EP0070827A1 - Appareil et procede de sechage d'un tissu par micro-ondes - Google Patents

Appareil et procede de sechage d'un tissu par micro-ondes

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Publication number
EP0070827A1
EP0070827A1 EP81901729A EP81901729A EP0070827A1 EP 0070827 A1 EP0070827 A1 EP 0070827A1 EP 81901729 A EP81901729 A EP 81901729A EP 81901729 A EP81901729 A EP 81901729A EP 0070827 A1 EP0070827 A1 EP 0070827A1
Authority
EP
European Patent Office
Prior art keywords
water
microwave
fabric
drying
dryer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP81901729A
Other languages
German (de)
English (en)
Inventor
Richard Dana Smith
Michael P. Uthe
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Individual
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Publication of EP0070827A1 publication Critical patent/EP0070827A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06F—LAUNDERING, DRYING, IRONING, PRESSING OR FOLDING TEXTILE ARTICLES
    • D06F58/00—Domestic laundry dryers
    • D06F58/20—General details of domestic laundry dryers 
    • D06F58/24—Condensing arrangements
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06F—LAUNDERING, DRYING, IRONING, PRESSING OR FOLDING TEXTILE ARTICLES
    • D06F58/00—Domestic laundry dryers
    • D06F58/20—General details of domestic laundry dryers 
    • D06F58/26—Heating arrangements, e.g. gas heating equipment
    • D06F58/266—Microwave heating equipment
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06F—LAUNDERING, DRYING, IRONING, PRESSING OR FOLDING TEXTILE ARTICLES
    • D06F58/00—Domestic laundry dryers
    • D06F58/32—Control of operations performed in domestic laundry dryers 
    • D06F58/34—Control of operations performed in domestic laundry dryers  characterised by the purpose or target of the control
    • D06F58/36—Control of operational steps, e.g. for optimisation or improvement of operational steps depending on the condition of the laundry
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B3/00—Drying solid materials or objects by processes involving the application of heat
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B5/00—Drying solid materials or objects by processes not involving the application of heat
    • F26B5/04—Drying solid materials or objects by processes not involving the application of heat by evaporation or sublimation of moisture under reduced pressure, e.g. in a vacuum
    • F26B5/048—Drying solid materials or objects by processes not involving the application of heat by evaporation or sublimation of moisture under reduced pressure, e.g. in a vacuum in combination with heat developed by electro-magnetic means, e.g. microwave energy
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06F—LAUNDERING, DRYING, IRONING, PRESSING OR FOLDING TEXTILE ARTICLES
    • D06F2103/00—Parameters monitored or detected for the control of domestic laundry washing machines, washer-dryers or laundry dryers
    • D06F2103/52—Parameters monitored or detected for the control of domestic laundry washing machines, washer-dryers or laundry dryers related to electric heating means, e.g. temperature or voltage
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06F—LAUNDERING, DRYING, IRONING, PRESSING OR FOLDING TEXTILE ARTICLES
    • D06F2103/00—Parameters monitored or detected for the control of domestic laundry washing machines, washer-dryers or laundry dryers
    • D06F2103/64—Radiation, e.g. microwaves
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06F—LAUNDERING, DRYING, IRONING, PRESSING OR FOLDING TEXTILE ARTICLES
    • D06F2105/00—Systems or parameters controlled or affected by the control systems of washing machines, washer-dryers or laundry dryers
    • D06F2105/28—Electric heating
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06F—LAUNDERING, DRYING, IRONING, PRESSING OR FOLDING TEXTILE ARTICLES
    • D06F2105/00—Systems or parameters controlled or affected by the control systems of washing machines, washer-dryers or laundry dryers
    • D06F2105/36—Condensing arrangements, e.g. control of water injection therefor
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06F—LAUNDERING, DRYING, IRONING, PRESSING OR FOLDING TEXTILE ARTICLES
    • D06F58/00—Domestic laundry dryers
    • D06F58/32—Control of operations performed in domestic laundry dryers 
    • D06F58/34—Control of operations performed in domestic laundry dryers  characterised by the purpose or target of the control
    • D06F58/45—Cleaning or disinfection of machine parts, e.g. of heat exchangers or filters

Definitions

  • This invention relates to machines for drying wet fabrics utilizing microwave energy in an atmosphere of reduced pressure.
  • the microwave energy elevates the temperature of the water within the fabric to the boiling point, which is quite low because of the reduced pressure, and the water vapor which is released from the fabric is removed by condensation external to the microwave field.
  • the hot air performs two functions; heat from the air vaporizes the water and the heated air, having a large capacity to hold water vapor, transports the water vapor from the chamber.
  • a normal load of wet clothes from a home washer weighs approximately 15 pounds. Most home dryers dry this load in perhaps 30 minutes. Large loads of difficult drying fabrics, such as Vietnamese towels, may take an hour.
  • Wool for example, may be washed safely in cold water, but must be air dried. If wool is exposed to the temperature of a conventional dryer, it will shrink and be rendered useless. As a result, most delicate fabrics are dry cleaned, meaning that they are immersed in hydrocarbon solutions to remove dirt and subsequently dried at a low temperature. Dry cleaning is expensive and the hydrocarbon vapors vented into the atmosphere pollute the air.
