Pressure drop for a rarefied-gas flow through a tube with a thermal gradient at low temperature

This paper presents calculations and experimental results obtained for a mo del pumping duct with a thermal gradient from room temperature to 80 or 15 K; the margin between numerical and experimental data is less than 10% at a ny flow regime. These results show that the pressure drop can be reduced dr astically when the pumping duct is cooled, even taking into account the the rmomolecular effect. Such a lowered pressure drop allows the use of smaller pumping systems. Moreover, since gas density varies inversely with tempera ture, the mass flow rate is several times higher for a pump operating at lo w temperature than for a conventional room-temperature pump. This modelizat ion of the pumping duct will be integrated in the cryomechanical pump proje ct. (C) 2001 Elsevier Science Ltd. All rights reserved.