Gas Diffusion Essay

OBJECTIVESDetermine the gas diffusion coefficient of acetone victimization the established Winkelmanns mannerKEYWORDSDiffusivity, Gas Diffusion Coefficient, Winkelmanns methodOVERVIEWThe friendship of physical and chemical properties of certain materials is important because very lots process engineering deal with the transformation and distribution of these materials in bulk. adept such property is diffusivity. Mass take away by diffusion takes organize when there is a dumbness gradient of the diffusing component. Naturally, the diffusion in gas strain is much faster than the diffusion in smooth-spoken phase due to the small spaces between the elements that hinder some other molecule movement. Other factors that will proceeds the diffusion are temperature, density, concentration and other external factors.1. INTRODUCTIONThis experiment has been designed for students experiment on the proficiency of determining diffusivity of the vapor of a volatile liquid based on the e stablished Winkelmanns method. In this method the volatile liquid is allowed to dissolve in a vertical glass supply over the hap of which a stream of vapor-free gas is passed. A irrigate bath is provided for maintaining a steady temperature so that there is no eddy current in the vertical tube and the great unwashed transfer takes place from the surface by molecular diffusion alone. The rate of drying up can be followed by the rate of drop cloth of the liquid surface. A traveling microscope is provided for determining, the liquid fall. With the knowledge of the concentration gradient, the diffusivity ofthe vapor of the volatile liquid can then be calculated.2.THEORYWhen a concentration gradient exists within a fluid consisting of both or more components, there is a tendency for each move outice to flow in such a direction as to cut out the concentration gradient. This is called mass transfer. Mass transfer takes place in any a gas phase or a liquid phase or in both simul taneously.When a liquid is allowed to evaporate in a narrow vertical tube and a steady temperature is maintained, mass transfer takes place from the surface by molecular diffusion alone. This is the technique developed by Winkelmann to determine the diffusivity of the vapor of a volatile liquid. By monitoring the evaporation rate, which is the rate of fall of liquid surface, and with the knowledge of concentration gradient, one may then calculate the diffusivity.The rate of mass transfer is failn by(1)where,D=diffusivity m2/sCA=saturation concentration at interface kmol/m3L=effective distance of mass transfer mCT=total molar concentration kmol/m3CBm=logarithmic mean value of CB kmol/m3Considering the evaporation of the liquid(2)where,L=density of liquid kg/m3M=molecular burthen kg/kmolCombining equations 1 and 2 we get,(3)Integrating and putting L = L0 at t = 0(4)Values of L0 or L will non be measured accurately but accurate values of (L L0) are available.Thus, rearranging equa tion 4or,(5)A plot of t/ against will give a slope s(6)Diffusivity D can then be calculated from equation 63.START UP AND SHUT- DOWN PROCEDURES3.1Start-up turn preceding to running an experiment, students are advised to perform the following start-up procedure1.Fill the water bath with clean (preferably filtered) water to approximately 30 mm from the top.2.Plug the mains business line to the electrical supply. Be sure that the voltage of the supply is correct to causal agent the equipment.3.Switch on the main power on the control panel.4.Adjust the set-point value on the temperature control to 50 C.WarningDo not set the temperature controller beyond 70 C.5.Switch on the bullet train. proceed the water temperature heats up to 50 C and remains constant.6.Switch on the commit pump. Adjust the needle valve so that a steady low velocity of air stream is sight at the end of the fictile tubing.7.The equipment is now ready for student experiment.b)Priming Procedure for the Capillary TubeBefore using the capillary tube in an experiment using acetone, students are advised to clean the inside of the tube.1.Prepare a weak solution of detergent.2.Use a Hirschmann pipette to fill the tube with the solution. Tapping the outdoors of the tube may be necessary if the solution is trapped and does not flow down.3.Turn the tube upside-down and shake. Empty the tube.4.Repeat steps 2 to 3 with acetone.5. The tube is now ready for student experiment.c)Shut-down ProcedureAfter the consequence of an experiment, students are advised to shut down the equipment as follows1.Switch off the heater and air pump.2.Adjust the set-point value of the temperature controller to approximately 5 degree on a lower floor the room temperature.3.Allow the water to cool down until it is safe to touch. Open the debilitate valve and empty the water tank.4.Detach the flexible tubing and clean the capillary tube for next use. (Refer to priming procedure)5.Switch off the main power. Unplug the main business if the equipment will not be used for a long period.4.EXPERIMENTAL PROCEDURES1. coiffure the start-up procedure as outlined in section 3.2.Initially switch off the air pump.3.Partially fill the capillary tube with acetone to a perspicaciousness of about 35 mm.4.Carefully insert the capillary tube through the satisfactory on top of the water bath cover. Do not over-tighten the fitting.5.Observe the sign level of acetone through the microscope. Record the level in the table.6.Connects the flexible tubing from the air pump line to one end of the capillary tube. Switch on the air pump.7.After 10 minutes, switch off the air pump. Disconnect the flexible tubing and detach the capillary tube from the fitting. Observe and record the level of the acetone.8. Repeat steps 5 to 6 at 10 minutes intervals.9. Record the time, acetone level and liquid fall in the table below.5.0RESULTTime,t(ks)Level ofAcetone, L(mm)Liquid devolve(L L0)(mm)t/(L L0)(ks/mm)6.0TUTORIALS6.1 Plot t/ aga inst. Determine gas diffusivity, D from the obtained slope, s. abandoned all of your calculation at the appendix in the experiment report. 6.2 examine the experimental value with the theoretical value that can be predicted from semiempirical equations (e.g. modified Maxwells equation by Gilliland). 6.3 Discuss the factors that effect the diffusion of acetone from the graph that have been plotted. 6.4 Base on fair game of the experiment and the theory in gas diffusion makes a cobblers last from your finding.7.0 SAFETY AND MAINTENANCE frequent Safety Procedure1.Always read and pick up the manual properly before attempting to operate the equipment. 2.Always wear proper arise during laboratory session. It is highly recommended that eye protection and gloves are used. 3.Be careful when use hazardous material. Always refer to the material safety data sheet. stave off inhaling in great amount any hazardous material. 4.Avoid any release onto electrical components to prevent electri cal shock. 5.Avoid touching hot surfaces (e.g. heater) to prevent uncase burn. 6.Always conduct experiment in a properly ventilated room.General Maintenance Procedure1.Do not operate the equipment if any of the components is found to be faulty. Consult the instructor for assistance. 2.Disconnect the equipment from electrical supply when not in use. 3.Drain the water from the water bath.4.Clean the water bath thoroughly after use.Values for weighing1. L = 760.0 kg/m32. M = 58.08 kg/kmol3. Partial pressure P* = 0.8062 atm4.where for acetone,CB1=0.0377 kmol/m3CB2=0.00731 kmol/m3CA=0.0304 kmol/m3CT=0.0377kmol/m3