US1588629A - Method of and apparatus for transferring heat - Google Patents

Description

METHOD OF AND APPARATUS FOR TRANSFERRING HEAT o 55. J1 gmi'.

ztness l- IYL/ENZDP wid/071155 l June 15 1926.

H. F. SMITH METHOD OF AND APPARATUS FOR TRANSFERRING HEAT Filed April 16,. 1923 2 Sheets-Sheet 2 :I I. 4i a .D

7775-1775:, '-755 IJYUEJYZDF l 5: JLM W :giran-'275277 Patented June 15, 1926.

UNITEDy STATES PATENT OFFICE.

HARRY F. SMITH, 0F DAYTON, OHIO, ASSIGNOR TO THE GAS RESEARCH COMPANY, OF DAYTON, OHIO, A CORPORATION OF OHIO.

METHOD OF AND API-ARATUS TRANSFERRING HEAT.

Application led April 16, 1923. Serial No. 632,452.

This invention relates to heat interchange,

and more particularly to the transfer of heat within-a furnace, oven, or the like.

One of the principal objects of the invention is to provide an efficient method of heat transfer, and a paratus for carrying out that method; whic method and apparatus 1s particularly applicable to` a furnace, oven, or the like. p

Another object of the invention is to provide a recuperator, for use with a furnace,-

or the like, which is simple in construction, particularly eiiicient in operation, and easy of maintenance.

Other objects and advantages of the invention will be apparent from .the description set out below when taken in connection with the accompanying drawing.

In the drawing, in which like characters of reference designate like parts throughout the several views thereof, l

Fig. 1 is a vertical, transverse, sectional view through a furnace equipped with a recuperator constructed in accordance with this invention; y

Fi 2 is a horizontal sectional view,.on an elarged scale, through the recuperator ,shown in Fig. 1,-the section shown being along a plane indicated by the line 2--2 of Fi 1' Fig is a, fragmentary sectional view along the line 3-3 of Fig. 2, with certain parts in elevation;

Fig. 4' isl a fragmentary -sectional view along the line 4--4 pf Fig. 2;

Fig. 5 is an enlarged vertical sectional Iview of one of the recupe'rator tubesshown in section'n Fi 4; and

Fig. 6 is a fragmentary sectional along the line 6-6 of Fig. 2.

The method of heat transfer embodied in view as showing a preferred embodiment of apparatus for carrying that method into effect, 1t is illustrated and described in connection with a recuperative furnace, or oven. l

The furnace illustrated in the drawing is, in fact, a form of 'coke oven, adapted for socalled low temperature distillation. This furnace consists of a body portion, designated generally by the numeral 10, which 1s built up of fire brick, or the like, in the conventional fashion. This furnace is so built up that it has a heating or distillation chamber 11, provided with what may be diameter, as designated b `rounding the upper end of the to support the said fitting, and 1s provided called a hearth 12, which constitutes the bottom wall of the chamber 11 and an arched top Wall 13, this arch being made in the regular or conventional fashion. The chamber .11 is indirectly heated, byproducts of combustion which pass through a series of pipes extending transversely across the bottomof the chamber, one of these pipes being shown and designated bythe numeral 15. Each of these pipes 15 is` immersed ina lead bath, which is designated generally by the numeral 16, the lead, during nace being maintained above its melting temperature, and serving to float shallow pans, each of which containsa thin layer of rather finely crushed material to be coked. As the pans are floated through the length of the chamber 11 the thin layer of'coal in each pan is quickly brought up -to the regular temperature and a redetermined amount of volatile driven ofi' t erethrough, the temperature to which the fuel is subjected, and the length of time it is treated being dependent upon the character of coke desired. Of course this type of recuperator is entirely applicable to any other type of furnace.

Extending downwardly through the walls yof the'furnace are a series of passages 20,

the lower end of each passage receiving-one upturned end of one of the pipes 15, the upper end of each passage being of smaller the numeral 21, and adapted to receive the uel supply pipe 22, whlch is mounted in a hollow fitting 23, the passage through this fitting being in register, and ali ment, with the passage 21. Each of the ttings is provided with a flange 24,

adapted to rest upon the brick work suradjacent its upper end vwith a ange 25, which is adapted to receive and support part of the brick work. Each of these fittings 23 is positioned within an enlargement 30, 'at the outer end ofeach of the recuperator passages or chambers 31, which are provided in the upper part of the furnace structure, that part of the furnace structure which constitutes the recuperator. Extending transversely from the body portion of each of the fixtures 23 is a hollow extension 26. shown most vclearly in Fig. 3, which is provided with two operation ofthe furpassage 21,

recuperator pipes or tubes 33, two pair of recuperator pipes being positioned within each of the passages 31.

