基于Delphi的多效蒸发设计与操作模拟软件的开发

蒸发是重要的化工单元操作之一,目前,蒸发操作广泛应用于制盐、制碱、制糖、食品、医药、造纸、抗菌素、海水淡化、原子能等工业生产中,同时也正被应用于环境保护中废弃物的浓缩处理过程.本文综合各类多效蒸发流程的特点,将顺流型、逆流型流程各分为5小类典型流程.在此基础上建立了普通型和带冷凝水闪蒸、原料预热、末效出料闪蒸等能量回收设备的复杂型顺、逆流多效蒸发流程的设计与操作模拟计算数学模型,利用Delphi编程工具软件,开发了可在Windows操作平台上独立运行的可视化模拟计算软件,并利用此软件对各类典型顺、逆流多效蒸发流程进行了工艺计算,通过对计算结果的分析,指出了效数、蒸发器面积等因素对多效蒸发经济性指标的影响,得出了理论上较优秀的流程类型.     

粉煤灰传热的影响研究

近年来国内外竞相开展利用粉煤灰等制备保温材料的研发工作,以粉煤灰传热为研究对象,对粉煤灰内的流场、温度场、高温壁面平均努谢尔数Nu进行研究;采用整场求解法方法进行数值求解,对网格的独立性和计算过程进行了验证;得到了粉煤灰传热一些基本数据,分析了粉煤灰温度场和流场随瑞利数Ra的变化规律。研究结果表明:随着Ra增加,开始流线均匀分布为一个顺时针大窝,逐渐变化为流线集中分布在流场外侧,而在中央基本上保持静止状态;当Ra很小时,无量纲等值线近似于平行高低温壁面的垂直线,随着Ra数逐渐增大,对应的温度等值线近似呈高温至低温的线性变化趋势;Ra小于10~5时,高温壁面Nu基本为2.37～3.31的定值;高温壁面底部努谢尔数Nu数大,最大值为30.8,上部Nu数小,最小值为1.19。     

平板式固体氧化物燃料电池的建模与仿真研究

基于气流模型以及热模型利用流体力学计算软件Fluent,建立平板式固体氧化物燃料电池（SOFC）的计算流体力学（CFD）模型。模型中采用电化学反应控制方程、质量、动量和能量守恒方程描述电池内的传热传质等物理过程,并对电池内部的运行电压、温度以及各种极化分布情况,进行了数值模拟。研究给出了顺流平板型SOFC与逆流平板型SOFC情况下,运行电压、温度和极化的分布。结果显示逆流平板型SOFC可获得更好的性能,具有更大的电功率密度和燃料利用率。     

烧碱蒸发结晶中氯化钠传质多相流模拟研究

由于烧碱蒸发结晶中氯化钠的结晶是非常复杂的多相传热传质过程,能否使晶粒合理分布以过滤除去是氯碱工业提高产品质量的瓶颈。因此本文对四效逆流蒸发分布器中氯化钠结晶过程进行了研究,将多相流理论应用于氯化钠工业结晶过程,以微元衡算为基础,引入碰撞因子,建立了氯化钠湍流传质模型,并用工厂生产数据对模型进行了验证,结果与生产实际吻合较好。该模型不但可用来优化烧碱生产过程中氯化钠晶粒的分布,指导工业结晶生产,而且可直接预测晶体生长特性。     

非均匀内热源对多孔介质内复合对流传热传质的数值研究

采用数值方法分析了具有非均匀内热源的竖直套管中复合对流传热传质,考查内热源分布系数M和热质二浮力比N对速度、温度、浓度分布以及Nusselt数和Sherwood数的影响,讨论了Da数对复合对流传热传质的影响.结果表明:当N＞1时速度V为正,其值随N的增加而增大:当N＜-1.5时,V则先负后正.随着M增大,内外壁面处流线...     

