are, therefore, not suitable for installations in which heating of a large area is required as in a large paper manufacturing machine, for example. Another disadvantage of currently available radiators is that the cross-sectional area of the flow passages is relatively small, and the volume of liquid that can be circulated through the now available radiators per unit of time is therefore quite limited. Consequently, the radiant energy output of currently available radiators is not sufficient for many applications.

A further drawback of currently available radiators is that the materials of which they are fabricated are relatively inefiicient emitters of radiant energy. For example, rolled sheet steel, a common radiator material, has an emissivity coefficient ranging from 0.65 to only 0.82 (a perfect emitter has an emissivity coeificient of 1.0). Because of their inefficiency as emitters of radiant energy, also, currently available radiators are unsuitable for many applications.

Another drawback of currently available radiators is that they emit radiant energy in a non-uniform pattern because there are no emitting surfaces between the radiator tubes. Uneven emission patterns are particularly disadvantageous in many radiator applications. For example, in material drying applications the non-uniform emission pattern may result in streaking of the material.

A further drawback of currently available radiators is that they are suitable only for relatively low temperature applications. Water, the most commonly employed heat transfer fluid, has a boiling point of only 212 F. Steam has also been employed as the circulating heat transfer medium but it too has drawbacks. As the steam temperature is increased above 212 F., its pressure rapidly increases to the .point where, for both economic and design considerations, it is not feasible to fabricate a radiator which is sufficiently strong to withstand the pressure of the steam circulated through it. In addition, provision must be made to continuously drain condensate from the 'ice radiator. This is often difficult, especially where the radiator has a curved or irregular configuration.

It is one object of the present invention to provide novel, improved radiators in which the foregoing disadvantages of the prior art are not present.

In general, the novel radiators of the present invention, by which the foregoing object is accomplished, include a novel planar array of plural, internested, sinuous tubes providing independent flow passages through which a fluid heat transfer medium is caused to flow in counterfiow relationship. These novel radiators can readily be made in any desired size and can be arranged to accommodate substantially higher volume rates of flow than currently available radiators of comparable size. Consequently, the radiators of the present invention maybe made larger and may be designed to produce a greater heat energy output than the radiators heretofore available.

The radiant surfaces of the novel radiators of the present invention are preferably coated with a highly emis sive substance, preferably a crystalline, crypto-crystalline or amorphous ceraamic such as very thin fused glass frits, preferably of the order of 0.003 to 0.007 inch thick. Such coatings inherently have low thermal conductivity, but, in my preferred thickness range, I have discovered that they have negligible temperature gradients through the coatlugs and emissivity coefiicients very close to 1.0 and are therefore virtually perfect radiators. In this manner, the efficiency of the radiators of the present invention can be increased well beyond the maximum efl iciencies attainable in presently available radiators.

Another novel feature of the present invention is the provision of conductive webs between and connected to adjacent tube runs in the radiators. These webs are radiation emitters and greatly increase the area of the radiant surfaces of the radiators of the present invent-ion over that of a currently available radiator of the same size.

By properly configuring these webs a substantially uniform temperature can be maintained across the entire radiant face of a radiator constructed in accordance with the principles of the present invention. These radiators, therefore, emit radiant energy in a substantially uniform pattern and at a uniform intensity, eliminating the problems arising from the non-uniform emission of radiant energy by conventional radiators.

These benefits are obtained to a quite appreciable extent by using webs having a uniform cross section. They may be achieved to an even greater extent, however, by using a web with a tapered cross section; i.e., a section which is narrower at its midpoint than at the edges where the web is joined to the tubes. By employing webs of tapered section, the ratio of emitted radiant energy to weight of plate is increased over that obtained from a web of uniform section. Consequently, for a given amount of radiated energy, a radiator utilizing tapered webs may be made lighter than one using uniformly sectioned Webs. Conversely, by employing tapered webs, a radiator having a materially greater radiant heat output than a radiator of equal weight with uniformly sectioned webs can be provided. In sum, the use of tapered webs beneficially increases the heat-output radiator weight ratio of the radiators provided by the present invention.

