# Pressure drop

Pressure drop is defined as the difference in pressure between two points of a fluid carrying network. Pressure drop occurs with frictional forces, caused by the resistance to flow, on a fluid as it flows through the tube. The main determinants of resistance to fluid flow are fluid velocity through the pipe and fluid viscosity. Pressure drop increases proportional to the frictional shear forces within the piping network. A piping network containing a high relative roughness rating as well as many pipe fittings and joints, tube convergence, divergence, turns, surface roughness and other physical properties will affect the pressure drop. High flow velocities and / or high fluid viscosities result in a larger pressure drop across a section of pipe or a valve or elbow. Low velocity will result in lower or no pressure drop.

## Calculation

Pressure Drop can be calculated using two values: the Reynolds Number, Re (determining laminar or turbulent flow), and the relative roughness of the piping, ε/D.

$Re =\frac{Dv\rho}{\mu}$

Where D is the diameter of the pipe, v is the velocity of the fluid, ρ is the density of the fluid, and μ is the dynamic viscosity of the fluid. The relative roughness of the piping is usually known; by cross referencing the Reynolds number with the relative roughness, the friction factor, f, is calculated.

$f=\frac{\Delta P \frac{\pi R^{2}}{2\pi R \Delta L}} {\frac{1}{2}\rho v^{2}}$

Where solving for ΔP will allow for the calculation of pressure drop through a pipe.[1][2]

## References

1. ^ Geankoplis, C. J. (2003). Transport Processes and Separation Process Principles. Upper Saddle River, NJ: Prentice Hall Professional Technical Reference.
2. ^ Welty, James (2008). Fundamentals of Momentum, Heat, and Mass Transfer. United States: Hamilton Printing.