US2004976A - Electric fluid heater - Google Patents

Description

June 18, 1935/ R. A. CARLETON 2,004,976

ELECTRIC FLUID HEATER Filed Aug. 7, 1931 4 Sheets-Sheet 1 2 5 INVENTOR.

F--- 2 ROBERT AQCHRLETDN 1g y VM,M,7FM\ M- ATTORNEYS June 18, 1935. "R. A. CARLETON ELECTRIC FLUID HEATER 4 Sheets-Sheet 2 .Filed Aug. 7, 1951 INVENTOR ROBERT A. CARLETON June 18, 1935.

R. A. CARLETON ELECTRIC FLUID HEATER Filed Aug. '7, 1931 4 Sheets-Sheet 3 INVENTOR. Ross/w A. CARLETON BY Flg. 6..

ATTORNEYS June 18, 1935. R. A. CARLETON ELECTRIC FLUID HEATER Filed Aug. 7, 1931 4 Sheets-Sheet 4 Fig. 10.

L78 75 ay AV/JF/AY/AIV/AV/AV/AV/AM Fig. 9.

&N mw V mm C A m E w R BY M M hfm 77M A TTORNEYS Patented June 18, 1935 i UNITED STATES PATENT OFFICE ELECTRIC FLUID HEATER Robert A. Carleton, Brooklyn, N. Y., assignor to National Electric Heating Company, Inc., New York, N. Y., a corporation of New Jersey Application August 7, 1931, Serial No. 555,801

8 Claims. (Cl. 219-38) This invention relates to improvements in elecalso been found desirable to incorporate a safety tric fluid heating apparatus of the type in which switch which will stop the flow of current to the the fluid is heated by direct contact with the heating units in case the amount offluid in the heating elements. heater drops below a predetermined minimum.

In electric heaters great difliculty has been In constructing the heater, it has been found 6 encountered in obtaining rapid heating and the that non-corrosive metals may very advantaheaters heretofore used have been of low eiilgeously be employed to prevent the fluid being ciency and rather prone to get out of order and treated from damaging the heater. When so need adjustment and repairs. constructed there is practically nothing in the The object of this invention is therefore to prodevice which is subject to deterioration or break- 10 vide an electric fluid heater which will operate age or which is liable to get out of adjustment. both rapidly and efliciently and which is of a It will thus be apparent that the heater as consufliciently rugged construction so that it will not structed according to this invention will possess easily get out of order. all those qualities of efliciency, durability, speed It is the further object of this invention to and automatic control which are desirable. 15 provide' a heater of this type which will operate For a more detailed description of the apparaeither on direct current or on alternating curtus of this invention, reference may be had to rent having any of the usual characteristics and the appended drawings and the description which will be adaptable for both domestic and thereof.

industrial use. In the drawings, Figure 1 is a plan view in 20 With these objects in mind, heating elements section of the apparatus. have been devised which have the form of thin, Figure 2 is an elevational view of the heater .closely -spaced ribbons of metal having a high in section taken on the line 2-2 of Figure 1 and electrir'al resistance, and a plurality of these elethis view shows the electrical connections to ments are held edgewise between supports to form the heater. 25 heating units. A series of these heating units are Figure 3 is an enlarged sectional elevation of mounted for use in parallel relation and electrithe heater units. cally connected so that the current flows through Figure 4 is a detailed sectional view of a part the alternate units in opposite directions. The of the heater units showing the method of supheater is swported within a tank where the fluid porting the ribbons; and 30 is caused to circulate between the closely spaced Figure 5 is a P View Of the Section hown ribbons from which it is heated. in Figure 4.

By the closely spaced, thin ribbon between Figurefi is a sectional elevation of a circulatwhich the fluid is caused to flow a very high rate ing fluid hea er embody n the p pl f his of heat transfer is accomplished and large nv 35 amount of current may be passed through the Figure 7 is a sectional view of the deviceshown heating elements and rapid heating of the fluid in Figure taken o h l ne 1. may take place. By arranging the units which Figure 8 is a sectional view of the device make up the heater so that the current flows in Shown in Figure 6 taken on e e ll8.

