US 2740756 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
April 3, 1956 A. G. THOMAS 2,740,756
' ELECTRICAL DRYING SYSTEM Filed April 19, 1951 2 Sheets-Sheet l 4-8 49 4e I? l I 17 w %/%7M INVENTOR A. G. THOMAS 2,740,756
ELECTRICAL DRYING SYSTEM 2 Sheets-Sheet 2 a 2 n 7/. S u n S h 3 7 i if 1 1:: m m 1:" 1 n N a W\ N n r u u r///// Ir//////! .7/ 7/6 I'////// I7///// I7/////I April 3, 1956 Filed April 19, 1951 '1 Rin q Mann.
mm mm WX NVENTOR United States Patent ELECTRICAL DRYTNG SYSTEM Albert G. Thomas, Chattanooga, Application April 19, 1951, Serial No. 221,84)?
6 Claims. ((Il. 204-138) This invention relates to electrical drying systems.
Many industrial installations of electronic drying, employing the heating efiect of varying magnetic or electro static fields, have been made. While these systems have been effective in many cases in accelerating the drying process, a serious deterrent has been the relatively high cost of operation. In numerous instances, this cost has been prohibitive. Another fault of prior electronic drying systems is that the objects to be dried have been heated to temperatures high enough to vaporize contained liquid. This is not a serious matter for some materials but others may be damaged by the temperatures necessary for vaporization.
It is an object of my invention, therefore, to provide an electrical or electronic drying system which will remove water or other liquid from clay, wood, fabrics, paper, or other materials rapidly and at relatively low cost as compared to previous practice.
Another object is the provision of a drying system which removes liquid from material without the necessity of vaporizing the liquid, thereby saving the energy loss as represented by the latent heat of vaporization; the liquid being electrically removed as liquid.
A further object is to provide a radio frequency drying system which induces uni-directional pulses of current in material to be dried, in order to move liquid out of the material electrically, even with poor electrode contact, or by capacitative action without any electrode contact with the material. I use the term radio frequency to mean frequencies above approximately 15,000 cycles per second as indicated on page 362 of Principles of Radio Communication by Morecroft; and on page 20 of The Radio Amateurs Handbook, 26th edition, 1949. For most purposes, frequencies above, say 10 megacycles, would not ordinarily be used in drying, but higher frequencies may be used in special cases.
An additional object is to provide an electrical system for moving liquid through earth, the liquid being oil, water or the like, for various purposes.
Other objects will be evident in the following description.
In the drawings:
Figure l is a part sectional elevation of an electrical drying system employing the principle of cataphoresis in novel manner. r
Figure 2 is a part sectional view of an electronic; drying system using both rectified half cycles from an oscillator or similar device, to remove fluid from material.
Figure 3 is a bottom plan view ofa bottom contact plate, with insulating border.
Figure 3a is an elevation of a pair of contact rollers and material therebetween.- 1
Figure 4 is an end elevation, in partsection, of a conveyor type drying system electrically connected according to the circuit shown in Figure 2.
Figure 5 is a fragmentary side elevation of an electronic drying system including a movable sheet of material between plates charged at radio frequency.
' indicate the magnitude of current.
2,740,756 I iiatented Apr. 3, 195.6
Figure 6 is a sectional elevation showing a bobbinof yarn or the like and associated charged members.
Figure7 is a part sectional elevation of a magnetic drying system.
Figure 8 is an elevation of a phased magnetic-drying system.
Figure 9 is an elevation of a magnetic drying system employing a rotary magnet.