  • the efficiency of a conventional dryer is approximately 50%. Inefficiency results from the inability to transfer heat from the air to the water to vaporize it, the necessity to heat the clothes themselves and the walls of the dryer during the latter stages of drying, and the necessity to have a hot airstream issue from the dryer to transport the water vapor out of the drying chamber.
  • Microwave heating is well known through the home microwave oven. These ovens cook food in a fraction of the time of a conventional oven by heating the food throughout rather than from its surface. Microwaves in the 915 MHz and 2450 MHz frequency ranges heat polar molecules throughout a substance. The polar molecules align themselves with the electromagnetic field and when the field is rapidly reversed, 915,000,000 times a second for example, the friction on the polar molecule twisting back and forth causes heating of the molecule. Water is a highly polar molecule as are certain fats. Molecules that are non-polar are little affected. Hence the cooking of the food results from heat generated from the polar molecules throughout the food itself. The convenience of the shortened cooking time is well established by the large market for microwave ovens.
  • Microwave drying is well known in the patent art. It has been applied to lumber., foods, polymers, clothes, seeds and other substances. Microwave dryers take advantage of the capability of the microwaves to reach into the depths of a material and selectively heat the water vapor while leaving the material generally unaffected. As anticipated, those materials most difficult to dry show the most drastic reductions in drying times.
  • Foster et al. U.S. Patent No. 3,771,234, teaches the drying of polymers by microwave energy while they are being transported through the plant in a pneumatic transport pipe. Drying to a moisture level of 0.5% occurred in three seconds. The drying temperature of one polymer, polyisobutylene, was reduced from 437°F. to 185°F., resulting in improved physical properties and appearance of the material.
  • Pope U.S. Patent No. 3,854,219, teaches the drying of clothes in a conventional type of clothes dryer by using microwave energy to evaporate the moisture from the chamber.
  • Pope anticipated a considerable improvement in performance over a conventional dryer, but provides no specific information.
  • Undeniably Pope' clothes dryer will provide superior performance over a conventional dryer, but drying speed will be limited by the use of preheated air to transport water vapor from the chamber. The full potential of microwave heating to reduce drying time and reduce drying temperature will not be exploited.
  • microwaves selectively heat the water molecules and do not significantly heat most of the materials to be dryed
  • increasing the power levels increases the rate of vaporization without affecting the material.
  • One method to remove moisture, quickly and dry material at low temperature is to evacuate and maintain the drying chamber at an absolute pressure of 1.5 inches of mercury or below. At that pressure water boils at 92°F. and the vapor will be transported out of the material and from the chamber as fast as it is generated. It is only essential that the material being dried is sufficiently porous to allow the vapor to reach its surface without exerting sufficient force to damage the material. Popcorn is a good example where water vaporized within a material is unable to escape rapidly and material fracturing occurs.
  • McKinney et al. U.S. Patent No. 4,015,341 teaches the drying of seeds with microwave energy under reduced pressure. The objective of this method is to dry seeds quickly yet minimize the temperature in the seed during drying to improve its germination capability when later planted. McKinney dried the seed at an absolute pressure of 2.4 in. Hg, at which pressure water boils at 107°F. He found that the temperature within the seed was 10°F. to 20°F. over the boiling temperature of the water.
  • McKinney teaches the generation of microwave power external to the vacuum vessel and the transmission of that power into the chamber by means of waveguides. McKinney further teaches the use of a cooled surface within the vacuum chamber to condense the water vapor and maintain the vacuum once the chamber is evacuated to the working pressure. Microwave drying is inherently efficient because the microwave energy is absorbed directly by the water molecules. However, according to the known art, magnetron type tubes are used to generate power for microwave ovens and industrial microwave dryers. The use of magnetron tubes was taught by Pope, U.S. Patent No. 3,854,219, for application to a clothes dryer. Magnetron tubes for microwave heating have an efficiency of approximately 50% in converting input electrical power to microwave power.
  • microwave drying methods attempt to use the waste heat in some way to speed drying, but its use is only partially effective compared to the microwave energy itself.
  • the development of radar during World War II provided the stimulus for a major development in tubes to generate microwave energy.
  • the magnetron tube which is used to generate energy for microwave ovens today is a descendant of this earlier work.
  • the tubes are generally rated at 1.5 kw.
  • the tubes need a magnetic field in order to operate; this field is supplied by either a permanent magnet or an electromagnet.
  • the combination of a magnetron tube and its magnet for a microwave oven weighs approximately 40 pounds.
  • Household dryers today are rated at perhaps 5.5 kw; a truly rapid household microwave dryer would be rated at 10 kw.
  • Use of magnetron tubes for a rapid household dryer at this rating would require that the power system alone would weigh 400 lbs., an intolerable weight for a household appliance.
  • Solid state technology has been developing rapidly over the past ten years.
  • the control systems on many pieces of equipment now use solid state technology as do computers.
  • solid state devices are smaller, more efficient, and more reliable.
