U.S. patent application number 13/783198 was filed with the patent office on 2014-09-04 for apparatus for drying clothes or other solids using microwave energy under reduced pressure with energy recovery while avoiding arcing.
The applicant listed for this patent is Dennis Eugene McCarthy. Invention is credited to Dennis Eugene McCarthy.
Application Number | 20140245630 13/783198 |
Document ID | / |
Family ID | 51420162 |
Filed Date | 2014-09-04 |
United States Patent
Application |
20140245630 |
Kind Code |
A1 |
McCarthy; Dennis Eugene |
September 4, 2014 |
Apparatus for Drying Clothes or Other Solids Using Microwave Energy
Under Reduced Pressure with Energy Recovery While Avoiding
Arcing
Abstract
An apparatus for drying clothes or other solids that includes a
rotating drum with microwave generator inside and rotating piping
connections for energy recovery via drum jacket while sealing
microwaves and pressure (vacuum), and selectable controls that
provide conventional heating at a preset drum outlet moisture
content, or not, depending upon the potential for metal in the
load, to avoid arcing.
Inventors: |
McCarthy; Dennis Eugene;
(Washougal, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
McCarthy; Dennis Eugene |
Washougal |
WA |
US |
|
|
Family ID: |
51420162 |
Appl. No.: |
13/783198 |
Filed: |
March 1, 2013 |
Current U.S.
Class: |
34/487 ;
34/604 |
Current CPC
Class: |
F26B 3/347 20130101;
Y02P 70/10 20151101; Y02P 70/40 20151101; D06F 58/04 20130101; F26B
11/0495 20130101; D06F 58/38 20200201; D06F 58/266 20130101; D06F
2103/08 20200201; D06F 58/30 20200201; D06F 58/26 20130101; D06F
2105/28 20200201 |
Class at
Publication: |
34/487 ;
34/604 |
International
Class: |
D06F 58/04 20060101
D06F058/04 |
Claims
1. An apparatus for drying clothes or other solids including those
containing some metal objects comprising: a. A metal drum designed
for external pressure with a sealing access door and heat transfer
jacket with internal baffles and means for connecting external
piping to and from said jacket and an end centered double pipe axle
providing conduits for fluid flow in and out of said drum and in
and out of said jacket and providing for rotation of said drum. b.
Double pipe rotary sealing units connected to said drum axle
providing for connection of said pipes to stationary piping. c. A
cylindrical metal canister located inside said drum and attached to
one end of said drum and open to said drum inlet pipe and removable
from said drum and providing a pressure vessel wherein high voltage
microwave generator components are mounted and said canister is
sealed from said drum cavity, including microwave antenna, except
through one or more orifices of predetermined size avoiding
microwave feedback and providing near atmospheric pressure inside
said canister at design air flow rate through said canister and
said drum while said drum pressure is less than one half of
atmospheric pressure. d. A set of rotary contacts providing
connection of stationary wires conveying residential single phase
alternating voltage to wires rotating with and inside said drum
axle providing power to said high voltage microwave generator
components inside said canister. e. An electric motor and means for
rotating said drum. f. An electric motor and vacuum pump to provide
a predetermined rate of air flow through said canister and said
drum and to convey that air and its moisture content to discharge
piping at a pressure higher than atmospheric pressure while
maintaining a predetermined negative gauge pressure inside said
drum cavity. g. An electric resistance heater mounted inside said
stationary inlet piping providing the design maximum inlet air
temperature for said drum. h. Electric manual and automatic
controlled switches that allow an operator to select a drying
process that will either both turn off the microwave generator at a
predetermined outlet air moisture content and simultaneously turn
on said resistance heater or not depending upon the nature of the
load being dried, while allowing the drying process to terminate
automatically at some predetermined final moisture content of said
outlet air in either case or to be terminated by said operator or
manually set timer switch.
2. The apparatus of claim 1 designed for drying various industrial
solids including pharmaceuticals and fine chemicals wherein said
drum cylindrical section transitions to a pipe flange and said
flange is connected to a valve for loading and unloading and
wherein said electric manual and automatic controls do not include
provision for switching from microwave drying to hot air
drying.
3. A method of drying clothes or other solids comprising
irradiation with microwaves under reduced pressure until a preset
moisture level is achieved and drying energy switches to
conventional electric resistance heating for those loads that may
contain metal objects inside a rotating drum with a drum jacket
providing energy recovery from air discharged from the drum.
