Noncontact Temperature Sensing of Heated Cylindrical Rod by Laser-Ultrasonic Method

Abstract

A new noncontact method to measure both surface and internal temperatures of a heated cylindrical rod is presented. In the method a laser ultrasonic technique that provides noncontact measurements of ultrasonic waves in such heated rod is effectively employed. To quantitatively determine both the surface and internal temperatures near the rod end, an ultrasonic thermometry that is a technique for measuring temperature by ultrasound has been developed by considering the direction and path of the ultrasonic waves propagating in the rod. The thermometry is basically a combined method consisting of ultrasonic wave velocity 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 rod end which is a heating surface where the thermal state is often unstable and normally 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 making noncontact measurements of shear and longitudinal waves propagating near the rod end during the gas burner heating. It has been shown that the ultrasonically determined temperature distributions almost agree with those measured using thermocouples. This chapter presents the basic principle of the ultrasonic thermometry and its experimental verification.