Turbulent flow creation

X 109 4 onwards 4 Big Bang expansion of universe - creation of space and time Formation of mass energy Turbulent flow Galaxies, stars Basic atoms in stars Heavier atoms in stars (nuclear reactions see Fig. 8.2)... 

In microfluidics, segmentation by stirring or creation of turbulent flow can not be expected because Reynolds numbers do not exceed 2000 (the limit for turbulent flow). Some methods for mixing in microfluidics have been developed. 

The most attractive and requiring detailed studying problem is to reveal the conditions of formation in tubular turbulent apparatus of novel unmatched quasi-plug-flow mode in turbulent flows at the expense of creation of corresponding hydrodynamic conditions in mixing zone and purposeful variation of apparatus construction [1,28,42-44]. 

Analysis of conditions of creation of the most important for production quasi-plug-flow mode and mathematical modelling of mixing process of two reacting liquids in the framework of K-e turbulence model have shown [31], that quasi-plug-flow mode formation in turbulent flows under fast chemical reactions is reached at the expense of production of initial components mixture and/or... 

The quasi-plug flow mode (plane front of reaction) is the most important condition for commercial production. The conditions of its creation were analysed and the mixing process of the two reacting liquids, within the K-e turbulence model, was mathematically simulated [7]. The results showed that during fast chemical reactions, the quasi-plug flow mode in turbulent flows is obtained due to the carry-over of the initial component mixture and/or reaction products into the reactant introduction... 

The understanding of mixing is essential for the optimization of a micro-TAS. Mixing procedures, well known from the macroscopic world, such as stirring or creation of turbulent flow cannot be scaled down due to the strong tendency of microfluidic flows to be laminar. 

It is commonly recognized that the turbulent flow is composed of eddies (swirling fluid) in different size, among which the large-scale eddies are responsible to the creation and transport of Reynolds stress, which is closely related with the type of flow and boundary conditions, while the small-scale eddies play the role of dissipation in the action with viscous force. 

Impediments to water flow resulting from inadequate equipment design or lodgement of foreign objects in the tubes can exercise a dramatic effect on the erosion-corrosion process. Much of this influence is linked to the creation of turbulence and the simple increase in fluid velocity past obstructions. The importance of these factors is quickly recognized when the phenomenon of threshold velocity is considered. 

The creation of eddies in a combustion zone is dependent on the nature of the flow of the unburned gas, i. e., the Reynolds number. If the upstream flow is turbulent, the combustion zone tends to be turbulent. However, since the transport properties, such as viscosity, density, and heat conductivity, are changed by the increased temperature and the force acting on the combustion zone, a laminar upstream flow tends to generate eddies in the combustion zone and here again the flame becomes a turbulent one. Furthermore, in some cases, a turbulent flame accompanied by large-scale eddies that exceed the thickness of the combustion wave is formed. Though the local combustion zone seems to be laminar and one-dimensional in nature, the overall characteristics of the flame are not those of a laminar flame. 

Experiments on transition for 2D attached boundary layer have revealed that the onset process is dominated by TS wave creation and its evolution, when the free stream turbulence level is low. Generally speaking, the estimated quantities like frequency of most dominant disturbances, eigenvalues and eigenvectors matched quite well with experiments. It is also noted from experiments that the later stages of transition process is dominated by nonlinear events. However, this phase spans a very small streamwise stretch and therefore one can observe that the linear stability analysis more or less determines the extent of transitional flow. This is the reason for the success of all linear stability based transition prediction methods. However, it must be emphasized that nonlinear, nonparallel and multi-modal interaction processes are equally important in some cases. 

Water falling and splashing over a series of steps or trays can result in effective aeration. Aeration is mainly achieved hy the mixing of air with the falling water in the underlying steps. The creation of turbulence in water is important, because better aeration results are obtained by increasing the water flow to an optimal rate. Cascade aerators do not require inlet heads thus, relatively large quantities of water can be treated in a comparatively small area, and they are easy to clean. The structure is simple and inexpensive. 

The creation of eddies in a combustion zone is dependent on the nature of flow of the unburned gas, i.e., the Reynolds number. If the upstream flow is turbulent, the... 

Formation of quasi-plug-flow mode in tubular turbulent apparatus and consequently of optimal conditions for application of external heat removal requires creation in apparatus volume of high turbulent mixing level determining by value of Dt, and Dt significantly depends on reaction zone geometry (see 3.1.2). 

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