用Visual Basic5.0语言开发多效蒸发系统优化设计软件

利用Visual Basic5.0语言开发多效蒸发系统优化设计应用软件。软件有两大功能模块,一是多媒体学习模块,利用模块可以学习不同流程的多效蒸发系统优化设计建模思路及模型求解算法;二是设计计算模块,利用该模块可以对不同的多效蒸发流程（并流或逆流）及设计情况（常规设计或优化设计）选择适宜的算法进行设计计算。软件采用了Access动态数据库和面向对象的编程技术,可在Windows9X操作平台下独立运行。软件界面友好、操作方使、运行可靠稳定。     

基于SiB2模型的土壤水分降尺度指标的适用性研究

土壤水分是地表过程的核心变量之一,强烈影响着陆表—植被—大气间的能量和水分交换。当前基于星载被动微波遥感的土壤水分产品的空间分辨率普遍较粗(25~40km),无法满足流域尺度水文气象、生态水文模拟及水资源管理等研究和应用的需求,而土壤水分降尺度是目前较为可行的解决方案之一。通过对不同降尺度指标的研究,分析确定每种降尺度指标的适用条件,为土壤水分的降尺度研究奠定基础。利用2013年5月1日~9月30日黑河中游人工绿洲试验区大满超级站的气象数据驱动SiB2模型,分别模拟了土壤水分、土壤表层温度、植被冠层温度以及地表蒸散发、土壤蒸发等变量,利用Penman-Monteith公式计算了地表潜在蒸散发;利用SiB2模拟结果与P-M公式计算结果估算获得常用的土壤水分降尺度指标:表观热惯量(ATI)、土壤蒸发(E)、土壤蒸发/实际蒸散发(E/ETa)、蒸发比(EF)、实际蒸发比(AEF)。通过对降尺度指标与土壤水分之间相关性分析可知,在植被的整个生长季,5种指标与土壤水分之间都具有较好的相关性。其中ATI、E、E/ETa以及EF这4种指标与土壤水分之间的相关性都随着土壤深度的增加而逐渐减弱;而AEF与植被根区土壤水分的相关性最好,更能反映根区土壤水分的动态变化。从可决系数来看,各降尺度指标与土壤水分的相关性排序如下:2cm:E/ETaEFEAEFATI;10cm:AEFEFE/ETaEATI;80cm:EFAEFE/ETaEATI。     

某型涡扇发动机进口空气流量测量参数敏感性分析

基于某型涡扇发动机飞行台试飞,以某型涡扇发动机进口空气流量的测量为研究对象;首先建立了发动机进口空气流量计算模型以及相应的误差计算模型,其次采用辨识方法确定了测量参数的敏感系数,最后针对测量参数的无量纲敏感系数随飞行高度和发动机状态的变化进行了分析;分析结果表明:发动机进口空气对测量截面半径最为敏感,其次为主流区总压、主流区总温和主流区总静压差,对附面层位移厚度敏感性较差,且在发动机设计状态附面层对空气流量的影响为3%。     

高热流微冷却器的换热性能研究

对以水为换热介质的微通道冷却器对模拟发热电子芯片进行冷却的换热性能进行了实验研究.通过测量流体的流量、进出口温度、发热片表面热流密度,获得了不同几何结构微通道冷却器在不同加热功率、不同Re数条件下的换热特性和冷却效果.结果表明,微通道冷却器可以有效地对表面热流密度高达5.34×105 W/m2的发热电子芯片进行冷却;微通道冷却器的换热性能随Re数的增大而提高,所提高的幅度随加热功率的增大而增大;微通道的几何结构对换热性能有显著影响,平均Nu数随微通道的宽深比增大而增大.     

一种接近最小热条件的精馏塔优化分析

建立了一种每块板上都允许存在中间换热器的接近最小热条件的复杂精馏塔模型,根据精馏过程的火用损最小,优化了回流比和塔内换热负荷。对于影响精馏过程用能的因素:理论板数、进料位置、进料热状况进行了分析,得出了,要设计一个节能的精馏塔如何选择合适的理论板数、进料位置及进料的热状况的方法。并比较分析了该塔和具有相同理论板数的传统简单塔的传质推动力,发现在这种塔的整个塔内的传质推动力比较平均,而整个精馏过程的火用损比简单塔的小。     

Single-phase laminar and turbulent heat transfer in smooth and rough microtubes

An experimental campaign was carried out studying laminar and turbulent heat transfer in uniformly heated smooth glass and rough stainless steel microtubes from 0.5 mm down to 0.12 mm. Heat transfer in turbulent regime proved to be coherent—within experimental accuracy—with the classic Gnielinski correlation for the Nusselt number. For the laminar case, an anomalous drop in Nusselt number for decreasing Reynolds number was observed in the smooth glass tubes. As the stainless steel tubes manifested relatively normal diabatic behaviour in this regime (apart from the evident influence of the thermal development region that increases heat transfer above the thermally fully developed value), the explanation of this unexpected diminution of the Nusselt number must be sought in the dispersion of heat, put in externally through the thin film deposited on the glass tube outer surface, to peripheral attachments to the test section. This distorts the measured energy balance of the experiment, especially as the convective force of the fluid diminishes, resulting in lower Nusselt numbers at lower Reynolds numbers.     

