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HighPressure HighTemperature Visual Cell for Interfacial Tension Measurements Volkmar Schoettle and Harley Y. Jennings Jr. Citation: Review of Scientific Instruments 39, 386 (1968); doi: 10.1063/1.1683378 View online: http://dx.doi.org/10.1063/1.1683378 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/39/3?ver=pdfcov Published by the AIP Publishing Articles you may be interested in High-pressure and high-temperature x-ray diffraction cell for combined pressure, composition, and temperature measurements of hydrides Rev. Sci. Instrum. 82, 065108 (2011); 10.1063/1.3600668 Highpressure hightemperature Raman cell for corrosive liquids Rev. Sci. Instrum. 66, 4347 (1995); 10.1063/1.1145326 Hightemperature, highpressure optical cells Rev. Sci. Instrum. 54, 993 (1983); 10.1063/1.1137515 Hightemperature, highpressure 10μm absorption cell Rev. Sci. Instrum. 54, 117 (1983); 10.1063/1.1137224 Velocity of Sound Measurements in HighPressure, HighTemperature Steam J. Acoust. Soc. Am. 32, 1511 (1960); 10.1121/1.1936324 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 129.49.170.188 On: Mon, 22 Dec 2014 00:03:07

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Page 1: High-Pressure High-Temperature Visual Cell for Interfacial Tension Measurements

HighPressure HighTemperature Visual Cell for Interfacial Tension MeasurementsVolkmar Schoettle and Harley Y. Jennings Jr. Citation: Review of Scientific Instruments 39, 386 (1968); doi: 10.1063/1.1683378 View online: http://dx.doi.org/10.1063/1.1683378 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/39/3?ver=pdfcov Published by the AIP Publishing Articles you may be interested in High-pressure and high-temperature x-ray diffraction cell for combined pressure, composition, and temperaturemeasurements of hydrides Rev. Sci. Instrum. 82, 065108 (2011); 10.1063/1.3600668 Highpressure hightemperature Raman cell for corrosive liquids Rev. Sci. Instrum. 66, 4347 (1995); 10.1063/1.1145326 Hightemperature, highpressure optical cells Rev. Sci. Instrum. 54, 993 (1983); 10.1063/1.1137515 Hightemperature, highpressure 10μm absorption cell Rev. Sci. Instrum. 54, 117 (1983); 10.1063/1.1137224 Velocity of Sound Measurements in HighPressure, HighTemperature Steam J. Acoust. Soc. Am. 32, 1511 (1960); 10.1121/1.1936324

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Page 2: High-Pressure High-Temperature Visual Cell for Interfacial Tension Measurements

THE REVIEW OF SCIENTIFIC INSTRUMENTS VOLUME 39. NUMBER 3 MARCH 1968

High-Pressure High-Temperature Visual Cell for Interfacial Tension Measurements

VOLKMAR SCHOETTLE AND HARLEY Y. JENNINGS, JR.

Chevron Research Company, La Habra, California 90633

(Received 5 October 1967 j and in final form, 20 November 1967)

This paper describes an apparatus for measuring a wide range of interfacial tensions at greatly varied pressure and temperature (1 to 817 atm and 25 to 176°C) by the pendent drop method. A visual cell, with specially con­structed seals, contains one of a selection of turret-rings. Each ring holds five needles with different sized tips, each of which can be rotated into operating position at any time. Unique details are illustrated.

INTRODUCTION

SOPHISTICATED oil recovery processes based on sur­face chemistry are being evaluated as a means of

recovering billions of barrels of crude oil that are unre­coverable through primary production mechanisms. These processes cannot be evaluated without a knowledge of the effects of temperature and pressure on the interfacial ten­sion of typical hydrocarbon-water systems found in reser­voir capillaries.

Accurate measurement of liquid-liquid and liquid-gas boundary tensions has challenged scientists and engineers for many years. Among the known means of measuring equilibrium interfacial tension, the pendent drop method has attained prominence in recent years, particularly for very low values. This method is based on the forming of a drop of liquid on a tubular tip, both being immersed in bulk fluid. Drop stability is maintained by keeping the drop size slightly below that which would spontaneously detach itself from the tip because of gravity or buoyancy. The drop and the tip are photographed in silhouette and the boundary tension is calculated from certain drop di­mensions and density relationships. The physical basis, calculation procedures, and equipment needed for pendent drop measurements have been discussed in earlier pub­lications.1•2

This paper describes a newly developed apparatus for forming, remotely manipulating, observing, and photo­graphing pendent drops with interfacial tension values as low as 0.001 dyne/ cm in the pressure range of 1 to 817 atm and concurrent temperatures from 25 to 176°C. These ranges cover the great majority of petroleum reservoirs, in both their natural state and under conditions imposed on them by planned heat injection processes.

