This document discusses psychrometrics and psychrometric processes. It defines key psychrometric concepts like dry bulb temperature, specific humidity, and psychrometric chart. It then explains various psychrometric processes like sensible cooling, heating, humidification, dehumidification, and combinations of these processes. These include the mixing of air streams using mass, moisture, and energy balances. Diagrams are provided to illustrate each process and how they affect dry bulb temperature and specific humidity on a psychrometric chart. An air washer is also described that can perform several psychrometric processes by varying the temperature of water sprayed into an air stream.

1. PSYCHROMETRY

2. DRY BULB TEMPERATURE
SPECIFICHUMIDITY
PSYCHROMETRI CHART

3. MIXING OF STREAMS
m1, w1, h1
m2, w2, h2
m3, w3, h3
mass balance
m1 + m2 = m3
moisture balance
m1w1 + m2w2 = m3w3
enthalpy balance
m1h1 + m2h2 = m3h3
The final condition will lie between the line joining two state points dividing the line in inverse
ratio of their masses of dry air
w1
w2
w3
h1
h3
h2
t3 t1t2
m1t1 + m2t2 = m3t3
1
2
3

4. PSYCHROMETRIC PROCESSES

5. SENSIBLE COOLING
Dry bulb temperature is to be decrease
Specific humidity should remain constant
SPECIFICHUMIDITY
DRY BULB TEMPERATURE
DPT < COIL TEMPERATURE < DBT
AIR
IN
COOLING
COIL
AIR
OUT
When air is passed through the cooling coil whose effective surface temperature is less than the
dry bulb temperature of air but more than the dew point temperature of air then the sensible
cooling is being done.

6. SENSIBLE HEATING
Dry bulb temperature is to be increase
Specific humidity should remain constant
SPECIFICHUMIDITY
DRY BULB TEMPERATURE
HEATING
COIL
AIR
IN
AIR
OUT
COIL TEMPERATURE > DBT
When air is passed through heating coil having temperature more than the dry bulb temperature
of air then only sensible heating is being done.

7. HUMIDIFICATION
Dry bulb temperature should remain constant
Specific humidity is to be increase
SPECIFICHUMIDITY
DRY BULB TEMPERATURE
WATER SPRAY
WATER SUMP
AIR
IN
AIR
OUT
HEATING
COIL
When air is passed through spraying water, then the water get evaporated, the heat required for
evaporation is given by air itself. The heat of air is being used to evaporate the water, the air get
cooled but we want temperature should remain constant. So, the heating coil is used to overcome
the temperature decreased of air.

8. DEHUMIDIFICATION
Dry bulb temperature should remain constant
Specific humidity is to be increase
SPECIFICHUMIDITY
DRY BULB TEMPERATURE
GLYCOL
GLYCOL
AIR
IN
AIR
OUT
COOLING
COIL
When the air passed through some absorbent (having affinity to absorb moisture) then the
absorbent absorbs the moisture of air, it means the moisture get condensed so, the heat is being
generated due to condensation, that he heat get added to air and hence air get heated up but we
want the temperature should remain constant so, the cooling coil is used to cool the absorbent
such that it can overcome the heat added to air.

9. HEATING & HUMIDIFICATION
Dry bulb temperature is to be increase
Specific humidity is to be increase
SPECIFICHUMIDITY
DRY BULB TEMPERATURE
WATER SPRAY
WATER SUMP
AIR
IN
AIR
OUT
HEATING
COIL
When air is passed through spraying water, then the water get evaporated the heat required for
evaporation is given by air itself. The heat of air is being used to evaporate the water, the air get
cooled but we do not want to cool the air. We want heat up so the water the is being circulated is
get heated by heating coils so that the temperature of air do not decrease it should increase.

10. HEATING & DEHUMIDIFICATION
Dry bulb temperature is to be increase
Specific humidity is to be decrease
SPECIFICHUMIDITY
DRY BULB TEMPERATURE
GLYCOL
GLYCOL
AIR
OUT
AIR
IN
When the air passed through some absorbent (having affinity to absorb moisture) then the
absorbent absorbs the moisture of air, it means the moisture get condensed so, the heat is being
generated due to condensation, that he heat get added to air and hence air get heated and
dehumidified.
We do not added any heat or removed hence, the process is
carried out along constant enthalpy line

11. COOLING & HUMIDIFICATION
Dry bulb temperature is to be decrease
Specific humidity is to be increase
SPECIFICHUMIDITY
DRY BULB TEMPERATURE
WATER SPRAY
WATER SUMP
AIR
IN
AIR
OUT
When air is passed through spraying water, then the water get evaporated the heat required for
evaporation is given by air itself. The heat of air is being used to evaporate the water, the air get
cooled and also the evaporated water get added into air so, finally air get cooled and moist.
We do not added any heat or removed hence, the process is
carried out along constant enthalpy line

12. COOLING & DEHUMIDIFICATION
Dry bulb temperature is to be decrease
Specific humidity is to be decrease
SPECIFICHUMIDITY
DRY BULB TEMPERATURE
ADP < DPT of incoming air
AIR
IN
COOLING
COIL
AIR
OUT
When the air is passed over the coil whose effective surface temperature is less than the dew
point temperature of air, then the dry bulb temperature of air decreases and also the moisture
holding capacity goes on decreases. And as the temperature of coil is less than the dew point
temperature of the air, the air can not hold all the moisture so the some content of moisture get
condensed. In this process air get cooled as well as get dehumidified, the process is named as
“COOLING AND DEHUMIDIFICATION”

13. AIR WASHER
DPT WBT T
w
2
3
4
5
6
7
8
1
WATER SPRAY
WATER SUMP
AIR
IN
AIR
OUT
EXTERNAL
COOLER OR
HEATER

14. PROCESS 1-2: COOLING AND DEHUMIDIFICATION ( water temperature < DPT )
The mean surface temperature is lower than the dew point temperature of air
PROCESS 1-3: SENSIBLE COOLING (water temperature = DPT )
The temperature of water is equal to the dew point temperature of air
PROCESS 1-4: COOLING AND HUMIDIFICATION ( DBT > water temperature > WBT )
The mean surface temperature of water is less than the dry bulb temperature of air but greater
than the wet bulb temperature of air
PROCESS 1-5: ADIABATIC SATURATION ( water temperature = WBT )
In this the water is circulated without heating or cooling
PROCESS 1-6: COOLING AND HUMIDIFICATION ( WBT < water temperature < DBT )
The mean surface temperature of water is less than the dry bulb temperature of air but greater
than the wet bulb temperature of air
PROCESS 1-7: HUMIDIFICATION ( water temperature = DBT )
The mean surface temperature of water is equal to the dry bulb temperature of air
PROCESS 1-8: HEATING AND HUMIDIFICATION ( water temperature > DBT )
The mean surface temperature of water is greater than the dry bulb temperature of air