Measuring Flow In Thermal
a. Hot Wire Anemometer
This method is quite simple: by using a wire heated by electric current, the current flowing in the wire is made to remain constant using a constant current source. If no air flow, the wire will cool (as we blow out the candles) by the cooling of the wire, the wire resistance decreases. Because of the constant current source is used, then we can not censor the voltage at the ends of the wire. Sensors of this type have a very good sensitivity to censor a slow gas flow. But unfortunately, the whole sensor installation is quite difficult.
Here applies the formula:
where: I = current wire
Rw = wire resistance
Kc = conversion factor, heat to electric power
Tw = temperature wire
Tt = temperature of flowing fluid
Hc = coefficient of the film (coating) of heat transfer
A = heat transfer area
Figure 3.65 Construction of Hot Wire Anemometer
b. Heat propagation
In the heat propagation techniques, the heater mounted on the outside of the pipe, the pipe is made of metal. On the left and right heating, fitted thermal insulation materials, and in this insulator mounted temperature sensors. When udaramengalir from left to right, then the left side temperature will be colder than the temperature right.
Figure 3.66 Heat propagation Flowmeter
The temperature sensor used may be a resistive sensor but commonly installed are thermocouple because it has a fast temperature response. Heat propagation flow sensor type long, heat the whole part of the air duct, requiring heating to tens of kilowatts, to reduce the thermal power used a new type with a small portion deflect air into the sensor.
c. Flowmeter Radio Active
Flow measurement techniques with active radio is by firing neutrons particles of an active radio transmitter. At a certain distance towards the outlet, mounted detector. If there is a stream, then it will be detected radioactive particles, the number of particles detected at certain intervals will be proportional to the velocity of fluid flow. Another technique that still uses active radio technique is by mixing radioactive substance into the fluid then in certain parts installed detector.
This technique is done if there is difficulty to measure, for example because the flow of materials consists of substances which are at various phases. Active radio engineering biaa also used in the treatment of seeking the position of blood vessels that bad for people with paralysis.
Figure 3.67 Flowmeter How Nuclear Radiation
