Defination- Pressure head (h) is defined as the height of a column of liquid of specific weight (w) required to give a pressure difference of p. Pressure head is a linear quantity and is a term used in Fluid Mechanics to represent the internal energy of a fluid due to the pressure exerted on its container.
Pressure head is also known as static pressure head or simply static head
For a imcompressible fluid, the pressure intensity 'p' at any point in the fluid is given by
p =wh
Or h = p/w
where h is the height of fluid column which causes the pressure and w is the specific weight of fluid.
This height of fluid 'h' is called the pressure head at the point.
NOTE- Pressure of one liquid in terms of other liquid can be expressed by using relationships-
(a) w1h1 = w2h2
(b) s1h1 = s2h2
(c) ρ1h1 = ρ2h2
Question - 1. A circular plate having a diameter of 2 metre is immersed in water vertically in such way that the distance between the centre of the plate ro the surface of the water is 4 meter. Calculate the total pressure on the plate.
Solution -
Given-
Diameter of the circular plate (d) = 2m
Distance between the centre of the plate to the surface of the water (X̄) = 4m
As we know p = wX̄A
We know w= Specific weight of water = 9.81
We have to find area of the plate and since the plate is circular so area of the circle is
A = π/4 d²
So A = π/4 (2)²
A = π m²
Now, p = wX̄A
So, p = 9.81 X 4 X π
p = 9.81 X 4 X 3.14
p = 123.27 KN
So total pressure on both sides of plates
P = 2 X p
P = 2 X 123.27
P = 246.54 KN
Solved.