US2790435A - High capacity fluid heater - Google Patents

Description

April 30, 1957 J. A. JOHNSON HIGH CAPACITY FLUID HEATER 2 Sheets-Sheet 1 Filed July 3l. 1952 ASE Agen/s.

April 30, 1957 A. JOHNSON 2,790,435

HIGH CAPACITY` FLUID HEATER Filed July 3l, 1952 2 She ets-Sheet 2 INVENTOR.

e, Agen/s HIGH CAPACITY FL HEATER John A. Johnson, Strahord, Pa., assigner to 'h'wermalResearch and Engineering Corporation, Conshohocken, Pa., a corporation of Delaware Application July 31, 1952, Serial No. 301,819

4 Claims. (Cl. 126-109) This invention relates to a huid heater, and more particularly a high capacity fluid heater. The invention is especially useful in continuously heating a rapidly moving stream of gas, to which use, however, it is not restricted;

The usual fluid heater is a unit of considerable size in proportion to its capacity. This is particularly true of gas heaters wherein fuel is burned to elevate the temperature of a gas. Generally speaking, known typesof huid heaters are not economical with respect to rapid transfer of the combustion heat of the fuel to the huid passingY through them.

I have now designed and constructed a novel uid heater of small size and exceedingly hioh capacity. Tests have proved that a heater constructed and arranged according to the invention has a far higher rate of heat transfer than conventional theory would'indic'ate as possible. In fact, tests have shown that such apparatus effects a rate of heat -transfer in the high temperature sectionsv which is more than twice that of the expected rate. For

a given heating capacity, therefore, the burner may he made in small, compact and convenient size, and a minimum volumetric space will be required to accommodate it.

According to the invention, combustionV is substantially completed in a burner, and the combustion products, containing little radiant emissivity are projectedv b`y the burner at high velocity into the heat-exchanging. pass of the heater. At the. same time, the fluid to be heatedis moved in counterflow direction through specially arranged and proportioneduid tubes in the heat-exchanging pass.

Thus the' combustion products projected' into the heatexchanging pass by the burner move athigh velocity over lthe heat-exchanging surfaces and give up theirheat byconvection rather than radiation. The aggregate cross sections of the fluid tubes and of the heat-exchanging pass of the heater may be varied to give optimum results.

The invention is shown by way of illustration in the accompanying drawings, wherein- Fig. 1 is a longitudinal mid-section through a heater constructed and arranged according to the invention;

Fig'. 2 is a cross-section of the heater taken on theV line II-H of Fig. l; and

Fig. 3is a longitudinal mid-section through a variant form of heater constructed and arranged accordingto the invention.

In the drawings, there is shown a high capacity fluid heater 101 comprising an inner cylinde-r 11" and a coaxial cylinder`12` of larger diameter surrounding the inner cylinder 11'. The heater 10 is here shown as supportedfin vertical position by a'suitable frame 13. A burner 14 extends into the upper end of the inner cylinder 11`for injectingftherein the products of combustion.

The burner ldmay be.of any type which' willemit at high velocity they productsV of substantially complete combustion. Th'eburner is preferably a'iiuid fuel-fair burner; and-it has beenfound-'advantageous to employ aburher of the type disclosed in my Patent No. 2,701,608, granted" 2,790,435 Patented Apr. 30, 1957 raice February. 8, 1955, for Burnen Other types of ,burner which will eifect substantially the same result may, of course, be vused.

. The upper-end of the inner cylinder 11fis closed around the burner. 14, and the lower end of the cylinder 11 open. The lower `end-of the coaxial outer cylinder 12l is closed (in a manner later to be described)'so that a heatexchanging pass is provided through the vinner cylinder 11; and the annular space between the cylinders 11 and 12;'` Viewed otherwise, the inner cylinder. may comprise a first heat-exchanging pass. and the Space between the inner and outer cylinders may comprisera. second heatexchanging pass surrounding the first heat-exchanging pass. The upper end ofthe larger cylinder 12 is open and a chamberrlS surrounds this open end andY has1a flanged opening 16 for exit of the combustion gases to a hue or stack. Accordingly, the highly heatedcombustion products fromthe burner 14 move at high velocity through the inner cylinder 11, and then reverse direction and move opposit'elyythrough the space between the cylinders'to the chamber 155- at the burner end of the cylinder 12,- where they leave theheater through the opening 16.l

