US2619579A - Electric air heater - Google Patents

Description

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Nov. 25, 1952 Flled May 4 1950 N0V 25, 1952 J. w. cARTlNHoUR ELECTRIC AIR HEATER 2 SHEETS--SHEET 2 Filed May 4, 1950 Gttorneg Snventor @@QMW Patented Nov. 25, i 1952 ELECTRIC AIR HEATER John W. Cartinhour, Baldwin, N. Y., assignor to Foster Wheeler Corporation, New York, N. Y., a corporation of New York Application May 4, 1950, Serial No. 159,937

Claims.

This invention relates to a heat exchanger for air or other uids and more particularly to an electric air heater.

In certain high pressure, high temperature service, utilizing large quantities of air for relatively short periods of time, for example only, the supply of air at approximately 104:0o F. and 3000 p. s. i. g. with entering -conditions at 650 F. and 3030 p. s. i. g., the heater must be capable of being placed in service at its full capacity in a matter of a few seconds and must maintain steady conditions thereafter.

This requires a heater having unique features which are objects of this invention and which may be grouped as follows.

`(1) Features enabling the exchanger to perform according to requirements;

(2) Features providing for safe operation; and

(3) Features contributing to an economic solution of the problem.

Single features do not necessarily contribute to only one of the groups and in several cases a feature contributes to all three.

The necessity for rapid starting combined with steady operating conditions is met in this invention by utilizing electric power as a source of heat. It can be made available with extreme rapidity and its rate of input can be controlled with a high degree of accuracy. Further, in order to reduce the time required to make heat available to a minimum, the heat storage capacity of the heating elements must be relatively small. This condition is satisfied by the use of high voltages and light resistive conductors. Moreover the relatively small mass of these resistive conductors alone contributes to the -economy of the structural design.

Although the primary purpose of the heating elements is to heat the air or other uid to the desired temperatures, it is important that they accomplish their function safety. Therefore, these elements must be arranged so that the danger of overheating is minimized. For this reason the heating elements utilized herein are tubular in form and arranged so that the air or other fluid to be heated iiows through them. The pressure drop through the tubular elements is sufficient to assure even distribution of flow through the various tubes, and the lcw rate per tube is high enough to provide relatively high heat transfer coeiiicients. Thus the use of small, light heating elements contributes to all three of the desirable unique features grouped hereinabove.

The tubular heating elements are enclosed in a (Cl. 21S-39) 2 A metallic shell, in a manner to be described, to provide appropriate distribution and flow of air through the elements. Since all metals lose strength at elevated temperatures, it is desirable to keep the shell temperatures as low as possible. For this reason the cool air of fluid to be heated is directed in such a way inside of the shell, by arrangements to be described, as to keep the shell at a uniformly low temperature. This reduces the cost of the shell by reducing its required thickness and, also, by eliminating the necessity for use of high-alloy materials for the shell. It also contributes to the safety of the shell or vessel by reducing thermal stresses which under the rapid starting conditions mentioned herein might eventually cause cracking of the shell and a serious operating failure. In addition, the maintenance of uniform shell temperature at gasket joints in the shell reduces the possibility of air or fluid leakage through them.

Other objects and novel features of the invention include the provision of structure adaptable for providing heat exchange between different iiuids at diiferent temperatures and also of structure adaptable for electrical heating of iiuids other than air having proper dielectric proper-' Fig. 4 is a fragmentary longitudinal section on` an enlarged scale taken along line 4-4 of Fig. 2

illustrating details of construction, and, also, Viewed in the direction of the arrows;

Fig. 5 is a fragmentary transverse section taken along line 5-5 of Fig. 4 also viewed in the direction of the arrows; and

Fig. 6 is an isometric view in diagrammatic form of the heating tube arrangement and electrical circuit involved.

Referring to the drawings, i0 denotes a hollow shell of metal or other deisrable material which is provided at its opposite ends with tubular end members i l and I2 of larger overall cross sectional dimensions than that of shell IIJ and each having two differently dimensioned internal portions lla, Hb and |2a, lZb respectively each:

diierent from that of the internal dimensions of shell in to define the respective shoulders IIc, IId and I2C, I2d. The end members II and I2 are secured respectively to the opposite ends of shell IB as by welding or the like at I3 and I4.

