Chemical Engineering Answers

By what percentage would the rate of absorption be increased or decreased by increasing the total pressure from 100 to 200 KN/m2 in the following cases: a. The absorption of ammonia from a mixture of ammonia and air containing 10% of ammonia by volume, using pure water as solvent. Assume that all the resistance to mass transfer lies within the gas phase. b. The same conditions as (a) but the absorbing solution exerts a partial vapour pressure of ammonia of 5 KN/m2. The diffusivity can be assumed to be inversely proportional to the absolute pressure.

Model distillation column with hold up taking necessary valid assumptions?

Model stripping section of an ideal binary distillation column taking valid assumptions

Show that when a Bingham plastic fluid flows under laminar condition through a tube of radius R and length L the volumetric flow rate, Q is given by 4 4 0 0 0 0 ( ) 4 1 1 8 3 3 L R R P P R Q L         −     = − +               Where 0  and R  are the yield stress and shear stress at the tube wall, respectively.

In a gas absorption experiment a viscous fluid flows upward through a small circular tube and then downward in laminar flow on the outside. Set up a momentum balance over a shell of thickness r in the film, as shown in figure 1 (Appendix A). Note that the “momentum in” and “momentum out” arrows are always taken in the positive coordinate direction, even though in this problem the momentum is flowing through the cylindrical surfaces in the negative r direction. i. Show that the velocity distribution in the falling film (neglecting end effects) is 2 2 2 1 2 ln 4 z gR r r v a R R         = − +               ii. Show that the mass rate of flow in the film is given by 2 4 2 4 4 1 4 3 4 ln 8 gR w a a a a   = − + − +     iii. Show that the result in (b) simplifies to the following equation, if the film thickness is very small ( Use a = +  1 , 1   ) 2 3 cos 3 gW w     = , Where W R = 2 and   = R .

A solid sphere of radius R is rotating slowly at a constant angular velocity '  ' in a large body of quiescent fluid as shown in figure 2 (Appendix-I). Develop expressions for the pressure and velocity distributions in the fluid using shell momentum balances (refer figure 3). Also find out the torque required to maintain the motion. Assume that the sphere rotates sufficiently slowly so that one can conveniently use the creeping flow assumption. Appendix-A Figure 1: Velocity distribution and z-momentum Balance for the flow of a falling film on the outside of a circular tube. Figure 2: A slowly rotating sphere in an infinite expanse of fluid Figure 3: Differential Volume Elemen

what is the difference between chemistry and chemical engineering

. A magnetic stirrer agitated vessel is used for absorption of CO2 in water at 298 K and 2

atm pressure. Water is fed at a rate of 1 L/min and the carbonated water leaves the vessel

continuously so that a constant volume is maintained in the contactor. The outlet water

contains 2.3 g CO2/L. The interfacial area of gas-liquid contact is 80 m2

/ m3

; the volume of

gas-liquid dispersion is 8 L. The solubility of CO2 in water can be found using Henry’s law.

At 298 K, the Henry’s law constant for CO2 is 1640 atm/mole fraction and it’s diffusivity in

water is 1.92 x 10-9 m/s. The density of liquid is 997 kg/ m3

. Calculate:

(i) The thickness of the liquid film, if the Film theory is applicable.

(ii) The contact time between the liquid element with the gas if the Penetration theory is

applicable.

(iii) The surface renewal rate if the Surface-renwal theory is applicable. (

For the absorption of dilute gas mixture in a packed column, derive that

y y lm

y y

N

e

toG







1 2

In the Danckwerts model, it is assumed that elements of the surface have an age

distribution ranging from zero to infinity. Obtain the age distribution function for this model

and apply it to obtain the average mass transfer coefficient at the surface, given that from the

penetration theory the mass transfer coefficient for the surface of age θ is

/( ) DAB

. (4)