US3429370A - Heat exchanger - Google Patents

Description

Feb. 25, 1969 c. c. BLACKMAN HEAT EXCHANGER Filed Jan. 8, 1968 COIL m47@ M Nid. IC 1W. .ma/ 3. m. C/ W Iv States 3,429,370 HEAT EXCHANGER Calvin C. Blackman, 24272 W. Lake Road, Bay Village, Ohio 44140 Continuation-impart of application Ser. No. 544,992, Apr. 25, 1966. This application Jan. 8, 1968, Ser. No. 696,255 U.S. Cl. 165-47 13 Claims Int. Cl. F28d 7 /02; F28f 1/00; C21d 1/06 ABSTRACT OF THE DISCLOSURE This is a continuation-in-part of application, Ser. No. 544,992 filed Apr. 25, 1966 entitled Heat Exchanger, now abandoned.

This invention relates to heat exchangers, and more particularly to cooling devices adapted for use in the bases of coil annealing furnaces.

In `annealing steel coils in batch type annealing furnaces, the coils are heated by radiation and convection to the desired temperature, soaked at this temperature for a predetermined time, and then cooled to ambient temperature. The coils must be cooled in the funace under protective atmosphere to a temperaure below which scaling will occur, after which the furnace covers can be removed and the coils cooled in the ambient atmosphere. Because of the large mass of the coils, their cooling from the soaking temperature is quite slow and time-consuming, and for most annealing cycles it is desirable to increase this cooling rate .as much as possible. This increase in cooling rate is accomplished in part by positioning heat exchangers in the gas passages in the base and cooling the circulating gas as it passes through exchangers. These exchangers have conventionally taken the form of water pipes having cooling ns welded thereto for heat dissipation. This arrangement, however, is highly susceptible to cracking and other damage due to the thermal shock of water being introduced into the tubes with the surrounding temperature being l000 F. or higher.

Accordingly, one of the main features of this invention is the provision of an improved heat exchanger, particularly adapted for use in the base of an annealing furnace, which is highly resistant to cracking and damage due to thermal shock.

Another disadvantage of the prior art cooling devices in annealing furnace bases is the fact they cool only the gases flowing by. Accordingly, another important feature of this invention is the provision of a cooling device for use in the bases of annealing furnaces, wherein the device is in direct contact with, or very closely adjacent to the coil support means of the furnace to provide conductive heat transfer.

Still other advantages of the invention, and the invention itself, will become more apparent from the following description of several embodiments thereof, which description is illustrated by the accompanying drawing and forms a part of this specification.

In the drawings:

FIG. 1 is a plan View of a portion of the diffuser of a bell type annealing furnace embodying the present invention;

FIG. 2 is a sectional view taken substantially along the plane designated by line 2 2 of FIG. 1;

FIG. 3 is a view similar to FIG. 2, on a reduced scale, of another embodiment of a cooling device according to this invention;

FIG. 4 is an embodiment of the heat exchanger device being utilized in conjunction with a main support plate of a furnace;

FIG. 4a is a plan view partially in section 0f the embodiment of FIG. 4.

FIG. 5 is a sectional view of a heat exchanger utilized with a solid slab coil support.

More specifically, referring to the drawing, the sup porting structure of an annealing furnace is shown. The supporting structure includes a support base 4 with insulation 6 thereon supporting a diffuser generally designated as 8. The diffuser includes a base plate 10 having a central opening 12. A plurality of ribs 14 are secured to the base plate 10 and extend radially outwardly from the opening 12. Baffie plates 16 .are provided over the ends of alternate ribs 14 to provide alternate unobstructed passage 18 between the ribs. A gas channeling vane structure 19* is disposed in the opening 12 and is constructed to channel gases from the opening 12 to the open passage 18. Coil supporting cover plates 20 are secured between the ribs 14 having the baffle plates 16 lat their ends. An annular coil support plate 21 overlies the gas channeling vane structure 19 and is disposed to support the inner wraps of a coil. A

fan is provided having an impeller 22 disposed in the central opening 12, which is driven to blow gases through the unblocked passages 18, as shown in arrows in FIG. l. This gas is circulated Within the furnace for cooling the coils. Heat exchangers 24 are disposed in each of the open passages 18.

As can best be seen in FIG. 2, each of the heat eX- changers has a large diameter tube 26 extending through the support base 4, the insulator 6 and an opening 27 in the base plate 10. The tube is preferably made of a 'heat resisting steel, such as A.I.S.I. type 321 stainless steel. The tube 26 has a bracket 28 welded thereto which rests on the base plate 10. An end cover 30 is welded to the tube 26, and a coil support plate 32 is secured to the end cover 30. The top of the plate 32 is on the same plane as the tops of the cover plates 20, and the plates 32 as well .as the cover plates 20 serve as coil support members, the bracket 28 supporting the load on the base plate 10. Although the cover 30 and plate 32 are preferably formed as separate elements, a single plate can serve as both a cover and a coil support plate, if such is desired. The opposite end of the tube 26 is provided with a water inlet 33.

