Gas Transfer Lab

[Name of the Institution]

Abstract

The main purpose of gastransfer lab is to introduce the students with the significantequipment of gas transfer and facilitate the students to understandthe theoretical and experimental concept of gas transfer. Thisenables to observe and compare the experimental data of gas transferwith the theoretical concept.

Gas transfer is aphysical phenomenon in which the exchange of gas molecule occursbetween gas-liquid interfaces. This results to increase the gasconcentration in the liquid. This interface is possible as long asthe phase is unsaturated with gas under the condition of pressure,absorption and temperature. Gas transfer decreases in the conditionwhen liquid is over saturated or to say stripping in gas occurs.Since the gas transfer between solid, liquid and gas is necessaryelements of the environmental process. The treatment of wastewaterrequires transferring the oxygen for the maintenance of aerobicdegradation. Furthermore, the gas transfer is used to eliminate theunwanted chemicals. The rate of diffusion of oxygen is lower ascompare to carbon dioxide . The solubility of carbon dioxide istwenty-four times more than oxygen. It implies carbon dioxidediffuses twenty times more rapidly than oxygen (Wanninkhof, 2012).

ln(C* – Ct)= ln(C* – Co)- KLat

Objectives

  • To understand the working of aeration kinetic during in the oxygen transfer system

  • To understand the concept about why and how aeration are utilized in an aquarium system.

Materialsand Methods

Equipment:dissolved oxygen probe, air pump, dissolved oxygen meter and airdiffuser. First, the beaker is set on the stir plate and attaches theDO meter and thermometer with lab quest unit. Take 500ml of waterusing graduated cylinder and transfer into the beaker keeping the DOprobe with the metal dot of 1 under the water surface. Stir thewater using magnetic stirrer make sure that stirring should be 200rpm. Record the room temperature for the determination of saturationconcentration C*. After adding 10 drops of cobalt chloride into thebeaker, add 4ml sodium sulfite into the 10ml of beaker solution .Using the transfer pipet, put 2ml sodium sulfite into the beaker bykeeping the stirrer on and diffuser off. Now, take the reading ofdissolved oxygen concentration (DO). For making the DO= 2-3 mg/L, add 8 drops of sodium sulfite. Wait approximately 4 minutes to makethe solution stabilize. Record the reading of temperature and makestir off and plug-in air diffuser on into the power source. Take thereading of dissolved oxygen concentration after every 20 seconds fora couple of minutes and then take the reading after every minute. Donot take the experimental reading more than 10 minutes. In the laststep, draw the graph of experimental data in between time andLn(C*-Ct) and obtain the value of mass transfer coefficient KLa. Byusing the trend line analysis, identify the value of slope in thelinear equation.

Results

Temperature

C* mg/L

Time

Ct mg/L

ln(C* – Ct) mg/L

23.5

8.75

0

8.44

-1.17118

24.5

8.5

0

2.83

1.735189

24.6

8.35

20

2.9

1.695616

24.6

8.35

40

3.24

1.631199

24.6

8.35

60

3.98

1.474763

24.6

8.35

80

4.74

1.283708

24.6

8.35

100

5.47

1.05779

24.6

8.35

120

6.00

0.854415

24.7

8.34

180

7.11

0.207014

24.7

8.34

240

8.01

-1.10866

24.7

8.34

300

8.19

-1.89712

24.8

8.38

360

8.26

-2.12026

24.8

8.38

420

8.32

-2.81341

24.9

8.4

480

8.36

-3.21888

24.9

8.4

540

8.37

-3.50656

Graph OfTime(s) Vs ln(C* – Ct) mg/L

ForFinding KLa

The slopeequation is y=-0.009x + 1.502

Let x= 1.695

Hence KLa=1.486/sec

Discussion

Three mainfactors can affect the process of gas transfer in plants and animals:

•Surface area of the membrane

Surfacearea is directly proportional to the gas transfer as when the surfacearea is bigger, air is circulating around the membrane thatincreasing the rate of gas transfer.

•Thickness of the membrane

Membranethickness is inversely proportional to the rate of the gas transferat which gas starts to diffuse from the high concentration area tothe low concentration area. Thicker membrane decreases the rate ofgas transfer and increases the velocity at which gasses flow.

•Concentrationgradient

Gastransfer can effect with the concentration gradient. It only possiblewhen the membrane divides the two surfaces due to the difference inthe concentration of gas. That difference supports the process of gastransfer because the gas starts the movement from high concentrationto low concentration area.

The use ofcobalt chloride detects the presence of water molecules. If the wateris present, cobalt chloride will modify the color from blue to purpleand from purple to pink. Cobalt chloride reacts with sodium sulfiteand forms complex molecules that have neutral charge ( no charge)(Ho, 2011) . The presence of hydroxide eliminate the cobalthydrogenation and leading to the following reaction:

Cobaltchloride is soluble

Sodiumsulfite is insoluble

Now, thebalanced equation:

2CoCl3(aq) + 3 Na2S(aq) = Co2S3(s) + 6 NaCl(aq)

Conclusion

“Thechance of an element of the surface being replaced with fresh liquidwas independent of the length of time for which it has been exposed.. The effects of temperature on the rate gas transfer effects on KLa”(Lessard, 2013).

References

Wanninkhof, R., Asher, W., Weppernig, R., Chen,H., Schlosser, P., Langdon, C., &amp Sambrotto, R. (2012). Gastransfer experiment on Georges Bank using two volatile deliberatetracers. Journal of Geophysical Research: Oceans, 98(C11),20237-20248.

Ho, D. T., Wanninkhof, R., Schlosser, P.,Ullman, D. S., Hebert, D., &amp Sullivan, K. F. (2011). Toward auniversal relationship between wind speed and gas exchange: Gastransfer velocities measured with 3He/SF6 during the Southern OceanGas Exchange Experiment. Journal of Geophysical Research: Oceans,116(C4).

Lessard, R. R., &amp Zieminski, S. A. (2013).Bubble coalescence and gas transfer in aqueous electrolyticsolutions. Industrial &amp Engineering Chemistry Fundamentals,10(2), 260-269.