非标准釜中双层桨的搅拌功率和气含率

在装有单层或双层蛇管换热器的搅拌釜中，分别以六直叶圆盘涡轮（ＤＴ）、四叶（４５°）折叶桨（４ＩＢＴ）或六叶（４５°）折叶桨（６ＩＢＴ）为上层桨，ＤＴ为下层桨，测定了不同双层桨的搅拌功率和气含率。结果表明，搅拌功率随蛇管层数、液位高度和桨间距的增加而增大，但气含率随液位的上升而下降。在装有双层蛇管换热器的搅拌釜中，ＤＴ与６ＩＢＴ双层桨的通气搅拌功率Ｐａ和气含率α的关联式为Ｐａ＝２．４９（Ｐ０２ＮＤ３／ＱＧ（０．５６））（０．３７）及α＝０．０２９Ｐ＿ｖ￣（０．４８）ｕ＿ｓ￣（０．４７）。     

通气式搅拌釜功率消耗的探讨

评估了通气式搅拌釜较有代表性的搅拌功耗关联式，指出大气穴形成之前，气体再循环将导致关系联式预测值偏离实际值４０％以上。用气体再循环系数对关联式进行修正，可得到适用于装有涡轮搅拌器的低粘体系的新的搅拌功耗关联式：当Ｇ≤２．５４时，Ｐｇ／Ｐ０＝０．７１Ｇ－０．８０；当Ｇ〉２．５４时，Ｐｇ／Ｐ０＝１．０；式中，Ｇ＝（Ｎｐ０／Ｎｐ０＾＊）＾０．６（ｄ／Ｄ）＾０．１５Ｆｒ＾０．０５［（１＋α）Ｎｑ］＾－０．     

刮壁搅拌桨在槽式釜中的功率损耗

研究了浮动式刮壁桨在槽式釜中流体的粘度，刮壁材料，刮板端角，刮板厚度以及搅拌雷诺数，刮板宽度，刮壁角度，刮壁高度对搅拌功率损耗的影响，发现：搅拌雷诺数，刮板宽度，刮壁高度和刮壁角对搅拌功耗有明显的影响，在一定条件下其他因素则对功耗的影响很小，得到刮壁功耗的经验关联式为Ｎｐ＝（１５６２／Ｒｅ＾０．９７７）（Ｗ／Ｄ）ｃｏｓα）＾０．３５３（ｎＬ／Ｄ），式中Ｒｅ=１～３００。     

生产羧基丁苯胶乳聚合釜的放大规律

根据羧基丁苯胶乳合成工艺的特点，乳液均成核机理和低皂聚合原理，拟定了聚合釜的放大规律应遵循的依据。通过冷模试验和工业性试验，推荐聚合釜适宜的搅拌器为改进四叶斜桨和四叶斜桨；回归试验数据得到改进四叶斜桨搅拌功能Ｎｐ＝２．７９（ＨＬ／Ｄ）｛（ｄ／Ｄ）＾－１４（ｂ２／Ｄ）＾０．８３－」（ｄ２－ｂ１）／Ｄ「＾－１４「（ｂ２－ｂ１）／Ｄ」＾０．８３×「（３－２ｂ１）／ｄ」＾５｝聚合釜。     

卧式双轴T型搅拌器在非牛顿流体中的搅拌功率特性

考察了卧式双轴Ｔ型搅拌在非牛顿流体中的搅拌功率与表观雷诺数（Ｒｅ＾＊）、弗劳德数（Ｆｒ）以及加料量的变化关系,实验结果表明：Ｍｅｔｚｎｅｒ常数Ｋｓ随加料量的减少而急剧增加;在层流区域,Ｎｐ．Ｒｅ＝Ｋｐ关系仍然成立且非牛顿流体功率曲线与牛顿流体重合。对实验数据进行关联得到了非牛顿流体搅拌功率准数关联式。     

气—液—固三相搅拦槽中液相氧传递性能的研究

在机械搅拌槽中使用翼形轴流桨（Ｋ４）、圆盘涡轮桨（ＤＴ）、６叶４５°斜叶桨（６ＰＴＤ、６ＰＴＵ）（排出流向下，向上）对低粘度三相体系的液相氧传递性能与悬浮液浓度、通气水平及搅拌功率之间的变化规律作了实验研究。实验得出：Ｋ１ａ∝（Ｐｇ／Ｖ）ｋ；当悬浮液浓度没有使液相表观粘性产生明显改变时，颗粒的存在、通气量的提高都有助于Ｋ１ａ的提高。翼形桨由于较好的轴向分散及混合性能，在相同的搅拌功率输入下，Ｋ１ａ保持较高的水平。     

