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A: Fluid Flow Experiments A1 - Friction Coefficient in TubesA2 - 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;
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water
Storagetank
pump
Buffertank
PI
PT ( 壓力計)
90º elbow Straight pipe
PT (壓力計接頭)
180º elbow
Globe valve
Orifice meter
45º elbow
flange Venturi meter
Ballvalve
Gatevalve
rot a
met
er
Expansion
Contraction
ReductionEnlargement
PI PI
T0 PT T0 PT
流體流動實驗裝置圖
Trap
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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;
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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
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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
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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
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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
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Pictures from Google to show different design of rotameter
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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
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Ultrasonic Flow Meter
non-invasive; two types: Doppler type (frequency shift ~ velocity) and transit time type (t ~ velocity) taken from Flow meter directory
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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);