【作者】 李敏霞；

【导师】 马一太；

【作者基本信息】 天津大学 ， 工程热物理， 2003， 博士

【摘要】 本文以目前国际上制冷热泵研究的关键问题——开发 CO2 膨胀机这一前沿性课题为研究对象，以开发高效率的 CO2膨胀机为目的，从而使 CO2跨临界循环不仅具有环保优势，同时节约能源。本文的研究为其实用化提供理论基础和实践经验。通过对采用回热器、提高压缩机效率、提高换热系数、利用膨胀机和优化循环等方法的比较发现，利用膨胀机可大幅度地提高 CO2跨临界系统性能系数。对膨胀过程进行不可逆热力学分析，根据 CO2 跨临界循环中膨胀过程不同初始参数，建立了膨胀过程中的流体流动的物理模型和泄漏模型，以及压力波的传播速度模型。这些模型的建立为膨胀机的模拟提供理论基础。利用膨胀机理论模型对膨胀机的运行特性进行分析，发现膨胀机的运行参数存在最佳点使膨胀机的输出功效率达到最大。在原有滑板滚动活塞膨胀机的基础上进行改进，对滑板膨胀机进行重新设计，开发了第二代滑板滚动活塞膨胀机并进行了理论分析。通过与原有滑板型膨胀机的对比，发现利用新型滑板可减小不可逆损失，新型滑板膨胀机的理论效率高于原有滑板型膨胀机。开发了 CO2 摆动转子膨胀机，对摆动转子膨胀机进行了动力学和不可逆损失的研究，计算表明摆动转子膨胀机的泄漏损失很小，其理论效率高于新型滑板滚动活塞膨胀机。对摆动转子进行了有限元受力分析，结果发现摆动转子的最大应力和变形发生在摆杆基部，数值并不很大，通过选择适宜的材料和合理设计，摆动转子是非常适合在 CO2 跨临界循环高压差环境下工作。对膨胀机的回收方式进行了较全面的分析，比较了各种形式的优缺点和可 - I -<WP=4>行性。提出发电方式可用于大型的系统，输出的电量可以驱动小型的设备。在小型系统中，压缩膨胀机较为有利。对压缩膨胀机在系统的布置方式进行了理论研究，研究表明压缩膨胀机提供双级压缩的第二级压缩形式的系统循环性能系数接近最优值，与主压缩机同轴双级压缩循环方式可以最大限度的提高系统的能效。选择了压缩膨胀机的开发形式，给出了具体的设计思路。分析了偏心轮轴的相位角对压缩膨胀机运行的影响，以及轴的受力情况。对开发的 CO2 跨临界循环原有型滑板膨胀机、新型滑板滚动活塞膨胀机和摆动转子膨胀机进行了实验研究。三个样机都能平稳运行。测试的新型滑板滚动活塞膨胀机的效率在 35％～47％之间。摆动转子膨胀机的效率则在 33％~44％之间，都高于原有型滑板膨胀机的效率，说明为减小泄漏的设计是有效的。通过实验得到膨胀机系统的运行特性，系统参数存在最优匹配的问题。实验验证了膨胀机存在最佳参数使膨胀机的输出效率达到最大的理论分析结论。更多还原

【Abstract】 The development of the carbon dioxide expander, which is now the keytechnology of the refrigeration and heat pump research, is the subject of thedissertation. This study is on the purpose of designing a highly efficient carbondioxide expander. Employing an expander, the carbon dioxide transcritical cycle notonly have the advantage of environmental protection but also save energy. So thispaper presents both theoretical analysis and practical experience for its application. Comparisons of different measures such as using internal heat exchanger,improving compressor efficiency, increasing the coefficient of the heat transfers,adopting an expander and optimizing the cycle, show that the utilization of theexpander in the carbon dioxide transcritical system can improve the coefficient ofperformance of the system. The expansion process in the carbon dioxide transcriticalcycle is analyzed based on the irreversible thermodynamics. According to variousinlet parameters of the expansion process, the models of leakage, fluid flow and thespread velocity of the pressure wave are set up. On the basis of the theoreticalexpander model, the characteristics of the performance are analyzed. There exist theoptimal parameters to maximize the efficiency of the expander. The second generation expander with the redesigned blade is developed on thebasis of the former rolling piston expander and its theoretical analysis has been made.The expander with the new blade runs well with less irreversible loss and itstheoretical efficiency is higher compared with the former one. In addition, a swingexpander is developed and studied in the respect of kinetics and the irreversiblelosses. The results illustrate that there is quite a little leakage loss in this kind ofexpander and its theoretical efficiency is higher than that of the rolling pistonexpander with a new blade. By the means of the finite element method, the stressanalysis of the swing piston has been done. The results indicate that the maximumstress and the most grievous distortion take place at the base of the piston blade,however the extreme value is not that large, so it is quite fit for the swing piston toperform under high pressure disparity by choosing the optimal material andreasonable design. In this paper, the methods of the power recovery of the expander have beenwell discussed. The merits, demerits and feasibility of various types have beenpresented. The type of generating electricity is suitable for the system with large - III -<WP=6>capacity, and its output of the generator can drive some small equipments. Theexpander-compressor is favorable for the system with small capacity. Thearrangements of the expander-compressor in the system are studied. The researchshows that the coefficient of performance of the system can approach the optimumvalue when the expander-compressor supplies the second stage compression for thetwo-stage compression system. When the expander is connected to the maincompressor in the two-stage compression system, the coefficient of performance ofthe system can reach the highest point. The developed structure of theexpander-compressor and the design philosophy are presented in detail. Theinfluences of both the phase of two crank-shafts and the strength on the shaft on thefunction of the expander-compressor are analyzed. The experiments on the rolling piston expander with conventional blade, theredesigned rolling piston expander and the swing expander in the carbon dioxidetranscritical cycle have been conducted. Three prototypes can perform steadily. Thetest efficiency of the rolling piston expander with new blade is from 35% to 47%,while that of the swing expander is from 33% to 44%, they are higher than that ofthe rolling piston expander with a conventional blade. The experimental resultsdemonstrate that the design is effective in reducing leak更多还原