气液两相喷射器内部流动的数值计算
发布时间：2018-11-05 08:40
【摘要】：满液式蒸发器具有比干式蒸发器更好的换热性能,因此被大中型工业制冷系统所采用。针对传统的满液式制冷系统中存在循环泵大量电能消耗的问题,有人提出了满液式喷射泵制冷系统。在该系统中使用气液两相喷射器来取代循环泵的使用。并且气液两相喷射器的性能直接影响满液式蒸发器的浸液率和蒸发换热性能,因此研究和优化气液两相喷射器具有重要意义,本文以数值计算为主要方法对气液两相喷射器进行了分析研究,主要内容如下： (1)通过研究调查,简要分析了满液式喷射泵制冷系统相对传统的满液式制冷系统所能产生的节能效益和节能意义。 (2)假设拉瓦尔喷嘴内为完全平衡两相流,提出通过两相流完全平衡的声速方程对气液两相喷射器拉瓦尔喷嘴的设计提出改进方法,并且结合经验方法,完成了气液两相喷射器的整体结构的基本设计。通过对比模拟结果得到的声速值与拉瓦尔喷嘴设计声速值,得到偏差在14.94%-24.42%,相对单相流声速计算方法,提出的拉瓦尔喷嘴改进方法已经大幅接近实际声速情况。 (3)通过加入R22的热力学参数,结合气液两相喷射器的设计方法,得出本文气液两相喷射器的基本物理模型。通过CFD方法分析了以R22为工作介质的气液两相喷射器的内部流动,通过对比模拟结果中两相流的主要参数空隙率值与经验值,得到两者偏差在11.65%以内,变化趋势的一致性,验证了两相流计算模型的准确性。 (4)分析了R22为工作介质的气液两相喷射器内部的压力、温度、密度和速度等参数的基本情况,分析两相之间的相变传质情况,捕捉到了该气液两相喷射器内部由于相变引起的喷嘴出口激波和扩散室入口凝结激波,并对其基本特性进行了分析和经验验证。 (5)得到了多组结构变化、工况变动时的气液两相喷射器的模拟结果,得到的气液两相喷射器的喷射系数范围为0.16～1.1,模拟结果表明喷射系数受凝结激波的影响显著。调整混合室长径比可以改变凝结激波的发生位置,在保证凝结激波存在的前提下,凝结激波发生位置到混合室出口的距离影响喷射系数的大小,在一定范围内,越接近混合室出口,喷射系数值越大,但到一定程度之后,喷射系数受凝结激波发生位置的影响变弱。随着气液两相喷射器的背压提高,凝结激波消失,喷射系数急剧减小。
[Abstract]:Full-liquid evaporator has better heat transfer performance than dry evaporator, so it is used in large and medium industrial refrigeration system. Aiming at the problem of high power consumption of circulating pump in traditional full liquid refrigeration system, a full liquid jet pump refrigeration system is proposed. A gas-liquid two-phase injector is used in the system to replace the circulating pump. And the performance of gas-liquid two-phase ejector directly affects the leaching rate and evaporative heat transfer performance of the full-liquid evaporator, so it is of great significance to study and optimize the gas-liquid two-phase ejector. In this paper, the gas-liquid two-phase ejector is analyzed and studied by numerical calculation. The main contents are as follows: (1) through investigation, The energy saving benefits and significance of the full liquid jet pump refrigeration system compared with the traditional one are briefly analyzed. (2) assuming that the Laval nozzle is a completely equilibrium two-phase flow, an improved design method of the gas-liquid two-phase injector Laval nozzle is proposed by the sound velocity equation of the two-phase flow, and the empirical method is combined. The basic design of the whole structure of the gas-liquid two-phase ejector is completed. By comparing the sound velocity values obtained from the simulation results with the designed sound velocities of the Laval nozzles, the method of calculating the sound velocities of the single phase flow with a deviation of 14.94 to 24.422 is obtained. The improved method of Laval nozzle is close to the actual sound speed. (3) by adding the thermodynamic parameters of R22 and combining the design method of gas-liquid two-phase ejector, the basic physical model of gas-liquid two-phase injector is obtained. The internal flow of gas-liquid two-phase injector with R22 as working medium is analyzed by CFD method. By comparing the main parameters of the two-phase flow in the simulation results with the experimental results, the deviation between them is within 11.65%. The accuracy of the two-phase flow calculation model is verified by the consistency of the variation trend. (4) the internal pressure, temperature, density and velocity of the gas-liquid two-phase injector with R22 as the working medium are analyzed, and the phase transition mass transfer between the two phases is analyzed. The shock waves at the nozzle exit caused by phase transformation and the condensation shock at the inlet of the diffusion chamber are captured in the gas-liquid two-phase ejector. The basic characteristics of the shock wave are analyzed and verified by experience. (5) the simulation results of gas-liquid two-phase ejector with different structure and working conditions are obtained. The jet coefficient of gas-liquid two-phase injector is 0.16 ~ 1.1. The simulation results show that the jet coefficient is significantly affected by the condensation shock wave. Adjusting the ratio of length to diameter of mixing chamber can change the location of condensate shock wave. Under the premise of ensuring the existence of condensation shock wave, the distance from the location of condensation shock wave to the outlet of mixing chamber affects the size of jet coefficient, and within a certain range, The closer it is to the outlet of the mixing chamber, the greater the jet coefficient is, but after a certain degree, the effect of the condensation shock on the jet coefficient becomes weaker. With the increase of the back pressure of the gas-liquid two-phase injector, the condensation shock wave disappears and the ejection coefficient decreases sharply.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TB657
