DRYING OF GRANULAR MATERIALS IN AGITATED FLUIDIZED BED

ＮＯＭＥＮＣＬＡＴＵＲＥＧ　　ｍａｓｓｆｌｏｗｒａｔｅｏｆａｉｒ　ｋｇｍ- 2 ｓ- 1Ｔｉ ｉｎｌｅｔａｉｒｔｅｍｐｅｒａｔｕｒｅ　Ｋｎｒｏｔａｒｙｓｐｅｅｄｏｆａｇｉｔａｔｉｎｇｍｅｃｈａｎｉｓｍｒ/ｍｉｎＷ ｍｏｉｓｔｕｒｅｃｏｎｔｅｎｔｏｆｐａｒｔｉｃｌｅｓｋｇ -Ｈ2 Ｏ/ｋｇ -ｄｒｙｓｏｌｉｄＷ0 ｉｎｉｔｉａｌｍｏｉｓｔｕｒｅｃｏｎｔｅｎｔｏｆｐａｒｔｉｃｌｅｓｋｇ -Ｈ2 Ｏ/ｋｇ -ｄｒｙｓｏｌｉｄｔｄｒｙｉｎｇｔｉｍｅｏｆｐａｒｔｉｃｌｅｓ　ｓｔｒ ｒｅｓｉｄｅｎｃｅｔｉｍｅｏｆｐａｒｔｉｃｌｅｓ　…     

Volatile organic compound adsorption in a gas-solid fluidized bed.

Fluidization finds many process applications in the areas of catalytic reactions, drying, coating, combustion, gasification and microbial culturing. This work aims to compare the dynamic adsorption characteristics and adsorption rates in a bubbling fluidized bed and a fixed bed at the same gas flow-rate, gas residence time and bed height. Adsorption with 520 ppm methanol and 489 ppm isobutane by the ZSM-5 zeolite of different particle size in the two beds enabled the differentiation of the adsorption characteristics and rates due to bed type, intraparticle mass transfer and adsorbate-adsorbent interaction. Adsorption of isobutane by the more commonly used activated carbon provided the comparison of adsorption between the two adsorbent types. With the same gas residence time of 0.79 seconds in both the bubbling bed and fixed bed of the same bed size of 40 mm diameter and 48 mm height, the experimental results showed a higher rate of adsorption in the bubbling bed as compared to the fixed bed. Intraparticle mass transfer and adsorbent-adsorbate interaction played significant roles in affecting the rate of adsorption, with intraparticle mass transfer being more dominant. The bubbling bed was observed to have a steeper decline in adsorption rate with respect to increasing outlet concentration compared to the fixed bed. The adsorption capacities of zeolite for the adsorbates studied were comparatively similar in both beds; fluidizing, and using smaller particles in the bubbling bed did not increase the adsorption capacity of the ZSM-5 zeolite. The adsorption capacity of activated carbon for isobutane was much higher than the ZSM-5 zeolite for isobutane, although at a lower adsorption rate. Fourier transform infra-red (FTIR) spectroscopy was used as an analytical tool for the quantification of gas concentration. Calibration was done using a series of standards prepared by in situ dilution with nitrogen gas, based on the ideal gas law and relating partial pressure to gas concentration. Concentrations up to 220 ppm for methanol and 75 ppm for isobutane were prepared using this method.     

EXPERIMENT OF IMPACT OF RIVER HYDRAULIC CHARACTERISTICS ON NUTRIENTS PURIFICATION COEFFICIENT

Hydraulic characteristics of a river are the key factors for river water quality improvement and river restoration. A simulated river was exploited to study the interactions between water contaminant purification coefficients and the characteristics of the river, such as the cross-section velocity, water depth, Reynolds number, and Froude number. To enhance the purification capacity of the river, detritus with 5 mm to 10 mm in diameter and contact surface area per volume of 87.6 m2/m3 were constructed naturally at the bed and along one side of the bank to form half shape of the river cross-section. During the one-month experiment (including 3 periods) from the third of November to the fourth of December, 2005, three categories of hydraulic conditions were investigated. Results show that the purification coefficient (K) of Total Nitrogen (TN) is closely coherent with the hydraulic retention time (T), river length (L), Reynolds number (Re) and Froude number (Fr). The relationship of K and T generally agrees with the power law under the three experimental water hydraulic conditions. Based on these results, the optimal Re and Fr ranges can be obtain to serve as a guideline for ecological re-engineering design to improve river water quality and restore river ecosystem.     

