Heat and Mass Transfer for a Nanofluid Flow in Fluidized Bed Dryer in Presence of Induced Magnetic Field

This research entails the study of heat and mass transfer of nanofluid flow in a fluidized bed dryer used in tea drying processes in presence of induced magnetic field. A mathematical model describing the fluid flow in a Fluidized bed dryer was developed using the nonlinear partial differential equations. Due to their non-linearity, the equations were solved numerically by use of the finite difference method. The effects of physical flow parameters on velocity, temperature, concentration and magnetic induction profiles were studied and results were presented graphically. From the mathematical analysis, it was deduced that addition of silver nanoparticles into the fluid flow enhanced velocity and temperature profiles. This led to improved heat transfer in the fluidized bed dryer, hence amplifying the tea drying process. Furthermore, it was noted that induced magnetic field tends to decrease the fluid velocity, which results in uniform distribution of heat leading to efficient heat transfer between the tea particles and the fluid, thus improving the drying process. The research findings provide information to industries on ways to optimize thermal performance of fluidized bed dryers.

Mathematical Modelling and Design of Helical Coil Heat Exchanger for Production of Hot Air for Fluidized Bed Dryer

In global industrialization, efforts have been made to increase the rate of heat transfer in heat exchanger, minimizing the size of heat exchanger to reduce cost as well as increasing the effectiveness. Helical coil heat exchanger (HCHE) has been proven to be effective in improving heat transfer due to its large surface area. In this study, HCHE was designed to provide hot air needed for fluidized bed drying processes. The HCHE design model was fabricated and evaluated to study the efficiency of the hot air output for a laboratory fluidized bed dryer. The mathematical model for estimation of the final (output) temperature of air, Taf, passing through the HCHE was developed and validated experimentally. The drying of bitter kola particulates was carried out with a drying temperature of 50C 3C and a bed height-to-bed diameter ratio (H/D) of 1.5. The time taken to dry bitter kola particulates to 0.4% moisture content was 1 hour 45 minutes. Hence, HCHE is recommended for use in the production of hot for laboratory-scale fluidized bed dryers.

Study of heat transfer by using DEM–CFD method in a randomly packed pebble-bed reactor

The pebble-bed reactor is one of the most promising designs for the nuclear energy industry. In this paper,a discrete element method-computational fluid dynamics(DEM-CFD) approach that includes thermal conduction, radiation, and natural convection mechanisms was proposed to simulate the thermal-fluid phenomena after the failure of forced circulation cooling system in a pebble-bed core. The whole large-scale packed bed was created using the DEM technique, and the calculated radial porosity of the bed was validated with empirical correlations reported by researchers. To reduce computational costs, a segment of the bed was extracted, which served as a good representative of the large-scale packed bed for CFD calculation. The temperature distributions simulated with two different fluids in this DEM-CFD approach were in good agreement with SANA experimental data. The influence of the natural convection mechanism on heat transfer must be taken into account for coolants with strong convective capacity. The proposed DEM-CFD methodology offers a computationally efficient and widely applied method for understanding the heat transfer process in a pebble-bed core. The method can also be easily extended to assess the passive safety features of newly designed fluoride-salt-cooled pebble-bed reactors.

Surface-particle-emulsion heat transfer model between fluidized bed and horizontal immersed tube

A mathematical model, surface-particle-emulsion heat transfer model, ispresented by considering voidage variance in emulsion in the vicinity of an immersed surface. Heattransfer near the surface is treated by dispersed particles touching the surface and through theemulsion when the distance from the surface is greater than the diameter of a particle. A film withan adjustable thickness which separates particles from the surface is not introduced in this model.The coverage ratio of particles on the surface is calculated by a stochastic model of particlepacking density on a surface. By comparison of theoretical solutions with experimental data fromsome references, the mathematical model shows better qualitative and quantitative prediction forlocal heat transfer coefficients around a horizontal immersed tube in a fluidized bed.

Comparison of Mass Transfer Characteristics between Countercurrent-Flow and Crosscurrent-Flow Rotating Packed Bed

