US1746522A - Low-tension fluid-heating apparatus - Google Patents

Description

Fe? M, E93@ R. A. CARLETQN LOW TENSION FLUID HEATNG APPARATUS Filed July 12, 1927 4; Sheets-Sheet l 4 if, T.. WW

NVENTOR. Rohm .-Co1ireon ATTORNEYS.

Feb. 11, 1930. R. A. cARLEToN LOW TENSION FLUID HEATING APPARATUS 'Filed July 12I 1927 4 Sheets-Sheet 2 m .5. m -wmm V m. T NVC. Am A im@ 7 5 Peb. ll, 1930. R. A. CARLETON 1,746,522

LOW TENSION. FLUID HEATING APPARATUS Filed July l2, 1927 4 Sheets-Sheet 3 Pk/ENTER: Rober A CGrleTon :EJLll-WMJff l #YT-rn RN 1.15

Feb. l1, 1930. R. A. CARLETON LOW TENSION FLUID HEATING APPARATUS 1927 4 Sheets-Sheet 4 Filed July l2 L UUHHUHHHHH n 1 l l l i I l Patented Fei. 11, 1930 UNITED STATES PATENT OFFICE LOW-TENSION FLUID-HEATING APPARATUS Application led July 12,

This invention relates to `improvements in lluid heating apparatus and the general object of the invention is to provide a simple and rugged apparatus, of low cost of construction, and of high eii'iciency, and in which practically no substantial deterioration of the heating elements will be produced by usage.

A further object of the invention is to provide an apparatus of this character in which radiation losses will be reduced to a minimum and no heat insulation required.

A further object of the invention is to provide an electric Huid heating apparatus of this character in which the heating element-s will present a maximum surface area and in which the fluid will be directly heated by contact with the large surfaces of the heating element, thereby permitting a rapid transfer of heat from the heating element to the fluid being heated, so that the same can be operated at a comparatively low temperature, or at a temperature slightly above that of the fluid being heated, thus avoiding pitting or deposits upon the surface of the heating element and decomposition or other chemical or mechanical changes in the fluid which otherwise would be effected by excessive temperatures.

A further object of the invention is to provide an electric heater in which the heating elements are heated by an electric current of loW potential.

A further object of the invention is to provide a heating apparatus in which the low ments by a step-down transformer and is insulated from the usual lighting or power systems which supply current to the primary circuit of the transformer in which, under the usual practice, one side ot the service is grounded, thereby avoiding dangerous voltages in the heating apparatus.

A further important object of the invention is to provide an electric heating apparatus of the character specified in which narrowly spaced heat-ing elements are immersed in the fluid to be heated and the current supplied to said heating elements is caused to pass through alternating heating elements in optension current is supplied to the heating ele- 1927. Serial Fo. 205,135.

posite directionss thereby substantially avoiding the effects of self-induction.

A further object ot the invention is to provide means for controlling the supply of the electric current to the heating elements so as to maintain a uniform maximum temperature of the fluid within, or delivered from, the apparatus.

A further object of the invention is to provide means operable by the flow of fluid supplied to the apparatus to control the current supplied to the apparatus and whereby cessation of flow of the fluid into the apparatus will interrupt the supply of the current to the heating elements.

A further object of the invention is to provide an electric heating apparatus of this character in which the heating 'elements may operate with a direct current or a single phase or a polyphase alternating current at any desired voltage or frequency depending upon the character of the material of the heating elements and the character of the fluid being treated. For example, the heating of Water and light liquids may require the use of a current of one hundred or more volts7 While with brine, strongly acid liquids, or the like, a low tension current ot two or more volts might be required.

The present invention contemplates the provision of an electric heating apparatus in which Va heating element, 0r plurality of elements presenting large surfaces are immersed and directly exposed to the fluid being heated and are supplied with a relatively low tension current ot' suilicient amperage to raise the heating elements to the desired temperature.

By the use of such relatively low tension currents leakage of the current through the fluid being heated is reduced to a minimum. By passing a current in opposite directions to alternating heating units, self-induction is Wholly or substantially avoided.

