Noncontact temperature sensing of heated cylindrical end using laser ultrasonic technique

A novel noncontact method to measure both surface and internal temperatures of a heated cylindrical rod end is proposed. In the method a laser ultrasonic technique providing noncontact measurements of ultrasonic waves in such heated rod is employed. To quantitatively determine both the surface and internal temperatures near the rod end, an effective ultrasonic thermometry has been developed by considering the propagation direction and path of the ultrasonic waves in the rod generated by pulsed-laser irradiation. The thermometry is basically a combined method consisting of ultrasonic wave velocities measurements based on pitch-catch configurations and a one-dimensional finite difference calculation for unsteady heat conduction. The advantage of the method is that there is no need to know the thermal boundary condition at the heating surface where the thermal state is often unstable and unknown. To demonstrate the feasibility of the proposed method, experiments with an aluminum rod whose end surface is heated by a gas burner are carried out. A laser ultrasonic system consisting of a pulsed laser generator (Nd:YAG, 1064 nm, 180 mJ) and a laser Doppler vibrometer (He-Ne, 633 nm, <1mW) is used for noncontact measurements of shear and longitudinal waves propagating in the aluminum rod during heating. It has been shown that the ultrasonically determined temperature distributions almost agree with those measured by thermocouples.