Short Notes: Fluid Properties | Short Notes for Mechanical Engineering PDF Download

 Page 1


Fluid Properties 
Fluid Mechanics is one of the important subjects in Mechanical Engineering for 
GATE and other exams. Fluid Properties chapter deals with topics such as Mass 
density, specific weight, viscosity and other properties which are basic for Fluid 
mechanics.
Fluid Properties fo r GATE Mechanical, ESE & Other Exams 
Ideal Fluid
Characteristics of Ideal Fluid
• A fluid having zero viscosity and zero surface tension.
• Ideal fluid is incompressible.
• There is no ideal fluid but air and water considered as ideal fluid.
Real fluid
Characteristics of real fluid
• Fluid having viscosity and surface tension.
• Real fluids are compressible
Properties of Fluid
Properties of fluid are
1. Extensive
2. Intensive
Intensive properties
• Intensive properties are independent from mass of system.
Page 2


Fluid Properties 
Fluid Mechanics is one of the important subjects in Mechanical Engineering for 
GATE and other exams. Fluid Properties chapter deals with topics such as Mass 
density, specific weight, viscosity and other properties which are basic for Fluid 
mechanics.
Fluid Properties fo r GATE Mechanical, ESE & Other Exams 
Ideal Fluid
Characteristics of Ideal Fluid
• A fluid having zero viscosity and zero surface tension.
• Ideal fluid is incompressible.
• There is no ideal fluid but air and water considered as ideal fluid.
Real fluid
Characteristics of real fluid
• Fluid having viscosity and surface tension.
• Real fluids are compressible
Properties of Fluid
Properties of fluid are
1. Extensive
2. Intensive
Intensive properties
• Intensive properties are independent from mass of system.
• Example - Temperature, pressure, density etc.
Extensive properties
• Properties which are depends on size or extent of a substance.
• Example - Total mass, Total volume, Total momentum etc.
Mass Density (p):
• Mass of fluid per unit volume at a given temperature and pressure.
• Mass density is function of Temperature and Pressure.
• Mass density for gases directly proportional to pressure and inversely 
proportional to temperature
• Practically, Mass density for liquid is content or little variable with pressure 
but inversely proportional to temp.
(p ) Mass density
Mass o f flu id (kg) 
Volume o f flu id (n r)
At 4°C and 1 atm pressure pW ater = 1000 kg/m3 
= 1 g/cc
Specific weight or weight density [w or r]
• Weight of fluid per unit volume known as weight density.
. . , weight(N)
Weight densih• = ---- - — -— —
Volume(nr)
_ (mass) x (g ) j mass _ |
volume [volume J
w for water at 4°C and 1 atm = 1000 x 9.8 N/m3 
= 9.8 kN/m3
g - ? acceleration due to gravity.
Note: g (acceleration due to gravity) is function of position on earth (spatial 
Parameter), so w is also a variable but consider constant [due to little variation].
Specific Volume:
• Specific volume is Reciprocal of specific mass.
• Volume of fluid per unit mass
• Unit of specific volume-
Specific Gravity or Relative Density
Page 3


Fluid Properties 
Fluid Mechanics is one of the important subjects in Mechanical Engineering for 
GATE and other exams. Fluid Properties chapter deals with topics such as Mass 
density, specific weight, viscosity and other properties which are basic for Fluid 
mechanics.
Fluid Properties fo r GATE Mechanical, ESE & Other Exams 
Ideal Fluid
Characteristics of Ideal Fluid
• A fluid having zero viscosity and zero surface tension.
• Ideal fluid is incompressible.
• There is no ideal fluid but air and water considered as ideal fluid.
Real fluid
Characteristics of real fluid
• Fluid having viscosity and surface tension.
• Real fluids are compressible
Properties of Fluid
Properties of fluid are
1. Extensive
2. Intensive
Intensive properties
• Intensive properties are independent from mass of system.
• Example - Temperature, pressure, density etc.
Extensive properties
• Properties which are depends on size or extent of a substance.
• Example - Total mass, Total volume, Total momentum etc.
Mass Density (p):
• Mass of fluid per unit volume at a given temperature and pressure.
• Mass density is function of Temperature and Pressure.
• Mass density for gases directly proportional to pressure and inversely 
proportional to temperature
• Practically, Mass density for liquid is content or little variable with pressure 
but inversely proportional to temp.