Desirably the fluid is caused to flow in a predetermined direction between narrowly spaced heating elements so that it is heated mainly by direct contact with the heating elements. Preferably the heating elements are of spiral form and the Huid is caused to How through the narrow spaces between the adjacent heating elements toward the center thereof and is delivered from a central outlet. rIhis construction permits the elements to present a maximum heating surface. Radiation losses are prevented for the reason that the cold fluid enters between the peripheral edges of the heating elements and after being heated is discharged through the central outlet so that the heating elements as a whole are surrounded by a body of cool fluid which does notradiate heat to any substantial degree through the wall of the receptacle, thereby avoiding the necessity `of external heat insulation. y

The present invention is adapted in itsv ap'- plication to various purposes, including the heating of aquiescent body of fluid, instantaneous heating of a flowing fluid such as water` the generation of steam, the superheating of steam, vaporizing volatile materials,-

evaporating liquids, concentrating liquids, as well as other uses.

Illustrative embodiments of the invention are disclosed in the accompanying drawings', 1n which, v

Fig. 1 is a vertical sectional view of apreferred form of apparatus for heating the flowing liquid or gaseous fluid;

Fig. 2 is a detail sectional view on line 2-2 Fig. 1, having in common with Fig. 1 an illustration of a single phase step-down transformer Fig. 3 isa vertical sectional view of a modified formof apparatus showing the manner in which a polyphase current may be supplied to the heating elements;

Fig. 4 is a horizontal sectional view on line 4-4 Fig. 3;

5 is a vertical sectional view of a slightly modified form of the apparatus particularly adapted for steam generation;

Fig. 6 is a horizontal sectional view on line 6-6 Fig. 5;

Fig. 7' is a vertical longitudinal sectional view of a form of apparatus particularly a cylindrical wall 1 of steel or other material adapted to withstand pressure under which the fluid is being treated, and also to resist corrosion. or chemical action by the chemicals contained in the fluid. The lower end of the cylindrical wall is connected by a flange 2, or other water-tight connection, with a head 3 of suitable material having a central boss pass in the op head above the fitting 7, is provided with an outlet pipe 12 through which the fluid may be discharged from thetank or receptacle.

Fluid may be aitroduced into the lower portion of the receptacle in any suitable manner. In the construction illustrated, however, the tubular member 6 is provided near its lower end with a web or closure 13 and the portion of the tubular member below said closure is provided with a series of ports 14 through which fluid introduced at the lower end of the tubular member is discharged into the lower portion of the receptacle. The tubular member 6 is provided above the closure 13 with a series of ports 15 which permit the fluid to flow from the receptacle into the chamber of the tubular member and thence through the outlet 12.

The heating elements comprise preferably a plurality of curved thin plates of relatively high resistance material, such as monel metal which is non-corrodible and generally resistant to chemical action. In the preferred construction the heating elements are in the form of two narrowly separated spiral plates 16l and 17 which are 'connected at their inner ends to diametrically opposite portions of the wall of the central tubular member 6. The outer ends of these spiral plates are connected to suitable terminals of an electric circuit so that the current will flow, for example, through the spiral plate 16 to the central tubular member 6, and from the central tubular member will posite direction through the spiral 17. By reason of this arrangement the magnetic field caused by the flow of current in one plate is neutralized by the magnetic field caused b v the flow of current in the other plate, thus substantially preventing the effect of self-induction and permitting the circuitl 21 and 22 which receive the lower ends of the spiral plates 16 and 17 respectively. The upper ends of the plates 16 and 17 are seated in similar spiral grooves in an insulating d isk 23 which is engaged by a spider 24 mounted upon the tubular member 6 and which may be clamped upon'the plates by a suitable nut 25.

Desirably the ends of the spider arms are connected by tension rods 26. By reason of this construction the spirally curved heating plates are held firmly in position and at all times maintained in narrowly spaced relation.

Any suitable means may be provided for supplying a suitable electric current to the heating plates.

In the preferred construction illustrated herein the heating -current is supplied from the secondary 27 of an adjustable step-down transformer 28. Low resistance conductors 29 and 30 lead from the secondary coil 27 of the transformer to low resistance conductor bars 31 and 32 which preferably are connected to the'outer edges of the spiral plates 16 and 17 throughout the length of the plates and are adapted to conduct a current of relatively low voltage of sufficient amperage to heat the plates 16 and 17 to the required temperature. A relatively high tension currentis supplied through the conductors 33 and 34- and a manually operable switch 35 to the primary 36 of the/transformer.

