Dry Air - Pressure and Temperature Calcualtions

Just curious, what is the volume of Vessel 1 & 2 and the flow rate?

The volume of Vessel 1 is large enough that it will not change during the sample time. The flow rate is 10 scfh. The volume of Vessel 2 (sample cell) is one cubic inch.

Thanks!

-Tom

I'll see what I can do . . .

I do not think the air temperature will change a lot. Your DP is -40 C, which means dry. Temperature (heat transport) takes place with the moisture in the air, and that is not a lot. I had a similar setup for cell calibrations with a setpoint DP from 30 to -150 C. Nothing happened there. Everything remained room temperature. It all depends on the temperature of your air in the dry vessel. If it comes from a cryo unit or evaporator, the air will cool down up to the end. If this is not allowed check energy content (entrophy and entalphy) of air and heat the air up with same energy.

Your pressures are so close to "ambient" or sea level that there is virtually now impact on density.

SO- with "dry air" (ie- no psychometric issues) the temperature difference (for standard air - 68F and bone dry) is driven by the calculation-

Delta T = delta energy / (air density X specific heat X time- if you are using delta energy per time)

or

delta energy = (air density X specific heat X time X Delta T)

In this case- using English terms- BTU/Hr = 0.075 X 0.24 X 60 min/hour X Delta T in F, or 1.08 X Delta T if F

If you want to get very specific, and you know the temperature of the starting air, you can Google "air properties" and get the density for air at different temperatures

At -40°C dew point temperature will only be an issue during pressurization. When you pressurize a vessel the air heats up when compressed and then will try to bring the vessel to the same temperature. With time both the air and vessel will come to ambient temperature. Your vessel #1 calculates out to be approx. 5 cu.in. With a volume this small ambient temperature will be more of a factor than the dew point. Also keep in mind that when the air is exhausted you will get a cooling effect which will effect the temperature of your vessels. Why is temperature an issue with your application?