【作者】 陈祖志；

【导师】 胡大鹏；

【作者基本信息】 大连理工大学 ， 化工过程机械， 2008， 博士

【摘要】 在天然气深冷加工工艺中,迫切需要能在高压下操作且高效的气体膨胀制冷设备。射流振荡制冷机是一种新型气体膨胀制冷机,其工作原理为:利用自激励射流振荡器生成的振荡射流来形成对一端封闭的振荡管的周期性入射,入射气因其能量通过载能气波的运动传递至振荡管内原有气体并经振荡管壁向环境散发损失而“冷却”。射流振荡制冷机无任何转动部件、只需简单静密封,因此特别适合用于高压天然气的加工处理。目前,射流振荡制冷机的研究还很不成熟,其性能参数(主要为等熵效率)离天然气工业生产的要求尚有一定的差距。本文结合国家863高技术项目“天然气压力能综合利用新技术研究”(No.2006AA052216)主要从实验和气体动力学数值分析两方面对射流振荡制冷机的性能与内部机理开展研究。(1)自激励射流振荡器是射流振荡制冷机的关键部件,它是在射流的附壁效应(也称Coanda效应)的基础上开发出来的,附壁射流的特性如偏转程度、附壁距离等是射流振荡器设计的基础性数据。射流振荡制冷机多工作在跨音速状态下,本文首先对跨音速附壁射流的特性作了数值模拟研究,分析了跨音速附壁射流的流动特征,考察了结构参数和操作参数对跨音速附壁射流的几何特性和压力分布特性的影响。结果显示,附壁射流的偏转程度和附壁距离取决于射流自身参数与压力分布,而压力分布又受元件几何尺寸和操作条件的影响,总结了附壁射流几何特性和压力分布特性受元件结构参数和操作参数影响的规律。(2)射流振荡器的稳定振荡是射流振荡制冷机工作的前提条件,其振荡频率的调制和总压损失的控制是改善制冷机性能的重要途径。本文将音波振荡器用于射流振荡制冷机,对跨音速音波振荡器的可振性、振荡频率和总压损失以及它们的影响因素作了实验和数值模拟研究。1)研究了喷嘴宽度、位差、分流劈距、控制管长度和宽度、分流劈形状、压比、压力值及介质物性对射流可振性和振荡频率的影响,得出了影响规律。通过流场分析,对音波振荡器振荡及其受各因素影响的机理均作了解释。2)对音波振荡器的总压损失作了数值分析,结果显示:在射流的下游,由于湍流耗散,总压将快速衰减;在低压比下(ε＜2.5),总压损失主要由湍流耗散引起;在高压比下(ε＞2.5),总压损失还来源于射流内部的波动,激波会引起总压的突降。此外,还考察了位差、分流劈距等结构参数对总压损失的影响。(3)对音波振荡器与振荡管结合部位的结构与尺寸对双振荡管射流振荡制冷机内流动参数的影响作了数值模拟研究,包括排气口宽度的影响、排气口结构的影响和位差的影响,结果表明,三者均较显著。随排气口增宽,射流对振荡管射气阶段射进振荡管的能量流量减小,排气口过窄时,排气不顺畅,导致机内的压力高,形成气波的强度弱,振荡管内气温低;而排气口过宽时,对振荡管射气时质量和能量均几乎全部从排气口处直接排出,两种情况均对制冷不利。计算了三种型式排气口结构的制冷机内的流动,发现排气口通道内的旋涡会阻碍射气时介质直接从排气口处排出,这对制冷有利。随位差的减小,射流稳定附壁阶段,其在单侧射流输出管内振荡的幅度减小,振荡管口的能量流量随时间的变化变得均匀。(4)对音波振荡器驱动的双振荡管射流振荡制冷机的性能作了实验研究。以等熵效率作为制冷机性能的评价指标,对等熵效率及制冷机内部压力和振荡管壁温度作了测试。1)基于对音波振荡器总压损失研究的结果,通过缩短音波振荡器的射流输出通道的方法来减小射流在振荡管上游的总压损失,提出了一种新型结构的射流振荡制冷机,实验得到,在相同操作条件下,新结构机器的等熵效率提高了10%以上。2)研究了控制管长度、排气口宽度和结构、分流劈结构尺寸和位差对制冷机性能的影响,得到:等熵效率随控制管的增长呈波动起伏式变化;存在最佳排气口宽度,且最佳排气口宽度受压比的影响;位差减小,等熵效率有所提高;分流劈结构尺寸及排气口结构对等熵效率均有较大影响。结合实验测得的压力、温度数据以及机内流场的数值模拟结果,对各因素影响制冷机性能的机理作了解释。更多还原

