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7/30/2019 UROP_Chow Jun Kang
1/23
UROP SUMMER 2012Water Purification Units for Low-income or DevelopingCountries and Regions
7/30/2019 UROP_Chow Jun Kang
2/23
ENERGYEMITTEDBYTHE SUN
2%
47%51%
percentage of energy distribution within thesolar spectrum
Ultraviolet light (UV)
Visible light
Infrared (IR)
7/30/2019 UROP_Chow Jun Kang
3/23
HEAT TRANSFER THROUGH RADIATION
A simple model is simulated with Plancks equation to calculatethe heat energy absorbed by water for electromagnetic wavewithin wavelength 400 2500 nm.
E = hf = hc /
E is energy (unit Joule)
h is Plancks constant (6.625 10-34 J s )
f is the frequency of the electromagnetic wave (unit s-1)
7/30/2019 UROP_Chow Jun Kang
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WATER ABSORPTION COEFFICIENT
Absorption coefficient
A measure of the rate of decrease in the intensity of
electromagnetic radiation (as light) as it passes through a
given substance
WaterAbsorption
Coefficient
Wavelength (nm)
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ENERGY ABSORBED BY WATER
By using Plancks equation and water absorption coefficient, graph
of energy absorbed versus wavelength is plotted.
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COMPARISON BETWEEN GRAPHOF WATER
ABSORPTION COEFFICIENTAND ENERGY
ABSORBEDBY WATER
Graph of Water Absorption Coefficient
versus Wavelength
Graph of Energy Absorbed by Water
versus Wavelength
2 graphs are similar. It could be said that the energy absorbed by water is mainly
determined by the water absorption coefficient
7/30/2019 UROP_Chow Jun Kang
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ENERGY ABSORBED BY WATER
Comparison is made between the total energy absorbed by water between
different region of wavelength (Visible light versus Infrared)
Estimated total energy is calculated with the aid of Matlab software.
It was found that the ratio of total energy between Visible light and
Infrared is 1:9.36 106, with total energy absorbed between 18002200 nm is the highest compared to the other regions.
Region of wavelength investigated:
Visible light: 400 700 nm
Infrared: 700 2500 nm
7/30/2019 UROP_Chow Jun Kang
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PARTIAL CONCLUSION I
With high ratio between energy absorbed by water
in the region of visible light and infrared, it can be
verified that infrared could be the main source of
heating water.
Since water absorbed the heat energy within the
region 1800 2200 nm the most, materials with
high transmittance of wavelength between this
region should be investigated.
7/30/2019 UROP_Chow Jun Kang
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CREATING HYDROPHOBIC SURFACE
Recipe used was fluoroalkylsilane coating.
Ingredient is (heptadecafluoro-1,1,2,2-
tetrahydrodecyl)trimethyloxysilane. (CAS:83048-65-
1)
Parameters to be tested:
Concentration 0.1 M and 0.01 M
Curing temperature 50C and 80C
7/30/2019 UROP_Chow Jun Kang
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CREATING HYDROPHOBIC SURFACE
Steps in preparing the coating layer:
1. Fluoroalkylsilne liquid is mixed with appropriate volume
of water to obtain the concentration required,
2. Few drops of hydrochloric acid, HCl is dropped into the
solution as catalyst.3. Glass sample is sonicated in water bath for at least 1
hour to remove any impurities on the surface.
4. Glass sample is then dip coated in the solution prepared
for 5 minutes.
5. Glass sample is kept at oven for curing purpose for 8hours.
6. Glass sample is put at room temperature for 1 hour.
7. Effect of hydrophobicity of glass sample is tested.
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TESTINGOF HYDROPHOBIC SURFACE
Testing Procedures:
1. The coated glass sample is fixed on the model formed.
2. About 50 ml of water is poured into the model.
3. Model is then heated on magnetic stirrer heating plate.
4. Observation is made and recorded throughout theheating process.
7/30/2019 UROP_Chow Jun Kang
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TESTINGOF HYDROPHOBIC SURFACE
Observation:
Observation Inference
Fumes started to form and
disappear repeatedly on the
bottom surface of glass sample
after heating up to 60C.
The model was not completely
sealed. This caused some water
vapour formed escaped
Water droplets formed on the
glass sample B is smaller.
The higher the concentration of
solution, the greater the effect ofhydrophobicity, thus the greater
the contact angle, the smaller
the water droplets formed on
the bottom surface of the glass
sample.
