US2000640A - Electric heater - Google Patents

Description

y 1935- R. A. F. JACKSON ET AL 2,000,640

ELECTRIC HEATER Filed April 6, 1954 2 Sheets-Sheet 1 a TLLL LL 25 29 .---v

fizven/ors FHA 2150195017 H \[Mfsan ally y 1935- R. A. F. JACKSON ET AL 2,000,640

ELECTRIC HEATER F iled April s, 1954 2 Sheets-Sheet 2 [Dy/917K015 51715195195017 H YM [5017 i Patented May 7, 1935 UNITED STATES PATENT OFFICE ELECTRIC HEATER Application Claims.

, This invention relates to electric heaters for fluids, particularly immersion heaters for liquids, of the type in which the heating element is enclosed within and insulated from a fluid-tight 5 tubular sheath, said element being substantially straight or uncoiled with reference to said sheath, the so, sheathed element being wound or bent into elongated tubular formation and adapted to contact directly with the fluid to be heated.

In accordance with the present invention we provide an electric heater for fluids, of the type aforesaid, in which the tubular formation of the sheathed heating element is mounted upon a terminal block or like base, said tubularformation being deformable, means extending within said tubular formation being provided for stiffening said tubular formation at or adjacent the base but allowing the remainder of the tubular formation to be deformed, said means also allowing circulation of the fluid therethrough into the tubular formation.

More specifically we provide an electric heater for fluids, of the type aforesaid, in which the tubular formation of the sheathed heating element is mounted upon and spaced from a terminal block or like base in order to allow circulation of the fluid into the tubular formation, characterized by the fact that said tubularformation is of bendable or deformable nature, a short rigid apertured 30 tube projecting from said base into said tubular formation in order to stiffen said tubular formation at the part where maximum sagging or bending thereof is likely to occur and also to prevent breaking of the terminal connections of the 35 sheathed element, said tube at the same time being short enough to allow the tubular formation to be bent to any required shape.

Preferably the tubular formation is stiffened additionally by longitudinal semi-rigid stiffening members incorporated with the windings of the tubular formation.

We will now describe some embodiments of our invention, simply by way of example, with reference to the accompanying drawings, whereonz- Fig. l is a diagrammatic view ofthe old form of bare coiled element.

Fig. 2 is an elevation of a sheathed element as utilized in the present invention.

Figs. 3, 4, 5 and 6 show in elevation, and in some 50 cases partly in section, examples of immersion heaters for liquids, in accordance with the present invention. Each figure is shown broken in two, as, to scale, the heaters are considerably longer than shown.

Fig. 7 is a section on the line VII-VII, Fig. 6.

April 6, 1934, Serial No. 719,392 Great Britain April 19, 1933 Figs. 8 and 9 are diagrammatic elevations illustrating practical applications of an immersion heater in accordance with the present invention- Fig. 10 is an enlarged longitudinal sectional view of a modified form of sheathed heating element in accordance with the present invention.

In the various figures the same references denote like parts.

The element l2 shown in Fig. 1 consists of bare high resistance, for example nickel-chrome, 10 wire which is coiled transversely of its length and then this coil is wound upon a refractory support as described above. When used in an immersion heater it is protected by a water-tight enclosing housing usually of cylindrical formation and 15 through which the heat is transferred to the liquid.

In the example of a sheathed element in accordance with the present invention, as shown in Fig. 2, the element'proper I3 is of high re- 20 sistance material, for example, nickel-chrome wire, but instead of being transversely coiled, is straight or substantially straight and is enclosed within a Winding M of asbestos yarn, a binding I5 of paper, and a jacket l6 of braided asbestos. The whole element is enclosed within a liquidtight tubular protective sheath H of tinned copper which is flexible or deformable.

If we assume that the element proper i3 has the same resistance per unit length as the element l2 (Fig. 1) when uncoiled, then obviously the resistance per unit length of the sheathed element shown in Fig. 2 is much less than that of the coiled element shown in Fig. 1. In fact when the element I2 is enclosed Within a plane housing the unital surface loading thereof is usually about 30 to watts per square inch, whereas the unital loading of the sheathed element is preferably about 2 to 5 watts per square inch, and the actual surface temperature is con- 40 siderably below that of a heater using an element in accordance with Fig. 1. This low loading is obtained owing to the fact that the element I3 is not coiled with respect to its sheath or housing. Obviously a similar result will be obtained as long as the element I3 is uncoiled, and even if it is of wave or undulating shape or in any other non-coiled manner permitting of a low unital loading. Due to limited space or other reason, however, the loading may be increased to 20 watts per square inch, or higher, the circulating efiect through the heater being retained, however.

Any suitable number of heating elements I3 may be enclosed Within a single sheath ll.

