多孔介质中超临界流体可调特性的模拟与分析——温度梯度的作用

多孔介质中超临界流体的可调性与流体流动与传热耦合过程密切相关.今针对各向同性二维正方形区域建立了多孔介质中超临界流体的流动与传热耦合传递过程数学模型.以超临界CO2为模型流体,采用COMSOL Multiphysics软件对模型方程进行数值求解.分析和讨论了多孔介质中温度梯度对超临界流体的流动特性和传递性质的影响特性.研究表明:温度梯度显著地影响计算区域中流体的速度分布,近加热壁区的流体出现了速度的加速层.流体的动力黏度和导热系数等性质的分布特性也受计算区域中温度梯度的作用而存在极小值,导致局部流动性能的提高和传热性能的下降.对于多孔介质中超临界流体的可调性,可通过边界上的温度梯度加以调节和控制.     

冷热原油交替输送研究现状与展望

冷热油交替输送是符合我国国情的一种输送工艺,具有很大的研究价值。我国的研究起步相对较晚,经过几十年的努力,取得了很好的成果。介绍了冷热油交替输送中管道土壤传热、管内非稳态传热流动研究的常用几种方法以及耦合计算的数学模型、求解步骤和原理,分析了近年来国内冷热油输送技术的成果。最后,结合国内的研究进展,对今后的研究做了展望。     

循环系统气固下行流动中气体流速测试方法探讨

本文通过分析循环流化床气固下行流动中气体的流动特点,评述了前人提出的有关循环系统中气体下行流速测量方法,提出气体示踪双检测系统的实验方法,并通过实验证实了该方法对循环系统中气体下行流动气速测定的可行性、稳定性和结果可靠性。     

管壳式换热器传热温差的优化及影响分析

针对典型的简单换热网络,分析得到了冷热流体的传热温差与总费用的关系式,得出最优传热温差的计算方法及过程,并分析了影响最优传热温差大小的各主要因素。所得的最优传热温差值可通过夹点分析技术在复杂换热网络的优化设计中得以应用。     

螺旋板式换热器气-液换热时流阻及传热计算

提出了螺旋板式换热器用于气-液热交换时的流动阻力以及传热设计的计算方法。螺旋板的设计采用不等间距、气体轴向流动、液体螺旋流动。文中描述了随介质参数的改变,换热器结构的相应变化。结构设计通过迭代计算而达优化目的,设计计算具有通用性。结果表明,与其它形式换热器相比,其传热系数高,流动阻力小。     

高初始含湿多孔介质喷雾干燥过程的热质耦合传递

多孔介质是大量干燥过程的主体,由于实际多孔介质干燥过程的复杂性,建立通用的干燥过程传热传质模型十分困难。通过分析喷雾干燥过程中高初始含湿多孔介质与干燥介质之间的传热传质机理以及各因素对传热传质的影响,根据马歇尔方程探讨了干燥介质与料雾之间的水蒸汽分压差在干燥过程中的变化情况,反映了多孔湿介质在喷雾干燥操作中的传热传质过程的几种特性,为确定实际生产中喷雾干燥器的操作条件指明了新的出路。     

螺旋板式换热器气－液换热时流阻及传热计算

提出了螺旋板式换热器用于气－液热交换时的流动阻力以及传热设计的计算方法。螺旋板的设计采用不等间距、气体轴向流动、液体螺旋流动。文中描述了随介质参数的改变，换热器结构的相应变化。结构设计通过迭代计算而达优化目的，设计计算具有通用性。结果表明，与其它形式换热器相比，其传热系数高，流动阻力小。     

格子Boltzmann方法模拟高Darcy数多孔介质内融化传热过程

采用Brinkmann-Forchheimer-Darcy方程描述多孔介质内流动过程,并通过选择合适的平衡态分布函数及非线性源项形式构建出表征融化相变温度场的分布函数演化方程。应用格子Boltzmann模型模拟了方腔内无多孔介质以及填充多孔介质自然对流融化传热过程,模拟结果与其他文献结果吻合较好,模型的正确性得到了一定的验证。模拟结果还表明液相的自然对流对融化传热过程有着重要的影响,并且在高Rayleigh 数或高Darcy 数情况下作用更强。在高Darcy 数情况下由于非Darcy效应的存在,增大Rayleigh 数以强化融化传热的效应要大于提高同样倍数Darcy 数的效应。     