一个基于多因素的冷却水管等效换热系数模型

基于热对流、传输微分方程及有限单元法,研究了冷却水流速、管壁粗糙度及导热系数对混凝土与冷却水之间的等效换热系数的影响。在分析各单因素影响的基础上,提出了包含冷却水流速、管壁粗糙度及混凝土导热系数等因素的冷却水管等效换热系数模型,可较好地预测多影响因素条件下混凝土与冷却水间的换热规律。模型表明,等效换热系数与冷却水流速、管壁粗糙度及导热系数均呈幂函数递增关系,其大小取决于多因素耦合效应。相较而言,粗糙度对等效换热系数影响仅在其取值较小时最显著;混凝土导热系数变化的影响较小;冷却水流速的影响介于二者之间。     

推移质运动对清水和宾汉体泥浆湍流结构的影响

通过试验研究了清水湍流和泥浆湍流中加入推移质后时均流速分布、脉动强度、概率密度分布、相关系数、频谱密度分布等的变化.试验结果证明,清水和泥浆湍流中加入推移质后时均流速减小,时均流速梯度增大,脉动加强.泥浆过渡区湍流上部为层流,有流核,加入推移质后,上部层流转变为湍流,流核消失.分析证明,这是由于推移质运动增大了雷诺应力和时均流速梯度,因而增大了时均流动向脉动传递的能量的缘故,清水湍流中加入推移质后脉速概率密度分布偏离正态,偏态系数加大.泥浆湍流中加入推移质后相关系数降低,脉动的随机性增大.泥浆湍流的脉动能量集中于低频脉动.由于推移质也可以吸收低频脉动能来支持其运动,所以加入推移质后泥浆湍流的低频脉动能量降低,高频脉动能量增大.     

NUMERICAL SIMULATION OF FLOW AND HEAT TRANSFER CHARA-CTERISTICS OUTSIDE A PERIODICALLY VIBRATING TUBE

Fluid flow and heat transfer characteristics outside a vibrating tube were numerically simulated by the dynamic mesh method. The mechanism of heat transfer enhancement via periodic vibration of the tube was explored by using the field synergy principle. It is found that the field synergy angle between fluid velocity vector and temperature gradient vector for a periodically vibrating tube is significantly smaller than that for a stationary tube, and it changes approximately according to the sinusoidal law in a vibration period. The effect of time phase of the vibration on the field synergy angle and convective heat transfer coefficient were also discussed. Results indicate that the vibration can enhance heat transfer and this effect is more remarkable when time phase angle ranges between 50° and 1400 in a half period. Especially when the time phase angle is 90°, the average field synergy angle outside the tube reaches the minimum, which leads to the best heat transfer performance.     

电机转速对文丘里混合充氧机工作性能的影响

为了解决传统混合充氧机能耗高、水下安装维护难的问题,研制了新型文丘里混合充氧机,重点研究了电机转速对文丘里混合充氧机工作性能的影响。结果表明,在电机转速200~1 400 r/min条件下,文丘里混合充氧机的循环水量与电机转速呈线性关系;建立了基于气泡羽流模型的径向混合水流运动模型,并利用实测流速数据优化了水流的能量损失系数及夹带系数,成功模拟了不同电机转速条件下的径向水流速度分布;研究了不同电机转速条件下的有效混合半径,确定了文丘里混合充氧机的合适安装间距。电机转速400~1 200 r/min条件下,当电机转速逐渐增大时,水体复氧速率、氧的总传质系数和氧的传质效率均随之增大,混合充氧性能随之改善。     

