v. ghazanfari

In this work, we attempted to simulate UF6 gas flow in the rarefied and continuum areas of the rotating cylinder using CFD, DSMC, and hybrid one-way and two-way CFD-DSMC methods. In the hybrid two-way CFD-DSMC method, the effect of two rarefied and continuum areas on each other is considered. The results were verified by the DSMC method. The results presented the two-way CFD-DSMC method was useful for three goals. The first purpose was to simulate the flow in the rarefied area using the DSMC method, which was more valid than the CFD method. The second goal was to reduce the computational time of the simulation of the continuum area using the CFD method. The third goal was to investigate the effect of the rarefied solution on the continuum solution. Comparing the results with the DSMC method, it was found that the two-way CFD-DSMC method causes a difference of only 2% for the separation power, while the computational cost is reduced by 60%.

One of the driving factors for creating axial flow inside the gas centrifuge rotor to increase the separation performance is the scoop. Due to the exposure of the scoop to the high Mach gas flow, the flow will be shocked, and strong gradients will occur in the flow.  In this research, the gas flow around the scoop in a two-dimensional state (r-θ) is simulated by the Direct Simulation Monte Carlo method (DSMC) using the dsmcFoam solver at different distances of the scoop from the rotor wall. The results show that increasing the distance of the scoop from the rotor wall and decreasing the contact angle of the gas flow with the scoop reduces the maximum temperature and drag force. For instance, increasing the distance of the scoop from the wall by 31% (from 8 to 10.5 mm) in 3800 Pa wall pressure and 85° contact angle, causing a maximum temperature decrease of 1.3% (from 596 to 588 K) and also the drag force is reduced by 49.4% (2412 to 1221 dyn). Furthermore, reducing the angle of the gas flow with the scoop by 11.8% (from 85 ° to 75 °) in 3800 Pa wall pressure and at the distance of the scoop from the wall equal to 10.5 mm causes a maximum temperature decrease of 6.8% (from 588 To 548 K) and the drag force is reduced by 50.3% (1552 to 771 dyn).

In this study, the effect of rarefied region in the rotor of the centrifuge was investigated. In a rotor of the centrifuge, the feed inlet is positioned in the rarefied area. The continuum hypothesis is not valid in the rarefied area; therefore, it desires to be analyzed by probabilistic methods like Direct Simulation Monte Carlo (DSMC). In the present study, Computational Fluid Dynamic (CFD) method is used to simulate the continuum area, and the DSMC method is employed in the rarefied area. An implicit coupled density-based scheme was performed for CFD method, and Variable Hard Sphere (VHS) and diffuse model were employed in the DSMC method. Also, the local Knudsen number was defined to determine the interface location between the continuum-rarefied regions (r=0.086 m). The comparison results of pure CFD and CFD-DSMC methods illustrated large differences between the flow properties in the rarefied regions. The results showed that the value of separation power obtained from pure CFD and CFD-DSMC solution is 10.5% different.

To increase the performance of a gas centrifuge, it is necessary to stabilize an axial flow inside the rotor. For this purpose, computer simulation is an effective method. In the present work, a specific solver (ICDB) was developed in OpenFOAM to simulate the gas flow in the rotor. Creating a solver is important because OpenFOAM is free and open-source software. According to a study carried out by a research group, high-speed airflow is considered on a flat plate to assess the accuracy of this solver. To validate the ICDB, the results are compared with those of Fluent software and other researchers. It is found that the results corresponding to ICDB solver are in good agreement with other effects. Moreover, using the ICDB solver and the fluent software, the uranium hexafluoride gas flow inside the axisymmetric rotor was simulated considering different drives such as the thermal drive (wall and caps) and the mechanical drive (scoop). The obtained results show that the developed solver in OpenFOAM can simulate the uranium hexafluoride gas flow inside the rotor.

In order to increase the performance of a gas centrifuge used in the uranium enrichment industry, the gas flow field inside it is studied and simulated. In the present work, the full Navier-Stokes equations using the CFD method are used to simulate the gas flow inside the rotor. For the CFD method, a density-based implicit coupling solver was developed in OpenFOAM software, which was used to simulate the gas flow inside the rotor. The separation power was improved in a sample rotor by adjusting feed flow parameters, wall pressure, wall temperature gradient, and scoop drag force. The results show that the process variable had an optimal value in which the separation power is maximum. In order to achieve the maximum separation power of 12.87 kg UF6 SWU/year, the optimum rotor conditions were determined at a feed rate of 90 g/h, wall pressure of 44 torr, the temperature gradient of 25 K, and drag force of 1557 dyne. This study can be considered an important step in improving the performance of centrifuge separation.

The performance of a uranium gas centrifuge which is used in the uranium enrichment industry depends strongly on the gas flow field. The computer simulation is vital to examine the gas flow field. Therefore, in the present study, the capabilities of OpenFoam software for simulating the gas flow inside the rotor for total reflux thermal drive-in axisymmetric mode has been investigated. The results corresponding to the OpenFoam ssimulation have been validated with those of analytical Olander’s model, numerical solution of the Harada’s study, and simulation using Fluent. The simulation results for gas flow inside the rotor of centrifuge showed that the density-based solver was properly chosen and the number of cells, 160×170, was compatible with mesh. The numerical results show that OpenFoam software was capable to examine the gas flow inside the rotor. Also, the simulation of the distribution of Knudsen number confirms the presence of the molecular region near the axis of rotation. OpenFoam is open-source software and there is the ability to solve the molecular region as well as the coding for coupling the continuous and molecular region, the feature which does not exist in the fluent software. The use of open foam is therefore recommended to simulate gas flow inside the rotor.