As discussed above, one of the advantages of the present invention is that its principles may be employed to fabricate very large radiators. Another novel feature of the present invention resides in the employment, in large radiators of the type described above, of conductive webs having T cross sectional configurations. By using such webs, even very large radiators may be made self-supporting, eliminating the need for intermediate radiator supports and for any stiffeners other than the conductive webs. Simpler and less expensive installation are two exemplary benefits that therefore result from the use of these novel conductive webs.

Another advantage of the present invention is that higher radiator temperatures may be achieved than has heretofore been possible. As a result, heat output is increased and the time required for drying and other heat treating steps may be materially shortened, increasing the speed and thereby lowering the cost of many processes. This highly desirable result is achieved by employing a liquid having an extremely high boiling point as the circulating heat transfer medium rather than water or steam as in present radiator systems. In addition, as the heat transfer medium always remains in the liquid state, none of the problems attending the use of steam as a heat transfer medium are encountered. Moreover, system components designed to withstand lower pressures and therefore much less expensive than the components employed in the lower temperature prior art steam heated systems may be employed since the system only need be pressurized to the extent necessary to circulate the liquid through the system.

In many processes involving the heating of sheets or webs of material, it is essential that the sheet or web be uniformly heated across its entire width. In heating such materials with radiators of the type disclosed by the present invention, the radiator is normally spaced from and disposed parallel to the sheet or web being heated. It will be apparent that, if the surface being heated and the radiator are the same width, the edges of the sheet receive less heat energy than areas toward the center of the sheet because some of the energy from the radiator will be directed beyond the edges of the surface being heated.

In the conventional installation, this variation in heat distribution is avoided by making the radiators substantially wider than the surface being heated so that there will be an angle of not greater than 45 degrees between the edge of the radiant surface of the radiator and the apposed edge of the surface being heated. The necessity of making the radiators wider than the surface being heated increases their initial cost and also their operational cost since more of the heat transfer medium must be circulated through them than would be necessary if they were the same width as the surface being heated.

I have found that the necessity of making the radiator Wider than the surface to be heated can be avoided by employing reflectors on the edges of the radiators to refleet the energy emitted therefrom back to the surface being heated. This substantially reduces the size of the radiator required, lowering both its initial and operating costs.

The principles of the present invention may also be utilized to advantage in heat exchangers employed to absorb rather than radiate heat. For example, the principles of the present invention may be eh'icaciously employed to provide a more efficient tube wall for the radiant sections of steam generating and similar fluid heating units.

As discussed above, the tubular heat exchangers of the present invention, due to the combined use of an emissive coating and conductive webs, are highly efficient emitters of radiant energy. Bodies that are good emitters are equally good absorbers of radiation, and can readily be shown that their absorptivities are equal to their emissivities. Therefore, heat exchangers employing the novel combination of conductive web and emissive coating discussed above are highly effective absorbers of radiations and may be advantageously employed in circumstances where absorption of radiant energy is required.

Other objects of the present invention include:

(1) The provision of novel, improved radiators which may be fabricated in sizes suiting them for distributing radiant energy over larger areas than has heretofore been possible;

(2) The provision of novel, improved radiators which are able to accommodate higher volume rates of flow of heat transfer fluid than radiators currently available and which have a greater radiant heat output per unit area of radiant surface than currently available radiators;

(3) The provision of novel, improved radiators having radiant surfaces that are more eflicien-t emitters of radiant energy than the radiant surfaces of the radiators heretofore available;

(4) The provision of novel, improved radiators which may be fabricated in such a manner that they will emit a substantially uniform pattern of radiation over their entire radiant surface;

(5) The provision of novel, improved radiators which have radiant surfaces of substantially greater area than heretofore available radiators of comparable size;

(6) The provision of novel, improved radiators in accordance with the foregoing objects which are inexpensively manufactured and which have a long useful life;

(7) The provision of novel, improved radiant heating installations employing a circulating liquid heat transfer medium and in which the radiators may be heated to higher temperatures than has heretofore been possible in systems of this type;

(8) The provision of novel, improved radiant heating installations having a circulating heat transfer medium which always remains in the liquid state;

(9) The provision of novel, improved radiators for surface heating applications which will distribute heat evenly across the entire surface being heated and which are, nevertheless, substantially no wider than the surface; and

10) The provision of novel, improved radiators which are self-supporting, even in very large sizes, thus eliminating any need for stiffeners or intermediate supports.

