Lecture 2 Fluid Statics Pressures
Lecture 2 Fluid Statics Pressures
Lecture 2 Fluid Statics Pressures
Chapter – 2a
Pressure, Pressure Head, Pressure measurements
dp = dz
dp = dz
p = z
Say; z = h
p = h
Or
p
h= (Pressure Head)
Pressure expressed in Height of Fluid
Water in a bottle
Sol’n
Fom table A.5, 20 = 9790 N/m3
= 9.79 kN/m3
with reference elev at liquid surface,
zA = zB = 75 mm = 0.075 m
zC =150 mm = 0.150 m
Note: for liquids, it is more convenient to work with gage pressures, hence,
at atmospheric pressure, pgage = 0
pB = psurface+ zA
pA = 0 + 9.79(0.075) =0.734 kPa
pB = 0 + 9.79(0.075) =0.734 kPa
pC = 0 + 9.79(0.150) =1.468 kPa
Note: to obtain values in absolute pressure, just add the atmospheric pressure,
hence, pA = pB =101.734 kPa , abs and pC = 102.468 kPa, abs
Example 2
An open tank contains water 1.40m deep covered by a 2-m
thick layer of oil (s=0.855). What is the pressure head at the
bottom of the tank, in terms of a water column?
Solution :
Solution 1 (In terms of pressure head)
0 - 9.81(13.6)(0.05)-9.81(0.020)= pp
s = (1.1)
Compressible fluids
From the basic equation of pressure on fluids,
න න or
p2 = 28.148 kPa,abs