Problem on Humidity - Process Calculations & Thermodynamics (PCT). Please refer same. If you wish to be part of detailed understanding of concepts through an interactive sessions, please register to ATTEMPT Batch#02 Course (April to October 2021). Write us at attempttosucceed@gmail.com or comment below so that we can revert back to you.

1. QUESTION) THE HUMIDITY OF AIR AT A DRY-BULB TEMPERATURE OF 65 DEG C IS 0.025 KG WATER/KG DRY AIR. THE
LATENT HEAT OF VAPORIZATION OF WATER AT 0 DEG C IS 2500 KJ/KG. THE PSYCHROMETRIC RATIO OF AIR IS 0.95
KJ/(KG DRY AIR)-K. CONSIDERING 0 DEG C AS REFERENCE TEMPERATURE, THE ENTHALPY OF AIR (IN KJ/KG) AT ITS
ADIABATIC SATURATION TEMPERATURE OF 35 DEG C IS _____.
ANSWER: 126 KJ/ KG
PSYCHROMETRIC RATIO is the ratio of the heat transfer coefficient to the product of mass transfer
coefficient and humid heat at a wetted surface.
It relates the absolute humidity and saturation humidity to the difference between the dry bulb
temperature and the adiabatic saturation temperature.
= unity implies that difference b/w
Adiabatic sat. temp. & wet bulb Temp. of
air-water vapor mixtures is small.
ABSOLUTE HUMIDITY
The mass of water vapour per unit volume of air
containing the water vapour.
SATURATION HUMIDITY
Relative humidity describes how far the air is
from saturation. When the dew point equals the air
temperature, the air is saturated and the
relative humidity is %100.

2. QUESTION) (CONTINUED)
ENTHALPY OF MOIST AIR = Enthalpy of dry air + Enthalpy of water vapour mixture.
= Sensible heat of dry air + latent Heat of Water Vapors
Enthalpy of dry air is calculated using specific heat of air = 1.006 kJ/kg deg C.
Enthalpy of Dry Air =
m*Cp*dt = 1*(35-0) = 35 …specific heat of air = 1 kJ/kg K (Remember !)
Enthalpy of water vapour mixture =
Humidity ratio (KG WATER/KG DRY AIR)*Latent heat of vaporization of water (KJ/KG)
= 0.025*2500 = 62.5 kJ/kg
+
Psychrometric ratio(KJ/(KG DRY AIR)-K)*Temperature difference b/w DBT and AST (K)
= 0.95*(65 – 35) = 28.5 kJ/kg dry air
A) + B) + C) = 35 + 62.5 + 28.5 = 126 kJ/kg
A)
B)
C)

3. QUESTION) (CONTINUED)
The MOLLIER DIAGRAM is a graphic
representation of the relationship
between air temperature, moisture
content and enthalpy.
An ENTHALPY–ENTROPY CHART,
also known as the H–S chart or
Mollier diagram, plots the total heat
against entropy, describing the
enthalpy of a thermodynamic
system.
A typical chart covers a pressure
range of 0.01–1000 bar, and
temperatures up to 800 degrees
Celsius.