Automodel Mode of Reaction Mixture Flow

A major problem in the solution synthesis of polymers is a one to three orders of magnitude increase of reaction mixture viscosity upon increasing the polymer concentration in a solution. For example, at 295 °C, the dynamic viscosity of cis-, 4-isoprene ruhher solutions in isopenthane is 90 P for 10%, 170 P for 13%, and 480 P 

It is very interesting and important practically that the viscosity of a liquid does not influence the motion of the major part of a medium in large-scale and highly turbulent flows [37, 38]. The flow pattern is, in this case, automodel in relation to viscosity. Its 

in particular, is demonstrated by the pressure loss in liquid flows within cylindrical tubular channels, where Ap is a function of Re in the laminar mode (Re 2300) and is independent of channel wall roughness [38]  

Re = (4-100) X 10 in a turbulent mode. The pressure drop Ap in the automodel flow area in relation to Re becomes independent of the hydrodynamic mode of the liquid however, it is still influenced by the roughness of the cylindrical channel walls  

Where L is the length of the tubular device, Sis the relative wall roughness, which is the ratio of the average height of asperities on an inner surface of the tubes (absolute roughness) to the tube diameter (the estimate of absolute roughness is 0.06-0.1 mm for new steel tubes, 0.1-0.2 mm for used but not corroded ones, and 0.5-2 mm [38] for contaminated old tubes). 

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The mixing of reactants on a microlevel is substantially influenced by the physical characteristics of liquid flows, in particular, by the density and viscosity (Figure 2.12). Increasing the viscosity and decreasing the density of the reactants fed into a tubular turbulent device, can result in the situation where the reaction mixture homogenisation will be limited by molecular diffusion, which is common in the case of polymer solutions. The analysis of Equations 2.26-2.28 makes it possible to propose the criterion for breaking the automodel mode of reaction mixture flow, i.e., reduction in the efficiency of tubular turbulent diffuser-confusor devices with an increase of the medium viscosity [29] ... 

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