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High Capacity Pulse Tube Cooler

Industry and Research Institutes

Gunar Schroeder

+49-351-4081-5129

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for Cryogenic High-Power Applications

Within the framework of the research project "Supraconducting High Current System for DC Applications", a high power cryocooler based on the pulse-tube (PT) principle was developed. The single-stage design has two pressure wave generators with a common drive, see Fig. 1. Unlike a classic PT cooler with orifice and buffer volume, the phase relation between pressure and mass flow can be fixed by the angle of rotation of the two pressure wave generators. This technique is called "active phase shift". This allows a much higher efficiency to be achieved, since the expansion energy at the warm end of the pulse tube is not dissipated but recuperated.

Figure 1: (left) Test setup of High Power Cryocooler, (right) view into the opened cold sec-tion

The cold head of this PT cryocooler is specially adapted to the application as a recooler / condenser. The cold surface is designed as a heat exchanger in order to be able to connect the media to be cooled directly to it. This enables optimum heat transfer between the internal thermodynamic process and the medium to be cooled, e. g. LN₂. Due to its special design, the PT cryocooler requires no valves and no moving parts in the cold section. This ensures a long service life, high reliability and low maintenance.
This PT cryocooler (high power cryocooler) is particularly suitable for use as:

Cooler for small condensers, e. g. for the condensation of O₂, N₂, H₂, etc.
Recooler for cryogenic cooling circuits with LN₂ or Lar, e. g. for HTC (High Temperature Superconductor) applications

The advantages of the system are:

High efficiency
Long service life and reliability with low maintenance requirements
Special system solution with heat exchanger and process connections integrated in the cold surface
Adaptability of the cryocooler to various special requirements
Adjustable cooling capacity via the revolution speed of the compressor

In the present configuration with the single-stage structure, a low temperature of 60 K is achieved. The cooling capacity is 300 W at 80 K. The temperature stability of the system was proven in an endurance test, see Fig. 2. Further modifications are planned to increase efficiency and cooling capacity. In addition, the pressure wave generators are to be further adapted in order to further reduce the dimensions of the system.

Technical Data — Figure 2: (left) Technical data of the high power cryocooler, (right) temperature of cold head as function of time, measured at the cold tip over a couple of days

Wir suchen Kunden und Projektpartner für mögliche Weiterentwicklungen oder auch Adaptionen für spezielle Anwendungszwecke. Denkbar sind zum Beispiel ein kompakteres System oder eine Weiterentwicklung des derzeitigen Kühlers zu noch mehr Kälteleistung, tieferen Temperaturen und höherer Effizienz.

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