Introduction describe what happened in the experiment. This


The Purpose of this lab is to study the
phenomena of tank draining and figuring out a mathematical model to accurately
describe what happened in the experiment. This lab experiment is useful to
understand on a small-scale, how tank draining works on theoretical and
technical aspect. This is important topic since it covers different areas of
Chemical Engineering.

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area that tank draining is important is the instance that you are going
implement a nozzle or pipe into a storage tank. Before you can implement it,
you would need to know how fast will the water draining from the tank to with
an exit velocity. Another application that values this project is if there is a
tank rupture, it is important to understand all the factors that was used in this
lab in order to perform investigations as well as conduct Process Hazard Analysis
and improve on Process Safety Management.


Experimental Equipment and Procedures

Figure 1: Stainless Tank

tank that has a cylindrical top with a conical bottom shape (Figure 1) was used
for this experiment. The bottom of the tank is connected to the to a schedule
40, 1.25″ tube. Which is connected to a tee reducer which is then have a tube
connected to six different tube sizes and Diameters.  

run the experiment, water will be filled up to the initial 30″ water height
above the tube. After the water has been filled to the set height, one of the
six tubes will be connected to the bottom of the pipe. To record data the, tee
that was connected to the pipe was opened and data was recorded at every inch
till a set water height was reached.

get a estimate theoretical model for the data for the tank draining, Several
assumptions were made here were the following assumptions:

The fluid is incompressible

The fluid is also inviscid

The friction in the cylinder section and the conical
section, as well as the pipe and reducer are negligible.

It is at constant density.

With these starting assumptions, the
model was begun by using the mass balance which is:. 
Since there is no mass flow in the mass balance simplifies to . The Bernoulli Equation used for this
model was the head form of the Bernoulli Equation is the head form the
Bernoulli which is


Several terms can be canceled out with
the following reasons:

Both pressure terms can be canceled out since both are
held at atmospheric pressure

The work term can also be canceled out since there is
no work being done on the system

Since the water has an initial height an assumption was
made that one of the height is zero.

simplified equation will end up being . The assumption can also be made that
the velocity at the free surface (v2) is smaller than the velocity at the tube
(v1) so that term can go away so all is left to solve for is the velocity which
comes out to be . Since this a constant density draining
and has continuity, a valid equation to use is  and set  as  since the water height is decreasing and
can solve for  with the equation:  . From this equation two separate models
were made for the cylindrical section and the conical section. is the area of the tube and  is the area of the cylinder section/conical
section. One term that needed to be defined is . To get this term, a velocity term
needs to be defined. The velocity term was determined by taking the derivative
of the best fit equation from the experimental plot of water height with
respect to time and plugging either the time used with the experimental data
(the time to drain the cylindrical section/conical section can also be used).
Once a velocity is found, that velocity can be used to find the Reynolds number
from the equation  (EQ.7) with D being the diameter of the tube and µ being the viscosity of the
water. The calculated Reynolds number used to find the friction factor. From the calculated for the Reynold
number in both the cylindrical section and conical section was calculated to be
laminar flow with each pipe which then the equation: 16/NRE to find the friction factor to find the head friction of the
tube which was calculated from the equation . For the first 8 initial fluid heights
which is in the cylindrical section of the tank, the area of the tubes is set
to be  and the areas of both the cylinder section and
the conical section are both  . For this lab, height was used to solve
for the time taken to drain the water. For the cylindrical section, EQ.9 and
EQ.10 was plugged into EQ.6 to get   . This equation is a
separable differential equation and was solved for t to get  However, got the friction from the tube
other than Tube No.1 (1/8″ ID, 24″ length) had very miniscule friction so it
could be safely assumed from the data that the  term for the rest of the terms were
negligible. For the conical section it was assumed that the conical section was
shaped like a true cone. This is useful for the fact that you can find the
tangential angel of the cone in order to find the height of the fluid at any
given radius. The tangential angle was solved from the equation . The angle was found to be 31.34. This
was plugged in to find the radius of the cone in . The squared tangential angle turned
out to be .36. EQ.12 was plugged into EQ.6 to get  . This is also a separable differential
equation and was solved for t. Since the friction can not be assumed negligible
in the first tube, the equation to solve for t was evaluated to be



   . For the other tubes the equation

each tube, the cylindrical derived equation will be used for the first 8 inches
of fluid height until there is no water left in the cylinder section. After
total drainage in the cylinder section, the equation for the conical section of
tank will be used for the rest of the water heights.

Experimental Results and Discussion


(Tube No.1)

is one of the scatter plot of the Tube (No.1) that is graphed as water height with
respect to time in height. The experimental data was compared to the
theoretical model that was generated from the mathematical model. The following
graphs were formatted the exact way as the graph above. (Tube No.2 D                                             data
with repsect ot time

the plotted data given above, one observation can be made in that the tank took
a substantial amount of time to drain rather than the experimental data points.
Another conclusion that can be made based off these graphs is that the length
of the tube seems to play a role in the accuracy between the theoretical and
the experimental. The most accurate that the theoretical model was Tube No.3

Relationship between theory and experimental results

As observed earlier, the theoretical
model data has some significant variation for each tube. However, it would be
safe to assume that the model closely models the draining of the water in the
cylindrical section than the conical section. This model is on the basis that
this is an unsteady state model for the fact that the cross-section area of the
tank is decreasing as the fluid height decreases. With the cylindrical section
of the tank it free surface and had constant cross-sectional area throughout
its section. On the other hand, the equation becomes unsteady when the water
height reaches the conical part of the section since the radius decreases as
height decreases.

            One Equation/Law used for tank draining situations is Torricelli’s
Law. It theorizes that the velocity of the fluid is the same as the velocity at
rest (Nevers, 2005). It can be defined
from the Bernoulli as   (Nevers, 2005). This equation does
not work with this model because this tank has two different shaped sections as
well as there is friction. The model uses a modified version of the Torricelli’s
Equation that factors in friction.

            The Graphs also indicates that the velocity of the water exiting
the pipe increases as the height of the fluid decreases. This phenomenon can be
described for the Coriolis effect. The Coriolis effect describes the motion of
the fluid in the x,y,z gradient as well as the radial direction in cylindrical
coordinates (McCabe, Smith, & Harriot, 2005). As the fluid flows
down the tube the velocity in cylindrical coordinate directions which causes a Coriolis
effect to occur in the conical section as the channel for the streamline of the
water decreases. This causes interaction in the boundaries of the conical section
and momentum to occur in the tank results in an increase in turbulence (Moore, 1967).



Conclusion and Recommendations

Conclusion, a general mathematical model for tank draining of water was created.
The results from the theoretical data varied with the experimental data given.
Some recommendations would be to analyze the conical section more in depth as
well as studying the effect of having an initial flow rate and investigating the
conical section since the theoretical time was relatively long compared to the time
in the experimental data



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