US3126469A

US3126469A - Water heater with resistance

Info

Publication number: US3126469A
Authority: US
Publication date: 1964-03-24
Anticipated expiration: 1981-03-24

Description

March 24, 1964 H. F. FELDMANN ETAL WATER HEATER WITH RESISTANCE FILM HEATING ELEMENT 2 Sheets-Sheet 1 Filed Dec. 29, 1960 EL ESfiANN SUTTON INVEN H RMAN F. F

BERT J BY a u/A/ ATTORNEY March 24, 1964 H. F. FELDMANN ETAL 3,126,469

WATER HEATER WITH RESISTANCE FILM HEATING ELEMENT Filed Dec. 29, 1960 2 Sheets-Sheet 2 in] 68 M 88 l l 86 96 9o FIG. 4

87 I l I I I I I I hr, -79 I I I I I IN V EN TORS HERMAN F. FELDMANN BYROBERT J.SUTTON MAM ATTORNEY United States Patent Office 3,126,469 Patented Mar. 24, 1964 3,126,469 WATER HEATER WITH RESISTANCE FILM HEATING ELEMENT Herman F. Feldmann and Robert J. Sutton, Chicago, IlL, assign'ors to General Electric Company, a corporation of New York Filed Dec. 29, 1960, Ser. No. 79,441 2 Claims. (Cl. 219--38) This invention relates to water heaters and more particularly to water heaters utilizing as heating elements conductive coatings or films sprayed on insulating surfaces. I It is generally known that conductive films such as metallic oxides, and the like may be deposited on a refractory support by various processes which usually include heating the refractory material to elevated temperatures. The resulting film acts as a resistance heater which may be employed to serve as the heat source for varying purposes. For example, US. Patent 2,678,990 issued to D. W. Quirk on May 18, 1954 employs such a film for heating the walls of an oven. The present invention contemplates a water heating element comprising a film coating applied to a cylinder having a suitable temperature resistant outer surface such as glass or other insulating material with which the liquid being heated is placed in contact. Heat is transmitted from the film to the cylinder to the water.

It is further known that it is necessary to protect the inner linings of water tanks sometimes by exceedingly elaborate mechanisms. For example, to protect the inner wall of a water heater tank against corrosion, it is conventional to fire on a vitreous enamel coating. Even under the bestmanufacturing conditions mass-produced tanks may have pinholes or other minute holidays or flaws exposing the base metal of the tank. Thus to protect the tank against failure at such locations, it is the practice to employ a magnesium rod, or a powered anode, immersed in substantially the entire depth of Water in the tank. The use of the magnesium rod or powered anode has proven to be very effective to protect the tank wall; but it has been found that the resulting galvanic currents traverse the conventional metallic sheathed immersion electric heater and pit or otherwise disintegrate themetal sheath to the point of early failure of the heating elements, Where these currents pass from the sheath to any electrically grounded portion of the tank. To protect such heating units it has been previously considered essential to provide various electrical devices and arrangements as shown in Dicome 2,810,815 and Boggs et al. 2,723,340. The present invention in one form (immersion heating) provides a mode of alleviating the necessity for such expedients by providing an electrically non-conductive heat surface which cannot generate or receive such galvanic currents. Thus the heater is inherently protected from galvanic current corrosion.

In a first embodiment of my invention I utilize a heater located externally of the water storage tank. Such heaters are known in the art as side arm heaters. Pursuant to the invention, the heater includes a cylinder having a conductive film on the exterior surface of the cylinder sidewall, placed in a thermosyphonic hydraulic circuit with the storage tank to complete the water reservoir system. Cold water is fed into the storage tank and the side arm. Asthe water in the side arm is heated, it rises and flows into the upper portion of the tank creating a pressure increase toward the bottom of the water tank. This forces a flow of cool water into the sidearm heat chamber. In this manner a thermosyphonic water circulation pattern is stimulated within the hydraulic parallel network.

