Hydrodynamics study of a fast liquid–liquid oxidation process with in situ gas production in microreactors

Hydrodynamics characteristics of a fast and highly exothermic liquid–liquid oxidation process with in situ gas production in microreactors were studied using a newly developed experimental method. In the adipic acid synthesis through the K/A oil (the mixture of cyclohexanol and cyclohexanone) oxidation with nitric acid, bubble generation modes were divided into four categories. The gas production became more intensive, unstable, even explosive with increasing the oil phase feed rate and the temperature. A novel automatic image processing method was developed to monitor the instantaneous velocity online by tracking the gas–liquid interface. The axial velocity at the same location was unstable due to the changing gas production rate. Furthermore, the actual residence time was obtained easily with being only 36% of the space–time minimally, beneficial for establishing accurate kinetics and mass transfer models with time participation. Finally, an empirical correlation was developed to predict the actual residence time under different conditions.     

Processing capabilities of micro ultrasonic machining for hard and brittle materials: SPH analysis and experimental verification

Micro ultrasonic machining (micro-USM) is an unconventional micromachining technology that has capability to fabricate high aspect ratio micro-holes, intricate shapes and features on various hard and brittle materials. The material removal in USM is based on brittle fracture of work materials. The mechanical properties and fracture behaviour are different for varied hard and brittle materials, which would make a big difference in the processing capability of micro-USM. To study the processing capability of USM and exploit its potential, the material removal of work materials, wear of abrasive particles and wear of machining tools in USM of three typical hard and brittle materials including float glass, alumina, and silicon carbide were investigated in this work. Both smoothed particle hydrodynamics (SPH) simulations and verification experiments were conducted. The material removal rate is found to decrease in the order of glass, alumina, and silicon carbide, which can be well explained by the simulation results that cracking of glass is faster and larger compared to the other materials. Correspondingly, the tool wear rate also dropped significantly thanks to the faster material removal, and a formation of concavity on the tool tip center due to intensive wear was prevented. The SPH model is proved useful for studying USM of different hard and brittle materials, and capable of predicting the machining performance.     

水动力水质模拟在黑臭湖体治理中的应用

为分析琵琶湖黑臭水体治理效果,应用水动力水质模拟方法,根据琵琶湖水体流动及污染物运移扩散规律等,构建水动力及水质数学模型,通过模拟现状、经工程治理后湖体的流场和污染物浓度场及湖体水质达标时间,对比分析工程治理前后的效果。结果表明,水体治理工程实施后,湖体流场变得均匀;湖体大部分水域COD浓度达到Ⅳ类水质标准;但因湖体现状TN浓度较高,水体治理工程实施后短时间内TN浓度仍严重超标;TP浓度经工程治理后降低明显,基本达到Ⅳ类水质标准。此外,根据湖体水质达标时间模拟结果,在保证工程实施后湖体补水入湖水质维持达标的情况下,至少需50d才可使湖体超标最为严重的TN达到Ⅳ类水质标准。     

低流量下等高差自然循环系统倒流现象实验研究

自然循环系统由于具有固有安全性而被广泛应用于核电站中。等高差自然循环系统是一种特殊的系统，其加热段与水箱之间是通过上下水平段连接。在低流量条件下，这类自然循环系统会发生水箱冷水倒流至上水平段的现象，目前对该现象的研究并不常见。对等高度差自然循环系统的上水平段倒流特性进行了可视化实验研究。实验结果表明，上水平段倒流长度随流量的增加而减小，随着加热段出口流体与倒流流体温差的增大而增加。研究发现，上水平段倒流现象主要受加热段出口流体惯性力和与倒流流体形成的浮升力共同影响，并且倒流现象的发生可以通过Richardson数来判定。     

流体力学教学中的传统教学与网络多媒体教学

通过论述传统教学模式与多媒体网络教学模式的利弊 ,提出了在流体力学教学活动中既要弘扬传统教学的优点 ,又要融入现代多媒体网络教学 ,两者有机地结合起来 ,高效率、高质量地培养出优秀人才。     

岩石渗透试验瞬态法的水动力学分析

压力脉冲瞬态法是一种专门进行岩石渗透率测试的新方法。对多孔介质渗流的水动力学分析表明,在岩石渗透试验的瞬态法中,水流动量方程可以不考虑流速的变化率。对于致密岩石,出现高速非Darcy流的特征不显著,在一般条件下Darcy定律仍然有效。给出压力脉冲瞬态法的物理模型和数学模型,采用等梯度假设简化连续性方程,针对上下游压力容器的不同控制条件,推导各种情况下压力测试曲线的解译公式。这些解译公式为分析不同控制方式下的试验过程和计算岩石渗透率提供了方便。实例表明,基于等梯度假设的解译公式对压力脉冲瞬态法所产生的渗透率测试曲线基本适用。     

双模制导航弹静稳定性数值分析

采用二阶Roe格式求解三维N-S方程,根据航弹雷诺数较高、计算网格不规则的特点,选用Spalart-Allmaras代数模型。首先,对卫星制导航弹绕流流场进行大量数值模拟,与风洞吹风试验数据对比,验证了数值方法的有效性。在此基础上对双模制导航弹在不同的攻角和不同来流速度以及不同舵偏角下的绕流流动进行数值模拟,对航弹的升阻特性、纵向静稳定性进行了详细分析,获取的气动参数分布规律对此类双模制导航弹气动布局设计具有一定的参考价值。     

大质量钨破片冲击多层间隙盖板炸药数值模拟与试验研究

为分析大质量破片对多层盖板炸药冲击起爆阈值的影响因素,采用SPH和FEM相结合的方法开展了不同盖板厚度和不同盖板间隔情况对起爆阈值影响的数值模拟。在此基础上,采用二级轻气炮作为加载手段,进行了大质量钨合金破片冲击不同盖板及间隙情况下炸药冲击起爆试验研究,获得了起爆阈值。数值模拟与试验结果相一致,表明采用SPH与FEM相结合的方法可以较好地模拟此类问题。通过拟合得到了大质量破片冲击起爆阈值速度与冲击角度之间的经验关系式。分析结果表明,大质量破片冲击产生的大量二次破片对起爆阈值速度和起爆延迟时间具有较大的影响。     

泵技术进展与发展趋势

泵作为一种典型的水力机械,在国民经济中扮演着重要的角色,其技术进展一直受到多个行业的关注。在各种应用需求的驱动以及材料、力学、信息和计算机等相关学科的带动下,泵理论和技术研究已取得巨大进展。人们对泵内流机理和运行特性的认识更为深入,数字化设计和信息化运维已得到广泛应用,泵产品已逐步具有生态友好和智能化特征。本文以2000年以来泵领域所取得的进展为重点,围绕旋涡泵、离心泵、混流泵、轴流泵和贯流泵等叶片式泵,从产品应用需求出发,针对泵的水动力学、设计技术、振动噪声、节能与运维技术等四个部分对技术进展进行综述,并对泵的发展趋势进行总结和展望。