Drying/ dehydation

Question 1

Define drying

Answer 1

Removal of water under controlled condition

Question 2

Industrial perferred drying agent

Answer 2

Air, as it has the capacity to absorb water under set condition

Question 3

Undesirable physical/ chemical changes during hot air drying

Answer 3

Oxdiation 
Browning
Reduction in moisture content 
Thermal degradation of active ingredient 
Emission of volatile components

Question 4

properties of air- water system

Answer 4

vapour pressure

Question 5

Vapour pressure

Answer 5

The pressure applied by the molecules which evapoured from the liquid to its surrounding for equilibration.

Question 6

Vapour pressure is depend on _______ only

Answer 6

temperature

Question 7

Humidity

Answer 7

the water content of air

Question 8

Absolute humidity

Answer 8

mass of water [kg] present in a unit mass of dry air

Question 9

Relative humidity

Answer 9

the ratio of absolute humidity of air to the saturation at the same temp

a measure of air saturation

Question 10

Dew point

Answer 10

The temperature when air is saturated with moisture (100% RH)
Absolute humidity is equal to saturation humidity, and water begins to condense out of air.

Happen as cooling proceeds

Question 11

Wet bulb temperature

explain

Answer 11

temp meaured by a wet thermometer in an air- water vapour mixture

The temp when free liquid surface is in equilibrum with moist air

Tested by : Thermometer bulb is surrounded by a wet cloth. The surrounding heat is removed by the evaporation of water and the latent heat is taken away from the bulb –> temp falls until surrounding air is saturated

Question 12

Dry bulb temperature

Answer 12

Temperatue of the air

meaured by a dry thermometer in an air- water vapour mixture

Question 13

Different types of drying

Answer 13

Osmotic dehydration
Spray drying
Freeze drying
Drum drying (drum driers)
Fluidised bed drying
Through circulation driers
Tray drier

Question 14

Description of drying kinetics

Answer 14

water removed from material throught the superficial film which behaves like a free water interface. (Intital moisture content is at Xi)

The water removed is constinously replenished from the bulk at a rate equal to the drying rate = constant drying rate period

Then the drying begins to fall at the critical moisture content (Xc). Surface begins to dry out –> surface temp rises

The moisture drop below a given value and surface water can’t be replaced at the same rate from the interior [falling rate drying period]
and reach the equilivrum moisture content (Xe)

Question 15

Drying rate is depend on ____? In dependent on ?

Answer 15

independent of suface conditions

increasingly dependent of the moisture movement within the material which usually occurs by capillary flow

Question 16

tray drier

Answer 16

material spread out on trays and trucked into a chamber

hot air is blown acoss the tray

drying time = mins/ hr

Inlet air temp = 120- 180’C

Question 17

Through circulation driers

Answer 17

material spread out on trays with screen bottom and trucked into a chamber

hot air is blown through the wet material

drying time = mins/ hr

Inlet air temp = 120- 180’C

Question 18

Fluidise bed drying

Answer 18

Wet solids are ‘fluiidised’, in a cylindrical vessel with a concial bottom

hot air pass through the solid at high veolocity

drying time = mins/ hr

Inlet air temp = 120- 180’C

Question 19

Necessary safety controls of drying process

Answer 19

Correct process conditions

Correct disinfection protocols for equipment

Recording and monitoring of the process

Batch traceability

Packaging/sealing under hygienic conditions

Testing to ensure adequate reduction of moisture

Suitable means of reducing oxygen may be necessary (preservatives)