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Microwave technologies

What are microwave heating technologies?

Microwave heating technology are used in the industry more and more often. Microwave systems are used not only for thawing, but also for cooking, drying, and pasteurization. The unlimited application possibilities translate into optimized production, efficiency, and effectiveness of processes – starting from the chemical industry, through the food and pharmaceutical industries, to mining and metallurgy. The list of applications keeps growing.

Microwave heating is more beneficial economically than conventional heat treatment. One of the most important advantages of microwave heating is its speed; it reduces the duration of processes that normally (using conventional methods) take days or hours to just minutes and seconds! An example is production of aspirin by the pharmaceutical industry: use of microwave driers makes it possible to shorten the heating process from over 2 hours to just 1 minute! Microwave systems also enable great energy savings, higher efficiency, and higher quality of the end product.

What are microwaves?

Microwaves are electromagnetic waves in the frequency band of 300 MHz to 300 GHz and wavelength in the range of 1 mm to 1 m. Microwave heating consists in transformation of the energy of a variable electromagnetic field into heat as a result of the so-called microwave dielectric heating effect. Radiation in the microwave band causes uniform alignment of dipole molecules (such as water particles) and ions in the created electric field. Because the field is variable, both dipole particles and ions try to become aligned in accordance with the field and oscillate and rub against one another and against other particles, thus transforming the energy supplied as a result of the rubbing into heat.

Most conventional heating and drying methods supply heat from a surface. As a result, moisture is removed from the surface very quickly but removal of liquids from the interior of a product is very ineffective. If the outside temperature is maintained on a sufficiently high level (as it is in an oven), moisture inside the material diffuses to its surface and evaporates. However, this is a passive and long process. In the process of microwave heating, the electromagnetic field acts on the entire material. Heating takes place nearly at the same time in all parts of a heated object (so-called volumetric heating).

The system comprises the following elements/tunnel arrangement:

  1. A stainless steel structure designed so as to ensure the highest level of hygiene.
  2. Product entry and exit tunnels.
  3. Touch screen PanelView Plus 7 – 12” to control the entire system.
  4. Platform – a structure that enables effective use of the space, placed in front of the machine. The generator is placed on the platform so as to facilitate access to and operation of the machine.
  5. A modular belt conveyor, 600 mm wide, ensuring continuous transport of the product across the entire machine. It is equipment with a system for monitoring the movement of the belt and to trace the product in the chamber, which ensures adjustment of the microwave power according to the extent to which the working chamber of the machine is filled. Also, the system monitors the integrity of the tape.
  6. Generator – a power electronics system enclosed in an electrical cabinet, equipped with a magnetron (an element responsible for generating microwave energy), control system elements, waveguide elements, and microwave accessories. It is the “engine” of the entire machine.
    • power 75 kW, continuous operation with the frequency of 915 MHz;
    • a 106 kVA 12-impulse HV transformer with a complete bridge rectifier;
    • a control box with all control devices and control circuits;
    • analog information about the value of the glow current and the coil current in a visible location on the outside of the generator cabinet;
    • a stainless steel enclosure;
    • internal LED lighting in both the main cabinet and the control cabinet;
    • a stainless steel cooling pump with an aluminum coolant distribution block;
    • a 4 A 30 kV rectifier block with an improved air cooling system for the block;
    • a complete interlock system monitored from the central control level;
    • a double system of disconnectors/switches to ensure the highest safety level.
  7. The set of antennas, with a correct operation monitoring system, ensures the best distribution of microwaves inside the chamber.
  8. Control system – enables recording recipes with descriptions and process parameters.
  9. Work chamber – this is where the microwave heating takes place. Depending on the process, the product may be thawed, dried, cooked, or pasteurized. The product enters and exists through properly designed tunnels that ensure safe operation. Microwaves are brought to the chambers through antennas that ensure even distribution of the microwave field so as to achieve the highest uniformity of the heating. Also, the chamber is equipped with a door that enables easy access after the work is completed and easy cleaning of the machine. It is provided with coded active safety elements and a system for monitoring and control of bolting elements from the control system level.
  10. Waveguide – a passive element of the machine responsible for transport of microwave energy from the generator to the work chamber of the machine. Thanks to the waveguide, the generator can be located in a separate location from the machine so as to enable better use of the available space.

How is a microwave heating system built?

Microwave heating systems consist of several elements. The “engine” of the machine is a generator with a microwave oscillator, called magnetron, located inside; the magnetron is responsible for the power of the machine. Microwave generators can be used as single microwave supply sources that usually supply 5-100 kW of energy during continuous operation. In the case of processes that require higher power, they can be used in combination with other generators. Microwave heating systems also have a heating chamber, a waveguide that transports microwaves from the generator to the heating chamber, and a control panel.

In industrial practice, microwave systems working with the frequency of 915 MHz (most industrial systems) and 2,450 MHz (home microwave systems) are used most often. Lower frequency allows for more efficient penetration of microwaves through the material, which translates into lower operating costs of such systems.