THE INFLUENCE OF KILN GEOMETRY ON FLOW MALDISTRIBUTION ACROSS TIMBER STACKS IN KILNS

ABSTRACT

A one-dimensional mathematical model is evaluated for flow through a timber-drying kiln. This model is used to develop recommendations for the design of the plenum chambers on either side of the timber stack. The variation of the vertical air velocity was explored for a sticker spacing of 20 mm and a board thickness of 50 mm. When the width of the plenum chambers is at least equal to the sum of the thickness of the stickers, flow maldistribution is substantially reduced in single-track kilns. The width of the plenum chambers of double-track kilns may be reduced to three-quarters of the sum of the thickness of the stickers, because the increase in timber-stack resistance to airflow mitigates the effect of pressure variations down the length of the plenum chambers.     

PROGRESS IN THE MODELLING OF AIR FLOW PATTERNS IN TIMBER KILNS

Progress in modelling air flow patterns in timber kilns using Computational Fluid Dynamics is reviewed in this work. These simulations are intended to predict the distribution of the flow in the fillet spaces between boards in a hydraulic model of a timber kiln. Here, the flow regime between the boards is transitional between laminar and turbulent flow, with Reynolds numbers of the order of 5000. Running the simulation as a transient calculation has shown few problems with convergence issues, reaching a mass residual of 0.2% of the total inflow after 40-100 iterations per time step for time steps of 0.01 s. Grid sensitivity studies have shown that non-uniform grids are necessary because of the sudden changes in flow cross section, and the flow simulations are insensitive to grid refinement for non-uniform grids with more than 300,000 cells. The best agreement between the experimentally-measured flow distributions between fillet spaces and those predicted by the simulation have been achieved for (effective) bulk viscosities between the laminar viscosity for water and ten times that value. This change in viscosity is not very large (less than an order of magnitude), given that effective turbulent viscosities are typically several orders of magnitude greater than laminar ones. This result is consistent with the transitional flows here.     

PROGRESS IN THE MODELLING OF AIR FLOW PATTERNS IN TIMBER KILNS

ABSTRACT

Progress in modelling air flow patterns in timber kilns using Computational Fluid Dynamics is reviewed in this work. These simulations are intended to predict the distribution of the flow in the fillet spaces between boards in a hydraulic model of a timber kiln. Here, the flow regime between the boards is transitional between laminar and turbulent flow, with Reynolds numbers of the order of 5000. Running the simulation as a transient calculation has shown few problems with convergence issues, reaching a mass residual of 0.2% of the total inflow after 40–100 iterations per time step for time steps of 0.01 s. Grid sensitivity studies have shown that non-uniform grids are necessary because of the sudden changes in flow cross section, and the flow simulations are insensitive to grid refinement for non-uniform grids with more than 300,000 cells. The best agreement between the experimentally-measured flow distributions between fillet spaces and those predicted by the simulation have been achieved for (effective) bulk viscosities between the laminar viscosity for water and ten times that value. This change in viscosity is not very large (less than an order of magnitude), given that effective turbulent viscosities are typically several orders of magnitude greater than laminar ones. This result is consistent with the transitional flows here.     

STACK-WIDE EFFECTS IN THE MODELING OF SOLAR KILNS FOR DRYING TIMBER

This study examines the stack-wide effects due to the humidification and cooling of air as it passes through a 6 m wide stack of Australian ironbark timber for conditions that are representative of those for solar drying (dry and wet-bulb temperatures of 60 and 50°C, respectively). A solar kiln model for a greenhouse-type design has been modified to account for the drying of timber boards and the possibility of stack-wide effects, in terms of moisture-content differences in the streamwise direction of air flow through the stack. The maximum difference between the moisture contents of the leading and trailing boards is predicted to be 0.011 kg kg^-1 for these conditions, compared with timber moisture contents of 0.15-0.35 kg kg^-1. Hence, the stack-wide effect is insignificant for these conditions in this greenhouse kiln design and may be ignored, reducing the simulation time by over 50%. In addition, 14 elements within a finite-difference model for the drying of the timber boards (25 mm thick) gives predictions of the drying time that are acceptably accurate, while minimizing the computational time.     

