反應釜外文翻譯---氣體誘導渦輪攪拌的攪拌反應釜中的二相流的研究

1、附錄 B：英文原文及翻譯A study on the two-phase flow in a stirred tank reactor agitated by a gas- inducing turbineabstractExperimental and numerical studies of a gas–liquid two-phase flow have been applied to a non-baffled laborat

2、ory-scale stirred tank reactor, mechanically agitated by a gas-inducing turbine. The dispersion of air as gas phase into isopropanol as liquid phase at room temperature under different stirrer speeds was investigated.

3、The X-ray cone beam computed tomography (CBCT) measurements have been taken at five different stirrer speeds starting from 1000 rpm at which the gas inducement occurs for the given operating conditions.The considerabl

4、e difficulties in acquiring the phase distribution due to beam hardening and radiation scattering effects have been overcome by developing a suitable measurement setup as well as by calibration and software correction

5、methods to achieve high accuracy. The computational fluid dynamics analyses of the stirred tank reactor have been performed in 3D with CFX 10.0 numerical software. The simplified numerical setup of mono-dispersed bubb

6、les, constant drag coefficient and the k–e turbulence model was able to capture both the bubble induction and dispersion and the free surface vortex formation. Despite the assumed simplifications, the numerical predict

7、ions exhibit a good agreement with the experimental data.Keywords:Stirred tank reactor; Gas-inducing impeller; CFD; X-ray computed tomography Mixing. 1. IntroductionGas–liquid mixing in stirred tank reactors is a commo

8、n process in the industry. It is regarded as one of the most difficult to tackle because of its complexities in terms of flow regimes and multiphase operations. Traditionally, the gas–liquid stirred tank reactor is eq

9、uipped with an impeller responsible for dispersing the gas phase, which is usually supplied via a single pipe or a ring sparger mounted beneath the impeller. The gas-inducing impellers provide an alternative gas inject

10、ion, in which case the gas is sucked via a hollow shaft and fed directly into the stirrer region (Evans et al., 1990). More gas bubbles can be broken-up into small ones when such configuration is applied, which consequ

11、ently could provide higher mass transfer (Rigby and Evans, 1998). Among the long lasting efforts to establish precise but practical measurement techniques for the analysis of multiphase fluid dynamic processes in chem

12、ical reactors (Boyer et al., 2002), methods based on ionising radiation are most promising since they are applicable at higher gas fractions,and they give linear measurements regardless of the structure complexity insi

13、de the vessel. An advanced tomographic technique is cone beam X-ray computed tomography (CBCT). With CBCT, a volume density distribution is reconstructed from a set of two-dimensional radiographs obtained from an obje

14、ct at different projection angles. This technique is especially suitable for time-integrated gas fraction measurements.The use of X-ray CT for gas hold-up measurements has been described by Pike et al. (1965), and rece

15、ntly by Hervieu et al. (2002), with application to two- phase flow in a pipe, by Kantzas and Kalogerakis (1996), who monitored the fluidisation characteristics of a fluidised bed reactor, by Reinicke et al.(1998), and T

16、oye et al. (1998), who used it in packed catalyst beds, and by Vinegar and Wellington(1987),who measured fluid transport in porous media. All the above-mentioned techniques yield time-averaged rather than instantaneou

17、s phase distribution images. Rotationally symmetric material distributions such as the phase distribution in an un-baffled reactor enables even a rather fast tomography, since one radiographic projection is sufficient

18、to compute a complete axial and radial gas hold Fig. 1 – Schematic view of the CBCT setup.The model fluid used was isopropanol at normal pressure and room temperature. The critical stirrer speed at which gas dispersion

19、at the stirrer blades occurs was estimated by optical observation to be of 1020 rpm. Then, the stirrer was successively driven with speeds in the range of 1000–1200 rpm at 50 rpm intervals. For each operation point, a

20、CBCT scan was performed. 2.3. Scattering correctionIn an additional measurement, a moving slit technique (Jaffe and Webster, 1975) was applied to synthesise an almost scattering free radiographic image of the reactor a

21、t moderate stirrer speed well below its critical value. The difference between such an image and an un- collimated cone beam Xray radiography of the same arrangement gives a measured value for the amount of scattered r

22、adiation intensity distribution in the detector plane. Subsequently acquired X-ray intensity distributions have been reduced by that amount to eliminate the contribution of scattered radiation which otherwise would ult

23、imately lead to quantitative errors in the reconstruction process. This approach is reasonable,since by dispersing little amount of gas into the fluid, the overall mass of the object is conserved and there are only sl

24、ight changes in the material distribution and thus only slight changes in the amount of scattered radiation are expected. 2.4. Beam hardening correction Polyenergetic X-ray radiation would be hardened when penetrating t

25、hick materials, as the effective attenuation coefficient becomes smaller with increasing penetration depth. If uncorrected, this leads to systematic errors in quantitative X-ray measurements. The adopted method for be

26、am hardening correction can be illustrated with the experimental setup presented in Fig. 1. Two radiograms, one of the reactors completely filled with the fluid and another for the same arrangement plus an additional a

27、crylic plate of thickness d = 0.01 m between reactor vessel and the detector were taken. Both images were synthesised from a series of slit images according to the method described above, and thus are assumed to be alm

28、ost free of scattered radiation. From both images, the calibration extinction radiogram E c (r S , r D ) can be computed according to the following equation(1)D SplateD S effD SD SplateD S cdr r lr r l r r E,, , 00cos

29、) , () , ( ln ) , ( ? ? ??? ? ? ?? ?where I denotes the measured intensities, is the effective attenuation coefficient of the plateD S eff , , ?acrylic plate according to a certain ray path between source and detector p

30、osition r S , r D , and is the angle between the ray and the detector normal. The indexes S and D stand for D S, ?source and detector respectively. After that, the plate is removed. Now any image taken from the reacto