Also provlded' in the walls of the furnace are a plurality of passages 35, which are` e passage 31 extends in one direction, while the extension upon the fixture at the other l end et the passage 3 1, associated with the .passin other pair of vrecuperator tubes extends in the opposite direction. Thus, as shown particularl in Fig. 2 the ltwo pairs of recuperator tubes mounted in each passage 31 are associated with two of th'e'pipes 15, each of these pipes 15 being connected at one end to a passave 20, and thus to the recuperator tubes within that end of the passage 31, and` at its other end to the passage 35, and thus to the space within the passage 31 surrounding the recuperator tubes.

As shown in Figs. '1 and 2 each air of adjacent passages 31 is connected, t rough `the passage 39, whichextends throughout the length of the furnace, with a'stack or flue 40.

Each pairof recuperator tubes is connected at its end opposite to the end which is connected to the fixture '23 toa second fixture 41, having a 'passage therein which opens inte an air inlet pipe 42 each pair of recuperator tubes being thus connected to a source of supply of'air.

During operation of the device air is introduced ,through the pipes 42 into each of the recuperator tubes, and lthose tubes, and then throu the fixujre 23 into the passages 20. 'At t e same time a combustible fuel is introduced through the pipe 22 and admixed with the air in the assa'ge 20 to form a combustible mixture W ich isburned, the hot products ofcombustion downwardly and thence across throug the pipe 15, thence upwardly through'the passage 35--36 into the paage 31 where they flow` over the recuperator tubesl Within that passage heatin those tubes, and the walls ofv theA passages, convection then passing off through the ue or stack 40. L

The arrangement is such that each recuperator passage has associated therewith two pipes 15, each of which is connected at one end to one of the pairs of recuperator tubes, and at the other to stack. Consequently the hot products of combustion flow in "one direction through one pipe 15 and asses through one half of the recuperator passage and in the opposite direction through the adjacent pipe and the other half of the recuperator passage.

It has been discovered that while some heat is transferred by convection from the hot products of combustion passing through the passages 31, and over the recuperator pipes therein, into the recuperator pipes, and Afrom those pipes it is then transferred in turn, by convection, to the fluid to be preheated which is passing through such pipes, a much greater quantity of heat is transferred to the walls' of the passagesy 31, by convection, as the hot products of combustion flow therethrough, and 'then transferred by radiation vfrom these walls to the re# cuperator tubes. For a given temperature differential the heat transferred by radiation from the walls in the passages 31 to the recuperator tubes is very much greater than the heat transferred directly from .the hot gases to the recuperator tubes by convection.

Preferably a plurality of plates 29,' made up of Vsonne material which will readilyrre` ceive heat by convection from the hot prducts of combustion and also of a material which is a ood radiator of heat, is positioned, substantia 1y parallel with the recuperator tubes, and thus substantially parallel with lthe direction of the flow of the products of combustion through the passages 31, these plates being thus positioned to effect ready transfer of heat, by radiation, into the re-` cuperator tubes. As shown, particularly in Fig. 4, each passage 3 1, andI eachof thetwo sets of paired recuperator tubes positioned therein, is provided 'with four of these plates, two being positioned between the two tubes, and one? between each tube andthe wall of the passage. 31'. Each of these plates has substantially twice as much surfaceexposed to'the hot fine gases, to absorbheat by convection therefrom, 'as has the corresponding part of the wall of the passage 31. Consequently the absorbing surface exposed to the hot products of combustion is very much increased, and the transfer of heat from the hot products of combustion by convection thus correspondingly increased. In addition these plates are so positioned as to break up into streams the lgases flowing through the passage 31 to effect more intimate contact between the gases and the sur faces to receive heat by convection. And each of these plates in turn radiates heat to the recuperator tubes. v

