Page 214 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

Specific Volume m.g
m
Weight
vγ = = = = p.g
Volume
v
v
Specific volume of a liquid is the volume of the fluid per unit weight. It is the recipi of specific weight.
Weight
m
m.g
vγ = = = = p.g
It is denoted by ‘V,, S.L. unit is m³/N.
Volume
v
v
Volume v P = Mass = m
v = = Volumes v m
Mas
Weight m v P = =
Volume
v = = Volume v
m
m.g
Weight
m
Weight
For the gas flow, specific volume is defined as the volume of the fluid per unit mass, this case it is a reciprocal of
=
p.g
=
vγ =
=
Volume
mass density. S.1. unit is m³/kg. v v
Volume
v
v = =
2 Massme m v
Volu
v = = Volume P = Mass = m
2 Mass m v = = v Volume v
Density of any substance Weight m
The concept of specific volume is practically more useful for incompressible fluid ie. gases.
Density
Density of any of water sub 4 stance
at
c °
Specific Gravity or Relative Density
Density of water at 4 c ° v = Volume = v
Specific gravity is the ratio of specific weight (or mass density) of fluid to the specific weight (or mass density) of
a standard fluid. 2 Mass m

du
τα
It is denoted by S or RD.
dy

du
τα Density of any substance
dy
Specific gravity= Density of water at 4 c °
du
dy du
For liquid, water and for gases, hydrogen or air is consider as a standard fluid.
dy
τ du
=
μ
τα
Specific gravity of water at a standard temperature 4°C is 1 and that of mercury is 13.6.
 du

 τ
dy

μ
 =


Viscosity or Dynamic Viscosity or Absolute Viscosity
dy
 
  du




du
dy
The property by virtue of which, a fluid offers resistance to deformation under the action of a shear force is called


dy
as viscosity or dynamic viscosity.
2
Newton
Pascal’s Law
μ =  Shear stress = N/m = 2 = τ sec
m/s μ
Velocity 
Sh

Newton
Pascal law states, “The intensity of pressure at a point in a fluid at rest is same in all direction.”
μ  = Change of stress ear   = N/m = du 2 sec
m

m
of
distance

Change
 
  Change of Velocity m/s     2

dy
  A French scientist, Pascal stated that the pressure applied at any point in liquid, at rest is transmitted equally in

m 

 Change of distance  m
all directions. This is known as Pascal’ law. Applications of Pascal’s law Pascal’s law is applied in many devices
like the siphon, hydraulic press, hydraulic lift, brahma press, air compressor, rotary pump and hydraulic brake.
Dyne.sec

These hydraulic machines are based on the principle of transmission of pressure in liquids. Principle of Hydraulic
2
2
cm
Dyne.sec

stress

Newton
N/m
sec
Shear

press Two cylinders having different cross sectional area are connected to each other by a horizontal connecting
=
=
μ =
m/s
2
Velocity 
Change

cm
of

tube. The apparatus is filled with a liquid. The two cylinders are fitted with air tight piston . By giving a small input
2


Newton sec   Change of distance   m m
force on a plunger of a small cross sectional area cylinder a large output force are produced on the ram of large
cross sectional area cylinder. According to Pascal’s law, small input pressure exerted on plunger is transmitted
2
m
Newton

sec
by the liquid to the ram without any loss. Therefore a small force can be used tp lift a much large force or weight.
1 m 2
Dyne.sec
100 1 cm 2
100
Force Newton sec
Area m 2
Force
Area 1
100
Force
Area
201
CITS : WCS - Electrical - Exercise 19