4U opposite directions through adjacent units the Figures 9 and 10 are sectional detail views Of self-induction in the heating units is neutralized the d ce of Figure 6 on an enlar d Scaleand the power factor and hence the efiiciency of As illustrated in Figu es 1 to 5 0f the drawthe device greatly increased. By clamping the 8 011601? t e Preferred Constructions p ythin ribbons edgewise between supports, they are ing the principles of this invention is a fluid held rigidly in position and this coupled with the heater in which the fluid is circulated through 5 structure which will be further described pro the heater by the convection currents set up by duces an electric fluid heater which is excepthe heating units. The heater comprises a tank tionally rugged and has little tendency to get out made up of an inner-shell 2| Su p d d Wi n of order or need adjustment. an outer shell 22 and insulated therefrom by In order that the temperature to which the insulating material 23. The inner shell is prei- 50 fluid is heated may be accurately controlled, it has erably of some non-corrosive metal such as been found desirable to control the amount of Monel metal, copper, or the like; while the outer current which flows through the heating elements shell 22 is usually of sheet steel. The insulating by use of a thermostat operated in accordance material may be any of the well known matewith the temperature of the heated fluid. It has rials such as asbestos, diatomaceous earth, mineral wool or the like. The fiuid enters the tank through an inlet 24 and leaves through an outlet 25. The top of the tank is open but is covered by a hood 26 from which fumes and vapors are exhausted through an outlet 21.

A heating device 28 is suspended within the tank near the bottom thereof by means of metal strips 29 which are supported from a ring 30 near the top of the tank. The ring; 30 is received in slots in lugs 3i which are welded or otherwise suitably fastened to the inner wall of the tank near the top, thereof. Bolts 32 hold the ring 30 tightly in place.

The heating device comprises a plurality of heating units each consisting of a thin metal rib bon formed into a closely sp'aced'spiral 33. The

spirals 33 are secured rigidly in place by being I clamped edgewise between radially extending insulating plates 34. Each of the insulating plates 34 is provided with a plurality of grooves 35 which receive the edges of the spiral ribbons. The radial insulating plates 34 may be of any suitable insulating material such as slate orporcelain. The outer insulating plates have grooves only onv their inner edges but the insulating plates between adjacent spirals of metal ribbon have grooves on the opposite edges and the as sistance of supporting two of the spirals.

The insulating plates 34 are supported by radially extending arms 35 to which they are attached by the bolts 31. The radial extending arms 36 areall secured to a frame member 38 I which extends axially of the spirals at the center thereof. Bolts 39 are used to secure the radial arms 36 to the frame member 38.

. Each groupof parallel radial arms 38 are secured together at their outer ends by a bar 40 to which they are bolted by the bolts 4|. bars 40 are parallel to the frame member 38 and are all attached at theirupper ends to a ringshaped strip 42 by means of angle brackets 43 which are bolted to the bars 40 by bolts 4! which secure the radial arms to the bars 40 and bolts 44 by which the angle brackets are fastened to the ring 42. The bottom ends of the bars 40 are similarly connected to a ring-shaped strip 45 and the ring- shaped strips 42 and 45 are 1nv turn bolted or otherwise suitably connected to the supporting strips 29.

The inner ends of the spirals 33 are all connected together by a connector strip 46, and the outer ends of the spirals are each separately connected to the source of current supply. These connections are made by meansof connecting strips which connect detachably to connecting strips 5| at a connection block 52 which is supported adjacent the units by a supporting member 53 suitably attached to the rings 42 and 45. The connecting strips 5| connect to insulated connecting ,bolts' 49 which extend through insulated and oil tight bushings in the tank wall. Current is supplied to the connecting bolts 49 outside of the, tank to energize the heating units. i