本文编号：2311532
[Abstract]:Full-liquid evaporator has better heat transfer performance than dry evaporator, so it is used in large and medium industrial refrigeration system. Aiming at the problem of high power consumption of circulating pump in traditional full liquid refrigeration system, a full liquid jet pump refrigeration system is proposed. A gas-liquid two-phase injector is used in the system to replace the circulating pump. And the performance of gas-liquid two-phase ejector directly affects the leaching rate and evaporative heat transfer performance of the full-liquid evaporator, so it is of great significance to study and optimize the gas-liquid two-phase ejector. In this paper, the gas-liquid two-phase ejector is analyzed and studied by numerical calculation. The main contents are as follows: (1) through investigation, The energy saving benefits and significance of the full liquid jet pump refrigeration system compared with the traditional one are briefly analyzed. (2) assuming that the Laval nozzle is a completely equilibrium two-phase flow, an improved design method of the gas-liquid two-phase injector Laval nozzle is proposed by the sound velocity equation of the two-phase flow, and the empirical method is combined. The basic design of the whole structure of the gas-liquid two-phase ejector is completed. By comparing the sound velocity values obtained from the simulation results with the designed sound velocities of the Laval nozzles, the method of calculating the sound velocities of the single phase flow with a deviation of 14.94 to 24.422 is obtained. The improved method of Laval nozzle is close to the actual sound speed. (3) by adding the thermodynamic parameters of R22 and combining the design method of gas-liquid two-phase ejector, the basic physical model of gas-liquid two-phase injector is obtained. The internal flow of gas-liquid two-phase injector with R22 as working medium is analyzed by CFD method. By comparing the main parameters of the two-phase flow in the simulation results with the experimental results, the deviation between them is within 11.65%. The accuracy of the two-phase flow calculation model is verified by the consistency of the variation trend. (4) the internal pressure, temperature, density and velocity of the gas-liquid two-phase injector with R22 as the working medium are analyzed, and the phase transition mass transfer between the two phases is analyzed. The shock waves at the nozzle exit caused by phase transformation and the condensation shock at the inlet of the diffusion chamber are captured in the gas-liquid two-phase ejector. The basic characteristics of the shock wave are analyzed and verified by experience. (5) the simulation results of gas-liquid two-phase ejector with different structure and working conditions are obtained. The jet coefficient of gas-liquid two-phase injector is 0.16 ~ 1.1. The simulation results show that the jet coefficient is significantly affected by the condensation shock wave. Adjusting the ratio of length to diameter of mixing chamber can change the location of condensate shock wave. Under the premise of ensuring the existence of condensation shock wave, the distance from the location of condensation shock wave to the outlet of mixing chamber affects the size of jet coefficient, and within a certain range, The closer it is to the outlet of the mixing chamber, the greater the jet coefficient is, but after a certain degree, the effect of the condensation shock on the jet coefficient becomes weaker. With the increase of the back pressure of the gas-liquid two-phase injector, the condensation shock wave disappears and the ejection coefficient decreases sharply.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TB657
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