Macro-mixing in a draft-tube airlift bioreactor

Airlift reactors are pneumatically agitated reactors that have been widely used in industries, particularly in bioprocesses. Extensive studies about the flow dynamics in airlift column reactors exist; however, most of these studies have focused on global hydrodynamic parameters using conventional techniques. The local flow characteristics, such as the macro-mixing and the turbulence intensity, are crucial for reliable design and scale-up, and they remain unclear. This work focuses on studying the macro-mixing in a draft-tube airlift bioreactor utilizing an advanced flow dynamic measurement technique, computer automated radioactive particle tracking (CARPT). True residence time distribution analyses for the overall column as well as individual regions, i.e., the riser, the downcomer, the top, and the bottom regions, are conducted for the first time based on CARPT measured particle trajectories. The effects of the superficial gas velocity and the top/bottom clearances on the macro-mixing are also discussed. The results suggest that although the flow structures in the overall draft-tube column reactor, as well as in the riser and in the downcomer, are close to plug flows, bypassing and stagnancy exist in the top and the bottom regions.     

Mechanical foam control in a stirred draft-tube bioreactor

The mechanical foam-breaking rotating disk (MFRD) was installed in a stirred draft-tube bioreactor and provided effective foam-breaking action. The device utilised the impact between atomised liquid particles projected from the disk and the ascending foam. The foam-breaking characteristics of the MFRD were investigated in relation to the air sparge rate and the impeller speed. Empirical equations were devised to describe and predict the critical foam-breaking regions of the MFRD under any operating conditions of the stirred draft-tube bioreactor.     

Spouting of two-dimensional beds with draft plates

Two slotted two-dimensional spouted bed units with flexible bed dimensions were used with draft plates to study spouting pressure drop and minimum spouting superficial velocity. The data were collected while varying slant angle, spout width, separation distance, length of bed, height of bed, and size of bed (geometrical similarity) using shelled corn, soybean, and wheat. The variables which affect the spouting pressure drop and air flow through the beds are discussed. Empirical correlations are developed following the principles of dimensional analysis and similitude. The developed correlations agree closely with the collected data.     

Spouting characteristics of small glass particles with water

Experimental data are reported for the minimum spouting velocity, bed pressure drop, maximum spoutable height and spout diameter which show that spouting of small particles with water represents a new spouting regime. The transition from large to small particle spouting occurs when the voidage at the inlet to the spout goes from unity to less than unity.     

Hydrodynamic behavior of single particles in a draft-tube bubble column

Velocities of single particles (magnetic tracer particles) were measured in the draft tube region and annular region of a draft-tube bubble columns by use of the magnet-detector coil technique. The relative particle to liquid velocity was also obtained. The observed distribution of particle velocity was broader than that of liquid velocity. The relative particle to liquid velocity depended significantly on superficial gas velocity. Those for the draft tube region had minimums with increasing gas velocity, while those for the annular region decreased monotonously. The effective drag coefficients for the particles were correlated with particle Reynolds number and gas holdup.     

Modelling batch drying of sand in a draft-tube conical spouted bed

A model has been built to predict the evolution of sand drying in a conical spouted bed with a non-porous draft tube. Three regions have been considered in the model, i.e., spout, annulus and fountain, and unsteady-state mass balances have been written for water in the solid and gaseous phases. The model has been validated by comparing its results with the experimental ones obtained in a previous study and it allows predicting the moisture content evolution of both the air and the sand during the drying process.     

Spouting characteristics of spf wood pellets

The spouting characteristics with ambient air of cylindrical wood pellets, 6.5 mm in diameter and 11.1 ± 4.1 mm long, were investigated using a transparent 152.4‐mm diameter semi‐circular cone‐based cylindrical column. Despite the previously unexplored shape of the pellets in the spouted bed mode, the measured minimum spouting velocities at different bed heights, the maximum spoutable bed height and the mean spout diameter above the conical base were all well represented by equations from the literature developed mainly for more rounded particles. Pellet attrition was found to be severe, so that the possible torrefaction of the pellets by the spouting technique without sacrifice of their integrity appears to be unlikely. © 2012 Canadian Society for Chemical Engineering     

大尺寸喷动床最低喷动速度的估算

最低喷动速度是喷动床设计的重要参数之一。过去人们习惯采用Mathur-Gisher公式来计算,但由于该公式是建立在小直径床层(D_c=0.076～0.3m)实验的基础上的,故在大直径床层上应用时,产生明显的偏差。本文通过实际数据分析,提出了大直径喷动床层最低喷动速度计算的经验公式。     

狭缝式矩型喷动床中多粒度颗粒体系的最小喷动速度

在150 mm×50 mm×1100 mm的矩形喷动床中,采用宽度为2, 4, 6 mm 的3种狭缝式气体分布板,研究了单一粒度组成和多粒度组成玻璃珠的最小喷动速度. 实验证明,矩形喷动床的最小喷动速度与物料的粒度和组成有关. 给出了最小喷动速度与颗粒粒径和粒度组成的关联式,作出了多粒度组成颗粒体系最小喷动速度的相图.     