Other objects and further novel features of the present invention will become more fully apparent from the appended claims and as the ensuing detailed description and discussion proceeds in conjunction with the accompanying drawing, in which:

FIGURE 1 is a diagrammatic illustration of a novel heating system employing radiators of the type provided by the present invention;

FIGURE 2 is a front elevation of one form of radiator constructed in accordance with the principles of the present invention;

FIGURE 3 is a top plan view of the radiator of FIGURE 2;

FIGURE 4 is a left-hand end view of the radiator of FIGURE 2;

FIGURE 5 is a section through the radiator of FIG- URE 2, taken substantially along line 55 of the latter figure with insulation added to one side of the radiator.

FIGURE 6 is a figure showing the temperature distribution across a web having a tapered section;

FIGURE 7 is a chart of the temperature distribution across the web of FIGURE 6;

FIGURE 8 is a partial front elevation of a second form of radiator constructed in accordance with the principles of the present invention;

FIGURE 9 is a top plan view of the radiator of FIGURE 8;

FIGURE 10 is a section through the radiator of FIG- 1IqJRE 8, taken substantially along line 1010 of the latter gure;

FIGURE 11 is a partial front elevation of a third form of radiator constructed in accordance with the principles of the present invention;

FIGURE 12 is a top plan view of the radiator of FIGURE 11;

FIGURE 13 is a section through the radiator of FIG- URE 11, taken substantially along line 12-12 of the latter figure;

FIGURE 14 is a front elevation of another form of the present invention which may be made self-supporting, even in very large sizes;

FIGURE is a section through the radiator of FIG- URE 14, taken substantially along lines 1515 of the latter figure;

FIGURE 16' is a view similar to FIGURE 15 of a radiator of the type illustrated in FIGURE 14, but employing a modified form of conductive web; and

FIGURE 17 is a view similar to FIGURE 16 of a radiator of the type shown in FIGURE 14, but employing yet another form of conductive web.

Referring now to FIGURE 1 of the drawing, heating system 20 includes a fluid heating unit 22, a novel radiator 24 constructed in accordance with the principles of the present invention, a closed system of flow conduits for circulating a heat transfer medium through the system, and a pump 26 for effecting flow of the heat transfer fluid through the system.

One of the novel features of the present invention resides in employing a high boiling point hydrocarbon liquid or a eutectic salt mixture as the circulating medium, permitting the medium to be circulated at extremely high temperatures in liquid form. Consequently, the heat transfer medium may be heated to very high temperatures and yet the heating system components need be designed to withstand only very low pressures.

The preferred heat transfer liquids for applications of the present invention in which the radiators are intended to operate at different temperatures include chlorinated biphenyls, polyphenyl alkyls, aryloryoxysilanes, and eutectic salts described in detail in parent application No. 323,848.

Referring again to FIGURE 1, heating unit 22 includes sinuous heating tubes 28 (only one of which is shown) through which the circulating medium flows and over which hot gases generated by combustion units 30 pass. Heating tubes 28 and one or more combustion units 30 are housed in an outer shell 32 which is preferably lined with an appropriate refractory (not shown) to radiate heat to heating tubes 28. The combustion units 30 may be either gas or oil burners or, if heating unit 22 is of larger capacity, may be coal fired.

The outlets of heating tubes 28 are connected to the main supply conduit 34 through which the heated circulating medium flows to radiator 24. From radiator 24, the circulating heat transfer medium is returned to heating unit 22 through main return conduit 36. In the illustrated diagrammatic figure, circulating pump 26 is interposed in return conduit 36. This location is not critical, but is merely exemplary of several'possible locations for the circulating pump.

