Spherical Acoustic Resonator Research Articles

Acoustic resonance determination of the effect of light hydrocarbons on wax appearance points in a Njord well fluid

Wax formation and deposition in pipelines and process equipment pose severe problems for petroleum companies. especially during transportation of crude oil in offshore environments. The light hydrocarbons present in the crude oil can play an important role in the shift of wax appearance points by increasing the solubilities of the heavier components. The following work was undertaken to study the effect of light hydrocarbons on wax appearance points in a Njord well fluid for Norsk Hydro, Norway. An automated high-pressure spherical acoustic resonator (50-mm-diameter) assembly designed and fabricated for that purpose has been used to measure resonance frequencies in a Njord well fluid (stabilized oil sample) provided by Norsk Flydro and blended with the appropriate amount of a synthetically prepared gaseous mixture containing six light hydrocarbons (CI to C6 ), at pressures from 2 to 107 bar and temperatures in the range 35 to 50 C. Results on the present method to locate the wax appearance points in the Njord well fluid are presented. A figure showing experimental wax appearance points as a function of pressure is presented. The results are compared with those predicted by the Norsk Hydro model.

The speed of sound in gaseous argon at temperatures between 110 K and 450 K and at pressures up to 19 MPa

The speed of sound uin gaseous argon has been measured along 21 isotherms at temperatures T between 110 K and 450 K. At T≥150 K, the greatest pressure on each isotherm was the lesser of 19 MPa and the pressure at which the estimated density was half its critical value. Below T=150 K, the greatest pressure on each isotherm was limited to that at which the estimated density was about 0.8 of the saturated-vapour density. The measurements were made using a spherical acoustic resonator and have an estimated accuracy which varies from 1·10 −5· uat low pressures to 7·10 −5· uat the greatest pressure on the isotherm closest to the critical temperature. Second, third, and fourth acoustic virial coefficients have been obtained from the results.

Speed of Sound in Gaseous Difluoromethane

The speed of sound in gaseous difluoromethane (HFC-32, CH[sub 2]F[sub 2]) has been measured by means of a spherical acoustic resonator. Sixty-seven speed of sound values were measured with an accuracy of [+-]0.01% at temperatures from 273 to 343 K and pressures from 20 to 250 kPa. The ideal-gas specific heats and the second acoustic virial coefficients have been determined on the basis of the speed of sound measurements. The second virial coefficients calculated from the present speed of sound measurements agree satisfactorily with literature values which were determined from pressure-volume-temperature measurements.

The speed of sound in (0.8CH 4 + 0.2C 2H 6)(g) at temperatures between 200 K and 375 K and amount-of-substance densities up to 5 mol·dm -3

The speed of sound has been measured in a single sample of (0.8CH 4 + 0.2C 2H 6)(g) at seven temperatures between 240K and 375K and at amount-of-substance densities between 1 mol·dm -3 and 5 mol·dm -3. These measurements were performed along isochores using a spherical acoustic resonator operating at frequencies in the range 5 kHz to 25 kHz. Further measurements were performed at lower densities along the isotherms at 200 K, 225 K, and 300 K. The results of the measurements are compared with the predictions of equations of state recommended for use in the calculation of natural-gas properties. Second acoustic virial coefficients determined for the mixture were combined with results for the pure components to obtain an interaction second acoustic virial coefficient for methane-ethane. This quantity was then used to determine the parameters in a site-to-site intermolecular potential-energy function for the unlike interaction. Ordinary interaction second virial coefficients calculated from this model are reported. New measurements of the speed of sound in pure methane are also reported for the isotherms at 200 K, 225 K, and 250 K with pressures up to 1.4 MPa. Second virial coefficients of methane in the temperature range 200 ≤ T/K ≤ 375 have been determined from an analysis of these and earlier measurements.

Trapping of single bubbles in cryogenic fluids

Single bubbles of helium gas of radius 10–20μm have been stably trapped in liquid nitrogen. A spherical acoustic resonator 5.0 cm in diameter is driven with ultrasonic transducers in a radial mode, and the acoustic radiation pressure provides the force holding the bubble at the center of the sphere. It should be possible to use this technique to trap bubbles in other cryogenic fluids such as argon, neon, and helium. Applications of the trapping are discussed, including a search for the emission of sonoluminescence from the bubble, study of the bubble oscillation dynamics using laser scattering, and the prospect of studying charged bubbles.

