Analytical prediction on the pump-induced pulsating pressure in a reactor coolant pipe

An analytical method is presented for predicting the amplitudes of pump-induced fluctuating pressures in a reactor coolant pipe using a linear transformation technique which reduces a homogeneous differential equation with non-homogeneous boundary conditions into a nonhomogeneous differential equation with homogeneous boundary conditions. At the end of the pipe, three types of boundary conditions are considered—open, closed and piston-spring supported. Numerical examples are given for a typical reactor. Comparisons of measured pressure amplitudes in the pipe with model prediction are shown to be in good agreement for the forcing frequencies.     

基于正交试验的光伏水泵性能优化

以光伏水泵为研究对象,基于试验测试和理论分析建立光伏水泵出水量计算预测方法。采用正交试验设计优化方案,选取泵叶轮结构参数为优化变量,通过数值模拟和试验研究的方法,对该光伏水泵的性能进行优化和试验验证。结果表明：经优化后,光伏水泵系统的最低出水值下降至330 W/m²,水泵每日工作时长提升;光照辐射强度稳态时的泵出口压力脉动相较优化前有小幅提升,光照辐射强度瞬态变化时泵出口压力脉动波动幅度更平稳;优化后的模型泵叶轮进口低压区面积明显减小,叶轮出口压力显著增加,同时叶轮流道内速度分布更为均匀。     

Modeling for shell-side pressure drop for liquid flow in shell-and-tube heat exchanger

A theoretical model for shell-side pressure drop has been developed. The model incorporates the effect of pressure drop in inlet and outlet nozzles along with the losses in the segments created by baffles. The results of the model for Reynolds numbers lying between 10³ and 10⁵ match more closely with the experimental results available in the literature compared to analytical models developed by other researchers for different configurations of heat exchangers.     

罗茨泵内部流场数值模拟研究

罗茨泵在运行中由于各种原因会出现振动大、噪音大、泄漏等问题,获得罗茨泵的流动信息对预知及解决故障问题具有非常重要的意义,建立罗茨泵流场数学模型,用CFD软件对其内部流场进行模拟,获得并分析内部介质的压力场、速度场、流量脉动曲线、进出口压差对流量影响。研究结果表明:两转子间隙处压差最大,形成较高涡流;排气口两侧有明显的涡流;出口流量在转子转动初始阶段达到峰值;进口流量和进出口压差成反比,进口流量的脉动系数和进出口压差成正比。验证了CFD数值模拟的准确性,为对罗茨泵的进一步研究和整体优化奠定了基础。     

High-Frequency Pulsatile Pipe Flows Encompassing All Flow Regimes

Time-varying pipe flows driven by a harmonically pulsating inlet velocity and spanning all flow regimes have been investigated by means of numerical simulations. The Reynolds number varied from 1000 to 5000 in response to the inlet velocity oscillations. The frequency of the pulsations was varied from 1 to 10 Hz. These frequencies are markedly higher than those previously studied (maximum value of 0.025 Hz). The motivation for the use of the elevated frequency range was engendered by practical applications such as cardiovascular and respiratory systems of mammals in addition to numerous industrial applications. The simulations made use of the modified Menter transitional model. The key conclusion found here is that the use of a quasi-steady model for the prediction of fully developed friction factors is not applicable for the higher frequencies considered here. The deviations between the actual and quasi-steady friction factor values increase markedly with increasing frequency. Backflow occurs near the wall as the flow transists from deceleration to acceleration. This transition gives rise to a change in the sign of the axial pressure gradient. The amplitudes of the pressure oscillations generated by the imposed velocity variations increase markedly with increasing frequency and diminish with increasing downstream distance from the pipe inlet. The effect of modifications of the Menter model was assessed by carrying out separate numerical solutions for the unmodified and modified models. The pressure oscillations corresponding to the respective models were compared, and it was found that the deviations are insignificant.     

