Gourav Tiwari's presentation introduces psychrometry, the science of air-water vapor mixtures. It discusses key psychrometric properties like dry bulb temperature, wet bulb temperature, and dew point. It also covers psychrometric processes such as sensible heating and cooling, which change temperature along constant humidity lines; and dehumidification and humidification, which change moisture content. The presentation aims to explain these concepts using a psychrometric chart to illustrate different psychrometric processes and how they affect air temperature and moisture levels.

1. A
PRESENTATION
ON
PSYCHROMETRY
Properties, Processes and Charts
By-
Gourav Tiwari
Thursday,January19,2017
1
Psychrometry by Gourav Tiwari is licensed under a Creative Commons Attribution 4.0
International License.

2. CONTENTS
 What Is Psychrometry?
 Properties of Psychrometry
 Psychrometric Processes
 Psychrometric Chart
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3. PSYCHROMETRY
 Psychrometry is the science dealing with the
physical laws of air – water vapor mixtures.
 When designing an air conditioning system, the
temperature and moisture content of the air to be
conditioned, and the same properties of the air
needed to produce the desired air conditioning effect.
 In other words, we can say that psychrometry is the
study of moist air or mixture of dry air and water
vapor.
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4. PROPERTIES OF PSYCHROMETRY
 Dry-bulb Temperature
 Wet Bulb Temperature
 Dew Point Temperature
 Relative Humidity
 Humidity Ratio
 Humidity
• Specific Humidity
• Absolute Humidity
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5. DRY -BULB TEMPERATURE
 The dry-bulb temperature is the temperature
indicated by a thermometer exposed to the air in a
place sheltered from direct solar radiation. The term
dry-bulb is customarily added to temperature to
distinguish it from wet-bulb and dew point
temperature.
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Dry Bulb

6. WET BULB TEMPERATURE
 Wet bulb temperature is the temperature recorded by
thermometer when the bulb is enveloped by cotton
wick saturated with water.
 The accuracy of a simple wet-bulb thermometer
depends on how fast air passes over the bulb and how
well the thermometer is shielded from the radiant
temperature of its surroundings.
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Wet Bulb

7. DEW POINT
 The temperature at which moisture starts to condense
out of the air is known as Dew Point.
 Dew point is also known as saturation temperature.
 Dew point temperature is determined by moving from
a state point horizontally to the left along lines of
constant humidity ratio until the upper, curved,
saturation temperature boundary is reached.
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8. RELATIVE HUMIDITY
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Relative
Humidity
Amount of moisture that a given
amount of air is holding * 100
=
Amount of moisture that a given amount
of air can hold in saturated state
50% RH 100% RH - Saturated
(percentage)

9. HUMIDITY RATIO/SPECIFIC HUMIDITY
 Actual weight of water in an air – water vapor mixture
 Amount of moisture per unit of dry air
 Can be defined as,
W=m/G
Where,
m = mass of water vapor in
air-water mixture
G = mass of dry air
It is generally expressed in
Kg/kg of dry air
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10. HUMIDITY
• Specific Humidity:
 Specific humidity is defined as the
proportion of the mass of water vapor per
unit mass of the moist air sample (dry air
plus the water vapor); it is closely related
to humidity ratio and always lower in
value.
• Absolute Humidity:
 The mass of water vapor per unit volume of
air containing the water vapor. This
quantity is also known as the water vapor
density.
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11. PSYCHROMETRIC PROCESSES
o Sensible Heating
o Sensible Cooling
o Dehumidification
o Humidifying
o Adiabatic Cooling
o Chemical Dehumidification
o Adiabatic Mixing(Moist Air & Water Vapor)
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12. Psychrometric Processes or
Air conditioning Processes
1. Sensible Heating :
It is addition of heat to moist air without the addition of
moisture. It follows a constant humidity ratio line on the
psychrometric chart.
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13. SENSIBLE HEATING
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14. 2. Sensible Cooling:
It is the removal of heat from moist air without the
removal of moisture. It also follows a constant W on the
psychrometric chart.
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15. SENSIBLE HEAT & COOLING PROCESSES
 Heating & Cooling process –
addition or removal of
sensible heat without
change in absolute moisture
content.
 NOTE: RH changes as
temperature changes.
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16. PSYCHROMETRY - DEHUMIDIFICATION
 Dehumidification by
cooling – in cooling coils
temp of air reduces and
the saturation point
(dew point) is reached.
 Further cooling results
in reduction of absolute
humidity.
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17. 3. Cooling and Dehumidifying:
It is the removal of heat and moisture from moist air, it
involves sensible and latent heat transfer.
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18. DEHUMIDIFICATION BY COOLING
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19. 4. HUMIDIFYING :
It is the addition of moisture to moist air without the
addition of heat.
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20. 5. Heating and Humidifying:
It is the addition of heat and moisture to moist air, it
also involves sensible and latent heat transfer.
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21. Thursday,January19,2017
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REMOVING SENSIBLE HEAT AND MOISTURE

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 A psychrometric process which involves the
cooling without heat loss or gain. Sensible heat
lost by air is converted to latent heat in the added
water vapor.
Adiabatic or evaporative cooling

23. HEATING AND DEHUMIDIFICATION PROCESS
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Heating and Dehumidification Process
• Also called as Chemical Dehumidification process

24. ADIABATIC MIXING OF MOIST AIR &
STREAM
 A psychrometric process that invovles no net
heat loss or gain during the mixing of two air
streams.
 Governing equation:
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-Thank You for your
Kind Attention….