Impact of industrial microwave power density of the four factors
First, the design of multi-cavity
Microwave technology to be exploited as a source of energy for heating, microwave drying, microwave insecticide , microwave sterilization and other industrial projects. Industrial microwave oven for a further expansion of the field of microwave technology .
Wavelength of the microwave spending the object geometry , and therefore the S -band single-mode microwave cavity geometry is small , the volume is not large, such a small volume of the cavity is not only used in industrial heating value , even in the microwave oven also no use value. This determines whether the microwave oven or industrial microwave ovens have to use over multimode electromagnetic mold cavity , from the electromagnetic theory of physics and know that any one of the resonant cavity , the over-molded state, wherein the possible the number of resonant modes of the cavity is proportional to the volume of .
In other words, the greater the volume , the number of patterns that may exist among the more , and the cavity of the microwave electric field distribution uniformity and proportional to the number and pattern , which is why people always want to design a larger volume cavity the furnace chamber to improve the uniformity of electric oven cavity . However, increasing the volume is one-sided pursuit of microwave power under certain circumstances, cause the power density decreases , of course, starting from the energy conservation law , as long as the increase in volume at the same time , the cavity around the metal border without increasing losses ( such as the use or close to ideal ideal metal material ) , even if the power density of the heating effect will not decrease a significant effect , but in practical cases , the conductivity of any metal material is limited, in particular stainless steel , its loss is aluminum 25 times , is 41 times that of copper , silver , 44 times, so as stainless steel as the material of the cavity , while the increase in volume is greatly increased the size of the cavity wall and loss , in this case using the increase the only way a large volume while increasing the microwave power input is correct conditions .
This is currently on the market a large part of the export volume used in household microwave oven magnetron 1kW ~ 1.6kW reasons, industrial microwave oven , since the volume of material to be heated considerations , the furnace chamber volume is usually between 500 to 20,000 liters , sometimes even larger. In such a large cavity of 915MHz or 2450MHz bands such as the use of the microwave magnetron as the microwave source , which apparently is working in a big " over-molded " state, in which the number of patterns that may exist very much . In this case , if the power density is sufficient , the field distribution in the oven cavity is ideal uniformity . The quality factor of the oven cavity is very high load , but when added to the material to be heated ( especially high moisture content of the material ), the oven cavity quality factor load sharp drop, this drop of up to 3 to 5 order of magnitude of the spectrum , and sometimes not even resonance , and a typical high-Q resonance system into a low Q microwave irradiation system .
Second, the shape of the material to be heated and the volume size , the furnace chamber size cross-sectional dimensions in particular the choice of the material mainly on account of the volume size and shape requirements , consideration should be given the choice of the longitudinal direction of the microwave output power and processing requirements.
Third, according to the level of moisture content of materials to be heated to select the volume of the cavity , especially the length size of the low water content can be shorter in length , or should be longer.
Fourth, according to the microwave source is fed to the mouth of the number , is a single or multi- feed antenna interface port , a single microwave source or a plurality of microwave sources ( in particular, a plurality of microwave sources independent of each other ) .
Fifth, the size of the cavity power density , high power density of the microwave will cause the following two effects .
1 , the furnace air or gas - vapor mixture dielectric breakdown ;
2, the internal stress caused by excessive damage to the material to be heated .
In summary, we design a multi- cavity mutual restraint should be based on several factors, especially the theory experimentally choose a reasonable size , in order to achieve a good uniform , efficient safe operation of high-volume industrial microwave.
Industrial microwave oven, because the power is large, it is often three-phase full -wave rectification of the non-filtered power supply system, the DC power supply so that the current pulse magnetron greatly reduced , so the microwave oven is not a phenomenon due to half-wave voltage doubler DC power microwave source due to the phenomenon of multi-frequency output , on the other hand , industrial microwave oven is usually in the microwave oven cavity with the source output circulator indirectly , such changes will not load on the microwave frequency and power source to produce traction phenomenon . These two factors make the use of industrial microwave oven magnetron performance is more stable .