Desirably suitable means are provided for controlling the voltage of the primary circuit of the transformer and also means desirably are provided for breaking the circuit to the primary upon cessation of flow of uid through the tank or receptacle.

In the construction illustrated herein a thermostat 37, which may be located within the receptacle, or preferably within the outlet pipe 12, in such a position that it is subject to the maximum temperature of the fluid, controls a high resistance branch or shunt, of the power circuit 38, 39, embodying or having within it a solenoid 40, or other device, adapted automatically to operate a contact arm 41 to cut in or out certain of the coils of the primary 36, thereby changing the voltage of the secondary and thus controlling the current delivered to the heating elements.

Preferably hydraulic means are provided for interrupting the primary circuit upon cessation of ilowof liquid through the apparatus. In the construction illustrated an inlet pipe 42. which communicates with the lower end of the tubular member 6, is provided with a pivotally mounted switch 43 which is operated hydraulically by thefiuid flowing into the receptacle to .complete a branch or shunt circuit 44 and 45 of the main power supplying circuit through a Contact breaking device 46 in the conductor 33 leading to the primary. This arrangement is such that when water is flowing through the inlet the branch circuit 44 and 45 is completed, thereby causing the closing of the contactor 46 to permit the circuit to ow through theprimary.

Upon cessation of the low of Water through the inlet 42 to the receptacle, the branch circuit 44 and 45 is broken and the contactor opened, thereby breaking the primary circuit and consequently de-energizing the transformer so that no current will iiow through the heating coils.

In the operation of the device the water entering into the lower portion of the tank or receptacle is caused by the imperforate lower head 20 to How outwardly and upwardly along the cylindrical wall of the receptacle. The liquid then flows between the spirals of the heating plates 16 and 17 to the center of the tubular member and enters ports therein and is finally discharged through the outlet 12. By reason of this construction cool fluid is always in Contact with the cylindrical wall 1 and the liquid is progressively heated, mainly by direct contact with both the inner and outer surfaces of the spirals throughout the greater part of the length thereof. As these spiral plates present large areas to a relatively small volume of iuid in the heater the fluid is very rapidly heated and the heated fluid is discharged from the outlet at its maximum temperature. By the employment of a low voltage current leakage of the current through the fluid is reduced to a minimum. As the low tension secondary current is insulated from the high tension primary current, danger to the operator is avoided.

The apparatus thus described is of simple construction which may be produced at a relatively low cost. It is automatic in operation. It provides a direct and rapid transfer of heat from the heating elements to the fluid being heated. It permits the heating of the iuid by heating units presenting large surface areas. rllhe temperature can be controlled at a small difference between that of the heating element and of the fluid and the close regulation of heat may be maintained at any temperature. rIhe construction is of a. rugged nature and as the heating elements are at all times immersed within the fluid they will not burn out. Inasmuch as cool Huid, which is introduced, is in contact with the wall of the receptacle or tank, no substantial radiation losses occur and no insulation is required. No deposit is formed upon them and no pitting of the heating elements occurs.

It will be obvious that apparatus embodying the 'invention may be made of any size or capacity and of materials suitable for the use for which the apparatus is applied.,

In Figs. 3 and 4 a modified construction is illustrated which is adapted for a water circulation system. This construction comprises a preferably cylindrical tank or receptacle 47 having upper and lower water- tight heads 48 and 49 andl provided with an inlet pipe near the lower-end thereof and an outlet pipe 51 at its upper end, the pipes 50 and 51 being adapted to be connected into a. Water storage tank or a circulating system.

In this construction a central, preferably tubular, member 52, having a screw threaded lower end, is seated in a boss 53 in the lower head 48 and is provided with spider arms 54 at a short distance above the head 48. Strips 55 of insulating material are secured to the upper faces of .the spider arms 54 and are provided with grooves in which the lower edges of the yheating elements are mounted. The heating elements may be of any desired form, such as cylindrical or preferably spirally f" formed plates narrowly separated from each other and so arranged that the current will flow in opposite directions through alternating plates.

