Numerical Modeling of Conductive Particle Trajectories in Roll-Type Corona-Electrostatic Separators

Several attempts have already been made to simulate particle trajectories in roll-type electrostatic separators. However, the predictive value of the results is limited by an excessive number of simplifying assumptions regarding the electric field distribution, as well as particle charging and discharging mechanisms. The present work is aimed at improving the existing models by taking into account: (1) the non-uniformity of the electric field in the active zone of the separator and (2) the effect of spark discharges occurring between the electrodes. Based on previous observations, the conductive particles were assumed to lift-off when no longer exposed to corona discharge. The numerical simulations were performed for particles of various sizes. The electric field was computed in each point of the trajectory using a finite element program. It was found that: (1) some of the smaller particles impact the static electrode and are deviated to the middling compartment of the collector and (2) field annealing which accompanies spark discharges significantly affects the trajectories of conductive particles. The results of this study could guide the design of new electrostatic separation applications.     

On the Achievable Rates of Multiband Ultra-Wideband Systems

In this work we study the achievable rates of memoryless signaling strategies adapted to ultra-wideband (UWB) multipath fading channels. We focus on strategies that do not have explicit knowledge of the instentaneous channel realization, but may have knowledge of the channel statistics. We evaluate the average mutual information of the general binary flash-signaling rates as a function of channel statistics and derive random coding bounds for m-ary PPM using different noncoherent receivers as well as an imperfect coherent receiver. Then we extend the results to multiband m-PPM signaling and show that for data rates on the order of 400 Mbits/s, at 4 m distance between the transmitter and the receiver, can be achieved using simple noncoherent receivers.     

Computing Large Deformation Metric Mappings via Geodesic Flows of Diffeomorphisms

This paper examine the Euler-Lagrange equations for the solution of the large deformation diffeomorphic metric mapping problem studied in Dupuis et al. (1998) and Trouvé (1995) in which two images I ₀, I ₁ are given and connected via the diffeomorphic change of coordinates I ₀○ϕ⁻¹=I ₁ where ϕ=Φ₁ is the end point at t= 1 of curve Φ _t , t∈[0, 1] satisfying ^.Φ _t =v _t (Φ _t ), t∈ [0,1] with Φ₀=id. The variational problem takes the form

Parallel multiple access interference cancellation in optical DS-CDMA systems

This paper investigates the Parallel Interference Cancellation technique in Direct Sequence Optical Code Division Multiple Access (ds-ocdma) system. In the proposed system, the estimated interference is removed from the received signal. We have developped a new approach to obtain the analytical expression of error probability in chip synchronous case, for Optical Orthogonal Codes (ooc). We have shown that under specific conditions between codes parameters and users’ number, the interference can be completely neutralized. Simulation results have validated the theoretical analysis. It is shown that the proposed receiver is effective in reducing significantly the effects of Multiple Access Interference (mai) compared to other interference cancellation systems.     

Effect of growth parameters on the heteroepitaxy of 3C-SiC on 6H-SiC substrate by chemical vapor deposition

Epitaxial 3C-SiC(1 1 1) films were grown on 6H-SiC(0 0 0 1) Si face on axis substrates by chemical vapor deposition under H₂, SiH₄ and C₃H₈ in a cold wall vertical reactor. Two temperatures were studied (1450 and 1700 °C) with various C/Si ratio and deposition time. It was found that under conditions giving high lateral growth (low C/Si and/or high temperature), homoepitaxial growth occurred even at temperatures as low as 1450 °C. For other conditions, the 3C-SiC polytype was detected and always together with the formation of double positioning boundaries whose density was found to depend on the growth conditions but not on the initial surface reconstruction. Single domain enlargement was observed when growth was performed at 1700 °C over a nucleation layer grown at 1450 °C.     

GIS integration model for geothermal exploration and well siting

The work involved in identifying geothermal fields can be simplified by means of a Geographical Information System (GIS), a decision-making tool used to determine the spatial association between exploration and environmental thematic maps. This methodology has been applied to part of the Sabalan geothermal field in northwestern Iran, and to the siting of exploration wells. The datasets used in the analyses consist of geological, geochemical and geophysical information. Boolean and Index Overlay knowledge-driven models were developed for site selection; the findings from these two models correlated well with the exploration data modeling. The results of the Index Overlay model were combined with those of an environmental suitability analysis for final selection of well sites. The results of exploration and environmental data modeling were combined to select and prioritize the sites of three exploratory wells in the study area.     

