微热管阵列平板太阳能集热器中空保温层厚度优化

为分析微热管阵列平板太阳能集热器的热性能,该文建立了集热器的CFD模型,对其进行数值模拟,将模拟结果与试验结果进行对比,验证了模型的可靠性。采用该CFD模型对集热器保温层厚度进行优化,结果表明,当实心保温层导热系数分别为0.02、0.03、0.04、0.05W/(m·K)时,优化的实心保温层厚度分别为4.5、5.0、5.5、5.5cm。合理设计的中空保温层(空气层与实心保温层相结合的保温层形式)集热器能够达到与实心保温层集热器相当的保温隔热效果,同时可使集热器保温层成本及质量降低25%~50%。最后,该文给出了保温层总厚度分别为4、5、6cm时的中空保温层厚度优化结果,为该类集热器保温层的设计提供了理论依据。     

Numerical study on two-phase flow in horizontal pipe

Two-phase flow in a horizontal pipe was investigated by using numerical and experimental visualization methods.A horizontal pipe was built for qualitative and quantitative flow visualization.The length of horizontal pipe flow system was 9.5 m and the inner diameter was 51 mm.High-speed video method was used for the qualitative visualization and PIV method was applied for the quantitative visua-lization.The same geometry model was used for the numerical study.Three flow regimes including stratified flow,elongated bubble and slug flow field were generated and visualized by using numerical and experimental methods.The results show that the numerical simulation results are qualitatively si-milar to that of the experimental results.In addition,more quantitative results can be analyzed by numerical method.Development and decay process of slug flow was investigated,showing that the decay of slug heavily depends on the magnitude of nose velocity and its lasting time.It can also be found that the liquid superficial velocity plays a significant role in affecting the slug frequency.When keeping the gas superficial velocity constant,the frequency will increase with the liquid superficial velocity.     

沟槽壁面对泰勒涡流稳定性影响的数值模拟

利用CFD数值模拟方法对光滑壁面与沟槽数量为18的2种同心圆柱模型内的泰勒-库艾特流动进行计算,在对比光壁模型的PIV试验与CFD数值计算结果后,发现两者吻合良好,验证了文中采用数值计算方法的准确性;针对泰勒涡流流态,定量分析了光壁模型R-Z平面上径向速度以及轴向速度的周期波动性,讨论了环隙中不同径向位置的径向以及轴向速度分布规律,获得了泰勒涡胞尺寸随着Re数增大而减小的变化规律;在相同的Re数下,沟槽数量为18的模型内也出现了泰勒涡流,通过比较2种不同结构模型内流场以及涡量场,发现沟槽的存在显著改变了流场分布,增大了环隙内涡量的大小及泰勒涡胞的尺寸,环隙中部指向外圆柱方向的径向速度也较光壁模型增大了20%,同时,计算获得R-θ平面内沟槽区域的流场分布表明该区域存在着明显的旋涡运动.     

Studying airflow and heat transfer characteristics of a horticultural produce packaging system using a 3-D CFD model. Part I: Model development and validation

A 3-D computational fluid dynamics (CFD) model of airflow and heat transfer processes within packed horticultural produce was developed. The model included explicit geometries of the product and package. Model results showed that airflow and temperature inside produce bulk were heterogeneous. The regions near the package vents showed relatively higher cooling air velocity and turbulence intensity. The coldest region was located behind the entrance vents. Pressure drops through entrance and exit vents were 51.1% and 45.2%, respectively. As the cooling air passed through the package vents and produce bulk, there was an increase in turbulence intensity. Validation of the model was conducted using experimental results. There was a good agreement between the predicted and measured results, average relative errors of predicted pressure drop and produce temperature were 13.80% and 16.27%, respectively.     

