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Diffusion & Convection_Part 1

Total questions: 7

Worksheet time: 1hrs 10mins

Name
Class
Date
1.

Consider loss of ethanol vapor by diffusion from a half-filled open test tube. At what point in the diffusion path will the contribution of the bulk flow term to the molar flux be maximum? (Allocation time: 2 min)

a)

At the liquid-gas interface

b)

In the bulk liquid

c)

In the bulk gas

2.

A sheet of Fe 1.0 mm thick is exposed to an oxidizing gas on one side and a deoxidizing gas on the other at 725°C. After reaching steady state, the Fe membrane is exposed to room temperature, and the C concentrations at each side of the membrane are 0.012 and 0.075 wt%. Calculate the diffusion coefficient (m2/s) of C if the diffusion flux is 1.4×10-8 kg/m2.s. (Allocation time: 15 min)

a)

9.87x10-12

b)

9.87x10-13

c)

9.87x10-11

d)

9.87x10-10

3.

In industries titanium is hardened through diffusion of carbon. The concentration of carbon at 1 mm into the surface of the titanium slab is 0.25 kg/m3 and at 3 mm the concentration is 0.68 kg/m3. The rate at which the carbon is entering into its surface is 1.27x10-9 kg/m2.s. Calculate the value of diffusion coefficient (m2/s) of carbon. (Allocation time: 15 min)

a)

5.91x*10-12

b)

5.91x10-10

c)

5.91x10-11

d)

5.91x10-13

4.

Define the convective mass transfer. (Allocation time: 3 min)

a)

The transport of material between a boundary surface and a moving fluid

b)

The transport of material between two immiscible moving fluids separated by a mobile interface.

5.

What are the factors affecting kc? (Allocation time: 5 min)

a)

The properties of the fluid

b)

The dynamic characteristics of the flowing fluid

c)

The geometry of the specific system of interest

6.

A value of kG was experimentally determined to be 1.465 x 10-3 kgmol/s.m2.atm for A diffusing through stagnant B. Given system's conditions are as follows: the partial pressure are pA1= 0.20 atm, pA2=0.05 atm and total pressure, Pt=1.0 atm. For the same flow and concentrations, predict the k'G for equimolar counterdiffusion. (Allocation time:15 min)

a)

1.279 x 10-3 kgmol/s.m2.atm

b)

1.279 x 10-4 kgmol/s.m2.atm

c)

1.279 x 10-5 kgmol/s.m2.atm

d)

1.279 x 10-6 kgmol/s.m2.atm

7.

A value of k'G was experimentally determined to be 1.279 x 10-3 kgmol/s.m2.atm for A diffusing through stagnant B. Given system's conditions are as follows: the partial pressure are pA1= 0.20 atm, pA2=0.05 atm and total pressure, Pt=1.0 atm. For the same flow and concentrations, calculate the flux of A for equimolar counterdiffusion. (Allocation time:15 min)

a)

19.2 kgmol/s.m2

b)

0.192 kgmol/s.m2

c)

1.92 kgmol/s.m2