Definition of a Fluid

• What is a fluid?

  * Substances that deform continuously under shear stress.
  * Includes both liquids and gases.

• Key Physical Properties

Below are the fundamental physical properties every fluid technician, student, or engineer should understand:

a. Density (ρ)

* Mass per unit volume (kg/m³).
* Importance: Affects buoyancy, pressure calculations, and fluid dynamics.

b. Specific weight (ω)

*Defined as the weight per unit volume at the standard temperature and pressure

c. Specific volume (υ)

*defined as volume per unit of fluid.​

 *S.I unit is m³/kg

d. Viscosity (μ)

* Measure of fluid resistance to flow.

1. Dynamic Viscosity (Pa·s)
2. Kinematic Viscosity (m²/s)

* Affects laminar or turbulent flow characteristics.

e. Pressure (P)

* Force per unit area (Pa or N/m²).
* Types: Atmospheric, gauge, absolute, and vapor pressure.

f. Temperature (T)

* Influences most other physical properties (viscosity, density, surface tension).
* Units: °C, K

g. Specific Gravity (SG)

* Ratio of fluid density to that of water (dimensionless).

h. Compressibility (β)

* Change in volume under pressure.
* Gases: Highly compressible
* Liquids: Nearly incompressible

Measurement Techniques

Devices used:

• Hydrometer (Density)
• Viscometer (Viscosity)
• Manometer or Pressure Transducer (Pressure)
• Thermocouple or Thermometer (Temperature)

Applications

• Engineering (pipe flow, pumps, turbines)
• Medicine (blood flow, IV drips)
• Environmental science (air and water quality)
• Industrial processes (mixing, heat exchange)