液滴碰撞对液膜内汽泡运动与换热影响

采用数值模拟的方法,研究了沸腾雾化喷射过程中热壁面薄液膜层受到液滴碰撞扰动时液膜层内汽泡运动,相界面变化和由此引起的壁面换热特性.模拟结果显示汽泡生长初期相界面变化与液膜层内二次核化特征与文献结果吻合良好,汽泡生长后期相界面变化存在滞后.讨论了液滴下降速度.液滴直径与初始位置,多液滴碰撞对液膜层内流动与壁面换热的影响.     

圆柱坐标系下生物组织中激光传输的七流模拟

提出了圆柱坐标系下生物组织中激光传输的七流模型,根据此模型进行的计算结果与直角坐标系下七流模型的计算结果比较,二者吻合较好.在此基础上,研究了组织光学性质对激光在组织内传输过程的影响,结果表明:散射效应使入射激光分布到更大的组织范围内,并使激光的穿透率降低,但其影响是有限的,即当散射系数增大到一定程度后,组织内的激光能量分布就不再有明显的变化.相对而言,吸收系数对组织内激光能量分布的影响比散射系数要大,各向异性系数增大使组织内的散射趋于前向散射,激光能量分布也更深入组织内部.     

Water adsorption performance of UiO-66 modified by MgCl2 for heat transformation applications

UiO-66 is a potential material for adsorption heat transformation (AHT) with high specific surface area, and excellent thermal and chemical stability. However, the low water adsorption capacity of UiO-66 in the low relative pressure range ($0< P/P_0< 0.3$) limits its application in AHT. We prepare the UiO-66 modified by MgCl$_{2 }$ through using the solvothermal method and impregnation method, and study their water vapor adsorption performances and heat storage capacities. Attributed to the extremely high saturated water uptake and excellent hydrophilicity of MgCl$_{2}$, the water adsorption performance of UiO-66 is improved, although the introduction of MgCl$_{2}$ reduces its specific surface area and pore volume. The water adsorption capacity at $P/P_0=0.3$ and the saturated water adsorption capacity of the UiO-66 (with MgCl$_{2}$ content of 0.57 wt%) modified by the solvothermal method are 0.27 g/g and 0.57 g/g at 298 K, respectively, which are 68.8% and 32.6% higher than the counterparts of pure UiO-66, respectively. Comparing with pure UiO-66, the water adsorption capacity of the UiO-66 (with MgCl$_{2}$ content of 1.02 wt%) modified by the impregnation method is increased by 56.3% and 14.0% at the same pressure, respectively. During 20 water adsorption/desorption cycles, the above two materials show high heat storage densities ($\sim1293 $ J/g and 1378 J/g). Therein, the UiO-66 modified by the solvothermal method exhibits the excellent cyclic stability. These results suggest that the introduction of an appropriate amount of MgCl$_{2}$ makes UiO-66 more suitable for AHT applications.     

伴随水力空化现象的对流换热数值研究

以水为介质,建立了液体流动的混合物多相流模型及空化模型,运用CFD方法对水平圆管内伴随有水力空化现象的受迫对流换热过程进行了数值研究,详细分析了管道入口压力、入口温度和限流孔与管道直径比等因素对水力空化及对流换热过程的影响规律。数值模拟结果表明,空化现象出现在圆管喉部(限流孔)壁面附近区域;与相同流量下无空化时的传热相比,在发生空化现象的区域,传热壁面被蒸汽所覆盖导致传热急剧恶化,而在远离空化发生区域的下游位置,由于空化的扰流作用使得加热壁面与流体之间的传热得到明显改善。     

NO在氧预吸附Ir(100)表面吸附和解离的第一性原理研究

采用第一性原理密度泛函理论和周期性平板模型研究了NO在O预吸附Ir(100)表面的吸附和解离, 并考察了预吸附的O对可能产物N₂, N₂O和NO₂的选择性的影响. 优化得到反应过程中初态、 过渡态和末态的吸附构型, 并获得反应的势能面信息. 计算结果表明, NO在O预吸附表面最稳定的吸附位是桥位, 其次是顶位. 桥位和顶位的NO在表面存在两条解离通道, 即直接解离通道和由桥位和顶位扩散到平行空位, 继而发生N-O键断裂生成N原子和O原子的解离通道. 此分离机理与洁净表面上NO解离机理相同, 但后一种解离方式优于前一种, 是NO在表面上解离的主要通道. 预吸附的O原子在不同程度上抑制了NO的解离, 导致桥位和顶位NO解离互相竞争. 在O预吸附Ir(100)表面, N₂气是唯一的产物, 不会有副产物N₂O和NO₂的生成, 与实验结果一致. 预吸附的O在N/O低覆盖度下几乎不影响N₂气的生成, 但在较高覆盖度下则促进了N₂气的生成.     

