گودرز احمدی

Research topic:

Gas lift is an efficient artificial lift strategy, routinely used to overcome the low productivity of the wells. In this research, the possibility of using two gases, carbon dioxide and nitrogen instead of natural gas, in the gas lifting process is investigated and compared. To maximize oil production, the optimization of the allocation of the limited amount of gas between 10 wells in the Iranian offshore brown oil field is performed.

In this research, all the wells were modeled by PROSPER software. First, all 10 wells data of an Iranian offshore oil reservoir were collected. Secondly, their model has been built and after validation, a simulation of the artificial gas lift was performed using carbon dioxide and nitrogen gas separately, then, the Gas Lift Performance Curve (GLPC) of all the wells are fitted with the appropriate experimental model in MATLAB software. In the following, using Solver Excel, the allocation optimization with a limited amount of gas was performed using two different gases.

According to the results obtained from the optimization, for a certain amount of available gas which is 15 MMSCFD, the total Oil production in the case of nitrogen gas injection is 3564 STBD more than carbon dioxide gas injection. Also, in all cases, due to the production potential capacity of well No. 8, the most amount of injected gas is allocated to it. The comparison of the two types of injected gas shows that the quantity of oil produced using nitrogen is 3424 and 3302 STBD (28 % and 24 %) greater than carbon dioxide gas when the gas is lowered to 12 and 9 MMSCFD, respectively.

In the present study, the sensitivity of particle dispersion within a room to the spatial position of the inlet and outlet air register was investigated using the Taguchi method and analysis of variance. For this purpose, 86400 particles with a size of 1µm were uniformly injected from the inlet register into the room at equal time intervals. Different positions for the inlet register (32 positions) and outlet register (4 positions) on the ceiling and floor of the room were considered. Subsequently, the behavior of the particles, as well as the particle deposition and dispersion within the room over a 60-second time period, were examined using the multi relaxation time lattice Boltzmann method. By employing the Taguchi method and L16 orthogonal arrays, the required number of experiments was reduced by 1/8. All specified experiments which suggested by orthogonal array are simulated, and the number of suspended particles in the room were measured. Following the experiments, the effects of each parameter on the output of the problem were determined based on a factor called the signal-to-noise (S/N) ratio and analysis of variance. According to the obtained results, the longitudinal position of the inlet register had the highest impact on the number of suspended particles in the room, accounting for 84.42% contribution. Additionally, the vertical position of the outlet register had the least impact, contributing only 0.16%.

In this work Multi-Relaxation Time Lattice Boltzmann Method (MRT-LBM) is used to investigate the effect of the inlet air position on particle motion in a room. The sub-scale modeled room is one-tenth the scale of a full-size room with dimensions of 0.914 m×0.305 m×0.457 m and two different positions (ceiling and floor) are considered for the inlet air with dimension of 0.101m×0.101m. Large Eddy Simulation (LES) with Standard Smagorinsky model is utilized to simulate the turbulent indoor airflow. Particles with 1 and 10 micrometer sizes are selected for investigation of particle dispersion and deposition on the walls of the room. Number of deposited particles and those exiting the room show that when the inlet air is on the floor, the number of particles leaving through the exhaust register with bigger size (10µm) is more than the case for ceiling position. For smaller particles (1 µm) there is no significant difference between the floor and ceiling position of the inlet air for particles leaving the room thought the exhaust register. Results show that the gravity force significantly affect the particle deposition, as the number of deposited 10 µm particles on the floor are about 100 times that of the deposited 1 µm particles when the inlet air position is at ceiling.

In this paper the Multi Relaxation Time Lattice Boltzmann Method in conjunction with the Large Eddy Simulation model was used to study the particle deposition in a room  with various diameters (10nm-10µm)and the effect of buoyancy, drag and Brownian forces to particle deposition on the different walls of the room has been investigated.  The sub-grid scale turbulence effects were simulated through a shear-improved Smagorinsky model. To simulate the particle deposition in the room, the particle injection process was initiated with 144 particles injected uniformly at the inlet with the same velocity as the airflow at every 0.05s; particle injection was stopped after 30s. Therefore, a total of 86400 particles were injected into the room. The present simulation results for the airflow showed good agreement with the experimental data and the earlier numerical results. The simulated results for particle dispersion and deposition showed that the numbers of deposited particles on the walls increases by augmentation of the time. When the particle injection started the concentration in the inlet jet region is more than other zones and that increases in the region far from the inlet by time. Present results will be interesting for designing air condition systems in the office and hospitals rooms.

