US2590336A - Explosion-proof heater - Google Patents

Description

March 25, 1952 LR; MAST EXPLOSION-PROOF HEATER 3 Sheets-Sheet l Filed Jan. 28, 1949 FIG. l.

@c @if INVEN-ron LOWELL f?. M1457' ATTORNEYS Filed Jan, 28. 1949 3 Sheets-Sheet 2 FIG. 4.

INVENTOR LOWELL R. MAST ATTORNEYS March 25, 1952 L, R, MAST EXPLOSION-PROOF HEATER 3 Sheets-Sheet 3 Filed Jan. 28, 1949 INVENTOR LOWE/.L R. MAST FIG. 6.

ATTORNEYS Patented Mar. 25, 1952 2,590,336 EXPLOSION-PROOF HEATER Lowell R. Mast, East Rochester, N.

to Electromode Corporation,

Y., assigner Rochester, N. Y.-

Application January 28, 1949, Serial No. 73,369

Claims. 1

This invention relates to an proof heater. .1 One of the objects of this invention is to provide an electric, explosion-proof heater which is simple, practical and thoroughly durable. Another object is to provide a heater of the above character which is eicient in operation. Another object is to provide a heater of the above character which can be inexpensively manufactured. Another object of this invention is to provide a heater of the above character which can be operated safely in explosive areas, such as atmospheres containing gasoline, petroleum, naphtha, acetone, benzol, lacquer, solvent vapors and natural gas. Another object is to provide a heater of the above character, none of the exposed parts of which ever become excessively hot even when operating under a full load. A

electric, explosion:

further object is to provide a construction of the above character in which the material is so disposed as to attain a high degree of strength without heavy construction. Still another object is to provide a heater of the above character which is not affected by extreme temperature changes. Other objects Will be in part obvious and in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, and arrangements of parts, all as will be illustratively described herein and the scope of the application which will be indicated in the following claims.

In the accompanying drawings, in which is shown one of the various possible embodiments of this invention,

Figure l is a perspective view of a pair of heaters connected in series;

Figure 2 is an exploded perspective view of the heater;

Figure 3 is a vertical section on an enlarged scale taken on the line 3-3 of Figure 1;

Figure 4 is a vertical section taken on the line 4-4 of Figure 3;

Figure 5 is a horizontal section taken on the line 5-5 of Figure 4; and

Figure 6 is a view on an enlarged scale of one of the heating elements partly in section.

Similar reference characters refer to similar parts throughout the several views of the drawings.

Referring now to the drawings, in general, the heater includes an explosion-proof connection box, generally indicated at 24 (Figure 2), on which are mounted a series of grid members, generally indicatedv at l8a, I8b, I8c and I 8d.

Each grid member has a heating element, generally indicated at ID in Figures 4 and 6, cast therein, the terminals 'I and I5 (Figures 3 and 4) on the lowerv ends of each heating element I0 extending into connection box 24. Each grid member is provided with ns which form vertical passageways, so that when the grid member I8 and the-connection box 24 are mounted in a housing, generally indicated at 9 (Figure 1), the air enters opening 9a, ilows upwardly through the grid member passageways and passes out of the heater through opening 9b. A baille, generally indicated at 3I (Figures 2 and 3), is positioned rearwardly of the grid members and spaced from the rear plate 30 of the housing to provide a passageway for secondary air circulation between the baiile and rear plate. Each heater may be used individually or as one unit in a series of heaters, such as shown in Figure 1.

As all of the grid members are substantially similar in construction, specic description of the grid members will be limited to grid member I8a. Grid member [8a is cast from aluminum or other metal-having a high thermal conductivity and includes a backbone portion` 2U (Figures 2, 4 and 5) having a plurality of ns I9a and ISb formed thereon and a heating element I0 cast therein. As is best shown in Figure 6, heating element I0 is U-shaped and includes a resistance wire II, the ends of which are connected to conductors 8 and I2. The resistance II and conductors 8 and I2 are tioned within a tubular steel or copper sheath I3. The space intermediate resistance II and conductors 8 and I2 and the sheath I3 is iilled by an oxide powder I4 which-is a highly elcient electrical insulator and at the same time a good conductor of heat. Conductors 8 and I2 are connected to terminals I and I5,Which.in turn are connected to wires leading to an external pOwer source (not shown).