200MW机组转子惰走润滑油压暂态过程试验研究

鉴于一些机组轴瓦烧坏事故发生在转子停机惰走过程,通过对某型国产200MW机组停机启动交流润滑油泵和之后停机过程若干参数的测量,对该型200MW机组润滑油压暂态过程进行了试验研究。结果表明,虽然交流润滑油泵出力在增加,但润滑油母管压力却呈下降趋势。得出了润滑油泵单独供油的切换转速和主油泵入出口压力变化的特性并进行了分析。     

微型柱塞泵非定常动网格流场模拟

微型柱塞泵可为冷却塔水轮机轴承润滑供油,提高油路效率。为分析微型柱塞泵运行情况、工作效率等,建立了柱塞泵三维结构和流域模型图,设定了柱塞泵网格运动边界,载入Fluent进行数值模拟得到了柱塞泵内部压力场分布情况,分析了柱塞泵泵腔压力与进、出油球形阀位移随时间的变化规律。结果表明,泵腔压力随时间分布呈类正弦函数规律,泵腔压力总体趋势由传动柱塞速度决定。研究结果为柱塞泵的推广应用提供借鉴。     

电控高压油泵供油效率仿真计算与分析

基于AMESim建立高压油泵的仿真模型,包括低压油路、燃油比例控制阀、凸轮、柱塞偶件、出油阀、进油阀等,利用仿真模型分析低压油路参数、柱塞顶隙容积对油泵供油效率的影响,通过高压油泵试验台试验对比验证仿真模型的准确性。结果表明:低压油路的控制压力较小时,油泵供油效率随着泄压阀控制压力的增大明显增加;当压力达到一定值之后,供油效率缓慢增加;在相同条件下,转速越高油泵供油效率越高;油泵供油效率随进出油阀余隙容积增加而逐渐降低。     

基于两方程湍流模型的均匀流中湍流动能衰减规律研究

通过理论推导和数值模拟,从湍流模型封闭系数的确定过程、输运方程扩散项的影响因素、入口边界条件和网格尺度等方面分析标准k-ε模型、标准k-ω模型和SST k-ω湍流模型在计算均匀来流时湍流动能的衰减规律及其本质物理区别;通过数值模拟分析中性大气条件下湍流动能的衰减规律.结果表明,在均匀流中,采用标准k-ε湍流模型,入口湍...     

高压蓄压泵泵油系供油过程的仿真研究

针对大功率柴油机共轨系统高压蓄压泵的供油过程,利用AWS HYDSIM软件建立仿真模型,分析出油阀、进油阀的运动过程和凸轮型线布置对供油性能的影响,为进一步提升高压蓄压泵的供油效率提供了理论依据。     

Numerical simulation of flow in centrifugal pump with complex impeller

Based on the Navier-Stokes equations and the Spalart-Allmaras turbulence model, three dimensional turbulent flow fields in centrifugal pump with long-mid-short blade complex impeller are calculated and analyzed numerically. The relative velocity and pressure distributions in the flowpart are obtained. It is found that the flow in the passage of the complex impeller is unsymmetrical due to the joint action between volute and impeller. The back-flow region is at inlet of long-blade suction side, near middle part of long-blade pressure side and outlet of short-blade suction side. The flow near volute throat is affected greatly by volute. The relative velocity is large and it is easy to bring back flow at outlet of the complex impeller near volute throat. The static and total pressure rise uniformly from inlet to outlet in the impeller. At impeller outlet, the pressure periodically decreases from pressure side to suction side, and then the static pressure sharply rise near the throat. The experimental results show that the back flow in the impeller has an important influence on the performance of pump.     

Performance evaluation and outlet load improvement of a rotating detonation combustor with different outlet nozzles

Outlet nozzles for a rotating detonation combustor were designed to meet a downstream turbine and reduce the high pressure and heat load caused by the oblique shock wave at the outlet. The effects of the rotating detonation combustor with two types of outlet nozzles were studied, and the performance and outlet parameters of the combustor were measured at an elevated chamber pressure and preheating temperature based on gas turbine conditions. The results showed that the outlet nozzles could cause changes in the wave collisions and folding of the weak flame front in the detonation formation process, but the basic propagation process was similar to that without a nozzle. The pressure ratio changed from 1.427 in the original model to 1.392 and 1.304 with the two types of outlet nozzles. Meanwhile, the outlet load was greatly improved. The peak values of the static temperature at the outlet dropped by 22.423% and 27.572% with the two types of outlet nozzles compared to the original model. In addition, the peak static pressures dropped by 75.737% and 83.722%, respectively. In addition, the outlet nozzles significantly reduced the unevenness of the outlet static temperature and static pressure distributions. This created a better outlet operating environment, thereby improving the performance of the rotating detonation combustor.     