The inner wall of shell ID is provided with a snugly tting tubular liner |5 preferably of sheet metal. ThisV liner I5 isv optional it shell I3 is itself of metal suitable for the intended purposes. Metal closure members I6, 16a tting within the recesses IIa and |2a with sealing gaskets G abut the respective shoulders I|c and I2Cv and areY tightened against the gaskets G and secured in place as by bolts and nuts I1, I'8. External re inforcements 20, 2| are provided for the respective closure members I6, |611. and these are held securely against the latter by segmental locking rings 22, 23 tting edgewise respectively" in the annular grooves 24, 25 in portions IIa and |2a of members and I2 and bolted tothe respective reinforcementsrz, 2| by bolts-25.

A- tubular shell 28 of sheetmetalor the like having smaller cross sectionalA external dimensionsthan the inner cross sectional dimensions of'A liner l5 or inner dimension of shellV Ill is loY catedV in a centralized position Within shellV Il),Y one-endY projecting into the portion 12b ofend member I2. The shell 23- is provided atvarious` external-points withV spacing fins or lugs 29 which centralize it relativerto liner I5 and shell I0- throughout its lengthr so that shell 28 and lining l5 define an` annular space Sextending fromthe shoulder IZ-d-to the far end of shell28. where the space Sv communicates with a chamber portion C of shell I 0.

.A- transversely extending partition 30 divides the inner shell int= a tube bearing compartment D toone side ofy the. partitionl 30 anda cold air space E at its opposite side. Openings 3| in. the wallof shell 28A provide communication between spaces. S and E for purposes presently to be described.

Aninlet nozzle- 33, preferably having a lining 34;, is secu-red as bywelding or the like at 35 about an opening 36 provided in shell I0 and its lining I and communicates with the annular space S. y An outlet nozzle 31 preferably having a lining- 3&is1secured as bywelding or the like at 39 about an opening 40 communicating with space S. An inner shell or tube 4I of smaller diameter than lining 3i!Y and ldefining with it an annular space passageway H- extends from the outer end. of nozzle 3`| inwardly and is secured as by welding or the like at 42 about an opening l43l in shell 2,8 which communicates with space D 'ofA the latter. Thus all internal surfaces of the shell Ill and its ends are in surface contact withairv or uid at itsv cool enteringtemperature and the shell. I0 remains substantially atv this temperature, during use;

Transversely extending metallic tube supports 45each fitting within an annular recess of aperipheral supportingY ring 55 are positioned at spaced apart points within the shell 28, the rings 45 fitting snugly but movably the internal diameter of shell 28. The particular ring @E of the tube support 45 in closest proximity to partitionV 35 abuts an annular segmental ring ll'll secured as by lugs' il or the like to the inner lsurface of shell 28. This ring 4l serves as a limit stop. The outermost supporting ring t5 adjacent the opposite end of shell 28 is provided with longitudinally extending expansion rods 48 which fit slidably vin openings provided in guide flanges @soldered or the like to the shell 28.

Each tube support 45 has a like number of identically arranged openings 50 (Fig. 4) in each of which a tubular bushing 5| of electric insulating material is mounted. Tubes 52 of electrical resistor material, for example, nickelchromium alloy, or other equivalent electric resistor material are threaded longitudinally through axially aligned bushings 5| in the respective tube supports 45, one end of each tube 52 communicating with chamber C, and the opposite end of each tube 52 communicating with chamber D. The tube support plates 45 t rings 46,*.andthelatter it the inner surface of shell 28` and, similarly,A bushings 5I t openings 50 and tubes 52: fity bushings 5I suiciently closely to limit leakage of air from space C to space D through' spaceFt'o a very small quantity, but the nts are' not close enough to prevent relative expansion or contraction of parts.

Theends of. all resistor tubes 52 projecting into chamber C in' each horizontal row of. tubes. (Fig. 6) are electrically interconnectedY by distribu-l tors` 53- and all theA latter are electrically connectedto a bustiY which in turn is connectedby a metalconductor` 55to af terminal 56 carriedby an insulator 51 that in turn extends outwardly of theA lining I5 and shell I0 through an opening that isV sealed appropriately around its edges at 5.3. The' other ends of allr tubes 52 projecting into.- chamber Dl ineach horizontal row are electrically interconnectedY by` distributors. 59'., and the latter are electrically connected to a bus 6D Whichis, for example, grounded by connection at 6I with the shell 28v which latter is connected electrically by the weldatAZ to the shell-Mwhich is in contact with. the grounded outlet nozzle. 3l.Y

Allthe tubes 52` are thus` connected in electrical parallel andmay be suppliedfrom .a common power source P connected toV the terminal 55 andto ground. Appropriate Voltage andcurrentv controls. (not shown)r are connected in the power circuit in the usual manner. While electrical parallel connection for tubes 52 is shown, it is to be understood that the. electricaly connection of the tubes 52, also, maybe either series or series-parallel depending uponthe type of electric power available at the place of use; the requirement' being that electric currentv flow inv theA tubes will be sufficient to heat them to necessary temperatures'to produce desired heatingv of the air or other fluidi flowing through the re-f sistor' tubes 52.