Dyes are complex organic compounds, which are widely used in textile, paper, and cosmetics industries. Dyes are also known environmental pollutants that must be removed to maintain environmentally friendly processes. For this purpose the use of advanced oxidation processes with use of highly active compounds such as hydroxyl radicals was proposed. In this study the photocatalytic degradation of BR46 cationic dye with the use of activated carbon-doped ZrO2 nanoparticle was investigated. Parametric study was performed for a range of pH (3–11), initial dye concentration (5-25 mg/ L), catalyst loading (0.03–0.18 g/ L), and UV lamp power (9-18 W). All testing were done in the 1 L cylindrical pyrex reactor with the height of 460 mm. The maximum removal efficiency of dye of 98.17% was observed for pH=11, initial concentration of dye = 15 (mg/L), catalyst loading= 0.15 (g/L) and UV lamp power = 18 W for a retention time of 120 min. The decolorization of BR46 followed the pseudo-first-order kinetic according to the Langmuir–Hinshelwood model (with kr = 1.135 mg/ L min, ke = 0.0124 L/ mg).

In the present research, the developed 3D Eulerian-Lagrangian model of the sediment transport in Part A of this series is used to predict the effects of the bed-roughness height, water temperature (viscosity) and density of sediment grains. The selected parameters for the analyses are important both for sediment transport hydraulics and also uncertainties of experimental data. The results indicated that increasing bed-roughness height causes decrease in the saltation characteristics and consequently bed-load transport rate. The effects of water temperature (viscosity) are significant in the range of sand size, and it is necessary to keep it in the control for reducing uncertainties of experimental data. The sediment density has significant effects in both sand and gravel ranges, and thus the use of grains with different density compared to natural sediment can impose significant effects on experimental results.

In the present research, a 3D numerical model of the sediment grain movement has been developed based on the Eulerian-Lagrangian perspective. The forces which act on sediment grains are non-linear drag force, the shear lift force, the rotational lift (Magnus) force, the buoyancy force, the added mass force, the Basset history force and torque. Second-order nonlinear ordinary differential equations have been used to calculate linear and angular velocity vectors and also the position of sediment grains. Two parts including turbulent fluctuations in 3D space and a stochastic bed-particle collision model have been considered in the modeling procedure. The verification of the developed model has been examined for two important issues including the minimum number of jumps for statistical convergence and the appropriate value of the time step. The validation of the model has been performed using reliable experimental data in terms of the saltation height, length and streamwise particle velocity for the ranges of fine sand to coarse gravel. To evaluate the qualification of the conceptual model, the effects of the elimination of some forces and turbulent fluctuations, where do not exist consensus on the use of these factors in the previous researches, have been studied. The results indicated that the developed model can be considered as a numerical lab to study different aspects of the sediment transport in the prediction step, which will be performed in the part B of this series.

The aim of this paper was to study the thermophoresis effect on the deposition of nano-particles from diesel engine exhaust after the dilution tunnel using a computational modeling approach. Dilution tunnel was used in order to dilute the exhaust gas to the extend that was suitable for the measurement systems. The Lagrangian particle tracking method was used to model the dispersion and deposition of nano-particles. For the range of studied particle diameters (from 5 to 500 nm), the Brownian, thermophoresis, gravity and Saffman Lift forces are considered. After verifying the code, the importance of different forces was evaluated. Due to the temperature gradient between the exhaust gas and the pipe walls, particular attention was given to include the thermophoresis force in addition to the other forces acting on nano-particles. The results showed that for the range of nano-particle diameters studied, the Brownian force was the dominant force for particle deposition. Furthermore, the thermophoresis force was important even for relatively low temperature gradient and cannot be ignorable especially for larger particles. The maximum thermophoresis effect occurred for 100 nm particles. The gravity had negligible effects on nano-particle deposition and can be ignorable for particles with diameter less than 500 nm. The Saffman lift also had negligible effects and its effect was noticeable only for the deposition of 500 nm particles. The results of this paper could provide an understanding of two-phase flow emission from diesel engines especially after the dilution tunnel.