Numerical Simulation of Vapor Bubble Growth and Heat Transfer in a Thin Liquid Film

A mathematical model is developed to investigate the dynamics of vapor bubble growth in a thin fiquid film, movement of the interface between two fluids and the surface heat transfer characteristics. The model takes into account the effects of phase change between the vapor and liquid, gravity, surface tension and viscosity. The details of the multiphase flow and heat transfer are discussed for two cases： （1） when a water micro-droplet impacts a thin liquid film with a vapor bubble growing and （2） when the vapor bubble grows and merges with the vapor layer above the liquid film without the droplet impacting. The development trend of the interface between the vapor and liquid is coincident qualitatively with the available literature, mostly at the first stage. We also provide an important method to better understand the mechanism of nucleate spray cooling.     

平板式阳极支撑SOFC多场耦合数值模拟

建立了平板式固体氧化物燃料电池多场耦合数学模型,利用商业CFD软件FLUENT对包括阳极和阴极多孔介质、致密固体氧化物电解质、燃料流道、氧化剂流道、电流收集双极板、外壳的单电池三维整体计算区域进行了数值模拟,得到了流场、温度场、组分浓度场、电流密度场、Nernst电动势、活化过电势和欧姆过电势等重要物理量的详细分布,并分析了影响电池性能的主要因素。模拟结果与SOFC研制单位提供的实验数据基本符合。     

颗粒床过滤器除尘特性数值模拟研究

运用CFD和DEM方法,建立三维随机填充固定床颗粒层除尘过滤模型,颗粒之间的接触采用"搭桥法"进行处理。数值计算得到的压降结果与实验值、关联式吻合较好,压降与床层厚度近似呈线性关系。在此基础上,数值研究了除尘效率与颗粒床床层厚度、气体流速、粉尘粒径、气流温度及流动方向的关系。粉尘粒径大于5μm时,增加床层厚度,增大气体流速,均可以有效地增加除尘效率。而粉尘粒径大于5μm时,在圆筒壁面恒热流密度冷却的条件下,气流温度越高,除尘效率越低。流动方向与重力方向相同时,可提高除尘效率。并拟合了分级除尘效率与St数的关系式,当St0.009时,分级除尘效率为一定值,当St≥0.009时,分级除尘效率随着lg(St)的增加呈线性增加的趋势。     

复合敏化乳化炸药的压力减敏

为了解敏化剂对乳化炸药压力减敏的影响,研究了化学发泡+空心玻璃微球和空心玻璃微球+膨胀珍珠岩2种复合方式分别敏化的乳化炸药压力减敏。依据乳化炸药爆炸冲击波的波峰值,计算了它在水下受到冲击波作用之后的压力减敏度,将复合敏化的乳化炸药与分别用单一敏化剂的乳化炸药压力减敏度作了比较和分析。结果表明,第1种复合方式敏化的乳化炸药压力减敏度介于单一敏化的乳化炸药之间,以10cm受压距离为例,压力减敏度分别为1.000、0.983、0.210;第2种复合敏化的乳化炸药压力减敏度小于单一敏化的乳化炸药,10cm受压距离的压力减敏度分别为0、0.274、0.618。分析认为,敏化剂颗粒或气泡的破损与其微界面周围局部破乳的综合作用是造成乳化炸药压力减敏的主要原因。     

Fourier and Wavelet Transform Analysis of Pressure Signals during Explosive Boiling

The transient pressure in a liquid-pool during explosive boiling of acetone is measured by a micro-pressure-measuring system. The Fast Fourier transform and continuous wavelet transform methods are applied to investigate the frequency characteristics. The results show that the dominant frequency of the explosive boiling is 0-2 MHz, and the bubble cluster formed by numerous tiny bubbles departs twice. Analysis and discussions are also conducted to explain the bubble evolution during the explosive boiling.