4. A method of drying pharmaceuticals or other fine chemicals or
other industrial solids comprising irradiation with microwaves
under reduced pressure inside a rotating drum with a drum jacket
providing energy recovery from air discharged from the drum.
Description
BACKGROUND
Prior Art
[0001] The following is a tabulation of some prior art that
presently appears relevant:
TABLE-US-00001 U.S. Patent Number Issue Date Patentee 3,410,116
1968 Nov. 12 Levinson 3,439,431 1969 Apr. 22 Heidtmann 3,854,219
1974 Dec. 17 Staats 4,057,907 1977 Nov. 15 Rapino, et al. 4,250,628
1981 Feb. 17 Smith, et al. 4,334,136 1982 Jun. 8 Mahan, et al.
4,356,640 1982 Nov. 2 Jansson 5,321,897 1984 Jun. 21 Holst
4,490,923 1985 Jan. 1 Thomas 4,510,361 1985 Apr. 19 Mahan 4,523,387
1985 Jun. 18 Mahan 4,703,565 1987 Nov. 3 Kantor 4,765,066 1988 Aug.
23 Yoon 4,829,679 1989 May 16 O'Connor, et al. 4,856,203 1989 Aug.
15 Wennerstrum 5,187,879 1993 Feb. 23 Holst 5,270,509 1993 Dec. 14
Gerling 5,315,765 1994 May 31 Holst 5,321,897 1994 Jun. 21 Holst
5,341,576 1994 Aug. 30 Tsutomo, et al. 5,396,715 1995 Mar. 14 Smith
7,665,226 2010 Feb. 23 Tsurata, et al. 8,015,726 2011 Sep. 13
Carow, et al.
BACKGROUND
Prior Art
[0002] Inventions applying microwave energy to drying of solids
have been around nearly since the residential microwave oven
entered the marketplace in the mid 1960's. For example, in U.S.
Pat. No. 3,410,116 (1968) to Levinson a device is described that
could be used as a microwave oven or converted to other uses,
including drying clothes. The source of drying energy was a
microwave generator, though not described in detail. However,
drying of household laundry using microwave energy has some
inherent problems that were not addressed in this early patent and,
perhaps, not completely addressed since. One of the most difficult
issues is that of arcing that can occur between metal contained in
clothing (zippers, rivets, buttons, coins, etc.) and a grounded
surface of the dryer. Microwaves are nearly totally reflected by
most metal surfaces, but some skin penetration does occur with
energy transfer to the metal. That energy releases electrons in the
metal. According to classical electromagnetic theory, a free charge
can exist only on the surface of a conductor, as the electric field
within the metal must remain zero. Accordingly, free electrons will
distribute as a surface charge and in such a way as to provide the
appearance of a uniform electric field emanating from the surface
when viewed at a great distance (infinity). If that electric field
is represented by lines perpendicular to the surface and directed
outward, those lines for a flat surface will be equally spaced. At
a curved surface, the charge will aggregate so that the field lines
will be closely spaced at the surface but will diverge and appear
equally spaced at a distance. The density of the surface charge
will be inversely proportional to the radius of curvature. This
means that sharp points on the metal surface can create a very high
electric field when viewed close to that surface. It is possible
that the electric field could exceed the breakdown voltage of air,
causing the air molecules to ionize and become conductive. An arc
results from the transfer of electrons from the metal surface to
ground. The energy associated with that arc can create high
temperatures that can damage associated objects. In a later attempt
to control arcing, in U.S. Pat. No. 4,523,387 (1985) to Mahan, a
non-conductive liner was added to the drum. In the present
invention, the drum surface must remain conductive to facilitate
heat transfer from the jacket. In U.S. Pat. No. 5,270,509 (1993) to
Gerling, an electronic system to monitor the electric field in the
drum was added which could interpret a sudden drop in that field
strength as arcing, and then reduce the microwave power. In U.S.
Pat. No. 5,396,715 (1995) to Smith a fire suppression system is
included triggered by a flame sensor. Smith makes the statement
that thermal damage to fabric is the result of rapid heating of
metal objects by microwaves. Rather, the damage is the result of
the arc that may occur between the metal object and some lower
potential, likely the grounded drum. However, some materials do
readily absorb microwaves (some plastics, some liquids, even some
crystals like graphite and doped silicon) and should such materials
be included with clothes burning of fabric could occur. Checking
pockets will always be part of successful microwave drying. Still,
arcing remains a problem which inhibits the application of
microwave drying to residential laundry.
