Two-Stage Metal Bellows Compressor for Oil-Free Helium Cooling
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Solution Overview
Problem
Conventional compressor devices, such as screw or reciprocating compressors, contaminate refrigeration systems with oil, while high-frequency compressors are not suitable for generating low temperatures, and existing membrane and diaphragm compressors face issues with sealing and helium permeability, leading to inefficiencies and short service life.
Innovation Solution
A compressor device utilizing metal bellows as the compression element, with a two-stage configuration where the working fluid expansion tank forms a second compressor stage, allowing for efficient compression and decoupling of operating frequency from pumping frequency, using check valves for gas flow control and hydraulic oil or water as the working fluid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional screw or piston compressors are used, then compression function is achieved, but oil contaminates the working gas and cooling device
Solution Approach 1:
The compressor device is divided into two separate chambers: a first chamber containing the metal bellows for gas compression and a second chamber containing the hydraulic fluid. This segmentation physically separates the working gas from the hydraulic fluid, preventing oil contamination while maintaining compression functionality.
Solution Approach 2:
A magnetic coupling mechanism acts as an intermediary to transmit mechanical energy from the hydraulic fluid chamber to the metal bellows chamber without direct fluid contact. The magnetic field transfers rotational motion through a non-contact interface, eliminating the need for shaft seals that could leak oil into the working gas.
2Productivity
If high-frequency compressors are used, then compression speed is increased, but they are not suitable for generating very low temperatures
Solution Approach 1:
The compressor operates at low frequency (1-10 Hz) rather than high frequency, matching the requirements of pulse tube and Gifford-McMahon coolers for very low temperature generation. The slow compression cycle allows proper heat exchange and phase separation necessary for cryogenic applications.
3Reliability
If elastic diaphragm compressors are used, then gas compression is achieved, but the seal is complex and service life is short
Solution Approach 1:
A metal bellows made of elastomer-coated metal or flexible metal alloy is used instead of conventional elastic diaphragms. This composite material provides both the flexibility needed for compression and the structural integrity for long service life, eliminating the need for complex sealing arrangements.
4Reliability
If balloon compressors are used, then gas compression is achieved, but helium permeability is high and service life is unsatisfactory
Solution Approach 1:
The metal bellows is constructed from elastomer-coated metal or flexible metal alloy, providing both flexibility for compression and extremely low helium permeability. The metal substrate with elastomer coating creates a barrier that prevents helium diffusion, solving the permeability problem of balloon compressors.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances efficiency by ensuring oil-free and helium-tight operation, improving the service life and reducing helium loss, while allowing for decoupling of operating frequency from pumping frequency, thus addressing the inefficiencies and contamination issues of previous technologies.
Implementation Method 1
a first metal bellows (6-1) arranged in a first compressor chamber (4-1)... a first metal bellows (6-2) arranged in a second compressor chamber (4-2)
Implementation Method 2
A liquid pump periodically forces liquid into the liquid volume of the working chamber, causing the elastic diaphragm to expand towards the gas volume and compress it
Implementation Method 3
The low-pressure working gas connections (20-1, 20-2) are equipped with check valves (22) that are permeable in the direction of the compressor stages (2-1, 2-2)
Implementation Method 4
The check valves (22) at the two high-pressure working gas connections (18-1, 18-2) are each followed by heat exchangers (32-1, 32-2) for cooling the compressed working gas
Data Source
Figure 1
Figure 2a
Figure 2b
AI summary
The invention relates to a compressor device, a cooling device equipped with it, and a method for operating the compressor device. Pulse tube coolers or Gifford-McMahon coolers are used for cooling magnetic resonance imaging (MRI) scanners, cryo-pumps, etc. These devices utilize gas compressors, and in particular helium compressors, in combination with rotary valves. The rate at which compressed helium is introduced into and discharged from the cooling device is in the range of 1 Hz. A problem with conventional screw or piston compressors is that oil from the compressor can enter the working gas and thus the cooling device, contaminating it. By providing a second compressor stage, the common pumping unit is used twice, resulting in a two-stage compressor device.In every flow direction of the working fluid, the working gas is compressed; in one flow direction in the first compressor stage and in the opposite flow direction in the second compressor stage. This increases the efficiency of the compressor system.