Operation Electrical. power' l? is connected to the tubesy 52 as described. Air is introduced through noz.-Y zle. 33 andis rst directedto flow in space S between lining l5 and shell 28 as an. envelope of air to maintain substantially uniform temperature of` the outer shell il and its lining |5- to space'or chamber C whence it flows through each of the electrically heated tubes '52 to space or chamber D being heated in its passage through the tubes; From chamber D the heated air flows outwardly through tube I in nozzle 3?. A small portion of the cold air entering nozzle 3'3 also flows from passage S through some of the openings 3I' into space or chamber E and from the latter outwardly through others of the openings 3| and through the annular space H and rejoins the heated air owing in tube 4I through openings 'lb in the wall of the latter. The cool air in chamber E and in space I-I acts to keep the hot end of shell I0 andv outlet nozzle 3l at substantlally the same uniform temperature as shell I0.

Although the invention has been described as an air heater, it is not limited in its application to air. Any fluid having proper dielectric properties can be heated in the exchanger described. The heater constructed and operated as described embodies all features outlined at the outset of this specification. The shell 28, members 45 and partition 30 act as bailies to direct the air or iluid in proper direction as described.

Modification With slight modification, and without the use of electric heating, the device can be utilized to provide heat exchange between any cold and any hot fluid. In such case, the material of tubes 52 need not be of electric resistor material, but may be of any other metal. Electric connections to the tubes can be eliminated and the end tube supports 45 and their rings 45 provide leak proof seals at opposite ends of tubes 52 and shell 23 so that compartment or chamber F is sealed 01T from chambers C and D. An inlet nozzle and an outlet nozzle each communicating with chamber F are provided. One of the two iluids is circulated via nozzle 33 through space S, chamber C, tubes 52, chamber D and outlet nozzle 3'! as previously7 described. The other of the two uids is fed into chamber F around the external surfaces of tubes 52 in heat exchange relationship with the fluid flowing through the latter tubes and finally out through the second outlet nozzle. Relative flow of the two fluids may be in counter current direction or the same direction as desired.

While specific embodiments of the invention have been disclosed, variations in structural detail within the scope of the claims are possible and are contemplated. There is no intention therefore of limitation to the exact details shown and described.

What is claimed is:

l. Apparatus for heating air or other fluids comprising an outer elongated shell, removable cover members at opposite ends of said shell, means for securing said cover members in fluidtight relationship with the outer shell, an inner shell supported within and extending longitudinally of the outer shell, the inner shell being so dimensioned and positioned within the outer shell as to denne a iiuid flow passageway around the inner shell between the inner surface of the outer shell and the cuter surface of the inner shell, tube supports spaced from one another and spanning in a duid-tight manner the crosssectional area of the inner shell and in spaced relationship with the opposite ends of the outer shell, one of the tube supports dening one side of a fluid inlet chamber within the outer shell between one end of said outer shell and said one support, the inlet chamber being in communica-- tion with the lluid passageway, a partition spanning the cross-sectional area of the inner shell intermediate the opposite end oi the outer shell and the other tube support, thereby deiining one end of a heated uid outlet compartment between said other tube support and the partition and a cool fluid space between said opposite end of the outer shell and said partition, the cool iluid space being in communication with said fluid now passageway to receive fluid therefrom, a fluid inlet nozzle in communication with the uid flow passageway adjacent said opposite end, a fluid outlet nozzle in communication withv the outlet compartment at said opposite end, tubes carried by said supports and extending in spaced relationship with one another longitudinally through the inner shell with their opposite ends extending into the respective inlet and outlet chambers, electrical connections interconnecting all the tubes at one end to a common conductor, electrical connections interconnecting all the tubes at the other end to a second common conductor, and means for connecting the said common conductors to a source of electric power whereby said tubes may be heated electrically and whereby the fluid to be heated will be directed from the inlet nozzle through the iiuid passageway in surface contact with the inner and outer shells and into said inlet chamber, then through the tubes being heated in iiow therethrough, and into said heated fluid outlet compartment chamber and thereafter through the outlet nozzle.

