闪蒸干燥器气相流场的模拟研究

针对目前旋流闪蒸干燥器的气相流场存在的一些问题,应用FLUENT6．0软件进行模拟,对平底、带叶片的旋流闪蒸干燥器的气相流场分布进行数值模拟和实验研究。并用实验数据对模拟结果进行了验证,取得了很好的一致性。同时,针对带气体分布器的闪蒸干燥器进行了模拟研究,分别对圆管形、圆锥形、方管形分布器进行模拟分析。结果表明,方管形干燥器能够使切向速度分布更加均匀,从而提高干燥能力。     

藕粉在旋流干燥器中的干燥动力学研究

实验研究了藕粉在旋流干燥器中不同操作参数下(进风温度50～80℃、气速1.5～3.5 m/s、进料速率0.001 7～0.002 7 kg/s)的干燥速率,建立了藕粉在旋流干燥器中的干燥动力学模型:U=a+bX+cX~2+dX~3,并进行了模型验证。结果表明该经验模型在一定因素水平范围内具有比较好的精度,研究结果对旋流干燥工艺参数的选择和旋流干燥器的设计有一定的参考价值。     

入口旋流对均一粒径液滴喷雾干燥塔影响的数值模拟

均一粒径液滴喷雾干燥塔(MDSD)在生产均匀尺寸颗粒产品中发挥着较大优势,进一步优化其干燥过程操作尤为重要。集成离散相(DPM)和反应工程法(REA)干燥方法,通过耦合分散室和主干燥室模型,本研究开发了完整的MDSD三维计算流体力学模型。并系统探究了在干燥过程中分散气旋流、热空气旋流以及二者共同旋流对颗粒运动和最终干燥效果的影响。模拟结果表明,在30°入射角下加入旋流效果最优。同时引入分散室和干燥室旋流后发现,同向旋流比反向旋流带来的干燥效果提升2%,更比无旋流操作下的干燥效果提升30%。欲达到同样的干燥效果,引入同向旋流,塔身可缩短近12%。     

旋流干燥器

介绍一种采用针轮转子、分级器和空气动力分离器的旋流干燥器。该干燥器通过低速针轮转子分散物料 ,又在分级器和空气动力分离器的辅助下通过高速针轮转子分离收集产品 ,使得干燥和产品充分收集能在同一干燥器的腔体内完成 ,显著简化了干燥系统 ,降低了系统阻力     

旋流干燥器内的流场和分散相颗粒受力分析

介绍了旋流干燥器的基本结构和工作原理,分析了旋流干燥器内的连续相流场的速度分布情况和分散相颗粒的受力情况。该研究结果对旋流干燥器传热机理的研究具有指导意义。     

入口旋流对均一粒径液滴喷雾干燥塔影响的数值模拟

均一粒径液滴喷雾干燥塔（MDSD）在生产均匀尺寸颗粒产品中发挥着较大优势,进一步优化其干燥过程操作尤为重要。集成离散相（DPM）和反应工程法（REA）干燥方法,通过耦合分散室和主干燥室模型,本研究开发了完整的MDSD三维计算流体力学模型。并系统探究了在干燥过程中分散气旋流、热空气旋流以及二者共同旋流对颗粒运动和最终干燥效果的影响。模拟结果表明,在30°入射角下加入旋流效果最优。同时引入分散室和干燥室旋流后发现,同向旋流比反向旋流带来的干燥效果提升2%,更比无旋流操作下的干燥效果提升30%。欲达到同样的干燥效果,引入同向旋流,塔身可缩短近12%。     

气-液旋流分离器流场数值模拟研究

为研究旋流分离器内部气体和液滴的运动情况和分离机理,用流体动力学软件Fluent对旋流分离器内部流场和液滴的运动状况进行了数值模拟研究,在模拟过程中,采用k-epsilon(2 eqn)方程来模拟气相旋流流动,采用Lagrange方法模拟液滴运动。模拟结果表明,旋流分离器内部流场呈旋转分布,分为内、外两个流场,在不同流动区域,气体压力场、速度场分布成规则变化;液滴的运动较为复杂,带有随机性;总体运动轨迹的形状与气相流场的分布趋于一致。     