In Figure l, moist object 1 may be a green brick tile, a piece of lumber, clay, vegetables, hay, or any other material. Electrically conductive plate 2 is supported by object 1 and may be solid or perforated, and of metal, carbon or the like. Object 1 is supported on metal or other electrically conductive plate 3 having perforations 4 through which water or other liquidzin object 1 may flow. Plate 2 is normally electrically con nected with contact 5 of double pole double throwreversing relay 6 having arm 7 normally pressed against contact 5 and arm 8 pressed against double contact-9. Lower contact 10 is connected to contact 5 through ,vari-. able resistor 11 and double contact 9 is connected to lower plate 3 by means of conductor 12. Variableresistor 23 is connected between plate 2 and contact 5 Arms 7 and 8 are fastened to insulating member 13 pivoted at 14 to plate 15 which is fastened to base 16. Tension spring 17, fastened to member 13 and plate 15 normally holds arms 7 and 8 against the respective contacts 5 and 9. Cam 13 has coaxial attached gear 1) and the two are rotatable onstub shaft Ziifixed to plate 15. Worm 21 ismeshed with gear l9 and is fastened to the shaft of motor 22 which may be a relatively slow speed type and can be suitably'energized.
Relay arms 7 and 3 are connected, respectively, to positive and negative lines 24 and '25 of a source of uni-directional or direct current either steady or fluctuating, but in one direction.
In operation, motor .22 is started so that it revolves cam 18 slowly, preferably. When bar 13 rests a ainst a low part of the camor is near it, the'positive terminal is connected to plate 2 and the current passes through green brick or other object 1 and out through plate 3 and conductor 12. Due to the effect of cataphoresis, water or other liquid in object 1 iscarried down through the brick, say, and drops out through holes 4. The amount of current can be adjusted by variable resistor 23. Ammeter 26 may be connectedin the circuit to This instrument can have a scale on either side of a zero point in order to measure current for either direction of-fiow.
As motor 22 continues to revolve, a high portion of cam 18 is rotated to a position so that it lifts bar -13 and 'so brings relay arms 7 and 8 down against contacts 9 and 10, respectively. This results in connecting positive line 24 to perforated plate 3 and negative line 25 to upper plate 2 so-that current flowthrough brick ,1 is reversed. The result is that water in the brick is rap-v idly redistributed andsome of it is carried backup to wet plate 2. The reason for this is that theclay'adjacent plate 2 rapidly becomes relatively dry and, it is necessary to adjust resistor 23 in orderto maintainthe current flow at the desired value. The plate ,2 can be quickly moistened, however, by the reverse flow-of current audit will be noticed that the raised portions of the cam are of considerably shorter arcuate length than the lower portions. The current for reverse flow can be adjusted by regulating variable resistor 1i Both .variable resistors 11 and 23 can be regulated automatically if desired, by suitable means controlled by the motor or cam.
In drying an ordinary green brick, for instance, having 18% to 20% of water, Ihave foundthat a desirable cycle is to pass about 2 amperes down through thebricl;
for 2 minutes and then to pass an approximately equal current through the brick in opposite direction for to seconds. This tends to keep plate 2 moist so that excessive voltages are not necessary in order to force current through the brick as it becomes drier. About 50% of the free water content of the brick can be removed in this way in to minutes. The cycles of downward and upward reverse current can be varied considerably, for different conditions. it is sometimes economical to apply the current and then to allow the brick to evaporate moisture, particularly it becomes heated. For this purpose one or more cam risers 27 of reduced height can be provided, so that arms 7 and it will be held between the relay contacts and the circuit is broken.
This method of drying bricks or other obg'ects removes a substantial part of the water in liquid form and not as vapor. The large heat loss due to the latent heat of vaporization is therefore largely avoided and greatly improved economy results as compared to past electrical or electronic methods of drying.