The above-described portion of the heating system is not, in itself, claimed to be novel; and an elaborate description of its components is therefore not deemed necessary. One suitable heating and circulating system is that shown in copending application No. 237,817, filed November 15, 1962, by Horace L. Smith, I r. for High Temperature Heating Apparatus (now Patent No. 3,236,292) to which reference may be had if deemed necessary for an understanding of the present invention.

The primary novelty of the present invention resides, in one aspect of the invention, in the novel radiator units which it provides and in their employment in heating systems of the general type described above.

Referring next to FIGURES 2-4 of the drawing, radiator 24 includes two sinuous,

internested tube assemblies

38 and 40 providing labyrinthine flow paths for the heat transfer medium circulated through heating system 20 by pump 26. Tube assembly 40 is formed from a single tube bent to form parallel, spaced, side-by-side straight runs 42 connected, alternately, by end bends 44 at the left-hand end of the radiator and end bends 46 at the radiators right-hand end. Tube assembly 38, like tube assembly 40, is formed from a single tube and consists of straight runs 48 interconnected by end bends 50 at the left-hand end of the radiator and end bends 52 at the radiators right-hand end. As is best shown in FIGURE 4, the end bends 44 and 46 of tube assembly 40 are also bent outwardly to one side of the radiator and the end bends 50 and 52 of tube assembly 38 are similarly displaced toward the other side of the radiator, permitting

tube assemblies

38 and 40 to be internested as shown in FIGURE 4 with the centerlines of the straight runs 42 of tube assembly 40 and the straight runs 48 of tube assembly 38 lying in the same plane.

Tube assembly 38 has an inlet 54 and an outlet 56. Tube assembly 40 has an inlet 58 and an outlet 60. As is shown by the arrows in FIGURE 2, the heat transfer medium flows in opposite directions through the two

tube assemblies

38 and 40, providing the most eflic-ient exchange of heat between the heat transfer fluid and the tube assemblies possible.

As is best shown in FIGURES 2 and 5, rectangular webs of conductive material 62, extending substantially the length of radiator 24, are interconnected between each straight run 42 of tube assembly 40 and the adjacent straight runs 48 of tube assembly 38, as by Welding. Similar webs 64 are fixed to the top of the uppermost tube run 48 and to the bottom of the lowermost tube run 42.

Conductive webs

62 and 64 increase the radiant surface of radiator 24 and, in addition help bring about a sub stantially uniform emission of radiant energy across the entire radiant surface of radiator 24, since the net effect of the internested tube assemblies, conductive webs, and the co'unterflow circulation of heat transfer fluid de-' scribed above is to maintain all of the entire radiant surfaces of radiator 24 at a substantially uniform temperature, as is explained in more detail in parent application No. 323,848. r a

Turning now to FIGURE 6, the web 68 interposed between tube runs 70 and 72 has a double tapered cross section; i.e., both sides of web 68 have a V-like configuration with the apex of the V at the midpoint of the web. In the illustrated exemplary example, web 68 is 9/ inch thick at its edges and V inch thick at its midpoint. The temperature distribution in web '68 is shown in graphical form by the curve '74 of FIGURE 7. There is a substantially more nearly linear distribution of temperature in tapered web 68 than there is in a uniformly sectioned web.

By employing double-tapered webs in the novel radiators .of the present invent-ion, the radiant heat output per unit Weight of web material is materially increased. As a result, a radiator of :a given radiant heat output may be made substantially lighter; or, conversely, for a radiator of given weight, the radiant heat output may be materially increased by employing double-tapered webs.

Another advantage of the double-tapered construction is that, for a web of given cross sectional area, a web having this construction will have a substantially larger area in contact with the tube runs to which it is joined than a uniformly sectioned Web of the same cross sectional area. Since the double-tapered construction has a larger area in contact with the tube runs, heat is conducted with greater efiiciency from the heat transfer medium flowing through the tube runs into the web, increasing the efficiency of the radiator.

