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

一个实验室规模的机器，可以作为斯特林发动机运行，一个维勒米耶热泵或在所谓的混合模式，具有发电和热泵的效果，是第一次实现在以前，dfg资助的项目。在观察到本项目中获得的实验结果和模拟结果之间存在一些系统偏差后，对所谓的附录间隙损失的简化分析近似及其潜在的简化假设进行了仔细检查，发现是不准确的。因此提出了当前项目的建议，目的是第一次在实验基础上改进数值模拟和现有的分析近似，即通过直接测量空隙中随时间和空间变化的气体温度分布。为此，首先对现有的一维差分模拟程序进行了扩展，并对其进行了数值模拟。其次，上述项目中开发的实验机器配备了细线热电偶探头，由于基于相似性的缩放，其间隙尺寸扩大，因此非常适合此类研究。在完成了工厂及其周边所需的变化和扩展后，首次高时间分辨率的气体温度测量已经成功进行。由于最初只批准了拟议资助期的一部分，因此提交此更新提案的目的是在相关参数变化的情况下进行拟议的实验研究，并在实验结果的基础上开发用于描述附录间隙中径向和轴向能量传输机制的增强工具，这些工具将使用相应的扩展计划进行验证。特别是，该机器提供的在斯特林模式，维勒米耶模式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振幅和相位的影响。对于实验数据的处理，围绕热电偶导线的振荡流动还应通过CFD建模，因为在某些情况下，探针显然不能在没有明显延迟的情况下追踪气体温度——与早期的可比测量经验相反，这些测量是在循环中的不同位置进行的。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，该计算基础也可用于其他用户，并在此基础上为最佳附录间隙几何形状提供通用设计方程。

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.