Terminals I and I5 have collar portions 4I and IB (Figure 6) which support insulators 42 and I1 mounted onvthe-lower ends of conductors 8 and I2. Insulators I'l and 42 insulate conductors 8 and I2 from sheath I3, insulate sheath I3 from terminals 1 and I5, and also serve to hold the oxide powder I4 within sheath I3. When grid member I 8a is cast, it is cast around and shrunk upon heating element I0 so that heating element I0 is centrally located within the backbone portion 20 of grid member I8a, as is best shown in Figures 4 and 5.

As pointed out hereinabove, the ns on grid member I 8a form passageways through which air centrally posiows as itis heated. The fins |9a and |9b (Figures 4 and 5) extend outwardly from each side of the backbone portion in pairs which are aligned with respect to each other. The center portions of each pair of fins branch outwardly from sides o-f backbone portion 20 of grid member ISa at uniformly spaced intervals in a direction taken from the front to the back of grid member |8a. The ns, with the exception of front fins 22 (Figure 3), are curved at their bottom and top extremities to :facilitate the entrance of air into and exit of air from the passageways 2| and have a constant curvature at the bottom but a decreasing curvature relative to one another at the top so that the cross sectional area of the upper portion of each passageway constantly increases as it is followed upwardly. This permits the air to expand as it is heated while traveling upwardly thru the grid member passageway 2|. Fins 22 are fiat, extend outwardly from the sides of thebackbone portion 2t adjacent ythel front edges thereof and theirA upper and lower endsare spaced from the upper and lowerv fins and positioned' immediately rearwardly thereof.

Asis best shown in Figures 3 and 4, grid member IBa'is castr with abase portion 23 'integral with backbone portion 20 and the lower ends of the rear ns. Thus, a rugged, essentially one piece grid member has been described which is highly efcient in converting electrical energy into heat energy. The total radiating area of each of the grid members is many times the sheath area of each heating element. Thus, each grid member increases the convection surface of each heating element'to a maximum and this results in each grid member having a high B. t. u. outputat a low operating temperature for safety and long life. f

Aspointed out hereinabove, the grid members lcaglb, |86 and |8dare mounted on connection box 24.7 The body 'of connection box 24 is cast and includes four integral substantially vertical side walls arid-atop.V The exterior surface of the top is datand-is machined to.0 02" feeler gage to permit ai close nt"w'ith the bottom surface of eachf'of the grid members which are also machined vto the same tolerances. vided-with'n apair of holes for each grid memb'er, Vsuchy as holes 43 and 44 (Figure 3), thru lwhichmthe lower ends of the heating element of eachfgrid e ,ber passinto the interior of the connection box when the grid members are mounted thereon. The base of each grid member is secured tdI the top of the connection box by a pair'ofscrews such'as screws 25 (Figure 4).

The lower edges'of the four walls of connection box 24 are also machined to close tolerances as well as the' top of a cover 21 so that cover 21 fits the bottom of box 24 VveryV closely. Cover 21 isv secured to the walls of 'the connection box by means of screws 28. Thus, all openings through the top and bottom of the connection box are closed in such a manner that tight flame paths are provided, thus preventing any llame from reaching externally of connection box 24 should an explosion occur therein. YConnection box 24 is of veryV heavy construction and isdesigned to withstand an'internal explosion pressure of 85 pounds per square inch and a hydrostatic pressurefof 350 pounds per squareY inch plus an appropriate safety factor.

