共查询到20条相似文献,搜索用时 15 毫秒
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对环形通道内液态金属钠沸腾两相流动特性进行了实验研究。实验中质量流速G≤2 000kg·m-2·s-1,系统压力p≤0.1 MPa,热流密度q≤550kW·m-2。两相流动摩擦压降通过在相同质量流量的单相流动摩擦阻力系数的基础上引入两相摩擦倍增因子来考虑两相的影响。实验结果表明:环形通道内液态金属钠两相摩擦倍增因子随Martinelli参数的增大有减小趋势。综合本文实验数据、Lurie等的实验数据以及Kaiser等的棒束实验数据,拟合得到了计算液态金属钠沸腾两相流动摩擦倍增因子的关系式。计算了本文拟合得到的关系式与各组实验数据间的相对标准偏差(RSD),表明本文关系式适用于计算环形通道内液态金属钠沸腾两相流动特性。 相似文献
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《Journal of Nuclear Science and Technology》2013,50(5):355-364
Density wave instability in a once-through boiling flow system was systematically observed using a uniformly joule-heated water loop operated at system pressures ranging from 20 to 43 ata. The test section consisted of two heated tubes connected in parallel and further paralleled by an unheated by-pass. The oscillatory behavior is analyzed as well as the effects brought on the threshold of instability by changes in the operating variables—mass velocity, system pressure, inlet resistance, inlet subcooling, by-pass ratio and exit quality. The experimental data are also presented in form convenient for verifying various analytical methods devised to predict the stability boundary. 相似文献
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核电站蒸汽发生器二次侧为两相对流沸腾换热过程,在设计过程中须保证其不发生两相流不稳定性。本工作采用时域法对垂直上升管内两相流不稳定性进行研究,建立了垂直上升直管内流动沸腾过程的一维模型,并编制计算程序。采用该程序模拟了流动沸腾过程气液两相流密度波的不稳定性,给出两相流波动过程瞬态参数分布,由此分析了密度波不稳定发生的机理,并分析了质量流速、系统压力、入口过冷度对不稳定的影响。结果表明,与已有实验及理论结果相比,瞬态参数计算结果与实验结果符合较好,可较好找到不同工况下直管内气液两相流发生不稳定的边界,结果优于Khabenski线算图方法。 相似文献
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《Journal of Nuclear Science and Technology》2013,50(12):903-914
A model is developed to describe the transition from annular flow to intermittent flow in a vertical two-phase flow system. Since the instability of the disturbance wave, which is a dominant wave shape at the boundary between annular flow and intermittent flow, is considered as a governing mechanism, this instability described by the concept of hyperbolicity breaking in the characteristic equation is included in the model. The developed model is validated by comparing its predictions of gas superficial velocity for the transition with experimental data available in the literature, and comparing those with the predictions of the other correlations. The comparison results show that the model gives better predictions for the transition condition than existing correlations, and the effects of fluid properties, geometry and liquid flow rate on the transition are well considered by the developed model. The average of prediction errors is 3% for the present model. The standard deviation of the prediction errors of the model reaches 28%, which is the smallest among the models compared here. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(6):389-399
The density wave instability in a once-through boiling flow system is analyzed using a simplified model characterized by lumped parameters and moving boundaries. An analytical solution of the stability boundary is derived in generalized form, which is then verified by comparison with experimental data obtained in a joule-heated system. Further comparison with published data obtained from experiments with sodium-heated steam generator indicates that the proposed model can be validly used for preliminary estimation of the stability boundary. Several dimensionless parameters governing the stability are also derived from the proposed model. 相似文献
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自然循环或重力注水过程的热功率、冷却剂流量等操作条件较小,易出现各种流动不稳定现象,影响核反应堆事故的发展进程,间歇式流动沸腾现象就属于其中的一种。以去离子水为工质,采用2×2加热棒束,对内径为32 mm竖直通道内的间歇式流动沸腾现象进行了实验研究,分析了不同热流密度下间歇式流动沸腾不稳定现象的变化规律,讨论了热流密度对间歇式沸腾周期的影响。结果表明,在一定的热流密度条件下,当加热通道内流体达到饱和并过热时,会发生周期性地剧烈喷涌及冷液回流现象,期间伴随泡状流、弹状流、搅混流及环状流等多种流动形态;间歇喷涌周期取决于沸腾停滞时间,随热流密度的不断增大,沸腾停滞时间缩短,间歇喷涌周期也缩短。当热流密度增大到一定程度时,间歇式流动沸腾现象消失,从而转变为另一种两相流动不稳定现象。 相似文献
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《Journal of Nuclear Science and Technology》2013,50(12):728-736
