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Rapid Cycle Liquid Nitrogen Cold Trap

IP.com Disclosure Number: IPCOM000080672D
Original Publication Date: 1974-Jan-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Carbone, QJ: AUTHOR [+2]

Abstract

The current design trend in cryogenic diffusion pump baffles (traps) is to enlarge the volume of the liquid nitrogen reservoir. This provides for extended operation in event of a liquid nitrogen supply failure, and improves temperature uniformity of the trapping surfaces. Typical liquid nitrogen traps can operate efficiently for up to six hours without refilling.

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Rapid Cycle Liquid Nitrogen Cold Trap

The current design trend in cryogenic diffusion pump baffles (traps) is to enlarge the volume of the liquid nitrogen reservoir. This provides for extended operation in event of a liquid nitrogen supply failure, and improves temperature uniformity of the trapping surfaces. Typical liquid nitrogen traps can operate efficiently for up to six hours without refilling.

While this conventional approach is ideal for operational characteristics, it presents a severe vacuum system maintenance problem. By such procedures, the cold trap must be warmed to room temperature before the vacuum system can be vented and serviced. Even when hot nitrogen gas purging is used, two to four hours are required to defrost the trap. For example, as can be seen in Fig. 1, the liquid nitrogen line cannot be forced from the reservoir by pressurization of the vent line. Even if this were possible, most trap reservoirs are rated zero PSI internal pressure.

Shown in the drawings is a simple solution to this problem, which involves the installation of a liquid nitrogen reservoir drain line and valve 1 in existing traps 2. By draining the reservoir and purging with hot nitrogen gases, defrosting can be accomplished in a fraction of the original time. A normally open cryogenic solenoid valve, not shown, can be used on the reservoir drain to provide a completely automated system shutdown, in event of emergency off or electrical failure.

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