Performance of Siloxane Mixtures in a High-Temperature Organic Rankine Cycle Considering the Heat Transfer Characteristics during Evaporation
Performance of Siloxane Mixtures in a High-Temperature Organic Rankine Cycle Considering the Heat Transfer Characteristics during Evaporation
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DOI：
10.3390/en7095548
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发表时间：
2014-08
期刊：
影响因子：
3.2
通讯作者：
T. Weith;F. Heberle;M. Preißinger;D. Brüggemann
中科院分区：
文献类型：
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作者：
T. Weith;F. Heberle;M. Preißinger;D. Brüggemann
以某沼气厂余热回收为例，研究了有机朗肯循环在高温热源中的应用。区分了两种不同的运行模式：纯电力和热电联产。以六甲基二硅氧烷(MM)和八甲基三硅氧烷(MDM)为工质。此外，还分析了这些组分混合使用的效果。对于纯发电，使用模拟工具Aspen Plus进行的流程模拟显示，在97/03wt%MM/MDM混合物的情况下，第二定律效率提高了1.3%，而对于热电联合模式，60/40wt%MM/MDM混合物的效率最高，与最有效的纯流体相比，效率提高了近3%。在热力学分析的基础上，对这些硅氧烷及其混合物的传热系数进行了测量，并用Kandlikar关联式来描述结果。在此基础上，对预热器和蒸发器的换热器面积进行了计算，以验证混合工质的换热性能较差是否会因换热面积的增加而降低效率效益。结果表明，与MM相比，其换热面积分别增加了0.9%和14%。
The application of the Organic Rankine Cycle to high temperature heat sources is investigated on the case study of waste heat recovery from a selected biogas plant. Two different modes of operation are distinguished: pure electric power and combined heat and power generation. The siloxanes hexamethyldisiloxane (MM) and octamethyltrisiloxane (MDM) are chosen as working fluids. Moreover, the effect of using mixtures of these components is analysed. Regarding pure electricity generation, process simulations using the simulation tool Aspen Plus show an increase in second law efficiency of 1.3% in case of 97/03 wt % MM/MDM-mixture, whereas for the combined heat and power mode a 60/40 wt % MM/MDM-mixture yields the highest efficiency with an increase of nearly 3% compared to most efficient pure fluid. Next to thermodynamic analysis, measurements of heat transfer coefficients of these siloxanes as well as their mixtures are conducted and Kandlikar’s correlation is chosen to describe the results. Based on that, heat exchanger areas for preheater and evaporator are calculated in order to check whether the poorer heat transfer characteristics of mixtures devalue their efficiency benefit due to increased heat transfer areas. Results show higher heat transfer areas of 0.9% and 14%, respectively, compared to MM.