In the device shown, there are three heating units and the heater is operated on a three-phase The ' device,

of the switches. Current to operate the magnetic switches is taken from the main line below the main switch 55 by a pair of wires and 60a. The wires 50 and 60a are connected to a. hand operated switch 6! which may break the circuit and thereby allow the magnetic switches to open and the main circuit to be broken. From the hand operated switch 6| thewires 60'lead to a. float operated switch 62 which has a float 52' inside the tank and operates to break the circuit if the fluid level in the tank falls below a predetermined minimum. From this switch the wire 60 leads to a thermostat switch 53 which has a heat sensitive element 64 extending into the tank and which'operates to break the circuit if the temperature in the tank exceeds a predetermined maximum. From this switch the wire 60 leads to a thermostatic control switch 55 having a heat sensitive element 56 extending into the tank. and operating to selectively connect the wire 50 to either the wire 61 which leads to the magnet of the switch 56 or the wire 68 which leads to the magnet of the switch 58. The thermostatic control switch 55 operates so that it opens the switch 55 and closes the switch 58 when the temperature reaches a predetermined maximum and reverses the operation when the temperature reaches a predetermined minimum. thus tending to keep the fluid ture.

In the circulating fluid heater as illustrated in Figures 6 to 10, the device comprises a tank 10 preferably of non-corrosive metal surrounded by a casing ll of sheet metal or the like and having insulation material 12 between the tank and the sheet metal casing. The tank is provided with an inlet 13 and'an outlet 74 and isclosed both at the top and at the bottom so that liquid may be forced to circulate therethrough under the pressure of a pump or similar circulating As in Figures 1 to 6, the heating units 33 are in the form of closely spaced spirals of metal ribbon held edgewise between radially ex tending insulating plates 34 which are in turn bolted to radially extending supporting arms.

A frame '15 having radially extending supporting arms 76 is mounted .on a rod 11 which extends axially of the spirals, the insulating plates 34 are fastened to the radially extending arms by means of bolts 13 and the frames 15 are spaced along the rod 1'! by means of collars 19 which surround the shaft 11 between the frames. The ends of the rod 11 are threaded to receive'nuts 79 which hold the framesin a spaced position upon the rod. The block 80 is bolted to the outer end of each 'of the radial arms 16 and rods 8| extend through the blocks 80 and are surrounded by collars 82 which space the blocks along the rod. Each of the rods 80 is also threaded-at its ends to receive nuts 83 which hold the blocks and collars in position thereon.

A flatring 85 lies on top of each set of blocks which are in the same horizontal plane and prevents the flow of fluid around the sides of the heating units. The rings 85'are cut out to surround the rods 8! and are clamped between the collars 82 and the blocks 80. Perforated plates 86 lie both above and below the heating device and are held in place by means of supporting strips suitably fastened thereto as by welding.

fit around in the tank at a fixed tempera- (ill by means of brackets 90 which are held on the top of the rods 80 by the nuts 83 and bolted to the sides of the tank 10 by bolts 9i.

Conducting strips 93 connect to the outer ends of a part of the spirals and connecting strips 94 connect the inner ends of a partof the spirals together. The connecting strips 93 extend through spacers 95 supported from the radially extending supporting arms and are suitably insulated therefrom by insulators 96. These connecting strips 92 connect with insulated bolts 91 which passthrough the wall of the tank and are connected on the outside with a suitable source of electric current.

As shown in the drawings, the connections 93 and 94 are so arranged that the heating spirals are connected in three series of four spirals each, and each of the series is connected across one phase of a three-phase alternating current which is supplied from a supply line 98 through a magnetic switch 99.

The magnetic switch 99 is controlled by a circuit I00 which receives its power from the main supply line 98 and may be broken by either a thermostatic switch l0! operated by a heat sensitive element I02 near the outlet of the heater or by a switch I03 which is connected to the intake of the heater and operates to break the circuit upon substantial cessation of the flow of fluidto the heater. This circuit may also be broken by a hand operated switch I04 and when broken by any of these switches the magnetic switch is opened to stop the flow of current to the heater. This prevents the flow of current to the heater when the fluid in the heater becomes too hot or ceases to flow and thus prevents damage to the fluid or the heater.

It will be apparent from the foregoing description that the fluid flowing through the heater will be caused to flow through the relatively small spaces between the metallic ribbons and will thus be subjected to the heating effect of a large, surface over which the fluid will pass in relatively small streams.

