Mixing rate evaluation

A fluorescent quenching experiment was devised to evaluate the rate of mixing of fluorescein and a quencher. Name an example of a quencher. Why did a simple mixing method of fluorescein and water not work to evaluate the mixing rate [466] (3 marks)... 

Further, mixing/turbulent diffusivity derived by considering that the mixing process in a liquid is caused by the random movement of inner substances based on the turbulent flow can also be used as an index for the evaluation of the local mixing rate. The mass balance in the flow field is written as... 

When tank mixes were evaluated, the BALAN Dry Flowable was first dispersed in the spray water (328 ppm hardness with iron) and then the other product was added. Table V describes the details of testing at a rate of 2.5 Ib/acre at 20 gal/acre with sparger-pipe agitation. After four repetitive evaluations in which the contents were sprayed out and in which there was no clean out between tankfuls, the screens were clear and there was no residue in the bottom of the tank. The system was not cleaned out between runs to better simulate continuous spraying in actual use. Table V also describes the same type of evaluation with a jet agitator rather than a sparger pipe. This resulted in little residue in the in-line screens and none on the bottom of the tank. 

An other approximation is to use the energy release rate evaluated on basis of the experimental as the critical energy release rate, since it is hardly dependant on the level of residual stress (see Table 6 as well as Fig, 7). This would give a critical energy release rate of about 650 J/m, Worth adding is that this value is only valid in mode I, and not in mixed... 

In order to gain quantitative insight about fluxes the mixing rate, Vm, must be evaluated. This requires knowledge of the concentration distribution of a chemical tracer that has a loiown time history or a built-in radioactive clock. To achieve this we use the steady-state equation, and the mass balance of dissolved inorganic carbon (DIG) and the naturally occurring (i.e. not bomb-produced) radioactive isotope of carbon, with a half hfe of 5730 y. 

The Da is extremely useful for initial evaluation of reaction conditions under which mixing effects must be considered. The reaction rate constant of the undesired reaction, A r2, can vary over several orders of magnitude. When experimental data are not available but the class of reaction is known, the magnitude of kR2 can be estimated within two orders of magnitude or less. The mixing rate in vessels should not vary by more than two orders of magnitude. With these bracketed values, upper and lower limits on Da can be readily estimated and used as a first measure of mixing sensitivity as follows ... 

Sections 6.3.1.4 and 6.4 on the use of the Damkoehler number concept, the need for effective location of a feed line may be evaluated from a comparison of nucleation and mixing rates. 

Scheme 6.6 Dushman reaction used for evaluation of mixing rate...

Bates TS, Kelly KC, Johnson JE, Gammon RH (1996) A re-evaluation of the open ocean source of methane to the atmosphere. J Geophys Res 101(D3) 6953-6961 Begemann F, Libby WF (1957) Continental water balance, ground water inventory and storage times, surface ocean mixing rates and worldwide water circulation patterns from cosmic-ray and bomb tritium. Geochim Cosmochim Acta 12 277-296... 

In terms of the chemical reactor, given a convex production rate expression, the mean production rate is greater than or equal to the production rate evaluated at the mean concentration, i.e, mixing the reactor contents lowers or does not change the overall production rate. 

In all of the work published to date the major concern has been with the description and evaluation of the blending characteristics of static mixers. In early discussions of mixing rate the concept of the number of sub-divisions of flow produced per static mixer element was used as an illustration of mixing rate. This was frequently interpreted as the hypothetical number of striations (r j) in a mixture pattern produced from equal volumes of segregated black and white materials. A relationship was proposed for the Kenics mixer. 

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