Enhancement of solid dissolution process under the influence of rotating magnetic field

The main objective of this work is to study the effect of rotating magnetic field (RMF) on the dissolution process of NaCl-cylindrical sample. The experimental investigations are provided for the explanation of the influence on the dissolution process of a solid body to surrounding its dilute solution in the experimental set-up with the RMF generator. The analysis indicated the strong influence of the localization NaCl-cylindrical sample on the enhancement of mass transfer process. The mass transfer process under the action of RMF is described by means of the dimensionless equation with the local magnetic Taylor number.     

A Mathematical Model for Vacuum Far-Infrared Drying of Potato Slices

A mathematical model of mass and heat transfer for vacuum far-infrared drying of potato slices is introduced in this study on the basis of energy and diffusion equations. The finite difference method is used to mathematically simulate the sample temperature and moisture content in different drying conditions. Calculated results are compared with the experimental findings at varying conditions of heater temperature (120°C, 140°C, and 160°C), chamber pressure (1500, 8000, and 15000 Pa), sample thickness (0.004, 0.006, and 0.008 m), and radiation distance (0.08, 0.12, and 0.16 m). Comparison results show that the model fits well the changes in sample temperature and moisture content at different times of drying, with the values of the coefficient of determination close to 1.0 and the relative error values less than 10%.     

多物理场耦合模拟微波蒸馏反应器：升温和沸腾过程

使用COMSOL Multiphysics软件建立了耦合电磁场、流体流动、传热以及物质传输的多物理场模型用于模拟蒸馏型反应器的微波能量利用过程,探究了蒸馏反应器中水负载在微波能辐射作用下从升温至沸腾过程,阐明了在升温阶段,样品温度呈上下层分布,上层温度较高,最大温差达20 K,自然对流的产生改善了温度分布的不均匀性;在沸腾阶段,由于下层温度较低,沸腾现象有延迟,气泡的产生消除了部分过热,其中表面蒸发量更大,最大时约为内部蒸发量的3倍,与此同时湍流现象明显改善了温度均匀性。探究了馈入功率对全沸腾状态的影响,揭示了全沸腾状态的最终温度取决于馈入功率和蒸发损耗功率的相对大小。研究结果可为微波辅助分离、反应等化工过程及装备设计提供理论基础与借鉴。     

水平表面结霜过程的实验研究

对水平表面在低温高湿条件下结霜过程进行实验研究, 分析了冷面温度、湿空气温度和表面特性等因素对水珠冻结和霜层生长的影响。结果表明:冷面温度越低, 过冷水珠冻结时间越短、冻结直径越小;在湿空气温度与冷面温度温差相等的条件下, 湿空气温度越低, 过冷水珠冻结时间越短、冻结直径越小;疏水表面上过冷水珠的冻结时间比裸铝表面晚。冷面温度越低, 湿空气流速越快, 则霜层生长越快。     

冻干技术的几个热点问题

从近两年参评国家自然科学基金的情况,平时为杂志评审文章的情况来看,当前主要有三个热点问题:一是生物材料冷冻干燥过程的传热传质,这是近几年来常胜不衰的老问题;二是冻干过程出现的理论问题,例如塌陷温度、玻璃态转化温度等;三是冻干技术与其它干燥方法的结合问题。本文将对这几个问题扩展开讨论,并分析创新点的选取与产生问题。     

热再生电池氨再生过程强化

利用低温热能的热再生过程是热再生电池（thermally regenerative battery，TRB）系统的重要组成之一，针对TRB的产电和热再生过程，研究了使用再生电解液的TRB产电性能以及温度和强化传热传质措施对热再生过程的影响。研究结果表明，产电过程中，使用再生电解液的TRB最大功率为5.7 mW，比初始电解液的TRB（最大功率为6.5 mW）低14%；热再生过程中，提高温度可以明显强化热再生过程，采用玻璃球床和搅拌措施也可以有效提高热再生过程的性能。     

Enhanced ammonia regeneration of thermal regenerated batteries

Regeneration using low-grade thermal energy is one of the most important components of the thermal regenerative battery (TRB) system. In this study, the effects of the regenerative electrolyte on the performance of TRB and the effects of temperature and mass transfer on the thermal regeneration are studied. The experimental results showed that the maximum power of TRB using regenerated electrolyte was 5.7 mW, which was 14% lower than that of TRB using initial electrolyte (6.5 mW). In the process of thermal regeneration, the increasing of temperature can obviously strengthen the process of thermal regeneration, and the performance of thermal regeneration can also be effectively improved by using glass balls bed and stirring.     