The uid to be heated enters the heater 10 through diametrically opposed supply pipes 17, 17, thereby avoidingunsymmetrical thermal distortion of the heater. TheI fluid passes from the pipes 17, 1f7 A hito-arl' intake manifold` 18. From the intake manifold; theV flid moves through a* number of tubes disposedy in the second heat-y exchang'in'g' pass 'and thence through a nurb'r df' tuliesy disposed' in the first hea`t-eir'changing pass; These' tuhesl may b'e header-connected or unitary according to the defsi'gn of the heater; and the uid receives its initial heat from' the' combustion gases in the" second heat-e'iichanging pass and its final heat from the combustion gasesN in the'y first heat-exchanging pass.

Y inthe' heater illustrated in Figs. 1 and Z-'thefluid which' is beingheated moves through a number of helical fluid tubes` 19 which are disposed in the second heat-exchanging pass-between the inner cylinder 11 andthe larger coaxiallcylinde-r 12. Thusl the huid` to' be heated receives its initial heat from the combustion gases passing through the second heating pass;

The -far endsv of the helical tubes arein communication withthe endsV of a. plurality'v ofV` straight fluid tub`es120 within theinner cylinder 11. It is-preferred` toA arrange the straight tubes 20 in a ring close torth'e longitudinalV wall` of the-inner cylinder, so`thatthe--ring so' formedv is coaxial withthecylinder 11. Thusithe huid-being'heated receives its hnal heat from the combustion gases passing through the innercyhnder 11, orin the first heat-exchanging pass.` Means'is provided'for receiving the heated huid from the discharge ends of theV straight-tubesz 20,' this-means being here shown as an outlet manifold 21 surrounding the burner 14.- Diametrically-opposite dis charge connections 22, 22 carryv the heated fluid 'from"th'e outlet manifold 21 and avoid unsymmetrical heating'at the manifold and consequent distortion of the'apparatus. Thedischarge connections 22, 22 are connected external-1 ly` of the apparatus toa conduit (not shown) which carries theheated uid `to-a point ofuse.

In theY construction described, the innercylinder 11r .and the larger outer cylinder 12-V are free to expand ,andl contract. independently, because they are independentlyy supported'by the frame 13 at one end of each, and each is` unconnected to the other at its opposite end. The-disn charge ends of the helical fluid tubes 19 and the intake end-s of the straight huid tubes 20 are fitted into 4a compositeheader 23 which closes the lower'endlof the larger cylinderA 12. The header 23 is` sl'idable in the largerf cylinder in conformity with expansion and contraction of thefstraightfluid ytubes Ztl. SuchA sliding ofthe header 2,3 also compensates nvpart for expansioiran'd lcontractionl .3 of the helical tubes 19, the helical form of which makes possible differential thermal expansion and contraction with respect to that of the straight tubes.

The composite header 23 comprises an annular chamber 24, the outside circular wall of whi-ch fits closely but slidably within the lower end of the'larger cylinder 12 beyond the open end of the inner cylinder 11. Closely fitted within the cylindrical space defined by the inner cylindrical wall of the annular chamber 24 is a shallow drum 2S'. When the annular chamber 24 and the shallow drum 25 are in position in the lower end of the larger cylinder 12, their inner end walls are substantially coplanar and close the lower end of the larger cylinder 12. The helical fluid tubes 19 have their discharge ends fitted into the inner end wall of the annular chamber 24 into which they discharge. Furthermore, the'intake ends of the straight fluid tubes 20 are fitted into the inner end wall of the shallow drum 25. Pins 26, welded or otherwise fixed in the outer plane wall of the annular chamber 24, extend through openings in an annular plate 27 bolted to a part of the frame 13 below the header and permit longitudinal expansion While preventing the header from turning as the helical tubes 19 expand and contract.

