Mechanical Work Potential
Mechanical Work Potential
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机械功潜力
DOI：
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发表时间：
2013
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通讯作者：
R. Miller
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文献类型：
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作者：
R. Miller
本文考虑了流体之间的换热对涡轮输出功的影响。为了正确地描述传热的影响，需要一个新的性质，“机械功势”，这是一种测量等熵涡轮在固定出口静压下从流体中提取的最大有用功的方法。在一个控制体积上，建立了一个性能平衡方程。由方程可知，通过热混合产生的熵对涡轮功没有影响。然而，它确实表明，第二个传热术语，“热产生”，确实改变了涡轮机的工作。热产生发生在涡轮的区域，传热发生在一个有限的压力差。这一项是瑞利勋爵在他的热声判据中提出的声能产生项的非线性版本。然后，利用平衡方程将产生热的局部区域与级效率的变化联系起来。该方法表明，在现代高压涡轮级中，由于自由流中的热混合引起的换热对效率的影响可以忽略不计，因此在设计过程中可以忽略。该方法还用于证明对流冷却引起的传热导致级效率提高~ 0.5%。这一点很重要，应该在设计过程中加以考虑。ASME版权所有©2013
This paper considers the effect of heat transfer between fluid streams on the work output of a turbine. To correctly characterize the effect of heat transfer requires a new property, ‘mechanical work potential’, which is a measure of the maximum useful work that can be extracted from a fluid by an isentropic turbine exhausting to a fixed exit static pressure. A balance equation for the property, over a control volume, is developed. The equation shows that entropy creation through thermal mixing has no effect on turbine work. It does, however, show that a second heat transfer term, ‘thermal creation’, does alter turbine work. Thermal creation occurs in regions of the turbine where heat transfer occurs across a finite pressure difference. The term is the non-linear version of the acoustic energy creation term proposed by Lord Rayleigh in his thermo-acoustic criterion. The balance equation is then used to link local regions of thermal creation to changes in stage efficiency. The method is used to show that, in a modern high pressure turbine stage, heat transfer due to thermal mixing in the freestream causes a negligible change in efficiency and therefore can be ignored in the design process. The method is also used to show that heat transfer due to convective cooling results in ∼0.5% rise in stage efficiency. This is a significant and should be accounted for in the design process.Copyright © 2013 by ASME