基于CFD技术的多级潜水泵优化设计

结合多级潜水泵的特点,针对后倾式叶轮及空间导叶的多级潜水泵,以效率最大为优化目标进行优化设计.为了提高优化的精度,对后倾式叶轮和空间导叶进行参数化拟合处理,选择叶轮和导叶的进出口角作为控制参数并在原模型基础上增加±20°作为优化范围,在不断进行流场校核的基础上基于遗传算法寻找目标函数的最优值,得到控制参数变化范围内的最优叶轮模型.数值模拟结果表明:当叶轮根部进口角为35.53°,出口角为27.32°,导叶进口角为15.48°,出口角为61.75°时获得最优模型,优化后的水泵效率提高了4.12％,单级扬程提高了,1.449 m,拓宽了水泵的高效区,提高了水泵的运行稳定性,泵性能得到了优化.     

光伏玻璃温室自然通风条件下的CFD模拟验证

基于计算机流体力学(CFD)数值方法,以光伏连栋玻璃温室为研究对象,在自然通风的条件下对室内温度场进行模拟验证。采用离散坐标(DO)辐射模型对光伏温室室内温度场的时空分布和变化规律进行了三维CFD模拟和试验验证。结果表明,光伏温室室内温度试验结果和模拟结果绝对误差均值为0.96℃,相对误差均值为2.94%。模拟结果和试验结果吻合,验证了模型的可行性。     

浆液池搅拌器固液两相三维数值模拟

对固-液悬浮搅拌槽中的固液两相流场进行研究,进而讨论固体浓度对搅拌槽内液相流场的影响规律,是固液搅拌研究工作的重要组成部分.本文应用商业计算流体力学软件fluent对浆液池中的流场进行模拟,基于N-S方程和标准的k-ε紊流模型,模拟出浆液池中液体的流动情况和浓度的分布,分析垂直面内和水平面内液相流的流场分布规律、固相颗粒浓度特点,并分析产生这种情况的原因,为搅拌器的设计和池液的改形提一些建议.     

涡轮增压器蜗壳内三维流场模拟分析

为提高涡轮增压器效率,对增压器内流场进行了模拟和分析。首先建立蜗壳和喷嘴环流动区域的几何模型;然后利用控制容积法对此模型中可压缩、粘性流体的三维流场进行数值模拟;最后根据计算结果,通过分析找出流动损失区域和流动损失的原因,并对增压器进行优化设计。数值计算方法和试验研究相结合可缩短优化设计周期,提高效率,这将为其它增压器的设计提供一种合理的方法。     

气吸振动式排种器吸种性能数值模拟与试验

建立了气吸振动式排种器吸种过程三维力学模型,基于Reynolds时均化的连续方程、Navier-Stokes方程和标准的k-ε湍流模型构成封闭方程组,并考虑真实气体的粘性和压缩性,运用CFD软件Fluent计算了籽粒在吸种口附近的受力,建立了力矩阵.采用二元线性插值法,通过计算吸孔的垂直吸种距离、径向吸种距离和有效吸种空间体积分析了排种器的吸种性能,绘制了籽粒吸种运动轨迹.分析了压差、吸孔直径对排种器吸种能力的影响.结果表明:增大吸孔直径和增加压差可以提高吸种性能,锥孔的吸种能力优于直孔和沉孔.以油菜籽粒为对象,通过性能试验得出了排种器的最佳工作参数.     

迷宫流道内固体颗粒运动的CFD模拟及PIV验证

针对迷宫流道灌水器结构细微复杂的特点,分别采用计算流体动力学CFD模拟方法和粒子图像测速仪PIV观测方法,对固体颗粒在迷宫流道内的运动规律进行了模拟研究与试验观测,并对2种方法的研究结果进行了分析,结果表明:CFD模拟不同直径、不同密度的固体颗粒运动时,其模拟轨迹线与实际运动线非常接近;当颗粒直径较小(65 μm)或密度较小(镁粒,1 740 kg/m3)时,CFD模拟的颗粒通过的路程与实际运动路程的偏差很小,而直径或密度较大的颗粒偏差比较大,其原因是直径或密度较大的颗粒实际运动时更加靠近主流区;采用CFD模拟颗粒运动速度是可行的,但颗粒实际运动时,保持高速的时间长于CFD模拟.