Mass transfer quiz 2018

MASS TRANSFER OPERATIONS QUIZ

Q. 1 A binary distillation column is designed by McCabe-Thiele method to get a distillate mole fraction of 0.9. The enriching section operating line has an intercept with y-axis at 0.3 mole fraction. The ratio of liquid to vapour molar flow rate in the enriching section is......................(rounded off to third decimal place).

Q. 2.According to the surface renewal theory, the unit of fractional rate of surface renewal is

m²S²
m²S^-1
mS^-1
S^-1

Q. 3 Two packed towers are designed for the same mass velocity of the gas. The first has liquid and gas flow rates of 30 kg/s and 1.2 kg/s, respectively, while the corresponding flow rates in the second tower are 67.5 kg/s and 1.8 kg/s. The ratio of the design diameter of the wider tower to that of the narrower tower is

2
1.8
1.5
1.225

Q. 4 A fiberboard sheet ( 1.5 m * 2.0 m * 15 mm ) is being dried by suspending it horizontally in a current of hot, dry air. The edges are insulated so that drying takes place only from the top and bottom surfaces. The wet sheet weighing 16 kg with initial moisture content of 60% loses moisture at a constant rate of 1.25 * 10^-5 kg m^-2 s^-1 until the moisture content falls to 30%. All moisture contents are on dry basis. The time required for drying during constant rate period (in hour) is .............(rounded off to third decimal place).

Q. 5 It is decided to extract A from a feed containing 20 mol% A and 80 mol% B in two ideal crosscurrent stages as shown below, using equal amount of pure solvent C in each stage.

Components B and C are immiscible, 60% of A in the feed is extracted in Stage 1. The equilibrium relation is given by Y* = 1.5X where X = moles of A per mole of B in raffinate Y' = moles of A per mole of C in extract in equilibrium with raffinate The mol% of A in raffinate form stage 2 is .................. (rounded off to second decimal place).