The double-tapered webs illustrated in FIGURE 6 and discussed above need not necessarily be employed to obtain the foregoing advantages. These may also .be obtained by employing a non uniformly sectioned web having one flat surface like a uniformly sectioned web and one V-like surface as is employed in the doubletapered web 68 of FIGURE 6.

The degree to which the beneficial results discussed above may be obtained is dependent upon the degree of taper and upon the webs cross sectional area. A double tapered web decreasing in width from inch at its side to inch at its midpoint will not only have a more linear temperature distribution than web 68-, but there will also be a materially smaller decrease in temperature from the edges to the midpoint of the web is discussed in parent application No. 323,848.

Referring next to FIGURE 5, the efiiciency of radiator 24 is substantially increased by enhancing the emissivity of the radiators radiant surfaces identified generally by reference characters 80 and 82. This is accomplished by coating radiant surfaces 80 and 82 with a highly emissive material. The coating may be applied in any suitable manner, as by chemical means such as anodizing, or by brushing, spraying, or rolling followed by subsequent baking or heat treatment, or by electrical deposition. Examples of suitable coatings are the colored silicone varnishes, lamp black applied in an appropriate vehicle, black enamel, lacquer and shellac.

Another highly suitable coating may be applied in accordance with the ebonizin g process disclosed in United States Patent No. 2,394,899, which may be utilized to provide a smooth black oxide film or skin about 0.001 inch thick on the radiant surfaces by applying it in the manner described in parent application No. 323,848.

I have also discovered that very thin ceramic coatings such as commercially available glass frit enamels may be fused to metal surfaces to provide emissivity coefiicients up to 0.98. Such coatings are highly durable :and will withstand relatively high temperatures without substantial impairment of heat transfer through the metal. Such coatings can be separated from their base, if at all, only with great difiiculty, and will retain their integrity as highly emissive surface coatings for relatively long periods of time. Glass frit coatings may be applied in the manner described in the parent application referred to above.

For most applications, one coating is all that is necessary to give good service performance. If severe corrosive conditions are to be encountered, one or more additional coats may be applied to the radiator.

The side of the radiator opposite the radiant surfaces is preferably coated with an appropriate insulating material 84 to prevent heat losses. If radiator 24 is employed in an application in which it is disposed between two areas or articles to be heated, insulation 84 is deleted; and a high emissivity coating is applied to both sides of the radiator.

Radiators of the type provided by the present invention may be advantageously employed to dry or otherwise heat treat continuously moving webs of materials. In many such applications, it is necessary to ensure that the radiant energy emitted from the radiator is distributed uniformly across the entire Width of the web or sheet being treated. Prior heretofore, this ha been done by making the radiator substantially wider than the web or sheet being treated so that there will be an angle not greater than 45 between the plane of the radiant surface of the radiator and the line connecting the edge of the radiator and the edge of the web or sheet being treated. Substantial reductions in the width of the radiator and, threfore, in its initial and operational cost may be achieved, in accordance with the principles of the present invention, by reducing the width of the radiator to the width of the sheet or web being treated and by fixing normally extending reflectors to the edge of the radiators surface, as described in detail in parent application No. 323,848.

The radiator 24a shown in FIGURES 8-10 is in many respects similar to the radiator 24 shown in FIGURES 2-5. Therefore, insofar as components of the two radiators are identical, like reference characters have been employed to identify these components except that the components of radiator 24a are followed by the letter a.

The two tube assemblies 38a and 40a of radiator 24a are formed in the same manner so only the fabrication of tube assembly 48a will be discussed in detail, it being understood that these remarks apply also to tube assembly 40a.

Referring first to FIGURE 8, tube assembly 38a consists of straight runs 48a and end bends 5001 which are independent members and are joined as by welding. Each of the end bends 50a is made up of three elbows, 96, 98, and 100, joined to each other and to adjacent straight runs 48a of the tube assembly as by welding. As is shown in FIGURE 10, end bends 50a have substantially the same configuration as the end bends 50 in radiator 24, permitting the two tube assemblie 38a and 40a to be assembled in internested relationship with the centerlines of the straight runs 42a in the tube assembly 40a and the straight run-s 48a in tube assembly 38a located in the same plane.