Plate 2 can be perforated also and water or other liquid such as an electrolyte can be used to moisten the area of the plate in contact with the brick. if it is desired to carry the drying much beyond it is preferable to use pulsating direct current, rather than continuous current. I have found that by using direct current pulsating at a frequency of 100,000 cycles or higher the dry inter-face between plate 2 and the brick is not so important a factor in increasing resistance or impedance. Apparently the pulsating charging between plates 2 and 3 provides a condenser effect with currents induced in brick 1 in one direction, i. e. downward so that water continues to drop out of holes 4 even though the brick is relatively dry. Troubles from arcing due to necessary high voltages, as in the former case, are largely obviated by employing the pulsating direct current, at high frequency. In some cases where the surfaces of object 1 are hard, rough, or both, it may be desirable to use electrically conductive rubber or similar material for plates 2 and 3. The rubber can be pressed against the object, like lumber, for instance. I have found that green bricks can be effectively dried with plate 2 lightly in contact with the brick or actually coated with insulating rust, by employing a circuit similar to that shown in Figure 2. If high frequency is not used, potentials up to hundreds of volts are necessary in order to force any appreciable current through the brick after the upper surface becomes somewhat dry. Under these conditions the severe arcing and heating make the operation impracticable. If rectified high frequency currents are used, however, from 2 to 3 ampers of pulsating direct current can readily be passed through the brick to bring the water content down to 50% in around 30 minutes. There is no appreciable arcing trouble under these circumstances. While I have used frequencies ranging from 50,000 to 1,000,000 or more pulsations per second, these are not necessarily limiting values. The unidirectional pulsating currents passing through the brick are largely induced since, with the same applied voltage, very much smaller currents will pass under continuous direct current, after the brick is partially dried.
If bricks are dried too rapidly they have a tendency to crack but much of this can be avoided by reducing the current or cutting it off temporarily when the temperature rises too high. The temperature should be kept below the boiling point of water, preferably at 160 to 180 degrees F. A somewhat higher temperature toward the end of the drying period is not objectionable however as it causes additional loss of water through evaporation and the brick is dry enough so that cracking is not so likely to occur.
In Figure 2, elements 28 and 29 may comprise bricks, fabric, lumber, paper, or any other material to be dried. These elements may be supported on metal or other conductive screens 31 and 33 electrically connected with the output terminals 34 and 36, respectively of oscillator 35. These output terminals are connected as indicated to the tank terminals of a Hartley power oscillator 35 but any suitable type of oscillator circuit can be employed. Further, the radio frequency energy can be supplied to the load circuit through a secondary winding, or through condensers, or in any well known manner. The oscillator circuit shown is widely used and therefor will not be described in detail. Push-pull oscillator circuits or other circuits can be used. The frequency may be varied by changing the inductance of winding L or the capacitance of condenser C or both. The frequency useful for drying by my system may range up to several megacycles per second or more. 1 have found, however, that effective movement of water or other fluid out of material can be accomplished with a frequency around to 250 kilocyclcs per second. In some cases even lower frequencies may be used.
Upper conductive plate 30 is suitably supported and may be solid or perforated as indicated and is electrically connected with the cathode of diode 37 the anode of which is connected with output terminal 36. Similarly, the upper plate 32 may be perforated and is electrically connected with the cathode of diode 38 the anode of which is connected with oscillator output terminal 34. The cathodes of the diodes may be supplied heating current by transformers, batteries, or other source of electrical energy.
The material to be dried, 23 and 29, may be in contact with conductive elements 3031 and 32-63 or these elements may be spaced from the material. it is often desirable to have the elements in contact with the mate rial or at least to have a close spacing between the elements and the material so that relatively intense pulsating uni-directional electrical fields will be induced in the material. While the material objects 28 and 29 are shown as separate, these could be different portions of one sheet of material. This sheet, or the sheets 28 and 29, can be dried while stationary or they can be moved between the elements 30-31 and 3233 by a belt or other conveyor. In the latter case it may be preferable that the conductive elements 30 and 32 do not touch the sheet or sheets 2829. Various connected groups of similar connected intermittently charged elements can be staggered and can overlap with respect to the width of the sheet so that all parts of the sheet will be subjected to the drying field.
The lower conductive elements 31. and 33 are shown as screens but may be perforated plates, belts, or solid plates in some cases.