(p ) Mass density
Mass o f flu id (kg) 
Volume o f flu id (n r)
At 4°C and 1 atm pressure pW ater = 1000 kg/m3 
= 1 g/cc
Specific weight or weight density [w or r]
• Weight of fluid per unit volume known as weight density.
. . , weight(N)
Weight densih• = ---- - — -— —
Volume(nr)
_ (mass) x (g ) j mass _ |
volume [volume J
w for water at 4°C and 1 atm = 1000 x 9.8 N/m3 
= 9.8 kN/m3
g - ? acceleration due to gravity.
Note: g (acceleration due to gravity) is function of position on earth (spatial 
Parameter), so w is also a variable but consider constant [due to little variation].
Specific Volume:
• Specific volume is Reciprocal of specific mass.
• Volume of fluid per unit mass
• Unit of specific volume-
Specific Gravity or Relative Density
• Specific gravity is the ratio of specific weight of fluid to the specific weight 
of standard fluid.
S cificGravit — sp^ficw eight ° f substaiice(fluid) 
specific weightof standardfluid
• Standard fluid
-*¦ Liquid - water at 4°C 
-*¦ Gas - Hydrogen or Air
• Specific gravity has no unit or independent form system of unit
• Relative density is the ratio of density of a fluid to the density of another fluid 
(not necessarily water). Whereas specific gravity is the ratio of density of a 
fluid to the density of standard fluid (i.e., water at 4°C).
• For taking water as a standard fluid, Specific gravity = Relative density =
{Density)fluid 
(Density)\\ater
Viscosity
• Viscosity is a quantitative measure of the internal resistance of a fluid to flow.
• Viscosity relates the strain rate and local shear stresses in moving fluid.
• Viscosity is a measure of resistance offered by a fluid layer to an 
adjacent layer of fluid at motion.
• Viscosity is due to the internal friction force which caused by cohesive force 
between fluid molecules (dominant in fluid) and molecular momentum 
transfer between particles due to collision (dominant in gases).
Assume a system having fluid between two plates.
AX
Note: Assume linear variation of velocity 
dp = Angle of deformation during 'dt’ duration 
Velocity at distance y from bottom plate
•" ( v ) =
y
{from similar triangle
U_V_
~y~T
}
If consider infinite small element than velocity gradient
Page 4


Fluid Properties 
Fluid Mechanics is one of the important subjects in Mechanical Engineering for 
GATE and other exams. Fluid Properties chapter deals with topics such as Mass 
density, specific weight, viscosity and other properties which are basic for Fluid 
mechanics.
Fluid Properties fo r GATE Mechanical, ESE & Other Exams 
Ideal Fluid
Characteristics of Ideal Fluid
• A fluid having zero viscosity and zero surface tension.
• Ideal fluid is incompressible.
• There is no ideal fluid but air and water considered as ideal fluid.
Real fluid
Characteristics of real fluid
• Fluid having viscosity and surface tension.
• Real fluids are compressible
Properties of Fluid
Properties of fluid are
1. Extensive
2. Intensive
Intensive properties
• Intensive properties are independent from mass of system.
• Example - Temperature, pressure, density etc.
Extensive properties
• Properties which are depends on size or extent of a substance.
• Example - Total mass, Total volume, Total momentum etc.
Mass Density (p):
• Mass of fluid per unit volume at a given temperature and pressure.
• Mass density is function of Temperature and Pressure.
• Mass density for gases directly proportional to pressure and inversely 
proportional to temperature
• Practically, Mass density for liquid is content or little variable with pressure 
but inversely proportional to temp.
(p ) Mass density
Mass o f flu id (kg) 
Volume o f flu id (n r)
At 4°C and 1 atm pressure pW ater = 1000 kg/m3 
= 1 g/cc
Specific weight or weight density [w or r]
• Weight of fluid per unit volume known as weight density.
. . , weight(N)
Weight densih• = ---- - — -— —
Volume(nr)
_ (mass) x (g ) j mass _ |
volume [volume J
w for water at 4°C and 1 atm = 1000 x 9.8 N/m3 
= 9.8 kN/m3
g - ? acceleration due to gravity.
Note: g (acceleration due to gravity) is function of position on earth (spatial 
Parameter), so w is also a variable but consider constant [due to little variation].