计算流体动力学(CFD)在化工领域的应用

计算流体动力学(CFD)是一种以流体为研究对象的数值模拟技术。相对于实验流体动力学而言,它具有资金投入少、计算速度快、信息完备且不受模型尺寸限制等优点。因此是研究流体动力学有力的工具。本文主要综述了CFD技术在化工领域内的填料塔、旋流分离器、生化反应器、干燥器、流化床、换热器方面的应用。     

气固逆、并流多级旋流干燥器的流体力学行为研究

针对PVC等颗粒的干燥过程要求，设计并建立了多级旋流干燥系统．对其操作方式、流体力学特性进行了较为系统的研究．实验对气固逆流和气固并流两种操作方式分别进行了探讨．在多级旋流干燥器中成功地实现了气固逆流接触．并对旋流板结构、开孔率和操作气速对床层压降及床层平均密度的影响进行了研究，给出了气固逆流及并流操作时的操作性能曲线和操作窗口．     

气流干燥器的数学模型研究

在聚氯乙烯干燥过程中,目前通常采用的是气流-旋风两段式干燥,通过对固体干燥原理、干燥过程的分析,将干燥过程分为表面汽化干燥与升温干燥2个阶段,根据气流干燥器的特点,结合各个阶段传质、传热的特点,分段建立了传质速率、传热速率方程,物料衡算、热量衡算方程。通过对气流干燥器的分析研究,确定了计算机模拟过程中的各个参数,从而确立了气流干燥器的数学模型。     

循环流化床中C类颗粒连续干燥的研究

循环流化床(CFB)作为一种新兴反应器,其结构简单、气固接触效率高、处理量大,成为气固二相干燥应用研究的新方向.文中在自建的循环流化床(内径0.104 m×高2.35 m)内,以玉米淀粉(dp=8 μm,ρp=800 kg/m3)为C类颗粒,进行了连续干燥.实验初步研究了进料速率、进风温度及气速等操作参数对淀粉平均停留...     

对撞流干燥的实验与理论研究

The experiments of one-stage semi-circular and two-stage semi-circular impinging stream drying as well as the vertical and semi-cricular combined impinging stream drying were carried out.The velocity distribution and the mean residence time of particles,and the influence of various factors on drying characteristics were studied.A mathematical model of granular material drying in a semi-circular impinging stream dryer was proposed,in which the flow characteristics as well as the heat and mass transfer mechanisms were considered.Reasonable numerical methods were used to solve the equations.Under various conditons,the calculated results of drying rate and moisture content versus time were obtained.The results indicate that constant drying rate period does not exist in a semi-circular impinging stream dryer.Appropriate semi-cricular stage number and curvature radius,flow-rate ratio,air velocity,and higher inlet air temperature should be used for enhancing the drying process.     

Experimental Studies on a Newly Developed Mixed-Flow Dryer

Mixed-flow dryers are of great importance in worldwide agriculture for the drying of grain, corn, and rice. Unfavorable dryer designs can result in uneven particle and air flow distributions and, thereby, cause inhomogeneous gas–solids contact and drying conditions. As a consequence, the grain drying can locally be very uneven with high fluctuations of the moisture distribution over the dryer cross section. The main reasons are design and construction of the dryer apparatus and the discharge device. A new mixed-flow dryer design has been developed that promises more homogeneous drying, higher energy efficiency, and increased product quality. Firstly, the new dryer design was proved with respect to particle flow. For this purpose, a new test dryer was constructed. A series of particle flow experiments was performed using colored tracer particles. The flow of the tracer particles was observed through a transparent acrylic front wall by image analysis. Based on a comparison with the traditional design, the advantages and disadvantages of the new design were evaluated. The experimental investigations were accompanied by numerical simulations of the particle flow pattern using the discrete element method. The effects of design properties and different air duct arrangements were studied. The present results show that we are at the beginning of a new development concerning the optimization of mixed-flow drying apparatuses.     