In a second embodiment of the invention, the heater cylinder is immersed within the tank. The cylinder includes a refractory outer surface in contact with the water being heated and the conductive film adhered to the inner surface of the heater cylinder. The immersed end of the cylinder is sealed-off to prevent any electrical contact between the heater and the water being heated. By the interposition of the insulating barrier between the heater and the water being heated, no galvanic currents are generated by the heater and as a result the heater can operate more efficiently than would be the case with immersed heaters of the conventional metallic sheath type.

It is therefore an object of the invention to provide a hot water reservoir including a refractory surface cylinder with a conductive film adhered thereto for heating water contiguous to the cylinder.

It is a further object of the invention to provide a water reservoir including a cylindrical side arm heater parallel to a water storage tank in which a conductive film is adhered to the outside of cylinder and water flows internally within the cylinder.

It is a further object of the invention to provide within thewater reservoir system a closed-end galvanically inert cylinder with a conductive film coating adhered to the inside of the cylinder and which cylinder is immersed in the water being heated. In this way galvanic current generation from the heater is eliminated.

It is a still further object of the invention to provide a water reservoir system which includes a cylinder with a conductive oxide coating adhered thereto in which the heat transfer pattern is from the oxide coating to the cylinder for transmission ultimately to the water being heated.

Other objects, features and advantages of the invention will be apparent from the detailed description of the presently preferred embodiments thereof, read in connection with the accompanying drawings in which:

FIG. 1 is a side sectional view through the center of. the first embodiment of my invention;

FIG. la is an alternate film heating cylinder in side sectional elevation for use in the embodiment of FIG. 1; FIG. 2 is a partial perspective view of the film heating cylinder of FIG. 1;

FIG. 3 is a partial section of a sidewall of the film cylinder of FIGS. 1 and 2;

FIG. 4 is a side elevationalview partially in section of a heater employing a second embodiment;

FIG. 5 is a perspective view partially in section of a heater as used in the second embodiment;

FIG. 6 is a cross sectional view of a heater taken at line 6-6 of FIG. 5;

FIG. 7 is a side elevational view of an insulating member used in the second embodiment.

Referring now to the drawings, FIG. 1 shows the first embodiment of the invention. This embodiment includes a reservoir system 10 including an upright cylindrical drum or tank 12 which may be fabricated from a suitable corrosion resistant coated metal such as porcelain enameled steel. An inlet tube 14 for cool water is joined to the tank along its cylindrical sidewall 16 adjacent the tank base and will feed the tank with cool water as required through a suitable opening 18 in the tank wall. A second tube or pipe 20 extends upwardly from tank top 22 to supply heated Water to the output system. A third pipe 24 extends through a Suitable opening 26 in the upper portions of sidewall 16 and provides communication between the tank 12 and side arm heater 30.

Side arm heater 30 comprises a hollow glass cylinder 32 open at both ends. The upper open end 34 communicates openly with pipe 24 in such a manner that this communication is sealed from the ambient surroundings. At its lower open end 36, cylinder 32 communicates with inlet pipe 14 in a manner of pressure-tight joinder similar to that of the upper communication. The glass used in fabricating cylinder 32 preferably is of the borosilcate type such as sold under the trademark Pyrex, or other vitreous or ceramic glass materials which are resistant to elevated temperatures. About most of the free vertical extent of the glass cylinder outer surface, there is adhered a film or coating 38 of metallic oxide such as tin oxide.

The usual method of adhering the film to the vitreous surface is to first heat the surface to be treated to a temperature between 600 C. and 700 C. A solution containing the oxide compound is directed, preferably in atomized spray form, against the surface to be coated for a time period sufiicient to produce a film of the requisite thickness which optimally is in the range of microns. Under the high temperaure conditions, the deposited oxide integrally unites with the vitreous surface and as a result the coating is thoroughly bonded to the vitreous surface such as the glass cylinder utilized herein.

