I need help in mass transfer ( chemical engineering )

ChE 4131: Transfer Science III, Mass Transport

Dr. H. A. Stretz

HW 1

Due Thursday Sept. 1

1. State in words the difference between a mass transfer coefficient and a diffusion coefficient. 2. Attach a plot of the mole fraction (concentration profile) of species 1 (range of 0 to 1) versus

relative position up the capillary, z/l. This graph MUST have labels on the axes and a figure

caption. The problem was described in class and the relevant figure in the book is Fig. 3.3-1.

3. Why is this function not linear as described by Fick’s Law? 4. Where is the mole fraction of species 1 at its highest? 5. Intuitively species 2 is a stagnant gas (no dynamic movement) and might have the same mole

fraction no matter what position up the capillary. Is this true? State a simple equation that

would allow you to plot the concentration profile of species 2 given the concentration profile of

species 1.

6. Calculate the rate of evaporation (grams/hour) of a chloropicrin gas into air at 25oC. Treat air as a pure substance. Draw and label the capillary setup applied to this problem from Figure 3.3-1.

Show all your work with units and starting with the relevant differential equation derived in

class. Show all assumptions. Note that the rate of evaporation for such a device would be equal

to the flux of species 1 at the top of the capillary.

PTOT 770 mm Hg

D1,2

0.088 cm2/sec

Pvap,1

23.81 mm Hg

L 11.14 cm

Density1 1.65 g/cm 3

Area

2.29 cm2