Ch 1-6 summary.docx - CBE 218 Chemical Engineering II Text...

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CBE 218 Chemical Engineering II Text book: Fluid Mechanics for Chemical Engineers, Noel de Nevers Summary (Chapters 1-6) Chapter 1 Introduction Fluid basics Fluid Mechanics is study of forces and motions in a fluid. Fluids: gases and liquids Gases : air, helium, hydrogen, nitrogen, carbondioxide, carbon monoxide etc Liquids : water, alcohols, gasoline, diesel, oils, milk etc Solids: steel, diamond, papers Complex fluids : toothpaste, bread dough, grease, gelatin, peanut butter, mayonnaise Viscosity basics Shear Stress ( ) = shear force/area Shear rate = dV/dy = -m dV/dy (velocity ‘V’ decreases with increase in ‘y’) (Newton’s law of viscosity) Units for viscosity viscosity = Poise= 1 g/(cm.s) =0.1 Pa.s; Centipoise (cP) = 0.01 P Pa = N/m 2 = kg.m/s 2 . 1/m 2 = kg/(m. s 2 ) P = 0.1 Pa.s = 0.1 kg/(m. s 2 ). S = 0.1 kg/(m.s) Kinematic viscosity ( ) = / Units of kinematic viscosity: cSt (centistoke) 1 cST = (1 cP)/(1 g/cm 3 ) = 10 -6 m 2 /s = 1.08 * 10 -5 f 2 /s  Fluid types Fluid types: Newtonian (time independent) and non-Newtonian Newtonian fluids: For these fluids shear stress is linearly proportional to shear rate. Non-Newtonian fluids: For these fluids shear stress is NOT linearly proportional to shear rate. Pseudoplastic (shear thinning): Viscosity decreases with increasing velocity gradient. Dilatent (shear thickening): Viscosity increases with increasing velocity gradient. Bingham: These fluids resist a small shear stress indefinitely but flow easily under larger stresses. Thixotropic (time dependent): Viscosity can DECREASE with time. Rheopectic (time dependent): Viscosity can INCREASE with time. Pressure (compressive stress) Pressure force units for conversion 1 lbf = 1 lbm . 32.2 f/s 2 1 kgf= 1 kgm. 9.8 m/s 2 Pressure = Force/Area Pressure force = Pressure * Area
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Absolute pressure - p abs - is measured relative to the absolute zero pressure - the pressure that would occur at absolute vacuum.
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