Phase volume method

The method assumes that the proppant is part of the internal phase, and the foam quality is effectively increased. The viscosity of the foam slurry is then estimated as being equal to the proppant-free foam, the quality being calculated using the internal-phase volume method shown in equation 2. 

The phase Doppler method utilizes the wavelength of light as the basis of measurement. Hence, performance is not vulnerable to fluctuations in light intensity. The technique has been successfully appHed to dense sprays, highly turbulent flows, and combustion systems. It is capable of making simultaneous measurements of droplet size, velocity, number density, and volume flux. 

However, as stated above, the partition coefficients measured by the shake-flask method or by potenhometric titration can be influenced by the potenhal difference between the two phases, and are therefore apparent values which depend on the experimental condihons (phase volume ratio, nature and concentrahons of all ions in the solutions). In particular, it has been shown that the difference between the apparent and the standard log Pi depends on the phase volume raho and that this relationship itself depends on the lipophilicity of the ion [80]. In theory, the most relevant case for in vivo extrapolation is when V /V 1 as it corresponds to the phase ratio encountered by a drug as it distributes within the body. The measurement of apparent log Pi values does not allow to differentiate between ion-pairing effect and partihoning of the ions due to the Galvani potential difference, and it has been shown that the apparent lipophilicity of a number of quaternary ion drugs is not due to ion-pair partitioning as inihally thought [80]. 

In the phase-Doppler method, the volume flux, V, is obtained from ... 

The biological applications of NMR include the study of the structure of macromolecules such as proteins and nucleic acids and the study of membranes, and enzymic reactions. Newer methods and instruments have overcome, to a large extent, the technical difficulties encountered with aqueous samples and the analysis of body fluids is possible, permitting the determination of both the content and concentration of many metabolites in urine and plasma. NMR is not a very sensitive technique and it is often necessary to concentrate the sample either by freeze drying and dissolving in a smaller volume cm- by solid phase extraction methods. 

The mass spectrometer is a very sensitive and selective instrument. However, the introduction of the eluent into the vacuum chamber and the resulting significant pressure drop reduces the sensitivity. The gas exhaust power of a normal vacuum pump is some 10 ml min-1 so high capacity or turbo vacuum pumps are usually needed. The gas-phase volume corresponding to 1 ml of liquid is 176 ml for -hexane, 384 ml for ethanol, 429 ml for acetonitrile, 554 ml for methanol, and 1245 ml for water under standard conditions (0°C, 1 atmosphere). The elimination of the mobile phase solvent is therefore important, otherwise the expanding eluent will destroy the vacuum in the detector. Several methods to accomplish this have been developed. The commercialized interfaces are thermo-spray, moving-belt, electrospray ionization, ion-spray, and atmospheric pressure ionization. The influence of the eluent is very complex, and the modification of eluent components and the selection of an interface are therefore important. Micro-liquid chromatography is suitable for this detector, due to its very small flow rate (usually only 10 p min - ). 

This phenomenon can be exploited for separation and concentration of solutes. If one solute has certain affinity for the micellar entity in solution then, by altering the conditions of the solution to ensure separation of the micellar solution into two phases, it is possible to separate and concentrate the solute in the surfactant-rich phase. This technique is known as cloud point extraction (CPE) or micelle-mediated extraction (ME). The ratio of the concentrations of the solute in the surfactant-rich phase to that in the dilute phase can exceed 500 with phase volume ratios exceeding 20, which indicates the high efficiency of this technique. Moreover, the surfactant-rich phase is compatible with the micellar and aqueous-organic mobile phases in liquid chromatography and thus facilitates the determination of chemical species by different analytical methods [104]. 

A commonly used method of sampling and analysis for volatile organic compounds In ambient air Is by concentration of the compounds on a solid sorbent such as Tenax and subsequent thermal desorption and GC/MS analysis of the collected compounds. The analysis phase, although not trivial, can be done well If proper care Is taken. However, the sampling phase of this process apparently Introduces artifacts and unusual results due to, as yet, unknown factors. A method to detect some sampling problems has been proposed and tested (7 ). This distributed air volume method requires a set of samples of different air volumes to be collected at different flow rates over the same time period at the sampling location. Each pollutant concentration for the samples should be equal within experimental error since the same parcel of air Is sampled In each case. Differences In results for the same pollutant In the various samples Indicates sampling problems. 