Experimental study of frosting on different wettability surfaces under magnetic field

The frosting laws of three kinds of wettable surfaces under different magnetic field strengths were studied under cold surface temperature T_w=-10℃ and -30℃, environmental relative humidity RH=60% and 80%. Through visual observation method,image binarization is processed and calculated,the effect of frost morphology,water droplets diameter,water droplets crystallization time,water droplets coverage,frost crystal coverage,frost layer thickness and frost density under the different magnetic field intensity and surface contact angle are well explained. The results showed that adding magnetic field in combination with hydrophobic surface,the diameter of water droplets decreases by about 40%, and the crystallization time is prolonged by more than 500 s,the distribution of condensate droplets is more sparse. Frost thickness and frost density decrease as the increase of magnetic field strength and surface contact angle,providing possibility of restrain the frosting effectively. As the temperature of the cold surface decreases and the relative humidity increases, the influence of the surface properties and the external magnetic field on the frosting process decreases.     

磁场作用下不同润湿性表面结霜实验研究

研究了在冷面温度Tw=-10℃和-30℃,环境相对湿度RH=60%和80%,3种润湿性表面在不同磁场强度下的结霜规律。通过可视化观测和图像二值化处理计算,分析了磁场强度和表面接触角对霜晶形态、水珠粒径、结晶时间、液滴和霜晶覆盖率、霜层厚度和密度的影响。结果表明:磁场作用下,疏水性表面水珠粒径减小40%左右,结晶时间延长500 s以上,凝结水珠分布更加稀疏;结霜厚度和密度随着磁场强度和接触角的增大而减小;随着冷面温度的降低和相对湿度的增大,表面特性和外加磁场对结霜过程的影响降低。     

a rview of: UNIFIED ANALYSIS AND SOLUTIONS OF HEAT AND MASS DIFFUSION

ABSTRACT

The objective of this study is the formulation of a finite element model that could be used to analyze the stress crack formation in a viscoelastic sphere resulting from temperature and moisture gradients during the drying process. Numerical solutions to the simultaneous moisture and heat diffusion equations describing moisture removal and heat intake process for the sphere are obtained. The distribution and gradients of temperature and moisture developed inside the sphere during drying are established. The calculated temperature and moisture gradients are used in a finite element analysis of the thermo-hydro viscoelastic boundary value problem to simulate the stresses in the body.

The model is used to solve a sample problem of drying a soybean kernel. The simulated drying curve for the soybean model is obtained and compared favorably with the experimental results reported in the literature. Tangential stress, as a criteria for failure, is shown to change from compressive to tensile stress as it approaches the surface. It reaches its peak value at the surface in one hour and then decays slowly. The effect of different drying conditions is studied and the results are discussed.     

具有预制孔隙的维生素C水溶液微波冷冻干燥

设计和组装了一套实验室规模的多功能微波冷冻干燥装置，探究了具有初始孔隙的非饱和物料微波冷冻干燥过程。以维生素C为溶质，采用“软冰”冷冻技术制备了初始饱和与非饱和的冷冻样品。结果表明，软冰冷冻制备的样品能够避免崩塌。在35℃和20 Pa条件下，初始非饱和物料的干燥时间比饱和物料缩短了30.4%。SEM表征显示，非饱和物料具有疏松的球状孔隙结构、连通性好，有利于水蒸气的迁移。采用吸波材料碳化硅辅助的微波加热能够进一步强化冷冻干燥过程。在相同条件下，非饱和物料的微波冷冻干燥(5 W功率)时间比常规冷冻干燥(0 W功率)缩短了28.1%，比饱和物料的常规冷冻干燥缩短了50.0%。吸波材料辅助的初始非饱和物料微波冷冻干燥实现了传热传质的同时强化。     