Effect of bed roughness on grain-size distribution in an open channel flow

Grain-size distributions of suspended load were studied in a laboratory flume over five sediment beds having different values of bed roughness at three different flow velocities. The experiments had been performed to investigate the influence of bed roughness, flow velocity and suspension height on the grain-size distribution in suspension. This study focuses on the determination of the proportionality parameter β_n in suspension which is the ratio of sediment diffusion coefficient to the momentum diffusion coefficient of the nth grain-size class. An empirical equation for β_n has been proposed which is valid for a wide range of normalizing settling velocity of sediment particles and bed roughness. Also, the bed roughness effect is studied on the parameter β for total concentration in suspension and on the reference concentration, which is very important in suspension studies. The Rouse equation with modified β_n and β was surveyed to know the grain-size distribution and total concentration in suspension that agreed well when compared with the experimental data.     

THREE-DIMENSIONAL NUMERICAL SIMULATION OF THERMAL-HYDRAULIC PERFORMANCE OF A CIRCULAR TUBE WITH EDGEFOLD-TWISTED-TAPE INSERTS

Three-dimensional numerical simulations and experiments were carried out to study the heat transfer characteristics and the pressure drop of air flow in a circular tube with Edgefold-Twisted Tape (ETT) inserts and with classic Spiral-Twisted-Tape (STT) inserts of the same twist ratio. The RNG turbulence model for mildly swirling flows, the enhanced wall treatment for low Reynolds numbers, and the SIMPLE pressure-velocity method were adopted to simulate the flow and heat transfer characteristics. Within the range of Reynolds number from 2 500 to 9 500 and the twist ratio y from 5.4 to 11.4, the Nusselt number of the tube with ETT inserts is found to be 3.9% ? 9.2% higher than that with STT inserts, and the friction factor of the tube with ETT inserts is 8.7% ? 74% higher than that of STT inserts. The heat enhancement is due to higher tangential velocity and asymmetrical velocity profile with the increase and decrease of the periodic velocity within an edgefold length. It is found that main factors affecting the heat transfer of ETT inserts are the twist angle and the gap width between the tube and inserts. A larger twist angle leads to a higher tangential velocity, and larger Nusselt number and friction factor. The thermal-hydraulic performance slowly decreases as the twist angle increases. The gap width between tube and inserts has a significant influence on the heat transfer, while little influence on pressure drops. The thermal-hydraulic performance increases in average by 124% and 140% when the gap width reduces from 1.5 mm to 1.0 mm and 0.5 mm. The larger the gap width, the higher velocity through the gap will be, which would reduce the main flow velocity and tangential velocity. So a small gap is desirable. Comparing experimental and numerical results at variable air flow and tube wall temperature, the numerical results are found to be in a reasonable agreement with the experiment results, with difference of the Nusselt number in a range of 1.6% ? 3.6%, and that of the friction factor in a range of 8.2% ? 13.6%.     

Biosorption of Pb2+ and Cd2+ in a fixed bed column with immobilised Chorella sp. biomass

The biosorption of Pb2+ and Cd2+ in a fixed bed column by immobilised Chlorella sp. was characterised in a fixed bed column. Effect of initial concentration of Pb2+ and Cd2+, pH, and pellet size on the biosorption capacity was studied, at laboratory scale, using a factorial experiment design 2(3), in a 10 cm heightx1 cm of diameter continuous flow column packed with immobilised biomass. Equilibrium uptake of Pb2+ and Cd2+, increased with increasing initial metal ion concentration. It was favoured to pH 5, with a pellet of 5 mm of diameter. Langmuir model described the biosorption equilibrium of both metals.The biosorption of each single cation was studied too in a large column (50 cm heightx5 cm of diameter) at bench scale with a range of flow of 40 to 80 mL min(-1). The mass transfer coefficient was determined fitting the experimental data to continuity equations that were discretised in the radial terms with orthogonal collocation method.     