To permit electrical connections to be made to the terminals ofthe heatingelements within the connection box, a'threafded hole is provided in The top is pro-y each of the end walls of connection box 24. Conduits, such as conduit 26, are threaded into these holes and hold the power lines or wires which connect the terminals to the source of power. The input wires are housed within conduit 26 so as to insulate the wires from any exposure to dangerous atmospheres, to reduce to a minimum the possibility of access of dangerous atmospheres to the interior of the connection box, and to' prevent any llame from any explosion occurring within the connection box from reaching externally thereof. The conduit 26 also may be used to join two or more heaters in series if more than one heater is to be used. If a heater is used alone, one of the holes in one of the ends of connection box 24 is plugged. Thus, the relatively small portion of the terminals and power lines which are in any way exposed are protected from contact with any7 dangerous atmospheres in the vicinity of the heater by being safely housed within box 24 and conduit 26 and should any explosion occur within the box, it will be. contained therein.

The assembly consisting of the grid members |8a, |812, |8c and |8d and connection box 24 is mounted within housing 9 (Figure 2), which includes a rear plate 30, a baille 3| attached to plate 39, and a streamlined front cover 32 which is bolted to plate 30. Plate 30 essentially comprises a sheet of steel of rectangular shape, the upper4 and side edges of which are flanged forwardly. To mount connection box 24 and the grid members on housing 9, the rear surface of connection box 24 (Figure 3) is provided with a pair of bosses, such as boss 49. A pair of screws, such as screws 29, pass through rear plate 30 and thread into each box and rmly secure the grid members and connection box 24, plate 30, and thus housing 9.

Batlle 3| includes side walls 31a, and 3 lb and a rear plate 3 Ic, the lower portion of which is flat and which is curved at the top to conform substantially to the shape of the rear fins of the grid members. Batlle 3| is attached by brackets 50 and 5| to rear plate 30 so that its rear surface is spaced from plate 30, thereby permitting a secondary circulation of air in this space, as indicated by the arrows 4B. The air passes upwardly along the back plate between connection box bosses 49, and thus keeps rear plate 30 cool. A uniform separation is provided between plate 3 |'c and the rear grid member fins to permit upward circulation of air between the baiile andthe rearmost ns.

The housing cover 32 has a front, a top, and two sides, but is open at the back'and bottom. It is fastened to the flanges on rear plate 30 by means of bolts, such as bolt 33 (Figure 3)'. Openings 9a'and 9b (Figure 1) :are provided. in the front portion of cover 32 corresponding in position to the entrances into and the exits from the passageways 2| between adjacent ns, s'othat air may circulate through the heater. Openingsv are also provided at the bottomof the sides to" permit the connection of conduits, such as lcon'- duit 26. To permit the heater tobewcon'nected to a wall, mounting brackets 34 are attached 'tor the rear surface of the rear plate 30.

In operation, electrical energy is converted inf to heat energy in the heating elements Il)J which` is transmitted through the gridl members to the radiating surfaces of their ns. Cool air from the area to be heated enters opening` 9d (Figure l), is heated as it flows upwardly throughthe passagewaysl 2| (Figure '3) and passes out ofn opening 9b (Figurel) `After leaving' the heater.'-

the warm air circulates through the room. At the same time, cool air flows upwardly between box 24 and baffle 3l and rear plate 3i). This air flows out of the housing between the upper edges of baille 3| (Figure 3) and opening 9b. This secondary air circulation keeps rear plate 30 cool.

