螺旋槽管脉冲流强化对流换热数值及场协同分析

通过数值模拟计算研究了在螺旋槽管内通入脉冲流后的强化换热机理.数值计算结果表明,脉冲流动能引起出口压力呈周期波动,波动幅度随脉冲流频率的增大而增大;脉冲流动能够使流体在螺旋槽管管壁附近产生漩涡,并出现周期性的生成、漂移和脱落;由于漩涡的作用,增强了流体的径向扰动和相对扰动;脉冲流动能够改善速度场与温度梯度场之间的协同程度,从而起到强化传热的效果.     

均相沉淀法制备AACHH阻燃晶须

以硫酸铝和尿素为原料,山梨醇为模板剂,利用均相沉淀法在高压釜中反应合成了NH4Al(OH)3.24(CO3)0.38.H2O(AACHH)阻然晶须,研究了CO2相对浓度对合成产物及形貌的影响.XRD、FT-IR、PM和TG/DTA分析结果表明:在通入10 min的CO2的条件下可以制备出形状完好的AACHH晶须,晶须长径比为10~20,晶须释放阻燃气体为NH3、CO2和H2O,完全分解其失重量为57.9%.     

1-(4′-乙炔基苯基)-4-正丙基-2,6,7-三氧杂双环[2.2.2]辛烷的合成

以正戊醛为原料经Cannizzaro反应,脱水,酯化,合环和引入炔基5步反应,总收率为5%,成功合成了1-(4′-乙炔基苯基)-4-正丙基-2,6,7-三氧杂双环[2.2.2]辛烷.目标化合物的熔点及1H NMR谱,MS与文献报道一致.     

A power-aware code-compression design for RISC/VLIW architecture

We studied the architecture of embedded computing systems from the viewpoint of power consumption in memory systems and used a selective-code-compression (SCC) approach to realize our design.Based on t...     

城市守旧与空间更新

讲创新的时候为什么要强调守旧呢?每一座城市都有历史,哪怕是一座新城市,从城市开始建设就形成自己的历史,而历史对每一座城市都是非常宝贵的。比如说一座城市必然是通过其城市的布局,     

土与混凝土接触面反向单剪本构模型

土与混凝土接触面的反向剪切性质是土木工程中一个重要的课题。根据接触面反向单剪试验结果,定量分析了正向剪切历史对不同含水率接触面反向抗剪强度、摩擦角、黏聚力等因素的影响,给出了相关的经验公式。提出了接触面临界正向剪切比的概念。根据改进的应力应变方程,建立了接触面正反向剪切模量公式,其包含了10个土体参数,均可通过接触面试验求得。确定了该公式中各参数的取值方法,推荐了初步的取值范围。进行了不同正向剪切比情况下的接触面剪切应力应变模拟,得到良好的模拟效果。研究成果可供相关的工程设计参考。     

The Phase Transformation of R_2O-CaO-SiO_2-F Glass-ceramics

The phase transformation of R2O-CaO-SiO2-F system glass-ceramics with various additions of K2O and F was investigated by DTA, XRD, SEM and other techniques. The crystallization and the microstructure of the obtained glass-ceramics were also evaluated. The phase separation occurred in CN1 specimen after being quenched in water, but phase separation did not appear in other quenched specimens with the content of K2O and F increasing obviously, showing K2O and F modified the structure of the glass-forming melts...     

Methods of Modifying the Brittle Behavior of Cementitious Composites

We put forward effective methods of increasing the tensile strain of cementitious composites with 2% PVA fiber and high fly ash content. The test results show that curing condition has a significantly effect on the tensile performance. It is approved that the specimens incorporated appropriate volume fraction rubber powder and lightweight aggregate greatly increase the tensile strain of composites at medium-term age, but indefinitely at long-term age. To a certain extent, EVA can limitedly enhance the tensi...     

一种基于H．264的自适应空域错误隐藏算法

H．264／AVC中Ⅰ帧的传输错误不仅会破坏当前的解码帧,还会在时间上扩散,对后续P帧的预测带来严重的影响。因此本文提出了一种通过计算受损宏块周围边缘方向的信息熵来自适应的选择双线性内插或方向性内插的错误隐藏方法。实验表明,该方法与单独使用双线性内插法或方向内插法相比,具有较好的误码掩盖效果,PSNR相比至少提高了0．27dB。