Theoretical investigation of flash vaporisation in a screw expander

Theoretical investigation of flash vaporisation in a screw expander
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螺杆膨胀机闪蒸的理论研究

DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
A. Brümmer
A. Brümmer
中科院分区：
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文献类型：
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作者：
H. Vasuthevan;A. Brümmer

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本文对三边闪蒸循环（TFC）中双螺杆膨胀机内液体喷射的闪蒸过程进行了理论研究。TFC工艺包括工作流体中的压力增加，随后将液体加热至接近沸点。将热液体注入螺杆膨胀机的工作室中。在此过程中，液体的压力下降到饱和压力以下，而液体的温度几乎保持恒定。因此，液体过热并处于亚稳态。液体射流寻求达到热力学平衡的稳定状态，因此部分蒸发。这种效应被称为闪蒸。因此，在工作室中存在由蒸气和液体组成的两相混合物。使用水作为代表性螺杆膨胀机几何形状的工作流体进行热力学模拟。对螺杆膨胀机的充模过程从两个不同的方面进行了模拟。第一种情况是在热力学平衡状态下喷射液体的蒸发，由此两相混合物完全被视为可压缩的均匀气体。第二种情况考虑闪蒸效率。它描述了闪蒸蒸汽的量，由液体和蒸汽区域组成。这两种模型进行了比较和分析方面的螺杆膨胀机的操作行为。
In the present study flash vaporisation of liquid injection in a twin screw expander for a Trilateral Flash Cycle (TFC) is examined theoretically. The TFC process comprises a pressure increase in the working fluid, followed by heating the liquid close to boiling point. The hot liquid is injected into the working chamber of a screw expander. During this process the pressure of the liquid drops below the saturation pressure, while the temperature of the liquid remains virtually constant. Hence the liquid is superheated and in a metastable state. The liquid jet seeks to achieve a stable state in thermodynamic equilibrium and is therefore partially vaporised. This effect is referred to as flash vaporisation. Accordingly, a two-phase mixture, consisting of vapour and liquid, exists in the working chamber. Thermodynamic simulations were carried out using water as the working fluid for representative screw expander geometry. The simulations presented are performed from two different aspects during the filling process of a screw expander. The first case is the vaporisation of the injected liquid in a state of thermodynamic equilibrium, whereby the two-phase mixture is treated entirely as a compressible and homogeneous gas. The second case considers flashing efficiency. It describes the quantity of flashed vapour and consists of a liquid and vapour domain. Both models are compared and analysed with respect to the operational behaviour of a screw expander.