Fluid Mechanics for Chemical Engineering

Chapter 4

Steady-State Hydraulic Circuits

4.1. Operating point of a hydraulic circuit

A hydraulic circuit encompasses all the elements that enable fluid circulation in an industrial system. It is made up of different elements such as:

– Pipes.

– Pumps to generate the flow.

– Blocking members, such as valves.

– Reactors.

The purpose of sizing a hydraulic circuit is usually to select the members of the circuit (pump, pipes, etc.) that enable the desired flow rate to be maintained in the circuit, for a known head change between the inlet and the outlet of the circuit.

In order to size a circuit, the engineer should consider two aspects:

1. Evaluate the head change in the circuit. Recall that the head is the fluid’s energy per unit volume, and that this energy is the sum of the pressure energy, kinetic energy, and potential energy (Chapter 2, section 2.2):

[4.1]

(z is the altitude of the fluid in the direction opposite to that of gravity). Evaluating the head variations provides insight into the energy losses associated with the various elements in the circuit. Energy losses per unit pipe length (referred to as “regular” or “frictional” head loss) are low in straight pipes, but cannot be neglected when pipe lengths are significant. Locally, large energy losses are also associated with particular items (valves, bends, cross-section expansions, etc.). These head drops, referred to as ...