EXPERIMENTAL AND COMPUTATIONAL ANALYSIS OF DOUBLE SLOPE SOLAR STILL

Ishan Kossambe

Need of the project

Fresh water is essential for all life forms on earth

The available fresh water on the earth is fixed, but the demand of fresh water is increased

The ocean is the only available source for large amount of water

But the ocean water contains high salinity, so there is a need to desaline the water

Problem Statement

Desalination of salt water using solar still which then can be used for drinking or other household purpose

Solar Still

Solar still is a device, which is used for desalination purpose Economical process but distillation rate is low Involves all the three modes of heat transfer The solar radiations falling on the glass cover pass through

the glass cover and strike the inside surface of the basin This leads to rise in temperature of the water and water

begins to evaporate. Temperature difference between water vapor and glass

leads to vapor condensation in glass cover The combination of gravity and surface tension causes

water to flow downwards and get collected in a trough leading into a storage tank

Experimental Setup

It is an insulated metallic basin covered by a transparent glass

Made up of GI sheet having a base area of 1.0 m x 1.0 m

The basin is double walled having 1” thermocol sheet sand-witched between the walls to reduce heat losses from walls.

The basin is painted with black epoxy paint from inside to increase its absorptivity and it is painted with silver enamel paint on the walls to create the adiabatic surface on the walls and reduce thermal losses

A transparent glass of 5 mm thickness covers the top of the still

Experimental Setup

Design Modifications

The setup available was very old The collecting passage was not having

proper slope First we tried to make the slope proper

using glass putty One more problem was with insulator

absorbing the condensed water This was eliminated by using a non

absorbing material (cello tape) placed over the insulator

Design Modifications

Still the collecting passage problem was not rectified

Then we tried sticking a electric pipe on to the glass surface itself

This pipe got bend due to intense sun heat Then electric pipe was replaced by high

temperature resistance pipe For the water to flow one side of the still

was lifted slightly by 5 mm

Experimental Procedure

Experiment was carried out from 1100 Hrs till 1300 Hrs

Solar still was filled with 10 liters of water

For every 20 min the reading were taken as tabulated below

Time Tg (oC) Tb (oC) Ts (oC) Ta (oC)Flux

(KW/m2)

Amount of water collecte

d

11:00 33 39 25 37.7 10.9  

11:20 53 55 56 38 11.4 40

11:40 56.7 58.8 60 38 11.7 100

12:00 59 62.8 63.5 38.5 11.8 210

12:20 62 67 67 37.1 11.6 320

12:40 65.2 63.9 70 38.3 11.3 450

13:00 68 74 73 38 11.1 620

Observation and Calculations

Pw (Pa) Pg (Pa)

Expt flow rate

(ml/m2min)

hew hcwAnlytical flow rate

(ml/m2min)

    0     0

16471 14259 2-

45.27002775-2.920248 20.4587631

19871 17027 3 -47.624171-

3.1156672

26.33361339

23321 18970 5.5-

50.44245846

-3.284999

9

32.58533648

27268 21785 6-

50.87247844

-3.486428

940.4365203

31089 25173 6.5-

67.83362287

-3.491067

5

46.16413147

35355 28495 8.5-

59.06693878-3.759033

56.52839511

Time vs Water Output

10:48 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 13:120

1

2

3

4

5

6

7

8

9

Water Output vs Time

ExperimentalAnalytical

Time

Wate

r o/p

(m

l/m

in)

Variation of Ambient temperature with time

10:48 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 13:1236

36.5

37

37.5

38

38.5

39

Variation of Amient Temperature with time

Ta (oC)

Time

Am

bie

nt

Tem

pera

ture

(oC

)

Variation of Solar Flux With Time

10:48 11:02 11:16 11:31 11:45 12:00 12:14 12:28 12:43 12:57 13:1210.4

10.6

10.8

11

11.2

11.4

11.6

11.8

12

Variation of Solar Flux with Time

Flux (KW/m2)

Time

Sola

r Flu

x (

KW

/m2)