制备γ—LiAlO2陶瓷芯块的工艺参数研究

本采用冷压－烧结工艺研究了γ－ＬｉＡｌＯ２陶瓷芯块密度ρ（克／厘米＾３）与压制压力Ｐ（ＭＰａ），烧结温度Ｔ（℃）烧结时间（小时）和添加剂量Ｍ（克ＰＶＡ／克干粉）等工艺参数之间的关系，由实验结果，可归纳出如下关系式：ρ＝２．５×１０＾－３Ｐ＾０．１９Ｔ＾０．７５ｔ＾０．０３３Ｍ＾－０．０５（Ｍ＞０），此式可作为制备γ－ＬｉＡｌＯ２陶瓷芯块的工艺依据。     

气固两相流量测量模型的研究：气力输送流动特性的实验探讨

通过对稀相气力输送粉料压损比与混和比比例关系式（ΔＰｔ／ΔＰｇ＝１＋Ｋｍ）中比例系数Ｋ的实验研究，获得了关于Ｋ的经验公式：Ｋ＝１／λｇ（２．５２７９／Ｆｒ＾１．５１８３）。建立了基于此比例关系式－速度法粉料流量测量模型｛ｍｓ＝ｋｃπ／２Ｄ＾３（ΔＰｔ－λｇＬ／ＤρｇＶｇ＾２／２）λｇ＝０．３１６４／Ｒｅ＾０．２５（Ｒｅ〉２３２０）κｃ：校正因子实验验证相应的粉料流量检测系统的测量精度为５％，满足工     

KTa0.55Nb0.45O3薄膜的介电和铁电及热释电性能研究

在ＢＴ／Ｐｔ／Ｔｉ／ＳｉＯ２／Ｓｉ衬底上用溶胶－凝胶法制备了ＫＴａ０．５５Ｎｂ０．４５Ｏ３（ＫＴＮ）薄膜,０．５μｍＫＴＮ－０．０８μｍＢＴ薄膜在２５℃,１．０ｋＨｚ时,其εｒ＝１１１４,ｔａｎδ＝２．５％;１２℃时,其中Ｐｒ＝２．１μＣ／ｃｍ＾２,Ｐｓ＝４．２μｃ／ｃｍ＾２,Ｅｃ＝５．８ｋＶ／ｃｍ,０．５μｍ厚ＫＴＮ膜的Ｃｕｒｉｅ温度为３５℃;１．０ＫＨｚ时,ＫＴＮ膜的εｒ＝１４１２,估算ＫＴＮ     

极谱法测定冷却水中的乙二胺四甲叉膦酸钠

在６．８×１０＾－４ｍｏｌ．Ｌ柠檬酸钠，醋酸－醋酸钠缓冲溶液（ｐＨ＝５．２＋中，Ｃｕ＾２＋可与乙二胺四甲叉膦酸钠（ＥＤＴＭＰＳ）络合，使铜峰降低，峰电位Ｅｐ＝－０．２４Ｖ（银－氯化银电极）。乙二胺四甲叉膦酸钠浓度在３－５０ｍｇ／Ｌ范围内与峰高降低值呈线性关系。采用ＪＰ３－１型示波极谱仪，二次微分，起始电位０．００Ｖ，终止电位－１．２０Ｖ测定，检出银为１ｍｇ／Ｌ，变异系数为３．２％－６．０％，回收率     

Gas-liquid flow through coils

Experimental investigations have been carried out to evaluate the two-phase pressure drop and the holdup for flow through helical coils. The coils were made of thick wall transparent PVC tube of diameter 0.01 m and 0.013 m. 24 coils were made at different coil diameter and different helix angles (0° to 12°). Three different liquids were used for the experimental studies and air was the gas. Empirical correlations have been developed to predict the two-phase friction factor and the liquid holdup as functions of the physical and dynamic variables of the system. Statistical analyses of the correlations suggest that they are of acceptable accuracy.     

Power Consumption in Gas‐Liquid Contactors Agitated by Double‐Stage Rushton Turbines

The dependence of power consumption on impeller spacing in unaerated and aerated gas‐liquid contactors agitated by dual Rushton turbine systems was studied, and the gas flow rate and viscosity effects were measured in relation to these parameters. The experiments were carried out in a 0.19 m i.d. vessel stirred by two Rushton turbines with a diameter d = 0.10 m; with blade length and blade height 0.25 d and 0.2 d, respectively. In tap water the impellers acted independently for spacings greater than 1.65 d, while in glycerol solutions the two impellers already acted independently at an impeller spacing equal to 1.2 d. In aerated systems, a notable increase in the power consumption with increasing impeller spacing could be detected for small gas flow rates and low viscosities, while a decrease in the Newton number with increasing Froude number could be observed at constant impeller spacing. The Newton number was not affected by flow number at high viscosity values.     

