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Unit Operation Lab K S Chou Ch E, N T H U 1. A: Fluid Flow Experiments A1 - Friction Coefficient in Tubes A2 - Flowmeters  Types of flowing fluid: gas.

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Presentation on theme: "Unit Operation Lab K S Chou Ch E, N T H U 1. A: Fluid Flow Experiments A1 - Friction Coefficient in Tubes A2 - Flowmeters  Types of flowing fluid: gas."— Presentation transcript:

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

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; 2

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

4 4

5 5 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;

6 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

7  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)

8 8 Function of surface roughness

9  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

10 10 Various Flowmeters  orifice meter, Venturi meter, rotameter, etc.  discharge coefficient = f(Re); for orifice meter: Vo = Co √(2 gc  P/  ) 圖 A2-2 銳孔流量計之流出係數與 Re 關係。 其測 壓點屬 corner tap

11 11 Venturi flowmeter and its discharge coefficient Vo= Cv/√(1-  4) √(2 g (ΔP/  )  = (d/D)

12 12

13 13 Pictures from Google to show different design of rotameter

14 14 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)  Claim to account for 20% of all flowmeters Taken from: Omega Engineering Technical Reference

15 15 Ultrasonic Flow Meter  non-invasive; two types: Doppler type (frequency shift ~ velocity) and transit time type (  t ~ velocity)  taken from Flow meter directory

16 16 Electromagnetic Flowmeters CEP, May 2010  Advantages: no pressure drops; no moving parts subject to wear; linear output over a wide range of velocities;  Disadvantage: fluid has to be conductive; often have temperature limits; (mho = 1/ohm)  One of the key technology: keeping magnetic field constant ; electrode material will contact process fluid and cleaning fluids (compatible issue);

17 17 Universal flow monitors (UFM) webpage

18 18

19 Consideration: Durability, pressure loss, control ability etc. Check valve: one direction flow 19

20 20 Pump performance: (taken from Walrus webpage)


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