集成小型堆和可再生能源的超临界CO2循环发电系统

  [目的]  小型模块化压水堆(小型堆)核电站由于温度参数低,其发电效率不到30%,为了提高小型堆的核能利用效率,可将小型堆与可再生能源组合,并以先进的超临界CO₂循环作为热能转换为电能的装置。  [方法]  基于简单回热模式的超临界CO₂循环,并在此基础上增加一次间冷和一次再热,将小型堆与太阳能、生物质能热源集成为新型混合发电系统,对其发电效率进行了分析。  [结果]  结果表明:对于高压透平入口温度390 ℃的系统,发电效率34.13%,对于高压透平入口温度550 ℃的系统,发电效率41.22%。此外,对系统的安全性分析表明:CO₂本身是具备核安全属性的工质,并且超临界CO₂循环还可以作为反应堆的非能动余热排出系统,确保在严重事故工况下,反应堆持续排出衰变热。  [结论]  集成小型堆和可再生能源的超临界CO₂循环发电系统具备良好的发电效率和核安全性。     

Effects of a kind of surface groove on flow loss in both rectangular and circular ducts at different Reynolds numbers

Pipes are widely used to transport gas,oil and water in industries.Drag reduction in pipes is an increasingly concerned problem to save energy.Some researches have indicated that the non-smooth surface with special structures can reduce flow loss.In this paper,an experimental investigation has been performed on the effects of a kind of surface groove on the drag in both rectangular and circular duct at different Reynolds numbers.In the experiment of the rectangular duct,total pressure at both inlet and outlet were measured.Static pressure on the wall was measured on the surface with smooth and grooved film respectively.In the circular duct,a boundary layer pressure probe was used to measure the total pressure distribution at both inlet and outlet.Four taps at inlet and outlet were used to measure static pressure.The loss coefficient is used to evaluate the effects of the surface groove on drag reduction.The experiment was conducted with the Reynolds number range from 1.28×10~4 to 2.57×10~4.The result shows a maximum drag loss reduction of approximately 2.4% in rectangular duct at Reynolds number of 2.4×10~4.A 10%reduction of pipe pressure loss by grooved surface is measured in circular duct at a Reynolds number of 3.0×10~5.     

Thermal-hydraulic modeling and transient analysis of pressurized water reactors

This paper examines a new dynamic moving boundary thermal-hydraulic fuel pin model (FUELPIN) for the transient analysis of a pressurized water reactor (PWR). FUELPIN is developed to accommodate the reactor core thermal-hydraulic model of the fuel pin and adjacent coolant flow channel, with detailed thermal conduction in fuel elements. Transient analyses using a known thermal-hydraulic analysis code, COBRA, and FUELPIN linked with a PWR system analysis code show that the thermal margin gains more by a transient MDNBR approach than the traditional quasi-steady methodology for a PWR. The studies of the nuclear reactor system show that moving boundary formulation is highly suitable for the transient thermal-hydraulic analysis of PWRs.     

Cracking in feedwater pipework of light water reactors: Causes and remedies

The present paper deals with cracking in ferritic pipework of light water reactor (BWR) feedwater systems whose causes are unsuitable design and manufacture and, at least occasionally, unsuitable water quality. Thus in two BWR plants in the German Federal Republic large circumferential cracks have been found in the circumferential welds in the main feedwater pipelines immediately adjacent to the reactor pressure vessel, and in a further BWR large longitudinal cracks have been found in pipe bends of the reactor water purification pipework connected to the main feedwater pipelines.The piping regions near the reactor pressure vessel feedwater nozzles represent a boundary region of varying thermodynamic states of the pressurised water. The reactor pressure vessel is heated to saturation temperature by the radioactive decay heat, and then cooler water, and sometimes (during start-up) cold water is injected into the reactor pressure vessel in order to maintain a constant water level about 2 m above the upper edge of the feedwater nozzles. In order to improve the state of knowledge regarding the stressing conditions under prevailing operating conditions, extensive strain and temperature measurements have been carried out. The results of these measurements carried out in several BWRs confirm the occurrence of rapid temperature changes in the feedwater pipework in the regions where it connects to the reactor pressure vessel, leading to varying stresses which at times reach the plastic region. These processes are triggered by special operating states such as start-up and shut-down or hot standby operation with feedwater flows smaller than 6% relative to normal operation under full load.     

