Mixtures stratification

Mixture stratification (or, in other words, the extent of premixing) is determined to some extent by injection strategies. In the next section, some of these strategies will be discussed. Note that LTC engines are still under development and so fuel delivery strategies are evolving. Other approaches, not discussed below, have been reported in the literature. 

Schematic of premixed edge flames in a counterflow burner (a) Mean velocity of the inner tube is greater than that of the outer tube, creating a stretch-induced edge flame, (b) Equivalent ratio of the mixture in the inner tube is different from that in the outer tube, creating a stratification-induced edge flame.

Epstein, N. and Pruden, B.B. Chem, Eng. Sci. 54 (1999) 401. Liquid fluidisation of binary particle mixtures - III. Stratification by size and related topics. 

If a powder flows poorly, the vibrator can be used, but it also causes powder segregation and stratification. The addition of glidant (occasionally lubricant) in the powder mixtures can readily increase flowability at the low concerntration. Talc or fumed silicon dioxide is an example of a glidant. If this is not sufficient to improve the flow, other means of flow improvement are necessary. There are two main factors that affect powder flow particle size and particle shape. The more spherical a particle is, the better it flows. Small particles are very cohesive and hence do not flow well, but increasing the particle size will improve flow. With the aid of spray drying or spheronizers, particles become spherical. 

At large surfactant concentrations emulsion films as well as foam films exhibit a layer-by-layer thinning (stratification) and metastable black films are formed [31,347,512], Such a behaviour has been reported for hydrocarbon films obtained from solutions of lecithin in either benzene or a mixture of chloroform and decane at concentration higher than 0.6-0.8% as well as in films from oxidised cholesterol in decane [31,512]. Manev et. al. [347] have reported stratification of O/W type emulsion films, toluene being added as a disperse phase, occurring within a surfactant (NaDoS) concentration range of 0.017-0.14 mol dm 3. The number of metastable states was 5-6. Compared to foam films of analogous composition, the respective emulsion films were thicker, due to the weaker intermolecular attraction and the stratification occurred at lower surfactant concentrations. 

In a 12-1. flask fitted with a reflux condenser and an efficient, liquid-sealed mechanical stirrer (Note i) are placed 2.5 1. of 95 per cent ethyl alcohol, 872 g. (3.5 moles) of piu e -dodecyl bromide (Org. S Ti, 15, 24) and 278 g. (3.85 moles) of powdered 90 per cent potassium cyanide (Note 2). The mixture is refluxed for fifteen hours, with stirring, in a water bath (Note 3). At the end of this time another 278-g. portion of potassium cyanide is added and the mixture refluxed, with stirring, for fifteen hours longer. The flask is allowed to cool, and a solution of 670 g. of 90 per cent potassium hydroxide in i 1. of water is added (Note 4). The solution is refluxed and stirred for thirty hours. The flask is fitted with a head for steam distillation (Note 5), and steam is passed in until foaming prevents further distillation. When the flask has cooled somewhat, the steam inlet is replaced by a separatory funnel with a stem reaching to the bottom of the flask, and 1500 cc. of concentrated hydrochloric acid (sp. gr. 1.18) or the equivalent amount of more dilute acid is added. The flask is shaken occasionally to prevent stratification of the hydrochloric acid. The dropping fimnel is then replaced by the steam... 

In clinical practice we used for risk stratification clinical, electrocardiographic, enzymatic variables and also imaging techniques and coronary angiography. In each case the parameters maybe used isolated or clustered in a score. The scores of risk may be formed only by clinical parameters or may be a mixture of clinical and other non-clinical parameters. The most useful data are the following ... 

It should be added that polyester resins are toxic, and with poor stirring of the mixture components the probability of stratification and level-by-level curing of the composition is high. 

The solid material obtained in Step 3 shall be weighed and placed in an extractor with 16 times its weight of deionized water. Do not allow the material to dry prior to weighing. For purposes of this test, an acceptable extractor is one which will impart sufficient agitation to the mixture to not only prevent stratification of the sample and extraction fluid but also insure that all sample surfaces are continuously brought into contact with well mixed extraction fluid. 

The term compatibihzing was defined by Gaylord in 1966 (133) as rendering a mixture of two or more polymeric materials permanently miscible so as to form a homogeneous composition that has useful plastic properties and which does not separate into its component parts. Actually, in his definition the term miscible was not appropriate and another term uniform would be better. A few years later, he defined another term compatibilization as absence of separation or stratification of the components of the polymeric alloy during the expected useful lifetime of the product (134). 

Ortmann, R., Arndt, S., Raimann, J., Grzeszik, R., and Wurfel, G. (2001) Methods and analysis of fuel injection, mixture preparation and charge stratification in different direct injected SI engines. SAE Paper 2001-01-0970. 

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