Energy Analysis of a New Design of a Photovoltaic Cell-Assisted Solar Dryer

In this study, a new type of solar dryer was designed and manufactured. This new solar dryer is composed of a heat pipe collector, a drying chamber, a load cell, an air circulation fan, photovoltaic cells (PvC), batteries, and halogen lamps. In this experimental study, tomatoes were used to test the drying process. The drying air was heated by the heat pipe collector and forced through the tomatoes by a blower fan during the daytime. The photovoltaic cells, which were used to run the fan, were also used to charge the batteries during the day. These charged batteries were used for running the halogen lamps during the night, when the halogen lamps were used to heat the drying-air-assisted photovoltaic cells. During the drying period, the drying air temperature, relative humidity, air flow rates, solar radiation, and loss of mass were measured in the solar dryer. Then, the measured data were used for energy analysis.     

The Drying of Sludge in a Cyclone Dryer Using Computational Fluid Dynamics

A control volume-based technique implemented in FLUENT (ANSYS Inc., Canonsburg, PA) computational fluid dynamics (CFD) package was applied along with the kinetic theory of granular flow (KTGF) to simulate the flow pattern and heat and mass transfer processes for sludge material in a large-scale cyclone dryer. The drying characteristics of sludge at the dryer inlet were obtained from a previous study on the drying of sludge in a large-scale pneumatic dryer. User-defined subroutines were added to extend FLUENT's capability to account for mixture properties and to simulate the constant and falling rate drying periods. The convective heat and mass transfer coefficients were modeled using published correlations for Nusselt and Sherwood numbers. Sensitivity analysis was conducted to determine the effect of gas-phase velocity and temperature on the final product outcome. Numerical predictions for the multiphase flow hydrodynamics showed a highly diluted region in the dryer core and a higher concentration of particles close to the wall region, an indication of nonuniform distribution of particles at a cross-sectional area. The numerical predictions for the hydrodynamic profiles qualitatively depicted the flow behavior natural to these designs. The work demonstrated the successful application of CFD in the design stage of a combined pneumatic-cyclone dryer model.     

Investigation of Particle and Air Flows in a Mixed-Flow Dryer

Even though the mixed-flow dryer is well established on the commercial market for the drying of grain, maize, and rice, there further potential as well as a need to optimize the dryer apparatus and to improve product quality. Unfavorable designs can cause uneven mass flow and air flow distributions, resulting in locally different drying conditions and, hence, uneven grain drying. The aim of the present article is to evaluate traditional designs of mixed-flow dryers by numerical and experimental investigation of particle and air flows and to discover design deficits. For this purpose, the dryer geometry and different air duct arrangements (horizontal and diagonal) were studied using the discrete element method (DEM) and computational fluid dynamics (CFD). Drying experiments were performed to evaluate the grain moisture and temperature distributions. With regard to particle flow, a typical core flow was detected as in silos with a retarded particle flow at the dryer walls and a fast flow region in the center of the dryer. This was caused by the wall friction effect and the half air ducts fixed at the side walls. With regard to the air flow, dead zones were discovered for the diagonal air duct arrangement. Based on the design deficits identified for the traditional geometry, a new geometry for the mixed-flow dryer that is still under development is discussed.     

Design and Modeling of Plug Flow Fluid Bed Dryers

Plug flow fluid bed dryers (PFFBD) have been used for drying of particulate solids such as salts, ion exchange resins, grains, and a variety of other products. The present article describes the use of a mathematical model for the scale-up of lab-scale batch fluidization data to design an industrial-scale PFFBD. Axial dispersion theory was used in conjunction with the tanks-in-series model to describe the non-ideal flow. The model was implemented in Matlab 6.5 and it can be used for easily fluidizing particulate materials. The proposed model is capable of analyzing both the exponential falling rate and constant rate drying periods. The model predicts the required dryer dimensions for a given throughput and desired final moisture content. The model can also be used to study the effect of different process parameters such as solids feed rate, inlet air velocity, and temperature on the required dryer dimensions and it can also be used to predict the moisture and temperature profiles along the length of the PFFBD.     

多层水平气流带式干燥机的数学模型

根据干燥传质传热学原理和干燥动力学特性，建立了水平气流带式干燥机干燥过程的数学模型。该模型可以预测干燥机合理的通风道高度、带翻转最佳时间和热风风速等。为优化多层带式干燥机的结构或设计新的水平气流带式干燥机提供了理论依据。