Summary Report

Sung Lee
Ch E 494
1/11/12
Semester Summary Report
For the Fall 2012 semester,I worked on designing a trough for the water-alcohol mixture
experiment. The objective of the experiment was to study the behavior of water and alcohol mixture
using the Sum Frequency Generator spectroscopy. In order to do so, I needed to know some of the basic
background knowledge on the surface tension driven flows of alcohol and water. An article “Surface-
Tension-Driven Phenomena” by V.GLevich and V.S Krylov had very useful information related to our
experiment. The balance of the forces acting in each phase of the liquid was provided by the article
(equation 1)
[p(2) − p(1) + σ (
1
R1
+
1
R2
)] ni = [μ(2) (
∂vi
(2)
∂xk
+
∂vk
(2)
∂xi
)− μ(1) (
∂vi
(1)
∂xk
+
∂vk
(1)
∂xi
)]nk −
∂σ
∂xi
(1)
where p is a pressure, μ is a dynamic viscosity, v is velocity, σ is a surface tension, R is an radius of
curvature and n is an number of components. The equation 1 was simplified under the assumptions for
the experiment (1). The left side term, which accounts for the shear stress term is equal to zero because
we are assuming or trying to build the trough where were the shear stress wouldn’t be an factor in the
experiment. Thus the left side becomes zero and you can move the surface tension term to the left and the
equation becomes

∂σ
∂xi
= [μ(2)(
∂vi
(2)
∂xk
+
∂vk
(2)
∂xi
)− μ(1) (
∂vi
(1)
∂xk
+
∂vk
(1)
∂xi
)]nk (2)
The current equation contains two directions of flows, i and k. We are trying to have the flow of the
alcohol on the surface of water liquid to be in one direction; x-direction (see figure 1). Then the equation
2 can be further simplified to
∂σ
∂x
= [μ(
∂v
∂x
)] (3)
Figure 1
The purpose of the simplifying the equation was to obtain estimate velocity of the alcohol as it is
dropped (meeting the assumptions) on to the water surface. This data was necessary to start designing
and coming up with an actual dimension for the trough. For estimation purposes, I chose ethanol and
water as the liquids used for the sample calculations. Then the equation 3 becomes
(σH20 − σethanol)
x
= [μH20
(
V − 0
h
)] (4)

where h is the height or depth of water in the trough and x is the measured distance the ethanol travels
(refer to figure 2).
Figure 2
What we are mainly concerned about is will the flow be too fast to measure data. So the equation 4 is
solved for velocity and it is
V =
h(σH20 − σethanol)
μH20x
(5)
For the height of the water,we estimated few values that we thought would be reasonable to run
experiments with under the assumptions. These heights ranged from 5mm to 1mm. The height was set at
a certain value and then the velocities and x were estimated. The compiled calculations are shown in
table 1.
Time (sec)
Total distance traveled (cm) h=1cm h=.5cm h=.25cm h=.2cm h=.15cm h=.1cm
20 0.07 0.14 0.28 0.36 0.47 0.71
40 0.29 0.57 1.14 1.43 1.9 2.86
60 0.64 1.29 2.57 3.21 4.29 6.43
80 1.14 2.29 4.57 5.72 7.62 11.43

Table 1
The measureable time is somewhere between 2 to 10 seconds. Anything below that was too difficult to
measure because it was too quick. When the total distance traveled exceeds 80 cm for most of the height,
the time was above 10 seconds. However, there was no point of designing the trough longer than it has to
be. The longer trough means higher cost. My goal in designing the trough was to not only build operable
design but that’s also cost effective.
With the sample calculations, I could now start the designing of the trough. I decided to keep the
general form of the trough shown in figure 1. The total length inside the trough would have to be at least
80 cm according to the data shown in table 1. Because we must also consider the back flow of the alcohol
bouncing back from the end wall, which could affect the SFG signal measurement,I decided to add 10cm
for safety margin. Thus the total length of the trough would be 90cm long. Also the width of the trough
was estimated to be 5cm because too wide width would raise a problem of the flow being in two
dimensional. With the length and the width estimated, the height of the trough needed to be calculated.
This value had to be more accurate because of the SFG, IR, and VIS beams have to be able to reach the
measuring point without interfering with the inner walls of the trough. The angles of the beams were
given by Chris Lee and there are shown in figure 3.