【Abstract】 High-performance expansion refrigeration equipment under high pressure is needed for natural gas’s expansion refrigeration.Jet-oscillation refrigerator is a new type of gas expansion refrigerator,in which self-induced jet oscillator is used to generate oscillation jet’s periodical injection into oscillation tube with one-closed end.In the oscillation tube,gas waves are produced owing to interaction between the injected gas and the intrinsic gas. Energy is rapidly transferred from the injected gas to the intrinsic gas by means of propagation of those gas waves,which results in temperature increase of the latter and then heat dissipation to environment across the oscillation tube wall.The refrigeration of the injected gas is obtained due to its energy loss.The jet-oscillation refrigerator has no moving part and its seal is simple.Hence,its use is not confined under the condition of high pressure.Yet,the refrigeration efficiency of the jet-oscillation refrigerator is at a low level presently,and could not satisfy requirement of natural gas’s industrial production. Performance and mechanism of the jet-oscillation refrigerator are investigated by experiment and numerical simulation in the current dissertation supported by Chinese 863 National Program Foundation "Study on new technology of combined utilization of natural gas’s pressure energy"(No.2006AA05Z216).(1) The self-induced jet oscillator is a key component of the jet-oscillation refrigerator and it is developed based on jet’s wall-attaching effect which is also called Coanda effect.The gas in the jet-oscillation refrigerator usually flows at transonic speed.Firstly,the current dissertation studies properties of the transonic wall-attaching jet by numerical simulation. Flow characteristics of the wall-attaching jet are analyzed.Effects of structural parameters and operating parameters on geometrical properties and pressure distribution are investigated。The results show that the deflection degree and attachment distance of the wall-attaching jet are determined by both the jet’s flow parameters and the pressure distribution which is influenced by the element’s geometrical sizes and the operating conditions.(2) The jet-oscillation refrigerator works on the basis of the jet’s steady oscillation.Either the frequency modulation of the jet’s oscillation or decrease of total pressure loss of the jet passing the oscillator is important approach to improve performance of the refrigerator.In the present dissertation,sonic oscillator is adopted and its oscillation properties and total pressure loss together with their influencing factors are investigated by experiments and numerical simulations. 1) Effects of width of the nozzle’s throat,wall offset,wedge distance,length and width of the controlling tube,the pressure ratio,the pressure value and properties of the working media on oscillation properties are all studied.Mechanisms of the jet’s oscillation and those factors’s affecting the jet’s oscillation are explaned by means of analyzing flow parameters during the jet oscillating.2) Numerical analysis of the jet’s total pressure loss reveals that at a certain position downstream of the jet,the total pressure begins to decay sharply due to turbulent dissipation.The total pressure loss of the jet passing the sonic oscillator is caused mainly by turbulent dissipation under the condition of low pressure ratio(the pressure ratio is less than 2.5).Under the condition of high pressure ratio(the pressure ratio is more than 2.5),the total pressure loss is moreover produced by gas waves in the jet among which shock wave could lead to the total pressure’s violent decrease.Additionally,effects of the geometrical sizes on the total pressure loss are studied and the mechanisms are analyzed.(3) The current dissertation numerically simulates effects of configurations and geometrical sizes between the sonic oscillator and the oscillation tube on flow field in the jet-oscillation refrigerator with two oscillation tube.The results exhibit that width and configuration of the gas outlet port together with the wall offset all have great effect on flow field in the refrigerator.During the jet striking the open end of the oscillation tube,the injected mass and energy flow rate decreases with widening of the gas outlet port.However,gas couldn’t be discharged freely while the gas outlet port is too narrow,which would lead to high pressure in the refrigerator.As a result,only low-intensity gas waves could be produced and the temperature of the gas in the oscillation tube stays low.With too wide gas outlet port,most of the energy would be discharged directively through the gas outlet port while the jet striking the open end of the oscillation tube.Flow fields with three types of gas outlet port are calculated and it is founded out that eddy in the gas outlet port would hind directive discharging of the gas.Therefore,the configuration in which eddy could be produced is advantageous to improvement of the refrigerator’s performance.With descend of the wall offset,during the jet attaching to one wall,the jet’s oscillating amplitude decreases which results in uniform variation of energy flow rate with time.(4) Performances of the jet-oscillation refrigerator with two oscillation tube driven by sonic oscillator are investigated by experiments.Isoentropy efficiency is introduced to characterize performance of the refrigerator.The isoentropy efficiency and pressure wave in the refrigerator in addition to temperature distribution along the oscillation tube wall are tested.1) Based on the numerical results about total pressure loss,a new type of jet-oscillation refrigerator is introduced on the idea of decreasing distance from outport of the nozzle to inlet port of the oscillation tube.The experimental results reveal that the isoentropy efficiency increases by more than 10%under the same operating conditions as a result of descend of the distance.2) Effects of length of the controlling tube,width and configuration of the gas outlet port, configuration and size of the wedge and the wall offset on isoentropy efficiency of the refrigerator are studied.The following conclusions are drawn.The isoentropy efficiency varies undulately with rise of the controlling tube’s length.There exists optimal width which corresponds to the greatest isoentropy efficiency and it is revealed that the optimal width is affected by the pressure ratio.The efficiency ascends with decrease of the wall offset.The configuration of the gas outlet port and the wedge’s configuration and size all have great effects on the isoentropy efficiency.Effect mechanisms of all the influencing factors on performance of the refrigerator are analyzed based on the tested data and the numerical results.更多还原