Sound-velocity measurements for HFC-134a and HFC-152a with a spherical resonator

A spherical acoustic resonator was developed for measuring sound velocities in the gaseous phase and ideal-gas specific heats for new refrigerants. The radius of the spherical resonator, being about 5 cm, was determined by measuring sound velocities in gaseous argon at temperatures from 273 to 348 K and pressures up to 240 kPa. The measurements of 23 sound velocities in gaseous HFC-134a (1,1,1,2-tetrafluoroethane) at temperatures of 273 and 298 K and pressures from 10 to 250 kPa agree well with the measurements of Goodwin and Moldover. In addition, 92 sound velocities in gaseous HFC-152a (1,1-difluoroethane) with an accuracy of ±0.01% were measured at temperatures from 273 to 348 K and pressures up to 250 kPa. The ideal-gas specific heats as well as the second acoustic virial coefficients have been obtained for both these important alternative refrigerants. The second virial coefficients for HFC-152a derived from the present sound velocity measurements agree extremely well with the reported second virial coefficient values obtained with a Burnett apparatus.

Acoustic resonance determination of sonic speed and the critical point for a typical retrograde gas condensate

Abstract A newly automated variable volume high pressure spherical acoustic resonator (150 mm dia) assembly has been used to measure sonic speeds in a typical retrograde gas condensate prepared by blending a field sample of C5+ stabilized condensate (Hobart Ranch condensate) with the appropriate amount of synthetically prepared gas containing light paraffins form methane to n-pentane, at pressures form 17.3 MPa to 15.0 MPa and temperatures in the range 255 K to 247 K. Results on the present method to locate the critical point for the gas condensate are presented with the comparison of D.B. Robinson et al.'s reported results in GPA RR's #89 and #96 for the same sample.

Acoustic cavity method for sonic speed measurements in liquids and stock tank oils

A miniature automated spherical acoustic resonator (50 mm dia) assembly has been developed to measure sonic speeds in liquids and stock tank oils (petroleum). The resonator is being used to determine sonic speeds and equilibrium phase boundaries. Comparison of experimental sonic speeds in liquid n-heptane with earlier measurements by different methods (J.W. Boelhower (1967) and M.J.P. Muringer, et al., (1985)) show good agreement. Results on the sonic speed and the location of wax drop out in two stock tank oils (filtered and unfiltered) are also presented.

Acoustic resonance determination of sonic speed and dew points in a natural-gas mixture and retrograde condensate

An automated high-pressure spherical acoustic resonator has been used to measure sonic speeds in a six-component natural-gas mixture at pressures from 2 MPa to 10 MPa and temperatures in the range 366 K to 243 K. The method permitted precise location of dew points, and these together with a portion of the phase diagram are presented for the natural-gas mixture. Experimental sonic-speed results are compared with values predicted by the MAXISIM model at Norsk Hydro a.s. The agreement is good.

Acoustic cavity method for phase boundary determinations: The critical temperature of CO2

A versatile acoustic method for the determination of points on phase boundaries in a fluid system is shown to be not only precise, but also capable of producing numerous experimental points in a short time as compared to other methods. The present method using a spherical acoustic resonator assembly operating under microcomputer control is capable of detecting any kind of chemical or physical changes which take place in the constant volume system as the temperature is slowly varied. Results on its use to locate the critical point of CO2 are given.

The dispersion equation in bounded viscothermal fluid: General formulation and applications

In the last century, G. Kirchhoff proposed a very fertile description of sound propagation in viscothermal fluid. He calculated the attenuation factors and speeds of propagation of harmonic plane waves in rigid‐walled tubes, which are solutions of the dispersion equation, for the wide tube case and the upper wavelength range, making approximations to the lowest orders possible. The problem of extending these classical Kirchhoff results to the case of higher‐order propagating modes was given by Beatty (1950), but the theory is not valid near the adiabatic cutoff frequency and for the evanescent modes. The initial purpose of this work is to provide an exact and unique general dispersion equation for all kinds of modes in cylindrical tubes. The main feature of this work is a new set of equations, derived from the basic classical theory of acoustic propagation in viscothermal fluid and valid not only in the frequency domain but also in the time domain. Three particular solutions of the general dispersion equation are two well‐known results, i.e., the equivalent specific impedance of a rigid plane wall (equivalent to the viscosity and thermal conduction effects inside the boundary layers) and the complex resonant frequencies of the spherical acoustic resonator, and a new one, i.e., the complex propagation constant of waves for all kind of modes in a rigid‐wailed circular tube. These results greatly facilitate calculations that are currently being worked on to obtain solutions to boundary problems such as the inertial mode coupling in acoustic gyros.

Acoustical determination of ideal gas heat capacities of three C-8 compounds

A versatile spherical acoustic resonator technique has been used for speed-of-sound measurements and the results reduced to gas-phase ideal gas heat capacity at constant volume for three volatile C-8 compounds (2-methylheptane, ethylcyclohexane and ethylbenzene). Mole fractions of the volatile compounds in argon were varied from 0 to 0.010 under isothermal conditions at various temperatures in the range 298.15–448.15 K.