There are many distinct advantages which the heater offers. The relatively small radiating surface area of each heating element is multiplied to a maximum when it is compared to the large radiating surface of the grid member it heats. This ensures maximum efficiency in transferring heat energy from the heating elements to the air being heated. Because of the manner in which the grid members are constructed, any heat energy generated by the flow of current through the heating elements is quickly conducted to the surface of the fins where it is circulated by convection through the area to be heated. Even though a complete heater weighing only about 85 pounds may draw as much as 2000 watts, the maximum grid temperature will be less than 500 F., and the maximum temperature will be only about 150 F. on the wall to which the heater is fastened, the ambient temperature in the above tests being as high as 104 Also, it should be noted that the heating elements which receive electrical energy and convert it into heat energy are completely covered throughout most of their length by grid members which serve to transmit the heat evenly to their entire radiating surface. In the small areas Where the grid members do not cover the heating elements and where electrical connections are made to the heating elements, the electrical connections and heating elements are completely enclosed in an explosion-proof box which is so constructed that should an explosion occur therein, it will be completely contained within the box. The heater is composed of a minimum number of parts which may be assembled easily and quickly and which provide a highly eliicient, safe, explosion-proof electric heater when once assembled. These advantages, in addition to the low operating temperatures of the grid members combined With their high B. t. u. output make it readily apparent that the heater has wide application Where safety is paramount, such as in pipe line pump houses, refinery meter houses, gasoline bulk stations, propane bulk stations and similar properties. It will thus be seen that a practical and eicient explosion-proof heater has been described in which the several objects hereinabove mentioned as well as many others, have been successfully accomplished.

Since many possible embodiments of the above invention may be provided, and since many changes may be made in the embodiment above set forth, it is understood that all matter hereinabove set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a heater, in combination, a grid member including a backbone portion having a plurality ofl ns thereon, said backbone portion including a base portion, an electric heating element cast within the backbone portion of said grid member and having its terminals extending from said base portion, a connection box including four walls and an integral top, said terminals extending through said top into the interior of said connection box, means connecting said base portion tightly to the top of said connection box, and a cover closing the bottom of said connection box.

means connecting said cover tightly to said box, the engaging surfaces of all portions of said connection box, said base portion and said cover being smooth to t closely to thereby provide tight ame paths from the interior of said connection box to the exterior thereof whereby the flame resulting from any explosion in the interior of said connection box will be completely dissipated in said flame paths before reaching the exterior ofv said connection box.

2. In a heater, in combination, a housing, said housing including a front Wall, two side walls, a rear plate and a top, a plurality of grid members, each of said grid members including a, backbone portion and a plurality of fins extending outwardly therefrom, the front portion of said housing including spaced openings positioned one above the other, said fins and said grid members being shaped to form passageways connecting said upper and lower openings in said front wall, a heating element cast within the backbone portions of each of said grid members, a connection box, the terminals on said heating elements extending into said connection box, said connection box completely enclosing said terminals and al1 electrical connections thereto, all exits from the interior of said connection box to the exterior thereof being tightly closed, said connection box being connected to but spaced from said rear plate, and a baille spaced from but conforming to the shape of the rear surfaces of the rearmost ns of said grid members, the upper end of said baille being positioned beneath the lower edge of the upper opening in said housing, said baille also being spaced from said rear plate whereby air ows upwardly between said fins and baille and said baffle and rear plate and thence flows out of said housing through the uppermost opening therein, said air absorbing the heat radiated by the rearmost ns and thus preventing excessive heating of said rear plate.

3. In an electric space heater, in combination, a grid element comprising a vertical elongated backbone member, an electric heating element associated with said backbone member, and a plurality of fins projecting horizontally from each side of said backbone member, said fins having vertical middle portions and ends curving toward the front of said backbone member thereby forming passageway to guide air being heated from the bottom of said grid element to the top, the top ends of said ns being spaced further apart than the bottom ends thereof to increase the size of said passageways at the top and thereby increase the free flow of air as it is expanded on heating.

4. In an electric space heater, in combination, a grid element comprising a backbone member having a plurality of i'lns for heating and guiding air and a flat base portion integral With said backbone member, an electric heating element in said backbone member and having its terminals extending from said base portion, a connection box connected to said base portion of said grid element, said terminals extending through holes in the adjacent side of said connection box, the engaging surfaces of said element and box being machined flat, and a conduit tted to said connection box for shielding a power line to said terminals, said connection box having a machined lower peripheral edge and a bottom cover which ts to said edge, the bottom cover and base portions being machined to t said connection box and provide tight flame paths from the interior of said connection box to the exterior thereof.

