Review of Models for Appendix Gap Losses in Stirling Cycle Machines

摘要

A thorough understanding of appendix gap losses may help to improve the efficiency of Stirling cycle machines by optimizing related design parameters, particularly the gap width. Reported deviations between theoretical predictions and experimental results suggest the need for further refinement of the available models, which can be classified into two groups. First, there are analytical closed-form approaches, the underlying assumptions of which will be discussed regarding their impact on accuracy. Second, there are some numerical, differential approaches. The general applicability of these appears to be limited due to a lack of sufficiently detailed experimental data and due to uncertainties concerning the modeling of the heat transfer. The existing modeling approaches may generally be improved by analytical solutions for the flow pattern and the temperature profile in the gap, which can be obtained, because the flow is found to be essentially laminar. However, inertia effects are not negligible, which results in complex solutions implying a phase shift between mass flow and heat flux. Although presently available solutions do not correctly account for the boundary conditions imposed by the displacer seal yet, further development of such solutions appears to be a most promising way to an improved modeling of the appendix gap losses.