The most accurate method for calculating frictional pressure drop in both laminar and turbulent regimes is the :
= Weld joint strength reduction factor (for high temperatures; equals at lower temperatures)
). The pressure drop across the fitting is calculated as a function of velocity head:
While a pure PDF can’t run macros, a better resource includes (using Adobe Acrobat forms) for Darcy-Weisbach and hoop stress.
tn=3.311−0.125=3.310.875=3.78 mmt sub n equals the fraction with numerator 3.31 and denominator 1 minus 0.125 end-fraction equals 3.31 over 0.875 end-fraction equals 3.78 mm Step 3: Schedule Selection Compare calculated ) to standard ASME B36.10M wall thicknesses for NPS 6: Wall Thickness = Schedule 80: Wall Thickness = The most accurate method for calculating frictional pressure
tnom≥3.6281−0.125=3.6280.875=4.146mmt sub n o m end-sub is greater than or equal to the fraction with numerator 3.628 and denominator 1 minus 0.125 end-fraction equals 3.628 over 0.875 end-fraction equals 4.146 space mm Step 5: Final Pipe Schedule Selection
Maximum 10% of the absolute operating pressure across the total run. 3. Fittings, Valves, and System Resistance
Pressure drop is the decrease in fluid pressure as it flows through a piping system. Every straight pipe run, elbow, tee, valve, and fitting creates frictional resistance that consumes energy and reduces downstream pressure. Accurate pressure drop calculation is fundamental to sizing pumps, compressors, and control valves.
Sizing a pipe is an engineering trade-off. Choosing a small pipe diameter reduces initial material costs but dramatically increases ongoing energy consumption (pumping costs) due to high pressure drops. Conversely, large pipes reduce energy costs but incur prohibitive capital expenses for piping, valves, supports, and installation. Accurate pressure drop calculation is fundamental to sizing
Re=ρvDμRe equals the fraction with numerator rho v cap D and denominator mu end-fraction = Fluid density ( kg/m3kg/m cubed = Fluid velocity ( = Inside diameter of the pipe ( = Dynamic viscosity ( Laminar Flow (
Once the hydraulic diameter is known, the pipe wall thickness must be checked to ensure it can safely contain the internal operating pressure. Codes and Standards
: Higher material and installation costs but lower friction and power consumption. Sizing Factors
hf=f⋅LD⋅v22gh sub f equals f center dot the fraction with numerator cap L and denominator cap D end-fraction center dot the fraction with numerator v squared and denominator 2 g end-fraction To convert head loss ( in meters) to pressure drop ( in Pascals): dynamic viscosity ( )
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Sizing a pipe involves balancing capital expenditures (the cost of larger pipes and valves) against operating expenditures (the energy cost of pumping fluids against friction). Step-by-Step Sizing Process Gather density ( ), dynamic viscosity ( ), vapor pressure ( Pvcap P sub v ), and operating temperature/pressure. Establish Volumetric Flow Rate ( ): Calculated from the plant material balance.
Systems must be sized so that downstream equipment receives fluid at the required operating pressure.