Part V — Fluid Mechanics and Hydraulic Machines

Chapter 5: Fluid Properties, Flow and Hydraulic Machinery

5.1 Properties of Fluids

Density (ρ) is mass per unit volume; for water, standard density is 1000 kg/m³. Viscosity is a fluid's resistance to shear/flow; kinematic viscosity (ν) is the ratio of dynamic viscosity to density. Specific gravity is the ratio of a fluid's density to the density of a reference fluid (water for liquids, air for gases).

5.2 Fluid Flow Concepts

Bernoulli's Theorem (energy conservation for ideal, incompressible, non-viscous fluid flow) states that the sum of pressure head, velocity head, and elevation head remains constant along a streamline. The Continuity Equation (A1V1 = A2V2) expresses conservation of mass for incompressible flow — as area decreases, velocity increases. Flow is classified as laminar (Reynolds Number generally below ~2000 in pipes) or turbulent (Reynolds Number generally above ~4000 in pipes).

5.3 Hydraulic Pumps

A centrifugal pump uses a rotating impeller to add kinetic energy to a fluid, converting it to pressure energy, and is the most widely used type of pump for moving liquids in industrial and municipal applications, well-suited to high flow rates at moderate heads. A reciprocating pump uses a piston/plunger moving back and forth within a cylinder (positive displacement principle) and is better suited to applications requiring high pressure at relatively low flow rates.

5.4 Hydraulic Turbines

Hydraulic turbines convert the energy of flowing/falling water into mechanical (rotational) energy, primarily for power generation. The Pelton wheel (an impulse turbine) is used for high head, low flow-rate applications, where water strikes curved buckets on a wheel via one or more jets at atmospheric pressure. The Francis turbine (a reaction turbine) is used for medium head, medium flow-rate applications and is the most widely used hydraulic turbine type worldwide. The Kaplan turbine (a reaction, propeller-type turbine with adjustable blades) is used for low head, high flow-rate applications.

5.5 Practice Set — Fluid Mechanics & Hydraulic Machines (14 MCQs)

1. The standard density of water is approximately:
   (a) 100 kg/m³ (b) 500 kg/m³ (c) 1000 kg/m³ (d) 2000 kg/m³
2. Bernoulli's Theorem states that pressure head, velocity head, and elevation head sum to a value that is:
   (a) Zero (b) Constant along a streamline (c) Always increasing (d) Dependent only on pipe material
3. The Continuity Equation (A1V1 = A2V2) expresses conservation of:
   (a) Energy (b) Mass (c) Momentum only (d) Pressure
4. Laminar pipe flow is generally associated with Reynolds Numbers:
   (a) Below ~2000 (b) Above ~4000 (c) Exactly 3000 (d) Above 10,000
5. A centrifugal pump uses a rotating impeller to convert kinetic energy into:
   (a) Pressure energy (b) Chemical energy (c) Thermal energy directly (d) Nuclear energy
6. A reciprocating pump operates on which basic principle?
   (a) Centrifugal force (b) Positive displacement, via a piston/plunger (c) Magnetic induction (d) Bernoulli's principle exclusively
7. A reciprocating pump is generally better suited to applications requiring:
   (a) High flow rate at low pressure (b) High pressure at relatively low flow rates (c) Zero pressure output (d) Only gas compression
8. A Pelton wheel is classified as:
   (a) A reaction turbine (b) An impulse turbine (c) A centrifugal pump (d) A reciprocating pump
9. A Pelton wheel is best suited for:
   (a) Low head, high flow-rate applications (b) High head, low flow-rate applications (c) Zero head applications (d) Only compressed air systems
10. A Francis turbine is classified as:
    (a) An impulse turbine (b) A reaction turbine (c) A positive displacement pump (d) A centrifugal compressor
11. A Francis turbine is best suited for:
    (a) High head, low flow-rate applications (b) Medium head, medium flow-rate applications (c) Only zero-flow conditions (d) Compressed air applications only
12. A Kaplan turbine is best suited for:
    (a) High head, low flow-rate applications (b) Low head, high flow-rate applications (c) Medium head applications only (d) Only impulse-type operation
13. Kinematic viscosity is defined as the ratio of:
    (a) Dynamic viscosity to density (b) Density to dynamic viscosity (c) Pressure to velocity (d) Velocity to density
14. Specific gravity of a liquid is defined relative to the density of:
    (a) Air (b) Water (c) Mercury exclusively (d) Steel

Answer Key

1.(c)

2.(b)

3.(b)

4.(a)

5.(a)

6.(b)

7.(b)

8.(b)

9.(b)

10.(b)

11.(b)

12.(b)

13.(a) 14.(b)