CHE481-V1-Midterm

Evaporation of 1 kg of water from a solution in a single effect evaporator requires about ________ kg of steam.

• 0.4 to 0.6

• 1 to 1.3

• 1.8 to 2

• 2 to 2.4

The maximum heat transfer coefficient from steam heating will be attained when the steam is

• Supersaturated

• Saturated

• Wet

• Subcooled

In a multiple-effect evaporator, the effect of boiling point elevation is to

• Reduce the economy

• Increase the economy

Multiple-effect evaporators are used to

• Increase the steam economy & decrease the capacity

• Increase the steam economy & the capacity

• Decrease the steam economy & the capacity

• Decrease the steam economy & increase the capacity

Mass transfer rate between two fluid phases does not necessarily depend on the _______ of the two phases.

• chemical properties

• physical properties

• degree of turbulence

• interfacial area

For ethanol-water system, the lowering of distillate quality from 95% to 92% will cause _______ plate requirement.

• no change in theoretical

• marginal decrease in the number of

• major decrease in the number of

Capacity of a rotary dryer depends on its ______.

• RPM

• inclination with ground surface

• both RPM & inclination with ground surface

• neither RPM nor inclination with ground surface

The equilibrium liquid composition compared to the vapor composition in case of azeotropic mixture is ________.

• less

• same

• more

• either more or less; depends on the system

200 kg of solids (on dry basis) is subjected to a drying process for a period of 5,000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 x 10^-3 kg/m^2⋅s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m^2/1,000 kg of dry solid. The moisture content at

the end of the drying period is (in kg moisture/kg dry solid) is ________.

• 0.5

• 0.05

• 0.1

• 0.2

It is desired to concentrate a 20% salt solution (20 kg of salt in 100 kg of solution) to a 30% salt solution in an evaporator. Consider a feed of 300 kg/min at 30°C. The boiling point of the solution is 110°C, the latent heat of vaporisation is 2100 kJ/kg and the specific heat of the solution is 4 kJ/(kg.K). The rate at which the heat has to be supplied in (kJ/min) to the evaporator is _______.

• 3.06 × 10^5

• 6.12 × 10^5

• 7.24 × 10^5

• 9.08 × 10^5