In the construction illustrated the heating elements comprise three spiral plates 56, 57 and 58, the central ends of vwhich are connected preferably at equal distances from each other to the central tubular member 52.

The outer ends of the plates are connected respectively to conductor bars 59, 60 and 61 which are in turn connected to conductors 62, 63 and 64 which pass through a block 65 of insulation in the wall of the receptacle and are connected to the secondary 66 of a three-phasetransformer'to the primary 67 of which current is supplied through the conductors 68, (39 and 70.

The resistance plates in this construction are so connected in the three-phase circuit of the secondary that the magnetic field,

. caused by the current flowing in one direction in outer plates, is neutralized by the magnetic field caused by the return flow of current in an intermediate plate; thus self-induction or induced voltage is greatly reduced, thus permitting the circuit to operate at a high power factor. Y

A suitable thermostat 71, located in the upper portion of the receptacle, and subject to the maximum heat of the fluid, may be employed to control a branch 72, 73 of the primary circuit having suitable means, as heretofore described, for regulating the voltage supplied to the secondary circuit of the transformer.

In Figs. 5 and 6 a modified form of apparatus is illustrated which is particularly designed for a steam generator. This construction comprises a preferably cylindrical boiler 74 having upper and lower heads 75 and 76 with a supply pipe 77 leading through the lower head for introducing water into the apparatus, and anoutletpipe 78 leadingfrom the upper head. The boiler desirably is surrounded by heat insulation 79. The heating elements in this construction, as in those previously described, comprise spiral plates 8O and 81 which are narrowly spaced apart with the spirals alternating and both connected at their inner ends to a central bar or tube 82 which is supported upon lower and upper side-shaped brackets 83 and 84 which are mounted upon suitable supporting lugs 85 and 86 extending inwardly from the wall 74 of the boiler. Suitable strips of insulation 87 and 88, resting upon the upper and lower arms of the spider, are provided with grooves to receive the ends of the spiral plates and 81 as above described. The boiler desirably is provided with a usual glass water gauge 89 and other usual boiler equipment.

In addition to these the boiler, in this particular construction, is provided with a pressure operated device 90 adapted to operate through an electric circuit 91 and 92 to control a switch 93 in a circuit 94 and 95 leading to a primary 96 of a step-down transformer. Conductors 97 and 98 lead from the secondary 99 of the conductor to bars 100 and 101 which are connected respectively throughout the edges of the high resistance heating units 80 and 81. A water level is maintained at a suilicient height to immerse the heating plates within the Water.

In the operation of this construction, when current is supplied to the primary of the transformer, the electrically operated switch 93 will be closed, thereby energizing the transformer and causing a low voltage current to flow through the conductors 97 and 98 and the relatively high resistance heating elements or plates. rIhe heat generated in the heating plates or elements is transmitted directly to the water in which the plates are submerged. The heating of the water will cause it to rise, thus causing an upward circulation of water between the plates and a downward circulation near the surrounding wall of the boiler. The water thus circulated will be rapidly raised to boiling temperature and the steam will collect in the upper portion of the boiler and may be delivered as rapidly as desired through the outlet pipe 78. When the steam in the upper portion of the boiler has acquired the desired pressure the pressure device 90 will operate to open the control switch 93 in the circuit leading to the primary of the transformer, thereby de-energizing the transformer and cutting olf the secondary current through the heating units. When the pressure of the steam in the boiler drops below the desired amount, the pressure regulating device will again close the switch 93, thus again energizing the transformer and causing; another heating cycle. 4 i

It will be obvious that should it be desirable the control switch and the transformer Vcan be so arranged that instead of disconform steam production at a desired pressure.

The principal advantages of this form of electric heater over other types of electric heaters now in use are low cost of manufacture; indestructibility; elimination of repairs or replacements; high efiiciency. due to comparatively large heating unit surfaces; the rapid transfer of heat from the plates to the surrounding liquid which is in direct contact with the plates; operation at a much lower temperature than other types of heating elements because of the large heating area; avoidance of overheating by reason of `the constant contact of the liquid with the heating elements and the rapid circulation of the liquid by reason of the rapid transfer' of heat thereto.

