The description given here is a gross over-simplification, but it does give a qualitative representation of the salient features of turbulent mixing. Interaction between these primary eddies and slow moving streams produces smaller eddies of higher frequency which undergo further disintegration until, finally, viscous forces cause dissipation of their energy as heat. Such eddies are anisotropic and account for much of the kinetic energy present in the system. In a mixing vessel, it is reasonable to suppose that the large primary eddies, of a size corresponding approximately to the impeller diameter, would give rise to large velocity fluctuations but would have a low frequency. Turbulent flow may be considered to contain a spectrum of velocity fluctuations in which eddies of different sizes are superimposed on an overall time-averaged mean flow.

If the Reynolds number of the main flow is sufficiently high, some insight into the mixing process can be gained by using the theory of local isotropic turbulence. Turbulent flow is inherently complex, and calculation of the flow fields prevailing in a mixing vessel is not amenable to rigorous theoretical treatment. Mixing is fastest near the impeller because of the high shear rates and associated Reynolds stresses in vortices formed at the tips of the impeller blades furthermore, a high proportion of the energy is dissipated here. Ultimately, homogenisation at the molecular level depends on molecular diffusion, which in general takes place more rapidly in low viscosity liquids. Mixing by eddy diffusion is much faster than mixing by molecular diffusion and, consequently, turbulent mixing occurs much more rapidly than laminar mixing. Turbulence may occur throughout the vessel but will be greatest near the impeller. The inertia imparted to the liquid by the impeller is sufficient to cause the liquid to circulate throughout the vessel and return to the impeller.

s), the flows generated in mixing vessels with rotating impellers are usually turbulent.

Richardson, in Non-Newtonian Flow in the Process Industries, 1999 (ii) Turbulent mixing The sensitivity of viscosity to temperature is higher in real gases than ideal gas behaviors.

The real gases viscosity tends to increase with an increase in pressure. However, there is some discrepancy between real gases and ideal gases behaviors. For the gas viscosity, kinetic theory of ideal gases explains that the dynamic viscosity of ideal gases is proportional to the square root of the absolute temperature and not sensitive to the pressure. The CO 2 can dissolve in oil at high pressure condition and the mobility of oil improves. During the in-situ combustion, a large quantity of CO 2 forms in reservoirs. In addition, the dissolution of gases such as CO 2 can reduce the viscosity of liquid hydrocarbons. This contribution by heat enables to deploy the exploitation of thermal recovery method in mainly heavy oil reservoirs. Because higher temperature makes both slightly less viscous water and much lesser viscous oil, the improved viscosity contrast favors relatively the oil flow rather than water flow. The more viscous the fluid, the more sensitive it is to the temperature change. Most liquids suffer the exponential relationship ( Seeton, 2006) between temperature and viscosity rather than linear form ( Fig.В 6.1). The viscosity decreases with an increase in temperature. The liquid viscosity is highly affected by the heat.

Viscosity units