共查询到18条相似文献,搜索用时 171 毫秒
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在液态金属自然循环回路的计算分析过程中,已有研究一般忽略散热损失,常导致计算结果与实验结果有较大的区别。为研究散热损失对液态金属自然循环回路稳态特性的影响,利用MATLAB/Simulink编制了含有散热损失模型的铅铋自然循环回路计算程序,并用实验结果进行了验证。利用该程序,分析了不同热功率、中间热交换器二次侧流量和环境温度下散热损失对自然循环回路稳态参数的影响。计算结果表明:通过减小散热损失可提高回路的自然循环流量;当二次侧流量较小时,散热损失对循环流量的影响更为明显;通过增加二次侧流量或适当增加热功率可减小散热量占总热功率的比例,提高热量利用率;当二次侧流量不变时,不同热功率下环境温度对回路的自然循环流量的影响不明显,但热量利用率会随环境温度的升高而增加。 相似文献
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为研究非对称条件下双环路自然循环稳定性的变化,以单环路自然循环载热系统为起点,采用无量纲分析方法,将单环路自然循环的无量纲控制方程组中关于位移项进行傅里叶展开,从而得到表征单环路自然循环载热系统的雅克比(Jacobi)矩阵,并进行验证。在此基础上,构建了双环路Jacobi矩阵分析模型,基于所构建的模型,分别开展不同负荷差和阻力差下双环路自然循环稳定性分析,以及回路几何特征对稳定性边界的影响。结果表明,对于某一双环路系统而言,存在2个临界雷诺数,当左、右环路引入负荷差大于这2个临界雷诺数时,系统将会变得不稳定。增大高径比、减少管道直径、增加加热段长度和减少冷却段长度可以增加回路稳定性区域范围,且反应堆回路稳定性边界对环路高径比、加热段长度较为敏感;此外,在自然循环回路形成的允许范围内,增加环路压降可以提高系统稳定性。 相似文献
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为认识超临界二氧化碳自然循环基本特性,开展超临界二氧化碳在简单矩形回路内自然循环特性的实验研究,研究系统压力和冷热段流体温差对自然循环流量的影响,分析回路结构对自然循环特性的影响。结果表明:循环流量存在峰值;峰值点前,随加热功率增加流量快速上升,峰值点后流量变化平缓;在本试验参数条件下未观测到流动不稳定现象;压力对循环流量影响与亚临界自然循环类似,压力越高循环流量峰值越大,回路冷热段温差对循环流量影响较大;加热段出口流体温度接近拟临界温度时,很小的回路温差变化即可引起循环流量较大变化;加热段布置方式对超临界二氧化碳自然循环流量变化特性影响较大,对回路稳定性的影响需要进一步进行实验验证。 相似文献
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《核技术》2015,(4)
硝酸盐自然循环回路(Nitrate natural circulation loop,NNCL)是研究熔盐自然循环特性的重要实验平台,可为氟盐冷却高温堆的非能动余热排出系统设计和验证积累经验。通过修改RELAP5/MOD4.0程序,对NNCL进行了系统分析,分析了不同加热功率、空气流量和入口温度等情况下的系统特性。结果表明,加热功率和空气流量是影响NNCL系统平衡温度和质量流量的重要因素,对系统稳态时的温度和流量有很大影响;自然循环达到稳定时所需时间较长,不同工况下需要8-27 h的稳定时间;在空气设计流量下,为了防止硝酸盐因温度过高而变质或因温度过低而凝结,加热功率应保持在20-40 k W。 相似文献
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The natural circulation boiling type SMR can experience flow instability during the startup transients due to the void reactivity feedback. A BWR-type natural circulation test loop has been built to perform the nuclear coupled startup transient tests for Purdue Novel Modular Reactor (NMR). This test loop is installed with different instruments to measure various thermal hydraulic parameters. The testing process can be monitored and controlled through PC with the assistance of LabVIEW procedure. The effects of power ramp rate on the flow instability during the nuclear coupled tests were investigated by controlling the power supply based on the point kinetics model with coolant void reactivity feedback. Two power ramp rates were investigated and the results were compared with those of the thermal hydraulic startup transients without void reactivity feedback. The time trace of power supply, system pressure, natural circulation rate, and void fraction profile are used to determine the flow stability during the transients. The results show that nuclear coupled startup transients also experience flashing instability and density wave oscillations. The power curves calculated from point kinetics model for startup transients show some fluctuations due to void reactivity feedback. However, the void reactivity feedback does not have significant effects on the flow instability during the startup procedure for the NMR. 相似文献
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小型核动力装置自然循环运行特性分析 总被引:1,自引:0,他引:1
本文以小型一体化自然循环反应堆为研究对象,用RELAP5/MOD3.2对反应堆系统、中间回路及二回路系统进行建模,对反应堆单双环路切换及偏环路运行时反应堆的自然循环运行特性进行数值模拟研究。计算结果表明:在反应堆自然循环运行工况下,进行单双环路切换及偏环路运行时,堆芯能重新建立稳定的自然循环。双环路切换至单环路后,堆芯出口温度降低,堆芯自然循环平衡流量降低但仍大于初始值的1/2;单环路切换至双环路运行时,堆芯流量、温度均与双环路稳定工况的一致;偏环路运行时故障环路循环流量降低,正常环路自然循环流量升高,堆芯总流量降低的数值为二者之差。 相似文献
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在海上小型堆设计中,需要考虑海洋运动条件对热工水力特性的影响。本文建立了海洋运动条件下的附加惯性力模型,并将该模型应用于RELAP/SCDAP程序中,得到了适用于海洋运动条件下的系统分析程序,利用修改后的RELAP5程序,分析了在摇摆条件下自然循环回路的热工水力特性。分析结果表明,摇摆条件下,自然循环回路的平均流量小于静止条件下的自然循环流量,环路流量波动滞后于横摇运动,冷却水温波动滞后于环路流量波动,摇摆幅值越大,频率越高,流量波动幅值越大。当摇摆较剧烈时,环路上出现倒流现象。增加加热功率或提高冷热源之间高度差可增加系统的自然循环驱动力,减小横摇运动对自然循环的影响。 相似文献
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Flow stability in a natural circulation loop: influences of wall thermal conductivity 总被引:1,自引:0,他引:1
In the study of single-phase natural circulation loops, flow stability has been an important subject because of the engineering needs for obtaining stable operating state. As an attempt of proposing method for stability control, this article studied the change of the flow stability due to the variation of the tube wall thermal conductivity. A nonlinear dynamical model was proposed to formulate the wall effects. It is suggested that in a loop made of better thermal conducting material, the flow is also more stable. Experiments were performed in three natural circulation loops; they are in the same shape and are at the same thermal boundary conditions. An unstable Lorenz flow was observed in a glass loop. In a copper loop and a copper–glass loop, both the flows were stable for any experimental cases. The results verified qualitatively the conclusions drawn by the model. 相似文献