It may also be "observed that the heating elements being of light material and in direct contact with the liquid'will cool quickly'if the current is shut off and the apparatus may therefore be very finely controlled to give a very accurate temperature adjustment.

The apparatus of this invention is useful for any kind of fluid heating, but the apparatus of Figures 1 to'6 is particularly adapted to heating and bodying or polymerizing linseed or similar oils. When bodying such'oils, the oil is heated to a selected temperature usually within the range of 560 to 625 F and maintained at the selected temperature for a period of time necessary for the desired bodying or polymerizing re action to take place which may require from one to tenhours or more, depending upon the kind or quality of the oil, the temperature at which it is treated and the body or viscosity required.

When heated to a certain temperature, which may vary with different oils, but is usually between 560 to 575 F. an exothermic reaction takes place within the oil, causing a relatively rapid rise in temperature, the degree and rate of tem perature rise depending somewhat upon the rate or speed the oil has been heated, the slower the rate of heat input at the critical temperature, the less the temperature rise due to the exothermic reaction.

When the oil is heated to or near its critical or reaction temperature, a relatively slight increase in temperature will cause cracking or breakdown of the oil molecules to take place. converting part of the oil into free fatty acids. carbon and other compounds that injiu'iousiy effect the quality of the finished oil and reduces its value for the purpose intended. It is therefore very important that the heating apparatus in which the oil is' heated be closely controlled and quickly respon sire to changes in temperature of the oil.

In usual constructions. theoil'isheated in open portable kettles of one to two hundred gallon capacity. wheeled over open fires of coal or coke. and the usual means of controlling the temperature of the oil is for the attendant to withdraw the kettle from the fire should the oil become too.

not and replace the kettle as it becomes too cool. under which conditions the temperature regulation is poor. the temperature of the oil varying in some instances 30] F. or more. Larger size kettles are sometimes used. in which event they are installed permanently in brick settings and heated by means of coke or oil fires.

During the heating operation the layer of oil in contact with the kettle bottom, the underside of which is exposed to a furnace combustion temi perature of 2400" F. or more, is overheated and cracked or decomposed, increasing the loss due to oil fumes and vapors. increasing the fatty acid content and causing darkening of the oil.

As stated. it is desirable to heat the oil in a regular and uniform manner,. avoiding the use of highly heated surfaces, and tomaintain the oil at a regular and uniform temperature throughout the period of time required to obtain the desired bodying reaction.

In the apparatus illustrated in Figures 1 and 2. the heating elements comprising the relatively thin ribbons closely spaced apart in the form of concentric spirals, presents the greatest possible heating surface area, uniformly distributed in the fluid in the receptatcle. and due to the thermosiphonic action of the hot oil rising through and between and in direct contact with the heating surfaces comprising the spirals of the heating element,creates a vigorous circulation, providing the maximum heat transferrate and the minimum temperature differential between the heating surfaces and the oil in contact therewith.

Due to the relatively small mass or weight of the high resistance metallic ribbons comprising the heating elements, and the relatively small temperature differential between the heating sur faces and the oil, the amount of heat stored in the heating elements and given off after the ele tric heating current is interrupted is negligible. 5

in I

lit)

the heating surfaces. Of the three main conditions influencing the rate ofheat absorption. the second and third are the more important. following example will illustrate the advantage of the arrangement of the heating element as shown in Figures 1 and 2, of the present invention.

Assuming a 1000 gallon oil fired oil bodying The the close spacing of the kettle, having a diameter of 66 inches and'a height of .110 inches, the oil filling the kettle to a height of 66 inches from the bottom, the heat being applied to the kettle bottom and for a distance of 12 inches up the sides, providing a total area. of 5840 square inches of heating surface. The heat must'be transmitted from the bottom and lower sides of the kettle inches.

The heater which is the subject or this inventhe vertical spacing ofthe heating elements presenting both sides of the ribbons as the heating surfaces with which the oil is in direct contact, there is a vigorous circulation of the oil created up through the said spirals and down the sides 'of the kettle between the outer turns of the walls of the kettle, which spirals and the side readily absorbs the heat generated in the heatingelements, tending to cool them and permitting the use of a relatively high rate of heat input per unit area of heating surface.