Sample A coated with 0.01 M solution
Sample B coated with 0.1 M solution
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TESTINGOF HYDROPHOBIC SURFACE
Observation Inference
In both cases, water droplets
remained on the glass sampleand did not slide down until
more condensed water vapour
stuck together.
The weight force acted on the
water droplets (the size/volumeof the water droplet was small)
could not overcome the
adhesive force acted on it and it
remained on the glass plate.
Observation:
7/30/2019 UROP_Chow Jun Kang
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PARTIAL CONCLUSION II
The higher the concentration of solution, the higher
the contact angle, the higher the hydrophobicity.
Unless a more hydrophobic coating is found, this
recipe would be the current best one.
7/30/2019 UROP_Chow Jun Kang
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TESTINGOF SLIDING ANGLE
Sliding angles, 15, 30, 45, 60 and 75 were
tested.
Procedure: Approximately equal volume of water is
dropped to the surface drop by drop. The sliding
action of water droplets is observed and recorded.
7/30/2019 UROP_Chow Jun Kang
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TESTINGOF SLIDING ANGLE
Observation:
Observation/Result Inference
About total 3 drops of water
were only able to drive thewater to slide down the
plane.
variation in angle does not
have significant effect onthe sliding of water droplets.
weight force acted on a
water droplet could not
overcome the adhesive
force as well as resistance
of the surface acted on thewater droplet.
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PARTIAL CONCLUSION III
It could be verified that different in sliding angles do
not have effect on the velocity of sliding of water
droplets.
7/30/2019 UROP_Chow Jun Kang
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ALKALINE GLASS ETCHING
Dissolution of glass surface to produce more silanol
group (Si OH) to increase its hydrophilicity.
Mechanism:
1st stage: exchange at the glass surface of an alkali (alkaline
earth) atom in the glass with a hydrogen atom in the water.
(Si O R)glass + H2O (Si O H)glass + R+ + OH-(aq)
2nd stage: dissolution occurs with the aqueous hydroxide ions,
OH- attack the Si O Si bonds to dissolve the silica in the glass.(Si O Si)glass + OH
- (Si OH)glass + (Si O-)solution
7/30/2019 UROP_Chow Jun Kang
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ALKALINE GLASS ETCHING
Procedure:
1. All apparatus are put into sonication bath to remove any
impurities attached on the surface of apparatus.
2. Glass sample is then immersed in the 0.1 M of sodium
hydroxide solution, NaOH.
3. Beaker containing the glass sample is put in a water bath
then is put in the oven at 50C for 1 hour.
4. Glass sample is taken out to dry for 1 hour at room
temperature.
5. Effect of glass etching is tested.6. Experiment is repeated by changing the concentration to
1.5M, temperature to 80C and curing hour to 3 hours and 2
days. When one of the variable is manipulated, other variables
are fixes as constants.
7/30/2019 UROP_Chow Jun Kang
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ALKALINE GLASS ETCHING
Observation: For parameter of concentration,higher concentration of NaOH led to flatter waterdroplet, indicating the higher hydrophilicity of theglass
The left diagram shows glass with etching of 0.1 mol dm-3 ofNaOH while the right one shows glass with etching of 1.5
mol dm-3 of NaOH. Observation showed that the water
droplet of the right diagram was flatter.
7/30/2019 UROP_Chow Jun Kang
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ALKALINE GLASS ETCHING
Observation: For parameter of reaction time, effect of
glass etching with reaction time of 1 hour was greater
than that of 15 minutes, but the effect with reaction
time of 3 hours and 2 days did not have much
significant difference with that of 1 hour.
Left diagram: Reaction time of 15
minutes
Bottom diagram: Reaction time of 1 hour,
3 hours and 2 days (from left to right)
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ALKALINE GLASS ETCHING
Observation: In terms of durability, result showed
that this effect could last for a week. More time is
required to verify the durability of the effect.
Glass sample was etched with concentration of
NaOH of 1.5 mol dm-3, temperature of 50C as well
as reaction time of 1 hour.
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PARTIAL CONCLUSION IV
The higher the alkaline concentration, the higher
the effect of etching.
1 hour would be the optimum hour for etching
process to take place.
Reaction temperature does not play a significant
role in affecting the effect of etching.
Durability of etching effect with longer than a week
has to be verified.