TITLE.PM5

PSYCHROMETRICS 483

dharm

\M-therm\Th10-2.pm5

W 1 = 19.6 gm/kg, W 3 = 11.8 gm/kg

tdb 2 = 17.6ºC, vs 1 = 0.892 m^3 /kg.

The mass of air supplied per minute,

ma =

250

892. = 280.26 kg/min.
     (i)The capacity of the cooling coil
     =mh ha()^12 −×^60 = .(..)−×
     14000

280 26 82 5 47 5 60

14000

= 42.04 TR. (Ans.)

The by-pass factor of the cooling coil is given by :

BF =

hh

hh

25

15

47 5 36 6

82 5 36 6

−

−

= −

−

.. = 0.237. (Ans.)

(ii)The heating capacity of the heating coil

= ma (h 3 – h 2 ) = 280.26 (55.7 – 47.5) = 2298.13 kJ/min =

229813

60

kJ/s

= 38.3 kW. (Ans.)

The by-pass factor of the heating coil is given by

BF =

tt

tt

db db

db db

63

62

−

−

0.3 =

t

t

db

db

6

6

25

17 6

−

−.

∴ tdb 6 = 28.2ºC.

Hence surface temperature of heating coil = 28.2ºC. (Ans.)

(iii)The mass of water vapour removed per hour

=280 26 −×^60 = −

1000

280 26 19 6 11 8

1000

.(WW 13 ) .(. .) × 60 = 131.16 kg/h. (Ans.)

Highlights

1. ‘Air-conditioning’ is the simultaneous control of temperature, humidity, motion and purity of the atmos-
   phere in a confined space.


2. ‘Psychrometry’ is an art of measuring moisture content of air.
   The science which investigates the thermal properties of moist air, considers the measurement and control
   of the moisture content of air, and studies the effects of atmospheric moisture on material and human
   comfort may properly be termed ‘Psychrometrics’.


3. When air is saturated DBT, WBT, DPT are equal.


4. Dalton’s law of partial pressure states, that the total pressure of a mixture of gases is equal to the sum of
   partial pressure which the component gases would exert if each existed alone in the mixture volume at the
   mixture temperature.


5. Specific humidity, W = 0622.p
   pp

v

tv−

.

6. Degree of saturation (μ) = Mass of water vapour associated with unit mass of dry air (
   Mass of water vapour associated with saturated unit mass of dry air (

W

Ws

)

)

.