Assessment of Impact of Filter Design Variables on Clogging in Stormwater Filters

Stormwater filters are widely used in stormwater management, sometimes as standalone structures (e.g. stormwater filter beds), or as part of porous pavements, soak ways, infiltration basins and trenches. Due to the high levels of sediment present in stormwater, clogging is the main operational issue for these systems. A laboratory-based study was conducted to investigate the effect of filter bed design variables on the clogging phenomenon in non-vegetated stormwater filters with high infiltration rates. Design parameters studied include: filter media particle sizes (0.5 mm, 2 mm, 5 mm); depth of the filter bed (100 mm, 300 mm and 500 mm); and filter media packing configurations (layered or mixed). The size of filter media particles significantly impact the clogging process, as well as the overall sediment removal performance of the filters; filters with smaller particles had better sediment removal efficiency, but subsequently shorter lifespan. Deeper systems had longer lifespan compared with shallower ones, notwithstanding deeper systems removed more sediment over their life span. Having two layers of distinct sized media in the filter bed improved performance (e.g. volume of water treated; sediment removed) over the single-layered systems. However, the three-layered systems behaved similarly to two-layered systems. Mixed systems also showed improved performance, as compared with single-layered systems, and were similar to the three-layered systems. This study therefore suggests that simple modifications to a stormwater filtration system can help improve sediment removal performance and/or reduce maintenance intervals significantly, while only slightly affecting sediment removal performance.     

Principles of an enhanced MBR-process with mechanical cleaning

Up to date, different physical and chemical cleaning protocols are necessary to limit membrane fouling in membrane bioreactors. This paper deals with a mechanical cleaning process, which aims at the avoidance of hypochlorite and other critical chemicals in MBR with submerged flat sheet modules. The process basically consists of the addition of plastic particles into the loop circulation within submerged membrane modules. Investigations of two pilot plants are presented: Pilot plant 1 is equipped with a 10 m(2) membrane module and operated with a translucent model suspension; pilot plant 2 is equipped with four 50 m(2) membrane modules and operated with pretreated sewage. Results of pilot plant 1 show that the establishment of a fluidised bed with regular particle distribution is possible for a variety of particles. Particles with maximum densities of 1.05 g/cm(3) and between 3 and 5 mm diameter form a stable fluidised bed almost regardless of activated sludge concentration, viscosity and reactor geometry. Particles with densities between 1.05 g/cm(3) and 1.2 g/cm(3) form a stable fluidised bed, if the velocity at the reactor bottom is sufficiently high. Activities within pilot plant 2 focused on plant optimisation and the development of an adequate particle retention system.     

泥沙起动条件分析及推移质输沙率公式

基于床面均匀泥沙颗粒相对位置关系,确定了瞬时作用流速及有效作用高度,建立了平坡泥沙起动条件与床面泥沙暴露度的关系。从理论上分析得到,泥沙跃移起动要求水流条件最高,滚动起动及滑动起动取决于泥沙颗粒的暴露角,且暴露角θ不随拖曳力系数C_D和上举力系数C_L的变化而变化。当暴露角θ小于42.8°时,泥沙更易于滚动起动;当暴露角θ大于42.8°时,泥沙更易于滑动起动。在此基础上,推导出了考虑两种起动模式的起动全概率公式,建立了床面推移质单宽输沙率公式。通过经典的推移质输沙率实测资料验证及误差计算表明,公式结构合理,计算精度较高,对于高、中、低输沙率都具有较好的适用性。     

FLUID CHARACTERISTICS OF ROTARY WING HEAT METER WITH SINGLE-CHANNEL

Fluid characteristics of a rotary wing heat meter with single-channel were studied through theretical analysis, numerical simulation and experiments. The obtained results show that the number of vanes can obviously influence the heat meter, but the water temperature seldom influence the meter , and the optimal number of vane is 6-8.     

泥沙起动流速的随机分析

泥沙起动流速是河流泥沙动力学基本概念之一,对泥沙运动及河床冲淤变形研究有着重要意义.天然河流中的泥沙运动多处在紊流状态下,其影响因素极其复杂,具有显著的随机性.本文在总结前人研究成果的基础上,从流体力学层面论述了以作用于泥沙颗粒上的局部流速表示泥沙起动流速的合理性,进一步拓展分析,指出了以往公式的不足,给出了以局部点流速表示的包括散粒体与粘性颗粒在内的全沙起动流速公式,继而与各家公式作了对比;基于随机理论,给出了泥沙普遍动、少量动、个别动的判据,并将均值流速概率化,扩展了泥沙颗粒起动的范围与认知.     

