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Unit Operation Lab

Unit Operation Lab. K S Chou Ch E, N T H U. A: Fluid Flow Experiments A1 - Friction Coefficient in Tubes A2 - Flowmeters.  Types of flowing fluid: gas (natural gas), liquid (tap water), solid, bubbled liquid, slurry, gas-solid (fluidization), solid-liquid-gas system;

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Unit Operation Lab

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  1. Unit Operation Lab K S Chou Ch E, N T H U

  2. A: Fluid Flow Experiments A1 - Friction Coefficient in Tubes A2 - Flowmeters • Types of flowing fluid: gas (natural gas), liquid (tap water), solid, bubbled liquid, slurry, gas-solid (fluidization), solid-liquid-gas system; • Fluid flow: transportation • friction coefficient, viscosity, pressure drop, power required for transportation, choice of pumps, choice of tubes;

  3.  Fermentation reactor: one example of solid-liquid-gas system

  4. Fundamentals • Pipes are connected by: screws, welding, flanges; • materials: many choices such as steel, PP, PVC, glass, ceramics etc; • Pipe specs: size, wall thickness; nominal value for diameter may have different meaning for different pipes (outside, inside, none above); often follow some standards such as IPS, NPS; • Selection of pipe size: mainly due to cost: material, installation, flow rate, density characteristics; power required; (cost ~ dia^1.5; power ~ dia^-4.8) • Fluids are powered by pumps;

  5. Friction Coefficient • Bernoulli eq. (incompressible fluid, steady state condition) • Pa/ + g Za/gc + a Va2/2gc = Pb/ + g Zb/gc + b Vb2/gc + hf • pressure energy + potential energy + kinetic energy + frictional loss = total energy • simplest case: pressure drop = frictional loss • (Pa – Pb)/ρ = hf

  6. fD = 4 fF = 4 Fw/(A K) • where fD = Darcy’s friction factor; fF = Fanning friction factor; Fw = friction force; A = area of flow; K = kinetic energy/vol; • Taking circular tube as example: fF = (-ΔP g D) / (2 ΔL ρV2)…. Get data on the right hand side to calculate friction factor • In general: f = f(e/D, Re) e = surface roughness of tube wall; Re = d u ρ/; changes in both velocity and viscosity would change Re • For laminar flow: fD = 4 fF = 64/Re • For turbulent flow: (depending on smoothness of tube) ex. smooth tube 1/√fF = 4.06 log (Re √fF) + 2.16

  7. Function of surface roughness

  8. fittings: splits, bend, elbow, U-tube, flanges, valves, etc • different loss due to different designs • empirical correlations are used mostly • General expression hf = Kf Va2/2 gc, with Kf as an empirical friction coefficient • Total friction loss = friction in straight tube + due to contraction + due to expansion + due to various fittings for this experiment

  9. 圖A2-2 銳孔流量計之流出係數與Re關係。 其測壓點屬corner tap Various Flowmeters • orifice meter, Venturi meter, rotameter, etc. • discharge coefficient = f(Re); for orifice meter: Vo = Co √(2 gcP/) Co determined experimentally Co can be assume to be 0.61 for large Re

  10. Venturi flowmeter and its discharge coefficient Vo= Cv/√(1-4) √(2 g (ΔP/)  = (d/D) For well designed meter, Cv usually about 0.98 More expensive, more space;

  11. Pictures from Google to show different design of rotameter

  12. Other Types of Flowmeters  Magnetic flowmeter: used for dirty fluids or slurry, such as waste water; no moving part; based on Faraday principle: voltage generated E ~ V * B (magnetic field strength) * D (length of conductor) Taken from: Omega Engineering Technical Reference

  13. Ultrasonic Flow Meter • non-invasive; (intrusive) two types: Doppler type (frequency shift ~ velocity) and transit time type (t ~ velocity) • taken from Flow meter directory

  14. Universal flow monitors (UFM) webpage

  15. Consideration: Durability, pressure loss, control ability etc. Check valve: one direction flow

  16. Centrifugal pump Positive displacement pump Pump performance: (taken from Walrus webpage)

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