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Under the heading "Physical disinfection technology" those methods based on physical principles as opposed to the purely chemical sterilization processes should be presented here. This is the appliance of electric and electromagnetic fields and waves. Depending on the frequency and amplitude the electromagnetic fields cause different effects to the media, which are to be disinfected or treated.
Electromagnetic waves in the frequency range of 30 KHz to 300 MHz are referred to as radio frequency (RF) or high frequency (HF). For the Dielectric RF heating➞ or Dielectric HF heating the frequencies 13.56 MHz, 27.12 MHz and 40.68 MHz are approved. In this method, the product to be heated, unlike microwave heating, is passed between large-sized capacitor plates and is heated via different frictional heating processes. In this manner, depending on the electrical power brought in, drying processes, thawing (meat, fish, poultry, vegetables, etc.) or disinfection processes can be realized.
principle of energy coupling with radio frequency heating equipment
The subsequent frequency range of 300 MHz to 300 GHz (Gigahertz) is called the microwave range, which corresponds with a wavelength of 1 m to 1 mm, according to the conversion formula λ = c / f (λ = Wave length, c = speed of light, f = frequency). For industrial microwave technology➞ the frequencies 915 MHz and 2.45 GHz are registered in Germany.
principle of energy coupling in microwave systems
How good or bad a substance can be warmed with electromagnetic waves depends on the dielectric properties of the substance/ mixture of substances. Polar liquids like oil and water or other polar substances such as certain salts can be warmed with high frequency electric fields very good. While microwave energy (e.g. 2.45GHz) couples to water very good, the RF (27,12MHz) is much better suited for the thawing of frozen water (ice).
The Infrared band follows the microwave band. Infrared radiation in the frequency range of 300 GHz to 400 THz (terahertz), which corresponds to wavelengths of 1 mm to 780 nm, are used for the surface heating of objects. Via infrared rays, surfaces can also be sterilized via the path of pasteurization. (Infrared technology (IR)➞)
The visible light (380 nm = blue / violet to 780 nm = red) follows the infrared band. To our knowledge it is not used for disinfection processes.
Beyond the spectrum of light there is the range of ultraviolet rays.
(UVC disinfection technology ➞)
classification of UV radiation in according to DIN 5031
UVC-Rays with the wavelength of 254nm are mainly used for Sterilization. By using special quartz glass, the UVC-band of 185nm can produce ozone from oxygen. Ozone in combination with UVC is also used to eliminate unpleasant odours (odour removal ➞) and remove fat from the kitchen exhaust air by the act of “cold fat burning”.
To our knowledge, the following range of X-rays, 1 nm to 10 pm (picometer), is not used for industrial disinfection processes either.
The range of gamma rays (10 pm) is industrially used for the sterilization of spices. The approval of gamma rays is provided by law with such high requirements that the engineering firm Merschbrock does not deal with this technology.
The energy of electromagnetic waves (E = hv, E = energy, h = Plank's constant, ν = frequency) increases steadily with increasing frequency and decreasing wavelength. The UV rays and all the shorter wavelength rays act ionizing. Ions are able to kill germs on oxidation processes.
Electromagnetic overall spectrum
By using high-voltage electric fields fields (10,000 volts and greater) ions and radicals can be generated from the gases of the atmosphere. These radicals are used for disinfection.
A special feature in the application of high voltage fields is called the dielectric barrier discharge (DBE) or atmospheric plasma.(Odour removal ➞)
With this method ozone, OH radicals and other oxidants are generated from the ambient air. With those, disinfection processes and - especially odour removal processes -can be realized in a very elegant manner.
Another application of high voltage fields is known under the keyword "electroporation" method for the sterilization of liquids.
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