2. Apparatus for heating air or other fluids comprising a cylindrically shaped outer shell, removable cover members at opposite ends of said shell, means for securing said cover members in fluid-tight relationship with the outer shell, a cylindrically shaped inner shell supported within and extending axially of the outer shell, the inner shell being of a lesser diameter than and so positioned within the outer shell as to define a fluid ilow passageway around the inner shell between the inner surface of the outer shell and the outer surface of the inner shell, tube supports spaced from one another and spanning in a huid-tight manner the cross-sectional area of the inner shell and in spaced relationship with the opposite ends of the outer shell, one of the tube supports deiining one side of a fluid inlet chamber within the outer shell between one end of said outer shell and said one support, the inlet chamber being in communication with the fluid passageway, a partition spanning the cross-sectional area of the inner shell intermediate the opposite end of the outer shell and the other tube support, thereby deiining one end of a heated iluid outlet compartment between said other tube support and the partition and a cool fluid space between said opposite end of the outer shell and said partition, the cool iluid space being in communication with said fluid now passageway to receive fluid therefrom, a fluid inlet nozzle in communication with the fluid flow passageway adjacent said opposite end, a fluid outlet nozzle in communication with the outlet compartment at said opposite end, tubes carried by said supports and extending in spaced relationship with one another longitudinally through the inner shell with their opposite ends extending into the respective inlet and outlet chambers, electrical connections interconnecting all the tubes at one end to a common conductor, electrical connections interconnecting all the tubes at the other end to a second common conductor, and means for connecting the said common conductors to a source of electric power whereby said tubes may be heated electrically and whereby the uid to be heated will be directed from the inlet nozzle through the fluid passageway in surface contact with the inner and outer shells and into said inlet chamber, then through the tubes being heated in flow therethrough, and into said heated fluid outlet compartment chamber and thereafter through the outlet nozzle.

3. Apparatus for heating air or other fluids comprising an outer elongated shell, removable cover members at opposite ends of said shell;

means for' securing saldi cover members influidtight relationship with the outer shell,v an inner shell supported within and extending' longitudinally of the outer shell, the innerl shell being so dimensioned and positioned within the outer shell as to define a iiuid flow passageway around the inner shell between the innerv surface of the outer shell and the outer surface of the inner shell, tube supports spaced from one anotherA and spanning'in a huid-tight manner the cross-sectional area of the innery shell andy in spaced relationship with'the opposite ends of the outer shell, one of the tube supports defining one side of a iluid inletvchamber within the outer shell between one end ofv said outer shell and said one support, the

inlet chamber' being in communication with the il'uld passageway, a partition spanning the crosssectional areaof the inner shell intermediate the opposite end of the outer shellV and the other tube support, thereby denning one end of a heated fluid outlet compartment between said other tube support and the partition andl a cool fluid space between said opposite end of the outer shell and said partition, the coolud space being in communication with said fluid iiow passageway to receive fluid therefrom, a. uid inlet nozzle in communication with the fluid flow passageway adjacent said opposite end, a iiuid outlet nozzle in communication with the outlet compartment at said opposite end,v said outlet nozzle oomprising an inner sleeve so dimensioned and positioned within the nozzle as to define a flow path around said sleeve between the outer periphery thereof and the nozzle, said sleeve being in communication at the inlet end thereof with the heated fluid compartment and at the outlet end withr the nozzle outlet, the flow path beingl in communication at one end thereof with said fluid passageway to receive fluid therefrom and at the opposite end with said nozzle outlet, tubes carried by said supports and extending in spaced relationship with one another longitudinally through the inner shell with their opposite ends extending into the respective inlet and outlet chambers, electricalv connections interconnecting all the tubes at one end to a common conductor, electrical connections interconnecting all the tubes at the other end to a second common conductor, and means for connecting the said common conductors to a source of electric power whereby said tubes may be heated electrically and whereby the fluid to be heated will be directed from the inlet nozzle through the fluid passageway in surface contact with the inner and outer shells and into said inlet chamber, then through the tubes being heated in flow therethrough, and into said heated fluid outlet compartment chamber and thereafter through the inner sleeve of the outlet nozzle.

