tailieunhanh - Intro to Practical Fluid Flow Episode 8

Tham khảo tài liệu 'intro to practical fluid flow episode 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Non-Newtonian slurries 131 Figure Friction factor for Bingham plastics plotted against the dimensionless fluid velocity. Use this plot when the PGDTF and the fluid velocity are known A minimum value of PGDTF is required to initiate flow of a Bingham plastic. The critical value of D for flow initiation is obtained when Tw Ty which gives D nit 2HC 1 3 and D must be greater than DUt for flow to take place. The existence of the critical value of D is evident from Figure where the curve of si against D approaches the critical value asymptotically at each value of He. When the friction factor is plotted against D the curve approaches the critical value as a vertical asymptote as shown in Figure . Other dimensionless groups that are useful are Q xPGBTF X 0 V T . Irnrp 5-52 si PB X PGDTF The following illustrative examples illustrate the methods. Illustrative example An application requires the slow removal of a dense laterite slurry from a thickener through a 7-cm diameter pipe. Calculate the minimum pressure 132 Introduction to Practical Fluid Flow Figure Data input screen for the calculation of the friction factor for a Bingham plastic. D is the independent variable gradient required to initiate flow in the pipe. What is the largest pressure gradient for which the flow remains laminar Calculate the flowrate through the pipe under a pressure gradient of 10kPa m see Figure . Bhattacharya et al. 1998 have measured the rheological properties of these slurries which behave approximately as Bingham plastics. Data Solids concentration by weight Cw 41 Maximum settled concentration by weight cw max dso for the solid particles pm. Density of solid p 3700 kg m3. pH of the slurry . Surface area per unit volume of solids So X 106 m2 m3. The coefficient of plastic viscosity is related to the concentration in the slurry by log10 PB wmax The yield stress is related to the solid concentration of the slurry by log1 l TỴ

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