How to calculate the pressure drop in a pressure vessel, when the following variables are known Flow rate, density or SG, Pressure, viscosity, Vessel ID, Inlet nozzle I.D
For a vessel the majority of the Dp is in the inlet/outlet. Since velocity is very limited in the vessel itself you could disregard pressure here. Any inlet or outlet devices (e.g. demisting) or internals etc. could also cause dP.