The diodes 37 and 38 may be any suitable type of rectifier for radio frequency currents. Ordinarily they will be evacuated and will have electrically heated cathodes and associated anodes as indicated. In view of the reversed arrangement of the diodes it will be seen that half cycles of alternating output current will pass through rectifier 37 in a direction to produce induced or con ducted uni-directional pulses in material 28 to carry fluid downward through screen 31 when terminal 36 is positive. Similarly, when terminal 34 is positive the induced or conducted uni-directional pulses passing through rectifier 38 cause fluid in material 29 to move out of the material and through screen or perforated plate 33. Therefore both halves of the cycle are used, for the sake efiiciency.
An important feature of my electrical drying system is that actual contact of the electrodes or charged plates with the material to be dried is not essential. The unidirectional induced pulses of current are developed in the material even though one or both charged plates are separated therefrom. This induced pumping action is highly effective in bringing water or other liquid out, of the material, at great saving of energy, since it is not necessary to vaporize the liquid. A further advantage is that the temperature of the material can be kept relative ly low and this is quite important with certain types of materials.
In operation, bricks or other objects 28 and .29, such as lumber, clay, fabrics or the like, are placed as shown,'between plates 30, 31 and 32, 33 and oscillator 35 is connected to a suitable source of energy. Then, as output terminal 36 becomes positive, current will flow through rectifier 37, plate 30, and object 28 to plate 31 and back to negative terminal 34. Current during this half cycle passes through object 28 as rectifier 38 blocks it in reverse direction. During the next half cycle when terminal 34 becomes positive and terminal 36 negative, current passes through object 29 and through rectifier 38 and back to terminal 36. During this half cycle rectifier 38 blocks current flow through object 28. This arrangement provides relatively high efficiency since pulsating unidirectional currents are used to remove water in liquid form and both halves of the cycle are usefully employed. Obviously the objects 28 and 29 do not have to be separate entities but can be different portions of the same material.
The system of using pulsating direct current is quite effective in drying since it combines the effect of cataphoresis with high frequency induction heating, and also current heating. The currents in one modification are applied to the material to be dried with consequent greater efiiciency as compared to past systems using alternatirig fields alone. As the brick or other object becomes dried so that the resistance tends to reduce the current, the condenser effect becomes more pronounced due to a drier dielectric and the uni-directional current pulses continue to remove water in liquid form. If desired, the frequency of oscillation can be increased as the object becomes drier so that the dielectric hysteresis heating will be'increased. The frequency can be raised to several megacycles or more for this purpose, or a high frequency can be usedfrom the beginning. Any number of bricks or other objects can be connected in parallel and the contact plates can be caused to travel as on a conveyor, the current being supplied by rails or trolleys. For the last stages of moisture removal unrectified high frequency heating can be employed to cause vaporization of moisture.
In Figure 3, the bottom plate is made of an inner perforated portion 3a and a border portion 3b of insulating material such as plastics, fibre, or ceramic material. In use, the current passes through the portion 3a, only, so that water brought down out of the brick'does not accumulate excessively at the edges, which results in softening the edges too much.
In Figure 3a, metal rollers 40 and 41 preferably comprise perforated cylinders, with roller 40 urged toward roller 41 by its weight or by a spring, being suitably mounted. .A sheet or other form of material 44 is supported on slide 45 and is fed between the rollers as they are revolved. Brush 42 in contact witha slip.ring on roller 40 is connected to the positive terminal of a source of current and brush 43 in contact with a slip ring on roller 41 is connected with the negative terminal of the potential source. Therefore material 44, consisting of clay, lumber, vegetables, or any substance, is partially dried by cataphoresis as it passes between the rollers. Direct or pulsating direct current can be used.
In Figure 4, like parts are designated by like numerals, as used in Figure 2. Oscillator 35 is shown in block form and rectifiers 37 and 38 are connected as before. Objects 28 and 29 which are to be dried are elongated sheets of material, seen endwise. These sheets may comprise fabrics, paper, plastic, plywood, or other material and are supported on mesh type wire belts 31 and 33 which are shown in section. These belts are movable over drums 46 and 47 mounted on central shaft 48 passing through the drums and bearing posts 49 extending from base 50. The metal drums may be rotated by a belt driving pulley 51 attached to shaft 48. The belts Sland 33 are passed over similar drums at the other end of the conveyor type drier and intermediate supporting drums can be used.