PPM Test of water

Two samples were collected 1. Water which was put inside the solar still2. Water which was collected out from the

solar still These samples were tested for calculating

various salt contents like1. Hardness of the water (CaCo3)

2. Chloride content3. Sulphate content

Test for Hardness

1. Take 20 ml or suitable portion of sample diluted to 100ml in to a conical flask.

2. Add 1-2 ml buffer solution.3. Add 1 or 2 drops of Erichrome black T and titrate

with standard EDTA (0.01 M) till wine red colour changes to blue. Note down to vol. of EDTA required. (A)

4. Run a reagent blank if buffer is not checked properly. Note the Vol. of EDTA required by blank (B).

5. Calculate Vol. of EDTA required by sample, C = (A-B).

Test for Hardness

Sample Volume of sample (ml)

Burette reading Volume of EDTA consumed (ml)

initial Final difference

1 20 0 17 17 172 20 0 1.4 1.4 1.4

Total Hardness as mg/l of CaCo3= (C x D x1000)/Volume of sampleWhere C- volume of EDTA required by sampleD-1 ml of EDT = 1mg of CaCo3 For Sample 1:Total hardness as mg/l as CaCo3= 17 x 1 x1000/20

= 850 mg/lThis is 0.085% of the total volume of the waterFor sample 2:Total hardness as mg/l of CaCo3= 1.4 x 1 x 1000/20

= 70 mg/lThis is 0.007% of the total volume of the water

Chloride Test

1. Take 100 mL of the sample or take appropriate amount and dilute it to100 mL

2. Fill burette with silver nitrate titrant.3. Add 2 to 3 drops of the potassium chromate indicator

to the sample.4. Titrate the blank with standard AgNO3. The end point

is the change of colour from yellow to brick-red (B)5. Titrate the sample in the same way to the same brick-

red color (use blank titration as reference colour and be consistent in end-point recognition.)(A)

6. Calculate ppm Cl- and record with one decimal.

Chloride Test

Parameters Sample 1 Sample 2

Sample Volume (ml) 20 20

Initial Burette reading 0 0

Final burette reading  29.5  1.4

Total Chlorides as mg/l = (A x N AgNO3 x 35450)/Volume of sampleWhere A- ml AgNO3 consumedFor sample 1:Total chlorides = 29.5 X 0.0141 x 35450/20

= 734.77mg/l This is 0.0734% of total volume of the waterFor sample 2:Total chlorides = 1.4 X 0.0141 x 35450/20

= 35mg/lThis is 0.0035% of total volume of the water

Sulphate Test

1. Measure 100 ml water sample or suitable portion of sample made to 100 ml with distilled water

2. Add 5 ml conditioning agent and a spoon full of BaCl2 crystals. Stir exactly for 1 minute

3. Pour the solution in to the glass cell of the turbidity meter and measure the turbidity

4. Prepare a calibration graph by using sulphate standard as described earlier

5. The standards can be made from 0 to 40 mg/l sulphate range by taking 0-40 ml standard solution and making up to 100 ml

6. Determine the concentration of given sample from the calibration chart plotted with known sulphate concentrations Vs turbidity

Sulphate Test

1 2 3 4 5 6 7 8 9 10 110

100200300400500600700

Turbidity vs suplahte concen-tration

Turbidity

Sulphate Concentration (mg/l)

Turb

idit

y (

NTU

)

For sample 1:Turbidity is found to be 490 NTU hence from graph sulphate concentration comes out to be 8.4 mg/l. That is 0.0084% of the total volume of the water.For sample 2:Turbidity is found to be 150 NTU hence from graph sulphate concentration comes out to be 2.5 mg/l. That is 0.0025% of the total volume of the water.

Comparison of Results

Test Before (mg/l) After (mg/l)

Hardness Test 850 70

Chloride Test 734 35

Sulphate Test 8.54 2.5

Computational Analysis

Half of the model is considered for analysis since its symmetric about the y axis

Solar still is modeled in solidworks and then imported into ICEM for meshing

Tetra meshing is done Number of nodes-1788804 Number of elements- 4951096

Computation Analysis

Mesh