A double bottom tank
containing seawater is 6m long, 12m wide and 1m deep. The inlet pipe
from the pump has its center 75mm above the outer bottom. The pump has a
pressure of 70KN/m2 and is left running indefinitely. calculate the
load on the tank top:
(i) If there is no outlet.
(ii) If the overflow pipe extends 5m above the tank top
IF YOU ARE NOTICING ANY ERROR KINDLY COMMENT BELOW
Given
L = 6 m
B = 12m
d = 1 m
The
load on the tank top:
(i) If there is no outlet.
(ii) If the overflow pipe extends 5m above the tank top
Solution
We know that pressure exerted by pump = 70 KN/m2
We need to find pressure exerted due to head of water.
It is given by the formula የ x g x h
Here head h = 1 - 0.075 = 0.925 m (Because total depth = 1 m and pump suction is at 75 mm above bottom )
Pressure exerted due to head of water = 1.025 x 9.81 x 0.925
= 9.30 KN/m2
So pressure at the tank top = Pressure exerted by pump - Pressure due to head of water
= 70 - 9.30
= 60.70 KN/m2
i) Load on tank top = Pressure on tank top x Area
= 60.70 x (L x B)
= 60.70 x (6 x 12)
= 4370 KN
ii) We know that Pressure exerted = የ x g x h
We need to find head at 70 KN/m2 pressure
70 = 1.025 x 9.81 x h
h = 70 / (1.025 x 9.81)
= 6.961 m
So max head above tank top = Head due to pump - head due to gravity
= 6.961 - 0.925
= 6.036 m
But in question it is given that overflow pipe at a height of 5 m. which is less that the maximum head .
It is given that pump is left running indefinitely. So for finding load on top we have to use the load on an immersed plane formula.
it is given by የ x g x a x h
So load on tank top = 1.025 x 9.81 x (6 x 12) x 5
= 3619.9 KN
for the 2nd part of the question (o/f pipe 5m above...) , should we not consider the pump pressure also , just like we did in the first part of the question? since it is mentioned that the pump is running indefinitely...!!!
ReplyDeleteplz correct me if im wrong