IndiaBIX Chemical Engineering: Mass Transfer Section 14 Flashcards
A natural draft cooling tower is filled with wooden grids, which covers about __________ percent of the tower height.
10-15
30-40
70-80
90-100
10-15
As the reflux ratio, in a continuous counter-current extraction is increased, the number of stages
increase
decrease
remain unchanged
can either increase or decrease, depends on the system
decrease
At 750°K and 1 atm, the approximate value of Schmidt number for air is
0.01
0.1
1
10
0.1
Calculation of mass transfer co-efficient is mostly/normally done using __________ theory.
surface renewal
film
penetration
none of these.
film
Chemisorption compared to physical absorption has
lower adsorption rate.
lower capacity of the solvent for the solute gas.
increased utilisation of stagnant zones of the liquid phase.
none of these.
increased utilisation of stagnant zones of the liquid phase.
Desulphurisation of petrol is done in a
Bollman extractor
rotating disc extractor
packed extraction column
plate type extraction column
rotating disc extractor
For absorbing a sparingly soluble gas in a liquid, the
gas side co-efficient should be increased.
liquid side coefficient should be increased.
gas side co-efficient should be decreased.
liquid side co-efficient should be decreased.
liquid side coefficient should be increased.
For the gas absorption, the height of a transfer unit, based on the gas phase is given by (G: superficial molar gas velocity, L: superficial molar liquid velocity, FG:mass transfer co-efficient, mols/m2 , a: in-terfacial area per unit volume of tower)
G/FGa
FG/Ga
Ga/FG
L/FGG
G/FG*a
In a single stage extraction process, 10 kg of pure solvent S (containing no solute A) is mixed with 30 kg of feed F containing A at a mass fraction xf = 0.2. The mixture splits into an extract phase E and a raf-finate phase R containing A at xB = 0.5 and xR = 0.05 respectively. The total mass of the extract phase is (in Kg)
6.89
8.89
10
8.25
8.89
In triangular co-ordinates, the ternery composition point falls __________ of the triangle.
in the corners
inside
on the sides
none of these.
inside
Penetration theory relates the average mass transfer co-efficient (K) with diffusivity (D) as
K âˆD
K âˆsqrt(D)
K âˆD^1.5
K âˆD^2
K âˆsqrt(D)
Penetration theory states that the mass transfer co-coefficient is equal to (where, De is diffusivity and ‘t’ is time)
(De.t)^1/2
(De/t)^1/2
(4De/pi*t)^1/2
(4De/t)
(4De/pi*t)^1/2
Pick out the system with maximum boiling azeotrope at 1 atm.
acetone chloroform
ethyl alcohol-water
benzene-ethyl alcohol
none of these
acetone chloroform
Rate of adsorption increases as the
temperature increases.
temperature decreases.
pressure decreases.
size of adsorbent increases.
temperature decreases.
Reboiler is considered as one theoretical plate, because
of the assumption that vapour and liquid leaving the reboiler are in equilibrium.
vapour is recycled to the column.
reboiler itself contains one plate.
none of these.
of the assumption that vapour and liquid leaving the reboiler are in equilibrium.