In the immersion heater shown in Fig. 3 a sheathed element such as IT is wound or coiled transversely into two concentric tubular members or formations having coils I8, Illa, the winding preferably being done before hand on a former. The heater is flexible or deformable, but is stiffened by the insertion of longitudinal stifieners such as Is and the whole is mounted upon a terminal box ill having a removable cover a and enclosing three series-parallel terminals 2 i. As will be evident from the drawings no return lead in the tubular formation isnecessary, as the latter is formed by lengths of the sheathed element wound side by side away from the base and then back again, thereby providing separate circuits which can be series-parallel connected to said terminals 2| for different degrees of heating. The base of the heater is screw threaded at 22 and is adapted to be screwed in water-tight manner into the wall 23 of a water tank or other container. Extending longitudinally within the heater is a central tube 2.4 provided with a number of holes or apertures 24a.

The coiled formations of the sheathed element are spaced from the base, thus allowing circulation of the water into the interior passage of the heater. The tube 24 serves firstly to stiffen the heater at its base where, as explained below, sagging is likely to occur, and moreover the tube 2d allows circulation of the water into the interior of the tube and thus through the heater.

imilarly the end of the tubular formation remote from the base is open to allow of circulation.

Assuming that the heater projects horizontally into the tank, then, when the temperature of the heater rises, the metal sheath tends to soften, and thus, with intermittent heating and cooling, there would in time be a tendency for the tubular formation to sag out of alignment. Moreover, the convection currents in the liquid engendered by the heating thereof also exert a continuous force tending to move the heater out of alignment. Further, owing to the necessity of spacing the tubular formation from the base, the terminal connecting leads of the sheathed element would be subjected to the maximum bending moment, and would thus in time tend to break. The use of the central tube 24 obviates these disadvantageous tendencies.

The adjacent coils l8, iSo are spaced apart from each other as shown, so as to allow free circulation of the liquid between the coils, thus giving a very large heat transfer area of the sheath in contact with the liquid.

The heater shown in Fig. 4 is similar to that in Fig. 3 except that a tubular member having coils ifia (but usually in this case of smaller diameter than shown in Fig. 3) is itself wound in a helical manner around the longitudinal axis of the heater, and preferably each of the resulting large coils are spaced apart, as also are the small coils lBa. Thus, it will be evident that the whole heater is provided with a multiplicity of interstices for circulation of the liquid to be heated.

The heater shown in Fig. 5 is similar to that shown in Fig. 3, but only one layer of coils [8a is provided and these coils are wound upon a screw-shaped former thus giving an undulating or screw shaped outline to the heater. This allows an improved heating eifect upon the liquid owing to the staggered disposition of the adjacent coils this forces the liquid to take a more sinuous path in circulating through the heater (for example in the direction of the arrows A).

In the construction shown in Figs. 6 and 7 the sheathed element 11 is bent into a series of sinuous longitudinally extending lengths or windings which are mounted upon a pair of formers 21 which allow circulation of the liquid through the central passage of the heater. Any desired number of concentric layers of the element may be provided.

Figs. 8 and 9 illustrate how an immersion heater as described in Figs. 3 to 7 inclusive may be mounted within a water tank. The part of the heater 28 extending clear of the inner tube 24 is bent as indicated in Fig. 8 to attain any suitable shape, and this also facilitates its insertion in the tank. The cold water enters the tank at inlet 29 and the heated water leaves at exit 30. The arrows indicate the manner in which circulation takes place, the cold water entering at the lower end of the heater 2!! and passing upwardly through its hollow interior, at the same time entraining side streams of water into contact with and between adjacent coils. As the water is heated it rises upwardly through the central passage of the heater.

As shown in Fig. 8, the tubular formation 0! the sheathed element is bent upwardly near the base, the horizontal part being maintained rigid by the aforesaid central tube 24. Obviously, but for this tube, a large bending moment would tend to cause the heater to sag adjacent the terminal box 20. The deformability of the heater enables the same to be bent before insertion into the water tank, and moreover, by adjusting the shape and inclination of the free end, the flow of the hottest water in the tank (that leaving the free end of the heater) can be directed adjacent to the hot water outlet, so that hot water is provided very soon after switching on, although the average temperature of the water in the tank may still be comparatively low.

In Fig. 9 the tank is indicated as being linked with a domestic fireplace boiler, the electric heater being used as a booster heater and preferably thermostatically controlled. The outlet 33 leads relatively cold water to the fireplace boiler, while warm water from the fireplace boiler enters at 3|. Cold water from the mains enters the tank at 32 and the hot water is drawn off at 39. In this case the electric heater 23 in accordance with the present invention projects downwardly into the tank, but the circulation is similar to that indicated in Fig. 8.