APPARATUS

This new pendent drop apparatus consists of a pressure vessel with view ports for observing a set of drop-forming tips within, a heating and temperature control system, a light source, and a camera. Figure 1 shows these parts mounted in operating position on an optical bench.

1 J. M. Andreas, E. A. Hauser, and W. B. Tucker, J. Phys. Chern. 42, 1001 (1938).

• H. Y. Jennings, Jr., Rev. Sci. lnstr. 28, 774 (1957).

386

Auxiliary equipment includes two pressure generators, a sample vessel, pressure gauges, rupture disks, and valves and tubes which control the charge of the bulk liquid and the movement of the drop-forming sample. Figure 2 illus­trates these parts schematically.

Means for advancing the drop-forming liquid into the lines and through the needle tips are twofold: one of the pressure generators handles the initial, coarse displace­ment, and partial opening and closing of a manual valve achieves fine adjusting of the drop by piston-like move­ment of the valve stem.

Conventional components of the air bath for cell heating are not shown, i.e., electrical heaters, an air circulator, and temperature controls. Also omitted from Figs. 1 and 2 are structural members that position the cell so the optical axis from the light source to the camera goes through the pendent drop. Construction and operation of the light source and the camera resemble those discussed in an

CA.MERA WITH GROUND GLASS SCREEN

HIGH PRESSl.IR£ CELL

FIG. 1. Sketch of the pendent drop apparatus.

ROTAnNC DEVICE r IV~_CU-:;U·~l+,~===~C"=:FO;-sR T=UR~RET-f'R_"C-r1-_-O DIiOP-FORIlIIlc:vm'(.

HANOOPERATEO PRESSURE G[Nf~ArOR

TO 817 AU

BOTTOMfNTRl

ROTATING DEVICE FOR TURRET-RING

FIG. 2. Schematic drawing of the apparatus.

p

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Page 3: High-Pressure High-Temperature Visual Cell for Interfacial Tension Measurements

INTERFACIAL TENSION 387

earlier paper.2 This paper, therefore, concentrates on a de­scription of the newly-designed high-pressure high-tem­perature test cell.

CELL CONSTRUCTION

The visual cell, shown in section in Fig. 1, is constructed of stainless steel, and is 11.5 cm o.d. and 19 cm long. The window openings are 2 cm diam, behind which are crown­type optical glass disks 3.8 cm diam and 1.9 cm thick, fine-annealed and tempered. All surfaces of the disks are ground and polished. The cell houses one 5-tip turret-ring at a time. This is rotated by two shafts through holes in the cell wall (shown in schematic form in Fig. 2). Two 2.06 mm holes in the same plane serve as filling, draining, and vent­ing passages for the bulk fluid. Two 1.32 mm holes, in a different plane, carry the drop-forming liquid. The latter holes are oriented vertically, the upper one for forming drops heavier than the bulk liquid; the lower one, for less dense liquids.

Measuring interfacial tensions for a given system over a range of conditions usually requires the use of a number of different tip sizes. As the interfacial tension changes, so does the drop size, and the tip size required. Changing the tips is a simple matter in an open atmospheric drop cell, but is a complex problem at, say, 176°C and 817 atm. This is the purpose of the aforementioned turret-ring (see also Fig. 3), which was designed to allow five built-in tips to be rotated into position while the cell is pressurized and heated. Each tip may be aligned with either the bottom or the top entry hole for the drop-forming fluid. To date we have worked with two turrets, i.e., 10 tips. Changing turrets requires draining the cell and removing one window.

A turret is essentially a ring of stainless steel, 4.43 em o.d., with five equally spaced radial holes in a common plane (Fig. 3). Each hole contains a press-fitted cylindrical Teflon plug, which carries both a drop-forming tip point­ing toward the center of the ring and a short tubular nipple pointing outward (both press-fitted). A hole through the center of the plug connects the bore of the nipple with the bore of the needle. An O-ring is lodged on that part of the nipple which protrudes from the plug.

