半圆电极对测量壁面处的湍流速度梯度脉动

壁面处湍流速度梯度脉动的测量对于深入了解壁面附近湍流的结构和传热、传质是很重要的.本文叙述了电化学法测量的原理,介绍了用一半圆电极对同时测量壁面上二维湍流速度梯度脉动的方法和测量结果.在直径0.194m的充分发展圆管湍流中,用碘和碘化钾溶液作为流动介质,半圆电极对直径为5×10~-4m,测得壁面处轴向和周向速度梯度的湍流脉动强度分别为0.3—0.33和0.11—0.12.     

STUDIES ON GAS-LIQUID-SUSPENDED SOLID MULTIDECK GAS LIFT REACTOR

Following the work on gas lift reactor (Pachuca tank) for gas-liquid-suspended solid 3-phase reaction,multideck gas lift reactors have been developed.This type of reactor has many unique advantages suchas realization of counter-current operation between gas and slurry,reduction of gas consumption and lower-ing of the amount of volatile components of the liquid which has to be recovered from the exit gas.The stability of the overflow tube of the reactor was studied.A semiempirical equation was derived tocalculate the flooding point of the reactor.The operating range of the overflow tube was also deter-mined.This multideck reactor has been operated successfully in a pilot plant of ammonia leaching of copperore.Results agree reasonably well with those predicted from small scale batch experiments.The extractionof vanadium from soda roasted steel slag in a 5-deck reactor with carbon dioxide in the gas phase wasalso satisfactory.Experimental results obtained from the continuous flow 5-deck reactor and those calcu-lated from batch experimental data with CSTR model were in agreement.     

MEASUREMENT OF TURBULENT FLUCTUATIONS OF VELOCITY GRADIENT ON THE WALL WITH A PAIR OF SEMICIRCULAR ELECTRODES

Measurement of turbulent fluctuations of vclocity gradient on the wall is important for thorough understanding of turbulence structure, mass transfer and heat transfer in the vicinity of the wall. This paper describes the principle of electrochemical technique as well as the measurement of two-dirnensional fluctuations of velocity gradient with a pair of semicircular electrodes. In a fully developed turbulent pipe flow with pipe diameter of 0.194 m and with a solution of iodine and potassium iodide as flow medium, the measured axial and transversal turbulent intensities of velocity gradient at the wall arc 0.3-0.33 and 0.11 0.12 respectively.     

MASS TRANSFER IN TURBULENT PULSATING FLOWS

The effect of flow oscillation to the mass transfer between turbulent fluid and solid wall was investigatedby measuring the mass transfer rate between fluid and pipe wall with imposed oscillating flow usingelectrochemical method.The velocity and concentration field in the viscous sublayer which controls the mass trans-fer in such a process was simulated by a simple wave model of single harmonics.Experimental results confirmthat the flow oscillation has no influene on time averaged mass transfer rate,but the phase difference betweenphase averaged velocity field and concentration field shifts with the frequency of imposed oscillating flow.Numeri-cal analysis reveals that the concentration boundarylayer which is responsible for the mass transfer is muchthinner than the viscous sublayer which greatly weakens the influence of imposed oscillating flow on mass transfer.     

LIQUID AXIAL BACKMIXING IN MULTISTAGE BUBBLE COLUMN

The characteristics of a staged bubble column can be described by a multi-stage backmixing model,provided: (1) Each stage can be considered as a perfect mixing reactor,and (2) The backmixing coeffi-cients do not vary with time and reactant concentrations.Experimental results indicate that the first conditionis approached under certain conditions,while the second assumption is correct.Studies were made using steady state chemical tracer method to determine the backmixing coefficientsof each plate between stages.The fluid flow through the holes of perforatcd plates is a stochastic process.From the statistical point,the experimental data could be correlated by semicmpirical equation developed.This equation can also be used to correlate the data reported by Nishiwaki for bubble column with plateshaving high percentage of opening area and large size holes between stages.Continuous oxidation of unsaturated sulfur compounds (mainly in the form of thiosulfatc and also somein polythionate form) in nickel ammonium carbonate solution were carried out in bubble columns with heightof 3400mm and diameters of 36 mm and 100mm respectively.The oxidation has to be taken in a multistagebubble column for high degree of oxidation.The axial concentration of unsaturated sulfur compoundsalong a multi-stage bubble column can be calculated from the backmixing model and the kinetic equationof oxidation.Results of calculation agree with the data taken along the column height.Equation was alsodeveloped to calculate the optimum temperatures of oxidation which agree favorably with the experimentalresults.     

多层气提式气、液、固三相反应器的研究

本文发展了多层气提式气、液、固三相反应器。研究了它的溢流管的稳定性,测定了液泛速度,并建立了一个计算液泛速度的经验方程式。 在连续流动的多层气提式反应器中进行了氨性溶液浸取氧化铜矿及碳酸化浸取钢渣提钒的试验。在间歇实验的基础上可以利用CSTR模型模拟连续流动的实验结果。 这种装置已成功地应用于工业性生产试验的设备上。     

多层筛板并流鼓泡塔中液体轴向混合的研究

本文检验了级内完全混合-级间有返混的模型对于多层筛板鼓泡塔中液体轴合混合的适用性。在空气-水系统中,用示踪剂研究了级间返混系数与设备参数、操作参数间的关系,对返混机理进行了考察,得到了返混系数与主要设备参数、操作参数间的关系式。实验中发现,气体分布板附近四层的返混系数受到气体分布板即端效应的影响。因此只有第四层以上的返混系数才逐层相等。     

多层鼓泡塔中液体轴向混合的研究

本文分两部分,在第Ⅰ部分中以实验验证了级内完全混合——级间有返混模型用于多层鼓泡塔的适用性。在空气-水系统中,用稳态示踪方法分别测定各级间的返混系数。从统计力学的观点,将本文及西胁昭雄在大孔径、大开孔率范围的实验结果进行了统一关联,得到一较普遍的关系式。第Ⅱ部分研究了碳酸镍铵溶液中不饱和硫化物在鼓泡塔中的氧化行为,应用返混模型及氧化速度方程,对塔内轴向不饱和硫浓度分布进行了计算,与实验结果比较,两者能基本相符。解析求出了塔内最佳氧化温度,也能与实验结果符合。