Mass Transfer

A. Flights (located in the inside shell of rotary dryer) lift the material being dried and shower it
down through the current of hot air/gases. It extends from the wall to a distance which is about
8-12% of the inside diameter of shell
B. Hold up of a rotary drier is defined as the fraction of the dryer volume occupied by the solid at
any instant. The best performance for rotary drier is obtained, when the hold up is in the range
of 0.05 to 0.15
C. Rotary dryer is suitable for drying sticky material
D. Recommended peripheral speed of a rotary drier is in the range of 10 to 30 metres/minute

A. With decrease in feed temperature, the number of plates required for binary distillation
decreases for a given ‘L/V’ ratio
B. The extraction per unit of total height for a short packed column is more effective than for a
tall column, in case of liquid-liquid extraction
C. Natural draft cooling towers are made of ferroconcrete and its cross-section is wider at the
bottom
D. Vander wall adsorption is also called chemisorption

A. For identical gas flow rates, less pressure drop occurs through a plate tower than through a
packed tower
B. Plate column can handle greater liquid loads without flooding than packed column, but the
liquid hold up is more in the case of plate column
C. For the same duty, plate columns weigh less than packed columns
D. All A., B. and C.

A. Fine solids cannot be leached in a Pachuca tank
B. Door classifier can be used for leaching of coarse solids
C. Vegetable seeds can be leached in either of Bollman extractor, Rotocel or Kennedy extractor
D. Very high temperature is not needed for the leaching of sugar beet

A. Bound moisture is removed during constant rate drying period
B. Free moisture is removed during falling rate drying period
C. The sum of free moisture and equilibrium moisture in a solid is called the critical moisture
D. The driving force for mass transfer in a wet solid is its free moisture content

A. Packed towers are preferred for vacuum operation, because the pressure drop through the
packing is less and they (packings) also lessen the possibility of tower wall collapse
B. Packed towers are preferred over plate towers for handling corrosive and foamy liquids
C. Diameter of randomly packed tower is normally more than 1.2 metres
D. Due to uneven supply and improper distribution of liquid, problem of channelling, loading &
flooding is generally encountered in packed towers

A. Different solids have different equilibrium moisture curves
B. Total condenser or reboiler is considered equivalent to one theoretical plate in McCabe-Thiele
method of theoretical plate calculation for distillation column
C. Heat removal load on cooler remains constant, even with increase of the reflux ratio in a
distillation column
D. Even a forced draft cooling tower cannot cool water below the wet bulb temperature

A. When the concentration difference for the mass transfer becomes zero at the bottom of the gas
absorption tower, then the upper end of the operating line touches the equilibrium curve
B. The average distance between the operating line and equilibrium line is large, when the liquidgas
ratio is also large in case of a counter current gas absorption tower
C. The operating line lies above the equilibrium curve in case of a gas desorber
D. With decrease in the liquid flow rate for a fixed gas flow rate, the slope of the operating line
decreases, in case of gas absorption process

A. In case of liquid-liquid extraction, no separation is possible, if the selectivity of the solvent
used is unity
B. With increase in temperature, the selectivity of the solvent used in solvent extraction
decreases
C. The selectivity of solvent used in solvent extraction is unity at the plait point
D. All A., B. and C.

A. In the McCabe-Thiele diagram for binary distillation, vertical feed line represents saturated
liquid feed and horizontal feed line represents saturated vapour feed
B. In small columns, local efficiency is larger than Murphree efficiency; in large columns local
efficiency is smaller than Murphree efficiency
C. For Laminar flow over a plate of length L, the local mass transfer co-efficient at a distance L
from the leading edge is 1.5 × 10-2m/s. Then the average mass transfer co-efficient for the
plate is 2 × 10-2m/s
D. The concentration and hydrodynamic boundary layers over a flat plate are of equal thickness,
if Schmidt number is equal to unity