Here we will discuss this post with one example
In this concept, salty water will be extracted from
a bore with the help of a pump through a filter i.e. suction filter. There is
one more pump which is basically utilized for increasing the pressure of the
water before it enters the reverse osmosis filter.
The reverse osmosis filter will extracts some
drinkable water from the high pressure flow of the saline water. However it
must be noted that most of the salty water is discharged as untreated water and
it will be used for general purpose.
Before the discharge water leaves the system it
passes through a device which forms part of pump B designed to recover as much
energy from the high pressure flow as possible. The potable water flowing out
of the reverse osmosis filter is then stored in a stainless steel tank for
later distribution.
The other important point is this that from where we
are securing energy for driving the pump and for this requirement we are using
here solar panel and battery system.
Technical analysis
In technical analysis we have to understand the
complete specifications of storage steel tank such as
The tank volume (V)
The dimensions of the tank radius (R) and depth (D_{T})
The minimum head (H_{MIN})
The total length (L) of steel required for the four
supports
The area (A) of sheet metal required to fabricate
the tank
The mass of the empty steel tank (M)
Requirement that we should have
R1. The system must produce potable water at a
minimum rate of 4000 L per day
R2. The system must be able to store at least 5
days of water supply, in case of break downs.
R3. The system must provide a minimum gauge
pressure at the outlet of 100kPa
We have some information as mentioned below
Total height should be
less than the 4 times of diameter of tank
The steel supports are to be concreted in to the ground to a minimum depth of 2 M
The steel supports material is available in 6 M length
Tanks are made of stainless steel
Other information is given in following table
Quantity

variable

value or equation

unit

Density
of potable water

ρ_{w} (rho
w)

1000

kg/m^{3}

Density
of stainless steel

ρ_{S} (rho
s)

8000

kg/m^{3}

Thickness
of stainless steel plate

t

1.5

mm

Cost
per square metre of stainless steel

C_{S}

100

$/m^{2}

Volume of tank
As we have information that system should have
ability to produce potable water at a minimum rate of 4000 L per day.
If we consider this capacity of system only then it
seems that minimum 4000 L/day will be consumed. We have also informed that
system must have ability to store at least 5 days of water supply, in case of
break downs.
Hence, capacity of storage tank must be approximate
200, 00 L. As this is design problem, we have to think in real
use and hence we will take some factor of safety of 25 %.
So, volume of tank must be 125% of 200,00L
Volume of storage tank = 250, 00 L
Volume of storage tank =25 cubic meter
Height and Radius
In order to determine the required specification, we
must assume that what will be the height to diameter ratio for water tank that
we are going to design.
Let the diameter to height ratio is
D/H= 1/3
Or H/D= 3
Where, height = H and
diameter = D
Volume of tank = πR^{2}H
πR^{2}H= πD^{2}H/4= πD^{2} x
3 D/4
Volume of tank = 3.142 D^{3}
25 = 3.142 D^{3}
D= 1.99 meter
Height of tank = 5.98 meter
Diameter = 1.99 meter
As we have information, that structure for support
material will be purchased in 6 m length and it must be assure that 2 m length
of supporting material must be inside ground for better supporting
We will purchase 6 m length of supporting materials
and we will cut this in two equal portion of 3 m length each.
In each 3 m length, 2 m will be inside the ground
and hence
H _{Min} = 1 m
As there are four support of having length of 3 m
each, hence we have to use two length of supporting material with total length of
steel of 12 m.
Total sheet metal required in m^{2} for fabricating the above specified tank
A = 2πRH + 2πR^{2}
R= 0.995 m
H = 5.98 m
A= 43.61 m^{2}
Thickness of metal sheet that we have selected is
1.5 mm
Mass of empty tank = volume of metal x density
Mass of empty tank = A x t x ρ = 43.61 x1.5/1000 x
8000
Mass
of empty tank =523.32 K
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