The radiator 24b shown in FIGURES 1ll3 is, in many resjects, similar to the previously described embodiments. Like components have therefore been identified by like reference character followed by the letter b.

Tube assembly 381) may be substantially identical to tube assembly 38a. Tube assembly 4%, like tube assembly 40a consists of straight runs and end bends (5012), which are independent members. Each of the end bends 501: includes two elbows 102 and 184 separated by a short length of tube 106 to which one end of each of the elbows is welded to form a U-shaped member. The other ends of the two elbows are welded to the juxtaposed ends of adjacent straight runs 48b.

One advantage of radiator 24b is that all of the end bends lie to one side of the radiator face 108. This feature is advantageous when it is desired to arrange the radiator in close proximity to a surface to be heated,

for example.

The radiator 118a illustrated in FIGURES 14 and 15 is, in most respects, similar to the radiators described previously, differing mainly in the construction of the conductive webs between the adjacent legs of the sinuous tube assembly. In radiator 118a, the conductive webs 128a have a T cross sectional configuration, providing a rectangularly sectioned stem 148 "and a double-tapered arm 150. T-section members of this configuration are widely available in a variety of sizes and materials from various producers of structural shapes.

Preferably, the T-sectional webs 128a are so dimensioned that the neutral axes of the web lie in the same plane as the centerlines of the tube assembly legs 124a. Thus arranged, the section modulus of the composite tube-web assembly forming radiator 118a is the sum of the section modulus of tube assembly 122a plus that of the webs 128a.

This provides a substantially higher section modulus than is obtained by using fiat conductive web such as those shown at '62 in the embodiment of FIGURE 2 for two reasons. First, the T-sectioned web 128a has a much higher section modulus than a fiat conductive web of the same width. Second, as the section modulii of the webs and the tube legs lie in the same plane, they are additive which is not the case when a flat conductive plate is employed.

Because of the substantially increased section modulus, radiators formed in the manner just described are substantially stiffer than those of the preceding embodiments; and, consequently, radiators of very long lengths which are entirely self-supporting may be readily fabricated. This, in turn, eliminates the need for auxiliary stiifening members and intermediate supports, obviating the expense and other disadvantages of such members.

Typically, tube assembly 122a may be schedule 40 tubing having an outside diameter of 1.5 inches with legs 124a spaced 4.5 inches on center. In this case standard three inch by three inch T-sectioned members (having a section modulus of 0.74) may be employed as conductive webs. The resulting composite tube-web radiator structure will have a composite section modulus of 0.887 and a weight of 25.15 pounds per square foot.

Even greater strength per unit weight of material may be obtained by employing webs having the cross sectional configuration illustrated in FIGURES 16 and 17. The

web 152 illustrated in FIGURE 16 is of generally T-shaped cross sectional configuration, having a rectangularly sectioned stem 154 and arm 156. Web 152 also has, at the edge of stem 154 opposite arm 156, a generally rectangularly sectioned flange or bulb section 158. For a radiator of the dimensions discussed above, in which web 152 would have the same stem and arm dimensions as web 128a, bulb section 158 would typically be on the order of 2.0 inches wide and 0.5 inch thick. The section modulus of web 152 is 2.46 as compared to the 0.74 section modulus of web 128a. The modulus of the composite tube assembly-web structure is 2.67 (as compared to a modulus of 0.887 for the embodiment illustrated in FIGURES 14 and 15); and the radiator weight is 32.5 pounds per square foot.

It will be apparent from the foregoing that, by employing the web 152 of FIGURE 16, a much stiffer web can be provided at very little increase in weight. Conversely, in comparison with the embodiment of FIGURE 14, an equally stiff radiator can be provided at a lower weight by employingwebs having the cross sectional configuration of web 152.