This embodiment of the invention is particularly adapted for household heaters of small size, such as for domestic steam or vapor` heating, but may be constructed of sufciently large capacity for various indus trial uses.

A further embodiment of the which is particularly adapted superheating, is illustrated in Figs. 7 and 8. This construction may be substantially like that disclosed in Figs. 1 and 2 with the exception that the cylindrical wall 102 desirably is made of steel, cast iron, or other suitable metal to withstand high temperatures and pressures, and is provided with removinvention,

' able heads 103 and 104. The high resistance conductors 105 and 106 desirably are of spiral form and are connected at their inner ends to a central tubular member 107 having ports 108. The central tubular member likewise is provided with a closure 109 near the inlet end of the receptacle with ports 110 in the wall of the tubular member to admit steam into the cylindrical chamber formed by the wall 102 and heads 103 and 104. The steam entering the chamber passes between the heating plates 105 and 10-6 and through the port-s 108 into the chamber of the tubular member and is delivered through the outlet 111 in the manner above described.

In this construction conductors 112 and 113 lead from the secondary 114 of a singlephase secondary of a transformer having a three-phase primary to conductor bars 115 and 116 which are secured to the longitudinal outer edges of the spiral conductors. These spiral conductors 105 and 106 are arranged in alternate relation and their inner edges are secured to the centraltubular member 107 as heretofore described.

In theI construction illustrated in Figs. 7 and 8 a thermostatic device 117 controls a branch circuit 118- and V119 having therein a solenoid 120, or other device for actuating a switch 121 to break the primary circuit when the steam reaches a predetermined temperature. Obviously the pressure operated device for steam receptacle or drum between the narrowly sep-` arated heating plates to the central tubular member from which the superheated steam is discharged. In the operation of this construction, as in those heretofore described, a rapid transfer of heat is maintained from the heating elements to the fluid which is circulated between them so that the Huid is heated mainly by direct contact with the heating elements. In this construction, as in those heretofore described, the current passes through alternating plates in opposite directions thereby neutralizing the effect of self-induction.

Obviously other means for regulating the current supplied to the transformer, such as those heretofore described, or other usual types of regulators, may be employed within the scope of the invention.

It will also 'be obvious that other types of heating units may be used, such for example, as a plurality of narrowly separated flat plates with means for passing the current through alternating plates in opposite directions. Preferably, however, curved lplates are employed for the reason that greater surface areas may be presented thereby. Such curved plates may be narrowly separated concentric cylindrical plates with means for passing the current through`alternating plates in opposite directions. It has been found, however, that spiral plates of the character herein described are the most desirable. The single spiral plate has been found to be very satisfactory where a direct current is employed by reason of the large area it presents when coiled within a receptacle or boiler which.

electric power to the district in which the inl stallation is made.

It will be understood that the particular embodiments of the invention disclosed herein are of an illustrative character and not restrictive of the scope or meaning of the following claims.

Having thus described the invention, what is claimed as new, and desired to be secured by Letters Patent, is:

- pass through to provide a continuous conductor, and meansl for connectlng the other edges of sa1d plates' in an electric circuit to cause the current to said plates in opposite directions, whereby effects of self-induction will be substantially neutralized.

'2. A fluid heating apparatus comprising a fluid-containing receptacle, a plurality of x heating elements of high electrical resistance present/ing large surface areas narrowly separated from one another and immersed in said fluid, conducting means electrically connecting all of said heating elements together at one end, means for supplying a polyphase current to the other ends -of said plates to cause the current to pass through alternating plates in opposite directions, whereby effects of self-induction will be substantially neutralized.

3. A fluid heating apparatus comprising a fluid-containing receptacle, a plurality of thin metallic plates of high electrical resistance presenting large surface areas narrowly separated from one another and immersed in said fluid and in direct contact therewith, conducting means electrically connecting all of said plates together at one end, means for supplying a polyphase current to the free ends of said plates to cause the current to flow in opposite directions through alternating plates, whereby effects of self-induction will be substantially neutralized.

