In this study, a PTC prototype was experimentally tested to yield its cooling performance at two different driving powers, two different cold-end temperatures and five different gravity orientations. A two-dimensional CFD model was validated using the experiment and used to investigate the effects of minor geometry features or imperfections that may exist in conjunction between the pulse tube and the flow straightener of the PTC. Due to the restrictions of 2D modeling, the CFD focused on two gravity orientation, vertical with cold head down (0°) (i.e., the ideal condition), and vertical with cold head up (180°). A parametric study regarding the size of the diameter change, the shape of the edge (sharp or round) and the size of the gap between flow straightener and the edge have been carried out using the CFD model.
When inclined, notable cooling deteriorations were noticed in the experiments. In terms of general trends, the sensitivity of the tested PTC with respect to misalignment with gravity generally agreed with the trend predicted by Swift and Backhaus’s theory [7, 8] if criterion for the safe operation was serval time larger. A sub-system CFD study having very similar but perfect geometry as the PTC prototype was also carried out. The calculated performance, for vertical configuration with cold tip at the bottom, agreed with the experiment. The predicted performance of the PTC for conditions where the PTC was tilted with respect to gravity deviated from experimental measurements. However, the CFD predicted cooling deterioration interestingly agreed with Swift and Backhaus’s original theory. A careful review of the results shown that the difference between experimentally measured and CFD-calculated performance parameters can be due to the combined effect of some seemingly minor off-design geometric features or imperfections that were not resolved in CFD. One specific feature, namely a diameter change in the junction between a flow straightener chamber and pulse tube, was identified, and was parametrically studied. The preliminary results indicated that the cooling performance of the PTC was actually very sensitive to this and other seemingly minor geometric features. Further study of these sensitivities is underway.
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