How to choose the right heater, first of all to consider the size of the heater power. In order to meet the time parameters of the conditions, the choice of power is to meet the heating medium required heat, is to ensure that the heater can achieve the purpose of heating, the normal operation of the first choice.
Since the thermal efficiency of the electric heating is approximately 1, it can be considered that the power of the heater is the calorific value.
1, power selection considerations
The calculation of power should take into account the following three:
⑴ from the initial state, according to the provisions of the time required to achieve heating medium to set the temperature (operating temperature);
⑵ in the working conditions, the heat enough to maintain the medium temperature;
⑶ should have a certain margin of safety, generally take 1.2.
Obviously, from the ⑴, ⑵ select the power of the larger, multiplied by the safety margin is the power should be selected.
2, the calculation of the required power from the initial state of heating
(1) static fluid heating
(2) flow fluid plus
(3) air duct heater atmospheric air heating
P meter - the required power of the heater (KW);
Dispersion - the heat dissipation (KW) of the container at the set temperature;
C1 - specific heat of the heated medium. (Kcal / (kg • ° C)
C2 - the specific heat of the container (system). (Kcal / (kg • ° C)
M1 - heated media quality. (Kg);
M2 - container (system) quality (Kg);
ΔT - Sets the difference between the temperature and the initial temperature. (℃);
T - the time specified from the initial heating medium to the set temperature. (H);
F - heating medium flow, (usually take the maximum flow). (M / min);
S - heat dissipation area. (M2);
Q loss - (insulation) material at the set temperature, the amount of heat loss per unit area. (Kwh / m)
3. Calculate the power required to maintain the medium temperature
P-The power required for the heater to maintain the medium temperature. (KW)
M1 Increases - Increases the mass of media per hour. (Kg / h)
This depends on the structure of the heater, the inverter can only change the frequency of alternating current, thus changing the speed of the motor to achieve the purpose of changing the output power of the motor. And the heater is not rotating, the frequency can not control the heating rate.
There are two simple ways:
1. With diode half-wave rectification, change the effective value of alternating current, to change the heating power and heating speed of the purpose; this method is the most widely used, the advantage of simple circuit structure easy to operate.
2. Transformer, with a small transformer transformer, the advantages of multi-file can be adjusted, the disadvantage is the circuit structure is more complex, high production costs.