US1721442A - Heat exchanger and method of making the same - Google Patents

Description

Patented .llully l6, W29.

Muir-an stares l PATENT @FFHCE.

ROBERT L. FRINK, OF LANCASTER, OEIU.

near nxonanenn AND METHOD or MAKING THE SAME.

Application. filed August 2, 1927. Serial No. 210,100.

leakage of gas to the 'air passages, or vice versa. This condition is particularly bad at the joints Where the refractory parts are brought together. In many industries heat exchangers, have been extremely limited in their usefulness due to this fact.

I'pro'vide a heat exchanger formed from a 'single body of material. .This material is preferably cast-inplace and is of a non-porous character. This gives a structure which is leak-proof under all conditions. The'problem of supporting the apparatus is materially simplified and the cost is lower. The material employed preferably comprises a refractory such as sillimanite, a low temperature cement, and glass forming constituents. An oxychloride cement gives good results. The material may be readily cast and upon heating it forms a glass-like bond for the refractory. When the refractory is in the glasslike bond, its transmissivity is increased. This is of material value for recuperator work.

I use a mold structure for casting the heat exchanger and-leave asubstantial portion of this structure in place. It is made of consumable material and burns away when the heat exchanger is put into operation or subjected to a drying fire. It is thus possible to make a heat exchanger of a pattern that it has heretofore been impossible to make in a unitary structure. v

In the accompanying drawings which illustrate a preferred embodiment of a recuperator.

Figures 1 to 3 inclusive are vertical sectional views showing the different steps in the construction of the recuperator, and

Figure 4 is a vertical transverse sectional view to enlarged scale showing a portion of the completed recuperator.

Figures 1 to 3 inclusive illustrate successive steps in the manufacture of the recuperator. The recuperator proper (see Figure 4) comprises a bottom slab 19 forming the top of a lower wind box, a top slab 20 forming the bott m of an ppe Wind bOX a d tubes 7 which connect the top and bottom slabs and are formed inte ral therewith.

I employ a refractory material containing a large percentage of sillimanite. A preferred mix is as follows Parts. Calcine'd sillimanite 2500 Boric acid, dry; 250 Silica, powdered to pass No. 80 screen 250 agnesium oxide, powdered to pass No.

100 screen 100 Borax, powdered to pass No. screen 150 The above batch is thoroughly mixed and is then wetted with a'solution of magnesium chloride of specific gravity 1.08. Sufiicient magnesium chloride solution is used to give the mix the desired consistency. For casting the bottom slab the mix, should have'a consistency of thick mud, that is, too stiff to flow of its own weight and requiring some puddling to get it to its final position.

The bottom slab 19 is cast on a support 21 which is made of wood or other consumable material. The casting of the bottom slab is shown in Figure l. The support 21 is shaped at intervals so as to provide for the casting of pedestals 19 integral with the base 19. This provides a self-supporting recuperator and there is no danger of portions of the recuperator sagging and cracking as would be the case if independent support means were employed. Cylindrical forms 22 are properly positioned on the bottom form 21 so as to define the location of the tubes 7. The cylindrical forms 22 are-also made of consumable material. Ordinarily mailing tubes have been used with great success.

Each form 22 is provided with a ring 23. This ring is spaced from the form 21 and providesa recess in the top face of the slab'19 v around each of the tubes 22.

Before the bottom slab has fully dried, the rings 23 are removed and the inner tubes 22 are surrounded with outer tubes 24. Mailing tubes have also been used for these forms. The rings 23 are made of such size that the tubes 24 fit into the recesses thus provided.

After the outer tubes 24 have been put in plaoe, the tubes proper are cast by pouring the material into the space between the tubes 22 and tubes 24. For the casting of the tubes a little thinner mix is required By reason of the fact that the bottom slab has not yet set, the tube material makes a firm and per? manent bond with the bot-tom slab,

50 ature the sillimanite becomes embedded in prises a board 25 which is bored to receive the tubes 24, as shown in F igure. 3. This board is preferably put in place before the tubes are cast so as to assist in positioning the tubes 24. Side form boards of any desired construction are used and the top slab is poured into this form. It will be noted from Figures 2 and 3 that the tubes 22 are made of sufficient length to project to the top of the slab 20. As in the case of the tubes and the bottom slab, the top slab is cast before the material forming the tubes has set, thus insuring a permanent bond between the tube material and the top slab.

If desired, metal instead of consumable material may be used for forming the tubes 22. The inner tubes may be readily withdrawn, but the remaining parts of the form are intended to be consumed after the recuperator material has set.

It is found in practice that the material acquires a sufficient set in about twenty four hours to permit of removing the side form boards and building up the encasing walls for the recuperator. The boards 21 and 25, and the tubes 24:, are left in place.

It is desirable to maintain the materials at a temperature of not less than 80 or 90 F. during the construction of the recuperator. If weather conditions are such that a lower factory temperature obtains, it is desirable to Warm the batch materials before the casting step After the recuperator has been completed, a drying fire may be built so as to make certain that the recuperator is thoroughly dried. As the temperature is increased, the forms are burned away, thus leaving the finished recuperator.

My batch material provides an oxychloride cement which is effective for bonding the sillimanite particles. The magnesium, the boron and the silicon embodied in the constituents of the batch react when the material is raised to a high temperature so as to produce glass. Therefore, when the recuperator is raised to its Working tempera glass bond. This is of particular value for recuperators embodying thin walled tubes. When the sillimanite is embedded in the glass bond, the transmission coefficient of the material is materially greater than the trans mission coefiicient when the sillimanite is embedded merely in the oxychloride cement. This makes for high efficiency of the recuperator. The provision of a glass bond is also of value in that it insures tight joints even though there should be a failure of the initial bond between the tubes and the top or bottom slabs.