4. A fluid heating apparatus comprising a fluid-containing receptacle, a plurality of thin metallic plates of high electrical resistance presenting large surface areas narrowly separated from one another and immersed in said fluid and in direct contact therewith, conducting means electrically connecting all of said plates together at one end, means forsupplying a polyphase current to the free ends of said plates to cause the current to flow in opposite directions through alternating plates, whereby effects of self-induction will be substantially neutralized, and means for causing the liquid to flow through in the same general direction through all of the spaces between said plates.

5. A fluid heating apparatus comprising a fluid-containing receptacle, a plurality of narrowlyspa'ced heating elements immersed in said fluid', means for passing an electric current through alternating elements in opposite directions, whereby effects of self-induction will be substantially neutralized, means for causing the fluid to flow in a predetermined` direction relatively to the surfaces of said elements and thermostatic means subject to directions, whereby effects of self-induction will be substantaially neutralized, means for causing the fluid to flow in a predetermined direction relatively to the surfaces of said elementsand means lautomatically operable by the flowl of fluid through said receptacle to cause the electric current to besupplied to said plates and to prevent the supply of said current. uponsubstantial cessation of said flow. y

7.' A fluid heating apparatus comprising a I fluid-containing receptacle, a plurality of narrowly separated, thin, spirally curved conducting plates of high electric resistance material presenting large surface areas, means for passing an electric current through alternating plates in opposite directions and means for causing the fluid to flow between said plates in the direction of the spiral.

8. A fluid heating apparatus comprising a fluid-containing receptacle, a plurality of narrowly spaced curved metallic plates of high electric resistance material presenting large substantially parallel vsurface areas extending longitudinally of said receptacle and in direct Contact with the fluid therein, means for introducing fluid into the lower portion of said receptacle, means for delivering the fluid from the upper portion of said receptacle and means for passing an electric current through alternating plates in opposite directions. A9. A fluidheating apparatus comprising a fluid-containing receptacle having a fluid inlet at one end and an outlet at the other end and a heating unit immersed in said fluid comprising a metallic plate of high resistance material of concentric spiral form arranged axially of said receptacle and presenting a large surface area, means for causing the fluid to flow from the periphery of said spiral toward the axis thereof in direct contact with said plate and means for passing an electric current through said plate.

10. A fluid heating apparatus comprising a cylindrical fluid-containing receptacle having a fluid inlet at one end and an outlet at the other end and a heating unit immersed in said fluid of concentric spiral form ar-` ranged axially of said receptacle and presenting a large surface area in direct contact with the fluid and with the spirals thereof narrowly spaced apart and means for passing an electric current through `said heating unit.

11. A fluid heating apparatus comprising a fluid-containing receptacle having a fluid inlet at one end thereof and a central tubular outlet extending axially of said cylinder and provided with ports, a heating unit immersed in said fluid comprising a plate of high resistance material of concentric spiral form extending outwardly from said tubular outlet and presenting a large surface area, imperforate heads of insulating material engaging the ends of said plate and operable to cause the Huid to flow from the peripheral edge of said plate toward the ports of said tubular outlet andy means for passing an electric current through said plate.

12. A uid heating apparatus comprising a cylindrical fluid-containing receptacle having a fluid inlet at one end thereof and a central tubular outlet extending axially of said cylinder and provided with ports, a heating unit of con-centric spiral form immersed in said fluid and extending outwardly from said tubular outlet and presenting a large surface area in direct contact with the iuid, imperforate heads of insulating material engaging the ends of said heating unit and operable to cause the fluid to flow from the peripheral edge of said unit toward the ports of said tubular outlet, and means for passing an electric current through said unit.

13. A fiuid heating apparatus comprising a fluid-containing receptacle having a fluid inlet at the lower portion thereof and a central tubular outlet having a closure at the lower portion thereof above said inlet and having ports in its wall above said closure, a plurality of narrowly spaced concentric spiral metallic plates of high resistance material immersed in said fluid and presenting large surface areas extending outwardly from said tubular outlet, imperforate heads of insulating material engaging the ends of said plate operable to cause the fluid to flow from the peripheral edges of said plates toward the ports of said tubular outlet and imeans for passing an electric current through said plates.

