What is a Hot Wire Anemometer & Its Working

In any field of meteorology, the precise amount of mean wind velocity as well as turbulent variations is a significant feature & the turbulence measurements area is one of the major anxieties of micrometeorology. The velocities of mean wind can be sufficiently measured with different anemometer devices like an up wheel as well as vane anemometers until the mean wind stays sensibly stable. So, due to the high inertia & slow response time of these devices, fluctuations are complex to determine. The two non-mechanical sensors which are currently in a higher state of improvement are quite capable of measuring turbulent fluctuations namely the sonic anemometer & the hotwire anemometer. These two instruments can identify a range of temperature fluctuations & eddy diameters. So these instruments are adaptable for the measurement of such quantities as turbulence spectrum and vertical fluxes of heat. This article discusses an overview of Hot Wire Anemometer.

What is a Hot Wire Anemometer?

A hot wire anemometer is one kind of instrument, used to measure the direction as well as the velocity of the fluid. So, this measurement can be done by measuring the loss of heat within the wire that is situated in the fluid stream. These devices use a thin wire and it is heated up electrically to some stage of temperature approximately higher than the range of ambient temperature.


Hot Wire Anemometers
Hot Wire Anemometers

This wire gets cool once the air flows throughout it because the resistance of metal mainly depends on the temperature. So a relation can be formed between the resistance of the wire as well as the speed of the liquid flow. In many situations, they will not be used for the measurement of a wind direction, simply when they are included with a wind vane. The hot wire anemometer usage mainly permits quick flow velocity that has to be calculated from the dimensions of electric voltage. The essential part of this anemometer is its thin wire. When it is forced up then the flow of heat takes from the thin wire to run across the wire.

Working Principle

The hot wire anemometer basic working principle is that once an electrically heated up wire is placed within the flow of the gaseous stream, after that the heat gets moved from thin wire to gas so that the wire temperature levels can be reduced. Due to this reason, the resistance value of the wire can also be changed. So this change within wire resistance permits us to measure the liquid flow rate.

Construction of Hot Wire Anemometer

The hot wire anemometer can be designed with two essential parts namely wheat stone bridge as well as conducting wire. In this construction, a conducting wire is located in the ceramic material. The wires which come from the ceramic material can be connected toward the Wheatstone bridge so that it measures the changes within the resistance value.

The hot wire anemometer working can be done using two methods namely constant current as well as constant temperature.

Constant Current Method

In the constant current method, the arrangement of a hot wire anemometer can be done within the flow of fluid wherever the flow of liquid speed can be measured. So, a constant magnitude level of current can be supplied from the wire. Also, the wheat stone bridge can be maintained at a fixed voltage level.

Current Constant Anemometer Method
Current Constant Anemometer Method

Once the wire is arranged in the flow of liquid, and then heat can be transferred from the wire to liquid because there is a relation between the heat as well as the resistance of a wire. Once the heat value is reduced, the resistance of the wire can also be reduced. Also, the wheat stone bridge measures the change within resistance value that is equal to the speed of the liquid flow.

Constant Temperature Method

In the constant temperature method, when the electric current supplies through wire then it gets heated. The arrangement of a hot wire anemometer can be done within the flow of fluid wherever the speed of the fluid flow can be measured. Once the wire is arranged within the flow of liquid, and then heat can be transferred toward the fluid from the wire.

Here, the temperature value of the wire can also modify and its operation can also be done on the principle where the level of temperature of the wire persists to be stable. The entire current that is necessary to bring the wire into the starting state is comparable to the flow of gas speed.

Constant Temperature Method
Constant Temperature Method

In these two operating methods, it is necessary to compute as well as to change the constant range of the time for the anemometer because; this is derived from the thermodynamic conditions that can be present at the wire.

The change is fairly difficult to work in the supersonic actions, whereas in the subsonic technique, test signals are almost certainly executed which includes either sine or square wave being fed like input for the circuit to develop an unbalanced wire heating. Alternatively, this kind of heating is not related to the unbalanced heat transmission switch in the flow & particularly for a wide range of frequency properties, this analysis looks to be uncertain.

Direction Measurement

Hotwire anemometer can also be used for measuring the direction of flow with the sensors including several thermal resistances. These resistors are placed to determine the flow of direction by the hot wire anemometer from a dissimilar heat emission.

The flow direction can be recorded in two otherwise three dimensions based on the number as well as hot wires arrangement/hot film elements. The wind direction can be determined by the weather vanes over the rooftops that are two-dimensional. Similarly, for the measurement of 3-dimensional, the plane is perpendicular toward the cardinal way that is also taken into account.

Advantages

The advantages of a hot wire anemometer include the following.

  • Less cost
  • Spatial separation
  • High-frequency response
  • Signal analysis
  • Small size
  • Accuracy is good
  • Good spatial & temporal resolution
  • Measurement of two-phase flow
  • We can simply measure Turbulent flows
  • Measurement of simultaneous temperature
  • Measurement of Multi-component
  • Less S/N ratio

Disadvantages

The disadvantages of a hot wire anemometer include the following.

  • High turbulence intensity
  • Breakage of Probe
  • Liquid flows
  • Contagion
  • Intrusive Technique
  • Signal noise
  • Heat transfer & Aerodynamic problems
  • Heat transfer among the probe as well as surfaces

Hot Wire Anemometer Applications

The applications of hot wire anemometer include the following.

Chemical Industry

These anemometers are used in chemical industries for different purposes.

  • In a chemical fertilizer plant, a hot wire anemometer is used to measure ammonia gas.
  • In the battery factory, it is used to measure the various gas flow in the sampling system, induced draft fan & monitoring the smoke cycle.

Metallurgical Industry

These anemometers are used in metallurgical industries for different purposes.

  • It is used in the metallurgical industry for controlling as well as the measurement of heating furnace gas.
  • Used in rolling mills to control oxygen, hydrogen, nitrogen & other gases in the treatment of gas.
  • Used in quenching furnace for gas metering within steelworks;
  • Coke oven gas measurement in iron & coking works

Power Industry

These anemometers are used in power industries for hydrogen measurement.

  • It is used to measure primary as well as secondary air within the blast furnace of the power plant;
  • Used to measure gas throughout gas distribution within the fuel system;
  • Various gases measurement in boilers as well as auxiliary systems;
  • Used in a gas furnace for gas measurement

Environmental Protection

These anemometers are used for environmental protection.

  • Used to measure the aeration tank within the sewage treatment method;
  • Used to measure the discharge of NOX & SO2 for gas measurement within biogas use process;
  • Used to measure the chlorine gas throughout chlorine treatment

Drug & Food Industry

These anemometers are used in the drug and food industries

  • Used for CO2 treatment within breweries
  • Gas flow measurement throughout thermal oxidation
  • In the ventilation system for processing the fresh air

Pulp & Paper Industry

These anemometers are used in pulp and paper industries

  • Used in boilers for measuring gas & air supply
  • It is used in wastewater treatment systems to measure gases
  • Monitoring of flue flow

Oil & Gas Industry

These anemometers are used in oil and gas industries

  • Used in energy exchange for measurement of natural gas & monitoring of torch gas
  • Used in well-filling gas recovery for fuel gas metering, leakage gas test & gas mass analysis

Thus, this is all about an overview of the hot wire anemometer. It is used to measure flow-velocity effectively and capable of high accuracy through least interference within the fluid path. But, it also needs huge care within the arrangement of probe, calibration & system calibration to understand the flow rate against the electrical signal. Here is a question for you, what are different types of anemometers?

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