Instead of measuring the weight directly we may calculate it from the volume and the density the drop volume method has been applied by Harkins chiefly to the measurement of the tension between two liquid phases, and it probably falls little short in accuracy from the previous method. More frequently it has been j modified, especially for biochemical purposes, as a drop number method that is, a known volume of liquid iFallbwed oo nov. of a tube, and the number of drops formed is compared with that formed by a standard fluid. This method is necessarily very rough. 

Therefore, passivation of the positive electrode by poorly conducting PbS04 can be reduced [348]. The porosity is important because it enables the expansion during the solid phase volume increase, which accompanies the transformation of Pb02 to PbS04. In the most popular construction, the electrode paste material (mixture of metallic lead with lead oxides) is held in a framework composed of lead alloys with additions of tin, antimony, selenium, and calcium [348]. Antimony improves the mechanical stability however, it increases the resistance and facilitates the selfdischarge of the battery. Better results are obtained for low antimony content and/or for lead-calcium alloys [203]. Methods of positive electrodes improvement, from the point of view of lead oxide technology have been discussed [350]. Influence of different factors on life cycle, nature, and composition of the positive active mass has been studied by Pavlov with coworkers [200, 351, 352]. 

In the area of methods development for analytical research, the robot is being used to perform accuracy and precision studies. A researcher can more completely evaluate each phase of methods development which include time dependent operations such as extractions and volume dependent operations such as partitioning or the use of bonded-phase extraction columns. It can serve as the ultimate ruggedness test for each part of a proposed method. 

Bibette has used this method to study the effect of osmotic pressure on the stability of thin films in concentrated o/w emulsions [96], by means of an osmotic stress technique. The emulsion is contained in a dialysis bag, which is immersed in an aqueous solution of surfactant and dextran, a water-soluble polymer. The bag is permeable to water and surfactant, but impermeable to oil and polymer. The presence of the polymer causes water to be drawn out of the emulsion, increasing the phase volume ratio and the deformation of the dispersed droplets (Fig. 10). 

From N2 absorption by BET method b X = crosslinker concentration, PV90 organic phase/aqueous phase = 10/90 (90% phase volume) PE = petroleum ether T = toluene. 

High molecular weight monodisperse polystyrene latexes have been prepared by this method [158]. A number of factors were found to influence the size and dispersity of the particles. The size decreased with increasing surfactant concentration and decreasing internal phase volume, and a more monodisperse latex... 

Samples that are 2 to 3 mm thick are suitable for imaging by CLSM and work well for products with solid fat content (crystal phase volume UNIT D3.1) between -10% and 50%. Fats with higher solid content must be thinner to allow sufficient light penetration. This method does not work well for samples with very high (>75% to 80%) solid fat content, as the samples are generally too opaque to allow sufficient light penetration. 

When colours are added to a food system, their characterisation is often more difficult due to interferences from other materials in the food or difficulty with their extraction from the food. This is particularly the case for high-protein foods, which bind colours very tightly and can make their quantitative analysis very difficult. However, analysis for azo-dyes in soft drinks is generally straightforward using modern methods. There is less interference than in other food systems and as the colours are already in solution, and not bound to other materials, this makes the analysis easier. In some cases, the colours can be analysed without prior concentration and in others they have to be concentrated by solid-phase extraction methods, for example, Ci8 cartridges followed by elution with a small volume of methanolic ammonia. 

Euler-Euler models assume interpenetrating continua to derive averaged continuum equations for both phases. The probability that a phase exists at a certain position at a certain time is given by a phase indicator function, which, for steady-state processes, is equivalent to the volume of fraction of the correspondent phase (volume-of-fluid technique). The phase-averaging process introduces further unknowns into the basic conservation equations their description requires empirical and problem-dependent input (94). In principal, Euler-Euler models are applicable to all multiphase flows. Advantages and disadvantages of both methods are compared, e.g., in Refs. 95 and 96. 

The computational fluid dynamics investigations listed here are all based on the so-called volume-of-fluid method (VOF) used to follow the dynamics of the disperse/ continuous phase interface. The VOF method is a technique that represents the interface between two fluids defining an F function. This function is chosen with a value of unity at any cell occupied by disperse phase and zero elsewhere. A unit value of F corresponds to a cell full of disperse phase, whereas a zero value indicates that the cell contains only continuous phase. Cells with F values between zero and one contain the liquid/liquid interface. In addition to the above continuity and Navier-Stokes equation solved by the finite-volume method, an equation governing the time dependence of the F function therefore has to be solved. A constant value of the interfacial tension is implemented in the summarized algorithm, however, the diffusion of emulsifier from continuous phase toward the droplet interface and its adsorption remains still an important issue and challenge in the computational fluid-dynamic framework. 

---