lab report 5.docx

1.0 INTRODUCTION Evaporation is a process of vaporization where the vapour from the boiling point solution is removed which causes a more concentrated solution to remain. An evaporator is a device used to turn the liquid form of a chemical into its gaseous form. A climbing film evaporator (CFE) is a special type of evaporator which provides a high heat transfer coefficient and a short residence time for the solution to be evaporated. Multi tube CFEs are used to concentrate solutions such as fruit juices that can be damaged by prolonged heat. It is designed to operate under vacuum, which reduces the evaporation temperature and increases the heat flux by either through batch or continuous process. In the application of CFE, it is normally used to study the evaporation and concentration of sensitive products such as milk, fruit juice and for desalination studies. There are also other types of evaporator which uses the same application as climbing film evaporator such as rising film evaporator, thin film evaporator, rotary evaporator and film on film evaporator.

2.0 OBJECTIVE The objective of the experiment was to determine the concentration of product concentrate of a once through experiment of grape juice (stimulated by KMnO4) and water mixture. Besides that, there were also few other objectives for the experiment: -

To determine the effect of vacuum levels on the evaporation rates To determine the influence of evaporation feed level on the evaporation rates To determine the effect of evaporation time on evaporation rates.

3.0 PROCEDURE 3.1 Effect of evaporator pressure 1. The valve for main cooling water supply is on. Subsequently, turn on cooling water valve to allow flow into the condenser. Ensure that circulating cooling water flow rate is 6 L/min. 2.

Before the experiment is started, ensure that V7, V9, V11, V12, V14 are closed.

3. Open valve V2, V3, V5, and close V1, V4, V6. Turn on the feed pump and in order to circulate the KMnO4 solution. Wait until the solution homogenous.

4. Collect a sample of feed from the feed tank by using V1. And measure its corresponding refractive index. Record this value. 1

5. Now with the feed pump turned on, open V6 in order to set the level of KMnO4 to 25 cm level. 6. Measure the volume of the KMnO4 solution inside the column by transferring into volumetric cylinder by opening the valve V14. 7. Repeat the column filling process by opening valve V6 and set to the level 25 again. 8. Starting at atmospheric pressure [vacuum pump is not used] . 9. The steam supply is turn on. Open the steam condensate purge valve to allow purging of condensate. 10. Before the steam is transferred, the purge valve is open, and main steam valve and steam supply valve are closed. Very carefully [ensure that you have put on your glove] open the main steam valve to 1/2 open. At the same time of opening the main steam valve and closed steam purge valve, start the stopwatch timing. 11. Observe the first bubble appearance and record the time taken. 12. Take the reading of steam flow rate and pressure 13. After 20 minutes, close steam supply valve, and open steam purge valve at the same time. No need to close the main steam valve to obtain the same steam flow rate and pressure for the next running. 14. Collect he samples of the Evaporator (via V14), concentrate and condensate (via V12). Concentrate and condensate samples may be taken afterward. But, the evaporator sample have to wait for a while (± 15 minutes). 15. The first sample taken is condensate. Easily, open V12. The second is concentrate. Use vacuum pump to collect the sample. Close V12 and Open V7 to let the liquid flow to the inlet transfer pump. Then close V7 and open V9. Turn on the vacuum pump and the liquid will be transferred to the condensate receiver tank 2. After all the liquid has been transferred, close V9 and easily, open V12 to collect the concentrate sample. Redo the vacuuming if the liquid is still remaining in the inlet transfer pump line. 16. Measure the volume and record the refractive index of all samples.

2

17. Return all the samples to the feed tank. (Before executing check with the lecture and ensure that you are cleared by the lecture to conduct these procedures). 18. Set the height of feed at 25 cm again. 19. Turn on the vacuum pump and set the at negative pressure 200 mmHg. (see the pressure gauge) 20. At this pressure, repeat step i through r. And similarly for negative pressure 400 mmHg, 600 mmHg, and 700 mmHg. (Ask the technician to demonstrate on how to relief the negative pressure in evaporator system)

3.2 Effect of evaporator feed level Steps (1) to (18) are the same as experiment 3.1 19. Set the height of feed at 50 cm again. 20. At this height, repeat step i through r. And similarly for height 75 cm and ‘ 100 cm.

3.3 Effect of evaporation time Steps (1) to (11) are the same as experiment 3.1. Set the evaporation process for 10, 15, and 20 minutes at constant evaporation pressure, constant height of feed and constant steam flow rate.

3

4.0 RESULTS Effect Of Vacuums Level On Evaporation Rates No .

Pressu re

(mmH g) 1

Level of KMnO 4

Time (first bubble )

Time (to boil)

Evaporate RI Volume

Concentrate RI Volum e

Condensate RI Volume

(ml) (cm)

(min)

(ml) (ml)

(min)

25

1.32

5.15

1.337

565

2

Atm press -200

25

0.59

1.26

1.339

400

3

-400

25

0.25

0.54

1.340 2

335

No .

