Measuring capillary

Measure capillary glucose every 1-2 hours measure electrolytes (especially K+, bicarbonate, phosphate) and anion gap every 4 hours for first 24 hours. 

When the osmometer is in operation, a nichrome wire of a suitable diameter is inserted into the capillary (the diameter of the wire is almost equal to the inner diameter of the capillary). The wire serves for adjusting the liquid level in the measuring capillary and is held in the capillary with the aid of a cork. 

J. D. Fairweather, P. Cheung, J. St-Pierre, and D. T. Schwartz. A microfluidic approach for measuring capillary pressure in PEMFC gas diffusion layers. Electrochemistry Communications 9 (2007) 2340-2345. 

According to the type of scale division, a distinction is made between two forms of compression vacuum gauges those with a linear scale (see Fig. 3.7) and those with a square-law scale (see Fig. 3.8). In the case of the compression vacuum gauges of the McLeod linear-scale type, the ratio of the enclosed residual volume Vc to the total volume V must be knovm for each height of the mercury level in the measurement capillary this ratio is shown on the scale provided with the instrument. In the case of compression vacuum gauges with a square-law scale, the total volume and the capillary diameter d must be known. 

If h is the difference in the mercury level between the measurement capillary and the reference capillary (measured in mm), then it follows from the Boyle-Mariotte law ... 

If during measurement the mercury level in the measurement capillary is always set so that the mercury level in the reference capillary corresponds to the upper end of the measurement capillary (see Figs. 3.7 and 3.8), the volume Vj is always given by ... 

An example of such an instrument is the U-tube vacuum gauge, with which the measurement of the pressure in the measurement capillary is based on a measurement of the weight over the length of the mercury column. 

This equation permits f to be evaluated from measurements of the rate of volume flow through the capillary the measurements are made by observing the rate of displacement of the air bubble in the measuring capillary of Figure 12.7a. 

Simple osmometers have also been developed by Adair particularly for aqueous colloidal solutions. A thimblc-typc collodion membrane is attached to a capillary tube and contains the solution, When equilibrium is established the difference in level inside and outside the capillary is measured, Capillary corrections are made. For organic solvents a dynamic type osmometer may be used. A membrane of large surface area is clamped between two half cells and attached to each half cell is a fine capillary observation tube. With such an apparatus, equilibrium is rapidly established between solution and solvent contained in the half cells, The volume of the half cell may be small (about 20 cubic centimeters), The level of the solvent is usually aiiangecl to be a little below the equilibrium position, and the height of the solvent in the capillary as a function of time is measured, This procedure is repeated with the level of the solvent just above the equilibrium position. A plot is then made of the half sum of these readings. 

These problems can be avoided by measuring capillary pressure curves of GDMs directly with water as the working fluid. A number of techniques have been recently proposed. Of the different types of GDM (carbon paper, carbon cloth, metal foam/mesh, etc.), only carbon paper GDMS have been studied to any appreciable extent using these methods. An ideal capillary pressure measurement technique must be able to vary water saturation in directions of increasing saturation from Sw = 0 to Sw -> 1 and decreasing saturation from Sw = 1 to Sw -> 0. This requires the application... 

It may be necessary to correct the experimental data for effects such as electro-osmosis in the measuring capillary tube and electro-osmotic leak back through the plug. 

Since pressure driven viscometers employ non-homogeneous flows, they can only measure steady shear functions such as viscosity, 77(7). However, they are widely used because they are relatively inexpensive to build and simple to operate. Despite their simplicity, long capillary viscometers give the most accurate viscosity data available. Another major advantage is that the capillary rheometer has no free surfaces in the test region, unlike other types of rheometers such as the cone and plate rheometers, which we will discuss in the next section. When the strain rate dependent viscosity of polymer melts is measured, capillary rheometers may provide the only satisfactory method of obtaining such data at shear rates... 

First, a typical power spectrum of capillary waves excited at the W/NB interface is shown in Figure 3.4a. The errors on the values of the capillary wave frequency were 0.1 kHz, obtained as the standard deviation of 10 repeated measurements. Capillary wave frequency dependence on CeHsONa is shown in Figure 3.4b. The frequency decreased significantly with increasing CeHsONa concentration. This indicated that interfacial tension was decreased by the interfacial adsorption of CeHsONa. 

Evaluation of Results. At the beginning and end of a polymerization, the level of the mercury meniscus in the measuring capillary was read. The scannings of the Compensograph (conversion-time functions) were corrected using the calibration plot (pen deflection vs. meniscus level). The final conversion of the d spersions was determined. All values are based on the polymer content of the dispersions (milligrams of polymer per gram of dispersion) thus calculated, and by the assumption of a linear correlation between volume contraction and conversion. 

The measuring cell, which is equipped with a water jacket for temperature control, simultaneously holds the measuring capillary and two platinum electrodes, one of which is immersed in the liquid under study while the second is situated exactly opposite to the capillary and controls the size of the bubble. The electric signals from the gas flow sensor PSj and pressure transducer PS2, the microphone and the electrodes, as well as the compressor, are connected to a personal computer which operates the apparatus and acquires the data. 

In other words, the apparent shear stress is determined by the pressure drop along the length of the capillary (i.e., pressure at the entrance of the measuring capillary) and the radius and length of the capillary. 

Filling the system with mercury (the measuring liquid) and measuring is done via a system of glass capillaries and stopcocks. This permits to work at different sensitivities simply by opening one of the stopcocks, thus giving the mercury access to a capillary which acts as a shunt with respect to the measuring capillary. 

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