  • Most of the applications to date have been in control applications because of the limited capability of the solid state devices to handle higher power_levels.
  • solid state devices of a particular design have been constructed to generate microwave energy directly. These devices have been applied to special communication applications, but advancing state of the art now makes versions of this technology practical for large volume applications, such as the microwave fabric dryer. Like other solid state devices, they are more efficient, smaller and more reliable than the tubes they replace. Their method of manufacture is a tightly held trade secret.
  • the principal object of the present invention is to provide a fabric dryer that dries fabric in onethird the time, or less, of current dryers and dries at a temperature low enough to protect heat sensitive fabrics, wool for example.
  • a further objective of the invention is to increase the efficiency of an electric dryer from 50% to 70% or better.
  • the present invention dries fabric quickly and at a low temperature by applying large amounts of microwave power to the wet fabric while it is. under reduced pressure.
  • the water boils at a low temperature (92°F. for example), protecting the fabric, and is condensed at the same low pressure by a direct contact condenser. Since the water transport and condensation function are not limiting, the rate of drying is determined by the amount of power available at the site and the capital cost of the microwave device to utilize that electrical power.
  • the power limit usually corresponds to the electrical service for an electric stove, approximately 12 kw. Using 12 kw of input power with a 10 kw solid state microwave array (new to the state of the art) drying times of 11 minutes are achieved for a home dryer with a 15 pound load of clothes.
  • the partial vacuum needed for the low-temperature water vaporization is supplied by a water jet exhauster, an inexpensive rugged device.
  • the subject invention could be used as a process dryer for commercial cleaners. Since wool and other fine fabrics may now be dried without harm, washing and microwave drying would replace dry cleaning for many fabrics. Dry cleaning processes are expensive and emit hydrocarbon fumes to the atmosphere. Small microwave dryers could be used by apartment dwellers. These units could be placed in motels as convenience dryers for those who had a light hand wash.
  • Figure 1 is a diagrammatical elevational, sectional view of the subject invention.
  • Figure 2 is an enlarged sketch of a portion of the structure of Figure 1 illustrating the interface between the door and the chamber showing the vacuum seal and radiation seal.
  • Figure 3 is a diagrammatical view of an alternative embodiment of the subject invention when the water pump and water reservoir are removed.
  • Figure 4 is a diagrammatical view of a second alternative embodiment of the subject invention where the water pump, water reservoir and spray condenser are removed.
  • Figure 5 is a diagrammatical view of a third alternative embodiment of the subject invention where the water pump, water reservoir, spray chamber and water jacket chamber are removed.
  • the wet fabric to be dried is placed in a spherical drying chamber 12 by means of a door 14 which is closed and locked after the fabric has been placed in the chamber.
  • the spherical chamber 12 is made of metal, such as mild steel.
  • a pressure seal 16 prevents air from the atmosphere from leaking into the drying chamber.
  • the pressure seal 16 is made of material that reflects microwave radiation and prevents microwave radiation leakage from the chamber.
  • a redundant microwave seal 18 is provided downstream of the pressure seal 16 to assure that no microwave energy leaves the interior of the drying chamber.
  • the distance between the lip 17 of the drying chamber and the lip 19 of the door is less than one-quarter wavelength to provide a natural barrier to the escape of radiation.
  • the arrangement of the microwave power array and its geometric relationship to the spherical drying chamber may take on various configurations depending upon such practical considerations as utility service convenience, cost, serviceability, and radiation antenna efficiency.
  • microwave dryer is not a communication device requiring phase focusing either in a predetermined plane or at a geometrical point.
  • resonance of the discrete microwave devices will not be highly dependent upon any microwave resonance characteristics of the spherical cavity. What is desired is a highly scattered microwave beam that can intersect wet fabric irrespective of the position of the fabric within the drying chamber.
  • the impedance reflected into the center of the power source array is a maximum and therefore the power output with a constant source voltage will be a minimum.
  • This reduction in wall reflections produces a reduction in load impedance as seen by the microwave source and will permit increased radiative power output. This is a desired characteristic of this invention.
  • the absorption of microwave energy by the polar water molecules can be characterized as a pure microwave resistance and therefore will, have little effect on the drive frequency of the solid state array unless the drying chamber has been mistakenly designed to be a resonant cavity.
  • the use of a spherical shape for the microwave chamber precludes this possibility. Since the microwave dryer operates on the principle of real microwave energy absorption, high Q tuning of the drying chamber may result in the defeat of the practical purposes of this invention.
  • Q ratio of stored energy per cycle of RF to input power per RF cycle. Therefore, for the purposes of this invention, a high voltage-standing-wave-ratio (VSWR) under dry and empty chamber conditions is desired. This is contrary to normal communication systems design practice.
  • the technique of matching the microwave power transistor array to the drying chamber will require specialized design techniques, for in this instance, low VSWR's and high transmission efficiencies are desired.
  • the back reflected wave from the opposite wall (bottom surface) of the spherical drying chamber will be used to sense the degree of dryness of the fabric being dried and to provide the activation signal to turn-off the microwave source at the completion of the drying cycle.