物流分布对板翅式制氢反应器性能的影响

建立了板翅式制氢反应器中的三维数学模型,并采用此模型对反应器内部的温度分布进行了数值计算,并且和实验结果相结合,对不同方式的燃烧气流分布的效果进行分析。计算和分析结果均表明:燃烧气流分布均匀与否对反应器性能的影响较大,通过改进气体分布可以有效地改善反应器内部的温度分布及反应性能。     

论年希尧在雍正官窑瓷业发展中的作用与贡献

年希尧博学多才,在文化与科学领域有诸多贡献,任雍正四年至十三年景德镇御窑厂督陶官,在雍正官窑瓷业发展中具有不可替代的重要作用,促使雍正官窑瓷业进一步发展。     

封头结构对板翅式换热器物流分配不均匀性的影响

纵向传热、温度场与物流分配不均匀对换热器效能的影响具有耦合关系,其中物流分配的不均匀会加剧其内部温度场分布的不均匀,增大换热器的纵向传热,导致其效能的下降,所以物流分配的不均匀在三者中对换热器效能的影响最为重要.因此,对引起物流分配不均匀的因素进行研究是板翅式换热器优化设计的重要内容.针对板翅式换热器内部流动特性对封头结构的影响进行了深入研究.研究发现：封头结构的影响主要体现在垂直于总管流动方向上.发现了封头结构的改进方法,通过改变封头结构的设计可以有效地改善换热器内部的物流分配.     

AIRFLOW BEHAVIOUR IN TIMBER (LUMBER) KILNS

ABSTRACT

Even drying of stacked timber boards in a kiln depends, amongst other things, on having a uniform airflow through the pile. A study of possible airflow maldistribution in existing kilns has been carried out using a Perspex model of a kiln, with water as the fluid, which has been designed to be geometrically similar to an actual kiln and have dynamically similar flows. Measurements of local velocities were possible by tracing the flow of fine gas bubbles. The standard kiln arrangements result in significant recirculation zones before and after the stack, with a non-uniform incident velocity profile. Different design alternatives for the geometry of the plenum spaces on either side of the stack have been investigated.     

燃料对隧道窑热工性能的影响

从国内现有使用不同燃料的陶瓷隧道窑的热肥利用率、千克瓷能耗等热工性能的现状,分析了各种燃料的燃烧性能及不同的燃烧系统设置对窑炉热工性能的影响,认为洁净的气体燃料和轻油是生产高档产品的优质燃料。     

AIRFLOW BEHAVIOUR IN TIMBER (LUMBER) KILNS

Even drying of stacked timber boards in a kiln depends, amongst other things, on having a uniform airflow through the pile. A study of possible airflow maldistribution in existing kilns has been carried out using a Perspex model of a kiln, with water as the fluid, which has been designed to be geometrically similar to an actual kiln and have dynamically similar flows. Measurements of local velocities were possible by tracing the flow of fine gas bubbles. The standard kiln arrangements result in significant recirculation zones before and after the stack, with a non-uniform incident velocity profile. Different design alternatives for the geometry of the plenum spaces on either side of the stack have been investigated.     