Mixing in multiple-impeller stirred tank reactors with boiling liquids

Mixing in a boil-off mechanically stirred tank reactor with multiple impellers was examined. Power consumption and gas hold-up were measured in boiling water in a 0.2 m i.d. stirred tank reactor with three four-pitched blade downflow disk turbines. Vapour was generated from both the immersed ring heater and the impellers. At low vapour generation rates, vapour was mainly generated from the impellers rather than from the heater, whereas nucleation occurred at the heater instead of the impeller at higher vapour generation rates. The mechanical power consumption decreased due to vapour generation. The change in boiling-to-non-boiling mechanical power ratio with varying impeller rotational speed and boiling rate was complicated and not monotonous except at higher impeller speeds and boiling rates. The gas hold-ups increased with increasing vapour generation rate but were rather small as compared to those in cold gas dispersing systems. Empirical correlations for power consumption and gas hold-up in boiling liquids were developed using the present experimental data.     

LIQUID PHASE MIXING IN MECHANICALLY AGITATED VESSELS

Liquid phase mixing and power consumption have been studied in 0.3, 0.57, 1.0 and 1.5 m i.d. mechanically agitated contactors. Tap water was used as liquid phase. The impeller speed was varied in the range 2-13.33 r/s. Three types of impellers namely disc turbine (DT), pitched turbine downflow (PTD) and pitched turbine upflow (PTU) were employed. The impeller diameter to vessel diameter ratio was varied in the range of 0.25 to 0.58. The effect of impeller clearance from tank bottom was also studied. Mixing time was measured using the transient conductivity measurement.

The PTD impeller was found to be the most energy efficient for mixing in liquid phase alone. Further, PTD (T/3) was found to be most energy efficient as compared with other impeller diameters. The effect of clearance was found to be design dependent and it was found to be diameter dependent in the case of pitched turbines.

Flow patterns of different impellers have been studied by visual observations (using guide particles). These observations were supported by the measurements using Laser Doppler Velocimetry. A model has been developed for the prediction of mixing time. In the case of all the three impeller designs, a fairly good agreement was found between the predicted and experimental values of mixing time.     

A comparison of cavern development in mixing a yield stress fluid by rushton and intermig impellers

Intermig impellers have been postulated as very efficient for mixing highly viscous non-Newtonian fluids (such as xanthan and mycelial broths). However, no formal characterisation has been published and no fair comparisons have been made, based on accurate power drawn measurements and using equal number of impeller stages and equal diameter, if compared (for example) with the performance of Rushton turbines. Characterisation of the shape, size, and evolution of the well-mixed zones or “caverns” were correlated with power drawn, for single and dual Rushton turbines and for one- as well as two-stage Intermig unslotted impellers. Cavern evolution studies were carried out in a mixing tank (diameter=0.205 m, H/T=1.6) equipped with an accurate air bearing dynamometer. Carbopol 940 (0.25 wt.-%) was used as a model, transparent fluid. Impeller to tank diameter ratio was 0.53 for both impellers. Caverns were visualised by injecting methylene blue in the well-mixed zones. A single Rushton turbine developed larger caverns if compared with one-stage Intermig of the same diameter under power drawn below 1.5 kW m^?3. At higher power drawn, both impellers behaved very similarly, reaching a limit in cavern volume of about 40% of the total liquid volume, even at very high (20 kW m⁰³) power drawn. A similar trend characterised dual combinations: below 3 kW m^?3, dual Rushtons gave larger cavern volume if compared with the performance of two-stage Intermigs. In either case, power drawn higher than 3 kW m⁰³ was sufficient to mix more than 90% of the liquid volume. The presence or absence of the slot in the Intermig did not influence cavern development. Experiments with a smaller if compared with those obtained with the larger Intermig (D/T = 0.53).     

Mixing characteristics and gas hold-up of a bubble column

The hydrodynamic behavior of a bubble column has been studied for various Newtonian and non-Newtonian liquids (water, glycerol, carboxymethylcellulose and polyacrylamide solutions). The mixing time, the power consumption, the circulation time and the gas hold-up have been measured in a cylindrical column (diameter: 0.254 m, height: 0.9 m) for three air sparger plates with different numbers and distributions of 1 mm diameter orifices. It is shown that the mixing efficiency decreases as the viscosity or the shear-thinning and elastic properties of the liquid increase. The viscosity of the liquid has little influence on the gas hold-up which is, however, strongly affected by the sparger plate characteristics and increases as the liquid phase becomes more elastic. A model for predicting gas hold-up is proposed.     