[0003] According to Paschen's Law, the breakdown voltage for air
will initially decline as the pressure is lowered from normal
atmospheric pressure, reaching a minimum as the pressure is
continuously reduced. For a vacuum dryer operating in that region
of the Paschen Curve with negative slope, arcing in the dryer may
be an even greater problem. A dryer operating at reduced pressure
must expect a greater incidence of arcing. If, as suggested, the
potential difference that causes arcing results from a building of
surface charge on metal objects, a mechanism that conveys that
charge to ground could avoid arcing. Such a mechanism exists
naturally with saturated fabrics. Liquid water, except when
extremely pure, has the ability to conduct surface charge to
ground. However, as the surface of the fabric dries, even though
water still exists inside the fibers, that conductivity will be
gone. So, at some point during the drying process, metal surface
charge will again build. If microwave energy is replaced at that
point with conventional heating, some overall efficiency is lost,
but that loss can be minimized with good sorting of loads.
[0004] One reason to apply microwave energy to drying is to provide
higher energy efficiency than the conventional method of hot air
drying. Microwaves will be absorbed by water molecules without
being significantly absorbed by the surrounding air. Air may still
be used to convey the vaporized water from the dryer, but the
energy associated with that air will not represent wasted energy.
It is also possible to minimize the temperature rise of the solid
material using microwaves. If there is no air movement, liquid
water will only be removed by raising the water temperature to the
point where its vapor pressure is equal to the atmospheric
pressure; i.e., to its atmospheric boiling point. However, if the
incoming air is relatively dry, the liquid water can be removed at
a lower temperature by contacting the water with moving air. The
driving force to transfer water molecules from the liquid surface
to the air is proportional to the vapor pressure of the water,
which in turn is determined by temperature. The higher the water
temperature, the faster the water will be removed. The same is true
for a higher air flow rate, and for better contact between solids
and air. It occurred to some that reduced pressure drying of solids
using microwaves has the potential to further reduce the drying
temperature by increasing the driving force for a given
temperature. That is, for the same temperature, the partial
pressure of water vapor will be greater at reduced total pressure,
improving the rate of transfer of water molecules to the air. For
example, U.S. Pat. No. 4,250,628 (1981) to Smith and Uthe describes
a method and apparatus for drying fabric under vacuum using
microwave energy and indirect heating from hot water at the bottom
of the drying chamber, which does not rotate. Air from a blower is
added to the chamber at the end of the cycle. There is no
discussion of the potential for arcing.
[0005] A rotating drum is helpful in most drying applications to
provide continuously good contact between air and solids which
facilitates mass transfer of water vapor to air and removal from
the dryer. However, a rotating drum presents sealing problems with
both microwaves and air, and especially so if the drum operates
under vacuum. For example, U.S. Pat. No. 4,765,066 (1988) to Yoon
describes an elaborate non-contact sealing system to allow for drum
rotation without leaking microwaves by controlling clearances at a
small fraction of the energy wavelength. The unit did not operate
under vacuum.
[0006] All similar inventions heretofore known fail to take full
advantage of the minimum temperature and energy efficiency possible
with microwave drying by combining a rotating drum, reduced
pressure, and energy recovery (including waste heat from the
microwave generator), while effectively sealing both air and
microwaves and avoiding arcing.
SUMMARY
[0007] In accordance with one embodiment a sealed drum, rotating on
a horizontal axis, loaded with clothes or other fabrics, is
supplied with outside air and irradiated with microwave energy from
a generator that rotates with and is located inside the drum, under
partial vacuum. Air exits the dryer through a filter and flows
through a vacuum pump which returns this moisture-laden air to the
outer jacket of the drum and finally the air is directed to a
trapped and vented drain. If the load may contain metal objects,
then, when a moisture sensor in the vacuum pump discharge detects a
preset reduced moisture level, the microwave generator is turned
off and an electric heater turned on to raise the temperature of
incoming air and continue the drying process without allowing
arcing from any metal objects in the fabric. Unlike microwave
energy, this heated air will transfer energy to the fabric as well,
but the temperature will at least be limited by the saturation
temperature of water at reduced pressure. When a further reduced
moisture level is detected by the moisture sensor, the drying
process is complete and all power to the apparatus--heater, vacuum
pump, and rotating mechanism--is shut down. Air is directed to and
from the rotating drum via dual flow rotating unions and through a
double pipe which also serves as the axle for the drum. Inside each
rotary union, the outer pipe is sealed via single mechanical seal
while the inner pipe is sealed via stuffing box (although a
mechanical seal is possible here also). When the load contains no
metal, as with sheets, towels, etc., and for other solids, a
selectable switch will allow microwave energy to continue drying
until the final moisture level is reached.
