Device for applying heated air to a cavity using microwave generators

A complete unit for simultaneous production of warm air and microwave energy is ready for delivery. The device contains three transmitters with wave-guides (8) for microwave energy, power components (9) and a fan (10). The fan blows cooling air past the power components and transmitters. The heated air can be used for removal of the water, that the microwave transmitters vaporize. The device can easily be moved from one cavity to another. With three transmitters connected one on each phase a balanced load of the mains is achieved. An induction motor drives the fan.

TECHNICAL FIELD 
Many products have to be dried after some treatment. For this hot air, 
infra-red radiation and lately microwave energy has been used. This 
treatment is usually performed in especially built rooms or volumes. With 
a permanent built in equipment those rooms will become more or less 
complicated as they have been designed for a specific use. The object of 
the present invention is to present a device, that is easy to move between 
different rooms for treatment and at the same time consumes as little 
energy as possible. 
BACKGROUND ART 
Airhandling has been well known a long time. Heating of air is also well 
known. Recently different kinds of treatment with microwave energy have 
come in use. Firstly those equipments were designed for a certain 
technical function or room. 
The present invention start from some of those known technical solutions 
and presents a low cost device for the generation of energy, where 
microwave energy as well as warm air is used. Those two kinds of energy 
are combined in an electrically ideal way. 
SUMMARY OF INVENTION 
It is especially characteristic for the invention that microwave energy and 
cooling air from its generation cooperate in a cavity, where microwave 
energy is the predominant kind of energy to be used for some operation 
like drying of paint or glue. 
Known transmitters of microwave energy consume comparatively much power. A 
highly developed cooling is therefore needed. It is characteristic for the 
invention that the device has one or more fans for air transport past 
microwave transmitters. This characteristic is enlarged with the need of 
air for transport of aqueous vapour from the treated objects. Typical for 
the device is, that the fans are designed to match this need of 
watertransport in a way that for cooling much oversized fans will be used, 
where the evaporation of water is large. 
An other distinctive mark is, that the whole device can be manufactured to 
a complete working unit, which furnish microwave energy as well as heated 
cooling air. All needed equipment for the time and humidity control can be 
found installed. This means that it will be easy to move the device for 
operation from one cavity to another, which means great economical 
advantage. 
Normally electric motors are run on three-phase current, induction motors. 
In order to avoid an unbalanced line load, the most advantageous device 
consists of three microwave transmitters so connected to the fan motor 
that a totally balanced load will be obtained. With three suitably 
connected transmitters low mutual disturbance will occur. 
An other characteristic for the invention is that due to standardization to 
rather small outputs, a massproduction and use of the invented device will 
result in, that the number of devices and not the their output will become 
design quantity.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows an ordinary design of the invented device. One sees a long 
narrow box 1, which has flanges 2 in the bottom, and a cover 3. In the 
cover there is a hole 4. If the box, that is shown schematically in 
perspective in FIG. 2, is turned over, three netting covered holes 5 and 
three protruding pipes 6 with rectangular cross section will be seen. The 
latter are the mouths of the microwave transmitter's wave-guides. 
In FIG. 3 the outer contour of a typical microwave transmitter is shown. 
Skilled men know, that usually a magnetron is the source of the microwave 
energy. Normally it is surrounded by cooling flanges 7, which in the 
figure is shown schematically as thin lines. There should be a driving 
component for the magnetron and a wave-guide 8. The wave-guide surrounds 
the apex of the magnetron. In FIG. 3, the wave-guide in view "a" is facing 
the observer. The rectangular cross section should especially be noticed. 
In FIG. 4 the box shown in the FIGS. 1 and 2 can be seen without the cover 
3. The box contains three transmitters for microwaves. Each of them has a 
wave-guide 8, that protrudes through the bottom of the box and is 
microwave-tight connected to the bottom of the box. Adjacent to the 
transmitters there is one power and one driving outfit, 9, to be found. To 
this should be added some condensers, which are not shown. The very 
transmitter of microwaves and its driving outfits are well known 
components and are not as such included in the invention. In the box there 
is also a fan 10 to be found. This fan sucks air from the environs through 
the hole 4 of the cover in the box and further out in a duct 11 along one 
side of the box. The duct is formed by a wall 12. In this wall there are 
apertures 13 for cooling air and 14 for air from the fan 10. An ordinary 
radial fan is displayed, but axial fans can be used. 
From the duct 11 air is pushed through the apertures 13 passing the power 
components on its way to the transmitters of microwaves and their cooling 
flanges and then out through the holes 5. Those holes are open for air but 
tight for microwave energy. They can be made of perforated plate 
preferably of aluminium, but wire netting with matching mesh can also be 
used. Skilled men know about those tightness questions. 
For the protection of transmitters and power components it has been found 
useful to cover the apertures 13 with filter cloth 15. As support for the 
filter a netting over the apertures 13 can be used. 
To distribute the cooling air through the box in a way, that all units get 
enough cooling, particular flow guides might be needed. In FIG. 4 those 
flow guides are marked 16. 
The box 1 can be fastened to a cavity by some known method. In FIG. 4 a 
rather durable bolt connection is indicated, the holes of which in the 
flange are shown i the figure. If the box is to be moved frequently there 
are other know methods for the fastening. It is however important, that 
the box is connected to every cavity in a microwave-tight way, when it is 
to be operated. 
