【作者】 胡大鹏；

【导师】 李志义；

【作者基本信息】 大连理工大学 ， 化工过程机械， 2009， 博士

【摘要】 压力振荡管内气体的流动是在周期性激励引起的管内气体的波动过程。波动过程涉及复杂波系的运动,并伴随能量的传递,振荡管壁上显示出相应的冷热效应。研究压力振荡管问题的关键是激励条件下波动流场的特性。压力振荡管流动及热效应的研究,对于丰富气波机械理论和完善工业应用技术具有理论意义和实用价值。目前,压力振荡管流动和热效应的研究已受到众多研究者的关注,以压力振荡管为核心部件的设备已在气体膨胀制冷和压力交换领域得以有效利用。这类设备具有结构简单、运转平稳和适应气液两相流等优点。但也存在管内带液、设备庞大和振动剧烈等问题,相关研究缺少对管内流动和热效应的系统深入的理论和实验研究。本论文采用数值模拟和实验测试方法对压力振荡管的流动及其引起的热效应开展了研究,主要工作和结论如下:①为了对压力振荡管中含有激波、膨胀波等波系的复杂流动过程进行多管和多周期模拟,本文建立了压力振荡管的数值模型,采用了滑移网格技术处理转动与静止部件之间的滑动。数值分析定量描述了振荡管内激波、膨胀波和分界面的不定常流动行为,确定由波动引起的管内能量转化的关系,为压力振荡管性能研究建立了数值模拟基础。②通过实验并结合数值模拟,对一端封闭压力振荡管流动及热效应进行了研究。建立了一端封闭压力振荡管实验平台,进行了多种规格和操作条件下的压力振荡管流动和性能实验。实测了管内波动瞬态压力、振荡管壁温等参数,分析了膨胀比、压力水平和频率等对一端封闭压力振荡管制冷性能的影响。研究发现:振荡管壁温沿管长迅速升高然后逐渐降低,管长、射流频率和膨胀比等参数均能影响管内流场和振荡管壁温的分布,运动的激波是影响壁温分布的主要因素。本文提出了一种突扩连通振荡管结构。研究表明,突扩结构能够有效地减轻反射激波对振荡管制冷性能的不利影响;在连通多振荡管后,突扩结构也能够减弱波系在不同振荡管之间的传播。为提高振荡管利用率并考虑振荡管集中排液和散热的需要,连通各振荡管后加入一换热设备。实验表明:采用封闭端突扩连通的压力振荡管的等熵制冷效率可提高15%,文中分析了突扩连通的压力振荡管的流动特点。③研究了音波型振荡器内流动和振荡特性,将其与压力振荡管结合,提出了无运转部件的射流振荡型气波制冷机。结果表明:欠膨胀附壁射流在较低的压比下流动就达到“壅塞”状态,入口压力对射流附壁的影响较小,增大膨胀比、位差、喷嘴宽度等参数均不利于射流附壁,设置分流劈有利于射流附壁。音波型振荡器的射流频率由控制管长度决定。随着膨胀比的升高,振荡管内入射波的强度逐渐增强,射流振荡型气波制冷机内部各类损失占总能量的比例逐渐减小,机器等熵制冷效率逐渐增大,该变化趋势基本不受控制管长度的影响。射流振荡型气波制冷机无任何转动部件,只需简单静密封,因此特别适用于高压气体的低温处理。④对两端开口压力振荡管流动及热效应进行了研究。建立了两端开口压力振荡管实验装置,进行了各种操作参数和结构参数对两端开口压力振荡管性能影响的实验。对两端开口压力振荡管进行了多管和多周期的数值模拟,定量描述了激波和接触面在振荡管内的运行规律,并根据管内波系的运动规律绘制了两端开口振荡管的理想波图。研究发现:在振荡管高温排气端口将产生一道反向压缩波,降低了振荡管的制冷性能。研究得出降低高温排气端口压力和采用两级排气腔结构可以有效地降低反向压缩波的影响。对振荡管与高压喷嘴的渐开和渐闭运动过程中产生的入射损失进行了实验和模拟研究,得出增大高压入口喷嘴宽度或调整高压入口喷嘴的射流角度均可以降低振荡管的入射损失。分析了射入与排出端口与振荡管之间间隙引起的泄漏损失,得出高压入口喷嘴与振荡管之间的间隙产生的泄漏损失较大,高温排气端口与振荡管之间的间隙产生的泄漏损失较小。以两端开口压力振荡管的研究为基础,本文提出了一种外循环耗散型新型气波制冷机,并测试和分析了各种操作参数和结构参数下制冷机的制冷效率。更多还原

