Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Content or effect of a constituent of a liquid mixture
Patent
1996-08-07
1998-11-17
Williams, Hezron E..
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Content or effect of a constituent of a liquid mixture
23 6453, 23 2406, 23597, G01N 2902, G01H 500
Patent
active
058362002
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to measurement of acoustical properties of fluid samples, more specifically to cells for performing such measurement.
BACKGROUND OF THE INVENTION
Acoustical methods for determining acoustical parameters of fluid samples, such as speed and attenuation of acoustical waves, and cells for performing such measurements are well known in the art. A preferred method for investigating fluid samples of small volume is the so-called resonator method.
A measurement cell for use in a resonator method is disclosed in international patent application, publication No. WO 92/03732, inventors Sarvazyan, Belonenko and Chalikian. This cell comprises a pair of thin, flat, waver-like electro-acoustical transducers which are positioned on opposite front faces of an essentially cylindrical cell body to define at least one resonator chamber adapted to receive a liquid sample to be investigated. A plurality of sample chambers which share the same pair of electro-acoustical transducer wafers may be provided in a single cell body to provide comparison measurements of test samples and fluids of known properties.
The cell disclosed in the Sarvazyan, Belonenko and Chalikian application is a sandwich structure or stack comprising an essential cylindrical main body forming the sample chamber or chambers, an acoustic transducer on each side of the main body and closing the axial ends of the sample chamber(s), and means for holding this structure together, i.e. end pieces and axial bolts or annular screw caps. Each sample chamber is accessible by a radial aperture in the wall of the main body through which a sample can be introduced. This aperture is closed by a flexible tubular membrane member which surrounds the cell body and serves to separate the sample from the surrounding. In operation the measurement cell is placed in an autoclave containing a pressurizing liquid. The pressure of the pressurizing liquid is increased by means of a piston pump and transmitted to the sample liquid by the flexible member which separates the sample and pressurizing liquids. One of the transducers is energized by high-frequency electrical waves of varying frequency and an output signal is obtained from the other transducer and processed to obtain desired information.
As A. P. Sarvazyan et al. disclose in Ultrasonics 29 (1991) pp. 119-124 each transducer of an acoustical resonator cell can be backed with liquid. In high pressure work the stress imposed on the transducers by a pressurized sample can be reduced by backing the transducers with the pressurizing liquid.
The known cells for acoustical measurements suffer from several drawbacks. First, the structure of the known cells is complicated and expensive to manufacture. The delicate, thin and brittle transducers must be carefully mounted and provided with apertures for accommodating axial bolts which hold the structure together. The bolts must be tightened with utmost care to avoid subjecting the delicate, thin and brittle transducers to excessive and uneven stresses.
A second problem is the compensation of the pressure exerted by the pressurized sample fluid on the transducers. Even if liquid backing is used, the known cells cannot be used for sample pressures exceeding about 20 MPa (200 bar).
It has been found that the cause of this problem is the flexible member which is used in the known cells to separate the sample fluid from the surrounding pressure transmitting fluid. The flexible membrane of the known cells must be relatively strong to secure proper sealing. When this strong membrane is deformed to pressurize the sample the deformation force unbalances the pressures of the fluids adjacent the front and back surfaces of the transducers which impairs the performances of the transducers. Eventually this may cause rupture of the transducers.
The flexible elastic membrane member used for sealing the sample chambers is also the cause of another problem. Under high pressure, capillary forces tend to cause the fluid into which the cell is submerged
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Belonenko Vladimir
Bunau Eugenij
Chalikian Tigran
Funck Theodor
Nikolashev Vijcheslav
Miller Rose M.
UHP Corp.
Williams Hezron E..
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