The film, as mentioned, covers the entire outer cylinder periphery and extends along most of the exposed length of the cylinder. On either side of the cylinder there is brushed on a silver conducting strip 40. These strips extend vertically on diametrically opposed sides of the cylinder exterior and may be on the order of inch in width. These strips in FIGS. 1 and 2 are shown greatly exaggerated in width and thickness for purposes of description. These conductive strips extend for the entire vertical height of the film coating and by virtue of their character as adhered to the oxide film, these strips may be used as electrodes through which power is applied to the film. Near its upper end as shown in FIG. 1, there is fastened about the cylinder a terminal ring 42 shown in detail in FIG. 2. The terminal ring may be of non-conductive material or at least coated with non-conductive material and serves to tightly hold suitable terminals 44 against each of the conductive strips 40. As seen in FIG. 2, the terminal ring 42 includes legs 46 which are squeezed together by bolt and nut 48 to compress the terminals 44 tightly against their respective conductive strips 40. Terminals 44 are then connected by suitable conductors to a source of electric power.

As is well known in the art, the electric power circuit to the terminals will include a conventional thermostat or temperature limit switch (not shown) disposed at an appropriate level on or within the tank 12 so as to be responsive to the water temperature.

The joinder of cylinder 30 to pipes 14 and 24, and the joinder of these pipes individually to the tank are all suitably sealed by generally known expedients to prevent water leakage from the reservoir system. The water seals may take the form shown of flanges 50 packed with packing glands or ring seals 52 as shown. Further, the side arm cylinder should be thermally insulated by means of insulating layer 54 about its exterior to retain the heat generated as much as possible.

In the FIG. 1a modification of the first embodiment, there is employed a cylinder 30a which in this instance is made of stainless steel or other suitable metal resistant to water corrosion. The cylinder may be fabricated in any manner to include end plates 31:: which are bonded to the hollow cylinder wall 32a to form a liquid impervious structure. At the center of each end plate there is a circular opening about which a pipe coupling 33a is bonded so that there is provided a single liquid impervious structure with threaded end caps for ready mounting into the water heater plumbing system.

About the outside of cylindrical sidewall 32a there is fired on a layer 34a of suitable refractory material which has a relatively pore free surface and which readily adheres to the metal sidewall. A material which has been found to adhere nicely to the stainless steel is a phosphatebonded ceramic coating, a typical composition of which comprises about 56% (by weight) of 400 mesh silica, 11% of 85% phosphoric acid; 6% of commercial grade fine hydrated alumina; 26.5% Water; and about 0.5% of a pickling liquor corrosion inhibitor. This coating 34a is of material which is insulating in character electrically and serves as a base for the resistive film heater 38a. The electrically conducting film 38a is adhered to the outside of the refractory coating in a manner similar to that previously described. As was the case with the structure of FIG. 1, there are provided silver strips 40a extending vertically for the entire sidewall height and extending horizontally for about a quarter of an inch on either side of the cylinder diameter. Suitable terminals 44a are connected to the strips to connect the strips and the film to a suitable source of electric current. Insulation of course should surround the side arm and the tank also to retain as much of the heat generated as is possible.

The operation of both forms of this first embodiment are essentially identical in principle and explanation of only the main form will be made. Cool water is fed into inlet tube 14 and the water is fed into the tank 12 and also into side arm 30. The inlet valve (not shown) which may be controlled in any manner will close shutting off the inlet at a location allowing continuing communication between reservoir 30, inlet pipes 14 and 24, and tank 12; this shut-ofi occurring when sufiicient water has flowed into the tank. Film heater 38 is then energized and the water in side arm 30 will then begin to heat. As the water heats, it then becomes less dense and the water pressure in the side arm decreases. Cool water from the tank will flow through tube 14 into the side arm forcing the heated water upwardly through tube 24 into tank 12. This manner of flow will continue until the tank attains the hot water condition which actuates the thermostat control to open the heater circuit. The opening of any valve or faucet (not shown) served by the pipe 20 will draw heated water from the tank and effect its replacement by cool water through tube 14.