  • An opening 20 in the drying chamber 12 is connected to a vacuum transfer line 22 which communicates with a spray condenser 24.
  • a radiation trap 21 in the line 22 prevents the escape of radiation.
  • the spray condenser 24 is comprised of a chamber which contains at the top a water spray nozzle 26 and lower down a vapor distribution plate 28.
  • the vapor transfer pipe 22 enters the spray chamber 24 through an opening 30 below the distribution plate 28, but above the bottom of the spray condenser 24.
  • a second opening 32 which is near the top of the spray condenser 24 communicates the interior of spray condenser 24 with a water jet exhauster 36 through a second vacuum transfer line 34.
  • a third opening 38 at the bottom of the spray condenser 24 is attached to a condenser water drain line 40 which communicates through an opening 42 in the vacuum transfer line 34.
  • the opening 42 in the vacuum transfer line 34 is located above the opening 38 in the spray condenser 24 such that a column of water exists in the condenser water drain line 40 to prevent air and water vapor flow through the condenser water drain line 40.
  • the opening 42 into the vacuum transfer line 34 is below the opening 30 connecting vacuum transfer line 22 into the spray condenser 24.
  • Water under pressure is supplied to the water jet exhauster 36 by a water pressure line 44 which communicates with a water pump 46.
  • a water drain line 48 communicates with the pressure line 44.
  • a valve 50 is located in the water drain line 48.
  • a water jet exhaust line 52 communicates with the water jet exhauster 36 and a water reservoir tank 54.
  • the water reservoir tank has a vent 58 to the atmosphere and a level control switch 60.
  • the water level 56 in the water reservoir tank 54 is maintained below the water jet exhauster 36.
  • An opening 62 in the water reservoir tank 54 communicates with the inlet to the water pump 46.
  • a temperature sensor 64 measures the temperature of the water entering the water pump 46.
  • a surrounding water jacket 65 is attached to the lower portion of the vacuum drying chamber 12 providing a water jacket chamber 66 therearound such that water within the water jacket chamber 66 is in direct contact with the exterior surface 67 on the lower portion of the drying chamber 12.
  • a hot water inlet line 68 containing a valve 70 is in communication with the water jacket chamber 66 and a cold water inlet line 72 containing a valve 74 is likewise in communication with the water jacket chamber 66.
  • a water drain line 76 is also in communication with the water jacket chamber 66. The inlet 78 to the water drain line 76 is located near the uppermost portion of the water jacket chamber 66.
  • An opening 80 located in the bottom of the drying chamber 12 is connected to a fluff jet pipe 82 which contains a valve 84 which communicates with the atmosphere.
  • the fluff jet pipe 82 is located such that the angle between the access of the pipe and the surface of the chamber is greater than zero degrees, but less than 60 degrees.
  • a radiation trap 86 is located in the fluff jet pipe 82 to prevent the escape of microwave energy from the drying chamber 12.
  • a solid state microwave array 88 is located within the drying chamber 12 and positioned so that the microwave radiation leaving its surface is generally directed at the fabric to be dried.
  • the solid state microwave array 88 is composed of solid state devices 90 mounted on a heat sink 92 which is cooled by cold water transmitted by a cold water cooling line 94. The heated water is removed from the heat sink 92 by means of a drain line 96. Electrical power, suitably modified, is transmitted to the solid state microwave array 88 by an electrical cable 98.
  • a cold water inlet pipe 100 communicates with a shut-off valve 101 and subsequently with spray condenser water valve 104 and with the cold water line 94 to the solid state microwave array 88.
  • the water pump 46 is actuated and begins circulating water through the water jet exhauster 36.
  • the water exiting the water jet exhauster 36 is returned to the water reservoir 54.
  • Valve 50 in the water jet line 48 is closed.
  • the water jet exhauster 36 draws the residual air from the dryer chamber 12 through the vacuum transfer pipe 22, the spray condenser 24 and the vacuum transfer line 34.
  • the hot water valve 70 to the water jacket chamber 66 is open allowing hot water with a maximum temperature of 140oF. to fill the water jacket chamber. 66.
  • the water at ambient temperature in the chamber at the start of the process is drained from the chamber through drain pipe 76.
  • the design of the water jacket chamber 66 is arranged so that incoming water largely displaces the water in the chamber.
  • the valve 70 is closed after the chamber 66 is- largely filled with hot water.
  • a solid state timer 110 allows the valve 70 to stay open for a preset time.
  • the heat from the warm water is easily transferred into the metal wall of the drying chamber 12 thereby warming it.
  • the warm wall in turn begins warming the wet fabrics in the dryer.
  • the pressure in the drying chamber has reached approximately 10 inches of mercury absolute as measured by a chamber pressure senser 106
  • the solid state microwave array 88 is turned, on and the microwave energy begins to heat the water molecules in the fabric.
  • the water in the fabric will begin to heat up but will not vaporize immediately because the pressure is too high.
  • the pressure in the chamber will reach 1.5 inches of mercury absolute and any water in the fabric that had reached 92°F. or above will immediately begin to vaporize. Any water that had reached a temperature in excess of 92°F. will be cooled by the vaporization until its temperature has been lowered to 92oF.