Pressu re

Time (first bubble ) (min)

1

25

1.32

5.15

2

(mmH g) Atm press -200

Level of KMnO 4 (cm)

25

0.59

1.26

3

-400

25

0.25

0.54

Time (to boil)

Evaporate Conc Volume entrat ion (ml)

(min) (M) 0.057 0.098 7 0.123 7

565 400 335

1.340 8 1.337 9 1.337 9

65

3.4

177

1.340 7 1.339

172

1.336

122

Concentrate Conce Volum ntratio e n (ml) (M) 0.136 65 2 0.075 177 8 0.075 172 8

58

Condensate Conc Volume entrat ion (ml) (M) 0.134 2 0.098 7 0.036 2

3.4 58 122

4

Graph for Effect of vacuum levels on Evaporation rates 6 5 4

time to boil (min) time for first bubble (min)

3

Time(min)

2 1 0 -450-400-350-300-250-200-150-100 -50

0

Pressure (mm Hg)

Sample Calculation Given RI = 1.337 Using this equation: y = 20.837x-27.802 Substitute RI into x, y = 20.837(1.337)-27.802 So, concentration = y = 0.0571 M

Effect of Evaporator Feed Level No .

1 2

Pressu re

(mmH g) Atm press Atm press

Level of KMnO 4

Time (first bubble )

Time (to boil)

Evaporate RI Volume

Concentrate RI Volum e

Condensate RI Volume

(ml) (cm) 50

(min) 0.48

(min) 1.54

75

0.44

2.22

1.338 2 1.338 5

(ml) (ml) 165

540

1.338

630

1.3379 240

1.338

92

1.337 7

170

5

No .

Pressu re

Level of KMnO 4 (cm)

(mmH g) Atm press Atm press

1 2

Time (first bubble ) (min)

Time (to boil)

Evaporate Conc Volume entrat ion (ml)

540

Concentrate Conce Volum ntratio e n (ml) (M) 0.0779 165

630

0.0758 240

(min)

50

0.48

1.54

75

0.44

2.22

(M) 0.082 1 0.088 3

Condensate Conc Volume entrat ion (ml) (M) 0.077 9 0.071 7

92 170

Graph for Effect of Evaporator feed level 6 5 4 time to boil (min)

3

Time (min)

time for first bubble (min)

2 1 0 20

30

40

50

60

70

80

Level of KMnO4 (cm)

Effect of Evaporation Time N o

Pressur e

Level of KMnO

(mmHg ) 1 2 3

ATM Press ATM Press ATM Press

4

Runnin g time (min)

Time (first bubble) (min)

Time (to boil)

Evaporate

RI (min)

(cm) 25

10

1.02

1.43

25

15

0.50

1.21

25

20

2.05

2.59

1.338 8 1.339 8 1.337 0

Concentrate

Volum e (ml) 570

RI

1.3385

Volum e (ml) 70

515

1.3392

125

565

1.3408

65

Condensate

RI

Volum e (ml) 20.5

1.338 4 1.338 6 1.340 7

40 3.4

6

N o

Press ure

Level of KMnO

(mm Hg)

Runnin g time (min)

4

Time (first bubbl e) (min)

Time (to boil)

Evaporate

(min)

Concentrat ion (M)

Volum e (ml)

Concentr ation (M)

Volum e (ml)

Concentr ation (M)

Volume (ml)

(cm) 1 2 3

ATM Press ATM Press ATM Press

Concentrate

Condensate

25

10

1.02

1.43

0.0946

570

0.0883

70

0.0862

20.5

25

15

0.50

1.21

0.1154

515

0.1029

125

0.0904

40

25

20

2.05

2.59

0.0570

565

0.1632

65

0.1342

3.4

Sample Calculation Given RI = 1.337 Using this equation: y = 20.837x-27.802 Substitute RI into x, y = 20.837(1.337)-27.802 So, concentration = y = 0.0571 M Runnin g time

Time (first bubbl e) (min)

(min)

Concentra tion (M)

10

1. 02

1.43

0.0946

15

0.50

1.21

0.1154

20

2.05

2.59

0.0570

(min)

Time (to boil)

Evaporate

Rate (1st bubbl e) 0.092 7 0.230 8 0.027 8

Concentrate

Rate (boiling)

Concentr ation (M)

0.0662

0.0883

-0.0954

0.1029

0.0220

0.1632

Rate (1st bubbl e) 0.086 6 0.205 8 0.079 6

Condensate

Rate (boiling)

Concentr ation (M)

Rate (1st bubble )

0.0617

0.0862

0.0845

-0.0850

0.0904

0.1808

0.0630

0.1342

0.0655

Calculation : Rate (1st bubble ) =

Concetration( M ) Time 1 st Bubble(min)

Rate (boiling ) =

Concetration(M ) Time boiling( min)

7

Effect of Evaporator Time 3 2.5 2 Time (min)

1st Bubble

1.5

Boiling Point

1 0.5 0 8

10

12

14

16

18

20

22

Running Time (min)