Advantages
[0008] In this embodiment, the continuous rotation of the drum
provides good contact between fabric and air, the low absolute
pressure inside the drum minimizes the temperature required to
vaporize the water, the microwave energy targets water molecules
while the energy normally wasted from the microwave generator is
utilized to enhance drying, and the energy represented by the
moisture laden air that leaves the drum is partially recovered via
the outside heat transfer jacket of the drum, along with some of
the heat of compression supplied by the vacuum pump. Using low
voltage rotary contacts, the microwave source has been mounted
inside the rotating drum. Most of the energy associated with the
inefficiency of converting house current to microwaves is taken up
by the incoming air and then transferred by convection to the
solids in the dryer. Additional waste energy from the microwave
generating equipment is transferred by conduction through the wall
of the enclosure to the solids on the outside of that wall.
Microwaves are sealed inside the drum by virtue of the small
diameter of the orifice(s) for air flow into the drum, the small
diameter of orifices in the support for the outlet filter media,
and the conductive elastomeric seal and the small dimension of the
gap between the form matching, overlapping door and the drum. Some
of the latent heat of vaporization of the water and the heat of
compression from the vacuum pump are recovered by directing air
from the vacuum pump to the dryer jacket. The space between the
inner drum and outer shell--the jacket--includes a spiral-wound
baffle intended to maintain air velocity to promote heat transfer
and prohibit bypassing as it directs the air flow across the drum
and to the outlet pipe. As moisture condenses, the air flow rate
and direction are intended to keep the liquid flowing so no buildup
occurs that would inhibit additional heat transfer and
condensation. This two-phase flow exits the dryer and enters a
typical trapped and vented sewer line. As clothes are dried, the
liquid water in the fabric will initially minimize any buildup of
charge on metal objects by its conductivity. At some point the
reduced moisture level will inhibit its ability to conduct charge
to the grounded drum, at which point the energy source will be
switched from microwaves to hot air, for those loads that may
contain metal, to complete the drying of fabrics, thus avoiding
arcing.
[0009] This embodiment provides a combination of low temperature
drying and energy conservation and recovery not currently
available. However, it should be noted that this embodiment, as
with current technology, will provide its maximum energy efficiency
when used continuously; that is, with one batch closely following
the last. Otherwise, the energy associated with the elevated
operating temperature of all dryer parts will be wasted following
each batch, lowering the efficiency per batch.
DRAWINGS
Figures
[0010] FIG. 1 shows a simplified view of the overall rotating drum
assembly and the associated air flow.
[0011] FIG. 2 shows a cross sectional view of the rotating drum and
the air flow direction through the microwave generator enclosure,
through the drum and out through the filter.
[0012] FIG. 3 shows a more detailed cross sectional view of the
microwave generator enclosure.
[0013] FIG. 4 shows a top view of the drum access door.
[0014] FIG. 5A and FIG. 5B show cross sectional views of the door
sealing mechanism.
[0015] FIG. 6 shows a simplified electrical wiring diagram for the
assembly including controls.