  • the time at which the microwave 88 will be turned on will be adjusted to insure that the temperature of the wet clothes does not exceed 92°F.
  • the speed of the pump 46 is reduced to maintain the pressure at 1.5 in. Hg or slightly below.
  • the water pump 46 and water jet exhuaster 36 are oversized to remove the air from the drying chamber 12 quickly and need not operate at full speed once the majority of the residual air has been removed.
  • the water in the clothes heated by both microwave energy and by heat conducted through the wall of the drying chamber 12 will vaporize at 92oF.
  • the microwave energy will be most heavily absorbed by the wettest portion of the fabric and will tend to vaporize more water in the wetter portions, causing a more uniform drying action.
  • the microwave energy will penetrate throughout the wet clothes causing the water to vaporize, even that water deep within the fabric. Because the fabric is porous, even this vapor evolved deep within the fabric will have little problem in finding its way out into the empty space of the drying chamber 12.
  • Heat will be conducted from the warmed wall of the drying chamber 12 to the wet surface of the fabric resting on the wall. Heat transfer by conduction will also occur to the water held in the fabric, and vaporization at 92°F. will likewise occur. The natural wicking action of the cloth will cause water from the interior of the fabric to flow toward the surface as water from the surface is vaporized. In addition, if any vapor is super-heated over the equilibrium temperature of 92°F., that super-heat will be conducted to the liquid water as the vapor passes through the fabric on its way to the chamber.
  • the heat transfer coefficient between the warm wall and the wet clothes at an absolute pressure of approximately 1.5 in. Hg is approximately 110 BTU/Ft 2 -Hr-F.
  • the vapor initially evolved from the fabric will pass through the vapor transfer line 22, the spray condenser chamber 24 and the vapor transfer line 33 into the water jet exhauster 36.
  • the vapor will be condensed by contact with the. cooler water jet in the vapor jet condenser.
  • the water in the reservoir 54 will be heated above the ambient temperature.
  • the water jet exhauster 36 is designed to pump non-condensible gases rather than to act as a condenser.
  • the surface area of the water jet is limited in area and hence its ability to condense water vapor is limited.
  • the water valve 104 opens admitting cold water to the spray nozzle 26 of the spray condenser 24.
  • the spray nozzle converts the cold water into a finely divided mist to expose a large surface area of the incoming cold water to the vapor flow.
  • the vapor passes through the vapor distribution plate 28 and flows upward countercurrent to the downward flowing water spray.
  • the cold water spray enters at a temperature ranging from 50°F. to 60°F. and is heated to perhaps 85°F. as the water vapor condenses on the surface of the droplets.
  • the large surface area assures efficient heat transfer.
  • any vapor not condensed in the spray chamber 24 passes into the water jet exhauster 36 where it is subsequently condensed.
  • the water jet exhauster will continue to remove residual air, any air that leaks into the system while in operation or any air that is deliberately admitted to the system while in operation.
  • the water leaving the spray nozzle 26 passes through the distributor plate 28 and collects in the bottom of the spray condenser 24.
  • the water flows through the condenser water drain line 40 into the vapor transfer tube 34 and into the water jet exhauster 36 where it is pumped into the water reservoir 54 by the oversized water jet exhauster 36.
  • the flow of water from the spray condenser gradually increases the water level in the water reservoir 54.
  • the water level switch 60 senses when this level has reached the upper limit and commands the control system to open the valve 50 on the water drain line 48. When the lower limit has been obtained, the valve is caused to close.
  • the fluff valve 84 is opened briefly admitting a jet of air into the drying chamber and directed in such a way that it causes the fabric to flip over in the drying chamber.
  • the brief introduction of air will be sufficient to increase the chamber pressure above 1.5 in. of Hg.
  • the water pump 46 is caused to operate at full speed to remove the air introduced by the fluff jet and restore the normal vaporization temperature and condensing action in the dryer.
  • the rearrangement of the fabric in the dryer also opens the folds in the fabric and fluffs the clothes.
  • the pump motor is slowed to half speed again. The procedure may be repeated several times in a drying cycle.
  • the heated wall becomes ineffective in transferring heat to the water remaining in the fabric and eventually 100% of the energy is supplied by microwave energy.
  • the fabric will be dried to a moisture content in the range. of 5% to 10% at which time it feels dry to the touch.
  • the solid state control 110 turns off the solid state microwave array 88, opens the fluff valve 44, opens the cold water valve 74 in the water jacket chamber 66 and closes the water valve into the spray chamber 24.
  • the air rushes into the drying chamber 12 through the fluff jet air pipe 82 and fluffs the fabric thoroughly.
  • the air subsequently fills the drying chamber 12, spray condenser 24 and the vapor transfer lines 22 and 34.
  • the water pump is turned off.
  • the cold water entering the water jacket chamber 66 cools the lower surface of the drying chamber 12 preventing heat soak into permanent press fabrics which would cause creases in the fabric should it not be removed promptly from the dryer. Finally the door is opened and the fabrics are removed. The dryer is ready to start the next cycle immediately.
