Fluid flow principles (Pressure drop, ΔP)

Pressure drop ExplanationPressure drop across equipment

1. Across reactor The pressure drop across a CSTR is insignificant as the feed at inlet and product at outlet are continuously moving in and out of the reactor respectively, simultaneously. If it were to be considered, then it can be said that the pressure drop is influenced by the mass flow rate of the inlet. According to Alicat Scientific, Inc.,

Under laminar flow conditions, pressure drop is proportional to volumetric flow rate. At double the flow rate, there is double the pressure drop.

Under turbulent flow conditions, pressure drop increases as the square of the volumetric flow rate. At double the flow rate, there is four times the pressure drop.

Pressure drop decreases as common mode pressure increases.

Pressure drop increases as gas viscosity increases. Since increasing the temperature of the gas increases its viscosity, pressure drop also increases as gas temperature increases.

2. Across valvesPressure drop in pipes

1. Pipe friction In order to determine pipe friction, the first step is calculating the Reynold’s number. Then, the type of flow will be known (either laminar, transition or turbulent). With that information, by referring to the Moody Chart, the friction factor, f can then be identified. This is then used to determine the head loss and pressure drop. Head loss is express by Darcy -Weisbach equation (used only for horizontal pipes).

2. Pipe componentsPressure drop for phase

1. Pressure drop for gas

2. Pressure drop for liquid

Appendix

Darcy -Weisbach equation

1. horizontal pipes

∆ P=ρghL

2. Vertical pipe difference or elevation

h f=∆ z+∆ pρg

3. Pipe components

Pressure drop for gas

Pressure drop for liquid

Pressure drop across valves for gas and steam

Pressure drop across valves for liquids

Reference

1. http://www.alicat.com/alicat-blog/accuracy-and-repeatability/whats-up-with-pressure-drop/