4. Apparatus for heating air or other fluids comprising an outer elongated shell, removable cover members at opposite ends of said shell, means for securing said cover members in fluidtight relationship with the outer shell, an inner shell supported within and extending longitudinally of the outer shell, the inner shell being so dimensioned and positioned within the outer shell as to denne a fluid flow passageway around the inner shell between the inner surface of the outer shell and the outer surface of the inner shell, tube supports spaced from one another and spanning in a fluid-tight manner the cross-sectional area of the inner shell and in spaced relationship with the opposite ends of the outer shell, one of the. tube supports defining one side of a uid inlet chamber within the outer shell betweenV oneV end, of said outer shell and said one support, the inlet'. chamber beingl in communication with the fluid passageway, a partition spanning the crosssectional area of the inner shell intermediate the opposite end of the outer shell and the other tube support, thereby defining one end of a` heated fluid outlet compartment between said other tube support and the partition and a cool fluid space between said opposite end of the outer shell and` said partition, the cool iiuid space being inr communication with said uid flow passageway to receive iluid therefrom, a fluid inlet nozzle in communication with the iiuid flow passageway adjacent said opposite-end, a iiuid outlet nozzle in communication with the outlet compartment at` said opposite end, tubes carried' by said supportsand extending in spaced relationship with oneanother longitudinally through the inner shell with their opposite ends extending into the respective inlet and outlet chambers, electrical connections interconnecting all the tubes adjacent one end of the outer shell to a common conductor, electrical connections interconnecting all the tubes adjacent the other end of said shell to a second common conductor, means at said oneend of the outer shell and extending into said inlet chamber for connecting the common conductor at said one end to a source of electric power, and means for connecting the common conductor at said other end to the source, whereby said tubes may be heated electrically and whereby the fluid to be heated will be directed from the inlet nozzle through the fluid passageway in surface Contact with the inner and outer shells and into said inlet chamber, then through the tubes being heated in flow therethrough, and into said heated fluid outlet compartment chamber and thereafter through the outlet nozzle.

5. Apparatus for heating air or other iluids comprising a cylindrically shaped outer shell, removable cover members at opposite ends of said shell, means for securing said cover members in fluid-tight relationship with the outer shell, a cylindrically shaped inner shell supported within and extending axially of the outer shell, the inner shell being of a lesser diameter than and so positioned within the outer shell as to define a fluid flow passageway around the inner shell between the inner surface of the outer shell and the outer surface of the inner shell, tube supports spaced from one another and spanning in a fluid-tight manner the cross-sectional area of the inner shell and in spaced relationship with the opposite ends of the outer shell, one of the tube supports defining one side of a fluid inlet chamber within the outer shell between one end of said outer shell and said one support, the inlet chamber being in commiu'n'cation with the fluid passageway, a partition spanning the cross-sectional area of the inner shell intermediate the opposite end of the outer shell and the other tube support, thereby defining one end of a heated fluid outlet compartment between said other tube support and the partition and a cool fluid space between said opposite end of the outer shell and said partition, the cool iluid space being in communication with said iluid flow passageway to receive fluid therefrom, a fluid inlet nozzle in communication with the fluid now passageway adjacent said opposite end, a fluid outlet nozzle in communication with the outlet compartment: at said opposite end, said outlet nozzle comprising an inner'sleeve so dimensioned andv positioned within the 'nozzles as to define a now path around said sleeve between the outer periphery thereof and the nozzle, said sleeve being in communication at the inlet end thereof with the heated fluid compartment and at the outlet end with the nozzle outlet, the low path being in communication at one end thereof with said fluid passageway to receive fluid therefrom and at the opposite end with said nozzle outlet, tubes carried by said supports and extending in spaced relationship with one another longitudinally through the inner shell with their opposite ends extending into the respective inlet and outlet chambers, electrical connections interconnecting all the tubes adjacent one end of the outer shell to a common conductor, electrical connections interconnecting all the tubes adjacent the other end of said shell to a second common conductor, means at said one end of the outer shell and extending into said inlet chamber for connecting the common conductor at said one end to a source of electric power, and means for connecting the common conductor at said other end to the source, whereby said tubes 10 may be heated electrically and whereby the fluid to be heated will be directed from the inlet nozzle through the fluid passageway in surface contact with the inner and outer shells and into said inlet chamber, then through the tubes being heated in flow therethrough, and into said heated fluid outlet compartment chamber and thereafter through the inner sleeve of the outlet nozzle.

JOHN W. CARTINEIOUR.

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

UNITED STATES PATENTS Number Name Date 1,356,818 Hadaway Oct. 25, 1920 1,615,166 Cowles Jan. 18, 1927 1,727,584 Carleton Sept. 19, 1929 1,787,801 Swoboda et al Jan. 6, 1931 1,926,958 Peterson Sept. 12, 1933 1,985,280 Carleton Dec. 25, 1934

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