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The state-of-the-art of theoretical investigations on the flow oscillations that occur in a boiling natural circulation loop has been presented here. Motivation behind the work is to develop a high-fidelity model that is capable of predicting nature of flow instabilities more accurately. At the low pressures and low heat fluxes conditions, the major four types of instabilities may occur in boiling natural circulation loop depending on operating conditions: Flow excursion, Geysering instability, Flashing-induced instability and Type I density-wave oscillations. The characteristics of different instabilities as well as the effects of different operating and geometric parameters on them have been reviewed. The objective of this review is to gather the research findings on the nonlinear stability phenomena in various boiling flow channel systems over a period of several years. This review indicates that most of the theoretical predictions of amplitudes and periods of the sustained oscillations are carried out using two models, namely, homogeneous equilibrium model (HEM) (still debatable) and drift-flux model (DFM) (more realistic) and are validated by experimental findings. This review work on theoretical investigations presented in this paper indicates that there are enough scopes for improving mathematical formulations of the natural circulation boiling loop (NCBL) for thermohydraulic instabilities. 相似文献
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《Annals of Nuclear Energy》2005,32(4):379-397
In this paper, two-phase flow instability in natural circulation loops of China Advanced Research Reactor (CARR) has been investigated. CARR is a low pressure and low power density research reactor. A natural circulation instability analysis model is developed for the natural circulation loop of CARR. The homogeneous flow model is used to establish the system control equations. The non-uniform heating and subcooled boiling heat transfer is included. The accumulation heat of the wall is also included. Numerical method of Gear is employed to solve the system equations documented in terms of ordinary differential equations. According to the calculation results, stability maps of the natural circulation loop, which confirm the presence of an instability region under the conditions of low equilibrium quality in the outlet and low pressure, are obtained. It is a special kind of density wave oscillation (DWO) that occurs in very low equilibrium quality region with the characteristics of geysering and ‘Type-I’ DWO at the same time. The calculation results show such oscillation course clearly. The variations of the mass flow rate, the pressure drop and the boiling boundary are analyzed separately. Especially, the phase-space trajectory of the boiling boundary and the mass flow rate is discussed. Finally the oscillation frequency is discussed. The calculated results have important significance for the safety operation and accidental analysis of CARR. 相似文献
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Expansion tank is an important component of all single-phase natural circulation loops. The tank serves the twin purposes of venting the air out during the loop filling and accommodation of the swells and shrinkages of the loop fluid during the transient. In the present study, experimental investigations have been carried out in a rectangular single-phase natural circulation loop to bring out the role of expansion tank in loop dynamics. The results on loop stability and transient behavior are discussed. The experimental investigations show that there is significant amount of heat exchange between the main loop fluid and the expansion tank fluid. First, the results of experimental studies are presented. The different flow regimes observed in these experimental investigations are discussed. Next, a model is presented for taking into account the heat exchange between the main loop fluid and the expansion tank fluid. Finally, the model is applied to simulate the dynamic behavior of different single-phase natural circulation loops. The investigations carried out in this study have helped in resolving the issue of hysteresis observed in these loops. 相似文献