The web 160 illustrated in FIGURE 17 is identical to that illustrated in FIGURE 16 except that the two

web arms

162 and 164 extending from the webs stem 154 are substantially wider at the outer edges 166 where they are connected to tube legs 124a by welds 168 than at their inner edges where they are integral with stem 154. This web configuration has approximately the same section modulus as the web 152 illustrated in FIGURE 16. Where maximum efliciency is desired, web 160 is preferred over web 152 since the double-tapered web portion provided by

flanges

162 and 164 permits maximum heat flow by conduction for the reasons discussed above and in parent application No. 323,848. However, this section is difiicult and expensive to roll and may be deemed inferior to web 152, which can be readily rolled, in applications where the ultimate in efliciency is not required.

For the sake of simplicity, only a single tube run has been illustrated in FIGURE 17. It will be apparent from the foregoing, however, that the T-sectioned webs illustrated in FIGURES 14-17 may equally well be employed in radiator embodiments such as those described previously in which internested tube assemblies are employed to permit counterflow circulation.

Also, as illustrated, radiator 118a has separate end bends 170 joined to tube legs 124a as by welding. It will be apparent that tube assembly 122a could equally well be formed from a single sinuous tube, if desired. Such modifications are, there-fore, to be understood as being within the scope of the present invention.

Many variations in the application of the principles of this invention to tubular heat exchangers utilized to absorb heat may be made without exceeding the scope of the invention. For example, these principles may be applied to water walls composed of straight tubes and upper and lower headers as well as to the illustrated tubular heat exchangers.

The invention may be embodied in other specific forms Without departing from the spirit or essential characteristics of thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

1. A radiant heating installation, comprising:

(a) a radiator having plural, sinuous, internested tube assemblies providing independent flow circuits, each of said tube assemblies have substantially parallel straight runs connected by end bends, the centerlines of the straight runs of the two tube assemblies being substantially coplanar and the runs of the two tubes being alternated and the end bends in one of said assemblies all lying to one side of the plane including said centerlines and the centerlines of the end bends in the other of said assemblies all lying substantially in said plane, whereby one side of said radiator is free of protruding obstructions over substantially its entire surface and is thereby adapted to be positioned in close proximity to an object thereadjacent.

(b) conductive webs between adjacent ones of said runs, each of said webs being a structural member connected to two tube runs only and subtending only a minor portion of each of the two tube runs to which it is connected, said webs being connected directly to said tube runs and extending generally the length thereof to increase the radiant surface of said radiators; and v (c) means for heating and then subsequently effecting simultaneous counterflow of a heat transfer fluid through said independent circuits.

2. The radiant heating installation as defined in claim 1, including a coating of high emissivity material on at least one side of said radiator.

3. The radiant heating installation as defined in claim 2, wherein said coating is a ceramic material fused to the radiating surfaces of said radiator.

4. The radiant heating installation as defined in claim 1, including:

(a) afluidheater;

('b) a supply line connected between said heater and the inlets of said tube assemblies;

(c) a return line communicating with the outlets from said tube assemblies and the heater; and

(d) a pump for forcing the heat transfer liquid seriatim through said heater and said tube assemblies.

5. The radiant heating installation as defined in claim 1, wherein the end bends in one of said assemblies each consist of three elbows.

6. The radiant heating installation as defined in claim 1, including:

(a) a layer of insulation on one side of said radiator;

and

(b) a coating of high emissivity material on the other side of said radiator.

7. The radiant heating installation as defined in claim 1, wherein each of said tube assemblies is a single tube.

8. The radiant heating installation as defined in claim 1, wherein the conductive webs between the tube runs have a rectangular cross section.

9. A radiant heating installation, comprising:

(a) a radiator having plural, sinuous, internested tube assemblies providing independent flow circuits, each of said tube assemblies have substantially parallel straight runs connected by end bends, the centerlines of the straight runs of the two tube assemblies being substantially coplanar and the runs of the two tubes being alternated and the end bends in one of said assemblies all lying to one side of the plane including said centerlines and the centerlines of the end bends in the other of said assemblies all lying substantially in said plane;

(b) conductive webs extending between and substantially the length of adjacent ones of said runs, said conductive webs having a tapered cross sect-ion and being thinner at their midpoints than at their edges; and

(c) means for heating and then subsequently effecting simultaneous counterflow of a heat transfer fluid through said independent circuits.