The rotating packed bed(RPB), mainly including the countercurrent-flow RPB(Counter-RPB) and the crosscurrentflow RPB(Cross-RPB) that are classified from the perspective of gas-liquid contact style, is a novel process intensification device. A significant measurement standard for evaluating the performance of RPB is the mass transfer effect. In order to compare the mass transfer characteristics of Counter-RPB and Cross-RPB with the same size, the liquid volumetric mass transfer coefficient(k_La_e) and effective interfacial area(a_e) were measured under identical operating conditions. Meanwhile, the comparison of comprehensive mass transfer performance was conducted using the ratio of ΔP(pressure drop) to kLae as the standard. Experimental results indicated that kLae and ae increased with the increase in liquid spray density q, gas velocity u, and high gravity factor β. Furthermore, compared with the Cross-RPB, the Counter-RPB has higher liquid volumetric mass transfer coefficient and slightly larger effective interfacial area. The experimental results of comprehensive mass transfer performance showed that the Counter-RPB had higher ΔP/k_La_e than the Cross-RPB with changes in liquid spray density and high gravity factor, and there exists a turning point at 0.71 m/s accompanied by a variation with gas velocity. Moreover, the relative error of experimental value to calculated value, which was computed by the correlative expressions of kLae, was less than 5 %. In conclusion, the mass transfer characteristics of RPB are deeply impacted by the manner in which the flows are established and the Cross-RPB would have a great potential for industrial scale-up applications.

Mass transfer characteristics in a rotating packed bed with split packing

The rotating packed bed （RPB） with split packing is a novel gas-liquid contactor, which intensifies the mass transfer processes controlled by gas-side resistance. To assess its efficacy, the mass transfer characteristics with adjacent rings in counter-rotation and co-rotation modes in a split packing RPB were studied experimentally. The physical absorption system NH3-H2O was used for characterizing the gas volumetric mass transfer coeffi- cient （kyae） and the effective inteffacial area （ae） was determined by chemical absorption in the CO2-NaOH sys- tem. The variation in kyae and ae with the operating conditions is also investigated. The experimental results indicated that kyae and ae for counter-rotation of the adjacent packing rings in the split packing RPB were higher than those for co-rotation, and both counter-rotation and co-rotation of the split packing RPB were superior over conventional RPBs under the similar ooerating conditions.

Interphase Mass Transfer in G-L-S Magnetically Stabilized Bed with Amorphous Alloy SRNA-4 Catalyst

Gas-liquid (G-L) and liquid-solid (L-S) mass transfer coefficients were characterized in a gas-liquid-solid (G-L-S) three-phase magnetically stabilized bed (MSB) using amorphous alloy SRNA-4 as the solid phase. Effects such as superficial liquid velocity, superficial gas velocity, magnetic strength, liquid viscosity, and particle size were investigated. Experimental results indicated that the G-L volumetric mass transfer coefficients (KLa) increased along with the magnetic strength, superficial gas and liquid velocities. Proper increase of liquid viscosity promoted KLa only in the range of lower liquid viscosity. The external magnetic field made L-S mass transfer coefficients (Ks) in the G-L-S MSB lower than those of conventional fluidized beds. Ks in the MSB almost kept constant as the su- perficial liquid velocity and superficial gas velocity increased and decreased with the liquid viscosity and surface tension, while increased with the particle size Ks showed uniform axial and radial distributions except of small de- creases close to the wall. Dimensionless correlations were established to estimate KLa and Ks of the MSB with SRNA-4 catalysts , which showed the average error of 5.4% and 2.5% respectively.

Equation of Radiation Heat Transfer in Multiple Combustion Boiler Furnace of Fluidized Bed and Pulverized Coal Firing

The equation for radiation heat transfer in a multiple combustion boiler furnace with nuidized bed and pulverized coal firing is derived from direct calculation of radiation heat transfer.

HYSTERESIS OF GAS-LIQUID MASS TRANSFER IN A TRICKLE BED REACTOR

1 INTRODUCTIONTrickle bed reactors are widely used in the process industry,particularly in petroleumhydroprocessing operations,and have been extensively studied by chemical engineers.In atrickle bed reactor,the gas and liquid flow cocurrently down through the packed bedand undergo chemical reactions.However,there exist multiple hydrodynamic stateswhich correspond to either uniform or,in most cases,nonuniform radial distributionof the gas and liquid flows in the packed section.Moreover,the hydrodynamic state

Hydrodynamics and oxygen transfer in a novel extra-loop fluidized bed bioreactor

In this paper, the characteristics of fluid mixing time in a novel extra-loop fluidized bed were studied. The results showed that the mixing time was shortened with the increase of fluid velocity. All the discrete numbers of the reactor were above 0.2. The serial number n was 2.5 -3.0. It was judged accordingly that the reactor fluid state was continous stirred tank reactor （CSTR） mainly. When the inspiratory capacity increased the mixing time of the reactor was shortened. Thus the air input was beneficial for the fluid mixing. During the three phases mixing process, the mixing time of the reactor could be decreased by the n increase of carrier and air loading together, but the change was not significant. The parameters affecting the reactor fluid state were fluid velocity, inspiratory capacity and carrier. KLa could be increased with the air loading increase, and at the same gas/liquid ratio when the pressure drop was high, KL~ value was increased. The amount of carrier complex influence on KLa. As the carrier loading continued to increase, its value had been dropped but the changes was not significant, and optimization condition was found at above 800 1 000 g carrier loading （pouzzolane） or 600 g PVC. Under gas/liquid ratio of 0.8% -5.2%, KLa was （0.62-1.37）×10^-2· s^-1.

