圆管内液态铅铋合金强制对流换热特性研究

圆管内液态铅铋合金的强制对流换热特性研究对加速器驱动的次临界核能系统的发展具有重要意义。运用大涡模拟方法,对恒热流密度条件下三维圆管内液态铅铋合金强制对流换热特性进行了数值计算,对比发现模拟结果和实验数据及关联式吻合良好。对比了不同入口速度条件下流场的速度和温度分布、传热Nu数、无量纲时均温度、无量纲均方根温度和湍流涡分布等,进一步分析了不同雷诺数对圆管内液态铅铋合金强制对流换热特性的影响规律。在恒热流密度条件下,随着Re数的增加,液态铅铋合金的Nu数逐渐增大,圆管不同截面的温差逐渐减小,湍流涡分布增多,提高Re数能够增强液态铅铋合金的传热性能。     

U型通道内部流动与换热的数值研究

应用数值方法研究了燃气轮机叶片内部U型通道内流动与顶部换热特性.采用SST k-ω模型,分析了U型通道内光滑和带凹坑顶部结构以及不同Re数和旋转数对U型通道内部流动和顶部换热的影响。结果表明:在静止条件下,带凹坑结构的通道顶部Nu数较高,并且随着凹坑深度的增加,通道顶部换热能力增强;并且凹坑结构对通道压降的影响较小。随雷诺数增大,凹坑对通道顶部换热增强的幅度降低。在旋转状态下,随着旋转数的增加,通道顶部换热能力增强,但通道压降增大。     

余热利用H型翅片受波动性影响的机理研究

本文对余热利用中常用安装有H型翅片的管翅式换热器在波动流动条件下的换热性能和流阻特性进行了数值模拟研究。揭示了非稳态波动流动的不同波动时均速度、波动幅度和波动周期对流动和换热的影响机理。结果表明,在不同时均速度下,Nu数随Re数的变化趋势基本一致,而Eu数具有明显的迟滞现象;在不同波动幅度下,Nu数和Eu数的变化都很大,在Re数的极小值附近尤为明显;在不同波动周期下,Nu数和Eu数在所有Re数范围内均基本相同,影响可以忽略。最终获得了波动流动下换热和阻力计算的关联式。     

自然对流对横纹管内湍流对流传热的影响

以熔盐为传热工质,对考虑熔盐自然对流情况下横纹管内的流动传热进行了数值模拟。结果表明:同一Re数,横纹管内下侧Nu数大于上侧Nu数,随着Re数的增加,管内下侧Nu数与上侧Nu数的差值逐渐减小。考虑自然对流影响的横纹管内平均Nu数与不考虑自然对流影响的横纹管内平均Nu数基本相等。强制对流的Re数越低,自然对流对横纹管单侧传热影响越明显。横纹管槽宽越小,槽深越深,自然对流对单侧传热影响相对越小。通过非线性拟合,分别得出横纹管内下侧传热Nudown/Nuave-b、上侧传热Nuup/Nuave-b与浮升力参数Bo的关联式。     

锯齿型通道湍流流动和换热的自维持振荡

采用RNG k-ε湍流模型对锯齿形通道内流动和换热进行了数值模拟。对以时均方程法模拟得到的流场、温度场以及U-V相图、Nu-θ相图进行了分析。研究表明,在本文计算的Re范围内,数值计算结果仍能反映出周期性通道内流动和换热的自维持振荡特性,无量纲速度U,通道平均Nu数随时间作周期性振荡,并且振荡幅度、频率随Re数的增大而增大。     

锯齿型通道流动与换热的自维持振荡实验研究

本文对锯齿型通道内流动与换热的自维持振荡特性进行了实验研究。从可视化实验中观察到,Re300时,流场随时间几乎没有明显的变化;Re300,流动出现了明显的回流现象,且随着Re数增大,回流形成的涡增大,流动产生的涡的位置随时间呈有规律的周期性变化;在恒热流边界条件下,通道上、下壁面温度沿流动方向的变化与数值模拟所得到的Nu数、壁温的变化规律一致。     

流向对管束外混合对流影响的数值模拟

用格子玻尔兹曼方法对微圆管管束外混合对流的换热情况进行了数值模拟研究。在充分验证程序正确性的基础上,对混合流动绕流时不同壳侧进液角度,不同雷诺数Re以及瑞利数Ra等方面对传热的影响进行模拟研究,对衡量传热效果的Nu数及温度场进行了对比,总结出了换热规律。为高效微管换热器的开发提供了理论指导。     

微圆管内流动凝结换热的实验研究

本文对水平微圆管内凝结两相流流型进行了可视化观察,对流动和换热特性进行了实验研究。实验中只观察到 三种流型:柱塞状流、环状流和毛细泡状流。柱塞状流在质量小流量时才出现,流量较大时,流型以环状流和毛细泡状流 为主。实验的Nu数在某一Re数下具有最大值,而流动凝结的压降随Re数的增大单调增大。     

