Microwave heating and its mechanism
The so-called microwave heating, through a microwave generator to generate microwave energy, and then the microwave energy is delivered to the microwave heater, the material in the heater by the microwave irradiation heat, Figure 1 is a typical microwave heating system.
Why can microwave heat the irradiated material? The simple answer is that microwaves can polarize molecules inside matter and cause intermolecular friction and heat. We use a popular method to explain the mechanism by which the media material is heated. The device shown in Figure 2 places a glass of water between the two plates of the capacitor. The capacitor is connected to a battery and a transfer switch.
Since the water molecule is composed of two hydrogen atoms and one oxygen atom, the charge in the water molecule can be divided into two types: positive and negative. The positive charge at the hydrogen atom and the negative charge at the oxygen atom make the water molecule " Polarity " . The oppositely charged molecules at both ends are called " polar molecules . " Water molecules are polar molecules. Under normal circumstances, due to the disorganized thermal movement of the molecules, the arrangement of the molecules is disorderly and irregular, in all directions, and in rapid changes, the polarities of the molecules cancel each Other out, so the water is not macroscopically polar . If the switch in Figure 2 is closed, the capacitor's plate is charged. One plate has positive electricity and one plate has negative electricity. At this time, an electric field is generated between the plates of the capacitor. The water molecules in the cup are oriented along the direction of the external electric field by the applied electric field, that is, the positively charged hydrogen terminal is inclined to the negative electrode plate of the capacitor, and the negatively charged oxygen terminal is inclined to the positive electrode plate of the capacitor. A part of the molecules in the chaotic movement are regularly arranged in the direction of the electric field. This neatly arranged polar molecule contains the "positional energy " transferred from the external electric field . If we put the switch to the right, the direction of the electric field generated on the capacitor plate is opposite to the front, and then the arrangement of the molecules is changed in the same direction. If we quickly flip the switch back and forth, i.e. quickly and constantly change the direction of the external electric field, the water molecules will quickly change their orientation and oscillate, due to the thermal movement of its molecules and between adjacent molecules. Interaction, the above-mentioned rule that the molecule oscillates with the change of the external electric field is disturbed and hindered, this produces the effect similar to the friction, the result is a part of the movement is aggravated, the water temperature rises and achieves the purpose of heating. This is a popular explanation of the microwave heating mechanism.
If the frequency of the applied electric field changes more, the polar molecules will oscillate faster and the more heat will be generated. With the increase of the external electric field, the larger the amplitude of molecular swing, the more heat will be generated. . If the capacitor plate of Figure 2 is not water, but something else, the heat generated under the same conditions will be different. This means that the amount of heat generated by the microwave irradiated by the material and the material The type and its electrical characteristics. Both experiments and theories have demonstrated that the microwave power lost in a unit volume of medium (which can also be understood as the heat generated per unit volume of medium per unit time) Pa has the following relationship between the electric field strength E and the frequency f :
Pa ≈tgδ?f ?E 2
Where tgδ is called the " loss tangent " of the medium, it is a physical quantity that represents the ability of the medium to absorb electromagnetic energy.
In addition, the ion conduction in the material can also cause the material to generate heat, and the ions in the material are caused to move under the action of the external electric field, and collide with the molecules of the material in the course of its movement. As a result of this collision, the object is produced. heat.
Why can microwave heat the irradiated material? The simple answer is that microwaves can polarize molecules inside matter and cause intermolecular friction and heat. We use a popular method to explain the mechanism by which the media material is heated. The device shown in Figure 2 places a glass of water between the two plates of the capacitor. The capacitor is connected to a battery and a transfer switch.
Since the water molecule is composed of two hydrogen atoms and one oxygen atom, the charge in the water molecule can be divided into two types: positive and negative. The positive charge at the hydrogen atom and the negative charge at the oxygen atom make the water molecule " Polarity " . The oppositely charged molecules at both ends are called " polar molecules . " Water molecules are polar molecules. Under normal circumstances, due to the disorganized thermal movement of the molecules, the arrangement of the molecules is disorderly and irregular, in all directions, and in rapid changes, the polarities of the molecules cancel each Other out, so the water is not macroscopically polar . If the switch in Figure 2 is closed, the capacitor's plate is charged. One plate has positive electricity and one plate has negative electricity. At this time, an electric field is generated between the plates of the capacitor. The water molecules in the cup are oriented along the direction of the external electric field by the applied electric field, that is, the positively charged hydrogen terminal is inclined to the negative electrode plate of the capacitor, and the negatively charged oxygen terminal is inclined to the positive electrode plate of the capacitor. A part of the molecules in the chaotic movement are regularly arranged in the direction of the electric field. This neatly arranged polar molecule contains the "positional energy " transferred from the external electric field . If we put the switch to the right, the direction of the electric field generated on the capacitor plate is opposite to the front, and then the arrangement of the molecules is changed in the same direction. If we quickly flip the switch back and forth, i.e. quickly and constantly change the direction of the external electric field, the water molecules will quickly change their orientation and oscillate, due to the thermal movement of its molecules and between adjacent molecules. Interaction, the above-mentioned rule that the molecule oscillates with the change of the external electric field is disturbed and hindered, this produces the effect similar to the friction, the result is a part of the movement is aggravated, the water temperature rises and achieves the purpose of heating. This is a popular explanation of the microwave heating mechanism.
If the frequency of the applied electric field changes more, the polar molecules will oscillate faster and the more heat will be generated. With the increase of the external electric field, the larger the amplitude of molecular swing, the more heat will be generated. . If the capacitor plate of Figure 2 is not water, but something else, the heat generated under the same conditions will be different. This means that the amount of heat generated by the microwave irradiated by the material and the material The type and its electrical characteristics. Both experiments and theories have demonstrated that the microwave power lost in a unit volume of medium (which can also be understood as the heat generated per unit volume of medium per unit time) Pa has the following relationship between the electric field strength E and the frequency f :
Pa ≈tgδ?f ?E 2
Where tgδ is called the " loss tangent " of the medium, it is a physical quantity that represents the ability of the medium to absorb electromagnetic energy.
In addition, the ion conduction in the material can also cause the material to generate heat, and the ions in the material are caused to move under the action of the external electric field, and collide with the molecules of the material in the course of its movement. As a result of this collision, the object is produced. heat.
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