Rate of Reaction vs Running Time for Evaporates 0.15 0.1 0.05 0 Rate of Reaction (M/min) -0.05 8 10 12 14 16 18 20 22

1st Buble Time Boiling Time

-0.1 -0.15 -0.2 -0.25 Running Time (min)

8

Rate of Reaction vs Running Time for Concentrate 0.15 0.1 0.05 0 Rate of Reaction (M/min) -0.05 8 10 12 14 16 18 20 22

1st Buble Time Boiling Time

-0.1 -0.15 -0.2 -0.25 Running Time (min)

Rate of Reaction vs Running Time for Condensate 0.1 0.05 0 Rate of Reaction (M/min) -0.05

5 10 15 20 25

1st Buble Time Boiling Time

-0.1 -0.15 -0.2 Running Time (min)

5.0 DISCUSSION

1. In this experiment a number of factors that affect the evaporation of a KMnO 4 substance ( ) are being studied. In the first part, the liquid is evaporated in three different pressure conditions. From the basic Physics

9

principle, as the surrounding pressure decreases, the boiling point of a liquid substance also decreases. 2. This effect is shown in the table and graph of Part A, whereby as the pressure inside the evaporator is decreased from atmospheric pressure to -200kPa and -400kPa, the time taken for boiling also decreased. This indicates a lower boiling point, thus the heating process occurs at a higher rate and more efficient under lower pressure. 3. The second part is to study the effect of initial feed level to the rate of evaporation process. The first feed level used is 50cm, then repeated with 75cm. The increase in feed level indicated that the volume of feed to be heated also increases, while the amount of heat supplied to heat the liquid is kept constant in both procedures. 4. Thus, the time taken for the 75cm feed to bubble and boil is more than the time taken for the 50cm feed, since the rate of heating is slower for the liquid with a higher volume. This is proven from the table and graph of Part B. 5. Besides that, from the data tabulated, it is observed that the concentration of feed at the evaporator, condenser and concentrate unit also varies and can be determined by the value of the refraction index (RI) from the refractometer. In every experiment, the concentration of feed at the evaporate is the highest, followed by the concentrate and the condensate. Errors & Modifications While conducting the experiment there are a few errors that had occurred and might affect the results of the experiment. The errors that are considered in this experiment are parallax error, inconsistency of the pressure drop in the pump and human error. 1) Parallax error - While observing the height of the liquid levels, the observant eyes might be in the parallax angle since the height of the column is more than student’s height. - While recording the volume of the liquid using the measuring cylinder, same parallax error might occurred since the position of the cylinder is on table lower than the position of the eyes.

not the the the

2) Inconsistency of pressure drop in the pump - The pressure reading in the pump always fluctuates and drops at constant value. We always need to adjust the pressure manually so that it maintains at desired level. 3) Human error 10

-

-

While recording the time using the stopwatch, human error might occur where there might be a time interval between the stopping time and the recorded time. While observing the bubbles with bare eyes, we might miss the first few bubbles which were too small to be seen, causing longer bubble time being recorded.

To overcome those problems that may lead to inaccurate results, we find some recommendations that should be taken into action which are: 1 A tool should be provided for the students to observe the height of the liquid in the column in the correct eye position. 2 While observing and recording the volume of the liquid in the measuring cylinder, a white paper should be placed at the back of the cylinder for a more accurate reading. 3 Equipment like the pump should undergo regular maintenance or replace with a new one since the current pump is always fluctuating. A digital reading pump is a better replacement compared to the analogue reading pump in giving a more accurate value.

6.0 CONCLUSION In this experiment, different parameters have been manipulated to study their effect on evaporation rates. The manipulated variables are vacuum levels, feed flow rate and evaporation time. In the first experiment, the value of vacuum levels inside the evaporator is varied from atmospheric pressure to -400mmHg. From the result obtained, it can be seen that as the pressure (vacuum level) decreases, the time for first bubble and boiling point also decreases. In the second experiment, the pressure is maintained at atmospheric pressure while the level of the feed is varied from 25cm to 75cm. From the results, we can see that as the level of feed increases, the evaporation time take place faster. This shows that evaporation time is indirectly proportional to the feed level. In the third experiment, the effect of evaporation time with time taken for feed to boil is determined. The time for the first bubble to appear and the feed to boil is recorded. From the result gained, we can see that as the running time increase, the rate of evaporation decreases. In the graphs provided, the rate of reaction against running time for evaporates, condensate, and concentrate is illustrated to show that the relation between evaporation time on concentration of product left.

11

Therefore, we can conclude that all the parameters tested give influence to the evaporation rates. All of these factors must be measured in order to attain absolute evaporation rates.

7.0 REFERENCES

1. McCabe W.M., Smith J.C., Harriot P., Unit Operations of Chemical Engineering 5th Ed., McGraw Hill. 2. Perry R.H., Green D., Eds. Chemical Engineers’ Handbook, 6 th Ed., McGraw Hill. 3. www.wikipedia.com/evaporation

12