Effects of Height to Diameter Ratio and Aeration rate on Liquid Mixing and Hydrodynamic Properties in a Bubble Column
Experimental measurements of overall gas holdup (eg), residence time distribution (RTD) and liquid mixing time (tm) have been carried out in an air-water system in a 17 lit bubble column with an 11 cm diameter, over a wide range of superficial gas velocity (0.14-1.46 ms -1 ) and height to diameter ratio (1.36-8.84). The bed expansion method was used to obtain holdup values and the change of slope related to eg versus superficial gas velocity (Usg) indicated the transition point from homogeneous to heterogeneous regime at Usg= 0.7-0.9 ms -1 . Besides, the experiments illustrated that H/D ratio had no effect on holdup values. The axial dispersion model was used with semi-closed boundary conditions for prediction of RTD, and hence, the axial dispersion coefficients (Dax). Moreover, fitting results of the model and experimental RTD curves achieved from tracer injection method attained the model parameter, Dax , in three H/D ratios of 4.73, 6.36 and 8.84. Results showed that an elevation in H/D ratio, caused a rise in Dax. On the other hand, the mixing time data declined with an increase in Usg; however enhancement of H/D ratio caused an increase in tm.
SIMULATION OF LIQUID-GAS FOR CPO-METHANOL MIXING PROCESS IN BUBBLE COLUMN REACTOR
The computational fluid dynamics (CFD) highly concern in understanding the complexity hydrodynamics of bubble column. Research on superheated methanol very important in investigate influence towards biodiesel production. The aim of simulation is to find the effect of various size of holes distribution and velocities superheated methanol towards crude palm oil (CPO) in bubble column reactor to predict the effect towards reaction rate between this materials. Superheated methanol gas was dispersed through bubble column reactor contains liquid crude palm oil. This process occurs at atmospheric pressure and temperature of 290°C. This analysis used ANSYS FLUENT fluid flow to simulate and compute the mathematical problem. According to the result from turbulent transient analysis of Volume of Fluid model (VOF), the value contact surface area and gas holdup is highly indicated at model C which is this model provide an open area ratio A=4.76% and at 6 m/s of velocity. Thus, even the percentage of an open area ratio was higher than others model, but with systematic arrangement of distance holes distribution, it will evade the bubble coalescence further increase the value of contact surface area and gas holdup. However, the investigated result also show that the maximum value of turbulent dissipation rate was indicated at model B compare with others model which is indicate higher contact time between methanol and oil. Further research with variety of parameters and others method is capable in detail prediction of superheated methanol hydrodynamics behaviour.
Refinement of crystal structure parameters using convergent‐beam electron diffraction: the low‐temperature phase of SrTiO3
The method to refine crystal structure parameters (atom positions and Debye–Waller factors) using convergent-beam electron diffraction (CBED), which is applicable to crystal structure analysis of a small specimen area down to a few nm in diameter, is studied. The line profiles of higher-order Laue-zone reflections are recorded using imaging plates. Theoretical intensities are calculated based on the dynamical theory of electron diffraction with the aid of the generalized Bethe approximation to shorten calculation time. The structural parameters are determined by fitting the experimental profiles with the theoretical ones using a nonlinear least-squares method. The present method has been applied to the low-temperature phase of SrTiO3. The structural parameter or the rotation angle of the oxygen octahedron has been determined to be \varphi = 1.12 (4)°, which shows good agreement with that obtained from electron spin resonance experiments.