A smaller diameter Water discharge tube 34 is telescoped inside of the larger tube 26 terminating in a bias cut adjacent the end cover 30. The bias cut is to allow for drainage, even though the tube 34 is pushed against the end cover 30. The tube 34 is sealed in the larger tube 26 by an end cap 36. A rubber sleeve 38 is clamped to the tube 26 and clamped around a rigid sleeve 40 depending from the bottom of the support base 4 to seal the interior of the furnace and prevent gas from escaping or entering the furnace around the tube 26.

A helically wound coil of wire 44, preferably of the same material as the tube 26, is wound around the outside of the tube 26 and acts as a heat dissipator. One end 46 of the wire is welded to the end of the tube 26 adjacent the cover 30, and the other end 48 is welded to the bracket 28. The convolutions of the coil are stretched as the wire is wound on the tube 26 so that the wire will be under tension, urging it into rm contact with the outside of the tube 26. Proper tension can be provided by using a coil of wire with approximately 1A inch pitch and stretch winding the wire to approximately '1/2 inch pitch.

With the construction of a heat exchanger as shown in FIG. 2, cold cooling water can be delivered to the tube 2-6 when the atmosphere therearound is at 1000 F. or higher, and there is no danger of the thermal shock cracking the coiled wire since the wire is resiliently secured to the outside of the tube. With conventional units employing fins welded or brazed to the tube, the thermal shock of cold Water tends to break the welds or brazed joints and also crack the thin sections of the ns themselves. This danger is not present in the present invention since under stress the wire 44 is free to move on the tube.

The tube 24 extends through the base plate 10, the insulation 6 and the support base 4 with clearance as shown and described. During heating and cooling of the furnace the base plate 10 will expand and contract which moves the opening 27 through which the tube 24 extends. As this opening 27 moves, the edges will tend to engage and move the tube 24 within the clearance between the insulation 6 and support base 4. The rubber sleeve 38 not only permits this lateral movement of the tube 24 but it also isolates the interior of the furnace from the exterior of the heat exchanger below the support base 4, thus maintaining a seal of the atmosphere within the furnace irrespective of the movement of the heat exchanger.

In order to remove the exchanger for replacement or repair, the clamps clamping the rubber sleeve 38 to the sleeve 40 and the tube 26 need merely be removed, the water inlet and outlets disconnected, and the heat exchanger as a unit can be lifted up through the support base 4, the insulation 6 and the base plate 10, and a new exchanger installed.

Referring now to FIG. 3, another embodiment of a cooling device according to this invention is shown. In this embodiment, telescoped tubes 26 and 34 with an end cap 30 are employed which are similar to those used in the embodiment of FIG. 2. Also, the tubes have a sleeve (not shown) similar to the sleeve 38 shown in FIG. 2. However, in the embodiment of FIG. 3, a hollow support column 50 is provided which surrounds the tube 26 above the base plate 10. The column 50 has a lower ange 52 which is secured to the base plate 10 and an upper ange 54 on which is Welded the coil support plate 32. Preferably reinforcing ribs 56 and 58 respectively are provided for the upper and lower flange 52 and 54.

The support column 50 has a hollow central bore 60 in which is disposed the tube 26. It is preferred that the tube 26 be very close to, but not actually touching the walls of the column 50. This allows for movement and expansion and contraction of the pipe during heating and cooling which otherwise might cause cracking. It is desirable to keep this space to a minimum, however, to afford maximum heat transfer characteristics between the tube 26 and the column 50 which column acts as heat dissipating means.

One of the advantages of the construction of heat exchangers in the diffuser base of the furnace as shown in FIGS. 1 through 3 over that of the prior art exchangers used in diifusers bases is that the top of the exchanger in this construction is connected in conductive heat transfer relationship with a coil supporting member of the base so that not only are the gases cooled as they flow in the passages around the heat exchanger, but also cooling of the support plates occurs by conduction. Thus, with a single device two separate types of cooling are provided which -will greatly improve cooling efliciency over the single type coolers of the prior art.

It is to be understood that in constructing furnaces it is diicult to exactly align the top of the plate 32 with the top of the cover plates 20. If plates 32 are even a little above the plates 20, they will bear a disproportionate share of the load. Also, the expansion characteristics of the cooling elements may differ from that of the plates 20 and ribs 14 and 16, although the plates 32 and 20 may be aligned initially. Sometime during the cycle, plates 30 may be moved upwardly more than the plates 20, thus substantially inducing the forces on the cooling devices which tend to cause cracking. Thus, it is often desirable to design the cooling elements so that the top of the plates 32 are slightly below the top of the plate 20.

