US2601167A - Furnace and heat retaining unit therefor - Google Patents

Description

June 17, 1952 s, E, NAVARRO 2,601,167

FURNACE AND HEAT' RETAINING UNIT THEREFOR Filed D90. 50, 1948 2 SHEETS--Sl-{EET l wsmaisiliank www k/JNIVHHINVMI June 17, 1952 s. E. NAVARRO 2,601,167

FURNACE AND HEAT RETAINING UNIT THEREFOR Filed Dec. 5o, 1948 2 SHEETS- SHEET 2 Patented June 17, 1952 FURNACE AND HEAT RETAINING UNIT THEREFOR Stanley E. Navarro, Cambridge, Mass.

Application December 30, 1948, Serial No. 68,302

3 Claims.

This invention relates to furnaces, heaters, boilers, and similar apparatus, intended more especially for use in domestic heating systems, although useful, also, for other purposes. For convenience all such heating apparatus will be herein referred to generically as a furnace or furnaces and the heating elements in them will be designated as burners In many types of apparatus of this nature, especially those thermostatically controlled and fired by gas or oil, the burner comes on in response to the call for heat by the thermostat and it continues to operate until the demand for heat has been satisfied. Then the furnace cools off and remains in that condition until another call for heat. At that time the entire furnace structure must be heated up again before any heat is delivered to the rooms supplied by the furnace. This has long been recognized as an undesirable condition from the standpoint of efficiency.

The present invention is especially concerned with the problem presented by these conditions, and it aims to devise a simple form of apparatus with which the efficiency of heating equipment of the nature above described can be substantially improved.

The nature of the invention will be readily understood from the following description when read in connection with the accompanying drawings, and the novel features will be particularly pointed out in the appended claims.

In the drawings,

Fig. 1 is a vertical, sectional view of those parts of a furnace with which the present invention is more closely associated, and illustrates the furnace equipped with two heat retaining units embodying features of this invention;

Fig. 2 is a plan view of the lower of said units; and

Fig. 3 is a plan View of the shell for a modified form of unit.

Referring first to Fig. 1; ythe construction there shown comprises a portion of the jacket 2 of a domestic hot water heater of a common type arranged to be red by gas and including a combustion chamber 3, furnace door 4, gas burner 5, and a flame spreader 6, all of which may be of any usual or suitable construction.

According to the present invention, upper and lower heat conserving units, indicated, in general, at A and B, are mounted in the combustion chamber, one above the other, and they are of novel construction. The lower unit B includes a metal shell 1, preferably made of boiler plate, or some equivalent heavy gauge metal plate, or of a casting. It has a bottom and sides, and its outer surfaces are preferably smooth so that they may be easily cleaned. This shell is filled with a refractory material 8 which may be of various compositions. One which I have found especially satisfactory consists of a mixture of asbestos fiber and Portland cement to which has been added a very substantial proportion of metal pieces, such as metal turnings, chips, lings, and the like, ordinarily regarded simply as scrap. For example, the non-metallic material may form, roughly, two-thirds of the bulk of the filling 8 and the metallic constituent one-third, or even less, the proportions being varied to suit the requirements of individual installations.

Through the bottom of the shell a multiplicity of holes 9 are punched or drilled, and the metal tubes I0 are set into the filling 8 in register with these holes so that a relatively large number of such tubes extend through the entire unit from the top to the bottom thereof. They are open at both the top and bottom surfaces of the unit and are unobstructed, so that air can flow freely through them. In domestic furnaces of the common sizes these tubes may consist of short lengths of iron pipe of, say, the three-quarter inch size, and if they are spaced apart by intervals of three or four inches they will give satisfactory results.

This unit is supported in the combustion chamber at a suitable distance above the flame spreader 6 so as not to interfere with the complete combustion of the fuel, a height of eight inches usually being sufficient, and the supporting means may be selected to suit the requirements of theparticular installation. As shown, the supports consist of fire bricks Il. Also, the size and shape of the unit B should be selected to suit the requirements of the furnace in which it is to be installed. One of the functions which it should perform is that of a baffle to direct the flame against the inner wall surface of the combustion chamber. Consequently, it should be made of an outline corresponding, in general, to that of the combustion chamber but somewhat smaller so as to provide a clearance of, say, one to three inches between it and said wall. Usually a clearance of about an inch and a half will be found preferable.

The upper unit A is of the same general construction as the lower unit but it generally is somewhat smaller in diameter and is not as thick. A typical thickness of the lower unit is six inches and that of the upper unit four inches, although the invention is not limited at all to such dimensions. It may be supported on the lower unit by rods l2. or in any other convenient manner. The various parts of this unit corresponding to those of the unit B are designated by the same, but primed, numerals.