新颖环形喷动床颗粒喷动特性实验研究

一种新颖的环形喷动床由内外两个不同内径、同心的垂立圆筒组成,在环形空间底部设置多个喷口,在喷口两侧布置倾斜的导流板.研究颗粒在这种喷动床内的流动特性,探讨喷口结构、颗粒种类以及床内载料量对环形喷动床颗粒喷动特性的影响.实验结果表明:颗粒在环形喷动床内分为三个明显不同的区域,即颗粒填充移动区、密相喷动流化区以及稀相夹带区.当颗粒出现分区喷动后,随床内载料量的增多,填充移动区的高度维持不变,始终等于导流板的高度,而密相喷动区的高度不断增加.风量和颗粒种类对床层最大喷动量、密相喷动高度以及床层压力分布规律有着十分重要的影响.采用不同的喷口结构时,在相同的载料量下,直向喷口的密相喷动区高度更大,而且床内各测点的平均压力大于采用斜向喷口时的相应测点压力.     

Hydrodynamic Characteristics of a Powder‐Particle Spouted Bed with Powder Entrained in Spouting Gas

Spouting of 3.7 mm polyvinyl chloride particles in a cone‐based cylindrical column is subjected to entrainment of FCC powder in the spouting air. It is found that the powder entrainment reduces the minimum spouting velocity, increases the bed pressure drop and reduces the maximum spoutable bed height. At any given bed height and value of U/U_ms, there is a critical value of powder loading ratio above which spouting gives way to slugging.     

一种新型的喷腾分解炉

本文在原腾分解炉的基础上,提出了一种改进方案,采用ｋ－ε－Ａｐ两相湍泫模型,对改进喷腾分解炉内气固两相流动特性进行了数值模拟。计算结果表明,采用腾分解炉加速射流改善炉内气流速度及物料浓度分布的方法是行之有效的。     

带导流管液固喷动床的最小喷动速度研究

在截面为矩形有机玻璃喷动床内，使用四种粒径的窄筛分球形玻璃珠，以常温水作为喷动和辅助液体。综合考虑床体的几何尺寸、操作参数以及液体和颗粒的物性特征，系统研究带导流管喷动床的最小喷动速度，得出最小喷动速度的经验公式，为设计和操作提供参考。     

Spouting of fine powder from vertically vibrated bed

Experimental and numerical studies of spouting of powder from vertically vibrated bed are performed. The powder flows out vigorously through a side orifice of the vertically vibrated vessel in which the powder is contained, provided that the vibration acceleration is greater than the gravitational one. The mechanism of the efflux and the relationship between the efflux rate and the vibration condition are examined. The interstitial air pressure in the bed is measured and is compared to the numerical analysis considering the relative motion of the powder bed to the vibrated vessel and percolation air flow. The outflow behavior of powder is observed by using a high-speed video camera. The experimental and the numerical results show that the powder spouts out intermittently with periodic air outflow, which is generated in response to the change of the gap between the bed and the vessel base. Furthermore, it is found that the efflux rate of powder is in proportion to the generated air pressure and in inverse proportion to the vibration frequency.     

环式喷水冷却装置的性能分析

根据传热学原理，建立了以轴向和径向变量为参数的二维喷水冷却模型，并研究了沿轴向采取不同换热系数的控制冷却技术。分析表明，环式喷水冷却装置具有较高的冷却效率和良好的冷却效果。     

Determination of Minimum Spouting Velocities in Conical Spouted Beds

Minimum spouting velocities in conical spouted beds have been obtained from pressure drops versus the superficial gas velocity curves, based on both increasing and decreasing the superficial gas velocity. It has been shown that the minimum spouting velocity from decreasing the superficial gas velocity is lower than from increasing the superficial gas velocity in most cases. This phenomenon is similar to that in conventional spouted beds and different from the early works. The experimental results also showed that there isn't significant difference in the pressure drop and U_ms under identical operating conditions between semi‐circular and circular conical spouted beds, and the same U_ms can be obtained from absolute pressure drops at any position above the gas inlet. The U_ms is found to increase with increasing the cone angle and static bed height, as well as the gas inlet diameter to a less extent.     

双喷嘴矩形喷动床中最小喷动速度的实验研究

在双喷嘴矩形喷动床内,以空气为喷动气体,研究了最小喷动速度的变化规律和影响因素。实验表明,双喷嘴矩形喷动床的最小喷动速度与颗粒粒径、床层高度及操作温度有关。并在综合考虑床层高度以及气体和固体颗粒的物性的基础上,得出了双喷嘴矩形喷动床最小喷动时雷诺数的经验关联式。     

Extraction from a solid with a bidisperse porous structure

A mathematical model is proposed for the process of extraction from a semi-infinite solid containing the pores of two types: large pores that extend to the surface and small pores that are connected to large pores. Effective transport coefficients in two types of pores are assumed to be different. The dependence of the flux of an extractant through the surface of the solid on time is found using the method of fractional differentiation. Theoretical results are compared with experimental data on the kinetics of the extraction of the target components from raw vegetable materials in apparatuses with an intensive hydrodynamic mode.