Transformation of the reabsorption characteristics of lignite treated by low and high temperature drying process

Abstract

The reabsorption characteristics of the lignite treated by low and high temperature drying process were addressed in the paper. The information about the moisture form, functional groups, effective water-filled porosities and equilibrium moisture content of the lignite before and after the drying process was investigated using Differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and a self-made reabsorption device, respectively. The results show that the low drying temperature (140, 190, 230?°C, 10?min, N₂) has little impact on the effective water-filled porosities of the resulted samples, whereas it has a great influence on the main oxygen-containing functional groups, which amount firstly decreases and then increases with the drying temperature increasing. In the case of the lignite samples dried under high-temperature (600, 700, 800?°C, 30?s, N₂), the amount of the effective water-filled porosity of the sample decreases and the amount of oxygen-containing functional groups increases as the temperature increasing. The reabsorption capability of the high temperature dried sample is much lower than that of the sample treated under low drying temperature. The reabsorption characteristics of the low-temperature dried samples are affected by the amount of the oxygen-containing functional groups, while the effective water-filled porosity is main factor for the lignite samples derived from high temperature drying process. Moreover, the work gives a good evidence that the high-temperature drying process is an effective choose for lignite upgrading.     

FINITE ELEMENT SIMULATION OF THE THERMO-HYDRO STRESSES IN A VISCOELASTIC SPHERE DURING DRYING

The objective of this study is the formulation of a finite element model that could be used to analyze the stress crack formation in a viscoelastic sphere resulting from temperature and moisture gradients during the drying process. Numerical solutions to the simultaneous moisture and heat diffusion equations describing moisture removal and heat intake process for the sphere are obtained. The distribution and gradients of temperature and moisture developed inside the sphere during drying are established. The calculated temperature and moisture gradients are used in a finite element analysis of the thermo-hydro viscoelastic boundary value problem to simulate the stresses in the body.

The model is used to solve a sample problem of drying a soybean kernel. The simulated drying curve for the soybean model is obtained and compared favorably with the experimental results reported in the literature. Tangential stress, as a criteria for failure, is shown to change from compressive to tensile stress as it approaches the surface. It reaches its peak value at the surface in one hour and then decays slowly. The effect of different drying conditions is studied and the results are discussed.     

Investigation into recovery of iron values from red mud dumps

The waste generated during the alumina production by Bayer’s process is popularly called red mud. This red mud is a rich source of iron values. Generally, the iron content in the red mud varies between 20% and 45% depending on the bauxite source. The present investigation was carried out to recover iron values from red mud. Red mud contains ultrafine particles and is highly alkaline in nature because of which it is difficult to recover the iron values from it using conventional beneficiation techniques. In the present investigation, the iron values were successfully recovered by reduction roasting followed by magnetic separation. During the process, the hematitic and goethitic iron-phase minerals present in the red mud sample are converted into magnetite and metallic irons, which are subsequently recovered using low-intensity magnetic separator. The results showed that an iron recovery of 61.85% with an iron content of 65.93% of iron concentrate could be obtained at roasting temperature of 1150°C, roasting time of 60 min, and magnetic field intensity of 0.18 Tesla.     

EFFECTS OF HALL CURRENT AND CHEMICAL REACTION ON OSCILLATORY MIXED CONVECTION-RADIATION OF A MICROPOLAR FLUID IN A ROTATING SYSTEM

This article is concerned with the analysis of the effects of thermal radiation on oscillatory mixed convection flow of a micropolar fluid in a rotating frame of reference in the presence of transverse magnetic field and Hall current. The influence of a first-order homogeneous chemical reaction and heat source effects is also analyzed. The governing partial differential equations with the appropriate boundary conditions are reduced to a set of ordinary differential equations using similarity transformations. The dimensionless governing equations for this investigation are solved analytically after using small perturbation approximation. The effects of various parameters on the velocity, temperature, and concentration fields as well as on skin-friction coefficient, Nusselt number, and Sherwood number with their amplitude and phase are discussed in detail. Numerical results are discussed with the help of graphs and tables. Present results are also compared with previously published work.     