Looking more closely at the heater during this operation, as electric current is fed to the conducting strips 40, current flows across the conductive film between the strips and the resistance of the film generates heat in a known manner. Since the flow of heat outwardly is greatly impeded by the layer of insulation shown schematically as 54, the greatest portion of the heat generated is transmitted through the cylinder wall into the water contiguous thereto. The heater being out of electrical contact with the water generates and receives from the water no galvanic currents. Thus, none of the current utilized by the heater is wasted by generating stray galvanic currents in the water. Thus, anodic protection is provided by this usage.

The second embodiment (FIG. 4) employs a tank 60 with one or more film heating cylinders 62 fitted internally within the tank to form the hot water reservoir system. The tank may be made of any suitable material for holding water and the like and would include an inlet pipe 64 toward the bottom of its tank sidewall 66 and an outlet pipe 68 extending vertically upward from the tank top 70.

Film heating cylinder 62 as shown in greater detail in FIGS. 5 and 6 is mounted to extend horizontally within the tank and includes the vitreous or glass structure 72 which terminates at the free end of the cylinder in a hemispherical end cap 74 formed integrally as part of the cylinder. The use of glass as the structural medium of the heat generating cylinder insures that the entire surface immersed in the tank is an insulating medium which will not accommodate electric current flow from the heater to the tank. The structure is fabricated .to be imperforate and water impervious. On the inner cylindrical sidewall of the vitreous cylinder there is sprayed a conductive coating 76 or film in the manner described previously for the first emboidment. The coating of approximately 5 microns thickness is applied about the entire interior of the cylinder in a relatively uniform film by any suitable process. Diametrically opposed on each side of the cylinder, conductive strips 78 such as silver are painted along the inner sidewall for virtually the entire length of the cylinder. These strips will of course conform to the curvature of the cylinder wall within the extent of their A to 4: inch width by virtue of their adhesion to the conductive film.

To complete the corrosion protection, a sacrificial magnesium rod 79 may be mounted to the top wall of the tank and where used should extend through the water in the tank for virtually the entire length of the tank. The rod is grounded at its mounted end so that a circuit is completed through it. The rod extends within the tank immersed in the water in a manner allowing it to plate out as a protective film on the tank walls due to galvanic corrosion currents in the water. The operation of such rods is shown, for example, in the cited Dicome and Boggs patents.

At the end at which the cylinder 62 is mounted to the tank, the glass cylinder wall 72 flows integrally into a conical frustum section 80 which terminates in an annular flange 82 normal to plane of the cylinder sidewall and extending outwardly. The flange is indented in regularly spaced locations 83 for mounting to the tank wall. The actual mounting of the cylinder is accomplished by the use of a sealing flange 84 which is secured to the tank wall adjacent the opening for the cylinder. Suitable flange gaskets or ring seals 86 are interposed between the sealing flange which preferably is of metal construction and the cylinder flange 82 which is of vitreous material as is the cylinder. Bolts 87 of suitable size and material may be permanently connected to the sealing flange to extend horizontally therefrom for positioning through the mating indentations 83 in the flange 82 and these bolts tightened in position by the use of nuts 88 as shown in FIG. 4. By the use of the expedients shown or similar mounting devices, a water-tight seal is formed about the joinder of the film heating cylinder and the tank to eliminate possible leaks from the tank to the cylinder or out of the tank altogether.

To connect the film to a source of electrical current terminal connectors 90 shaped to conform to the frustoconical section of the heater Wall and extending horizontally therefrom are employed. For holding these terminals in place, a porcelain or similar material insulator 92 is used which is frusto-conical in shape and designed to fit internally within the frusto-conical section 80 of the heater. Within the exterior surface of the insulator there are provided two grooves 94 diametrically opposed and extending in parallel along the slant height of the insulator outer surface. These grooves must be of a depth which readily accommodates the terminals 90 but which allows the terminals to extend slightly outwardly from the conical sidewall. By these relative dimensions, it is insured that contact will be completed from the terminals to the conductive strips without fear of the terminals becoming lost in the mating grooves 94. Any suitable means for holding the insulator and thereby the terminals firmly in place may be used. These may include flange gaskets such as 96 which would cover the area between the cylinder flange and the sealing flange while allowing terminals 90 to protrude insulatedly therefrom.