CORRELATION BETWEEN HYSTERESIS OF GAS-LIQUID MASS TRANSFER AND LIQUID DISTRIBUTION IN A TRICKLE BED

The hysteresis of gas-liquid mass transfer rate and the corresponding radial liquiddistribution in a trickle bed reactor are measured to provide evidence for the correlation between thesetwo behaviors.Experimental results indicate that the hysteresis of gas-liquid mass transfer originatesfrom the nonuniformity of the hydrodynamic state of gas-liquid flow and the radial maldistributionof local kgia corresponds very well to the radial maldistribution of liquid flow in the bed.The localliquid flow rate is also found to be nonuniform in the azimuthal direction.In view of maldistributedliquid flow even in the pulsing flow regime,the conventional plug flow model seems oversimplifiedfor describing the behavior of a trickle bed.

燃煤锅炉改燃兰炭燃烧工艺及效益分析

兰炭因热值高、硫含量低的特点被广泛应用于散煤替代,燃煤锅炉改燃兰炭是实现资源合理利用、降低污染物排放和改善企业经济效益的有效途径。以河北某循环流化床锅炉改燃兰炭工程为例,燃烧系统采用掺烧灰渣的方法,解决改燃后机械未完全燃烧导致损失大和物料循环不稳定问题,确定了兰炭和灰渣的最佳掺混比为9∶1;配风系统采用控制总量并降低一次风率的方法,解决兰炭着火困难的问题,确定了最佳一次风比例为55%;换热系统采用增加锅炉尾部受热面的方法,解决因燃料热值提升较大产生的蒸汽超温和锅炉效率下降问题。改燃扩容后锅炉烟尘、SO2和NOx排放分别比原锅炉降低了73%、94%和55%,以原锅炉35 t/h的额定功率运行,每小时节约燃料成本5.51%,产吨蒸汽所需燃料成本降低6.47元。

新型简易移送垫在手术室围手术期过床转运的应用效果

目的探讨新型简易移送垫在手术室围手术期过床转运的应用效果。方法选取2022年8月至2023年2月南昌市第一医院100例手术患者为研究对象,按随机数字表法分为对照组(50例)和观察组(50例)。对照组使用传统搬运方法,观察组使用新型简易转运移送垫搬运,比较两组的不良事件发生率、患者舒适满意度、过床搬运时间及医护人员腰肌损伤发生率。结果观察组的不良事件总发生率低于对照组,差异有统计学意义(P<0.05);观察组患者舒适度高于对照组,差异有统计学意义(P<0.05);观察组过床搬运时间短于对照组,差异有统计学意义(P<0.05);观察组医护人员腰肌损伤总发生率低于对照组,差异有统计学意义(P<0.05)。结论通过新型简易转运移送垫在术后手术室与临床科室过床搬运的应用,从而避免搬运过程中坠落、管道脱落或牵扯等不良事件发生,给患者增加舒适及安全感,提高患者舒适满意度,降低临床医护人员搬运时导致的腰肌劳损的发生率,值得临床推广。

功能性填料在超重力旋转填料床中的应用和研究进展

填料作为旋转填料床的核心部件,是物料微观混合和传质反应过程发生的重要场所。填料的结构、材质组成、填装方式决定了填料的功能性,进而直接影响到旋转填料床的传质性能、使用寿命和应用范围,故而增强填料的功能性显得尤为重要。功能性填料通过改变常用填料的表面性质、调节形态、设计结构等手段,使填料具有如吸附、催化、疏水等的功能特性,在提高旋转填料床的性能和运行效果方面表现出优异的成效。综述了在旋转填料床中功能性填料的主要分类与特点,总结分析了近年来功能性散装填料和规整填料在旋转填料床中的应用情况,从增强传质特性和改善液体流动行为方面分析了填料功能特性的体现,并对功能性填料的发展方向和工业化前景做出了展望。