An account is given of experiments on incipient boiling pressure pulses imparted by liquid sodium, performed in a forced convection loop. The sodium is heated by direct current applied to the liquid metal itself in a vertical tube of 14.9 mm inner diameter through which the medium pumped. The experiments were carried out with the following ranges: Input power: 6–12kW,Pressure at condenser: 0.6–1.0 kg/cm2, Inlet temperature: 780°–850°C, Flow rate: 1.0–3. 5 l/min Typical pressure pulses registered during incipient boiling presented the form of damped oscillation. The initial pressure pulses were dependent on the location of boiling inception along the test section, the incipient boiling pattern and the degree of superheat. The initial pressure pulses observed were in the range of 0–3. 5 kg/cm2. The pressure pulses increased with the degree of superheat, which ranged 0°–150°C. The magnitudes of pressure pulses exceeded the saturation vapor pressure corresponding to the temperature of superheated liquid. Consideration of a simplified model indicated that, during incipient boiling, the pressure in the vapor phase oscillates while approaching asymptotically the saturation pressure. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(7):491-500
Instability of two-phase flow at low flow rate conditions is investigated analytically and experimentally. By applying the drift flux model, a linear analysis is conducted to study the effect of slip which is considered to play an important role at low flow rate conditions. Results obtained are compared with those of other analytical works and the reason for apparent variations is discussed. Some notes are also given on the lumped parameters which govern instability characteristics, and on the often-observed relation between the period of oscillation and the transit time. Experiments are conducted using R-113 at the test fluid. The results are analyzed in terms of the stability boundary and the period of oscillation. In the analysis it must be assumed that the flow is laminar. It is found that the instability observed experimentally is typical in the gravity term of the heated section is the dominant destabilizing term in the momentum equation. 相似文献
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实验研究了横向均匀和非均匀(多项式和正弦分布)加热条件下垂直矩形通道(2 mm×60 mm×1 000 mm)的沸腾压降特性,实验段为双面加热,有效加热面尺寸为56 mm×700 mm。工作流体为去离子水,通过改变入口压力和流量边界开展不同参数工况下的实验研究。结果表明,两相压降梯度随饱和压力的增加而减小,随质量流速的增加而增大,含气率对两相压降的影响与质量流速有关,横向功率分布形式对流动沸腾压降也有重要影响。基于均匀加热实验数据对现有的两相压降预测模型进行了评价,发现使用等效黏度假设的均相模型极大低估了实验值,且预测结果的分散度较大;分相模型中Müller-Steinhagen和Heck、Li和Wu关系式预测效果最好,平均绝对误差分别为11.8%和12.3%,且大多数预测值在±20%误差带内。本文基于Müller-Steinhagen和Heck关系式形式引入邦德数Bo考虑表面张力的影响,拟合得到新的预测关系式,该关系式对实验数据的预测误差在±8%的误差范围内。 相似文献
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对环形通道内金属钠起始沸腾壁面过热度进行实验研究。实验段长800 mm,环形通道外径10 mm,内径6 mm。电加热元件最高热流密度为846 kW/m2,进口过冷度为63.1~287.8 ℃,质量流量为7.2~122.0 kg/h,系统压力为0.85~28.79 kPa。实验结果表明,起始沸腾壁面过热度随热流密度和进口过冷度的增加而升高,随质量流量和系统压力的增加而降低。拟合得到了关于起始沸腾壁面过热度的半经验关系式,关系式计算结果与实验数据符合良好。 相似文献
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SUN Rulei ZHANG Dalin ZHOU Jiancheng SONG Gongle TIAN Wenxi SU Guanghui QIU Suizheng 《原子能科学技术》1959,54(9):1537-1549
The flow boiling pressure drop characteristics of a vertical rectangular channel (2 mm×60 mm×1 000 mm) were studied under transverse uniform and non uniform heating. The test section was double-sided heating with an effective heating area of 56 mm×700 mm. Three kinds of heating power distributions (uniform, polynomial and sinusoidal) were selected, and the working fluid was deionized water. A wide range of operating conditions was obtained by varying the inlet pressure and mass flux. The results show that the pressure drop gradient decreases with the increase of saturation pressure and increases with mass flux. The influence of vapor quality on two-phase pressure drop is related to mass flux, and the transverse power distribution has an important effect on the flow boiling pressure drop. Based on the experimental data of uniform heating, the existing two-phase pressure drop prediction model was evaluated. The homogeneous model using the equivalent viscosity assumption significantly underestimated the experimental values, and the data dispersion is relatively large. The Müller-Steinhagen and Heck and Li and Wu formulas are found to be the best with mean absolute errors of 11.8% and 12.3%, and most of predicted values are within ±20% error band. In this study, a new correlation based on the form of Müller-Steinhagen and Heck formula was proposed, and the Bond number Bo was introduced to consider the effect of surface tension. The prediction error of the new correlation for experimental data is within 8% error band. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(10):1094-1098
