urop_chow jun kang

7/30/2019 UROP_Chow Jun Kang

1/23

UROP SUMMER 2012Water Purification Units for Low-income or DevelopingCountries and Regions


2/23

ENERGYEMITTEDBYTHE SUN

2%

47%51%

percentage of energy distribution within thesolar spectrum

Ultraviolet light (UV)

Visible light

Infrared (IR)


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)


4/23

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)


5/23

ENERGY ABSORBED BY WATER

By using Plancks equation and water absorption coefficient, graph

of energy absorbed versus wavelength is plotted.


6/23

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


7/23

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


8/23

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.


9/23

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


10/23

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.


11/23

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.


12/23


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


13/23


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:


14/23

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.


15/23

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.


16/23

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.


17/23

PARTIAL CONCLUSION III

It could be verified that different in sliding angles do

not have effect on the velocity of sliding of water

droplets.


18/23

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


19/23


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.


20/23


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.


21/23


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)


22/23


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.


23/23

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.

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