The greater rate of -heat absorption, due to heating elements or spirals of high resistance ribbons, as compared to the direct fired kettle heated by oil mentioned above is illustrated by the following example;

Heating speed ratio.

Electrica y hcflted -".375

, 11,37s fired kCttlC Q or the electrically heated kettle, due to the close spacing and arrangement of the heating surfaces will have a. heating speed, other conditions being equal, 11,378 times that of the oil fired kettle.

Heating surface ratio Electrically heated kettle 49,500 square inches Oil fired kettlc Q s 5,840 square inches or the electrically heated kettle by reason of the greater area of heating surface exposed, will have a heating-speed 8.5 times that of the oil fired kettle, or the electric kettle may be operated at the same speed as the oil fired kettle, but-at a temperature-difference between heating surface and oil of but 11.8% that of the oil firedkettle. The above heating speed and heating surface ratios may be readily increased to anydesired degree by reducing the distance between adjacent'turns of the spirals, and using a greater length of, or by increasing the width of the high resistance ribbons, thereby increasing the area of the heating surface. I

Due to the arrangement. of the heating surfacesin the electrically heated kettle, which creates a vigorous circulation of the oil uniformly through the spirals comprising the heating elements, the velocity flow of the oil in contact with the said heating surfaces, will, the viscosity of the oil, be from 10 to times greater than in the oil fired kettle using the botto the centre of the mass of oil, or to a distance of approximately ing elements comprising the to a polyphase electric tom and lower sides only as the heating surface. In the operation of the kettle, the oil being placed in the receptacle, the push button switch 6 is closed, causing the magnetic switch56 tov close and the electric heating current to pass by means of the main switch 55, the magnetic switch 56 and electrical connections to the electric heatribbons 33 of high resistance metal, causing heat to be generated therein and transmitted to the oil that is in direct contact therewith. The oil circulatingvigorously upwardly through the spirals comprising the heating elements and down the space between the outer edge of the spirals and the sides of the kettle, iS quickly and uniformly heated to the desired degree.

If it is assumed that 1000 gallons of linseed is to be heated from a temperature of 60 F. to 585 F. and maintained thereat for a period of four hours to attain the desired viscosity, that at 560 an exothermic reaction occurs in the oil, causing a temperature rise of 20, that there is required an electrical input at the rate of 300 kw. for 2 hours to raise the oil from-60 to 560, that the electric energy required to supply radiation losses and maintain the oil at .585" is at the rate of 8 kw.' Therefore the thermostatic control switch 65 is set at 560 and when the temperature of the oil reachis that degree, thermostat will then act to open the magnetic switch 56 and to close the magnetic switch 58, the electric heating current then passing by'means of the auto-transformer 51 or other suitable electric power reducing device, by way of the magnetic switch 58 'to the heating elements in the kettle, being reduced by means of the auto-transformer to an electric capacity of slightly more than that required to maintain the oil at 585 orlO kw. Due to the exothermic reaction mentioned above, the tem perature of the oil will continue to rise to 585, whereupon the thermostatic switch 63 will act to open the control circuit, causing the magnetic switch 58 to openand interrupt the electric heating current supplied'resistance elements. Should the temperature of the oil become less than 585, thermostatic switch 63 will act, causing magnetic switch 58 to close and supply the electric heating current to the heating elements, thus acting to maintain the oil in receptacle, accurately, at a determinate degree of heat.

It is desirablethat the control system used to regulate the electric current supplied heating elements be so. arranged as to avoid the frequent turning on and off of relatively large electric currents that may cause disturbance to the electric power supply system. In the preferred method of control hereinbefore described-the high electrio capacity current of 300 kw. is turned on at the start .of the heating period, and after the oil' is heated to the desired temperature, the high through heating elements at all times except when they a. .3 immersed to a predetermined degree in the oil, so that accidental overheating oi the heating elements is avoided.

It will be obvious that many other embodiments of the invention may be made by those skilled in the art and it will therefore be understood that theparticular devices and arrangements and methods of use shown and described herein are of an illustrative character and are not restrictive and that various changes in form, construction and arrangement of parts may be made within the spirit and scope of the iollowing claims and such suitable electric current may be employed whether direct, single, or polyphase alternating, as may be available and adapted to the particular requirement of the apparatus used.