  • the solid state microwave array 88 is mounted on the door 14, but may be mounted anywhere in the upper portion of the drying chamber 12 whereby the microwave may be generally directed at the fabric to be dried.
  • the solid state microwave array 88 is composed of one or more solid state devices mounted on a heat sink which is cooled by water as shown in Figure 1, but may be cooled by air.
  • the power line 98 to the microwave array passes through an interlock (not shown) which prevents electrical power from being connected to the microwave array if the door 14 is not closed and latched.
  • the solid state microwave array radiates microwave energy directly from the surface of the solid state devices and operates typically at either 915 MHz or 2450 MHz, two frequencies approved by the FCC for microwave heating devices or other frequencies in the range of 500 MHz to 50,000 MHz, depending upon authorization by the FCC. Also, it is not important for purposes of this invention that the microwave power signal be broadbanded in frequency. The requirements of this invention are not technically related to the requirements normally encountered in microwave communications. Neither frequency bandwidths nor frequency stability are important parameters in microwave fabric drying as disclosed herein.
  • the microwave array is mounted entirely within the metal cavity 13 of the drying chamber and supplied with 220V single phase power to the power cable 98 penetrating the wall.
  • microwave heating devices mount the microwave source external to the chamber and transmit the microwave energy into the chamber by means of a waveguide. Placing the microwave source within the cavity eliminates waveguide losses and reduces the risk of microwave leakage from the external power equipment and waveguide.
  • the microwave energy released into the cavity 13 will either be absorbed by water directly on its first pass through the cavity or be reflected from the metal wall successively until it either intersects water molecules and is absorbed or its energy is expended in wall losses in cumulative contacts with the walls.
  • the vacuum drying cavity is designed so as to minimize microwave wall absorption when operated empty.
  • the internal dimensions of the cavity will directly depend upon the frequency of radiation, and these dimensions can be computed through use of accepted and well-known transmission line equations.
  • a temperature sensor 64 in the inlet of the water pump 46 measures the temperature of the water entering the pump. If that temperature exceeds 85°F. it lights a warning light and commands the water valve 104 to the spray condenser 24 to open from the initiation of the cycle. If the temperature of the water exceeds 88°F. it signals the control system to shut down the microwave power until the temperature has dropped below 85°F. In a particular application, if the 85°F. temperature level is exceeded frequently, the cold water flow rate through the nozzle 26 is increased to reduce the water temperature in the reservoir.
  • Fabric has a certain amount of lint that inevitably becomes airborne during most drying operations.
  • Conventional dryers which blow air through the fabric encourage lint generation. In the microwave fabric dryer little lint generation is anticipated during most of the drying cycle except during the brief applications of the fluff jet 82 to turn the clothes.
  • the low absolute, pressures existing within the drying chamber 12 will not provide sufficient aerodynamic support to allow the material to remain airborne after the jet has subsided. Nevertheless a lint filter 19 is provided over the opening 20 into the transfer pipe 22 to prevent most of the lint that does fly from entering the vacuum system.
  • lint will find its way into the circulating water of the vacuum system.
  • a lint filter 45 is included in the water flow circuit.
  • the solid state control will sense excessive pump output pressure through a sensor 43 and signal a warning light to clean the filter.
  • the water jet exhauster - water pump combination has several advantages over mechanical vacuum pumps for the dryer application.
  • the water jet exhauster is capable of rapid pump down from atmosphere because of its inherently high flow rate at the higher subatmospheric pressures. Further, the system is not sensitive to lint or dirt or to condensed water. vapor. Finally, it provides a condensing function in addition to its vacuum producing function.
  • conventional electric dryers have an efficiency of 50% based upon the incoming electrical energy.
  • the subject invention has a substantially higher efficiency because of the absence of the hot air stream issuing from the dryer and the high efficiency of the solid state microwave array 88.
  • the overall efficiency of the subject invention is approximately 70% using solid state devices in the microwave array with a conversion efficiency of 90%. Only 4% of the total power is used for the water pump to provide the vacuum. If the water jacket chamber is eliminated from the subject invention and 100% of the heat of drying is supplied by the solid state microwave array 88, the efficiency would be 86%.
  • FIG 3 is a diagrammatical view of the invention without the water pump and the water reservoir.
  • the water inlet line 44 to water jet exhauster is attached directly to the cold water line through a shut off valve 41.
  • the water exhaust line 52 from the water jet exhauster now goes directly to the drain.
  • the standby water valve 49 is opened and the main water valve 41 is closed.
  • the standby flow rate is perhaps one-quarter that of the full flow, but is adequate to maintain the pressure at 1.5 in. Hg after it has been obtained.
  • the water consumption with this simplified version is approximately five times as great: as the preferred embodiment of the present invention described with respect to Figure 1. Drying time is approximately the same.
  • Figure 4 is a diagrammatical view of still another alternative embodiment of the subject invention which is a further simplification over the first alternative embodiment.
  • the spray condenser has been eliminated and all the condensation of vapor occurs in the water jet exhauster 36. Elimination of the spray condenser alone may also be practiced with the preferred embodiment of the invention.