In the modified form of sheathed element shown in Fig. 10 the element proper I3 is enclosed within a jacket 16 of braided asbestos and is mounted therein in spaced and insulated manner by means of a plurality of glass beads 35 each having a diametral passage through which the element is threaded. The whole is enclosed within a tinned copper sheath H. This form of element is very flexible while providing a sound form of heat resisting insulation.

Any of the constructions described with reference to Figs. 3 to '7 may also be applied for use in heating air or other gases, although in some cases it may be desirable slightly to modify the construction. The heaters may be disposed vertically or at any desired angle so that the cool air or gas enters at one end and circulates through the heater to its point of discharge. Preferably the internal passage through the heater is divergent from inlet to outlet to allow for the expansion of the gas when heated.

For purposes of heating certain liquids or gases, a non-corroding sheath for the heating element may be necessary. For example, for purposes of heating oil, the sheath will usually be made of steel. Normally, however, in order to prevent rusting, the sheath is preferably of non-ferrous material.

Any of the coils of the heating element described above may of course be of any suitable shape besides circular, and the disposition of the coils or lengths or windings may be varied. The shape and cross-section of the sheath may also be varied, and the term tubular as herein referred to is not to be taken as limiting to circular cross-section.

The means for insulating the element from the sheath may take various forms, for example paper, asbestos, cambric cloth, powdered insulating material, mica, carbon, or refractory beads or nodules or other refractory substances, or any combination of these.

The sheathed element may be formed by drawing the insulated element through a tubular sheath, or alternatively, by winding or rolling metal tape or strip around the insulated element and tinning and pressing the insulated element to render it non-corrosive and fluid-tight.

Thermostatic or other automatic heat control is preferably provided in conjunction with the heater.

The heater in accordance with the present invention is very useful for heating oil and similar substances in which it is necessary to have a heater with low heat emission per square inch of surface, this being necessary in the case of oil to prevent carbonization and combustion. The heater, however may also be applied for example, for heating jam or chocolate boilers. wash boilers, washing machines and the like, and for other suitable heating purposes.

In order to improve the rigidity of a heater made up of the sheathed element described above, bent or coiled in any formation, the element may, in addition to or instead of the, stiffeners such as l9, be mounted upon a core formed of wire mesh or like open work so as to facilitate circulation of the fluid.

In the construction of the sheathed element in accordance with the present invention any parts thereof may be made of relatively low resistance, for example, ordinary nickel wire instead of nickel chrome wire, and these low resistance parts form suitable integral connections between two heating units, so that special connections are not necessary.

A heater in accordance with the present invention may also be adapted for steam raising in small quantities. Further, it may be constructed for use with any commercial voltage.

We claim:-

1. An electric heater for fluids, a terminal base,

the tubular formation of a sheathed heating element mounted upon the base, said tubular formation being deformable, means extending within said tubular formation for stiffening said tubular formation at or adjacent the base while allowing the remainder of the tubular formation to be de-- formed, said means also allowing circulation of the fluid therethrough into the tubular formation.

2. An electric heater for fluids, a terminal base, a tubular formation of a sheathed heating element mounted upon and spaced from the base in order to allow circulation of the fluid into the tubular formation, characterized by the fact that said tubular formation is of bendable or deformable nature, a short rigid apertured tube projecting from said base into said tubular formation in order to stiffen said tubular formation at the part where maximum sagging or bending thereof is likely to occur and also to prevent breaking of the terminal connections of the sheathed element, said tube at the same time being short enough to allow the tubular formation to be bent to any required shape.

3. An electric heater as in claim 1, wherein said tubular formation is stiifened by additional longitudinal semi-rigid stiffening members incorporated with the windings of the tubular formation.

4. An electric heater as in claim 1, wherein said tubular formation is stiffened by a core of wire mesh or like openwork upon which the tubular formation is mounted and which allows circulation of the fluid.

5. An electric heater as in claim 1, wherein adjacent windings of the sheathed element are spaced apart so as to allow circulation of the fluid therebetween and provide a maximum surface area in contact with the fluid to be heated.

6. An electric heater as in claim 1, wherein the interior of the tubular formation is divergent from inlet to outlet in order to allow for expansion of the fluid as it is heated.

7 An electric heater as in claim 1, wherein the tubular formation of sheathed element is of screw or undulating shape.

8. An electric heater as in claim 1, wherein the sheath for the heating element is of non-ferrous material.

9. An electric heater for fluids as in claim 1, wherein the tubular formation is formed by lengths of the sheathed element wound side by side away from the base and then back again, thereby providing separate circuits which can be series-parallel connected for different degrees of heating.

10. An electric heater as in claim 1, wherein the tubular formation is formed by coiling said sheathed element transversely of itself to tubular formation, and then again coiling the resultant coiled structure transversely to tubular formation.

ROBERT ALFRED FREDERICK JACKSON.

ANDREW VICTOR. WILSON.

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