Thermal Anemometer Measurement

							THERMAL ANEMOMETER MEASUREMENT


The Kurz thermal anemometers use two RTDs, one
heated 50 to 100’C above the ambient. The other
monitors the ambient. The current required to keep
the velocity element heated is the parameter
calibrated in our wind tunnel
Working Principle:-
A heated sensor is inserted in to the flow stream. The fluid
mass flow rate is related to the convective heat transfer which
is dependent on the temperature difference between the fluid
heated sensor and the fluid and the thermal properties of the
fluid.

The heat transfer from the heated RTD sensor (Rp)
referenced to the temperature of the ambient gas
stream RTD sensor (Rt). A constant temperature
difference between the heated sensor and the
temperature sensor is maintained by a modified
Wheastone bridge circuit in which the heated sensor is
controlled element.
MASS RATE :-
What does the thermal flow sensor measure?
Because of the equations of forced convective heat transfer, the o/p of
any thermal anemometer is proportional to the sensors Reynolds
Number(Re), it’s measure mass rate per unit area.

                        Re=P * vd/μ

P – Actual Density (kg/m3)
V – Actual Velocity m/s
d – Sensor’s diameter
μ – Gas viscosity