Electric heating – Microwave heating – Fluid heater
Reexamination Certificate
2000-07-28
2001-06-19
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
Fluid heater
C219S688000, C219S710000, C219S738000, C219S746000, C219S759000
Reexamination Certificate
active
06248987
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a microwave installation set for controlling the temperature of a heat bath. A process fluid used as a heat medium (heat bath) is to be heated to, and maintained at, a predetermined temperature with an accuracy of better than 1/100° C. The heat bath is provided to maintain a well-defined temperature in containers filled with substrates under laboratory conditions.
Generally, closed (the heat bath is contained in a housing which can be closed) as well as open (openly accessible heat bath) temperature control arrangements are used. The conventional temperature control systems include resistance heating arrangements in the form of heating coils in order to achieve a uniform mixing of the heat bath medium by heat transfer and pumped circulation. A temperature controlled heat bath of 5 liter liquid having an electric power input of 2 kW requires about 20 minutes to reach a temperature of 90° C.
It is the object of the present invention to provide an electromagnetically compatible (EMC) microwave-based system as an economical alternative to the conventional resistance heating and temperature control arrangement.
SUMMARY OF THE INVENTION
In a microwave system for heating, and controlling the temperature of, a heat bath including a containment for a liquid, with a wall on which the microwave system is mounted, the microwave system comprises a microwave source operating at an ISM frequency of 2 to 5 GHz, a microwave conductor for conducting microwaves from the microwave source to a resonator through a ceramic window disposed in the resonator wall, the resonator has a common wall portion with the containment, which common wall portion consists of a grid having a mesh width that prevents passage of microwave radiation but provides for communication of the liquid between the resonator and the containment.
The hollow conductor is provided with a tuning unit for tuning the microwave system. An operating and measuring unit is coupled with the microwave generator for controlling the heating of the liquid and to ensure a uniform temperature thereof.
Preferably, the microwave energy enters directly into the metallically shielded resonator which is filled with a microwave coupling liquid having a dielectricity number &egr;
r
for heating of the liquid, and wherein the microwaves generate a plurality of electromagnetic vibration modes corresponding to the tuning. The position of the tuning unit in the wave conductor determines the various modes which are important for the local or the overall heating of the liquid in the resonator volume.
It is impossible to prevent the occurrence of reflections in the microwave conductor system, which detrimentally affect, or may even damage, the microwave source. To avoid those reflections, a Bragg-type mirror is disposed in the microwave conductor at the entrance to the microwave source, which blocks the reflection returning from the ceramic window as a linearly polarized wave.
The technical concept according to the invention is different from conventional thermostatic heat baths in the handling, the dimensions and the appearance although this may not be directly apparent.
The physics employed for the temperature control is as follows:
In order to make it possible to heat a material by microwaves, such material must have electromagnetic in-coupling properties. The dielectric properties of the heat carrier water are given as example in the following table:
Dielectric properties
&sgr;
At 3 GHz
Temperature
&egr;
v
&egr;″
[s/m]
Water (dest.)
25° C.
76.7
12.0
2.0
Water (+NaCl)
25° C.
67.0
4.87
7.0
Water (dest.)
95° C.
52.0
2.44
0.4
The dielectricity number &egr;
v
indicates the capability of the material to have refraction effects on a wave, the electric conductivity &sgr; provides a quantitative value for the penetration capability of a wave into a material. The table shows the changes of the dielectric properties of water at different temperatures for pure water and water including an electrolyte.
The use of microwaves provides free and direct access to the heat bath for the user in such a way that the user is not exposed to the electromagnetic effects of the microwave. This is made possible by the electrically conductive mesh screen which is provided as separation wall between the heat bath and the resonator and which permits liquid to pass so that the liquid can be circulated. However, the screen prevents microwaves from passing as the mesh width is selected depending on the chosen microwaves so as to prevent passage of the microwaves.
Below the invention will be described in greater detail on the basis of the enclosed figures.
REFERENCES:
patent: 3778578 (1973-12-01), Long et al.
patent: 4152567 (1979-05-01), Mayfield
patent: 4165455 (1979-08-01), Mayfield
patent: 4711983 (1987-12-01), Gerling
Feher Lambert
Link Guido
Thumm Manfred
Bach Klaus J.
Forschungszentrum Karlsruhe GmbH
Leung Philip H.
LandOfFree
Microwave system for heating, and controlling the... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Microwave system for heating, and controlling the..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Microwave system for heating, and controlling the... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2434728