Effect of Axial Agitator Configuration (Up-Pumping, Down-Pumping, Reverse Rotation) on Flow Patterns Generated in Stirred Vessels

Single phase turbulent flow in a tank stirred with two different axial impellers - a pitched blade turbine (PBT) and a Mixel TT (MTT)- has been studied using Laser Doppler Velocimetry. The effect of the agitator configuration, i.e. up-pumping, down-pumping and reverse rotation, on the turbulent flow field, as well as power, circulation and pumping numbers has been investigated. An agitation index for each configuration was also determined. In the down-pumping mode, the impellers induced one circulation loop and the upper part of the tank was poorly mixed. When up-pumping, two circulation loops are formed, the second in the upper vessel. The PBT pumping upwards was observed to have a lower flow number and to consume more power than when down-pumping, however the agitation index and circulation efficiencies were notably higher. The MTT has been shown to circulate liquid more efficiently in the up-pumping configuration than in the other two modes. Only small effects of the MTT configuration on the power number, flow number and pumping effectiveness have been observed

Study on Parallel Computation and Load Balance Strategy Based on Multiblock Structured Grid

从并行计算流体力学程序的稳定性和效率两大问题入手,针对多块结构网格的通用数据传输方法和基于遗传优化算法的负载平衡方法,并在已有串行多块结构网格程序基础上发展了相应的并行程序。该并行程序以物理区域分割为基础,采用MPI实现消息传递,适用于各种不同的并行机体系结构,具有很好的可移植性。大量数值实验证明,本文发展的并行程序具有良好的稳定性和并行效率,可以进一步应用于大规模实际工程计算

Gas-liquid mass transfer : a comparison of down-and up-pumping axial flow impellers with radial impellers

The performance of a down- and up-pumping pitched blade turbine and A315 for gas-liquid dispersion and mass transfer was evaluated and then compared with that of Rushton and Scaba turbines in a small laboratory scale vessel. The results show that when the axial flow impellers are operated in the up-pumping mode, the overall performance is largely improved compared with the down-pumping configuration. Compared with the radial turbines, the up-pumping A315 has a high gas handling capacity, equivalent to the Scaba turbine and is economically much more efficient in terms of mass transfer than both turbines. On the other hand, the uppumping pitched blade turbine is not as well adapted to such applications. Finally, the axial flow impellers in the down-pumping mode have the lowest performance of all the impellers studied, although the A315 is preferred of the pitched blade turbine

Short Term Effects of Hurricane Irma on the Phytoplankton of Lake Louise, Georgia, USA

Natural disturbances such as fires and severe storms can have profound impacts on the hydrology and ecology of inland waters, potentially altering the structure and function of the ecosystem for extended periods of time. Studies of the initial impacts are, however, uncommon. Here we report on the short-term impacts of Hurricane Irma in the structure of the phytoplankton association in Lake Louise, a small blackwater lake in southern Georgia. Irma hit the region on September 11, 2017, with tropical storm force winds. The event corresponded to a period during which we were conducting routine weekly monitoring of environmental conditions in the lake. Parameters monitored included temperature, dissolved oxygen, conductivity, and light from the surface to a depth of 6 m. Chlorophyll concentrations and the structure of the phytoplankton were also determined at 1 m intervals from the surface to a depth of 5 m. An increase in the overall abundance of phytoplankton in the upper meter of the lake and a decrease in the abundance of phytoplankton deeper in the water column were observed immediately after Hurricane Irma. These decreases were followed by a bloom involving several species of cyanobacteria beginning about four weeks after the passage of the hurricane. Signatures of the passage of the hurricane were erased in early December as cooler temperatures created isothermal conditions in the lake

Agitation strategies for the culture and detachment of human mesenchymal stem cells (hMSCs) from microcarriers in multiple bioreactor platforms

