Tensiometers

Fig. 2. (a) Schematic of a tensiometer and (b) a hydraulic analogy showing the negative value of the total head, /. 

Spannungs-messer, m. strain gage tensiometer Elec.) voltmeter, -optik, /. photoelasticity. 

Tests were performed at 75°C using a University of Texas Model 500 spinning drop tensiometer. Active surfactant concentration in the aqueous phase prior to oil addition was 0.50% wt. The Kem River crude oil was from the Patricia Lease. The pH of the deionized water surfactant solutions was 8. The pH of the aqueous NaCl surfactant solutions was 9.5 unless otherwise noted. values represent the average deviation of two or three measurements at different times (0.75-1 h apart). D.I., deionized. 

Tests were performed at 75°C using a University of Texas Model 500 spinning drop tensiometer. Active surfactant concentration in the aqueous phase prior to addition of the oil phase was 0.5% wt. Interfacial tension values are the average of duplicate or triplicate determinations. 

The dynamic interfacial tension behavior of reacting acidic oil-alkaline solutions has been studied for both an artificially acidified synthetic oil and a real crude oil at various concentrations [131,132] with either a drop volume tensiometer or a spinning drop tensiometer. 

S. D. Ball. Comparison of transient interfacial tension behaviours of oiUalkaline systems as measured by the drop volume and spinning drop tensiometers. PhD thesis, Ottawa Univ, 1995. 

Tensiometer Measures the matric potential of a given soil, which is converted to soil moisture content Commonly consists of a porous ceramic cup connected to a pressure-measuring device through a rigid plastic tube... 

Figure 26.13 shows the double-ring device currently being used. It consists of a 12 ft by 12 ft outer ring and a 5-ft diameter inner ring.22 Tensiometers are embedded at various depths to establish the depth of water penetration into the soil so that hydraulic conductivity can be calculated. 

Equipaent and Procedures. Crude o iI/aqueous i nterfac ia I tens i ons were measured using a spinning drop tensiometer built at the Alberta Research Council and designed for operation at elevated temperatures [211. The main difficulty in operating at elevated temperatures was the wear on the bearing improved operation was... 

Oil drops of 2-5 /iL were introduced into 0.4 cm i.d. capillary tubes containing the aqueous phase. The more viscous heavy oils were heated for a short period to facilitate this addition. The tubes were then sealed with a tightly fitting silicon-rubber septum. A teflon screw was used to apply pressure on the septum after the capillary tube was inserted into the shaft of the tensiometer. In this manner, temperatures up to 200°C were achieved without loss of liquid. 

Modifications of the conventional spinning drop tensiometer were required for operating at temperatures up to 200°C. Measurements carried out with heavy oil samples required the use of D20 instead of H20 to maintain a sufficient density difference between oil and water. For accurate measurements, considerable care must be used to ensure that heavy oil drops do not lag behind the rotation of the capillary tube in the tensiometer. Also, repeatability of measurements conducted with chemically ill-defined substances may be hampered by the inhomogeneity of the oil drops. 

Interfacial Tension (IFT) Measurements. All IFT measurements were done using a University of Texas Model 300 Spinning Drop Interfacial Tensiometer. The basic principle is to introduce a drop (about 2 p ) of an oil sample into a glass capillary tube (1.5 mm I.D., 78 mm long) filled with the aqueous medium. The tube is then spun about its main axis. The oil drop will elongate to a length determined by the IFT value of the system. Details of the theory and application can be found elsewhere (15.16). According to the equipment manufacturer, the formula used to calculate IFT value is ... 

The sensoric principle of the dynamic bubble-pressure tensiometer is based on the differential Laplace pressure between two capillaries from which a controlled gas flow is released. At the lower end of a capillary which points into the liquid, a gas bubble is formed which increases its radius with increasing gas pressure (see... 

Recently, a very practical bubble pressure tensiometer was developed using elegant pressure transducer mechanics which only needs one capillary made from a high-tech polymer [51, 52]. The tensiometer is able to measure at different immersion depths but needs calibration in order to make the resulting data comparable to surface tension values from other sources. It was shown in a series of measure-... 

T. Muller-Kirschbaum, E. J. Smulders, Das On-line Tensiometer, SOFW-Journal 1992, 118, 427-434. 

Figure 5.12. From left to right, a tensiometer, soil drying can (A) and porous block (B) and meter, used with B, for determination of soil water.

Field methods of measuring soil water are primarily designed to measure water in the range of -10 to -1500 kPa of pressure. However, different instruments have different ranges as shown in Table 5.1. Tensiometers, porous blocks, and thermocouple psychrometers are usually installed in the field and measurements are taken on a regular basis. Neutron probe and time domain reflectometry (TDR) equipment are usually carried to the field each time a... 

Explain why tensiometers and porous block methods are most useful in the field. 

Figure 3. A modern automatic tensiometer. Photograph supplied by Fisher Scientific Co.

Surface Tension Measurement. Surface tension was determined with a Rosano Tensiometer (Arenberg-Sage Inc., Jamaica Plain, Mass.) utilizing a sand-blasted platinum blade. 

Surface and interfacial tension measurements were made at 40° C with a Model 300 Spinning Drop Tensiometer obtained from the University of Texas at Austin, Chemistry Department. 

Experimentally, the method is capable of good precision. A so-called chainomatic balance has been used to determine the maximum pull, but a popular simplified version of the tensiometer, as it is sometimes called, makes use of a torsion wire and is quite compact. Among experimental details to mention are that the dry weight of the... 

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