DRAWINGS
Reference Numbers
[0016] 11 120/240 VAC rotary contacts [0017] 12 air regulating
valve [0018] 13 dual flow rotary union [0019] 14 pillow block
bearing [0020] 15 rotating vacuum drum [0021] 16 lip-sealed drum
door [0022] 17 dry vacuum pump [0023] 18 drum rotating mechanism
[0024] 19 high voltage capacitor [0025] 20 high voltage diode
[0026] 21 magnetron tube [0027] 22 wave guide and microwave antenna
cover [0028] 23 high voltage microwave generator canister [0029] 24
high voltage transformer [0030] 25 baffle to provide for load
rotation [0031] 26 air filter [0032] 27 insulation [0033] 28
rotating vacuum drum baffled jacket [0034] 29 canister mounting
flange [0035] 30 canister air flow baffle [0036] 31 low voltage
microwave generator wire connector [0037] 32 slotted hinge [0038]
33 tapered lever arm [0039] 34 locking door handle [0040] 35
tapered arm guide [0041] 36 tapered arm shackle [0042] 37 door
lifting handle [0043] 38 conductive elastomeric seal [0044] 39
inlet air electric resistance heater [0045] 40 inlet heater
temperature control switch [0046] 41 minimum vacuum switch [0047]
42 outlet air (low, low low) moisture switch [0048] 43 magnetron
tube temperature limit switch [0049] 44 canister critical flow
orifice(s) [0050] 45 manual selector switch [0051] 46 momentary
contact start switch [0052] 47 drum proximity switch [0053] 48
momentary contact stop switch
DETAILED DESCRIPTION
FIGS. 1, 2, 3, 4, 5A & B, 6
First Embodiment
[0054] FIG. 1 provides a simplified external view of all mechanical
components of the unit. Arrows in this figure indicate the rotation
of the axle and drum assembly--everything between the stationary
housings of the dual flow rotary unions 13. The bodies of these
unions and the inlet/outlet pipes connected to them, opposite the
drum axle, are all stationary components. The drum axle is
supported by pillow block bearings 14 on both sides of the drum 15.
The bearing housings need to be supported by the frame of the
entire unit, but the frame is not shown, nor is any overall
enclosure shown, which would surely be part of any appliance sold
for residential use. The drive motor and mechanism for rotating the
drum 18 are shown, but not in detail. The drum may be belt, chain,
or gear driven, and the motor may be fixed or variable speed. The
sheave, sprocket, or gear teeth can encircle the drum or be
attached to the axle, although that will extend the length of the
unit. The drum opening door 16 is depicted as an elliptical shape,
but could be any shape. The radius of the door surface that seals
to the drum must conform closely to the outside radius of the drum.
The drum is shown as cylindrical with flat ends gusseted to the
outside pipe of the axle. The ends could be of any formed shape.
Although formed ends could be designed for external pressure with
thinner metal, the flat end was chosen to simplify the connection
and sealing of the generator canister and outlet filter
housing.
[0055] FIG. 2 shows a cross sectional view of the drum and its
internal parts, along with an internal view of the double-pipe axle
near the drum. An arrow follows the air flow through the drum.
Insulation 27 is shown, which is critical to provide for energy
recovery.
[0056] FIG. 3 shows a cross sectional view of the canister 23 that
houses the high voltage microwave generator components (capacitor
19, high voltage diode 20, magnetron tube 21, magnetron tube
temperature limit switch 43, and transformer 24). The air flow
baffle 30 is required to direct all air flow across the magnetron
tube cooling fins, and then through the pressure determining
critical flow orifice(s) 44. The maximum diameter of the orifice
must be a small fraction of the wavelength of the microwaves
generated. If the area of one such orifice is not sufficient to
provide the design air flow rate, then multiple holes must be
drilled such that the combined area does provide that flow as the
pressure drops from near atmospheric to near the vacuum pump
suction (absolute) pressure. The canister flange 29 is intended to
attach to the end of the drum (perhaps by welded studs and nuts)
and be sealed by a gasket from the vacuum inside the drum, while
grounded to the drum through the attachment. A pin type low voltage
wire connector 31 provides electrical connection/disconnection for
installation and maintenance purposes.
[0057] FIG. 4 shows a top view of the drum access door 16. The type
of closure shown is merely one that would work. A closure designed
for residential use would likely require a more aesthetically
pleasing design, replacing details for the hinges 32, tapered lever
arm 33, locking door handle 34, tapered arm guide 35, tapered arm
shackle 36, and door lifting handle 37, while maintaining
function.
[0058] FIG. 5A and FIG. 5B show cross sectional views of the access
door 16 and the mechanism from FIG. 4 which provides compression of
the elastomeric seal 38 material. Though required at the start of
the cycle, as the drum is evacuated the negative pressure inside
the drum may eventually provide adequate force to sustain the seal.
Still, the mechanical compression is required to initiate the
process.
[0059] FIG. 6 is a simplified wiring diagram showing the low
voltage 120/240 VAC motor and control wiring.