Specific Volume:
• Specific volume is Reciprocal of specific mass.
• Volume of fluid per unit mass
• Unit of specific volume-
Specific Gravity or Relative Density
• Specific gravity is the ratio of specific weight of fluid to the specific weight 
of standard fluid.
S cificGravit — sp^ficw eight ° f substaiice(fluid) 
specific weightof standardfluid
• Standard fluid
-*¦ Liquid - water at 4°C 
-*¦ Gas - Hydrogen or Air
• Specific gravity has no unit or independent form system of unit
• Relative density is the ratio of density of a fluid to the density of another fluid 
(not necessarily water). Whereas specific gravity is the ratio of density of a 
fluid to the density of standard fluid (i.e., water at 4°C).
• For taking water as a standard fluid, Specific gravity = Relative density =
{Density)fluid 
(Density)\\ater
Viscosity
• Viscosity is a quantitative measure of the internal resistance of a fluid to flow.
• Viscosity relates the strain rate and local shear stresses in moving fluid.
• Viscosity is a measure of resistance offered by a fluid layer to an 
adjacent layer of fluid at motion.
• Viscosity is due to the internal friction force which caused by cohesive force 
between fluid molecules (dominant in fluid) and molecular momentum 
transfer between particles due to collision (dominant in gases).
Assume a system having fluid between two plates.
AX
Note: Assume linear variation of velocity 
dp = Angle of deformation during 'dt’ duration 
Velocity at distance y from bottom plate
•" ( v ) =
y
{from similar triangle
U_V_
~y~T
}
If consider infinite small element than velocity gradient
du _ V 
d\¦ L
--------(a)eq.
dx = Vdt (Displacement of point p to c during dt duration)------(b) eq.
tm \(dfi) = d p = — 
d /3 = ^ (From eq.(b))
fhi
d/3= — xdt (Front eq.(a)) 
dy
_ d /3 du ...
= > - £ = -r-----------«*-(0
dt dy
Angular deformation rate is equal to velocity gradient.
According to Newton
• Rate of deformation is proportional to shear stress 
So
r = c
d £
dt
dv
r cc — (From eq.{c)) 
dy
dv
av
p -» Absolute viscosity or Dynamic viscosity or Coefficient of viscosity
unit:
, , v du(m/ )
i N / , = u — - A ! 
V / m 1 dy (m )
u =
dB(m /s)
, N - S k g
Resultant unit — >— r oi —— 
m s-m
other unit poise
1 N - S 1A
---- — =10 poise
m
Note: Viscosity of water at 20°C = 1 centipoise 
Poise is a CGS unit: poise=Dyne-s/cm2
Kinematic Viscosity:
• Kinematic viscosity is the ratio of dynamic viscosity (p) and density (p).
• Kinematic viscosity denoted by (v)
Page 5


Fluid Properties 
Fluid Mechanics is one of the important subjects in Mechanical Engineering for 
GATE and other exams. Fluid Properties chapter deals with topics such as Mass 
density, specific weight, viscosity and other properties which are basic for Fluid 
mechanics.
Fluid Properties fo r GATE Mechanical, ESE & Other Exams 
Ideal Fluid
Characteristics of Ideal Fluid
• A fluid having zero viscosity and zero surface tension.
• Ideal fluid is incompressible.
• There is no ideal fluid but air and water considered as ideal fluid.
Real fluid
Characteristics of real fluid
• Fluid having viscosity and surface tension.
• Real fluids are compressible
Properties of Fluid
Properties of fluid are
1. Extensive
2. Intensive
Intensive properties
• Intensive properties are independent from mass of system.
• Example - Temperature, pressure, density etc.
Extensive properties
• Properties which are depends on size or extent of a substance.
• Example - Total mass, Total volume, Total momentum etc.
Mass Density (p):
• Mass of fluid per unit volume at a given temperature and pressure.
• Mass density is function of Temperature and Pressure.
• Mass density for gases directly proportional to pressure and inversely 
proportional to temperature
• Practically, Mass density for liquid is content or little variable with pressure 
but inversely proportional to temp.
(p ) Mass density
Mass o f flu id (kg) 
Volume o f flu id (n r)
At 4°C and 1 atm pressure pW ater = 1000 kg/m3 
= 1 g/cc
Specific weight or weight density [w or r]
• Weight of fluid per unit volume known as weight density.