Naturally a switch board for the electrical connection and control also 
belongs to the equipment. Those components are so well known, that they 
are not needed in the figures. Obtaining a balanced load of the main power 
supply is however a characteristic feature of the invention. This is 
achieved, as FIG. 4 discloses, through star or delta connection of three 
microwave transmitters, one per phase, combined with one three-phase 
motor. A result of this is, that the microwave transmitters do not 
mutually interfere, as they have their maximum output timed out of phase. 
The electrical phase difference of 120 degrees between maximum output for 
the different transmitters might also be used in a way, that different 
maximum outputs from the transmitters can be foreseen, as they do not 
mutually interfere and back radiation is eliminated. Although equal output 
power from all the three transmitters is a general goal, in some cases it 
might be advantageous with a possibility to adjust the power to the 
objects, which are to be dried. This can be achieved through a 
disconnection of one or two microwave transmitters. Sometimes this 
possibility to control the total output can be valuable. 
As all needed equipment for the production of energy is installed in a 
small box, the device will be completed already at the producing factory 
ready for further installation on any cavity. This has the advantage, that 
an individual box can be used on different cavities, if the mechanical 
connection to the cavity is made microwave-tight. Alumina coated tape can 
be used, if the cavity does not have microwave traps. Those are known by 
the man skilled in the art. 
Its has proven advantageous to produce series with relatively low output of 
microwave energy. For larger need of power one uses several boxes with 
transmitters. A result is naturally larger series but also a possibility 
to distribute the energy over larger surfaces. This is especially brought 
to light in big plants for moving products, where the time element can be 
of importance. With several transmitters along a moving web for instance 
of paper one gets a possibility to furnish different amounts of energy 
over a great distance, and can run the web at high speed and get a uniform 
heating. Printed paper, veneered particle board and glued wood belong to 
the products, which can be treated with microwave energy and the 
associated hot air for the removal of vaporized water. 
The need for cooling air to the microwave transmitters and their power 
components is one design size for the built in fan in the box. This 
quantity of air is a minimum needed fan capacity. Knowing the need of 
water vapour removal a matching air capacity can be added, when designing 
the fan. The whole can be built into the box 1. As it is advantageous 
normally, to run the microwave transmitters and their power components at 
an undeviating temperature, some throttles for the cooling air control 
might be required. Skilled men know about how to install those throttles. 
Different kinds of regulators might also be needed. 
It could be of advantage, when large quantities of air and energy is 
required, to split the box and use a units like that shown in FIG. 5. This 
alternative is however inferior to that in FIG. 4. Important is that three 
units of the latter type are used together, if the load advantage with 
three-phase, characteristic for the invention, shall be realized. 
It has been disclosed in the figures that the fan 10 is situated near a row 
of microwave transmitters, but this is only one of many successful 
positions, which are covered by the following claims. The fan might also 
be positioned above the transmitters and blow down its air in a duct 11, 
like that in FIG. 4. 
When very large amounts of hot moisture carrying air is required, any known 
equipment for further heating of the cooling air from the box, can be 
installed outside the netting covered holes 5, which are microwave-tight. 
In the Swedish patent application SE 900 3703-7 a spraying chambers is 
disclosed, in which microwave energy can be used for the drying of paint. 
It is characteristic for the invention, that a device of present design 
can be used on several chambers. After that a cord has been connected to 
the device and the chamber is adapted to the box, devices can be moved 
from one chamber to another when required. 
In FIG. 6 is shown a set up where one microwave device is used on two 
chambers. The figures are taken from the mentioned Swedish patent 
application. FIG. 6a thus shows a suitable designed chamber. 
Characteristic for this chamber is the lack of parallel surrounding 
surfaces around a working volume A, which means, that stationary waves 
will be avoided. In FIG. 6b two chambers have been put beneath each other. 
To that is added a cover for one of the working volumes. The cover is 
shown as a separate unit 20 in this figure. It is this cover, that well 
exemplifies the possibility to move the invented energy transmitter from 
one volume to another. 
The cover is mounted in FIG. 6c. The right chamber could for instance be 
used for drying of paint whereas the in the other, the left, a dried 
product is taken out, a new is set in and treatment of this new object 
will proceed. After the treatment in the left chamber the product in the 
right chamber will normally be dried and the cover can easily be moved 
from one chamber to the other. The working sequence is repeated and the 
box is moved again from chamber to chamber. 
In FIG. 6d a section of a chamber is displayed. Its aperture to the right 
is closed by a cover 21. In the figure this cover is hung at the upper 
edge on a rail 22 and resting on its lower edge in a slot 23. The other 
two edges of the cover are connected to the outer frame of the chamber in 
a microwave-tight way. In the cover a device 24 for microwave energy is 
tightly mounted. Other generators 25 of microwave energy might also be 
found in each chamber, but generally those are not needed. The fan from 
the invented box often makes the fan 27 in the chamber needless. Now a 
pushing fan is used instead of a sucking. Other combinations of fans are 
covered by the following claims. The displayed arrangement is naturally 
only an example of how the invented device for microwave energy can be 
used as part of a cover or door to a large volume. 
Typically for the method is, that several essentially equal devices can be 
used together on one cavity. It will thus be possible to produce those 
devices in larger series than it would if they were produced individually 
adapted to special requirements. 
INDUSTRIAL APPLICABILITY 
The invention implies a rationalization of the manufacturing of generators 
for microwave energy. Instead of designing and adapting every generator to 
the individual need, one chose a number equal and complete smaller 
devices, which can be manufactured in large series. As the complete device 
can easily be moved, one gets a inexpensive possibility to use microwave 
energy on several places in an enterprise.