When such an installation is started up, with the furnace entirely cold, all of theseparts must be heated up, including the water in the surrounding jacket, before any heat wlll be delivered to the radiators. During this period the units A and B serve to confine the flame and the flow of products of combustion mainly against the surrounding wall of the combustion chamber. But they also retard the rate of flow of these combustion products through the furnace and into the stack. Thus the heat transfer to the surfaces is improved and less heat goes up the stack. It has been found in the operation of furnaces equipped in this manner that the stack temperatures run considerably lower than when not so equipped. For example, a typical stack temperature is 400 F. In actual* installations made in accordance with this invention the stack temperature has been found to run under 300 F. By proper adjustment of the draft and fuel supply this lower temperature can, in any event, be maintained as a maximum.

In addition to directing this heat on to those surfacesv where it is most needed, the holes through the units provide a sufficient flow of gases to prevent the formation of any dead spaces in the combustion chamber. In other words, an ample circulation is maintained throughout the combustion chamber.

Later, when the thermostat cuts off the burner 5, the heat retained in the units A and B is slowly released to the surrounding surfaces of the combustion chamber and the rate of cooling of the furnace is correspondingly reduced, with the result that when the next call for. heat comes in and the burner is turned on in response to that call, the ensuing heating-up period is materially reduced. It is during this period that a great deal of heat in the ordinary installation is lost up the stack. By shortening this period in successive cycles of operation a material improvement in efficiency of the installation is realized.

This effect is similar, in a thermal sense, to the mechanical advantage gained by the use of a fly wheel on a single cylinder gas engine, and I have found that the efficiency of a heat retaining unit of this general type isimproved materially when a substantial proportion of its mass consists of a non-metallic material. Itis for this reason that I prefer to make the filler 8 of a mixture of metallic and non-metallic materials, as above described. If a unit of this type is made entirely of metal, a slight. improvementin efficiency may be obtained, but the metal gives up its heat so rapidly that this improvement isfnot substantial. With a mixture of metallic' and non-metallic but refractory material, the rate of release of the heat stored in the unit during. that portion of the operating cycle in which the burner. is on is later released only gradually, and this fact substantially increases the efficiency of the installation.

In making some installations of units of this type the furnace door is not large enough to permit the passage through it of`a shell of the desired size. This difficulty can be avoided by making the shell in two sections, as illustrated in Fig. 3, where the sections i3 and 14 are essentially alike, are provided with overlaps I5, and are secured together by bolts IB extending through the overlapped portions of the rim. The sections can be passed through the door individually and assembled inside the combustion chamber, after which the filling may be introduced and allowed to harden. Assembly of these sections inside the furnace is facilitated by spot- 4 welding the tubes to the bottom plate portions of the respective sections prior to introducing them into the furnace. Also, this assembling operation is made easier by inserting the desired number of bolts through the overlapped sections of the rim only in order to hold the parts together without necessarily bolting the bottom sections together. That is, the shell may be rotated inside the furnace to bring the sections to be bolted together alternately at the furnace door or feed door where the fastening operation can be easily performed.

While I have herein shown and described a preferred embodiment of my invention, it will be evident that the invention may be embodied in other forms without departing from the spirit or scope thereof.

Having thus described my invention, what I desire to claim as new is:

l'. In a furnace provided with a combustion chamber and having a burner in the lower part thereof, a heat absorbing and radiating. unit positioned transversely in said chamber above said burner and comprising a metal shell including bottom and side walls and a heat retaining ma terial approximately filling said shell, a multiplicity of tubes extending through said filling material from top to bottom thereof and open at both the top and bottom of the unit, means supporting said unit in said chamber, the unit being of such dimensions and outline as to provide a narrow clearance only between it and the adjacent walls of the combustion chamber, said filling material being composed ofl a mixture of nonmetallic refractory material and metallic pieces dispersed in it.

2. A furnace structure according to preceding claim 1, including a secondA heat radiating unit positioned above said first unit and of similar construction to the latter unit, and means maintaining said secondunit spaced vertically from the first unit, whereby a large proportion of the hot gases passing through the tubes of the lower unit will also flow through the tubes of the upper unit.

A heat conserving unit for furnaces comprising a metal shell provided with bottom and side walls and a heat radiating material approximately filling said shell, said filling including refractory non-metallic material mixed with metallic elements, and a multiplicity of metal tubes extending through said filling from top tobottom thereof andopen at bothl the top and bottom ofA the unit.

STANLEY E. NAVARRO.

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

UNITED STATES PATENTS Number Name Date 489,874 Orton Jan. l0, 1893 508,689 Engelman Nov. 14, 1893 760,262 Shoals May 17, 1904 1,255,503 Biggs Feb. 5, 1918 1,667,133 Schrader Apr. 24, 1928 1,725,974 Brautigam Apr. 27, 1929 2,147,803 Steck Feb. 21, 1939 2,266,551 Harvey Dec. 16, 1941 2,278,486 Quigley Apr. 7, 1942

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