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