Heat/mass transfer from a neutrally buoyant sphere by mixed natural and forced convection in a simple shear flow

Building on the work of Yang et al. in 2011, the finite difference method and the Boussinesq approximation were applied to solve the time‐dependent Navier‐Stokes, convection diffusion and continuity equations in spherical coordinates. An idealized condition, the mass transfer from a neutrally buoyant sphere in a horizontal simple shear flow with natural convection was numerically simulated for the first time in this work. In the hybrid transfer case, the outwardly spiraling streamlines enhanced the transfer process, but the counter‐gravity spiraling streamlines near the sphere hindered the natural convection and the spatial dilution action weakened the natural convection transfer process. These competing effects led to nonmonotonic behavior of the Nusselt number with Reynolds number. Results from these previously undocumented cases were summarized into correlations for predicting Nusselt numbers at finite Reynolds numbers for various Grashof and Prandtl numbers. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2816–2827, 2018     

空气横掠沉没于多孔泡沫金属中错列管束的对流传热

对空气横掠沉没于多孔泡沫金属中正三角错列传热管束的对流传热进行了试验研究。结果显示,多孔泡沫金属使得流体的流动阻力明显增加,但阻力增加的倍数随Reynolds数的增大而减小;多孔泡沫金属对对流传热具有明显的强化作用,强化效果随Re的增大而减小。与横掠错列光管束相比,本试验范围内,流动阻力增加的最大倍数为12.727,最小倍数为10.109;对流传热的最大强化倍数为2.78,最小强化倍数为2.08。总结出了适合于试验范围的对流传热的气流量纲1阻力系数的表达式和传热计算关联式。综合强化对流传热及增加流动压降两方面可知,多孔泡沫金属较适合于流体较小流速的场合。     

CO2化学吸收法中再生气的陶瓷膜余热回收特性

在CO₂化学吸收法工艺中,采用富液分流工艺,利用在贫富液换热器前分流的冷富CO₂吸收剂溶液回收再生塔顶排出的热再生气（一般为CO₂和水蒸气混合气）的余热,有助于降低CO₂再生热耗。本文在乙醇胺（MEA）基富液分流化学吸收工艺中,以纳米级多孔亲水陶瓷膜作为分流冷富液和热再生气之间的换热介质,利用水的热质耦合传递强化余热的回收性能。以余热回收通量为指标,探讨了分流的MEA富液流量、温度、质量分数、CO₂负荷和热再生气流量及再生气中水蒸气摩尔分数对陶瓷膜热回收性能的影响,并对比了不同分离层孔径陶瓷膜的余热回收性能。结果显示,陶瓷膜的余热回收性能随MEA富液流量的增加而增加,但却随富液温度的升高而大幅下降。同时,随着气体流量和再生气中水蒸气摩尔分数的增大,热回收通量均会增大。由水传质所引发的对流换热对热回收通量具有促进作用,可占总热回收量的10%左右。由于CMHE-10陶瓷膜的分离层孔径与孔隙率均大于CMHE-4陶瓷膜,因而其水传质通量大于CMHE-4陶瓷膜。但CMHE-10陶瓷膜的有效热导率却低于CMHE-4陶瓷膜,因而热回收过程中其水蒸气的冷凝总量要小,导致其热回收性能低于CMHE-4陶瓷膜。     

真空条件下浓度对LiCl溶液沸腾特性的影响

沸腾换热是一种高效的换热方式,为研究除湿溶液再生的沸腾换热过程,搭建真空再生沸腾特性测试实验台,对水和质量分数分别为30%、32%、34%的LiCl溶液进行实验研究,得到溶液浓度对溶液沸腾热流密度及沸腾表面传热系数的影响。结果表明,浓度升高,表面张力增大,汽化核心数减少;黏度增大,气泡脱离困难,使扰动量减少,溶液的热流密度降低;随着浓度的增大,表面张力增大,气泡生成及脱离阻力增大,对LiCl溶液的扰动程度降低,使溶液的沸腾传热系数减小。温差增大使壁面过热度增大,气泡生成增多,加强对溶液的扰动,使溶液的热流密度及沸腾传热系数增大。     

Al-Li合金定向凝固的热溶质对流

研究了亚共晶二元Ａｌ－Ｌｉ合金垂直向上定向凝固期间热溶质对流共晶生长的影响,结果表明,晶体生长初期,对流对共晶生长影响较小,能够获得规则的共晶组织,当存在非稳定性对流时,在生长方向上,β相（ＡｌＬｉ）呈非连续的短棒结构;在水平方向上,β相呈波形排列,并且还发现,非稳定性对流中存在着最不稳定波,且这种波对共晶生长上的影响最强烈,它使共晶组织粗大,并且迎着流体流动方向生长。     

铝基复合材料凝固过程的研究进展

综述铝基复合材料凝固过程的研究成果和存在的问题。介绍铝基复合材料的凝固时增强体与基体合金之间的相互作用模型，基体合金的凝固过程以及对流对组织的影响。凝固时，材料的热物理性能、液态合金的粘度与及界面自由能的变化影响了颗粒增强体的行为。同时，增强体和液态合金对流改变了材料的连续性和微观结构。     

锅炉对流管爆裂原因分析

采用化学分析、金相检验及力学性能测定等方法，对锅炉对流管爆裂原因进行了分析。结果表明，长期超温运行而引起的蠕变是导致爆裂的主要原因。     

STUDIES OF MIXING IN A CONCENTRIC TUBE AIR-LIFT REACTOR CONTAINING XANTHAN GUM BY MEANS OF AN IMPROVED FLOW FOLLOWER

The influence of a pseudoplastic non-Newtonian fluid upon the hydrodynamic performance and mixing parameters of a concentric tube air-lift fermenter has been studied using a range of dilute xanthan gum solutions (0-0.5% weight by volume). Liquid circulation times vary in a complex pattern with increasing gum concentration. At low concentrations, circulation was more; rapid due to drag reduction whilst at the highest concentrations circulation times were increased. The column voidage decreased with increasing gum concentration and bubbly flow in the riser was replaced by slug flow. For all gum concentrations the effective dispersion coefficient for a single passage around the loop was increased relative to tap water. An improved radio-pill flow follower system for hydrodynamic studies is described.     

高速电主轴单元的热态特性分析

由于电主轴系统高速运转时,产生大量的热,并导致热变形,本文基于ANSYS对高速电主轴单元的热态特性进行分析。文中采用有限元法对高速电主轴系统模型进行建模,并计算了电主轴系统的发热量及各部位热对流,通过ANSYS进行分析,得到了高速电主轴单元的温度分布、主轴端部的轴向和径向偏移量及位移图。从热态性能中可以分析得出热感应预载荷,并计算得出相应的强度和临界速度。同时研究发现,为了获得更多的预载荷,应该考虑热感应预载荷的影响。     

A stencil of the finite-difference method for the 2D convection diffusion equation and its new iterative scheme

The paper gives the numerical stencil for the two-dimensional convection diffusion equation and the technique of elimination, and builds up the new iterative scheme to solve the implicit difference equation. The scheme's convergence and its higher rate of convergence than the Jacobi iteration are proved. And the numerical example indicates that the new scheme has the same parallelism and a higher rate of convergence than the Jacobi iteration.