ULTRASONIC METHOD OF FLOW MEASUREMENT 561 cosity coefficients can be measured. The instrument is essentially an acoustic impedance meter analogous to the common electrical impedance meters measuring the real and imaginary electrical network components. For many industrial applications, there is a far greater need for an instrument to measure flow properties of materials on a continuous and automatic basis during processing than there is for more sophisticated laboratory-type equipment. Five years ago, an ultrasonic viscosimeter (2) was introduced for this purpose. This instrument employs a probe and computer as shown in Figs. $ and 6. The active portions of the probe consist of a 2.0 X 0.125 X 0.010 inch metal strip that is immersed in the material to be measured. A com- pressional elastic wave is caused to propagate along this strip in an axial direction and particle motion is along the direction of propagation. Con- sequently, the fiat surfaces of the strip shear the material in which the probe is immersed and energy is extracted from the ultrasonic wave travel- ing in the strip by the surrounding liquid. The electronic computer con- tinuously measures the amount of energy extracted from the strip and indicates the viscosity of the liquid causing this absorption on a meter or recorder controller. Although the probe is sensitive to both viscosity and rigidity of the liquid, no attempt is made to separate the two properties, since, for the majority of industrial applications, it has been found that a knowledge of the viscosity coefficient is adequate for production and quality control purposes. APPLICATIONS OF ULTRASONIC VISCOMETER To date, the ultrasonic viscometer has not found wide use in the cos- metics industry. The primary reason for this is that the characteristics of materials that are measured by this instrument relate to the high frequency (28 kc. per second) shear rather than the zero frequency or uni- directional shear characteristics that have long been employed by the industry. Unless the material is NewtonJan, the properties as measured are not the same. For many applications, information of flow properties taken at high shear frequencies are of little use, but this need not always be the case. For example, if the viscosity of a material in process is to be measured in order that the size of a pump to force the material through 100 feet of pipe is to be determined, the pump itself sees the unidirectional flow properties of the material rather than the high frequency shear proper- ties, so ultrasonic measurement would serve little purpose unless the ma- terial was NewtonJan. However, if correlation can be established be- tween the low frequency properties of the material and the properties measured by the ultrasonic instrument, then the ultrasonic information can be employed as a continuous and automatic process control device to maintain the viscosity of this same material constant.

562 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS - .. ß ' ': % 2,' ,,,': .% ,•.. :.:.,..:,:..:.•..:.,.:••:....: '.... ,: '.,...•:"..:' '.. 4 ...... :........ ....... : .... "..z.. ,..:::..4.....•,.•:.::'.-'•.i2::::•.'.•'57:?/•:•.:,::,.ß,•.'•½...:..•g%:•:'•.•'•i•'..."• .... •' ..• ' ,.: "',,,4•,,•-•.•,•-• •:-:'..'.:•"'"•:•'•E* :•:" '-•'••.-'•'.•.-•-,..•':::: ' . •..•.....3.• .. -?:.•.d,..•,,...•, k.. ..?.-2:•:.w. •: ....• :.. ?•e.,.• ::.:'... ..:•:• ,':.•,•.:?•.:•.,,::2. .... • .......... '.. .... ................... , Figure 5.--Probe of Ultrasonic Viscometer. -•.•,,•,•...•....• • ...... • • .................. - .... . ._ % ': ,?:. , Figure 6.--Computer of Ultrasonic Viscometer. blany'processes exist in which thinning or thickening agents are added to a'base stock. The words "thinning and thickening," as normally used, relai:e to the low frequency flow properties. However, if it is found that the ultrasonic measurements vary in a reproducible manner with addi- tion of thinning or thickening agents, once proper correlation curves are established, the ultrasonic data can be used as a continuous control meas- uring instrument. The advantage of doing this is that an instrument that is small, continuous and automatic, and has no moving parts offers many operating advantages over ':the' unidirectional shear devices, all of which require moving elements of orf'•: 'kind or another.