Figure 3
The estimated width was 5 cm. With the thickness of the wall being 0.5cm, the inner width is 4cm.
Assuming that the measurement of the alcohol flow is taken in the center of the trough, the necessary
height of the inner wall can be calculated using the simple math. The angle of the VIS beam is used to do
the maximum height calculation since it’s angle is the lowest (56.4ᵒ).
Tan(56.4°) =
Hvis
w
2
→ Hvis = 1.505 cm
Figure 4

The maximum inner height the trough can be with given angles is 1.5cm. Like mentioned again, one of
my goals in designing is to minimized the cost, meaning reducing the dimensions of the trough as much
as possible. The height calculated is maximum the inner wall of the trough can be before it starts to
interfere with the VIS beam. So any values less that 1.5cm would work. The depth of the water is going
to range from 0.5cm to 0.1cm. Because we must be able to fill the trough with 0.5cm of the water,the
reasonable height of the inner wall is about 1cm. There is also the thickness of the bottom of the trough
which will be 0.5cm. Thus the total height of the trough would be 1.5cm. The dimensions of the trough
are shown in figure 5 and 6.
Figure 5
Figure 6

The basic dimension of the trough was discussed in the group meeting with Chris Lee and Ali
Borhan. We decided that the dimensions were okay. Then we needed to come up with the material type
and a method to introduce the alcohol on to the water surface. The materialtype was decided to be plexi
glass which doesn’t interfere with SFG beam. Also it’s transparent so it is easy to make observations as
the experiment is running. Determining methods to introduce alcohol was difficult because we did not
want to create any disturbances. More detail drawing of the ideas is shown in figure 7 and 8.
Figure 7
Figure 8
At the end of the meeting, the best idea was to have two thin films which we can adjust the
separation between them. We add alcohol into the films and slowly increase the separation till a droplet
of alcohol forms. Then the droplet is brought onto another film which is rests on the inner wall of the

trough. When droplet is touches the film then it would flow down the film and onto the water surface.
This wouldn’t create any disturbances because amount of alcohol is very small and also the flow rate
would be very slow as well. We thought this was difficult to carry out so we decided to talk to Don Lucas,
an Engineering Aide/ Chemical Engineering Shop Supervisor for his advice. Basically we wanted to ask
him if it is possible to make something like this with film control of adjusting separation. If not, what his
thinks is good idea (operation point of view) to add alcohol on the water surface. Another thing we
wanted to ask Don was the way to adjust the height of the water (figure 9)
Figure 9
. We thought to do this by placing 1mm film on to the bottom of the trough which would raise
the water by 1mm. We wanted to run experiments with the height of water ranging from 5mm to 1mm
with 1mm increments. I’ve arrange a meeting with Don Lucas and came to his office with ask these
questions.

After the first meeting with Don, we learned that the alcohol dispensing idea we originally had
was difficult to make. It would be difficult to find a way to adjust the separation with good control. It
would involve lot of parts and that would increase the cost. There were some questions Don had for us:
 How thin does the film have to be?
 What’s underneath the thin film going to matter?
I’ve done some research to find answers to those questions. I’ve learned that the minimum thickness of
the plexi glass was about 1.5mm (2). Since we want to increase the height of water by 1mm increments,
adding film to the trough to adjust height wouldn’t work. Also if we place the film on to the trough there
will be some leak where water is placed underneath the film. Since we are dealing with very small
volume, small changes to height would affect our results.
One of the methods Don suggested was using syringe pumps to carefully add alcohol on to the
water surfaces. We thought that was something we can do and also wouldn’t cost that much. I thought
was ways to use syringe pumps to add alcohols (figure 10).
Figure 10
I basically took the same idea as before and replaced the two films with syringe pumps. We could unload
alcohol on to the film resting on the trough with the pump. Still the alcohol has to flow down covering