孔隙分布对多孔介质内流动和传热的影响

采用Sierpinski地毯分形技术建立多孔介质内流动和传热模型,通过改变固体基质位置研究了孔隙分布结构对多孔介质内流动特性和热效率的影响,3种孔隙分布为每分形一次固体基质分布在中心位置(A)、分布在中上方(B)和分布在右上方(C),当流体稳定流过多孔介质时,不同的孔隙分布表现出不同流动和传热特性. 结果表明,孔隙分布是影响多孔介质传输特性和传热效率的重要因素,无量纲渗透率k*C>k*B>k*A,多孔介质孔隙率大于0.8时更明显;流体流过不同孔隙分布的多孔介质时,相同孔隙率时与流体接触的固体基质面积A>B>C,传热效果A最佳、C最差. 孔隙分布影响了无量纲局部熵产率,在3种孔隙分布下用Be表示的热传导引起的熵产率占主导.     

双套管双管板换热器流动及传热性能数值模拟

采用CFD软件方法,研究双套管双管板换热器传热及流动特性.对隔绝腔连同内外套管的环形间隙内分别充入空气、水、甲苯气体和氩气4种介质进行模拟.结果表明:不同介质对传热有不同影响,充入水时的换热效果最好,甲苯气体的最差;壳程介质在流体接管进、出口附近存在回流和绕流且速度较小,管程介质流动较为均匀,受壁面边界层影响,速度在管...     

氢气纯度分析方法准确性的探讨

ONACCURACYOFANALYSISOFOFHYDROGEN1前言我公司目前应用的氢气纯度分析方法有两种,一种是爆炸反应法,另一种是焦性没食子酸吸收法。几年来,人们对两种分析方法的准确性曾有过褒贬不一的评论。这里我们也谈谈自己粗浅的观点。2爆炸法测定氢气纯度一定量的氢气样品与适量的空气之均匀混合物因反应后生成液体水而引起气体体积减少,减少的体积等于参加反应气体体积之和。其中l／3为氧气,2／3为氢气。根据氢气取样量和反应前后混气体体积之差,以及氢气在反应中的体积比例关系,可计算出样品的氢气纯度。计算公式式中：A一混…     

COMPARISON OF METHODS OF ANALYSIS OF GYPSUM1

The different analytical methods proposed for the evaluation of gypsum have been subjected to an experimental test. A combination method, consisting of a fusion with KHCO₃ and determination of CaO by KMnO₄ titration, the SO₃ by Andrews method of titration of BaCrO₄ has been found to give very reliable results with the least consumption of time.     

SEDIMENTATION OF BINARY MIXTURES OF PARTICLES OF UNEQUAL DENSITIES AND OF DIFFERENT SIZES

A model is developed for the sedimentation from a suspension of two particle species of unequal densities and of different sizes. The composition and the thickness of various layers in the sediments are predicted using graphical and analytical methods. The model predictions were in excellent agreement with experimental results, when the particle size ratio was ≥ 108. When size ratio of the particles was 2.60 and 4.31 the agreement occurred in about 50 percent of the cases.     

HEASUREHENT OF INSTANTANEOUS RATES OF LOSS OF VOIATILE COMPOUNDS DURING DRYING OF DROPS

A novel technique serves to monitor instantaneous rates of loss of a volatile solute from a suspended drop during drying. A highly sensitive electron capture detector is used to monitor concentrations of SF6 released into a flowing gas stream from a suspended, drying drop. Simultaneously, the appearance and morphological development of the drop are monitored with a video camera. This provides the wherewithal of relating instantaneous rates of loss of the volatile solute to particular events during the development of particle morphology.

Initial experiments have been carried out with drops of aqueous solutions of glucose, sucrose, maltodextrin and coffee extract. The results clearly display the onset of the volatiles-retentive selective diffusion phenomenon. There is also substantial loss of the volatile component later in the drying process, when the drops undergo repeated ex ansion, bursting and cratering due to the formation of internaf bubbles. These experiments appear to be the first quantitative demonstration of major losses accompanying changes in drop morphology.     

