Effect of Component Geometry on Flow Non-uniformities in a Large Pulse Tube Cryocooler
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Lewis, M. A.
Taylor, R. P.
Radebaugh, R.
Bradley, P. E.
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Abstract
A single-stage pulse tube cryocooler was designed to achieve 50 W of refrigeration power at 50 K when driven by a pressure oscillator that can produce up to 2.8 kW of acoustic power at 60 Hz. Initial experimental data produced no-load temperatures that were considerably higher than expected. Improvements were made to the warm end heat exchanger, aftercooler, and diffusion bonding of the copper screen matrix materials, which produce significant improvements to the low end temperatures. The primary diagnostic tools utilized were four equidistant azimuthally spaced thermocouples located at the aftercooler exit and at the center planes of the regenerator component and the pulse tube component. The tools provided the information on the temperature distribution throughout the system and how the specific geometry changes throughout the pulse tube cryocooler would affect overall performance. This paper addresses the specific geometry changes to several major components of the cryocooler and their effect on the cryocooler performance. These include the transition piece from the inertance tube where the helium gas is entering and exiting the warm end heat exchanger and the pulse tube. Pulse tubes with various aspect ratios are tested to find the optimum aspect ratio. A major modification to the cold end heat exchanger matrix design will be implemented for more uniform gas flow through the diffusion bonded copper screen stacks. The effect of interspersing various amounts of copper screen along the stainless steel regenerator packing is also investigated.
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2008-05
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