In order to facilitate transfer of the lieat which isirnparted to the walls of the tubes to the air, or other Huid, passing therethrough, each tube has therein some perforated material, or bod such as wire screen, which is a good absor r of radiant heat, is constructed to present a large surface for contact with the fluid passing therethrough isa and to break that fluid up into fine streams to effect intimate contact between the fluid and the surfaces. As shown, particularly in Figs. 4 and 5, each of these tubes is provided with a centrally arranged partition upon each side of which two layers of screen 46 are positioned, although this number may be varied as desired to give the most satisfactory results. It has been found, however, that there is a very definite limit to the depth of penetration of the heat energy radiated from the tubes, and that beyond a certain point increasing the number of layers of screen is of little or no value. The partition 45 may be dispensed with but it both helps to maintain the screens in place and` also tends to increase the efficiency of heat transfer. In arranging the screens care should be taken to not unduly interfere with the transfer or flow of the air, or other fluid, through the recuperator pipe.

yThe partition 45 should, preferably, be opaque to radiant heat. This partition may be composed of heat resisting iron alloy,"or any other material which is opaque to radiant heat energy and adapted to withstand high temperatures. Each of these scieens, and also the partition 45, receives heat by radiation 'from the heated recuperatorv tubes, and also serves to break up the air, or other fluid, passing through the tube, and over the screens into fine streams, to thus effect intimate contact between the surface of these screens and the air. Furthermore these screens present a large surface area for contact with the air to be heated by convection, and for a given temperature differential the heat transfer by convection from the screens to the air passing through the tubes is directly dependent upon the heated surface with which the air is brou ht in contact. In addition it has been foun that even though the temperature differential, and the surface of contact remain constant, a greater heat input from the screens into the air can be secured if the air is divided into fine streams so that intimate contact is secured between the surfaces of the screens and the air.

In practicing this method of heat transfer, using apparatus of the kind illustrated, or of similar character, the heat energy which is4 liberated when the fuel is burned in the presence of the oxygen of the air, or rather much of the heat energy that remains in the products of combustion after they leave the furnace chamber as fiue gases, is transferred in part to the recuperator tubes, and in part to surfaces associated with those tubes, which surfaces are good radiators of heat. These heated surfaces in turn transfer heat energyY b v radiation into the reeuperator tubes. The heated reeuperator tubes, of course, transfer some heat energy by convection into the air, or other fluld, passing through them, but they transfer' much more recuperator tubes toV receive heat energy by radiation therefrom and to transfer that energy by *convection into the fluid passing through the tubes. rial may be yused if desired. Finely spun glass wool, for example, would function very satisfactorily and any other type of material which is a good absorber of radiant energy, and which is so constructed as `to expose a large surface of contact to the fluid passing therethrough, and to divide that lfluid up into fine streams so as to b'rlngit into intimate contact with the said iuid, will function very satisfactorily.

While the method herein described, and the form of apparatus for carrying this method into effect, constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to this precise method and form of apparatus, and that changes may be made in either without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

But other matel. In an oven of the character described, a

combustion chamber, vmeans for burning air and fuel to heat the interior of said chamber; a recuperator passage thru which the heated products of combustion pass to a stack 'or vent, said passage being arranged transversely of the combustion chamber, and having ateach end 4an opening thru which the heated products of combustion enter the said passage from opposite sides of said chamber; a burner element at each end of' the passage, two recuperator tubes within said passage, the adjacent ends of said tubes being each provided with an air inlet, the opposite ends of said tubes being connected each respectively to one of the said burner elements.

2. An oven o-f the character described comprising a combustion chamber, means for burning air and fuel to heat the interior lil() connected at its outer end to a burner element, and at its other end to an air supply.

3. In an oven of the character described, a recuperator comprising a pair of recuperator tubes, constructed for positioning Witlr in a recuperator passage, an air supply fitting associated with the said tubes, havin'g la single inlet opening, and two outlet openings, each' of said outlet openings being adapted to cooperatively receive the opening in one of the recuperator pipes; and a burner element, having an offset extension thereon, said extension being provided With two openings therein, each adapted to receive in register the open end of one of the pair of recuperator tubes.

4. In an oven of the character described,- With which is used preheating means comprising recuperative elements adapted to readily` absorb heat energy by radiation and to retransfer such hea-t energy by radiation the heat-absorbing and radiating parts of such preheating means being good absorbers and good radiators,-a recuperator passage, a recuperator tube thereina plate positioned Within the passage, on each side of the tube and spaced from the wall of the tube! and.

from the wall of the passage, each said plate being positioned to receive heat energy by convection and to transfer heat energy there -from to the recuperator tube by radiation.