Unlike cell culture for biopharmaceuticals, where the product of interest is usually a recombinant protein, for regenerative medicine, the cells form the basis of the therapeutic. For the expansion of cells for allogeneic purposes, work, mainly in spinner flasks, has led to culture on microcarriers. For processes involving mass transfer and reaction with particles in stirred reactors (e.g., crystallization, catalytic reaction), it is essential that particles are at least just fully suspended, agitator speed NJS, for effective mass transfer to and from the particles. Though gentle agitation has generally been recommended, it has not previously been defined in such a precise way as the minimum effective agitation intensity for cell culture on microcarriers where transfer of nutrients to and metabolites from them is essential. This criterion has been applied here for four sizes of stirred bioreactor (15 mL ambrTM (Sartorius Stedim), 125 mL spinner flask, 250 mL DASGIP (Eppendorf) and 5 L Sartorius Stedim). If the agitation intensity at NJS for the particular bioreactor adversely affects the quality and quantity of the cells, then that configuration is inappropriate for cell culture. In addition, it is critical that the stem cells are successfully detached and separated from the microcarriers in a manner that again does not adversely affect cell quality or the quantity. Indeed, effective cell recovery will reduce overall cost of goods by increasing process efficiency and enabling process intensification. However, surprisingly, few published studies have harvested greater than millilitre samples of the microcarrier culture, typically by enzymatic digestion aided by extensional flow using a pipette. At larger scales, such an approach becomes impractical and in addition, the enzymes can also damage the cells if exposure is prolonged. Thus, a new method is required. Given the sensitivity of particles of the size of microcarriers to abrasion (or if crystals, to secondary nucleation), it was decided to try a short period of intense agitation at agitator speeds significantly greater than NJS to enhances the removal of the cells by the action of the enzyme. This presentation outlines our work using NJS for cell culture in the four different bioreactors and the new technique for detaching cells in-situ in the three smallest. In total, cells from four donors were used with two microcarrier with and without surface coatings (two types), four enzymes and three growth media (with and without serum), a total of 22 different combinations. Stresses on cells on microcarriers may come from turbulence and from microcarrier impacts with themselves and with impellers. For turbulence, it has generally been considered that if the Kolmogorov scale of turbulence, lK is greater than ~ 60% of the size of the microcarrier (dmicro = ~200 mm), damage to attached cells should not occur. For the stresses from impacts, they increase very dramatically with increases in agitator speed, N (µ N~4). The latter concept led to the use of an enhanced agitator speed (~ 2 to 5NJS) being used during enzymic detachment for 7 minutes. Once detached, the cells were smaller than lK and thus cells should not be damaged. To suspend cells in the rectangular ambrTM required a high NJS which led to lK = ~ 0.25dmicro, much smaller than has generally been accepted can be used without impacting process performance. Yet the cells grew well and maintained the desired quality attributes. With the spinner flask, lK = ~ 0.6dmicro but the growth was similar and again the quality attributes were maintained. The results were essentially the same in both the DASGIP and Sartorius bioreactors though lK = ~ 0.3dmicro. After detachment, cells were separated from the microcarriers by filtration and in each case, \u3e 95% cells were recovered regardless of the bioreactor, the detachment enzyme, the microcarrier or the donor. In addition, the cells always met the desired quality attributes and were able to proliferate. These criteria for culture and detachment, well grounded in agitation theory seem a promising approach to scale up; and for comparing the effectiveness of different bioreactors. The relatively high agitation intensities at NJS leading to lK values much smaller than generally accepted as appropriate for cell culture is rather notable. That finding along with the new detachment technique may also interest manufacturers using microcarrier culture with other animal cells such as CHO for vaccines

Testing hypotheses of the cause of peripheral thinning of the Greenland Ice Sheet: is land-terminating ice thinning at anomalously high rates?

Recent observations have shown that the periphery of the Greenland ice sheet (GrIS) is thinning rapidly and that this thinning is greatest around marine-terminating outlet glaciers. Several theories have been proposed which provide a link between climate and ice thinning. We present surface elevation change (<i>dh/dt</i>) data from NASA's Program for Arctic Regional Climate Assessment (PARCA) laser altimetry surveys for fourteen and eleven of the largest outlet glaciers in Southern Greenland from 1993 to 1998 and 1998 to 2006 respectively to test the applicability of these theories to the GrIS. <br><br> Initially, outlet glacier <i>dh/dt</i> data are compared with data from concurrent surveys over inland ice (slow flowing ice that is not obviously draining into an outlet glacier) to confirm the effect of ice flow on surface thinning rates. Land-terminating and marine-terminating outlet glacier <i>dh/dt</i> data are then compared from 1993 to 1998 and from 1998 to 2006. Finally, ablation anomalies (the difference between the "normal" ablation rate from 1970 to 2000 and the ablation rate in the time period of interest) calculated with a positive degree day model are compared to both marine-terminating and land-terminating outlet glacier <i>dh/dt</i> data. <br><br> Our results support earlier conclusions that certain marine-terminating outlet glaciers have thinned much more than land-terminating outlet glaciers during both time periods. Furthermore we show that these differences are not limited to the largest, fastest-flowing outlet glaciers – almost all marine-terminating outlet glaciers are thinning more than land-terminating outlet glaciers. There was a four fold increase in mean marine-terminating outlet glacier thinning rates below 1000 m elevation between the periods 1993 to 1998 and 1998 to 2006, while thinning rates of land-terminating outlet glaciers remained statistically unchanged. This suggests that a change in a controlling mechanism specific to the thinning rates of marine-terminating outlet glaciers occurred in the late 1990s and that this change did not affect thinning rates of land-terminating outlet glaciers. <br><br> Thinning rates of land-terminating outlet glaciers are statistically the same as ablation anomalies, while thinning rates of marine-terminating outlet glaciers are not. Thinning of land-terminating outlet glaciers therefore seems to be a response to changes in local mass balance (principally increases in air temperature) while thinning of marine-terminating outlet glaciers is principally controlled by ice dynamics. The mechanism by which this dynamic thinning occurs is still not clear although its association with marine-terminating outlet glaciers suggests perturbations at marine termini (calving) as the likely cause

Testing an Algae-Based Air-Regeneration System

The potential of an air-regeneration system based on the growth of unicellular algae on the surface of porous ceramic tubes was evaluated. The system is fairly robust with respect to environmental conditions and is capable of maintaining algal cultures for up to 365 days. Under standard conditions (50-66 micro mol/sq mm s (PPF), 450 micro mol mol of CO2), mature tubes can remove CO2 at a rate of up to 90 micro mol/sq m min. Under these conditions, approximately 200 square meters of area would be required for each member of the crew. However, the rate of uptake increases with both photon flux and CO2 concentration in accordance with Michaelis-Menton dynamics. An extrapolation to conditions of saturating light and carbon dioxide indicates that the area required can be reduced by a factor of at least 2.5

Subglacial drainage processes at a High Arctic polythermal valley glacier

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