Operation
FIGS. 1, 2, 4, and 6
[0060] Initially, an operator would open the door and lift the door
to a position which it will maintain. The operator would then load
the drum with wet clothes or other fabrics from a washing machine,
close the door and use the locking handle 34 to seal the door. (The
hinges 32 are slotted so that the door can move to the drum
uniformly when the drum begins to experience negative pressure.)
The operator would choose the proper position of the selector
switch 45, depending upon whether the load may contain metal
(zippers, buttons, rivets, etc.). Then, the operator would push the
(momentary contact) start switch 46 to begin the drying cycle. The
microwave generator is not switched on until the minimum vacuum is
achieved, measured at the vacuum switch 41, indicating that the
drum door is adequately sealed.
[0061] FIG. 1 shows the overall flow of air through the rotating
drum and vacuum pump assembly. Outside (room) air initially flows
through an adjustable valve 12 which is designed in conjunction
with the flow orifices inside the drum and the size of the vacuum
pump 17 to provide the expected flow rate. However, adjustment of
the valve must be limited to preclude any significant vacuum in the
microwave generator canister. Air then flows through the inside
pipe of the dual flow rotary union 13 and into the drum assembly.
The dielectric breakdown voltage associated with high voltage
connections, although there are several different modes, varies
with reduced pressure in a manner similar to that predicted by
Paschen's Law. Consequently, the canister 23 that contains the high
voltage microwave generating components, shown in FIG. 2 along with
other drum internal parts, is designed to operate near atmospheric
pressure to avoid breakdown and arcing. Details of the parts inside
the canister are shown in FIG. 3. The canister and main drum 15
cavity are separated by a small diameter critical flow orifice(s)
that allows the design air flow to drop from near-atmospheric
pressure to the significant vacuum in the drum. The minimum air
flow is that required to maintain the magnetron tube temperature
below the maximum acceptable temperature for proper operation.
Beyond that, the air flow is designed to provide an acceptable
drying time. Other pressure drops in the system include that across
the filter 16 orifices and the friction losses in the piping.
However, these losses are designed to be small. The vacuum pump 17
is designed to provide the design air flow rate at the desired drum
vacuum (absolute pressure), which in turn is selected to provide a
maximum saturated water temperature in the drum. The proper flow
rate could be attained without the external valve 12, but including
the valve provides some flexibility in the design.
[0062] Inside the drum, air is contacted with fabric which is
tumbling as the drum rotates, accentuated by the drum baffles 25.
Although three are shown, this number may be greater. Microwaves
directed from the wave guide 22 fill the drum and are absorbed by
water in the fabric before and after microwaves are reflected by
the grounded metal inside surfaces of the drum. The drum can be
made of various metals, but aluminum is a good choice for a fabric
dryer to provide high thermal conductivity, resistance to water/air
corrosion, and to minimize the weight of the unit. The drum must be
designed for the anticipated operating vacuum. Design for full
vacuum will provide maximum flexibility in any future vacuum pump
substitution.
[0063] As air exits the drum it flows across a filter material to
remove lint, such material supported by a metal housing 26 drilled
with many small diameter holes designed to provide minimal pressure
drop at the design air flow rate, with diameter at a small fraction
of the wavelength of the microwaves generated. From the filter
housing 26 air flows through the inside pipe of the opposite side
rotary union 13 and then to the vacuum pump 17 inlet. From the pump
discharge, compressed (approximately atmospheric pressure) air
flows past the moisture sensor 42 and to the outer pipe of the same
side dual flow rotary union 13. Through the annular area of the
double-pipe axle of the rotary drum, the air flows into and through
the drum jacket 28, from the jacket to the annular area of the
opposite side double-pipe axle, and then transitions from rotating
axle to the stationary discharge pipe through the same rotary union
that conveys inlet air and rotating low voltage supply wires. The
jacket area must exclude that required to accommodate the door.
This will require abrupt changes in direction of the spiral path
that directs the flow from the inlet to the outlet side of the
jacket.
[0064] When a new drying cycle is initiated, the vacuum pump must
provide an acceptable minimum vacuum at the vacuum switch 41
(indicating that the door seal is acceptable) before microwave
heating can begin. Because the initial air flowing through the
vacuum pump may be relatively dry room air, the final low moisture
switch 42 must be bypassed briefly so that the heating can begin
and moisture laden air can make its way to the moisture switch.
