How to calculate the power when choosing microwave equipment to heat materials?

When designing or choosing microwave equipment for heating, the power capacity of the equipment should be estimated first.

Firstly, several necessary data should be obtained:

1) Specific heat capacity C of processed materials. The specific heat of water is about 1 kcal/kg/c;

2) the weight of material to be processed per hour W;

3) the weight of liquid to be evaporated per hour W’

4) the latent heat of vaporization of evaporated liquid Q, the heat of vaporization of water 540 kcal/kg;

5) the dielectric constant of processed material-epsilon;. The dielectric constant of general materials is 1-5. The dielectric constant of water is 80, and glass and ceramics are 2-2000 or more according to different materials;

6) the dielectric loss of processed materials is tgδ. Generally between 0.05-0.3, glass and ceramics 0.01-0.5.

1. Microwave power consumed by material heating:

microwave power consumed by P-in the form of

and

temperature rise and degree of T-material;

specific heat of C-material, kilocalorie/kilogram/

W-material weight, kilogram;

t-microwave action time, hour

2, microwave power consumed by material drying

and microwave power consumed by P-in the form of

p>p>p> and kilowatt;

Q> p>p>- Latent heat of liquid evaporation, or heat of vaporization. Water is 540 kcal/kg;

Other parameters are the same as the previous formula

3. The estimation of total power of the power supply:

The microwave power calculated from the above two formulas is the ideal microwave power required. In fact, in the microwave heater, the microwave power can not be absorbed by all the materials, and part of it will be consumed by the heater itself, and part of it will be lost in the waveguide fed to the microwave. When traveling wave heater is used, the power that is not absorbed by the material is absorbed by the water load at the terminal. Therefore, when choosing microwave equipment, considering the absorption efficiency, the capacity should be increased appropriately.

P’= P/η P’ - Selected microwave heating equipment power capacity, kilowatt;

P-calculated microwave power, kilowatt;

eta; - Microwave absorption efficiency, generally around 50%-80%.

Because when microwave tube converts DC electric energy into microwave energy, it consumes a part of electric energy, heating cathode of tube consumes electric energy, and electromagnet consumes a small amount of electric energy. Therefore, the total power consumed by microwave heating equipment is the sum of these parts.

p>4. Microwave power absorbed by materials at different microwave frequencies:

P=(1/1.8)fE2ε R tgδ*10-2 P-unit volume material absorbed power; watt/centimeter 3

f-microwave frequency, H;

E-electric field intensity, volt/cm;

tgδ -dielectric loss coefficient;

epsilon; r-silon dielectric constant of materials.

p>Because the electric field intensity is difficult to measure in practice, it can only be roughly converted. For example, in a rectangular waveguide, the material temperature rise is calculated because of its impedance of 377 ohms, such as microwave power of P (watt) and narrow waveguide size of B (centimeter):

f-microwave frequency, H;

epsilon; dielectric constant of r-material;

C> specific heat, card./Gram /degree.

is a general calculation method. In practical application, we judge the microwave absorption of materials by experiments. Therefore, limited to the current level of our country, many materials of TG & delta; no equipment for measurement. According to experience, the actual microwave power required is estimated by 0.8-1.2 kilograms of microwave power per kilowatt per hour for dewatering.