低温余热发电用有机工质换热特性研究

发布时间：2019-06-12 02:18

【摘要】：工业是我国能源消费的最主要部门，我国工业能耗占总能耗的70%以上，但其能源的利用率非常低，工业能耗中很大一部分的能量转化为载体不同、温度不同的工业余热。以钢铁行业烧结工序为例，烧结工序中就有50%左右的热能被烧结烟气和冷却机废气带走，废气带走的显热占烧结总能耗的20%以上。可见，工业余热的高效综合利用是实现我国节能减排战略目标的重要途径。采用低沸点有机工质为循环工质的有机朗肯循环发电是中低温余热资源利用的一种有效方式。有机工质流动沸腾换热系数的测定是有机朗肯循环发电系统的一个重要组成部分，本文对有机工质的管内流动沸腾换热特性进行了数值模拟分析；设计和搭建了双循环有机工质沸腾换热特性实验系统，为低温余热有机朗肯循环发电用有机工质换热特性的进一步实验研究奠定了基础。论文首先对气液两相流的基本参数和流动沸腾换热的特征进行了分析。分析了截面含气率及截面含液率、质量流量、质量含气率、质量流速、体积流量、体积含气率、汽相真实流速、汽相折算流速、滑动比、滑动速度、两相流的流型、水平管流动沸腾换热的区域等流动沸腾换热的基本特征。然后对有机工质管内的流动沸腾换热特性进行了数值分析研究。建立了有机工质管内换热模型，模型包括湍流模型和多相流模型。利用CFD软件，对两种典型有机工质R245fa和R123在水平光滑管内的流动沸腾换热特性进行了分析计算，得到R245fa和R123在水平管内的流动沸腾换热过程中的温度场、速度场、和换热系数的分布及变化规律。通过改变入口边界条件，模拟出了工质质量流速、蒸发温度、工质加热温度对沸腾换热的影响规律。模拟分析结果表明：流动沸腾换热系数同时受工质质量流速、工质蒸发温度及加热温度的影响。在相同的蒸发温度及加热温度下，流动沸腾换热系数随工质质量流速的增加而迅速增加；在相同的蒸发温度及质量流速下，随着工质加热温度的增大，流动沸腾换热系数先较快增加，然后增加逐渐变缓；在相同的加热温度和质量流速下，随着工质蒸发温度的增加，流动沸腾换热系数逐渐降低。在以上理论分析和模拟计算的基础上，，设计和搭建了双循环有机工质沸腾换热特性实验系统。
[Abstract]:Industry is the most important department of energy consumption in China. China's industrial energy consumption accounts for more than 70% of the total energy consumption, but its energy utilization rate is very low. A large part of industrial energy consumption is converted into industrial waste heat with different carriers and different temperatures. Taking the sintering process of iron and steel industry as an example, about 50% of the heat energy in the sintering process is taken away by the sintering flue gas and cooler exhaust gas, and the sensible heat taken away by the waste gas accounts for more than 20% of the total sintering energy consumption. It can be seen that the efficient and comprehensive utilization of industrial waste heat is an important way to achieve the strategic goal of energy saving and emission reduction in China. Organic Rankine cycle power generation with low boiling point organic working fluid as circulating working fluid is an effective way to utilize medium and low temperature waste heat resources. The measurement of flow boiling heat transfer coefficient of organic working fluid is an important part of organic Rankine cycle power generation system. in this paper, the flow boiling heat transfer characteristics of organic working fluid in tube are simulated and analyzed, and an experimental system for boiling heat transfer characteristics of double cycle organic working fluid is designed and built, which lays a foundation for further experimental study on the heat transfer characteristics of organic working fluid used in organic Rankine cycle power generation at low temperature. In this paper, the basic parameters of gas-liquid two-phase flow and the characteristics of flow boiling heat transfer are analyzed. The basic characteristics of flow boiling heat transfer, such as section gas content, cross section liquid content, mass flow rate, mass gas content, mass flow rate, volume gas content, real vapor phase velocity, vapor phase conversion velocity, slip ratio, sliding velocity, flow pattern of two-phase flow and flow boiling heat transfer area of horizontal tube, are analyzed. Then the flow boiling heat transfer characteristics in organic working fluid tube are studied by numerical analysis. The heat transfer model in organic working fluid tube is established, which includes turbulence model and multiphase flow model. The flow boiling heat transfer characteristics of two typical organic refrigerants R245fa and R123 in horizontal smooth tube were analyzed and calculated by using CFD software. The distribution and variation of temperature field, velocity field, heat transfer coefficient and heat transfer coefficient of R245fa and R123 in horizontal tube were obtained. By changing the inlet boundary conditions, the effects of mass flow rate, evaporation temperature and working fluid heating temperature on boiling heat transfer are simulated. The simulation results show that the flow boiling heat transfer coefficient is affected by the mass flow rate of the working fluid, the evaporation temperature and the heating temperature of the working fluid. At the same evaporation temperature and heating temperature, the flow boiling heat transfer coefficient increases rapidly with the increase of the mass flow rate of the working fluid; at the same evaporation temperature and mass flow rate, the flow boiling heat transfer coefficient increases rapidly at first and then slows down with the increase of the working fluid heating temperature; at the same heating temperature and mass flow rate, the flow boiling heat transfer coefficient decreases gradually with the increase of the working fluid evaporation temperature. On the basis of the above theoretical analysis and simulation calculation, an experimental system for boiling heat transfer characteristics of double cycle organic working fluid is designed and built.
【学位授予单位】：北京工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM617

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