【Abstract】 The fluid flow in pressure oscillating tubes is a type of fluid waves under periodic input The process of such flow involves both energy transfer and various patterns of wave motion, resulting in thermal effects on the wall of the tubes. Understanding the characteristics of how the internal wave-flow filed responding to external stimuli is one of the fundamental problems in studying pressure oscillating tubes. The research into the flow and thermal effects has theoretical and practical values for the development of "wave" machines.The flow and thermal effects of pressure oscillating tubes has attracted wide attention in the area of air expansion refrigeration and pressure exchange. Various pressure-oscillating-tube based equipments have been developed and effectively applied. Such equipments usually have a simple structure, can work smoothly under different conditions and are able to adapt to gas-liquid two-phase flow. However, they also have some disadvantages, for instance, containing liquid inside the tube, large sized and vibrating strongly. To date, there has been limited theoretical and experimental research to look into the flow and thermal effects inside the tubes systematically.The aim of this research is to investigate the flow and thermal effects in pressure oscillating tubes and their potential values for practical applications. This thesis presents a detailed account of the techniques developed, the platforms designed and the numerical simulation and experiments conducted to validate the results, including:(1) To simulate the complex flow process containing both shock and expansion waves in a multiple-tube system over multiple periods. Numerical models, where a sliding-mesh method was employed to describe the relative slip between rotary and static components, were established for investigating the performance of pressure oscillating tubes. The numerical analysis was applied for quantitative modeling of the unsteady-flow behaviors of shock waves, expansion waves and the separation interface. It was also used for describing the energy transfer caused by wave flow inside the tubes, thus, laying a foundation for numerical simulation and performance analysis of pressure oscillating tubes.(2) To analyze the flow and thermal effects of one-end-closed pressure oscillating tubes through experiments and numerical simulation. An experimental platform was constructed and applied for studying the flow and performance of the tubes with different sizes under different operating conditions. The parameters such as inner transient pressure and outer wall temperature were measured in real time. The effect of expansion ratio, pressure and frequency on the refrigeration performance was examined. The results indicated that the tube-wall temperature increased rapidly at the open end and then decreased gradually along the tube. The flow and the distribution of the tube-wall temperature were affected by several parameters, including the length of the tube, jet flow frequency and expansion ratio. The results also demonstrated shock waves were a major factor affecting the distribution of the tube-wall temperature.In this study, a sudden-expansion structure, where an expansion chamber was connected to pressure oscillating tubes, was proposed. It has been identified that the expansion chamber can weaken the reflected shock waves, thus, enhancing the refrigeration performance. It was also found that the chamber can weaken the wave transfer between tubes in a multiple-tube system. To enhance the efficiency, discharge liquid and disperse heat, a heat exchanger was attached to pressure oscillating tubes. The experiments indicated that attaching an expansion chamber at the close end of the tubes can improve the isentropic refrigeration efficiency by 15%. In the study, the flow in such tubes was also investigated.(3) To investigate the flow and performance of pressure oscillating tubes propelled by an integrated jet oscillator. The pressure, velocity and flux in a bistable wall-attaching jet flow unit were analyzed. The influence of operating parameters (e.g. pressure and pressure ratio) and structural parameters (e.g. potential difference and nozzle width) on the flow velocity, wall-attachment effect and jet-pressure recovery was studied. In order to understand oscillation characteristics in a sonic under-expansion wall-attaching jet oscillator, experiments were designed to test and examine the oscillating frequencies of the sonic oscillator with different control-channel lengths. The refrigerating efficiencies of Jet-Oscillation Gas Wave Refrigerators working at different oscillating frequencies were measured.(4) To investigate the flow and thermal effects of double-end-open pressure oscillating tubes. An experimental platform was constructed for testing the effect of operating and structural parameters on the performance of the tubes. Numerical simulation was conducted to provide a quantitative and graphic depiction of the flow of shock waves and the separation interface in a multiple-tube system over multiple periods. The results indicated that a backward compression wave was generated at the high-temperature discharge end. This reduced the refrigeration performance. Accordingly, a structure with a two-stage discharge chamber was proposed to decrease the temperature at the high-temperature discharge end and, as a result, reduce the influence of the backward compression wave. Numerical simulation and experiments were conducted to examine the injection loss during the process of gradually opening and closing of the high-pressure nozzles. The results indicated that the loss can be reduced to a certain degree by increasing the injection-nozzle width or adjusting the jet injection angle. The analysis on the leakage loss demonstrated that there was a larger amount of the loss due to the clearance between the tube and the high-pressure injection nozzle as compared to that caused by the clearance between the tube and the high-temperature discharge nozzle. Based on the above results, we proposed a new external-circulation dissipative gas wave refrigerator. Its refrigeration efficiencies under different operating and structural parameters were measured.更多还原