5. In an electric space heater, in combination,

agotarse 7 a; heating eiefet *ha-ving, a `maeiii'ned lbase portion -with terminals extending therefrom, 'a -con-v nection box 'having a machined top for'receiving saidba'se portion, holes for said terminals and 'a machined lower peripheral edge, a'bottom cover machined to't said edge, and means fior "connecting said base :portion and said-cover firmly to said connection '150x 'to provide tight name paths from the interior of said connection box,

said connection box and said coverbeing 'heavilyv surfaces, and means for fastening said cover tol :said box to form a tight it therewith, the edges of -said box being suic'iently thick so that. said :surfaces between said 'cover vand said boxform a .ame path suiiicient to dissipate all heat to a non-combustible temperature Vbefore it escapes to theatmosphere.

7, In a space heater, in combination, a "grid member comprising a vertical backbone element, heating' means associa-ted with said backbone element, and a plurality of iins projecting horizontally from said backbone element thereby forming passageways to guide air being heated from the bottom of said lgrid memberV to the top, said iin's comprising verticall portions curved at their bottom and top extremities to facilitate entrance of air into and exit'of air from said passageways Aand having a constant curvature at the bottom but a decreasing curvature relative to one another at the` topiso thatV the cross sectional area of the upperA portion of each passageway constantly increases as4 it is followed upwardly, thereby permitting air to expand as it is heated while ris,- ing through said passageways. l

3,' In a space heater, in combination,A a heatingelement and a housing enclosing said heating element, said housing having a vertical Wall with a'pair of spaced openings positioned one above the other, and said heating element comprising a vertical backbone member, heating meansassociated with said backbone member, and a plurality of ns projecting horizontally from said back; bone member, said ns being spaced from each other and having vertical portions curved at their vertical spaced respective'extremities toward said housing openings, to form passageways for guiding air being heated from the bottom opening up through said housing and out the top opening.

'9. In a's'pac'e heater, in-combination, a heating element anda housing enclosing said heating-lele; ment, said housing having a verticalwall with a pair of spaced openings positioned one "above the other, and said heating element comprising a backbone portion, a plurality of ns extending o'utw'arcllyy thereof, and heating means associated with: said backbone portion, said iin's being'shaped to'fform passageways to connect said openings and to increase the cross sectional area of the upper portion of each of said passageways, thereby-directi'ng air admitted inthe lower of said openings through said passageways and out theV uppercf said openings and thereby permitting said air to expand fre'elyj as it is heated.

1G. An explosion proof terminal connection box comprising, in combination, a box member fone side of which is open, a conduit fitted to said box member for shielding a power line leading tothe interior of said box, said box member having openings in one of its-walls for receiving electrical terminals and having a machined flat surface adjacent said terminal openings, the marginal surface adjacent the open side of said box being .machined flat, electrical apparatus with terminals extending through said openings and having a machined surface which is tightly secured to said wall of said box to cover said terminal openings and to provide tight flame paths leading therefrom between said box and said electrical apparatus, a cover for said box machined to t tight upon the marginal surface adjacent the open Aside of the box, and means to secure` said coverv tightly to said box to provide tight name paths leading from the interior` thereof whereby tight flame paths are provided from all points in the interior of said box member to dissipate completely all flame resultingV from an explosion Ain the interior of said box to a noncombustible temperature before it reaches the atmosphere. f

LOWELL R. MAST.

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

Y UNITED STATES PATENTS Ntunber Name Date 1,956,617 Jarre May 1, '1934 2,199,279 soverhnl Feb. 22, 1938 2,153,477 ouey May 16, 1939 2,240,922 Bissell May c, 1941 2,313,786 van Daam Mar. 16, 1943 2,317,426 wnson Apr. 27, 1943 2,335,233 Bush Nov. 30, 1943 l2,453,875 Shannon Nov. 2, 1948 2,455,339 Walton Dec. 7, 1943

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