Hi all,
I have a gas stream (air) that contains about 10 % water at 100 deg C (Partial pressure 0.1 bar RH~10%), what would be my water concentration at 40 deg C ? Do i just look for the corresponding humidity at 10% RH at 40 C in the Psychrometric chart ?
Yes, you have to look at the psychrometic chart. If you start at 100g water in 1kg air at 100°C, at 40°C the relative humidity of 100% corresponds to 50g water in 1kg air. You must have some water falling out as droplets or water film on a surface.
Ingo Riess . Thanks for your reply, lets say that the RH at 100 C is x %, then do i look for the absolute humidity at 40 C for x% RH ? is that what you say ?
Not necessarily: You look at how much water (in g/kg) is in the air at 100°C. Then - assuming the same amount of water in air - look up where you are at 40°C. If you are below saturation, you will see the relative humidity. If you are above saturation, you will have 100% humidity plus water.
Ingo Riess : Thanks for your answer. it helps. Let me just summarize your answer to again confirm and improve my understanding
100 C 10% RH (10kpa partial pressure) will give me approx 70 g per kg of water. That amount would correspond to 25% RH at 70 deg C (7.8kpa partial pressure) and at 40 deg C it would be over the saturation line(7.4 kpa + water droplets) ??
At 100°C water is boiling. At this temperature, any concentration of water vapour in air is possible. It is my understanding that the term "relative humidity" does not apply at 100°C. Are you looking at temperature in °F? But in principle, your procedure is correct. Cooling down from 40°, the air/water mixture remains on the line of saturation, any excess water is in droplets.
Hi, i agree that 100 is the right temperature to be mentioned. Just wanted to confirm the procedure.. thanks a lot
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