Chemical storage of solar energy kinetics of heterogeneous SO3 and H2O reaction—Reaction analysis and reactor design

The first energy recovery step in the ammonium hydrogen sulfate (AHS) cycle is the formation of H₂SO₄(l) from H₂O(g) and SO₃(g). It has been determined that the optimum way to accomplish this is by the use of a double pipe tubular reactor. In this paper, a mathematical model for the reactor is presented, applied to the three reaction zones, and a method of numerical solution discussed. Three horizontal pilot-scale configurations, 0.234 × 10⁶ to 5.863 × 10⁶ kJ/h energy release, are discussed and sizing presented. Also, the results for a vertical configuration are presented. The need for additional work on two-phase gas-liquid flow in condensing systems and in annuli has been identified. The most important conclusion is that a high temperature can be achieved in the reactor by the use of a front end adiabatic section followed by nonadiabatic sections to recover the heat released.     

原模型泵装置效率换算方法研究

基于泵段模型试验和泵装置模型试验数据,分析了泵性能变化对流道损失的影响,发现泵性能变化对进水流道损失影响很小而对出水流道损失影响较大.建立了模型泵装置性能向原型换算的新方法,并对不同的性能换算公式进行比较分析.实例研究表明,新的换算方法准确可靠,其精度能满足生产实际的需要.     

Numerical study of internal flow field and flow passage improvement of an inlet particle separator

By performing gas flow field numerical simulations for several inlet Reynolds numbers Re (from 2 × 10⁵ to 9 × 10⁵) and byflow ratios x (from 10% to 20%), the present study has proposed to improve the flow passage of an inlet particle separator. An adjacent objective of the study is to lower pressure losses of the inlet particle separator (IPS). No particle has been included in the gas flow for a k-epsilon turbulence model. The velocity distribution in different sections and the pressure coefficient C_p along the duct have been analyzed, which indicates that there exist important low-velocity regions and vortices in the separation area. Therefore, the profile of streamlines along the original passage has been considered. This profile illustrated a vacuum region in the same area. All investigations suggest that the separation area is the most critical one for fulfilling the objective on pressure losses limitation. Then the flow passage improvement method has focused on the separation area. An improved shape has been designed in order to suit smoothly to the streamlines in this region. Similar numerical studies as those for the original shape have been conducted on this improved shape, confirming some considerable enhancements compared with the original shape. The significant vortices which appear in the original shape reduce in amount and size. Besides, pressure losses are greatly decreased in both outlets (up to 30% for high Reynolds number) and the flow is uniform at the main outlet. Subsequent engineering surveys could rely on expressions obtained for C_p in both outlets which extend the pressure losses for a wide range of inlet Reynolds numbers. As a result, the numerical calculations demonstrate that the flow passage improvement method applied in this study has succeeded in designing a shape which enhances the flow behavior.     

On the application of probabilistic fracture mechanics to the reliability and inspection of pressure vessels

A probabilistic fracture mechanics model was developed to analyse the failure probability of a typical high power density reactor pressure vessel. The major causes for the nuclear reactor pressure vessel failure include fatigue, corrosion fatigue and brittle failure. All these causes are greatly affected by the stress loading conditions, material properties (aged by neutron damage), and defects embedded in the structure. Both an analytical first-order second-moment approximation and a hybrid methodology were employed in this study. In addition to the static scatter of the pre-existing cracks and material properties, a random walk model based on the operating history was introduced to represent the random occurrence of the abnormal transient stresses. The failure mode is defined as the brittle failure caused by a critical crack, meaning the stress intensity factor around a critical crack exceeding the fracture toughness of the pressure vessel material. Through a sample study on a typical high power density nuclear power plant, it was found that the vessel failure probability is about 4 × 10⁻⁴ at the 40th year of operation and the failure rate is in the order of 5 × 10⁻⁶ per vessel per year, which had reasonable agreement with the value of 10⁻⁴−10⁻⁶ as reported based on real-world statistics. In addition to the failure probability caused by fatigue crack growth, the reliability of a Low Temperature Overpressure incident was also evaluated.