Belts 31 and 33 are endless and serve to carry the sheets 28 and 29 under plates 30 and 32 which extend lengthwise above the mesh type belts and are spaced from sheets 28 and 29 although the spacing is preferably small in order to provide intense uni-directional high frequency fields. a
The electrical connections are essentially the same as shown in Figure 2. In this modification, however, the conductor connected with output terminal 34 of the oscillator is connected to screen 31 through slip ring 52 on shaft 48. Brushes'making contact with metal screens or belts 31 and 33 could be used. These belts are not electrically connected by the metal drums and shaft since the shaft is split, being joined by insulating connector 48a. It is not essential that two screen belts be used since the sheets can be placed on one belt and the two plates 30, and 32, can be suitably connected. The terminal 36 is connected to screen33 rthrough slip ring 48b.
In operation, the oscillator is energized to provide a frequency of preferably 100,000 to 1,000,000 cycles per second, or more, and shaft-48 and the drums are rotated to carry sheets of material 28 and 29 under plates 30 and 32. The high frequency uni-directional fields developed between plate 30 and screen .31, and between plate 32 and screen 33 causemovement of water out of sheets 23 and 29. This water, or other liquid, passes through the screensand drops into elongated drain pans 53 and 54- which may have suitable connected discharge pipes. The length, and rate of movement of the screens 31 and 33 can be so chosen that the-conveyed material will be dried to the desiredextent'by the time it reaches the discharge end of the device.
The sheet of material 28 can be moved between elongated charged plates 30 and 31a without being in contact with either, as shown in Figure 5. The sheet 28, which may be cloth, paper, or any moist material, is moved by rotated drums 46+46a and is guided by similar drums 55-.--55a. The induced, unidirectional energy pulses at radio frequency, preferably, will drive the moisture out of sheet 28, the water or other fluid moving in the direction of the current pulses. The plates 30 and 31a are connectedina rectified radio frequency circuit as indicated in Figure 4. A similar sheet can be placed parallel to the sheet shown, and another plate used so that both rectified halves of the wave will be used. Relatively high potential pulses are desirable in order to accentuate the inductive action potentials up to several thousand volts or more can be used effectively.
In some cases it may bex'desired to increase the moisture content of material. This need arises for instance in putting moisture back into leaf tobacco after it has been dried. In that case the water can be sprinkled over the leaves which can be spread over conveyor screens 31 and 32 and the induced unidirectional pulses will force the water into the leaves. Other plants, vegetables, or different types of material can be moistened in this manner.
In Figure 6 is shown a bobbin 56 of yarn or the like wound around perforated metal tube 57 which can be set in metal contact ring 58 which may be suitably supported. Cylindrical metal sheet 58 may be split and is forced over the bobbin, being clamped around it as a result of the resiliency of the metal. The sheet 58 may be perforated, if desired, so that air or vapor can enter or escape. It is not essential that the metal 53 touch the yarn since the induced high frequency pulses applied to the elements 57 and 58 will cause movement of water out of the yarn. If actual contact occurs, however, lower potentials can be used and the conductive transportation of water, or cataphoresis, is effective. As the yarn becomes drier the induced unidirectional capacitative pulses are principally efiective in moving the enemas water and when movement of the water largely ceases or becomes slow, high frequency unrectified energy can be applied to elements 57 and 58 to vaporize the remainder of the contained moisture. Even for the last stages of drying, however, there is an advantage in maintaining rectified high frequency or radio frequency unidirectional pulses since these pulses cause heating as well as movement of water. There seems to be a tendency of the unidirectional pulses to move the vapor out of the yarn as Well as water. It is often preferable that element 58 be connected to the positive terminal of a source of unidirectional pulses, the tube 57 being connected to the negative terminal. This arrangement results in the water being moved toward the central perforated tube. The water is therefore collected and concentrated in a smaller space than if the movement were in opposite direction. This assists in removing the water since the unidirectional pulses of energy are more effective, the wetter the yarn. In case the yarn is rotated, in order to use also the effect of centrifugal force, element 57 would be made positive.
