In attempt measuring low ppm analyte gas, I use Nitrogen gas at 10 sl/m as carrier to flow the mixed gas into a 40 Liter testing chamber. Using commercial RH meter, I found that the RH inside the chamber dropped drastically from ~ 70 % down to < 20% . Anybody can help to explain this phenomena?
In fundamental thermal science, RH is highly sensitive to the moisture content but changes in the temp of a gas or gas mixture will also affect RH. Decrease in RH when gases are mixed, without any apparent removal of moisture, might be due to gas mixture temp increase. However, the chamber volume might also be a factor. For a constant mass of moisture within the mixture, the vapor pressure will be reduced proportionally to the overall mixture pressure reduction as it enters a larger space.
Tq Dr. Wan for your informative explanation. I do check the temperature in parallel with the RH measurement and the variance is in the range of 1 degree Celcius. If we know the diameter of the tube entering the chamber as well as the pressure when the mix gas enter the chamber, can we calculate the drop in pressure?
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