Analysis of Unsteady Gas Temperature Measurements in the Appendix Gap of a Stirling Engine

Abstract

This contribution presents the experimental setup and the results of stationary cylinder wall temperature and unsteady gas temperature measurements in the appendix gap of an experimental machine, which can be switched between different regenerative cycles. Direct measurements in the gap are important for the validation and verification of existing analytical modeling approaches for appendix gap losses because these losses may reduce the power of Stirling engines significantly; so far, no direct measurements have been conducted to prove the modeling assumptions. The gas temperatures are measured by newly developed fine-wire thermocouple probes, the design of which is explained in detail. The results show curved axial wall temperature profiles and roughly sinusoidal gas temperature fluctuations, which are dependent on the radial and axial positions. In the axial center of the gap, the assumption of laminar flow conditions is largely fulfilled; whereas at the open end of the gap, intermittent disturbances are observed, presumably due to turbulent eddies entering the gap from the cylinder volume during the inflow period. A comparison to analytically calculated temperatures shows a qualitatively good agreement in the main section of the appendix gap.