The principle of inducing radio frequency energy in material in one direction maybe applied to move fluid in many different types of substances or structures. It might be employed for moving oil in the earth toward a well and it can alsobe used for drying roads, air fields,
or other areas of the earth, for construction purposes, for instance.
In Figure 7, magnet core 59 is made of soft iron, silicon steel or the like and is preferably laminated. Winding 60 surrounds a leg of the core and its terminals 61 and 62 are connected in series with an intermittent direct current circuit preferably varying at relatively high frequency. The coil 60 may, for instance, be connected in series with rectifier 37 or with a commutator. If the liquid in object 63, placed between the poles of magnet 59, is conductive the varying magnetic fields will tend to force the liquid out of a surface of object 63 as a result of reaction with the fields.
Figure 8 is a diagrammatic representation of two pairs of opposed magnets 64 and 65 which can be energized alternately by phased alternating currents or pulsating direct currents in order to produce a rotating magnetic field. This rotating field, reacting with conductive fluid in object 66, forces fluid out of the object.
In Figure 9 magnet 67, which may be of the permanent or electro-magnetic type, is mounted on shaft 68 which is rotatable in bearing posts 69. Pulley 70 is attached to the shaft 68 and may be used to rotate it. The magnet has a plurality of north poles 71 and associated south poles 72 spaced therefrom. If magnet 67 is rotated rapidly the magnetic fields between the pairs of poles will be swept through material 73, suitably supported, so that any conductive fluid in this material will be forced out of one face in case the fields are similarly aligned, or out of two faces if the fields are oppositely aligned. Suitable electrolytes like ammonia, acids, or the equivalent can be mixed with or absorbed in material to be dried so hat better conductivity will.
be provided, for either electrostatic or electromagnetic drying.
Various modifications of the invention can be made without departing from the principles I have disclosed.
What I claim is:
1. The method of removing liquid from material by electro-osmotic action, said method comprising, placing said material between electrically conductive elements, and establishing between said elements uni-directional radio frequency pulsating currents.
2. The method of claim 1, said frequency being more than 15,000 pulsations per second.
3. The method of removing liquid and vapor from material, said method comprising, passing uni-directional radio frequency pulsating current through said material to cause movement of liquid from said material until a predetermined degree of dryness thereof is effected, and then heating said material by induced unrectified radio frequency energy to cause vaporization of liquid therein.
4. The method of removing liquid from material, said method comprising, passing unidirectional radio frequency pulsating current through said material to cause movement of said liquid therefrom and adjusting the magnitude of said current to prevent substantial generation of vapor, continuing the application of said pulsating current until a predetermined degree of dryness of said material is produced, and then heating said material by unrectified high frequency currents to efliect further drying action by production of vapor.
5. The method as described in claim 4, said unrectified frequency being increased as said material becomes drier.
6. The method of removing liquid from material by electro-osmotic action, said method comprising, placing conductive elements in contact with said material, and passing uni-directional radio frequency pulsating current through said elements and material.
References Cited in the file of this patent UNITED STATES PATENTS 670,350 Schwerin Mar. 19, 1901 782,233 Gardner Feb. 14, 1905 1,796,584 Volmer Mar. 17, 1931 1,871,269 Hobrock Aug. 9, 1932 2,042,145 Darrah May 26, 1936 2,320,474 Ross June 1, 1943 2,325,652 Bierwirth Aug. 3, 1943 2,328,225 Morey Aug. 31, 1943 2,373,165 Cawein Apr. 10, 1945 2,447,374 Smyser Aug. 17, 1948 2,516,570 Hartwig et al. July 25, 1950 2,549,966 Grouse Apr. 24, 1951 2,582,020 Emery Jan. 8, 1952 2,582,806 Van Nes et al Jan. 15, 1952 2,596,743 Vermeiren May 13, 1952