Fluid Mechanics for Chemical Engineering

Chapter 6

Transient Flows in Hydraulic Circuits: Water Hammers

This chapter deals with the most common “water hammer” phenomenon, which refers to vibration and noise occurring when a valve is abruptly closed in a hydraulic circuit. This phenomenon results from a strong disturbance in the pressure field in the vicinity of the valve, which is generated when the circuit is closed. This disturbance then propagates along the circuit in the form of a sound wave, creating discomfort due to the associated noise. It may also have more significant consequences, such as damage to, or failure of, the circuit.

In this chapter, we describe the water hammer phenomenon and the preventative devices. We also obtain the estimates of the over-pressures and of the phenomenon’s characteristic times using simple methods.

Basically, this chapter introduces the notion of waves, particularly considering the case of sound waves. Waves have a fundamental role in fluid mechanics, irrespective of whether they are sound waves, surface gravity waves, or internal waves in oceanography and meteorology. Engineers cannot ignore wave propagation processes in fluid mechanics, and the wave water hammer phenomenon is an appropriate case study to introduce in this book on wave propagation in fluids.

6.1. Sound propagation in a rigid pipe

Let us consider the circuit depicted in Figure 6.1, composed of a straight rigid pipe of length L, with one end terminating at a valve, while the other opens into a tank of infinite ...