Question 13.7: Air at 300 K and 20 per cent humidity is to be heated in two......
Air at 300 K and 20 per cent humidity is to be heated in two stages with intermediate saturation with water to 90 per cent humidity so that the final stream is at 320 K and 20 per cent humidity. What is the humidity of the exit stream and the conditions at the end of each stage?
At \theta _{1} = 300 K and 20 per cent humidity: \mathscr{H} _{1} = 0.0045 kg/kg, from Figure 13.4, and at \theta _{2} = 320 K and 20 per cent humidity: \mathscr{H} _{2} = \underline{\underline{0.0140\ kg/kg}}
When \mathscr{H} _{2} = 0.0140 kg/kg, air is saturated at 292 K and has a humidity of 90 per cent at 293 K.
The adiabatic cooling line corresponding to 293 K intersects with \mathscr{H} = 0.0045 kg/kg at a temperature, θ = 318 K.
Thus the stages are:
(i) Heat the air at \mathscr{H} = 0.0045 from 300 to 318 K.
(ii) Saturate with water at an adiabatic saturation temperature of 293 K until 90 per cent humidity is attained. At the end of this stage:
\mathscr{H} = 0.0140 kg/kg and θ = 294.5 K
(iii) Heat the saturated air at \underline{\underline{\mathscr{H} =0.0140\ kg/kg\ from\ 294.5\ to\ 320\ K}}