It is desirable that this distance be kept as small as pracical since gases are comparatively poor conductors for conduction heat transfer. If this distance becomes more than about 3/16 inch, then the effective heat transfer by conduction becomes minimal. However, up to about this W16 inch distance, a significant amount of conduction heat transfer takes place. Therefore, when the surface of the plate 32 is no more than about 3/16 inch from the coil, cooling of the coil by conduction according to this invention does take place and for heat transfer purposes the plate 32 may be considered a support plate and substantially in the plane 0f the other coil cover plates 20.

One way to reduce the air gap between the coil and the plates on the ends of the heat exchanger and still not cause undue stress on the heat exchanger is to provide a resilient high heat conducting material on the top surface of the plate 32. This preferably takes the form of steel wool or the like, although other devices such as coiled wire in the nature of a soft spring, or other types of similar heat conducting and heat resisting material may be used. This will allow for some misalignment and still provide direct contact below the coil and the support plate for conductive heat transfer.

With respect to heat transfer characteristics, the same relationships are true between the walls of the column 50 and the tube 26. The column 50 will act as a better heat dissipator the less clearance between it and the tube 26.

Expressed another way, wherever clearances are required and conduction heat transfer is to be accomplished, the spaces as clearance should be kept to a minimum and in no instance exceed about 3716 inch. This applies to distance between tubes and plates, and plates and coils and any other articles between which conduction heat transfer is to take place.

It is also contemplated that a heat exchanger of telescoped tubes similar to those shown in either FIG. 2 or 3 could be installed directly in conjunction with the ribs and cover plates 20, as shown in FIGS. 4 and 4a. In this addition to coolers of the type shown in FIGS. l through 3 in the gas passages.

Also, some coil supports on furnace bases employ a solid slab of steel rather than the rib and plate construction shown in the drawing. FIGURE 5 shows the heat exchanger used in this type of construction. The slabs designated as 62 have openings formed, one of which is shown at 64. These openings can terminate short of the top of the slab, as illustrated, or they can extend completely through the slab. The tubes 26 are disposed in the openings. Again, the problem of air gap is present and to prevent cracking some clearance must be provided, but a minimal amount is desired, As described above, this should not exceed BAG inch (average radial clearance) at the locations where conduction heat transfer is desired. ilf this air gap is too great, it can be packed with steel Wool, or other resilient heat conducting material as described above. In this type of installation as well as that of FIGURE 4, the gases would not be owing past the heat exchangers, but they would provide conduction cooling of the coils.

Having thus described my invention in several embodiments thereof, I am aware that numerous and extensive departures may be made therefrom without departing from the spirit or scope of the invention as defined by the appended claims.

'In the claims:

1. In a heat exchange apparatus, a furnace base structure having charge support means including gas channels for circulating gas, the improvement comprising a cooling device including fluid tight tube means in conductive heat exchange relationship with said charge support means, and means to supply and exhaust cooling fluid to and from said tube means whereby to cool a charge by cooling of the base structure on which the charge is supported.

2. The device of claim 1 wherein a portion of the charge support means is disposed at the end of said tube means and is in conductive heat transfer relationship with the charge to be supported.

3. The device of claim 2 wherein resilient high heat transfer material is disposed on the surface of said portion of said charge support means.

4. The device of claim 2 wherein column means surround said tube means and mount said portion of charge support means on the base plate.

5. The device of claim 1 wherein said charge support means includes plate means having an opening therein and said tube means are disposed in said opening.

6 The device of claim 5 wherein resilient high heat transfer material surrounds said tube means in said opening.

7. The device of claim 1, wherein said tube means is supported by said furnace base structure.

S. The device of claim 1 further characterized by resilient sealing means disposed to permit lateral movement of said tube means in response to movement of said base plate during heating and cooling.

9. The device of claim 8, wherein said means to permit movement of said tube means includes a resilient sleeve around said tube means and disposed to seal the atmosphere within the furnace.

10. The device of claim 1, wherein heat dissipating means surround said tube means.

11. The device of claim 10, wherein said heat dissipating means includes helically wound spring means maintained against said tube means under tension.

12. The device of claim 1, wherein said means to exhaust cooling fluid includes second tube means disposed within said first tube means extending a substantial portion of the length thereof.

13. The device of claim 12, wherein said second tube means is cut on the bias.

References Cited UNITED STATES PATENTS 2,325,677 8/1943 HOak 266-5 2,537,024 l/1951 Bay 165--173 X 2,649,285 8/1953 Brown 165-142 X 3,011,766 12/1961 Hess 165-9 1,634,319 7/1927 Callaghan 266-4 ROBERT A. OLEARY, Primary Examiner.

T. W. STREULE, JR., Assistant Examiner.

U.S. Cl. X.R.

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