LECTURE 3
Properties Of Fluids
By Dr. Mohamed Fekry
2 nd Sem.1434
PROPERTIES OF FLUIDS
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Density (r) and Specific Volume (v)
Specific Gravity (SG)
Specific Weight (g)
Density of ideal gas
Coefficient of Compressibility (k)
Coefficient of Volume Expansion (b)
Viscosity (m)
Surface Tension (s)&
Capillary Effect (h)
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OBJECTIVES
When you finish reading this chapter, you should be able
to: Have a working knowledge of the basic properties of
fluids and understand the continuum approximation
 Have a working knowledge of viscosity and the
consequences of the frictional effects it causes in fluid flow
 Calculate the capillary rises and drops due to the surface
tension effect
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Density (r): mass per unit volume
Specific Volume (v): volume per unit mass
…………… m3/kg
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Specific Gravity, or relative density (SG):
the ratio of the density of a substance to the density of some
standard substance at a specified temperature (usually water at
4°C, for which rH2O 1000 kg/m3)
- Dimension or dimensionless quantity?
r w = 1 g/cm3 = 1 kg/l
SG s = r s in units of g/cm3 or kg/l
the numerical value of the specific gravity of a
substance is exactly equal to its density in g/cm3
or kg/L
Hydrometer
A direct-reading instrument for indicating the density or
specific gravity of liquids is called hydrometer.
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- What would you
conclude about
substrates with specific
gravity less than 1.0?
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specific weight (g):The weight of a unit volume of a
substance
g = w/v = m.g/v = (m/v) . (g) = r g
The specific weight of water for ordinary temperature
variations = 62.4 lb/ft3, or 9.81 kN/m3.
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Density of Ideal Gases
The density of a substance, in general, depends on temperature and
pressure.
The density of most gases is proportional to pressure and inversely
proportional to temperature.
Any equation that relates the pressure, temperature, and density (or
specific volume) of a substance is called an equation of state.
The simplest and best-known equation of state for substances in the
gas phase is the ideal-gas equation of state, expressed as
Where:
P is the absolute pressure,
v is the specific volume,
T is the absolut) temperature, in the SI is the Kelvin scale
r is the density, and
R is the gas constant.
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Temperature conversion
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Example: If the constants for the following gases are:
R air = 287 J/Kg.K
R H2 = 4127
R CO2 = 189
Find the densities and the specific weights at 200 Kpa and 37.8 °C
Solution
Ideal gas law
r = P/RT
r = (200000)/(37.8 + 273).R = 643.2 / R (kg/m3)
g = r. g =
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