The turret-ring, thus assembled, is put into the cell from the camera side (Fig. 1). The ring fits the cell loosely, but "floats" between the five O-rings, which prevent metal-to­metal contact and keep the two fluids separate at this point.

The turret is rotated by two geared pinions on shafts that penetrate the cell wall 180° apart. These pinions mesh with beveled gear teeth cut into one face of the turret ring. The operator turns the pinion shafts with socket wrenches that reach through holes in the wall of the heater chamber. The axial component of the tooth pressure on the turret ring is supported by the ring's other face, which runs in

OROP-FORMING LIQUIO PORT

FIG. 3. Turret-ring in cell.

contact with the retainer component of the window as­sembly on that side. One pinion would theoretially have sufficed, but two pinions, 180° apart, give smoother rota­tion to the ring and fix it squarely to the cell axis.

Theoretically, the more tips a turret possessed, the broader would be the range of application. Five was chosen, for reasons of geometry: more tips would either have limited drop size or would have required the needles to be shorter, thus forming the smaller drops far from the optical axis. The choice of an odd number also avoided simultaneously joining the top and bottom liquid entry holes to tips (see Fig. 2).

The 10 tips used to date range from 0.114 to 4.50 mm outer tip diameter. (The outer diameter appears on the photograph and serves as dimensional reference for the drop.) The desired range of tip diameters called for three different designs, as shown in Fig. 4. The large, shaped tips

SHAPED TIP

TWO LARGEST NEEDLES

~ SIX INTERMEDIATE

STZE NEEDLES

FIG. 4. Tip desigo.

SUPPORTED TIP

TWO SMALLEST NEEDLES

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Page 4: High-Pressure High-Temperature Visual Cell for Interfacial Tension Measurements

388 V. SCHOETTLE AND H. Y. JENNINGS, JR.

HIGH PRESSURE

nREMOVED PORTION

~pB!!B\:-.::,~ ", I I I I I: I I

I

\ COMMERCIAL' \ SEAL RING

FIG. 5. Details of seal between vessel and cover plate.

were machined from commercial tubing; all others were cut from syringe needle stock. The two smallest tips, 0.114 and 0.254 mm in diameter, needed the backing of a larger needle, as shown.

All closures are sealed with O-rings and backup rings (Fig. 5), although the maximum pressures used exceed the limit normally suggested for O-ring applications. The O-rings are a special Nitrile rubber compound of 90 Shore hardness that exhibits high resistance to extrusion at operating temperatures. Backup rings are commercial U-shaped Teflon seal rings, normally offered for recipro-

I 0-.,11: IHOTASEAL!

I JI:

LOW PRESSURE CONDITION HIGH PRESSURE =NDITION

FIG. 6. Steps of window pressurization.

cating and rotary seals, altered by cutting off one shoulder to obtain an L shape. The effectiveness of this seal-ring combination at 817 atm is increased by the fact that the leak path is under metal-to-metal contact, i.e., there is zero clearance. Figure 5 shows the seal between the cell body and the cover plate and the preparation of a backup ring.

The same, though inverted, configuration exists at the seal between the cover plate and the glass disk, as shown in Fig. 6. However, this sealing process is somewhat different in detail, as the following description of the installation procedure explains. The O-ring and the backup ring are inserted in the cover plate. The glass disk is laid on the O-ring, which leaves a clearance between the glass a~d cover plate. Another O-ring, which serves only as an elastIc pad for the inward face of the glass disk, is placed into the glass-retainer; then the glass-retainer is screwed into the cover plate. Thus the glass floats safely between two O-rings during assembly, compressed only enough to seat the pressure-sealing O-ring. Rising pressure finally brings the glass in contact with the cover plate and eliminates any escape clearance for the seal rings.

This cell makes it possible for the operator to measure liquid-liquid boundary tension at elevated pressures and temperatures as easily as he does the atmospheric condi­tions. The complete apparatus described in this article was used to measure the interfacial tensions for benzene-water and normal decane-water in the intervals between 25 and 176°C and 1 and 817 atm, and the results have been pub­lished.a These systems have been studied by other in­vestigators, but no one else has reported data taken at temperatures as high as 176°C. The experimental work progressed smoothly during the course of these measure­ments; even though experiments have continued to this writing, we have had no window failures. All patent rights to the development are reserved by Chevron Research Co.

3 H. Y. Jennings, Jr., J. Colloid Interface Sci. 24,323 (1967).

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