Question

In an air conditioning system, air is to be cooled and dehumidified by means of a cooling coil. The data are as follows:                                                                                                                

Initial condition of the air at the inlet to the cooling

Dry bulb temperature = 25⁰C

Partial pressure of water vapour = 0.019 bar

Absolute total pressure = 1.02 bar (102kPa)

Final condition of the air at the exit of the cooling coil:

Dry bulb temperature = 15⁰C

Relative humidity = 90%

Absolute total pressure = 1.02 bar (102 kPa).

Other data are us follows:

Specific gas constant for air = 287 J/kg K

Specific gas constant for water vapour = 461.5 J/kg K

Saturation pressure for water at 45⁰C = 0.017 bar (1.7 kPa)

Enthalpy of dry air = 1.005 t kJ/kg

Enthalpy of water vapour

h = (2500+1.88t) kJ/kg.

where t is temperature in ⁰C.

determine

      (a) Moisture removed from air per kg of dry air,

      (b) Heat removed by the cooling coil per kg of dry air.