The operation of this embodiment is quite simple. Cool water is pumped or otherwise fed into the tank 60 via inlet tube 64 until sufficient Water is in the tank. At that time, current is fed to terminals 90 and current will flow between the parallel conductive strips along the conductive film. The film will resistively heat and the heat generated will flow outwardly from the heater through the vitreous cylinder into the water maintained in the reservoir system. As the water is heated, suitable controls (not shown) may thermostatically control the functioning of the heater, outflow of heated water and inflow of cool water to be heated. The action of such controls is well known in the art and forms no part of the present disclosure.

By the use of glass as the medium extending into the tank, there is produced a galvanically inert heater. It is, of course, quite well known that a major problem resulting form the use of immersion type heaters is that of galvanic corrosion of the heater while immersed within the tank. It is also known that providing an insulating coating on the outside of a sheathed heater can serve to somewhat reduce the galvanic currents tending to corrode the tank interior or the heater sheath. One form of insulating an immersed sheathed heater is shown in the U.S. Patent 2,649,532 issued on August 18, 1953. By my use of a heater encased in a glass cylinder and immersed in the tank, no galvanic currents can be generated by the heater or can be conducted by it to the tank walls adjacent thereto. By utilizing my principle, the heater is permanently isolated from all electrical contact with the water in the tank and as a result, no galvanic currents can flow between the heater and the adjacent Water. In this manner, there has been shown a construction designed to protect the heater from the corrosion which would otherwise be induced.

While there has been described what are at present considered to be the preferred emboidments of the invention it will be understood that it is intended to cover in the appended claims all such improvements and modifications which fall within the true spirit and scope of the invention.

What is claimed is:

1. A water heater comprising an imperforate tank for storing water therein, an inlet path for feeding cool water to said tank, an outlet path for feeding out heated water from said tank, means interposed between said paths for heating water stored in said tank, said interposed means comprising an electrically insulating hollow cylinder extending horizontally into said tank, a closed-off end integrally formed at one end of said cylinder to provide an imperforate Watertight structural member within said tank, a conductive film adhered uniformly about the inner wall of said cylinder, means for sealing the opposite end of said cylinder about said tank wall to provide a water impervious seal about said opposite end of said cylinder, said seal comprising a frusto-conical section integrally formed to said opposite end of said cylinder, flange gaskets externally of said section for protecting said section, means for connecting said film with a source of electric current including a frusto-conical insulator adapted to fit within said section, slots in said insulator, terminal members mating within said slots, conductive strips extending in spaced parallel relation along said cylinder sidewall in contact with said film and in electrical connection therewith to conduct heating current to said film, said cylinder transmittive of said generated heat from said film through said insulating cylinder to heat the water adjoining said cylinder within said tank.

2. Electric resistance heating means adapted to be inserted through a wall of a vessel to heat the contents thereof, comprising a tubular body structure having a substantial portion of its length of cylindrical shape, one end of said structure having an integral closure and the opposite end portion being expanded into a non-cylindrical configuration, the interior and exterior walls of said body structure being of heat resistant electrical insulation material, and impervious to the contents of said vessel; an electrically conductive oxide film in intimate heat transfer contact withthe inner wall of said cylindrical portion; electrically conductive strips extending axially along said conductive film, said strips being angularly displaced one from the other and extending along the inner wall of said expanded portion; a terminal carrier of insulation material being arranged for removable insertion into the said expanded portion for surface engagement with adjacent wall surfaces thereof; and electric terminal strips fixed on the external wall of said terminal carrier for intimate electrical contact with said conductive strips to afford means for connecting the same to electric power; said expanded end portion of said body structure further having means 7 adapted to be secured to said vessel wall while maintaining said structure electrically insulated therefrom.

References Cited in the file of this patent UNITED STATES PATENTS 540,073 Reed May 28, 1895 1,459,307 Laise et a1 June 19, 1923