Homogeneous technique, definition

A fundamental difference exists between the assumptions of the homogeneous and porous membrane models. For the homogeneous models, it is assumed that the membrane is nonporous, that is, transport takes place between the interstitial spaces of the polymer chains or polymer nodules, usually by diffusion. For the porous models, it is assumed that transport takes place through pores that mn the length of the membrane barrier layer. As a result, transport can occur by both diffusion and convection through the pores. Whereas both conceptual models have had some success in predicting RO separations, the question of whether an RO membrane is truly homogeneous, ie, has no pores, or is porous, is still a point of debate. No available technique can definitively answer this question. Two models, one nonporous and diffusion-based, the other pore-based, are discussed herein. 

The definition of friction factor using mean fluid properties has been most widely used because it reduces to the correct single-phase value for both pure liquid and pure gas flow. This technique is very similar to the so-called homogeneous model, because it has a clear physical significance only if the gas and liquid have equal velocities, i.e., without slip. Variations of this approach have also been used, particularly the plotting of a ratio of a two-phase friction factor to a single-phase factor against other variables. This approach is then very similar to the Lockhart-Martinelli method, since it can be seen that (G4)... 

Although I.G.C. experiments are easy and fast one must question the quantitative reliability of the technique. There is a problem in removing the effects of both surface adsorption and diffusion limitation in the stationary phase . It has not been definitely proven that any choice of loading weight or extrapolation procedure can remove both these effects. A further limitation of the technique is that it can only be used to give information at temperatures at least 50 °C above the T s of the homogeneous systems being studied in order to reduce the effects of surface adsorption and diffusion limitations. 

Alternatively a method may be defined as a defined application of a particular technique or techniques to obtain an analytical result . The approved definition for a method of measurement is, A logical sequence of operations, described generically, used in the performance of measurements . The method will encompass a range of procedures or steps such as sample preparation, sample extraction and measurement technique. Also it may be appropriate to have a procedure on how to obtain a representative, homogenous sample. A procedure is a set of instructions that are sufficient for the analyst to carry out the work. 

Phase. Commonly defined as a uniform, homogeneous, physically distinct, and mechanically separable part of a system. Unfortunately, mineral phases are often not uniform, homogeneous, or mechanically separable except in theory. Sophisticated microscopic and spectroscopic techniques and operational definitions are needed to define some mineral phases. 

The overall rate coefficient is k = 3 x 10 exp(—60,000/Rr), but, as the surface effect was not examined, the measured activation energy cannot be definitely ascribed to the C-S bond dissociation energy. Using the same technique, the thermolysis of methyl benzyl sulfide was found to produce CH3SH and dibenzyl from CHjS and PhCH2 radicals between 469 and 644 °C the reaction is homogeneous and first order, with E = 51.5 kcal.mole" ... 

However there is still a great discussion about the definition of their representative properties and even about the proper meaning of the word "microemulsion". Indeed such a name would indicate a dispersed system while microemulsions show the appearence of true solutions,i.e., of homogeneous systems. Since an essential requisite for the existence of a microemulsion is the presence of water (l), we think that a study of the fundamental properties of such systems should require the use of experimental approaches specifically apt to reveal "in primis" the behavior of water. Moreover,besides of course the hydrocarbon,being the other components necessary for the existence of a microemulsion amphiphilic compounds acting as surface active agents, also techniques suitable for the study of systems with a high surface-to-volume ratio, are requested. 

We have chosen the term real samples to describe materials such as those in the preceding illustration. In this context, most of the samples encountered in an elementary quantitative analysis laboratoi course definitely are not real but rather are homogeneous, stable, readily soluble, and chemically simple. Also, there are well-established and thoroughly tested methods for their analysis. There is considerable value in introducing analytical techniques with such materials because they permit you to concentrate on the mechanical aspects of an analysis. Even experienced analysts use such samples when learning a new technique, calibrating an instrument, or standardizing solutions. 

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