Hydraulic Calculation - Ensure your fluid is delivered to the destination

In this article, i am going to briefly share about the basic principal of the process hydraulic calculation, one of the most important activity that a process engineer shall understand in the beginning of their career.

Say that we have a fluid located inside a vessel (Vessel-1) and we would like to displace it to the other location (Vessel-2) e.g. other separator or tank. First thing first, we have to understand that the driving force for a fluid to flow is the difference of pressure. The fluid will flow from the location with the higher pressure to the lower pressure location. To understand better, refer to the schematic below.

Basically, the hydraulic calculation is an activity to ensure that the available pressure at the upstream side (P1) is sufficient to flow the desired amount of fluid from one location to other location. Available P1 has to be higher than the downstream pressure (P2) plus the pressure drop between point-1 and 2  (ΔP) or on the other hand the target downstream pressure (P2) has to be lower than the available pressure (P1) minus the system pressure drop (ΔP). The pressure drop between Vessel-1 and Vessel-2 will be governed by following factor:

• Amount and properties of fluid flowing from point-1 and point-2 (related with volumetric rate and fluid velocity).
• Length of piping between point-1 and point-2 (L)
• Elevation difference between point-1 and point-2 (z1, z2)
• Size (inlet diameter - ID) of piping connecting vessel-1 and vessel-2 (This hydraulic calculation is also a follow up activity to define if the selected line size from the pipe sizing activity - refer to this article - is adequate for the system)
• Friction factor (f), related with the pipe roughness based on different type material.
• Pipe configuration and routing (related to number and type of valves, fittings, instrumental items) between point-1 and point-2. Some common type of pipe fittings are shown in the figure below. Each fittings could be characterized by a constant called "K-factor" or Equivalent Length (dummy length to be added to the length of piping as the characterization of a fitting). One of the most common used paper for the reference of the "K-factor" of a fitting is from Crane Technical Paper 410 or Perry Chemical Handbook. In general those factors is summarized with this following mechanic energy balance equation:
  

Typical Fittings in the piping system,  Source : http://www.lnktrading.com/

Some Typical Fittings K-factor, Source: Perry's Chemical Handbook 8th edition

• Equipment between the point-1 and point-2, for example if there is any air cooler, shell & tube heat exchanger, etc. This data usually stated on the equipment datasheet.

To understand better about this hydraulic calculation. I will develop a tutorial about how to perform a simple hydraulic calculation. Hopefully, this brief article could be helpful for you.

Latest update : 10 August 2020