14. A fiuid heating apparatus comprising a fluid-containing receptacle having a fiuid inlet at the lower portion thereof and a central tubular outlet having a closure at the lower portion thereof above said inlet and having ports in its wall above said closure, a plurality of narrowly spaced concentric spiral heating elements presenting large surface areas extending outwardly from said tubular outlet, imperforate heads of insulating material engaging the ends of said heating elements operable to cause the fluid to fiow from the peripheral edges of said heating elements toward the ports of said tubular outlet, and means for passing an electric current through said heating elements.

15. A fluid heating apparatus comprising a fluid-containing receptacle having a fluid inlet at the lower portion thereof and a centrel tubular outlet having a closure at the lower portion thereof above said inlet and having ports in its wall above said closure, a plurality of narrowly spaced spiral plates of high resistance material presenting large surface areas extending outwardly from said tubular outlet, imperforate heads of insulating material engaging the ends of said plate operable to cause the Huid to flow from the peripheral edges of said plates toward said tubular outlet and means for passing an electric current through alternating plates in opposite directions, whereby edects of selfinduction will be substantially neutralized.

16. A Huid heating apparatus comprising a cylindrical fluid-containing receptacle, a tubular member extending centrally therethrough having in its wall inlet ports communicating with the lower portion of said receptacle, a closure above said inlet ports and a plurality of series of other ports above said closure, a plurality of narrowly spaced thin plates of high resistance material presenting large surface areas extending outwardly from said tubular member, an imperforate head of insulating material mounted upon said tubular member above and in proximity to said closure, engaging the lower ends of said plates and a similar head engaging .the upper ends of said plates operable to cause the fluid to fiow from the peripheral edges of said plates toward saidI tubular member and means'for passing an electric current of low potential through alternating plates in opposite directions, whereby effects of selfinduction will be substantially neutralized.

17. A fluid heating apparatus comprising a fluid-containing receptacle, a plurality of narrowly spaced heating elements immersed in said fluid, means for passing an electric current of relatively low voltage through said heating elements including a step-down transformer having terminals of its secondary circuit connected respectively to alternating heating elements to cause the current to flow through said alternating plates in opposite directions, means for supplying a current of relatively high voltage to the primary of said transformer, a thermostat subject to substantially the maximum temperature within the receptacle and means operable by said thermostat for controlling the current supplied to the primary of said transformer.

18. A fluid heating apparatus comprising a fluid-containing receptacle having an inlet and an outlet, a plurality of narrowly spaced platesof high resistance material immersed in said fluid, means for passing an electric current of relatively low voltage through said plates including a step-down transformer having terminals of its secondary circuit connected respectively to alternating plates to cause the current in said plates to fiow through alternating plates in opposite directions, means for supplying a current of relatively high voltage to the primary of said transformer, a thermostat Subject to the temperature of the fluid passing through the outlet of said receptacle and means operable by said thermostat for controlling the current supplied to the primary circuit of said transformer.

19. A Huid heating apparatus comprising a fluid-containing receptacle having an inlet and an outlet, a plurality of narrowly spaced plates of high resistance material immersed in said iuid, means for passing an electric current of relatively 10W voltage through said plates including a step-down transformer having terminals of its secondary circuit connected respectively to alternating plates to cause the current in said plates to flow through alternating plates in opposite directions, means for supplying a current of relatively high voltage to the primary of said transformer, and means operable by the How of iiuid through said inlet to control the current supplied to the primary circuit of said transformer.

20. A fluid heating apparatus comprising a fluid-containing receptacle having an inlet and an outlet, a plurality of narrowly spaced plates of high resistance material immersed in said fluid, means for passing an electric current of relatively low voltage through said plates including' a step-down transformer aving terminals of its secondary circuit connected. respectively to alternating plates to cause Ithe current in said plates to flow through alternating plates in opposite directions, means for supplying a current of relatively high transformer, means operable by the flow of fluid through said inlet to control the current supplied to the primary circuit of said transformer, a thermostat subject to substantially the maximum temperature of the iuid in said receptacle and means operable by said thermostat for controlling the current supplied to the primary circuit of said transformer.A

In testimony whereof, I have signed my name to this s ecifiaction.

R BERT A. CARLETON.

voltage to the primary of said e

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