Numerical model for Stirling cycle machines including a differential simulation of the appendix gap
Numerical model for Stirling cycle machines including a differential simulation of the appendix gap
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斯特林循环机的数值模型，包括阑尾间隙的微分模拟
DOI：
10.1016/j.applthermaleng.2016.09.176
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发表时间：
2017
影响因子：
6.4
通讯作者：
中科院分区：
文献类型：
--
作者：
一维微分模型是斯特林发动机和其他再生机设计优化的重要工具，因为它们需要比多维CFD模型少得多的计算时间，并且还能够描述各种损失机制，包括它们的相互依赖性。到目前为止，所谓的附加间隙损失--由绝缘圆顶周围的环形间隙引起的热损失，通常连接到暴露在高温或低温下的活塞或置换器上--通常没有直接包括在微分模型中，因为基于简化分析模型的现有估计仅预测了这些损失的中等程度。相反，这些估计因此简单地叠加在数值结果上。然而，最近的调查结果表明，这些损失被低估了，因为分析模型是基于部分有问题的假设。要调查其实际幅度，现有的一维差分模拟代码，这是能够模拟各种再生周期所需的组件从一个图书馆的选择，扩展了另一个气缸组件，其中包括一个差分模型的附录间隙。这一贡献提出并讨论了通过这种扩展的模拟代码得到的结果相比，一个简化的和更增强的分析模型的预测。事实证明，数值结果高度依赖于气体和壁之间的轴向对流和径向热交换的建模，并且差距中的不稳定流动和温度分布可能需要通过增强的方法来考虑-可能基于复数。此外，给出了仿真代码的介绍性概述，特别关注模型结构、基本假设和适用性限制、离散化技术以及微分方程系统的制定和求解。
One-dimensional differential models are an important tool for the design optimization of Stirling engines and other regenerative machines, since they require far less computing time than multi-dimensional CFD-models and are yet capable of describing the various loss mechanisms including their mutual interdependencies. So far, the so-called appendix gap losses – thermal losses caused by the annular gap around the insulating dome, which is typically attached to pistons or displacers exposed to elevated or cryogenic temperatures – have usually not been directly included in differential models, because available estimates based on simplified analytical models only predicted a moderate magnitude of these. Instead, these estimates were therefore simply superimposed on the numerical results. However, recent findings indicate that these losses have thus been underestimated, since the analytical models are based on partially questionable assumptions. To investigate their actual magnitude, an existing one-dimensional differential simulation code, which is capable of modelling various regenerative cycles by selection of the required components from a library, was extended by another cylinder component that includes a differential model of the appendix gap. This contribution presents and discusses the results obtained by this extended simulation code in comparison to the predictions by a simplified and a more enhanced analytical model. It turns out that the numerical results are highly dependent on the modelling of both axial convection and the radial heat exchange between the gas and the walls, and that the unsteady flow and temperature profiles in the gap presumably need to be considered here by enhanced approaches – possibly based on complex numbers. Furthermore, an introductory overview of the simulation code is given, particularly focusing on the model structure, the basic assumptions and limitations of applicability, the discretization technique as well as the formulation and the solution of the differential equation system.
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