GB2219384A

GB2219384A - Improvements in or relating to cryogenic refrigerators

Info

Publication number: GB2219384A
Application number: GB8912082A
Authority: GB
Inventors: Nachman Pundak
Original assignee: Ricor Ltd
Current assignee: Ricor Ltd
Priority date: 1988-06-03
Filing date: 1989-05-25
Publication date: 1989-12-06
Also published as: IL86611A0; GB8912082D0; IL86611A; FR2633035A1

Abstract

A cryogenic helium-filled close-cycle refrigerator comprising a compressor unit (1) which is connected by a gas passage (3) to an expander unit (2). A reciprocating displacer/regenerator (10, 11) is located in the expander unit (2). The regenerator (11) is exposed to a steep thermal gradient where its cold end is at the expansion member cryogenic temperature, and its other end is at a temperature which is above the ambient temperature. The displacer/regenerator assembly (10, 11), due to its cryogenic temperature, acts as a cryogenic pump and condenses all the gaseous residuals (other than Helium, Hydrogen and Neon) in the refrigerator internal volume. These residual gases, such as water vapors, air residuals, derivatives of the bearing grease, organic derivatives of the motor windings, and the like, when condensed in or around the displacer tend to affect and degrade the normal dynamic and thermodynamic functioning of the refrigerator. Absorbent materials like activated charcoal are added to the regenerator at an adequate amount and location, the gaseous contaminants then being controlled and their degrading effects eliminated. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO CRYOGENIC REFRIGERATORS The present invention relates to cryogenic refrigerators and in particular to means for controlling and/or at least reducing (if not eliminating) degrading effects in the cold end of a cryogenic closed cycle refrigerator, such as one operating the stirling cycle and of the type comprising a mechanical compressor and an expander unit.

In this type of refrigerator, the compressor unit has a gas passage to the expander unit where the working gas pressure waves are transmitted from the compressor to the expander.

The working fluid in most of these cryogenic refrigerators comprises a high grade pure Helium. The expander unit usually contains two essential elements: the displacer and the regenerator. In most of the design concepts, the regenerator which is made of screens or spheres is located inside the reciprocating displacers.

Gaseous contaminants (other than Helium, Hydrogen and Neon) which are present in the internal volume of the refrigerator tend to diffuse into the cold regions of the displacer/regenerator assembly to condense and be trapped on these surfaces. These condensed contaminants affect and degrade the dynamic functioning of the displacer or degrade the heat exchanging process of the regenerator.

According to one aspect of this invention there is provided a regenerator for the expander unit of a cryogenic closed cycle refrigerator of the said type, said regenerator incorporating a gas absorbent material.

According to another aspect of this invention there is provided a cryogenic closed cycle refrigerator of the type comprising compressor unit and an expander unit characterised in that a quantity of a gas absorbent material (e.g. comprising activated charcoal or the like) is included in the regenerator of the refrigerator expander.

According to yet another aspect of this invention there is provided a method of controlling the impact of gaseous contamination on the function of the regenerator of a cryogenic closed cycle refrigerator, characterised by inserting absorbent material to the regenerator.

By adding appropriate gas absorbent materials such as activated charcoal in an adequate amount and appropriate locations throughout the regenerator the impact of gaseous contamination on the expander's dynamic functioning and the regenerator's thermodynamic efficiency can be controlled-.

The contaminants are absorbed by the absorbent materials.

Those modes of failures which are specially significant when the refrigerator is exposed to high ambient temperature can be at least reduced (if not wholly eliminated) and reliability can thus be improved.

It will be appreciated that the absorbent material is to be introduced into the regenerator or displacer in locations and in quantities as required by the conditions of the case in hand.

One embodiment of the invention will now be described with reference to the accompanying drawings of which: Figure 1 illustrates schematically a stirling type cycle refrigerator compressor and expander unit, and Figure 2 illustrates the displacer/regenerator assembly partly in section.

Turning first to Fig.1, there is shown a split cryogenic cooler system comprising a compressor unit generally designated by the numeral 1 and an expander unit generally designated by the numeral 2. The two units 1 and 2 are connected by a conduit 3.

Both units, the compressor unit 1 and the expander unit 2 are generally of conventional, well known construction comprising in the compressor unit a cylinder 4 within which plies a piston whose piston rod 6 is functionally connected with a motor (not shown). The expander unit 2 comprises a conventional casing 7 which is in communication with a pneumatic volume space 8 via a passage 9. Within casing 7 is positioned a cold displacer 10 in which is placed the regenerator 11. This latter is shown in greater detail in Fig.2 and is also of generally known design. It consists of a tubular body 12 in which is provided a stack 13 of metal wire screen pieces. This arrangement is also well known.

However, the novel feature of this part of the system resides in the introduction of an absorbent material in the spaces between individual pieces of wire screen forming the stack 13. This absorbent material is of the kind comprising activated charcoal, and is placed between the wire screen pieces from top to bottom of the tubular member 12.

In use, the regenerator 11 is exposed to a steep thermal gradient where its cold end is at the expansion chamber cryogenic temperature, and its other end is at a temperature which is above the ambient temperature. The displacer/regenerator assembly 10,11 (due to its cryogenic temperature) acts as a cryogenic pump and condenses all the gaseous residuals (other than Helium, Hydrogen and Neon) in the refrigerator internal volume. These residual gases, such as water vapors, air residuals, derivatives of the bearing grease, organic derivatives of the motor windings and the like, are absorbed into the absorbent material so as to be prevented from condensing in or around the displacer and affecting or degrading the normal dynamic and thermodynamic functioning of the refrigerator.

It has been found that gaseous contamination of the expander's function is prevented to a maximum degree by placing the absorbent material as has been described.

Claims

1. A regenerator for the expander unit of a cryogenic closed cycle refrigerator of the said type, said regenerator incorporating a gas absorbent material.

2. A regenerator according to claim 1, wherein said absorbent material comprises activated charcoal or the like.

3. A cryogenic closed cycle refrigerator of the type comprising a compressor unit and an expander unit, characterised in that a quanitity of a gas absorbent material is included in the regenerator of the refrigerator expander.

4. A refrigerator as claimed in Claim 3 characterised by including a pneumatically activated expander.

5. A refrigerator according to Claim 3 or Claim 4, wherein said absorbent material comprises activated charcoal or the like.

6. A method of controlling the impact of gaseous contamination on the function of the regenerator of a cryogenic closed cycle refrigerator, characterised by inserting a gas absorbent material to the regenerator.

7. A method as claimed in Claim 6 when applied to a regenerator which includes a stack of wire screens, characterised in that the absorbent material is inserted into the spaces between pieces of the wire screen forming the stack in the regenerator.

8. A method as claimed in Claim 6 or Claim 7, wherein said absorbent material comprises activated charcoal or the like.

9. A regenerator substantially as herein described with reference to and/or as illustrated in Fig.2 of the accompanying drawings.

10. A refrigerator substantially as herein described with reference to and/or as illustrated in the accompanying drawings.

11. A method according to claim 6 and substantially as herein described with reference to the accompanying drawings.