Spherical cavity resonators: Effects of imperfect geometry

Spherical acoustic resonators are useful tools for high‐accuracy measurements of the speed of sound in gases partly because of the insensitivity of the radial‐mode eigenfrequencies to imperfect geometry. The mean frequencies of acoustic and electromagnetic (microwave) multiplets are also insensitive to geometric imperfection. The effects of imperfect geometry have been investigated experimentally by joining two metal hemispheres with variable‐thickness cylindrical spacers. The effects of this distortion on the acoustic and electromagnetic eigenvalue spectra have been studied. The results are compared with the theoretical prediction [J. B. Mehl and M. R. Moldover, Phys. Rev. A 34, 3341–3344 (1986)] that the frequencies of the radial acoustic modes and the mean frequencies of acoustic and electromagnetic multiplets depend, in the lowest order of shape‐perturbation theory, on the cavity volume. The effects of cavity size thus drop out of suitably chosen ratios of acoustic and electromagnetic eigenfrequencies leading to the possibility of direct determination of the ratio of the speed of sound to the speed of light.

Acoustic determination of the ideal-gas heat capacity of n-heptane at high temperatures

A novel high-temperature spherical acoustic resonator has been developed to obtain values of the ideal-gas heat capacity at constant volume of n-heptane, based on measurements of perturbations in the speed of sound through a reference gas (argon) caused by small successive additions of n-heptane. The resonance frequencies in ( n-heptane + argon) were measured at 25 K intervals over the temperature range 298.15 to 473.15 K. Mole fractions of n-heptane were varied from 0 to 0.031. The ideal-gas vapor-phase heat capacities at constant volume were evaluated from the obtained resonance frequencies at their respective temperature.

Second acoustic virial coefficients of argon between 100 and 304 K

The speed of sound in argon has been measured in the temperature range 100 to 304 K and the pressure range 13 to 500 kPa using a spherical acoustic resonator. Values of the second acoustic virial coefficient obtained from the results are in excellent agreement with those calculated from the latest interatomic potential-energy function for this system.

Spherical acoustic resonators in the undergraduate laboratory

A spherical acoustic resonator is reported that measures the speed of sound in gases with very high accuracy using comparatively simple instrumentation. The resonator can be used to illustrate, in a quantitative fashion, the temperature and pressure dependence of the speed of sound, the effects of thermal conductivity, and the splitting of nearly degenerate modes.

Gas‐filled spherical resonators: The current state of experiment and theory

In the past decade, spherical acoustic resonators have proved to be useful tools for high‐accuracy measurements of the speed of sound in gases. Applications include thermophysical property determinations, acoustic thermometry, and the recent redetermination of the gas constant. The complex resonance frequencies of the resonator are described by a theoretical model that includes the effects of the viscous and thermal boundary layers, shell motion, imperfect spherical geometry, and other, less important, effects. The theoretical model is tested by comparing the consistency of speed‐of‐sound determinations using different modes, and by comparing the resonance half‐widths with the theoretical predictions. The current level of agreement of experiment and theory will be reviewed.

Measurement of the universal gas-constant R using a spherical acoustic resonator

We report a new determination of the Universal Gas Constant R: (8.314 471 ±0.000 014) J·mol−1K−1. The uncertainty in the new value is 1.7 ppm (standard error), a factor of 5 smaller than the uncertainty in the best previous value. The gas constant was determined from measurements of the speed of sound in argon as a function of pressure at the temperature of the triple point of water. The speed of sound was measured with a spherical resonator whose volume was determined by weighing the mercury required to fill it at the temperature of the triple point. The molar mass of the argon was determined by comparing the speed of sound in it to the speed of sound in a standard sample of argon of accurately known chemical and isotoptic composition.

Thermophysical properties of alkanes from speeds of sound determined using a spherical resonator 2. n-Butane

The speed of sound in gaseous butane between 250 and 320 K has been obtained from measurements of the frequencies of the radial modes of a spherical acoustic resonator. Perfect-gas heat capacities and second and third acoustic virial coefficients have been calculated from the results. Methods of calculating ( p, V m, T) virial coefficients from acoustic results are discussed in detail and values for butane are given.

Measurement of the universal gas constant R using a spherical acoustic resonator.

• The uncer­ tainty in the new value is 1.7 ppm (stan­ dard error), a factor of 5 smaller than the uncertainty in the best previous value. The gas constant was determined from measurements of the speed of sound in argon as a function of pressure at the temperature of the triple point of water. The speed of sound was mea­ sured with a spherical resonator whose volume was determined by weighing the mercury required to fill it at the temperature of the tri~le point. The molar mass of the argon was determined by comparing the speed of sound in it to the speed of sound in a standard sample of argon of accurately known chemical and isotoptic composition.