管外包覆多孔介质强化换热的数值研究

本文对管外包覆多孔介质的无限长圆管绕流的流场和温度场进行数值模拟,研究了多孔介质层的无量纲厚度ep,达西数D_a以及雷诺数Re对流动和强制对流换热特性的影响。研究结果表明,管外包覆多孔介质后的强制对流换热效果明显强于光管条件下的效果,换热增强了2.8~5.4倍;壁面平均努塞尔数Nu随e_p和Re的增大而增大,随Da的增大而减小;管壁处的流动阻力系数C_D随ep的增大而增大,随D_a的减小,先增大后减小,当Da小于1×10~(-5)时,阻力系数保持不变。     

过渡流下后向台阶流动与瞬态传热特性研究

为了研究过渡流下后向台阶的流动与瞬态传热特性,建立了二维不可压缩后向台阶流动的数值传热模型,采用非定常数值方式模拟了后向台阶的内部流场,比较了台阶下游底面瞬时努塞尔数Nu和时均努塞尔数Nu_m的分布,分析了台阶下游通道内温度分布规律。结果表明:过渡流下台阶底面Nu数沿着流动方向出现多个峰值,Nu数始终围绕Nu_m数发生波动。Re数为700时,主回流区未出现二次回流,Nu数在主回流区下游才发生波动;Re数为1200时,主回流区出现二次回流,Nu数在主回流区就发生了波动。台阶下游通道内温度沿法向呈阶梯式变化,Re数越大,近底面处的温度变化梯度也越大。     

关于"太阳在银河系中所受引力与到银心距离r的关系"的讨论

讨论了银道面内的引力场强分布和太阳在银河系中所受引力与到银心距离r的关系，指出引力场强g并不是与r的平方成反比，这是由于银河系的大小和形状不能忽略造成的．强调了万有引力定律的适用条件．     

On the calculation of the bremsstrahlung in the region of the plasma frequency

On the basis of the classical theory of radiation produced in incomplete Coulomb interaction, a formula is derived for the coefficient of the bremsstrahlung of fully ionized plasma. In the region of rectilinear approximation a comparison is made with the results of the quantum formula derived from the Born approximation. Furthermore, the influence of dispersion upon the emission coefficient is taken into account; some relations for the region of dispersion are given.     

On the predictability of the positions of the convergence zones in the ocean

The disagreement between the experimental and calculated positions of the first convergence zone are known from many publications. The most probable cause for such a disagreement, namely, the incorrect specification of the input data for the calculations, is considered. The lack of simultaneity between the hydrological surveys of the region and the acoustic experiments is emphasized. The experimental data obtained by the author in five ocean regions are presented. These data characterize the diurnal variability of the distance from the source to the nearest boundary of the convergence zone. The relations proposed by different researchers for calculating the sound speed from the temperature, salinity, and hydrostatic pressure are analyzed. It is shown that these relations lead to a substantial difference in the estimated depth dependence of the hydrostatic gradient of the sound speed. The position of the first convergence zone is calculated for the propagation conditions determined by vertical temperature and salinity profiles with the subsequent recalculation of these profiles into sound speed profiles by using eight different formulas known from the literature. It is shown that different formulas lead to different values of the distance to the first zone; this difference is substantially greater than that between the calculations and experiment. The necessity of improving the recalculation relations in view of the experimental data on sound propagation in natural oceanic waveguides, including the data on the actual positions of the convergence zones, is emphasized.     

Dependence of the Intensity of the Spectral Lines and the Composition of the Sample and the Plasma Parameters of the Unipolar Arc

The investigation was made of the dependence of the intensity of Tl, Ga, Mo, Mg, Mn, Sn, Bi, Ni, Zn, Pt and Au spectral lines and the plasma parameters (temperature T, electron concentration n_e, degree of 6 ionnization α) from concentration of lithium additive.     

Extracting the wavefunction of the LSP at the LHC

We consider associated production of squarks and gluinos with the lightest supersymmetric particle (LSP), or states nearly degenerate in mass with it. Though sub-dominant to pair production of color SU(3)-charged superpartners, these processes are directly sensitive to the wavefunction composition of the lightest neutralinos. Exploiting event-shape variables - including some introduced here for the first time - we are able to identify the composition of the LSP by selecting events involving a single high-pT jet recoiling against missing transverse energy. We illustrate the proposed technique on a set of benchmark cases and propose methods for applying these results in more realistic experimental environments.     

Set the controls for the heart of the Sun

In this paper we describe experiments conducted with high-power lasers that are attempting to replicate, for a very short time and in miniature, conditions found in the Sun. Experiments to date have reached conditions in the outer part of the Sun. To reach the Sun's centre requires compression of material to very much greater than solid density and heating to over ten million degrees. To achieve this, a new class of experiments and a new generation of high-power lasers are required.     

On the Question of the Source of the Apokamp

Technical Physics - The object of this work is the apokamp—a new type of plasma jet, which is formed from a bright offshoot emerging at the bending point of a channel of a high-voltage...