5. In an oven of the character described,- with which is used preheating means coniprising recuperative elements adapted to readily absorb heat energy by radiation and to retransfer such heat energy by radiation the heat-absorbing and radiating parts of such preheating means being good absorbers and good radiators-a recuperator passage, a recuperator tube therein, a plate positioned within said passage on each side of the said tube each of said plates being .spaced from the tube and from the wall of the passage and being positioned to receive heat energy by convection and to transfer 'heat energy therefrom to the recuperative tube by radiation, and a. radiant lieat-ei1ergy-absoibing body within said tube.

6. In an ovenof the character describedfwith which is used preheating means comprising recuperative elements adapted to readily absorb heat energy by radiation and to retransfer such heat energy by radiation the heat-absorbing and radiating parts of such preheating means being good absorbers and good radiators-*a recuperator passage having a pair of recuperator tubes therein. each of said tubes being connected at one end to a supply of gas to be heated and atthe othery end to a burner, and a plurality of plates positioned Within said passage and in heat-radiating relationship with the said recuperatoi' tubes, each of said plates being positioned to receive heat energy by convection and to transfer heat energy to its as- .sociated' recuperator tube by radiation, there being one plate positioned bet-Ween each'tubeand the corresponding Wall of the said recuperator passage and ytwo plates between the two tubes, the said plates being spaced respectively from the tubes and from the walls of the said passage.

7. For use in a preheater, a recuperator tube, the outer surface of Which is adapted to receive heat energy by convection and by the absorption of radiant heat energy and the inner surface of Which is adapted to transfer heat energy from the tube primarily by radiation, a partition Within said tube which is opaque to radiant energy, and a layer of screen within said tube upon each side of the said partition, Which screen is the said tube, and to divide said luid into streams to effect intimatecontact between the said (luid and the surfaces of the said screens.

8. In heattransferring apparatus of the character described, a recuperator tube of heat-resistant n'iaterial, and a perforated body positioned within said tube to receive heat energy therefrom primarily by radialion.

S). In heat-transferring apparatus of the character described, a recuperator tube of heat-resistant material, and a plurality of perforated partitions enclosed Within said tube to receive heat energy from said tube primarily by radiation.

l0. In heat-transferring apparatus of the character described, a recuperator tube of heatresistant material Which is substantially rectangular in cross-section, and a perforated body of heat-resistant material positioned within said tube to receive heat energy therefrom primarily by radiation.

11. In heat-transferring apparatus of the character described, a recuperator tube ot heat-resistant material, a perforated body of heat-resistant material positioned within said tube out of substantial heat-conducting connection with said tube to receive heatenergy from the tube primarily by radiation.

12. The method of' transferring heat energy from a highly-heated fluid, to impart such heat energy to a fluid to be heated, which comprises imparting heat energy from said highly-heated fluid to a heating body by direct contact of said heating fluid with said heating body., rapidly draining away from said heating body the heat energy being imparted thereto by the lsaid highlyheated fluid by radiation to a second body, and rapidly draining from such second body the heat energy imparted thereto `by radiation from the heating body by passing in llU 1intimate contact therewith substantially the entire quantity of fluid to be heated.

13. A recuperator tube for utilization in transferring heat energy from high-temperature gases flowing over the outside of the tube, and to impari: heat energy to a 'gas owing thru said tube to heat said gas to a high temperature, which' comprises a tube of heat-resistant material, and a plurality of sections of wire screen composed of heatresistant material positioned within. said tube and out of substantial heat-conducting connection with said tube to receive heat energy from the' saidv tube primarily by radiation. i

14. In an oven 1 of the character described,with which is used preheating meansl comprising reouperative elements` ing parts of such preheating means being good absorbers and good radiators,-a recuperator passage, a recuperator tube therein, a plate positloned Within the passage/between the tube and :the Wall of the passage, said Aplate being positioned to receive heat energy b vconvection and to transfer heat energy t eiefrom `to the recuperator' tube by radiation.

In testimony whereof. I hereto aix my signature.

HARRY F. SMITH.

20 by radiation the heat-absorbing and radiatj

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