In order to investigate the effect of considering liquid density dependence on local fluid temperature in the thermal-hydraulic stability, a linear stability analysis is performed for a boiling natural circulation loop with an adiabatic riser. Type-I and Type-II instabilities were to investigate according to Fukuda-Kobori's classification. Type-I instability is dominant when the flow quality is low, while Type-II instability is relevant at high flow quality. Type-II instability is well known as the typical density wave oscillation. Neglecting liquid density differences yields estimates of Type-II instability margins that are too small, due to both a change in system-dynamics features and in the operational point. On the other hand, neglecting liquid density differences yields estimates of Type-I stability margins that are too large, especially due to a change in the operational point. Neglecting density differences is thus non-conservative in this case. Therefore, it is highly recommended to include liquid density dependence on the fluid subcooling in the stability analysis if a flow loop with an adiabatic riser is operated under the condition of low flow quality. 相似文献
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在低压流动沸腾不稳定性实验中,研究了自然循环流动在不同入口过冷度下的演化过程。对实验中的流动沸腾不稳定性入口流量信号进行快速傅里叶变换,基于振幅和频率特性区分了3种流动脉动模式:小幅流量脉动、复合流量脉动和逆流。分析了加热功率和入口过冷度对自然循环不稳定性的影响。根据加热段出口水温变化得到了出口的流型变化,当流量波动振幅较小时加热段出口流体始终是饱和状态,而当流量波动振幅较大时,加热段出口为单相液体和两相混合物交替通过。给出了这3种流量脉动的边界图,分析了热流密度和入口过冷度对流量脉动模式的影响。结果表明:出口含气率大于0时发生流动不稳定性,热流密度达到间歇干涸型临界热流密度时发生逆流。 相似文献
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对环形通道内液态金属钠沸腾两相流动特性进行了实验研究。实验中,系统压力为3.6~110.0kPa,热流密度为11~600kW·m~(-2),流速为0.02~0.45m·s~(-1)。实验结果表明,液态金属钠沸腾传热系数与壁面热流密度和系统压力有强烈关系,而与入口过冷度和质量流速无关。在本文实验数据基础上,拟合得到了计算液态金属钠沸腾两相传热系数的关系式,通过与各组实验数据间的比较,证明本文关系式适用于计算环形通道内液态金属钠沸腾两相传热系数。 相似文献
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《Journal of Nuclear Science and Technology》2013,50(11):774-790
This paper deals with local sodium boiling in the downstream of a six-subchannel blockage in an electrically heated LMFBR fuel subassembly mock-up. The first series of experiments were conducted to measure temperature distributions in the downstream of the blockage under non-boiling conditions. The measured temperature rise due to the blockage agreed fairly well with the calculation by the LOCK code. The second series of experiments were performed to investigate local boiling phenomena. In the local boiling region, no flow instability was observed since the sub-channels near the wrapper wall were still filled with sub-cooled liquid. In the nearly bulk boiling region, however, considerable upstream voiding occurred and then the inlet flow decreased, leading to final dryout. The boiling caused a considerable increase in acoustic noise intensity. The root-mean-square (RMS) noise level of approximately 20 mbar obtained in the present local boiling experiments with sodium was much higher than that (approximately 0.5 mbar) in the ordinary nucleate boiling experiments with water. The peak observed in the hertz ranges was due to the repetition of bubble formation and collapse. In the kilohertz ranges, however, resonance peaks were superposed on a smooth curve with a broad peak at approximately 7 kHz. The frequency (2.9 and 20.2 sec?1) of bubble formation decreased with the increase of the bubble size at its point of maximum development. The product of the bubble frequency and the equivalent diameter was found to be constant. 相似文献