The side walls of the recuperator are indicated at 26 in Figures 3 and 4. As above stated, these side Walls are cast after the recuperator tubes have been formed. They are made from the same batch material and be-.

come integral with the top and bottom slabs. They operate under different conditions than do the tubes 7 for the reason that no heat is applied to their exterior faces, Whereas both faces of the tubes are subjected to some heat, the exterior by reason of the heat of the combustion gases from the furnace, and the interior by reason of the fact that the air sup plied to the tubes is preliminarily heated in the tubes 8. In any event, the tubes 7 are made materially thinner than the side walls 26 so that after a short period of operation a glass bond extends through the entire thickness of the tubes, while a glass bond exists for only a relatively short distance from the interior surfaces of the Walls 26. This pro vides a high degree of insulation for the side walls because, as stated above, the sillimanite in the oxychloride cement has a coeflicient of heat transfer materially less than the coefficient when sillimanite is embedded in the glass bond.

In case a tube becomes broken or porous, it may be very readily patched, or may be broken out and its ends closed off entirely. The batch material may be put inplace and regardless of whether the glass bond has been formed on the recuperator or not, the patching material makes a permanent and leakproof oint with the recuperator structure.

The material employed for making the recuperator is more particularly described and claimed in my copending applications Serial Nos. 136,883 and 359,366. The furnace construction is described and claimed in my copending application Serial No. 160,986, filed January 13th, 1927.

While I have illustrated and described the preferred form of my invention, it will be understood that it is not thus limited, as the invention may be otherwise embodied or practiced within the scope of the following claims.

1. A heat exchanger comprising a slab member having hollow heat exchanging tubes extending therefrom, the tubes and the slab member being integral'with one another.

2. A heat exchanger comprising a slab member having hollow heat exchanging tubes extending therefrom, the tubes and the slab member being integral with one-another, and being formed of refractory material.

3. A heat exchanger comprising a slab member having hollow heat exchanging tubes extending therefrom, the tubes and the slab member being integral with'one another, and bilaing formed of a material which is cast in p ace.

4. A heat exchanger comprising a slab member having hollow heat exchanging tubes extending therefrom, the tubes and the slab member being integral with one another, and

' being formed of a cementitious material.

5. A heat exchanger comprising a unitar body of material forming spaced apart containing materials adapted to form a glasslike bond for the refractory when the recuperator is raised to high temperature.

7. A heat exchanger formed of a refractory material in a glass-like bond.

8. A heat exchanger comprising a relatively thin Walled tube and a relative thicker casing wall, the tube and the casing wall both being made of a batch comprising refractory material, a cement adapted to set at low temperatures, and material adapted to form a glass-like bond for the refractory material at high temperature.

9. A heat exchanger comprising spaced apart slab-inembers, tube members extending therebetween, and wall members encasing the tube members, all of said members being formed integral with one another.

10. The method ofmakingaheat exchanger, which comprises forming the same from a mix containing a refractory material, a low te1nperature cement and materials adapted to form glass upon being raised to elevated temperature, allowing the cement to set and thus define the size and shape of the heat exchanger structure, and then raising such structure to high temperature so as to cause the production of a glass-like bond for the refractory material. I

11. The method of making a heat exchanger, which comprises forming relatively thin walled recuperator tubes, and a relatively thicker encasing wall from a batch containing a refractory material, a cement adapted to set at low temperatures, and materials adapted to form glass at high temperatures, permitting the cement to set and'thus define the size and shape of the heat exchanger and then raising the heat exchanger to such temperature that a glass-bond is formed through substantially the entire thickness of the tubes, but through a portion only of the thickness of the encasing wall.

12. The method of making a heat exchang er, which comprises forming the heat exchanger from a batch material containing a refractory material, an oxychloride cement and glass making constituents, permitting the oxychloride cement to set, and then raising the heatexchanger to such a temperature that the glass making constituents will react.

13. The method of making a heat exchanger from a batch material, comprising a refractory, a low temperature cement and glass forming constituents, the heat exchanger having a slab and tubes extending therefrom, the steps consisting in first forming the slab, then before the cement in the slab has finally set,

forming the'tubes, and thereafter raising the temperature of the slab and the tubes so as to cause the act.

14. The'method of making a heat exchanger from abatch containing a refractory, a 10W temperature cement and glass forming constituents, which comprises first forming one heat exchanger portion, then, before the low temperature cement has finally set, forming an ad acent heat exchanger portion, and thereafter ralsmg the temperature of the heat eX- changer so that the glass forming constituents react.

15. A heat exchanger formed of a batch containing a refractory, a low temperature cement, and a glass forming constituent. I

16. A heat exchanger formed from a batch comprising a refractory material, an oxych'loride cement, and glass forming materials.

In testimony whereof I have hereunto set my hand.

ROBERT L. FRINK.

glass forming constituents to re? CERTIFICATE OF CORRECTION.

Patent No. 1,721,442. Granted July 16, 1929, to

ROBERT L. FRINK.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 3, line 52, for the compound word "glass-bond read "glass-like bond"; same page, line 87,-claim l5, strike out the article "a" and for the word "constituent" read "constitutents"; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 10th day of September, A. D. 1929.

r M. J. Moore, Acting Commissioner of Patents,

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