In order .that the fluid which is being heated may pass from the annular chamber 24 to the shall-ow drum 25, a plurality of large elbows 28 are fixed, as by welding, in the lower part of the inner cylindrical wall of the annular chamber 24, and extend through the lower plane wall of the shallow drum 25.

A target 29 of suitable refractory material is conveniently fixed externally to the inner plane wall of the shallow drum 25. The target 29 serves to protect the shallow drum from the direct action of the high velocity, highly heated combustion'products, 'and also serves to deflect these products from the open end of the cylinder 11 toward the annular passage between the cylinders 11 and 12.

In operating the heater 10, the burner injects into the end of the cylinder 11 the products of substantially complete combustion. The combustion products leave the burner at Ia very high velocity and also pass through the cylinder 11 at high velocity. Leaving the lower end of the cylinder 11, the combustion gases travel reversely through the space between the cylinders 11 and 12 at even greater velocity than that in the inner cylinder 11, the flow area of the second heat-exchanging pass being lreduced-in one test construction by over l2 percent. Thus, the quantitative `rate vof heat delivery per unit of temperature difference is at least maintained. It is to be noted that effective heat exchange at such relatively high velocity results from the fact that substantially no radiance is present in the combustion gases, and that convection heat transfer is largely relied upon. Furthermore, by employing convection heat transfer, it is possible to add such heat to the fluid` being heated at an exceedingly rapid and controlled rate. Thus, for a given capacity, a far smaller heater may be employed than would be the easewere radiant heat employed primarily.

lIn order to increase the rate of heat transfer in the `second heat-exchanging pass, the unrestricted flowarea of the second pass is made smaller `than that of the Vfirst pass. In one embodiment of the invention which has been constructed and tested, the unrestricted flow area of the second pass was made 87.8% of that of the first pass.

Because of the increased velocity of the substantially non-radiant combustion products through the second heating vtransfer pass greater heat transfer occurs in this pass than would otherwise be the case.

The fluid to be heated is also moved through the heater at high velocity. It has been found possible and advantageous to pass the fluid to be heated through the apparatusat a speed of 150 F. P. S. and higher. In one test installation rthe speed of the fluid through the helicaltubes 19 was 233 F. P. S. and through the straight tubes l20 was 296 F. P. S. Furthermore, it has been found ad vantageous to employ a higher speed of fluid travel in that part of the heater where the products of combustion are at their highest temperature and a lesser speed of fluid travel where the heat exchange takes place at lower temperature. It may be here noted that in the test installation referred to 11 helical tubes of 5s diameter and 32 straight tubes of 1/2" diameter were employed. It was found that in this heater 60% of the heat added to the gas 4being heated was transferred thereto in the helical tubes 19.

In the embodiment of the invention which is illustrated in Fig. 3, a gas burner 14a is shown extending into the upper end of the inner cylinder 11. Here the straight tubes 20 are not connected to helical tubes through a header, but for simplicity and economy, are directly connected to straight fluid tubes 19a which are disposed in the second heat-exchanging pass between the inner cylinder 11 and the larger coaxial cylinder 12. As here `shown the straight tubes 20 and the tubes 19a in the second heat-exchanging pass are integral, forming a plurality of U-tubes. However, integral construction is not necessarily employed.

The straight tubes 10 pass through an annular ceramic spacing plate 30 at the lower end of the inner cylinder 11, which serves to hold the tubes in proper horizontal circumferential position. A large central opening 31 in the plate 30 serves to provide ample space for passage of the combustion products.

Bafllcs 32, extending through the insulating lining of the larger cylinder 12 and into the second heat-exchanging pass between the cylinders, suitably direct the combustion products in their contact with the fluid tubes 19a. This insulating lining is carried downwardly into the bottom of the larger cylinder 12 as shown at 33 in Fig. 3, and is formed to direct the combustion products passing through the central opening 31 in the ceramic spacing plate outwardly and reversely into the second heat-exchanging pass.

The forms of the invention here described and illustrated are presented merely as examples of how the invention may be applied. Other forms, embodiments and applications of the invention, coming within the proper scope of the appended claims, will, of course, suggest themselves to those skilled in the fluid heating art.