Having thus described the invention, what I claim is:

1. In a fluid heating apparatus, the combination of a receptacle for containing the fluid, a heating element consisting of a long narrow ribbon of high electrical resistance material wound in a spiral having a diameter substantially greater than its width, means supporting the element substantially horizontally in the receptacle, and a source of electrical heating current connected to the element for heating the same.

2. In afluid heating apparatus, the combination of a receptacle for containing the fluid, a plurality of heating elements each consisting of a long narrow ribbon of high electrical resistance material wound in a spiral having a diameter substantially greater-than its width, means supporting said elements substantially horizontally in the receptacle in vertically spaced relation, and a' source of electrical heating current connected to said elements for heating the same.

3. In a fluid heating apparatus, the combination of a receptacle for containing the fluid, a heating element consisting, oi a long narrow ribbon of high electrical resistance material wound in a spiralhaving a diameter substantially greater than its width, means supporting the element substantially horizontally in the receptacle, a source of electrical heating current connected to the element for heating the same, and means maintaining the level of the fluid in the receptacle substantially above'the top of said element to insure thermosiphonic circulation of the fluid over both surfaces of the ribbon.

4. In a fluid heating apparatus, the combination of a receptacle for containing the fluid, a plurality of heating elements each consisting of a long narrow ribbon of high electrical resistance ,material wound in a spiral having a diameter substantially greater than its width, means supporting said elements substantially horizontally in the receptacle in vertically spaced relation, a source of electrical heating current connected to said elements for heating the same, and means maintaining the level of the fluid in the receptacle above the upper element to insure thermosiphonic circulation oi! the fluid over both surfaces of the ribbon.

5. A fluid heating apparatus comprising a fluid containing receptacle, a plurality of electric heating elements comprising thin ribbons of high electrical resistance metal, edge supported in a closely spaced spiral form, in said receptacle and immersed in said fluid, means to cause the fluid to flow in a predetermined direction between said elements and in direct contact therewith, means for passing an electric heating current through said high resistance metallic ribbons, thermostatic means subject to the temperature oi the fluid to selectively control themagnitude of the electric heating current passed through said heating elements, and thermostatic means subject to the influence of the temperature of the fluid to automatically control the supply of electric current to said electric heating elements.

6. A fluid heating apparatus comprising a fluid containing receptacle, a plurality or superimposed electric heating elements comprising thin ribbons of high electrical resistance metal, wound in a closely spaced spiral form, means supporting said elements in superposed spaced relation in said receptacle and immersed in said fluid, means to cause the fluid to flow in a predetermined direction between said elements and in direct contact therewith, means for passing an electric heating current through said high resistance metallic ribbons, and automatic means operable by a predetermined minimum height of the fluid within said receptacle to disconnect the supply of electric current to said elements.

'7. A fluid heating apparatus comprising a fluid containing receptacle, a plurality of electric heating elements comprising thin ribbons of high electrical resistance metal, edge supported in a closely spaced horizontal spiral form, in said receptacle and immersed in said fluid, means to cause the fluid to flow in a predetermined direction between said elements and in direct contact therewith, means for passing an'electric heating current through said high resistance metallic ribbons, thermostatic means subject to the temperature of the fluid to selectively control the magnitude 0! the electric heating current passed through said heating elements, thermostatic means subject to the influence oi the temperature of the fluid to automatically control the supply of electric current to said electric heating elements and automatic means operable by the height or the fluid within said receptacle to con- .trol the supply of electric current to said elements.

8. A fluid heating apparatus comprising a fluid containing receptacle, having an inlet and an outlet, a plurality of electric heating elements comprising closely spaced spirals of relatively narrow metallic ribbons of high electrical resistance wound in spiral form, means supporting said elements transversely, one above the other within said receptacle andimmersed in said fluid, means for passing an electric heating current through saidhigh resistance metallic ribbons, means for causing the fluid to flow uniformly between said heating elements and in direct contact therewith.

ROBERT A. CARLETON.

Images