How to Determine Pressure Drop in Pipe Fitting with Cross Section Change?
- The pressure drop in a pipe fitting is a result of various factors including fluid velocity, pipe geometry, viscosity of the fluid, and the type of fitting being used. The pressure drop is essentially the difference in pressure between the inlet and outlet of the fitting due to these factors.
- There are several methods to calculate pressure drop in pipe fittings, and the appropriate method depends on the specific situation and the accuracy required. Here are a couple of commonly used methods:
Darcy-Weisbach Equation:
- This is one of the most widely used equations for calculating pressure drop in pipe fittings.
- This is given on the webpage for pressure drop through pipe based on Reynolds number
- The equation is given by:
Where:
- ΔP is the pressure drop across the fitting (Pa)
- f is the Darcy friction factor (dimensionless)
- L is the length of the fitting (m)
- D is the diameter of the fitting (m)
- ρ is the density of the fluid (kg/m³)
- V is the velocity of the fluid (m/s)
- The Darcy friction factor (f) depends on the Reynolds number and the roughness of the pipe walls. You need to refer moodys factor
- This equation is suitable for both laminar and turbulent flow.
Coefficient (C)-value Method
- This method involves using C-values (also known as resistance coefficients) to represent the pressure drop caused by various types of fittings.
Each type of fitting has an associated K-value that is determined experimentally. The pressure drop across the fitting is then calculated using the equation:
ΔP= C*K*V^2
Where:
-
- ΔP is the pressure drop across the fitting (Pa or mm of Water column )
- C is the pressure loss coefficient (dimensionless)
- K is the correction factor (the unit conversion factor), roughness factor, temperature change factor
- V is the velocity of the fluid (m/s)
- This method is simpler to use compared to the Darcy-Weisbach equation, but it may not be as accurate in all situations
- Remember that these equations provide approximations and are based on certain assumptions. They might not account for all complexities such as turbulence, heat transfer, and specific flow characteristics.
- For accurate results, it’s recommended to consult engineering handbooks, and software tools, or seek guidance from experts in fluid dynamics and piping systems.
Calculation of Pressure Drop in Fitting
- Enter the input value from your pipe fitting
- V is the average inlet velocity (m/s)
- ρ is the Density of fluid (kg/m3)
- C is the pressure Loss coefficient (dimensionless)
- Note the pressure Loss coefficient from the following tables
Pressure Loss Coefficient Factor for Piping
- Various types of pipe fitting are given as standard geometry. You can refer ASHRAE handbook or API 560 for more details on loss coefficient
- Pressure loss coefficient for Internal flow with obstacles
- Pressure Loss coefficient for internal flow
Reference
- Pressure Drop in Pipes and Duct by ASHRAE Ducting,
- ASHRAE Chapter 34, Duct Design based on pressure Drop