茶多酚提取方法进展

本文综述了国内外现有茶多酚提取方法的现状以及近期的研究进展，并对其优缺点进行了评价。这将有助于中低档茶的综合利用和茶多酚的进一步开发应用。     

ANALYSIS OF RECENT MEASUREMENTS OF THE VISCOSITY OF GLASSES

Viscosity of Simple Soda-Silicate 500° to 1400°C Comparison of the results given by English with those of Washburn, Shelton and Libman, indicates a discrepancy in the absolute values of log₁₀ viscosity amounting to 0.6, those of Washburn et al., being relatively too high. If correction for this is made, the isothermal curves of log₁₀ viscosity as a function of soda content are smooth up to 50% Na₂O, showing no inflection. The observations as a function of temperature T are all represented within accidental error by an equation of the type where all three constants vary regularly with the composition. Change of Viscosity of Glass (6SiO₂, 2Na₂O) due to Molecular Substitution of CaO, MgO and Al₂O₃ for Na₂O The effect is clearly brought out by plotting (from the results of English) the change of log₁₀η due to the substitution as a function of temperature. The curves each show a sharp bend at a temperature between 840° and 1050°C, which is designated the aggregation temperature T_a. If we divide these curves by the corresponding percentage substituted, we get curves for each oxide which are straight and parallel below the aggregation temperatures, the slopes (increase of change of log₁₀η per 100°C) being −0.056 (CaO), −0.055 (MgO), −0.018 (A1₂O₃) per per cent oxide substituted. For substitution of 1/2 molecule the slopes are −0.325 (CaO), −0.23 (MgO) and −0.18 (Al₂O₃) per 100°. At the aggregation temperature the change of log₁₀η per per cent is a minimum, 0.03 to 0.06 for CaO, 0.12 for MgO, 0.07 for Al₂O₃. Evidence of Aggregation in Glasses, from viscosity Measurements The sharp bends in the plots of change of log₁₀η due to substitution of an oxide for Na₂O, suggest the beginning of molecular aggregation at these temperatures. These aggregation temperatures are close to the devitrification temperatures, but the effect on the viscosity curves cannot be due to actual devitrification since it does not change with time. Taking the aggregation temperatures as equal to devitrification temperatures, additional isotherms are roughly sketched into the equilibrium triangle of the system Na₂O-CaO-SiO₂. Change of Viscosity of Glass (4SiO₂, 2Na₂O) due to of Substitution of B₂O₃ for SiO₂ The change of log₁₀η (from the results of English) is plotted as a function of temperature, and also the change of log₁₀η per per cent B₂O₃. The curves are more complex than for the substitution for Na₂O.     

环氧树脂羟基值测定方法的研究

利用乙酸酐、吡啶和浓硫酸混合的乙酰化试剂测定环氧树脂中羟基值含量的方法具有操作简便、滴定终点明显和分析结果误差小等优点。     

骑式摩托车油箱喷涂工艺的改进

面对日益激烈的市场竞争,摩托车油箱外观质量越来越成为影响销售的因素之一。文章介绍了改进工艺后的油箱涂装,该涂装体系提高了油箱外观的丰满度,降低了油箱涂装的生产成本。     

几种针状焦性能对比

针状焦分石油系和煤系两大类,这主要取决于针状焦的原料来源。在同一系列中由于原料不同和工艺条件不同 ,针状焦的各自性能也不相同。针状焦是生产超高功率石墨电极和高功率石墨电极的主要原料 ,针状焦的性能对石墨电极的质量有至关重要的影响。所以对针状焦性能以及其对石墨电极质量影响的研究十分必要的。以下是常用的几种进口针状焦和国产针状焦的性能对比。１原料性能分析对比原料试样包括４种针状焦 ,其中两种为进口针状焦：三菱针状焦和新日化针状焦;另两种为国产针状焦：鞍山针状焦和锦州针状焦。其中除锦州针状焦是石油系针状焦外…     

聚酰亚胺的合成法

本文评述了缩聚型聚酰亚胺的主要合成方法和近年来国际上在合成中所做的探索。