. . , weight(N)
Weight densih• = ---- - — -— —
Volume(nr)
_ (mass) x (g ) j mass _ |
volume [volume J
w for water at 4°C and 1 atm = 1000 x 9.8 N/m3 
= 9.8 kN/m3
g - ? acceleration due to gravity.
Note: g (acceleration due to gravity) is function of position on earth (spatial 
Parameter), so w is also a variable but consider constant [due to little variation].
Specific Volume:
• Specific volume is Reciprocal of specific mass.
• Volume of fluid per unit mass
• Unit of specific volume-
Specific Gravity or Relative Density
• Specific gravity is the ratio of specific weight of fluid to the specific weight 
of standard fluid.
S cificGravit — sp^ficw eight ° f substaiice(fluid) 
specific weightof standardfluid
• Standard fluid
-*¦ Liquid - water at 4°C 
-*¦ Gas - Hydrogen or Air
• Specific gravity has no unit or independent form system of unit
• Relative density is the ratio of density of a fluid to the density of another fluid 
(not necessarily water). Whereas specific gravity is the ratio of density of a 
fluid to the density of standard fluid (i.e., water at 4°C).
• For taking water as a standard fluid, Specific gravity = Relative density =
{Density)fluid 
(Density)\\ater
Viscosity
• Viscosity is a quantitative measure of the internal resistance of a fluid to flow.
• Viscosity relates the strain rate and local shear stresses in moving fluid.
• Viscosity is a measure of resistance offered by a fluid layer to an 
adjacent layer of fluid at motion.
• Viscosity is due to the internal friction force which caused by cohesive force 
between fluid molecules (dominant in fluid) and molecular momentum 
transfer between particles due to collision (dominant in gases).
Assume a system having fluid between two plates.
AX
Note: Assume linear variation of velocity 
dp = Angle of deformation during 'dt’ duration 
Velocity at distance y from bottom plate
•" ( v ) =
y
{from similar triangle
U_V_
~y~T
}
If consider infinite small element than velocity gradient
du _ V 
d\¦ L
--------(a)eq.
dx = Vdt (Displacement of point p to c during dt duration)------(b) eq.
tm \(dfi) = d p = — 
d /3 = ^ (From eq.(b))
fhi
d/3= — xdt (Front eq.(a)) 
dy
_ d /3 du ...
= > - £ = -r-----------«*-(0
dt dy
Angular deformation rate is equal to velocity gradient.
According to Newton
• Rate of deformation is proportional to shear stress 
So
r = c
d £
dt
dv
r cc — (From eq.{c)) 
dy
dv
av
p -» Absolute viscosity or Dynamic viscosity or Coefficient of viscosity
unit:
, , v du(m/ )
i N / , = u — - A ! 
V / m 1 dy (m )
u =
dB(m /s)
, N - S k g
Resultant unit — >— r oi —— 
m s-m
other unit poise
1 N - S 1A
---- — =10 poise
m
Note: Viscosity of water at 20°C = 1 centipoise 
Poise is a CGS unit: poise=Dyne-s/cm2
Kinematic Viscosity:
• Kinematic viscosity is the ratio of dynamic viscosity (p) and density (p).
• Kinematic viscosity denoted by (v)
u
v = —
p
Units:
1.
m2
sec
2. stoke
j l stoke = 1 O'4
And stoke
cm2 
sec.
Classification of fluid according to relation between shear stress and rate of 
deformation:
Newtonian Fluid:
• Fluid follow the Newton’s law of viscosity
T =
• Example - Water, petrol, diesel, alcohol, all gases etc.
Non-Newtonian Fluid:
Thixotropic {pseudo-plastic}
• Slope of curve b/w "shear stress - deformation rate" is decreases 
with increasing in deformation rate.
• Also known as "shear thinning" fluids
• Example - Printer ink
Dilatant:
• Slope of shear "shear stress - deformation rate curve" increase with rate of 
deformation.
• Example - Quick sand
• Also known as "shear thickening" fluid.
Ideal Plastic / Bingham Plastic:
• Having an initial yield stress and then exhibit a linear relationship between
, du 
i and— 
dy •
• Example - Toothpaste, drilling mud etc