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S I M U L T A N E O U S H E A T &

M A S S T R A N S F E R

•Humidification

•Dehumidification

•Cooling Towers

•Humidification Terms

HUMIDIFICATION

Addition of vapors/water in gas stream

DEHUMIDIFICATION

Removal of vapors/water from a gas stream

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COOLING TOWERS

In industry cooling of water required for

Hot condenser water

Process hot water

Cooling water used in heat exchangers/coolers

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INDUSTRIAL APPLICATIONS

Pharmaceutical Industry

Fertilizer industry

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INDUSTRIAL APPLICATIONS

Paper industry

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HUMIDIFICATION TERMS

Humidity H

Mass of vapours associated with unit mass of dry

gas

Humidity of saturated gas Ho Humidity of the gas when it is saturated with

vapours at a given temperature.

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HUMIDIFICATION TERMS

Percentage humidity(%H)

Percentage humidity =

Humidity

Humidity of saturated gas

Humid volume

Volume occupied by unit mass of dry gas and its

associated vapours.

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X 100

HUMIDIFICATION TERMS

Humid heat (S)

Heat required to raise unit mass of dry gas

and its associated vapour through unit

temperature difference at constant pressure

or

S = Ca + H*Cw

For air water system

S = 1.00 + 1.9 H kJ/Kg K

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Ca= Specific heat capacity

of gas

Cw= Specific heat capacity

of vapour H = humidity

HUMIDIFICATION TERMS

Dew point Temperature at which the gas is saturated with

vapour. As the gas the cooled, the dew point is

the temperature at which condensation will first

occur.

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HUMIDIFICATION TERMS

Saturated volume Humid volume of saturated gas

Percentage relative humidity

partial pressure of vapour in gas

= x 100

Partial pressure of vapours in saturated gas

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FOR UNIT VOLUME OF GAS

General gas equation; PV = nRT

For unit volume; V = 1 P = nRT

From above equation

Mass of vapour = Pw Mw

RT

For air- water system

Humidity (H) = 18 Pw

29 P 12

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n = mass/ molecular weight

EXAMPLE 13.1

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EXAMPLE 13.2

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HUMIDIFICATION AND WATER COOLING

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15

Questions: Related problems: Do

yourself

Thank you Questions