冲动式透平平面叶栅内气－固两相流动的试验研究

本文利用高速摄影和图象处理技术真实地再现了平均粒径ｄｐ＝７００μｍ的固体位子流经冲动式透平平面叶栅的瞬间过程，分析了粒子在叶栅内的运动轨迹及其在叶栅内的浓度和速度分布特性。文中还对沿叶栅表面分布的纯气流压力和气相压力进行了测量。结果表明：粒子的尺寸和初始位置对粒子在叶栅内的运动轨迹有很大影响；在粒子与叶片碰撞比较频繁的部位附近，粒子相互聚集，形成粒子聚集区，在此区域内，粒子的浓度比较高，粒子的速度更为复杂；在粒子聚集区附近，气相压力相对纯气流压力的变化值比较大。     

基于DTS的灌注桩完整性检测方法研究

为了完善DTS应用于灌注桩完整性检测的理论,基于有内热源的径向热传导理论和试验,针对桩径为300,400,600,1 000 mm的灌注桩,对沿桩中心轴线方向内置光纤热源的热传导特征进行研究;取最大过余温度1 K,对加热功率与温度场的相关性进行计算分析。确定了桩体内置光纤热源径向热传导特征、桩径、加热功率的定量关系,分析了DTS检测桩缺陷对光纤布线及加热功率的要求,最后给出了考虑DTS测试精度的合理光纤加热功率的确定方法。     

Numerical investigation of flow and heat transfer performances of horizontal spiral-coil pipes

The flow and heat transfer performances of horizontal spiral-coil pipes of circular and elliptical cross-sections are studied.The numerical results are compared with the experimental data,to verify the numerical method.The effects of the inlet water mass flow rate,the structural parameters,the helical pitch and the radius ratio on the heat transfer performances are investigated.Performances of the secondary fluid flow with different radius ratios are also investigated.Numerical results demonstrate that the heat transfer coefficient and the Nusselt number increase with the increase of the water mass flow rate or the helical pitch.The maximum heat transfer coefficient and the maximum Nusselt number are obtained when the radius ratio is equal to 1.00.In addition,the fluid particle moves spirally along the pipe and the velocity changes periodically.The particle flow intensity and the spiral movement frequency decrease significantly with the increase of the radius ratio.Besides,the secondary flow profile in the horizontal spiral-coil pipe contains two oppositely rotating eddies,and the eddy intensity decreases significantly along the pipe owing to the change of curvature.The decreasing tendency of the eddy intensity along the pipe increases with the increase of the radius ratio.     

EXPERIMENTAL STUDY OF CONDENSATION HEAT TRANSFER CHARACTERISTICS OF HORIZONTAL TUBE BUNDLES IN VACUUM STATES

To develop an excellent heat transfer element under the vacuum condition,experiments about the heat transfer performance of horizontal tube bundles of different materials under various vacuum condition...     

EXPERIMENT STUDY ON SEDIMENT INCIPIENCE IN BACKWARDFACING STEP FLOW

Flow over a backward-facing step was studied to investigate the effect of large-scale vortex structures on sediment incipience. The transient flow velocity field at the downstream of the backward-facing step was obtained using the technique of Particle Tracking Velocimetry (PTV). The optical amplification technique was employed to measure the instantaneous flow velocities near the bed and the instantaneous bed shear stress was given. The experimental observations revealed a new insight into the oscillation of the large-scale structure and the three-dimensional characteristics of the flow. In particular,very high turbulence intensity,instantaneous horizontal velocity near the bed and the bed shear stress near the reattachment point were observed. The sediment incipient probability obtained from the sequent images of sediment particles near the bed indicates that the critical instantaneous shear stress of the sediment incipience is independent of flow conditions.