Vimal Shah

High temperature ultrasonic sensor for the simultaneous measurement of viscosity and temperature of melts

An ultrasonic sensor that simultaneously measures temperature and viscosity of molten materials at very high temperature is described. This sensor has applications as a process monitor in melters. The sensor is based on ultrasonic shear reflectance at the solid–melt interface. A delay line probe is constructed using refractory materials. A change in the time of flight within the delay line is used to measure the temperature. The results obtained from this sensor on various calibration glass samples demonstrate a measurement range of 100–20u200a000 P for the viscosity and 25–1500u200a°C for the temperature.

Measuring Newtonian viscosity from the phase of reflected ultrasonic shear wave

In this paper, an acoustic shear impedance model is employed to obtain a relation between the viscosity of a Newtonian fluid and phase characteristics of ultrasonic shear wave reflection from a solid-fluid interface. The phase and magnitude of the reflection coefficient can be decoupled in this model. The decoupling allows an independent relation between the acoustic shear impedance (viscosity-density product) and phase of the reflection coefficient. The model was experimentally verified for different fluid-solid combinations. Comparison of the results with the commonly used absolute reflection coefficient method demonstrates that phase measurement provides improved measurements.

Effect of viscosity on ultrasound wave reflection from a solid/liquid interface

A study of the simulated reflection of a wideband ultrasound shear wave from the solid/viscous fluid interface is presented. Various parameters affecting reflection factors including the material properties of the solid, fluid properties like density and viscosity, and the operating frequency are discussed. Simulated ultrasonic response waveforms are compared with the experimentally obtained data for NIST traceable calibration standards of viscosity. A good agreement was observed between the simulated and experimental waveforms at various viscosities and for different solid substrates.

Torsional Waveguide Sensor for Molten Materials

Viscosity of the molten glass is a key variable in determining the quality of the final glass product. At low viscosities the melt can be highly corrosive. At high viscosities the melter can become plugged. “Melt viscosity is the most important processing property; it controls processing rate, product homogeneity, and heat transfer within the molten glass [1]. “ Thus, the viscosity is an important parameter which can be used by the vitrification industry for the processing of waste material and by the glass industry for production of high quality glass products. The major problem in measuring the viscosity of the molten waste product is the extremely hot and corrosive environment.

Sensor Development for High Temperature Viscosity Measurement

In previous years, we have presented several results on viscosity measurements using conventional and laser ultrasound techniques [1,2,3]. These results are based on experiments conducted at room temperature. The principle[1], in essence, is to launch ultrasonic shear waves at the interface of a solid and a viscous fluid. The amplitude and phase of the reflected waves were correlated to the viscosity of the fluid.

Measurement of Viscosity in Liquids Using Reflection Coefficient: Phase Difference Method

Measurement of viscosity of fluids is a critical parameter in determining the state of the fluid (ie. edible products), and the state of the forming solid (ie. molten metals and glasses). Experiments to measure viscosity using ultrasound, have been carried out since as early as 1951 [1]. Ultrasound has potentially offered a non-invasive, in-line method of property and process monitoring [2,3]. Early research has demonstrated that viscosity measurement can be accomplished by ultrasound using different linear and nonlinear techniques [4]. This paper is devoted to furthering the technique called shear reflectance method [5].

Viscosity Measurement with Laser Ultrasonics

In the previous year, results were presented in which the viscosity of calibration liquids were determined by measuring the reflection coefficient of laser generated shear waves. [1] The shear waves were launched with a pulsed Nd: YAG laser into an aluminum wedge and detected using a piezoelectric transducer. This year results are presented from a totally noncontact system, generating the shear waves with a pulsed laser and detecting the reflected shear waves with a laser interferometer. The design of the wedge was modified so that the shear waves are incident to the solid-liquid interface at nearly normal incidence. They reflect off this interface and are incident on the surface of detection at greater than the critical angle. This allows for the largest possible out-of-plane displacement, which can then be detected with the interferometer. This type of arrangement has been used with both aluminum and graphite wedges.

Shear Wave Wedge for Laser Ultrasonics

Ultrasonic shear waves are a useful tool for determining the mechanical properties of various materials. One example is the use of shear waves to measure viscosity. The viscosity can be determined from the shear wave reflection coefficient. The reflection coefficient from a solid-liquid interface is a function of the viscosity and density of the liquid, as well as the angle of incidence and the material properties of the solid. [1,2]

Wave Propagation in a Newtonian Fluid with Viscosity Gradients Profiles

Plane compressional wave propagation in a fluid is significantly affected by the shear viscosity of the fluid [1]. Several different theories have been developed [2,3,4] to understand effects of viscosity on wave propagation characteristics. Presence of concurring phenomena such as thermal conductive losses and molecular relaxations [5] has frurther complicated the study of wave propagation. In liquids however, the effect of thermal conductivity is not comparable to the viscous losses [1]. In such cases, it has been possible to associate viscosity with the wave propagation characteristics.

Effect of Surface Coatings on Generation of Laser Based Ultrasound

Ultrasonic techniques are being currently used in a wide range of applications. However, there are situations where it is difficult to utilize ultrasound for NDT purposes. They are severely limited in non-contact applications due to attenuation in air. Since the present day technology requires a physical contact or a couplant between the transducer and the specimen surface to minimize diffraction effects, the temperatures sensitive piezoelectric transducers are not suited for hostile operating environments and extreme temperature gradients. Another drawback of piezoelectric transducers is the narrow banded source signals. Generation of very high frequency ultrasound becomes difficult and expensive. Complex contoured specimens are, also, difficult to handle, since traditional ultrasound is sensitive to the normalization of the incident ultrasonic beam. As with all mechanical devices, the rate of scanning of these transducers is very slow.