  • the rate of vapor condensation will be reduced because the vacuum exhauster has limited surface area for vapor contact. Drying times will be increased as will water consumption over the original invention.
  • a less powerful solid state microwave array 88 is selected to match the vapor condensation rate of the water jet exhauster 36.
  • FIG. 5 is a diagrammatical view of yet another alternative embodiment of the present invention representing a further simplification in design.
  • the water jacket chamber 66 has been eliminated from the design. This omission can apply to the preferred embodiment or any of the other alternative embodiments.
  • the heat from the water jacket chamber contributed approximately 15% of the heat to dry the fabric. Hence, if the water jacket chamber is eliminated, the drying time would increase. This heat could, however, be supplied by increasing the size of the solid state microwave array 88. Subscale Tests
  • the apparatus for the microwave dryer tests was composed of a 250 mm plastic vacuum dessicator of poly-carbonate material placed inside a Sears Roebuck 1.5 kw microwave oven operating at a frequency of 2450 MHz using a magnetron tube to generate the microwave energy.
  • a one-half inch aluminum vacuum line 24 inches in length was connected to the dessicator and led from the inside of the oven to the outside of the oven through a hole in the oven wall.
  • a spray condenser was constructed of PVC pipe couplings and end caps measuring 4-1/2 inches in inside diameter and with a height. of 12 inches.
  • the vacuum line from the dessicator was connected into the side of the spray condenser 4 inches from the bottom.
  • an aluminum distributor plate with 1/32 inch holes on 1/8 centers was mounted.
  • a 1/8 inch spray nozzle with a solid 30° spray cone was mounted at the top of the spray chamber; the flow rate of the nozzle was 0.36 gpm with a pressure differential of 30 psia.
  • a second 1/2 inch vacuum line led from the upper surface of the spray condenser to a laboratory type water jet exhauster. Cold water from a household outlet was used to power the water jet exhauster. The spent water was directed to the drains. Water collecting in the bottom of the spray condenser was piped to an evacuated reservoir 3.75 in. in diameter and 18 feet long located at a level below the spray condenser. Calibrated bourdon vacuum gauges were used to measure the system pressure.
  • the wet fabric was weighed and placed in the dessicator which was located inside the oven.
  • the water jet exhauster was activated and allowed to run until an absolute pressure of 1.5 in. Hg was achieved in the system.
  • the spray condenser was subsequently activated, and the microwave oven turned on. The oven was operated for a specific time. At the termination of the test run the vacuum was broken, the specimens were removed from the dessicator and were weighed. The overall efficiency of the microwave heating was subsequently calculated.
  • the energy input was measured as the power into the oven for the duration of the test.
  • the useful energy was measured as the loss of water times the heat of vaporization at 92°F. Cloth loads ranging from 7 ounces to 37 ounces of wet weight were tested.
  • Cloth for testing was usually taken directly from a washer after washing; moisture content of the specimens ranged from 55% to 25%. Fabrics made from cotton, synthetics, wool, Indian madras and a rubberized material (Spandex) were tested; Tests ran from 6 to 12 minutes after a pressure of 1.5 in. Hg had been established in the system.
  • the overall efficiency of the microwave drying cycle was approximately 40-45%.
  • a 14.2 oz. dry cotton cloth specimen was dried from a 36% moisture to 8% moisture in 12 minutes at a pressure of 1.5 in. Hg.
  • Microwave efficiency was 40% for this test.
  • the Sears Roebuck microwave oven used for the experiments used a magnetron tube for microwave generation.
  • magnetrons in microwave ovens are only 50% efficient in converting input power to microwave power.
  • the oven contained a browning plate which absorbed microwave energy. Consequently, the low efficiencies obtained in the experiments compared to the solid state microwave power devices of the subject invention are explainable.
  • the objective of the heat transfer test was to measure the surface heat transfer coefficient between a warm surface and wet fabric in a partial vacuum where the temperature of the surface was in excess of the vaporization temperature in the partial vacuum.
  • a 44 square inch copper plate with a copper tube brazed to its lower surface was mounted horizontally within a 250 mm. vacuum dessicator. Hot water connections and drain connections were made through the wall of the dessicator.
  • a 1/2 inch vacuum line was attached to the dessicator and connected to the spray condenser of the vacuum system previously described. Eight layers of wet cotton cloth were placed over the 44 square inch surface covering it.
  • the dessicator was closed and the pressure reduced to 1.5 in. Hg absolute. Hot water at 140oF. was allowed to flow through the coil at a high flow rate for five minutes.
  • the vacuum was broken, the specimen was removed and the specimen was weighed. As expected, the measured heat transfer coefficient varied directly with the moisture content of the fabric. The results were as follows:
  • microwave fabric dryer While the invention is believed to have been described above in sufficient detail for one skilled in the art to construct a microwave fabric dryer, an example of a typical microwave fabric dryer operating as a home clothes dryer is given.