边流效应对固定床吸附器穿透曲线的影响

在半工业吸附装置上实验研究了边流效应对固定床吸附器穿透曲线的影响,建立了非定态二维数学模型描述这种影响．实验结果表明,在床径／粒径比为90时,固定床内边流效应对穿透曲线影响仍很大,中心与壁面穿透时间相差可达4h,模型预测结果表明,实验结果与预测结果能很好吻合．     

基于某梭式窑热平衡测试的陶瓷工业窑炉节能技改研究

基于对某公司梭式窑进行热平衡测试,根据计算结果,结合目前热工设备和燃料燃烧等新技术(如采用天然气作燃料,使用高温空气燃烧技术、富氧燃烧技术),通过进行Matlab编程分析研究,得出进行技改的节能潜力。同时根据企业技改面临的资金、技术等难题,提出要大力推动合同能源管理在陶瓷工业技改方面的应用。     

A NEW INSTRUMENTATION FOR MEASURING THE SMALL SCALE MALDISTRIBUTION OF LIQUID FLOW IN TRICKLE BEDS

A measurement system was developed to study the small scale liquid distribution in a trickle bed reactor. The system can measure the radial profile of liquid flow rate quasi-simultaneously with a rectilinear array of 29 measuring cells with 10×10 mm² area, or the liquid flow rate with a single cell dynamically. The liquid flow rate in each cell was determined according to an electric conductivity method. A carefully devised system of calibration guarantees the standard deviation of measurement below 2%.     

对流循环和滑移汽泡机制在管束核态沸腾换热中的影响

对管束核态沸腾引起管束效应的对流循环和滑移汽泡两种机制作了模型假设和定量计算。并在实验基础上拟合了管束核态沸腾平均换热系数计算公式,分析了两种机制对换热的影响。     

INFLUENCE OF MIXING INTENSITY ON THE MASS TRANSFER COEFFICIENT ACROSS LIQUID-LIQUID INTERFACES

The influence of mixing intensity on the liquid-liquid mass transfer have been investigated using a binary system (water/n-butanol) in a modified stirred cell type contactor which overcomes the shortcomings associated with the previous contactors. It is observed that the mass transfer coefficient is affected by the degree of mixing intensity in both phases. The dependence of the aqueous and organic mass transfer coefficients on the mixing rate is about the same when both phases are agitated at the same speed and these coefficients become asymptotic values for the coefficients obtained at non identical agitation rate in both phases.     

辊道窑烧嘴喷射角度对窑内湍流气流影响的研究

应用k -ε两方程湍流模型 ,对辊道窑烧成带的湍流旋流流动进行了理论分析 ,并用计算流体力学软件Fluent进行数值模拟 ,研究了烧嘴的喷射角度对烧成带内的湍流旋流流动的影响及其对制品烧成的作用     

谈清代民窑纹样款的装饰性

通过对清代民窑纹样款的特征、构图形式、和装饰艺术性的论述,在展现它的装饰美同时,也让其历史价值和艺术价值得到进一步的落实和提升。我们在对古代纹样款的研究中也会有更新的认识,从而在进行现代陶瓷装饰上的创作中,不断的对其进行研究、利用和吸收,同时也宏扬了中国传统的陶瓷艺术文化。     

超细硅微粉对堇青石窑具多晶结构与性能影响的研究

本文主要探讨添加不同含量硅微粉对堇青石窑具多晶结构和性能影响，用以说明超细硅微粉能促进固相反应和坯体烧结的依据，从中确定硅微粉适宜的添加量，有助于选择堇青石窑具的较好配方。     

不同质量分数的添加物对吉州窑黑釉的影响

采用不同质量分数的添加物对吉州窑黑釉进行焙烧,期望制得一种能在低温下快速烧成的釉料。用扫描电镜、能谱仪、红外光谱分析仪等仪器对加入不同质量分数的添加物的黑釉焙烧后进行了结构、成分及形貌分析。结果表明:在800℃烧成时,加入5wt%添加物能与原黑釉良好地结合,产生了理想的效果,制得薄薄的、疏松的表面结构。     

梭式窑的码坯方法和烟道设计对温度场及流场影响的探讨

通过对使用中的梭式窑的码坯型式的分析及窑车中烟道的改造 ,探讨了它们对梭式窑内温度场及流场的影响 ,为梭式窑烧成的优化及结构的最佳化提供依据