Question

A mixture of dry air and water vapour is at a temperature of 25C. It is under a pressure of 100kPa. The dew point temperature is 15C. What is:

a) Partial pressure of the water vapour?

b) Relative humidity?

c) Specific humidity?

d) Specific volume of the dry air?

Answer 1

Corresponding to Dew point temp 15 c and dry bulb temp 25 c

following are the properties fo Air, water vapour mixture from psychrometric chart

1.) partial pressure of watre vapour

Wet bulb temp = 18 C Corresponding to Dew point temp 15 c and dry bulb temp 25 c from phychrometric chart

Saturation pressuer corresponding to wet bulb temp from steam table P_w = 2062 N/m2

= 2062/133.3 =15.47 mm of Hg

Barometric pressure = P_b = 100 *10^3 N/m2 = 100000/133.33 = 750 mm of Hg

Pressure of water Vapour is given by

Puting value

Following value can be taken directly frompsychrometric chart

Realtive humidity = 54%

Specific humidty = 0.0106 Kg/Kg

Specific volume = 0.86 m^3/kg