  • the microwave dryer will take a normal 15 pound load of wet clothes and dry them in 11 minutes. It requires 12 kw of electric power at 220 volts AC single phase, approximately the same as an electric stove. To dry a normal load of clothes it requires 1.8 kwh of electric power, 32 gallons of cold water and 4 gallons of hot water. It is the same size as a conventional dryer and slightly heavier. The overall efficiency is 72%. It is capable of drying wool and other heat sensitive fabrics without shrinking. It is top loading for convenience and it has a cool wall feature to prevent creasing of permanent press clothes.
  • the drying chamber is a sphere 1.6 feet in diameter with a wall thickness of 1/16 inch; the volumetric capacity is 2 cubic feet.
  • the sphere is spun from mild steel and has a theoretical crushing pressure of 1500 pounds, ten times atmospheric pressure. It weighs 225 pounds.
  • the spray condenser is a cylindrical plastic vessel with an internal diameter of 5.5 inches and a height of 16 inches.
  • the flow rate of cold water to the spray nozzle is 2.7 gal/min.
  • a commercial 1-1/2 inch water jet exhauster is used, driven by a 30 gallon per minute 80 psi water pump powered by a 2 hp electric motor.
  • a 20 gallon water reserve is employed. Extensive use of plastic is made for all components except the drying chamber.
  • the solid state microwave array has a power input of 10 kw with a 90% efficiency. It is manufactured as an assembly along with its special controls and mounted on the door of the dryer. Interlocks, similar to those used with microwave ovens, are used to prevent activation of the microwave array unless the store is closed and locked. Safety will be improved over the microwave ovens because the microwave generator is contained entirely within the steel enclosure.

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  • Engineering & Computer Science (AREA)
  • Textile Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Microbiology (AREA)
  • Health & Medical Sciences (AREA)
  • Molecular Biology (AREA)
  • Drying Of Solid Materials (AREA)

Abstract

Dans une secheuse, des tissus sont seches rapidement et a basse temperature en les soumettant a une energie de micro-ondes dans une atmosphere de pression reduite. L'energie de micro-ondes eleve la temperature de l'eau dans le tissu jusqu'a son point d'ebullition, qui est tres bas a cause de la pression reduite, et la vapeur d'eau qui se degage du tissu se condense a l'exterieur du champ de micro-ondes a la meme pression reduite. Dans un mode de realisation, la secheuse est formee comme une secheuse de vetements ou la chambre de sechage (12) est un conteneur spherique metallique sous vide (12); l'alimentation en energie de micro-ondes se fait par un dispositif a micro-ondes a circuits integres (88) dans la chambre de sechage (12). La vapeur d'eau est condensee par un condenseur a atomisation (24) a l'exterieur de la chambre de sechage (12), et la pression reduite est obtenue par un dispositif de refoulement de jets d'eau (36) qui fonctionne en partie comme un condenseur. Le temps de sechage est accelere en rechauffant la surface inferieure (67) de la chambre de sechage (12) avec de l'eau chaude, et un jet d'air provenant d'une lance de soufflage d'air (82) laine le tissu apres sechage.
EP81901729A 1981-02-06 1981-02-06 Appareil et procede de sechage d'un tissu par micro-ondes Withdrawn EP0070827A1 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US1981/000171 WO1982002761A1 (fr) 1981-02-06 1981-02-06 Appareil et procede de sechage d'un tissu par micro-ondes

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EP0070827A1 true EP0070827A1 (fr) 1983-02-09

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Publication number Priority date Publication date Assignee Title
GB2210439B (en) * 1987-09-26 1991-08-07 Susan Christine Wilson Microwave/radio frequency drying/ironing cabinet
GB2217824A (en) * 1988-04-27 1989-11-01 Nicholas Parsons Drying apparatus
IT1246691B (it) * 1990-11-16 1994-11-25 Merloni Antonio Spa Dispositivo di condensazione, particolarmente per macchine lavatrici asciugatrici
DE59204851D1 (de) * 1991-06-11 1996-02-08 Hak Anlagenbau Gmbh Fuer Verfa Verfahren zur entfernung verdampfungsfähiger stoffe und anlage zur durchführung des verfahrens
CN107694871A (zh) * 2017-11-17 2018-02-16 江苏帕尔克玩具有限公司 一种积木喷漆工序中用烘干装置
CN110201984B (zh) * 2019-06-24 2024-01-26 中国石油天然气集团有限公司 一种含油物品微波去油回收装置及其使用方法

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Publication number Priority date Publication date Assignee Title
US2528476A (en) * 1942-03-20 1950-10-31 Thomas Lipton Inc Method and apparatus for dehydration
DE1410814B1 (de) * 1961-11-04 1972-05-31 Boewe Boehler & Weber Kg Masch Chemischreinigungsmaschine
US3771234A (en) * 1969-09-09 1973-11-13 Exxon Research Engineering Co Microwave drying process for synthetic polymers
US3854219A (en) * 1973-06-18 1974-12-17 Gen Electric Electronic dryer
US4057907A (en) * 1974-07-18 1977-11-15 Rapino Norman G Method and apparatus for drying clothes
US4015341A (en) * 1975-12-22 1977-04-05 Mcdonnell Douglas Corporation Seed drying process and apparatus

Non-Patent Citations (1)

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See references of WO8202761A1 *

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