Bubble measurement gravity methods

The determination of density (specific gravity) (ASTM D-287, ASTM D-891, ASTM D-941,ASTM D-1217, ASTM D-1298,ASTM D-1555, ASTM D-1657, ASTM D-2935, ASTM D-4052, ASTM D-5002, IP 160, IP 235, IP 365) provides a check on the uniformity of the gasoline, and it permits calculation of the weight per gallon. The temperature at which the determination is carried out and for which the calculations are to be made should also be known (ASTM D-1086). However, the methods are subject to vapor pressure constraints and are used with appropriate precautions to prevent vapor loss during sample handling and density measurement. In addition, some test methods should not be appUed if the samples are so dark in color that the absence of air bubbles in the sample cell cannot be established with certainty. The presence of such bubbles can have serious consequences for the reUabiUty of the test data. 

Piezocrystals can be used for biomass concentration estimation since the compressibility of a sample is a function of cell concentration and affects the voltage output of the crystal strongly [146]. A more promising technique is acoustic resonance densitometry (ARD) [147, 148]. In this method, the specific gravity or relative density of the cell-containing sample is measured. Blake-Coleman et al. report the application of this method during on-line biomass concentration estimation for cultivations of Erwinia chrysanthemi and E. coli [147, 148], while Kilburn et al. monitored mammalian cell cultures by ARD [149]. The measurements are affected by gas bubbles and foam and thus they must be performed in an external flow loop if these factors are significant. 

Pendant or Sessile Drop Method The surface tension can be easily measured by analyzing the shape of a drop. This is often done by optical means. Assuming that the drop is axially symmetric and in equilibrium (no viscous and inertial effects), the only effective forces are gravity and surface or interfacial forces. In this case, the Young-Laplace equation relates the shape of the droplet to the pressure jump across the interface. Surface tension is, then, measured by fitting the drop shape to the Young-Laplace equation. Either a pendant or a sessile drop can be used for surface tension measurement. The pendant drop approach is often more accurate than the sessile drop approach since it is easier to satisfy the axisymmetric assumption. Similar techniques can be used for measuring surface tension in a bubble. 

The high mobility of the bubbles issued from the Archimedes thrust would be eliminated if the experiments could be carried in weightless conditions in an orbital space station. In such circiun-stances, once a bubble had been formed, it would no longer escape the investigator it could be subject to an electric field alone, which would impose only moderate movement. In the meantime, under these ideal conditions measurements independent of gravity can be performed by the so-called method of the spinning bubble. 

The capillary rise method was the earliest technique by which surface tension was measured and, indeed, was the technique by which the force itself was recognized. If a narrow tube of radius r is partially inserted into a liquid, the liquid rises up inside the tube to some equilibrium position as shown in Fig. 22. This occurs because the attractive interaction of the wetting liquid (aqueous solution) with the solid surface is stronger than that of the gas phase. Gravity opposes the rise, and the equilibrium height H corresponds to the minimum free energy of the system. The treatment is based on the Laplace equation that gives the pressure difference across a curved interface due to the surface or interfacial tension of the liquid [62]. Let us assume that we have a spherical bubble Of gas in a liquid... 

---