I claim:

1, A high capacity fluid heater of relatively small size for rapidly heating by convective heat exchange a fluid continuously passing therethrough, said heater comprising: a first heat-exchanging pass; a second heat-exchanging pass surrounding said first heat-exchanging pass; and a burner for emitting at high velocity the highly heated products of substantially complete combustion positioned to inject such products into said first heat-exchanging pass; in combination with a plurality of fluid conveying tubes helically positioned in said second pass for initially conducting therethrough in a direction counter to that of the combustion products the fluid to be heated in said heater; a plurality of straight parallel fluid conveying tubes disposed within said first pass equi-distantly about the axis of said burner for conducting the fluid heated in said second pass through said first pass in a direction counter to that of the combustion products in said first pass to give such fluid additional heat, the flow area for the products of combustion in said second pass being less than the flow area for the products of combustion in said first heat-exchanging pass; and a header connecting the discharge ends of said helically positioned tubes with the intake ends of said straight tubes; whereby the heat exchange between the combustion products and the'llud in said tubes is gradual and progressive from the entrance of such fluid into the heater to its withdrawal therefrom and is effected predominantly by convective heat.

2. Apparatus in accordance with claim 1 wherein said header comprises an outer enclosed annular cylinder positioned adjacent one end of said second heat-exchanging pass in uid communication with said helical tubes and an inner enclosed drum positioned centrally of said outer cylinder in uid communication with said straight tubes, means dening at least one enclosed passageway providing uid communication between said outer cylinder and said inner drum, said outer cylinder and said inner drum being supported solely by said helical and straight tubes, and means on said outer cylinder operable to prevent rotation of said outer cylinder -relative to said uid heater.

3. A high capacity uid heater of relatively small size forrapidly heating by convective heat exchange a uid continuously passing therethrough, said heater comprising: a rst heat-exchanging pass; a second heat-exchanging pass surrounding said rst heat-exchanging pass; a burner for emitting at high velocity the highly heated products of substantially complete combustion positioned to inject such products into said first heat-exchanging pass; and a plurality of fluid conveying tubes positioned in said second pass for initially conducting therethrough in a direction counter to that of the combustion products the fluid to be heated in said heater; in combination with a plurality of straight uid tubes conveying tubes extending through said rst pass and connected with said first-named tubes for conducting the uid heated in said second pass through said first pass in a direction counter to that of the combustion products in said iirst pass to give such uid additional heat; an intake manifold adjacent said burner connecting the ends of all of said tubes in said second pass for supplying thereto the uid to be heated; a header connecting the opposite ends of said last-named tubes with the plurality of straight tubes;

and a discharge manifold adjacent said burner connect ing the opposite ends of said straight tubes; whereby the heat exchange between the combustion products of the tluid in said tubes is gradual and progressive from the .entrance of such fluid into the heater to its withdrawal therefrom and is effected predominantly by convective heat, and whereby entrance and exit of the products of combustion and of the fluid being heated are positioned adjacent one another in said heater for convenient control and maintenance.

4. A method of convectively heating uid comprising passing the products of substantially complete combustion at high velocity through a first heat-exchanging pass, thence passing such products at higher velocity through a surrounding second heat-exchanging pass, passing the fluid to be heated rst through the second heat-exchanging pass in a direction counter to that of the combustion products therein, and then passing such uid through the first heatexchanging pass in a direction counter to that of the combustion products therein, the velocity of the uid undergoing heating being greater than 200 feet per second in said first heat-exchanging pass, and substantially 27 percent less in said second heat-exchanging pass.

References Cited in the le of this patent UNITED STATES PATENTS 106,392 Morris Aug. 16, 1870 1,841,230 Vuia et al Jan. 12, 1932 2,037,493 Biersack et al. Apr. 14, 1936 2,086,647 Sterrick July 13, 1937 2,174,663 Keller Oct. 3, 1939 2,223,856 Price Dec. 3, 1940 2,224,544 Keller Dec. 10, 1940 2,505,696 Villager Apr. 25, 1950 2,621,635 Joosten Dec. 16, 1952,

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