Theoretical and Experimental Investigation of Thermal Losses in the Appendix Gap of Regenerative Gas Cycles

一台实验室规模的机器可以作为斯特林发动机、Vuilleumier热泵或所谓的混合模式运行，同时具有发电和热泵效应，这是在之前由DFG资助的项目中首次实现的。在观察到本项目中获得的实验结果和模拟结果之间的一些系统偏差后，对所谓的附录间隙损失的简化解析近似及其基本简化假设进行了仔细审查，发现其不准确。这引起了本项目的建议，该项目旨在改进数值模拟，并首次在实验基础上提供这些损失的现有分析近似，即通过直接测量空隙内在时间和空间上变化的气体温度分布。为此，首先将现有的一维差分模拟程序扩展为缝隙的数值模型，并成功地进行了试验。其次，在上述项目中开发的实验机配备了细丝热电偶探头，其特点是由于基于相似性的缩放而扩大了间隙尺寸，因此特别适合于此类研究。在完成了工厂及其外围设备所需的更改和扩建后，首次成功地进行了高时间分辨率的气体温度测量。由于最初只批准了拟议资助期的一部分，因此提交这一更新建议的目的是在相关参数变化的情况下进行拟议的实验研究，并根据实验结果开发用于描述附录空隙中的径向和轴向能量传输机制的增强工具，该工具应使用相应的扩展程序进行验证。特别是，该机器提供的在斯特林、Vuilleumier和可能的混合模式之间切换的选项可以在这里最有利地使用，以便研究循环压力的幅度和相位的影响。对于实验数据的处理，热电偶导线周围的振荡流动还应由CFD模拟，因为在某些情况下，探头显然不能在没有显著延迟的情况下跟踪气体温度-这与早期的可比测量经验形成对比，尽管可比测量是在周期的不同位置进行的。该项目的最终目的是为一维模拟提供一个实验建立的计算基础，也可供其他用户使用，并在此基础上提供最佳附录间隙几何形状的通用设计公式。

A laboratory-scale machine that may be operated as a Stirling engine, a Vuilleumier heat pump or in a so-called hybrid mode featuring both a power generation and a heat pump effect was first realized within a previous, DFG-funded project. Having observed some systematic deviations between experimental and simulated results obtained in this project, the simplified analytical approximations for the so-called appendix gap losses and their underlying simplifying assumptions were scrutinized and found to be inaccurate. This gave rise to the proposal of the current project aiming at the improvement of the numerical modelling as well as the available analytical approximations for those losses on an experimental basis for the first time, i.e., by direct measurements of the both temporally and spatially variable gas temperature profiles in the gap. For this purpose, an available one-dimensional differential simulation program was firstly extended by a numerical model of the gap and tested successfully. Secondly, the experimental machine developed in the aforementioned project, which features enlarged gap dimensions due to similarity-based scaling and is therefore exceptionally well-suited for such investigations, was equipped with fine-wire thermocouple probes. Having completed the required changes and extensions of the plant and its periphery, first gas temperature measurements at high temporal resolution have been performed successfully. Since only a part of the proposed funding period was initially granted, this renewal proposal is submitted for the purpose of conducting the proposed experimental investigations under variation of the relevant parameters and developing enhanced tools for the description of the radial and axial energy transport mechanisms in the appendix gap on the basis of the experimental results, which shall be validated using the accordingly extended program. In particular, the option of toggling between Stirling-, Vuilleumier- and possibly hybrid mode provided by this machine can be most profitably used here in order to investigate the effects of both amplitude and phasing of the cycle pressure. For the processing of the experimental data, the oscillating flow around the thermocouple wire shall additionally be modelled by CFD, since in some cases, the probes apparently do not allow tracing of the gas temperature without a significant delay - in contrast to earlier experiences with comparable measurements, which were performed at different locations in the cycle though. The final aim of the project is to provide an experimentally founded calculation basis for the one-dimensional simulation, which may also be applied by other users, and - on this basis - universal design equations for the optimum appendix gap geometry.