10. The radiant heating installation as defined in claim 9, wherein the cross sections of said webs are symmertical relative to the plane including the centerlines of the straight runs of the tube assemblies.

11. A radiant heating instalaltion, comprising:

(a) a radiator having plural, sinuous, internested tube assemblies providing independent flow circuits, each of said tube assemblies have substantially parallel straight runs connected by end bends, the center lines of the straight runs of the two tube assemblies being substantially coplanar and the runs of the two tubes being alternated and the end bends in one of said assemblies all lying to one side of the plane including said centerlines and the centerlines of the end bends in the other of said assemblies all lying substantially in said plane;

(b) T-sectioned conductive webs between and extending substantially the length of adjacent runs; and

(c) means for heating and then subsequently efle-cting simultaneous counterflow of a heat transfer fluid through said independent circuits.

12. The radiant heating installation, as defined in claim 9, wherein the neutral axes of said webs lie substantially in the plane of the centerlines of the straight runs of the tube assemblies.

13. The radiant heating installation as defined in claim 9, wherein said webs have a stem and flanges extending normally and in opposite directions therefrom and said flanges have tapered sections and are wider at their free edges than at the flange-stem junctures.

12 14. The radiant heating installation as defined in claim 9, wherein at least some of said webs have a stern and flanges extending normally and in opposite directions from one edge thereof and an integral bulb section at the opposite edge of said stern for increasing the section modulus of the web.

References Cited by the Examiner UNITED STATES PATENTS 754,522 3/1904 Vollrnann 165171 966,070 8/1910 Bailey 126271 2,888,228 5/1959 Jarvis 248-316 2,982,841 5/1961 MacCracken 165107 X 3,001,382 9/1961 Mills 62380 3,039,453 6/1962 Andrassy 165171 X FOREIGN PATENTS 911,068 2/1946 France.

25,068 1898 Great Britain.

ROBERT A. OLEARY, Primary Examiner.

N. R. WILSON, A, W. DAVIS, Assistant Examiners.

Claims

1. A RADIANT HEATING INSTALLATION, COMPRISING: (A) A RADIATOR HAVING PLURAL, SINUOUS, INTERNESTED TUBE ASSEMBLIES PROVIDING INDEPENDENT FLOW CIRCUITS, EACH OF SAID TUBE ASSEMBLIES HAVE SUBSTANTIALLY PARALLEL STRAIGHT RUNS CONNECTED BY END BENDS, THE CENTERLINES OF THE STRAIGHT RUNS OF THE TWO TUBE ASSEMBLIES BEING SUBSTANTIALLY COPLANAR AND THE RUNS OF THE TWO TUBES BEING ALTERNATED AND THE END BENDS IN ONE OF SAID ASSEMBLIES ALL LYING TO ONE SIDE OF THE PLANE INCLUDING SAID CENTERLINES AND THE CENTERLINES OF THE END BENDS IN THE OTHER OF SAID ASSEMBLIES ALL LYING SUBSTANTIALLY IN SAID PLANE, WHEREBY ONE SIDE OF SAID RADIATOR IS FREE OF PROTRUDING OBSTRUCTIONS OVER SUBSTANTIALLY ITS ENTIRE SURFACE AND IS THEREBY ADAPTED TO BE POSITIONED IN CLOSE PROXIMITY TO AN OBJECT THEREADJACENT. (B) CONDUCTIVE WEBS BETWEEN ADJACENT ONES OF SAID RUNS, EACH OF SAID WEBS BEING A STRUCTURAL MEMBER CONNECTED TO TWO TUBE RUNS ONLY AND SUBTENDING ONLY A MINOR PORTION OF EACH OF THE TWO TUBE RUNS TO WHICH