Evaporation

Question 1

generally refers to the removal of water, by vaporization, from aqueous solutions of non-volatile substances.

Answer 1

Evaporation

Question 2

It is an operation that converts a liquid into a vapor leaving behind a concentrated solution or a higher boiling liquid

Answer 2

Evaporation

Question 3

In evaporation, several rate processes occur. Name them.

Answer 3

First, heat is transferred from the heating medium to the solution. Second, mass and heat are simultaneously transferred from the
liquid to the vapor phase.

Question 4

Two basic processes involved in evaporation

Answer 4

Transfer of Heat
Transfer of Mass

Question 5

The heat supplied includes

Answer 5

 The sensible heat for the solution to reach its boiling point.
 Latent heat of vaporization for the water evaporated

Question 6

controls the overall rate of evaporation and the effect of the other transfer processes is only minor.

Answer 6

The transfer of heat from the heater to the solution

Question 7

is generally provided by the condensation of a vapor, such as steam, on one side of a metal surface with the evaporating liquid on the other side.

Answer 7

The heat required for evaporation

Question 8

Why is it necessary to remove the vapor from the evaporator for the continuation of vaporization?

Answer 8

the pressure above the solution soon equals the v.p. of the water and boiling stops.

Question 9

An evaporator consists of

Answer 9

1. Heat Exchanger capable of boiling the solution
2. and a device to separate the vapor phase from the boiling liquid.

Question 10

The solution in the evaporator body is violently mixed and therefore homogeneous in composition, except in the case of

Answer 10

long tube vertical evaporators and turbulent evaporators.

Question 11

To find ℎ𝐹 𝑎𝑛𝑑 ℎ𝐿:

Answer 11

1. Use concentration-enthalpy diagram if available
   If concentration-enthalpy diagram is not available, instead specific heat of the feed should
   be given, use boiling point of the solution as base temperature

Question 12

Each unit in such a series is called an

Answer 12

effect

Question 13

is the principal means in use for economizing in the energy consumption.

Answer 13

multiple effect evaporation

Question 14

the method of reusing the latent heat is

Answer 14

multiple effect evaporation

Question 15

In the _______ feed operation, the feed is introduced in the first effect and passed from effect to effect parallel to the stead flow.

Answer 15

forward

Question 16

Disadvantage of forward feed operation

Answer 16

all the heating of cool feed is done in the first effect, so that less vapor is generated from each unit mass of steam, resulting in lower steam economy.

Question 17

In the _____ feed operation, feed is introduced in the last effect and the concentrated product is taken out from the first effect.

Answer 17

backward

Question 18

are required between effects in backward feed operation

Answer 18

Pumps

Question 19

The backward feed operation is used when

Answer 19

1. feed is cold, since less liquid must be heated to the higher temperature existing in the early effects
2. also used when the product is viscous that high temperature existing in the early effects
3. also used when the product is viscous that high temperature is needed to keep the viscosity low enough to give reasonable heat transfer coefficient.

Question 20

In the _____ feed operation, the fresh feed is introduced directly into each effect and evaporated to find concentration in each effect

Answer 20

parallel

Question 21

The parallel type of operation is used when

Answer 21

feed is saturated solution and solid crystal are product, as in the manufacture of common salts.

Question 22

is used only for special applications, as when liquor at an intermediate concentration and a certain temperature is desired for addition processing.

Answer 22

Mixed feed operation