MHD flow of radiative micropolar nanofluid in a porous channel: optimal and numerical solutions

The flow of a radiative and electrically conducting micropolar nanofluid inside a porous channel is investigated. After implementing the similarity transformations, the partial differential equations representing the radiative flow are reduced to a system of ordinary differential equations. The subsequent equations are solved by making use of a well-known analytical method called homotopy analysis method (HAM). The expressions concerning the velocity, microrotation, temperature, and nanoparticle concentration profiles are obtained. The radiation tends to drop the temperature profile for the fluid. The formulation for local Nusselt and Sherwood numbers is also presented. Tabular and graphical results highlighting the effects of different physical parameters are presented. Rate of heat transfer at the lower wall is seen to be increasing with higher values of the radiation parameter while a drop in heat transfer rate at the upper wall is observed. Same problem has been solved by implementing the numerical procedure called the Runge–Kutta method. A comparison between the HAM, numerical and already existing results has also been made.

     

Soret and MHD effects on bioconvection wall jet flow of nanofluid containing gyrotactic microorganisms

Various applications of bioconvection phenomena in the field of medicine and biotechnology boost us to present the study of laminar wall jet flow in this specific direction. For the purpose, we have considered nanofluid containing gyrotactic microorganisms in the presence of normally applied magnetohydrodynamic forces along with Soret effects. Boundary layer approximation and similarity transformation are utilized to convert governing equations into ordinary differential equations. Influence of different emerging parameters on velocity, temperature and concentration profiles of solute, nanoparticle and motile microorganisms has been investigated. The role of physical quantities like Nusselt number, Sherwood number and density number of microorganisms is also highlighted. Increase in Nusselt number and density number of motile microorganism is observed for incremental values of bioconvection Peclet number. Soret number reflects increasing effect on Nusselt number and decreasing effect on Sherwood number because solute diffusion faces resistance due to higher values of Soret number and in return decreases rate of mass transfer. Also bioconvection Rayleigh number imposes decreasing effect on density number of the motile microorganisms.

     

Numerical analysis of natural convection in shed roofs with eave of buildings for cold climates

A numerical study has been carried out on partially heated triangular enclosures with eave. The eave and inclined wall has a cold temperature. The laminar, two-dimensional, steady governing equations of natural convection are solved in the streamfunction-vorticity form using a finite difference technique. Streamline, isotherm and Nusselt number are presented for different parameters such as aspect ratio AR=H/L from 0.25 to 1, ratio of eave length E=L/n where n changes from 3 to 7 and Rayleigh number from 10³ to 10⁶. It is observed that the heat transfer decreases with increasing aspect ratio for small Rayleigh number but increases for higher Rayleigh number. Heat transfer also increases with decreasing eave length.     

Thermophoresis and MHD mixed convection three-dimensional flow of viscoelastic fluid with Soret and Dufour effects

Heat and mass transfer effects in three-dimensional mixed convection flow of viscoelastic fluid over a stretching surface with convective boundary conditions are investigated. The fluid is electrically conducting in the presence of constant applied magnetic field. Conservation laws of energy and concentration are based upon the Soret and Dufour effects. First order chemical reaction effects are also taken into account. By using the similarity transformations, the governing boundary layer equations are reduced into the ordinary differential equations. The transformed boundary layer equations are computed for the series solutions. Dimensionless velocity, temperature, and concentration distributions are shown graphically for different values of involved parameters. Numerical values of local Nusselt and Sherwood numbers are computed and analyzed. It is found that the behaviors of viscoelastic, mixed convection, and concentration buoyancy parameters on the Nusselt and Sherwood numbers are similar. However, the Nusselt and Sherwood numbers have qualitative opposite effects for Biot number, thermophoretic parameter, and Soret-Dufour parameters.