the entire film so that it would create one direction flow. Also it must be done with slow flow rate and
small enough volume so that it doesn’t create any disturbances.
I’ve looked at some of the syringe pumps that we could use for the experiment. One of the useful
models was Harvard Apparatus Syringe Pump PHD 2000 Series. This model has the smallest compatible
syringes sizes of 0.5μl. Also the minimum flow rate was 0.1X10-9
l/hr. These numbers was fairly small
and we decided that this model could work. Also we could attach multiple 0.5μl syringes which give us
more control over covering the entire film as the alcohol travels down on to the surface of water (3). We
still had to address the problem of adjusting the height of the film. We decided to adjust the depth of
water by simply adding certain amount of water using the syringe pumps that will give us desired height.
This could be easily done since we know the dimension of the trough. To change to different height we
would dump the water out, clean the trough and add different amount of water. This is a bit of tedious
work but this was better than spending more money to build something that would raise the bottom of the
trough or thin film that would go on the bottom. Then I came up with different ways to adjust the film
(which the alcohol would be unloaded). I thought the distance the alcohol travels till it hits the water
surface needs to be constant for all the depth since that would affect the flow rate of the alcohol. One of
my ideas to adjust the film according to the depth was to prepare three slots on the inner wall each 1mm
apart (Figures 11 and 12). Then as we increase the depth of the water,we could simply attach the film
into the next slot. This way the distance alcohol travel would be the same as the previous depth.

Figure 11
Figure 12
Notice the distance alcohol travels to hi the water surface at height 1 and 2 are the same.
After couple of meetings with Don he told me that the slots can be planted on the inner wall but
the accuracy of the distances between them can’t be guaranteed. He told me this idea could work and be

cost effective as well, but if it won’t be very accurate. I really wanted everything to be accurate because
we are dealing with small amounts of liquids. Thus any error could result in influencing the data
significantly. So I brought this up in the next meeting. Then Borhan told me that the alcohol doesn’t
necessarily have to travel the same distances since it won’t affect the flow rate greatly. The distances will
be very short considering the dimension. Then we decided to simply have a wedge of where we can
attach the syringes and slowly pump alcohol on to the wedge (figure 13 and 14). Its dimensions were the
same as that of the inner sides of the trough so that it could easily be placed and displaced.
Figure 13

Figure 14
One of the final additions to our design was adding a well on the wedge. The idea is to initially
fill the well with the alcohol then using the syringe pumps to add more alcohol (very small amounts) till
the well overflows. This would create a sheet of alcohol liquid to flow down the wedge so that the entire
surface of the wedge would be covered. Also we needed to increase the thickness of the bottom of the
trough because we want to drill screw holes. This was necessary to adjust the trough on to the experiment
table. Since the trough is very long I thought it was good idea to place it on the table firmly. Also since
we are measuring SFG beam from IR and VIS aligned at some spot, we need to make sure that the trough
won’t be moved when someone accidently hit the table or something. The screws were about 1cm. Thus
the total height of the trough would be 2.5cm. We also thought of the cover to minimize liquid loss due
to evaporation. We were afraid of this because we are dealing with small amount of water. We originally

thought to make covers out of plexi glass but after talking to Don, we realized that it would be cost
inefficient. Easier and simpler way to prevent evaporation would be using the wraps to cover the trough.
When everything was finished, I had to convert the units from metric systems to inches. Attached is the
final design of the trough and wedge.
Reference
1. Levich, V.G., Krylov V.S, Surface-Tension-Driven Phenomena, Institute of Electrochemistry,
Moscow, USSR, July 2011
2. Thickness Tolerances of Acrylic Sheet,
http://www.eplastics.com/Plastic/Plastics_Library/Thickness-Tolerances-of-Acrylic-Sheet-
Plexiglass, Dec 2011.
3. PHD 2000 Syringe Pump Series User’s Manual,
“http://www.instechlabs.com/Support/manuals/PHD2000manual.pdf”

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