RFI_7.24.2019.docx

Questions The leak rates stated below as 500 CFM or 1000 CFM respectively. Is that SCFM (atmospheric) or ACFM at the lowest pressure? 500 SCFM at 5 Torr equals 76,000 ACFM.

A more normal leak rate might be few pounds per hour of air leakage. Are they putting a gas into the this vessel? Does it have a lot of water vapor?

As a straight calculation you need to average 5600 CFM of pumping speed to take a 200,000 ft3 chamber from 750 to 5 mm Hg. Abs.

Answer The 500 CFM-mmHg and 1000 CFM-mmHg leak rates specified are somewhat conservative, but not dramatically so. Recent data indicates an actual typical value of 200 CFM-mmHg. In simple term from the source data, this is an average pressure-rise slope of 0.06 Torr per hour in the 200,000 ft^3 vessel.

During a typical hold period between wind tunnel runs (i.e. leaks only), no air is being intentionally bled into the vessel – all valves are closed. During intermittent operation of the wind tunnel, process air that partially refills the vacuum vessel is dry, sourced from a high-pressure air source with nominal dew point < -40 degF at atmospheric pressure.