Question

On a warm summer day in Oslo, the temperature is 21 degree C and the relative humidity is 70%. What is the absolute humidity? What is the humid volume of the air? What is the specific enthalpy of the air, taking H_2O (L, 0 degree C, 1 atm) as a reference state? What is the wet bulb temperature? What is the dew point temperature?

Answer 1

Explanation:

According to the psychrometric chart at dry bulb temperature of $21^{o}C$ and RH 70%, the absolute humidity = 0.011 kg/kg dry air

Formula to calculate humid volume is as follows.

       $\nu_{H} m^{3}/kg$ dry air = $\frac{22.41}{273}TK (\frac{1}{28.97} + \frac{1}{18.02}H)$

                     = $(2.83 \times 10^{-3} + 4.56 \times 10^{-3} H) T K$

                     = $(2.83 \times 10^{-3} + 4.56 \times 10^{-3} \times 0.011) \times 294$

                       = 0.847 $m^{3}/kg$ dry air

Hence, humid volume of air is 0.847 $m^{3}/kg$ dry air.

Specific enthalpy of dry air  = specific heat capacity of dry air × dry bulb temperature

                    = $1.006 kJ/kg ^{o}C \times 21^{o}C$

                    = 21.126 kJ/kg dry air

Hence, the specific enthalpy of the air is 21.126 kJ/kg dry air.

As per the psychrometric chart at given conditions wet bulb temperature = 17.5 $^{o}C$

As per the psychrometric chart at given conditions dew point temperature = 15.5 $^{o}C$