Introduction to Fluid Machineries and Hydraulics

The field of mechanical and industrial engineering is very wide. One of the sub-branches of this field is the study of Fluid Machineries. When you study fluid machineries, you will be encountering the following important terms, topics and concepts.

Pre-requisite subjects and concepts

Before you study fluid machineries, you should have taken up fluid mechanics first for you to understand the whole discussion. As mentioned above, fluid machineries deal with machines that use fluids as medium. So, you must know the basic properties of fluids:

• Density – the ratio of the fluid mass to the fluid volume
• Specific weight – the weight per unit volume of the fluid
• Specific gravity – a dimensionless ratio of the density of the fluid to the standard density. Typically, air or water is being used as standard density (reference)
• Viscosity – the resistance to shearing force or flow.
• Surface tension – the work necessary to transfer the molecules from the inside of the fluid (commonly liquid) to the surface to create one new unit area of the surface.
• Capillarity – rise and fall of a fluid. Capillarity is essential in small tubes but is negligible in larger diameter tubes.
• Bulk modulus of elasticity – the ratio of the change in pressure to the corresponding volume change per unit of the volume.

When it comes to computations in this subject, Bernoulli’s principle and equation is the common concept being used. This principle was derived from the law of conservation of energy, which states that in a system of steady flow along a streamline, the sum of all forms of mechanical energy will be the same at all points. Thus, making the sum of kinetic energy and potential energy remain constant.

Basic concepts of fluid machinery

Fluid machinery is the study of machines which use fluid as the major working substance. Note that when we talk about fluids, it could either be a gas (typically air or oxygen) or a liquid (typically water), as long as it has the ability to flow.  The main common purpose of fluid machines is to transfer the mechanical energy of the rotor into flow energy (kinetic energy).

Common types

Fluid machineries are often classified according to the working substance it uses. Basically, when the fluid used is gas, the machine is commonly referred as a fan (a blower or exhauster), or a compressor. On the other hand, if the fluid used is liquid, it is commonly termed as hydraulic machines or pump.