     

Thin film evaporation effect on heat transport capability in a grooved heat pipe

A theoretical model predicting the heat transfer performance occurring in a grooved heat pipe is developed. The model includes the effects of groove geometry, thin film evaporation, contact angle, and film condensation. The numerical results show that the groove geometry significantly affects the thin film evaporation and condensation. The thin film evaporation plays a key role in the total effective thermal conductivity and determines a limit for the maximum amount of heat transport through the micro regions for a given evaporator geometry. While the contact angle can influence the capillary limitation, it significantly affects the thin film evaporation and the total effective thermal conductivity of a groove heat pipe. In order to verify the theoretical analysis, an experimental investigation on a grooved heat pipe was conducted. The current investigation will result in a better understanding of thin film evaporation and its effect on the maximum heat transport in a grooved heat pipe.     

Magnetohydrodynamic three-dimensional nonlinear convective flow of viscoelastic nanofluid with heat and mass flux conditions

The present research focuses on three-dimensional nonlinear convective flow of viscoelastic nanofluid. Here, the flow is generated due to stretching of a impermeable surface. The phenomenon of heat transport is analyzed by considering thermal radiation and prescribed heat flux condition. Nanofluid model comprises of Brownian motion and thermophoresis. An electrically conducting fluid is accounted due to consideration of an applied magnetic field. The dimensionless variables are introduced for the conversion of partial differential equations into sets of ordinary differential systems. The transformed expressions are explored through homotopic algorithm. Behavior of different dimensionless parameters on the non-dimensional velocities, temperature and concentration are scrutinized graphically. The values of skin friction coefficients, Nusselt and Sherwood numbers are also calculated and elaborated. It is visualized that the heat transfer rate increases with Prandtl number and radiation parameter is higher.

     

Double-diffusive convection with variable viscosity from a vertical truncated cone in porous media in the presence of magnetic field and radiation effects

This work is focused on the study of combined heat and mass transfer or double-diffusive convection near a vertical truncated cone embedded in a fluid-saturated porous medium in the presence of thermal radiation, magnetic field and variable viscosity effects. The viscosity of the fluid is assumed to be an inverse linear function of the fluid temperature. A boundary-layer analysis is employed to derive the non-dimensional governing equations. The governing equations for this investigation are transformed into a set of non-similar equations and solved numerically using the fourth-order Runge–Kutta integration scheme with the Newton–Raphson shooting technique. Comparisons with previously published work on special cases of the problem are performed and the results are found to be in excellent agreement. A parametric study illustrating the influence of the radiation parameter, magnetic field parameter, viscosity-variation parameter, buoyancy ratio and the Lewis number on the fluid velocity, temperature and solute concentration profiles as well as the Nusselt number and Sherwood number is conducted. The results of this parametric study are shown graphically and the physical aspects of the problem are highlighted and discussed.     

Thin film evaporation in microchannels with interfacial slip

We investigate the role of interfacial slip on evaporation of a thin liquid film in a microfluidic channel. The effective slip mechanism is attributed to the formation of a depleted layer adhering to the substrate–fluid interface, either in a continuum or in a rarefied gas regime, as a consequence of intricate hydrophobic interactions in the narrow confinement. We appeal to the fundamental principles of conservation in relating the evaporation mechanisms with fluid flow and heat transfer over interfacial scales. We obtain semi-analytical solutions of the pertinent governing equations, with coupled heat and mass transfer boundary conditions at the liquid–vapor interface. We observe that a general consequence of interfacial slip is to elongate the liquid film, thereby leading to a film thickening effect. Thicker liquid films, in turn, result in lower heat transfer rates from the wall to liquid film, and consequently lower mass transfer rates from the liquid film to the vapor phase. Nevertheless, the total mass of evaporation (or equivalently, the net heat transfer) turns out to be higher in case of interfacial slip due to the longer film length. We also develop significant physical insights on the implications of the relative thickness of the depleted layer with reference to characteristic length scales of the microfluidic channel on the evaporation process, under combined influences of the capillary pressure, disjoining pressure, and the driving temperature differential for the interfacial transport.     

A numerical investigation of Benard convection using finite elements

The results of numerical calculations based on the finite element for the two dimensional Benard convection are presented. The fluid is confined between two horizonal solid walls and is subjected to a vertical temperature gradient. Aspect ratios of 10.0 and 10.5 are used. The effect of the hydrodynamic boundary conditions on the vertical walls on the number and the size of cells is demonstrated. Values of average Nusselt number are presented for various Rayleigh numbers ranging from 1710 to 10,000. The conduction mode of heat transfer is replaced by the convection mode at a Rayleigh number of 1710, with the latter mode becoming more prominent at higher Rayleigh numbers. The calculation of the length of each cell and the heat flux compare very well with the values reported in the literature.