Closed cycle refrigeration loop in which trays holding molecular sorbent are made to serve as cooling baffles improves the performance of high vacuum systems. High performance is obtained with almost no decrease in pumping speed

Knechtel, E. D.

Pitts, W. C.

English

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December 1971	 Brief 71-10478 
NASA TECH BRIEF 
Ames Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the. Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Improved Molecular Sorbent Trap for High-Vacuum Systems 
.
The problem: 
To improve the performance of high-vacuum sys-
tems -which use molecular sorbent traps. Such sys-
tems can be improved by the addition of chilled 
baffles connected in series with the sorbent traps, 
but these tandem combinations often reduce pumping 
speeds by a factor of two. 
The solution: 
Provide a closed-cycle refrigeration loop in which 
the trays holding the molecular sorbent are made 
to serve as cooling baffles. High performance is 
obtained with almost no decrease in pumping speed.
How it's done: 
Stainless steel coils are welded onto the unused 
surfaces of the trays which contain the sorbent. The 
ends of the cooling lines are brought out through 
holes in the trap wall and are welded vacuum-tight. 
A closed-cycle refrigerant, such as a Freon, is cir-
culated through the coolant coils. (Cold water may 
be an effective refrigerant, but liquid nitrogen is 
generally preferable.) Sorbent traps constructed in 
this manner reduce oil back-streaming because 
the molecular sorbent is more efficient at lower 
temperatures, and the cold metal surfaces themselves 
are effective collectors of condensable material. 
In a prototype vacuum system, the ultimate pres-
sure 4 x 10 torr without refrigeration of the sorbent 
trap was reduced to 1.5x10 torr with refrigeration 
at —30°C. 
Note: 
No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B71-10478 
Patent status: 
No patent action is contemplated by NASA. 
Source: E. D. Knechtel and W. C. Pitts

Ames Research Center

(ARC-10056) 
Category 03 
This documett was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately ownedrights.
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Improved molecular sorbent trap for high-vacuum systems

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