Microwave drying will continue until the moisture sensor detects
sufficiently low moisture to indicate the potential buildup of
charge on metal objects (depending upon the selector switch
position). At this point, energy from microwaves is replaced by
that from room air heated by an electric resistance element 39,
controlled by an in-line temperature switch 40, while the air flow
rate and vacuum remain essentially unchanged.
[0065] Hot air vacuum drying continues until the moisture sensor
detects a low moisture level that indicates the load is acceptably
dry. At this point all power would be interrupted except that the
(now open) final low moisture switch will be bypassed during that
part of the final revolution required to bring the drum door to the
normal load/unload position. A mechanical proximity switch 47 is
held closed by the drum except at a single position of the drum.
This means that once per revolution the proximity switch will open
briefly. As long as the moisture switch is made, the opening of the
proximity switch has no effect.
[0066] When the drum stops, the operator would open the locking
mechanism and raise the door to the sustaining open position and
manually unload the dryer. The operator could stop the drying
process at any time by pushing the (momentary contact) stop switch
48.
Alternative Embodiment
[0067] An additional embodiment would employ the same basic design
but would not include the electric resistance heater 39 and the
second moisture switch 42 set point. This embodiment would be used
to dry other solids, such as pharmaceuticals or fine chemicals. In
this case, the lack of metal objects would eliminate the arcing
potential. To eliminate the possibility of corrosion and chemical
contamination, 316L stainless steel would be a better choice than
aluminum for drum construction. The door assembly of the first
embodiment is replaced with a welded flange and bolted butterfly
valve with conductive elastomeric seal. The flange diameter would
accommodate installation and service of the microwave generator
canister. With the butterfly valve full open, it would be possible
to replace the filter media. Depending upon the nature of the solid
chemical being dried, the media inside the filter may differ as
required to keep fine solids out of the vacuum pump and piping.
This industrial dryer designed for gravity discharge may be
elevated to accommodate the height of the product container.
Advantages
[0068] From the above description, a number of advantages of the
dryer apparatus are evident: [0069] (a) Energy that would otherwise
be wasted from microwave generation, air heating, water
vaporization, and vacuum pump compression is at least partially
recovered via conduction and convection inside the drum and then
from condensation and conduction through the jacket. [0070] (b)
Microwave energy is absorbed almost exclusively by water and drying
temperature is minimized. Besides energy efficiency, this low
temperature drying may be helpful for synthetic fabrics or
temperature sensitive solids. [0071] (c) Microwave sealing is
accomplished without complex traps. [0072] (d) A simple control
function allows an operator to dry clothes that may contain metal
objects without arcing.
Conclusions, Ramifications, and Scope
[0073] This dryer apparatus is a relatively simple machine that can
be constructed using readily available components and uncomplicated
fabrications that lend themselves to mass production. There will be
some challenges. For example, the double pipe drum axle center line
must coincide with the drum center line within a very small
tolerance to make the drum rotate without deflection. And, the
overall dimension from the rotary contacts 11 on one end to the
vacuum pump suction piping on the other must be such that the unit
could be placed in a typical residential laundry room. This
consideration does not apply to the industrial application.
[0074] If such a unit should become widely used, the energy savings
could offset a higher cost, and could have ramifications at the
grid level that will be helpful to all. More sophisticated
appliances are now more likely to be widely accepted by energy
conscious consumers. The relatively rapid low temperature drying
will have both energy and time saving advantages that will be
interesting to industrial users who need to dry high value
temperature sensitive pharmaceuticals and fine chemicals.
[0075] Although the description above contains a number of
specificities, these should not be construed as limiting the scope
of the embodiments but as merely providing illustrations of these
embodiments. For example, the door of the dryer designed for
residential laundry could have a variety of shapes and closure
mechanisms. The ends of the drum could be formed shape rather than
flat. The butterfly valve suggested for loading and unloading of an
industrial dryer could be another type of valve with large diameter
opening--perhaps an iris valve, if one could be designed to seal
under vacuum. And, the transition from the drum to valve flange
could be a shape other than cylindrical to encourage gravity
discharge of non-free flowing solids.
[0076] Thus the scope of the embodiments should be determined by
the appended claims and their legal equivalents, rather than by the
examples given.
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