Theoretically and experimentally founded simulation of the appendix gap in regenerative machines
Theoretically and experimentally founded simulation of the appendix gap in regenerative machines
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基于理论和实验的再生机器阑尾间隙模拟
DOI：
10.1016/j.applthermaleng.2019.114530
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发表时间：
--
影响因子：
6.4
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中科院分区：
文献类型：
--
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再生机器，如斯特林发动机，如果它们被设计成高效率的，则可对解决目前的环境问题作出重大贡献。这就需要对各种损失，包括所谓的附录空白损失，有透彻的了解和准确的模型。为此目的，一些分析模型以及一些一维数值方法已经开发到目前为止。在这方面的贡献，这些所获得的结果进行比较的参考情况下，一个有据可查的实验机。它揭示了关于最佳间隙宽度以及损失的大小的显著差异。特别是对于大的间隙宽度，观察到的分析和数值模型之间的偏差增加。后者甚至预测了一个不切实际的最大值。这种差异可以通过额外考虑移动密封所做的p，V功来解决。小间隙宽度处的进一步偏差可归因于损失和实际壁温梯度的相互依赖性，这包括在数值模型中。而是在分析模型中假定预设值。这也适用于新开发的增强模型，该模型可靠地预测了最佳宽度，但高估了整个损失的大小。这强调了需要一维差分模拟，除了分析建模。然而，这些都需要单独的建模方法的径向和轴向的能量传输。不幸的是，这些的选择显著影响结果。由于迄今为止提出的方法都没有理论或实验依据，因此没有正确选择的基础。为了解决这个问题，上述分析模型被认为是，因为它是理论上的基础，并进一步支持最近的实验结果在这方面的贡献。因此，它是用来解析推导的相移与壁的热交换和焓和质量流量的相互关系的相关性。因此，一个理论和实验建立的参考模型是现在可用的。将该参考模型的计算结果与其他数值方法的计算结果进行比较，发现基于抛物线径向温度分布和理想活塞流假设的经验模型的计算结果与参考模型的计算结果基本一致。由于该模型更易于使用，因此可以推荐用于一般实际使用。然而，参考模型可以用于复查目的和进一步的优化工作。
Regenerative machines, such as the Stirling engine, may contribute substantially to the solution of the present environmental problems, if they are designed for high efficiency. This requires a thorough understanding and an accurate modelling of the various losses, including the so-called appendix gap loss. For this purpose, some analytical models as well as a few one-dimensional numerical approaches have been developed so far. In this contribution, a comparison of the results obtained by these is performed for the reference case of a well-documented experimental machine. It reveals significant discrepancies regarding the optimum gap width as well as the magnitude of the loss. Particularly for large gap widths, increasing deviations between the analytical and the numerical models are observed. The latter even predict an unrealistic maximum. This discrepancy can be resolved by additionally considering the p,V-work done by the moving seal. Further deviations at small gap widths can be attributed to the interdependence of the loss and the actual wall temperature gradients, which is included in the numerical models. Instead, a preset value is assumed in the analytical models. This also applies to a newly developed, enhanced model, which predicts the optimum width reliably, but overestimates the magnitude of the loss throughout. This underlines a need for one-dimensional differential simulations in addition to analytical modeling. However, these require separate modeling approaches for both the radial and axial energy transport. Unfortunately, the choice of these significantly affects the results. Since none of the approaches proposed so far is theoretically or experimentally founded, there is no basis for a correct choice. To solve this problem, the aforementioned analytical model is considered, since it is theoretically based and further supported by recent experimental results presented in this contribution. It is therefore used to analytically derive correlations for the phase-shifted heat exchange with the walls and the interrelation of enthalpy and mass flow. Thus, a theoretically and experimentally founded reference model is available now. Comparing the results obtained by this reference model and the other numerical approaches, it is found that an empirical model based on the assumption of parabolic radial temperature profiles and ideal plug flow yields almost the same results as the former. Since this model is easier to use, it can therefore be recommended for general practical use. The reference model may, however, be used for countercheck purposes and for further optimization work.
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