颗粒分辨的乙炔选择性加氢固定床反应器数值模拟

乙烯产量是反映国家石油化工发展水平的关键指标。构建了颗粒分辨的乙炔选择性加氢固定床反应器模型,分析圆柱形颗粒堆积结构对传递过程以及操作条件对其反应性能的影响。结果表明,床层压降主要集中在反应器入口段,该段乙炔加氢反应速率最高,但在后半段催化剂颗粒未被充分利用,而且反应器内存在明显的径向温度梯度。入口压力的增加和空速的降低均有利于提升乙炔转化率,但同时会降低乙烯选择性,其中乙烯选择性对压力更敏感,而乙炔转化率对空速更敏感;反应温度和氢炔比的提高均有利于促进乙炔生成乙烯的速率,但会导致乙烯富集在催化剂颗粒的外表面,其进一步向颗粒内部扩散时过度加氢生成乙烷,使乙烯选择性降低。

气固鼓泡床结构双流体传热模型及其模拟验证

介尺度结构显著影响非均匀气固复杂系统内的流动传递反应特性。构建了结构双流体传热模型用于模拟复杂气固系统内的流动传热过程,按照流动控制机制将鼓泡床系统划分成由气体主导的气泡相和颗粒主导的乳化相两个相互渗透的连续流体,进而确立考虑介尺度结构影响的控制方程及本构关系,其中相间曳力、乳化相黏度、相间传热系数及各相热导率均采用合理的经验关联式进行封闭。利用双流体传热模型与显式解析壁面流动和传热边界层方法相结合,对安装加热管的鼓泡床系统进行了模拟。结果表明:结构双流体传热模型可成功预测鼓泡床系统内固含率的轴向分布及床层壁面传热系数的变化规律;模拟结果与实验数据吻合较好,密相区壁面传热系数模拟值与实验值的相对误差小于10%,稀相区壁面传热系数的模拟值与实验值在同一量级,表明结构双流体传热模型可准确刻画鼓泡床系统内气固两相的流动传热特性。

不同长径比填充床蓄冷器储释冷特性研究

在相同操作条件下模拟分析16组具有相同总体积、不同长径比的蓄冷器(组),比较准稳态的储冷量、释冷量、储释冷效率。结果表明:经过20次储释冷循环后达到准稳态。单体蓄冷器长径比从0.6增加到3时,储冷量/释冷量逐渐增加,但储释冷效率逐渐降低。并联数量从1增加到6时,蓄冷器组的储冷量、释冷量、储释冷效率均呈下降趋势。设计蓄冷器几何结构时,建议采用长径比为2的单体形式或串联形式。若必须并联,应尽量减小并联数量。

甲烷化固定床反应器及催化剂数值模拟研究进展

对固定床在甲烷化数值模拟方面的研究进展进行了综合评述。比较了固定床反应器中一维、二维和三维模拟方法差异。一维和二维模拟计算量小,可用于优化甲烷化工艺。三维模拟更接近真实反应器,计算结果与实验结果的误差更小,更有利于反应器的结构优化。关注甲烷化固定床反应器传热研究,探索模拟关键点。描述了甲烷化反应器数值模拟中所使用的催化剂模型的发展,三维催化剂模型模拟能准确预测出催化剂内部反应的细节,更适合研究不同形状的催化剂对甲烷化反应的影响。推断出今后甲烷化反应器数值模拟的重点和研究方向。

移动床生物膜反应器内典型水质因素对氧转移能力的影响

在污水处理节能降耗与“双碳”战略背景下,为进一步实现污水处理环节的提质增效与节能降碳,从提高氧转移能力的角度出发,在移动床生物膜反应器内,开展了水质因素对氧转移能力的影响研究,并从气泡Sauter平均直径、气泡平均上升速度和气含率等方面,定量分析了氧转移能力影响机制。结果表明:当十二烷基硫酸钠(SDS)浓度由0增大至10 mg/L时,不同载体填充率条件下的氧转移能力均降低;但当SDS浓度由12增大为20 mg/L时,氧转移能力逐渐提高;生物膜载体的存在削弱了SDS对氧转移能力的影响。当总溶解性固体(TDS)值由2000增大至12000 mg/L时,提高了氧转移能力;当TDS值大于12000 mg/L后,氧转移能力趋于不变。随着pH值增大,提高了氧转移能力。在实际污水处理过程中,根据不同水质条件下的氧转移能力变化,通过调节曝气强度等方式,可降低污水处理环节的能耗与成本。

特种电机转子系统的临界转速分析

针对我公司开发的压裂泵试验台电机在特殊工况下的运行特点进行了研究。采用传递矩阵法,对压裂泵试验台电机在两台电机串联运行的情况进行了分析计算,为了提高计算效率,应用Matlab平台在传递矩阵法的基础上进行了程序编制,并对电机转子结构进行了等效处理,最终实现对此种特殊工况的临界转速计算。通过对这种等效计算方法的研究,为压裂泵试验台电机以及其他特种电机的研发提供了技术支撑。