5/26/15

1

Using molecular sieves, water vapor was removed from nitrogen gas in a packed bed at 28.3C. The column height was 0.268 m, with the bulk density of the solid being equal to 712.8 kg/m3. The initial water concentration in the solid was 0.01 kg water/kg solid and the mass velocity of the nitrogen gas was 4052 kg/m2h. The initial water concentration in the gas was c0 = 926 kg water/kg nitrogen.

Sample Problem #5:

t (h)

0

9

9.2

9.6

10

10.4 c (kgH2O/kgN2)

5/26/15

2

A2 is the sum of the areas of trapezoid above data points

A2= (12.8-9.6)(1)-0.5[(0.098+0.023)(109.6)+(0.254+0.098)

(10.4-10)+(0.451+0.254)(10.8-10.4)+(0.68+0.451)

(11.25-10.8)+(0.774+0.68)(11.5-11.25)+(0.923+0.774)

(12-11.5)+(0.978+0.923)(12-11.5)+(1+0.978)(12.8-12.5)]

Therefore, A2 = 1.33

Fraction of bed used up to the breakpoint time =

1

1 2

9.6 0.889.6 1.33

AA A

= =+ +

Length of unused bed =

2

1 2

1.33 0.268 0.0339.6 1.33

A H mA A

= =+ +

For a proposed length of 0.4m

By ratio and proportion:

b b

old new

t tH H

=

9.6 0.40.268

therefore, tb,new = =14.33h

new A1 = 14.33, A2 is still 1.33

Fraction of total capacity used =

1

1 2

14.33 0.914.33 1.33

newAnewA A

= =+ +