Studies in multiple impeller agitated gas-liquid contactors

Experiments have been performed to study the effect of the density and the volume of the tracer pulse on the mixing time for two impeller combinations in the presence of gas in a 0.3 m diameter and 1 m tall cylindrical acrylic vessel. The tall multi-impeller aerobic fermenters, which require periodic dosing of nutrients that are in the form of aqueous solution, is a classic case under consideration. Conductivity measuring method was used to measure the mixing time. Two triple impeller combinations; one containing two pitched blade downflow turbines as upper impellers and disc turbine as the lowermost impeller (2 PBTD-DT) and another containing all pitched blade downflow turbines (3 PBTD) have been used. Other variables covered during experiments were the density and the amount of the tracer pulse, the impeller rotational speed and the gas superficial velocity. Fractional gas hold-up, Power consumption and mass transfer coefficient have also been measured for both the impeller combinations. Influence of aeration and impeller speed on the mixing time has been explained by the interaction of air induced and impeller generated liquid flows. Three different flow regimes have been distinguished to explain the hydrodynamics of the overall vessel (i.e., multiple impeller system). A compartment model with the number of compartments varying with the flow regimes have been used to model liquid phase mixing in these flow regimes. A correlation for the prediction of the dimensionless mixing time in the loading regime has been proposed in order to account the effect of the density and the amount of the tracer pulse on the mixing time. Correlations have also been proposed to predict fractional gas hold-up and k_La.     

POWER CONSUMPTION IN MECHANICALLY AGITATED CONTACTORS USING PITCHED BLADED TURBINE IMPELLERS

Power consumption was measured in mechanically agitated contactors of internal diameter 0.3 m, 0.57 m, 1.0 m and 1.5 m. Tap water was used as a liquid in all the experiments. The impeller speed was varied in the range of 0.3-13.33 r/s. Three types of impellers, namely disc turbine (DT), pitched-blade downflow turbine (PTD) and pitched blade upflow turbine (PTU) were employed. The ratio of the impeller diameter to vessel diameter (D/T) and the ratio of impeller blade width to impeller diameter (W/D) were varied over a wide range. The effects of impeller clearance from the tank bottom (C), blade angle (φ), total liquid height (H/T), number of impeller blades (n_b) and blade thickness (t_b) were studied in detail. Power consumption was measured using a torque table

Power number was found to have a strong dependence on the flow pattern generated by the impeller. Unlike, DT and PTU, the power number of PTD was found to increase with a decrease in clearance. The PTD (T/3) was found to have the lowest power number in all the vessels and the power number increased with either a decrease or an increase in the impeller diameter from T/3. The dependence of power number on impeller diameter was found to be more prominent when the D/T ratio was more than 0.3. In general, the power number was found to increase with an increase in blade angle and blade width. The effect of blade width was found to be more prominent in larger diameter vessels. A correlation has been developed for power number in the case of PTD impellers.     

Effect of Dual Impeller‐Sparger Geometry on the Hydrodynamics and Mass Transfer in Stirred Vessels

The understanding of the effect of impeller‐sparger configurations on gas dispersion and mass transfer is very important to improve the performance of gas/liquid contactor systems. The influence of the impeller positions, the upper turbine diameter, the sparger ring diameter and its location in regard to the lower impeller on the power consumption, the volumetric mass‐transfer coefficient and the overall oxygen transfer efficiency were studied in a nonstandard curved bottomed reactor with an agitated system with dual disk style turbines. In the range of the gas flow rates studied, the most efficient impeller‐sparger arrangement for the oxygen transfer is the impeller system with turbines of different diameters located at C = 0.25 and IC = 0.5, and with the sparger of smaller diameter than the lower impeller settled below the impeller. A new model to estimate the k_La with an average relative error of 8 %, which takes the reactor operation conditions and the influence of the impeller‐sparger geometry into account, was also proposed.     

Experimental and CFD investigation of power consumption in a dual Rushton turbine stirred tank

Power consumption of a mixing system is a key variable in chemical and bioprocess engineering, the determination of which is of interest of many processes. Besides, prediction of the flooding-loading transition in an aerated stirred tank is crucial for the correct design of aerated stirred tank reactors. In this research, laboratory investigation has been carried out on local and total power consumption of a single phase as well as gas-liquid phase systems in a fully baffled stirred tank equipped with dual six-blade Rushton turbines; moreover, the flow regime behavior of a gas-liquid system was investigated. Results have been compared with data obtained from CFD simulation of experimental setup and the data available in the literature. Reasonable agreement between the experimental and simulation results indicates the validity of the CFD model. Using predicted data some empirical correlations have been derived which present new relations in estimation of power consumption and flow regime transitions in stirred tanks with dual Rushton impellers.