Mechanism of seeded infiltration growth process analysed by magnetic susceptibility measurements and in situ observation

Using the magnetic susceptibility measurements (MSM) at high temperature and in situ video observation, the mechanism of seeded infiltration growth (SIG) process was investigated. This process offers the opportunity to verify the main phase transition by measuring the magnetic force acting on the sample. The heat treatment process which adjusted from MSM and video observation, allows to obtain the single domain YBCO superconductor.     

Predicting the Thermal Behaviour of Wood During Linear Welding Using the Finite Element Method

A numerical model to simulate the temperature behaviour of wood welding samples during the welding process was developed to understand the influence of material parameters on the welding temperature. A finite element method and the CAST3M software were used to simulate and model the temperature changes during welding of beech wood. This model takes into account the different properties of the wood welded bondline, the geometry of the sample and the external conditions. The energy produced by the friction welding of the wood samples was determined from infrared thermography measurements for the welding process and inputted into the model. The comparison between the predicted and experimental results shows that the model is reliable. The applied pressure, the vibration, the extrusion of material and the chemical reactions, particularly exothermic reactions, are not taken into account in this model and thus probably explain the differences existing between actual and simulated values. However, this numerical simulation gives information on the distribution of the temperature in the sample. The model predicted that the temperature difference between the centre and the side of the sample is not higher than 4°C. This means that the border effects are negligible. The model was tested for different welding times. According to the model a heat flow about 70 kW/m² is necessary at the welding line to ensure a satisfactory bonding for the chosen sample geometry. Welding of large wood pieces has also been simulated in this study.     

磁场调控磁性纳米流体流动和传热研究进展

磁性纳米流体在实现能量高效和可控传递领域极具发展潜力。本文综述了磁场作用下磁性纳米流体对流换热及沸腾换热的最新进展,主要包括强制对流换热、混合对流换热、自然对流换热、池沸腾换热及管内沸腾换热等方面的实验研究,分析了磁场类型、强度、梯度、频率、方向及磁铁位置等对磁性纳米流体流动和热传输特性的影响,指出可通过改变外加磁场来实现对磁性纳米流体流动和传热的控制,并探讨了磁性纳米流体流-磁耦合作用下的传热机理以及目前所面临的挑战。在此基础上,提出了未来磁场调控磁性纳米流体对流换热和沸腾换热的主要发展方向：制备稳定的磁性纳米流体,建立系统有效的流动和传热理论模型,并从微介观尺度诠释热-流-磁耦合协同换热机理。     

Influence of transverse rotating magnetic field on enhancement of solid dissolution process

The main objective of this work is to study the effect of transverse rotating magnetic field (TRMF) on the enhancement of solid dissolution process in the novel type reactor (TRMFR). The application of magnetically driven fluidization (MDF with homogeneous and heterogeneous systems) on mass transfer process is presented. A study of the effect of ferromagnetic particles content on solid–liquid mass transfer has been made. The experimental investigations are provided for the explanation of the influence on the dissolution process of a solid body to surrounding its dilute solution in a novel type reactor with the ferromagnetic particles suspended. The mass transfer coefficient is calculated from a kinetic equation and correlated in the relationship including standard and magnetic dimensionless numbers. The overall enhancements due to TRMF and MDF were compared. Unique correlating relations were obtained to generalize the experimental database. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

熔融结晶洗涤分离过程的传递行为

通过对熔融结晶洗涤分离的操作模式和提纯机理进行分析,按照滤饼洗涤原理建立了流体流动模型,得到晶层内的压力分布。同时对晶层进行质量和热量衡算,建立了传质和传热模型,求得了晶层内杂质浓度分布和温度分布表达式。分布表达式表明了压力、浓度、温度与之相关的参数的关系,这个结果对熔融结晶洗涤分离过程的参数确定和操作过程的进一步实验研究具有重要的应用价值。