Decreasing rate period flow stress

If flocculation occurs slowly, the viscosity, measured at low rates of shear, increases with time during the rest period after an efficient shearing. When this happens the paint is said to be thixotropic. If there is no dependence on time or on the previous treatment of the paint and if the viscosity decreases as the rate of shear increases, then the paint is said to be pseudo-plastic. If there is a minimum stress required before any flow can occur at all, the viscosity behaviour is said to be plastic. All these types of behaviour are, of course, contrary to Newton s equation and are grouped together under the heading of non-Newtonian viscosity. 

Surge is an instability of flow through compressor which appears as a periodical sweep. This phenomena causes a lot of noise, a sudden increase in temperature, an increase in blades stress and mechanical damages. The phenomena is due to a decrease in flow rate at specific speed and as a result of inability of fluid to pass over from current pressure ratio. In this situation return flow is appeared also. It usually starts with period stall and with further reduction in flow rate which leads to surge. Necessary condition for occurrence of surge is to be at positive... 

Betsed on laboratory test loop measurements the kaolin and fluidic ash slurries can be determined as time independent non-Newtonian yield pseudo-plastic suspensions. On the contrary a considerable effect of shearing during initial period of flow in pipe was found out for fly ash-gypsum mixture, see Fig. 2. However, after a relative short time about one hour, the decrease of pressure losses finished and slurry became stabilised. This behaviour is probably due to physico-chemical activity of ash and gypsum after mixing with water. The Fig. 3 shows plot of wall shear stress t, versus pseudo-shear rate (8 V/D) for the kaolin slurry flow in three different pipes and for representative ash-water mixtures in pipe of diameter D = 17.5 mm. The transition between laminar and turbulent flow is shown by the steep change in slope of the flow curves. 

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