Stability limits and NO emissions of premixed swirl ammonia-air flames enriched with hydrogen or methane at elevated pressures

This study reports measurements of stability limits and exhaust NO mole fractions of technically-premixed swirl ammonia-air flames enriched with either methane or hydrogen. Experiments were conducted at different pressures from atmospheric to 5 bar, representative of commercial micro gas turbines. The full range of ammonia fractions in the fuel blend, x_NH3, was considered, from 0 (pure methane or hydrogen) to 1 (pure ammonia), covering very lean (φ = 0.25) to rich (φ = 1.60) equivalence ratios. Results show that increasing pressure widens the range of stable equivalence ratios for pure ammonia-air flames. Regardless of pressure, there is a critical ammonia fraction above which the range of stable equivalence ratios suddenly widens. This is because flashback does not occur anymore when the equivalence ratio is progressively increased towards stoichiometric and rich blowout occurs instead. This critical ammonia fraction increases with pressure and is larger for ammonia-hydrogen than for ammonia-methane. Provided that enough hydrogen is blended with ammonia (x_NH3 < 0.9), flames with very lean equivalence ratios (φ < 0.7) can be stabilized and these yield competitively low NO emissions (<200 ppm), regardless of pressure. For this reason, very lean swirl ammonia-hydrogen-air flames are promising candidates for micro gas turbines. However, N₂O emissions have the potential to be unacceptably large for these operating conditions if heat loss is too large or residence time is too short. As a consequence, the post flame region must be considered carefully. Due to the lower reactivity of methane compared to that of hydrogen, very lean swirl ammonia-methane-air flames could not be stabilized and good NO performance is limited to rich equivalence ratios for ammonia-methane fuel blends. The equivalence ratio above which good NO performance depends on pressure and bulk velocity.     

Experimental and Numerical Simulation of Dry Pressure Drop in High‐Capacity Structured Packings

Experimental and numerical studies were conducted on the performance and capacity of structured packings for mixture separation with very low separation factor. Different formations and conditions of the innovative structured packing PACK‐2100 with high surface area were studied to evaluate the main characteristics such as dry pressure drop. In addition, numerical simulation was performed to describe the details of the flow structure in these modified structured packings. Three‐dimensional computational fluid dynamics modeling of PACK‐2100 allowed for comparing the pressure drop in both laminar and turbulent flow regime. The obtained experimental and numerical data demonstrate the potential contribution of the packing to high‐efficiency systems with low separation factor.     

Production capacity estimation by reservoir numerical simulation of northwest (NW) Sabalan geothermal field, Iran

A three dimensional numerical model of the northwest (NW) Sabalan geothermal system was developed on the basis of the designed conceptual model from available field data. A numerical model of the reservoir was expressed with a grid system of a rectangular prism of 12 km × 8 km with 4.6 km height, giving a total area of 96 km². The model has 14 horizontal layers ranging in thickness between 100 m to 1000 m extending from a maximum of 3600 to −1000 m a.s.l. Fifteen rock types were used in the model to assign different horizontal permeabilities from 5.0 × 10⁻¹⁸ to 4.0 × 10⁻¹³ m² based on the conceptual model.Natural state modeling of the reservoir was performed, and the results indicated good agreements with measured temperature and pressure in wells. Numerical simulations were conducted for predicting reservoir performances by allocating production and reinjection wells at specified locations. Three different exploitation scenarios were examined for sustainability of reservoir for the next 30 years. Effects of reinjection location and required number of makeup wells to maintain the specified fluid production were evaluated. The results showed that reinjecting at Site B, immediate adjacent to production zone, is most effective for pressure maintenance of the system.On the base of existing data and assumptions the reservoir can sustain producing fluid equivalent to 50 MW_e of electricity for more than 30 years. The reservoir can produce the maximum amount of fluids equivalent to 90-100 MW_e for only 5 years, but the production capacity decreases to 50 MW_e after 20 years of operation because of pressure and enthalpy drop. The reservoir can sustain 50 MW_e over 100 years that can be defined as a sustainable production level of the field.     

Vacuum enhanced membrane distillation for trace contaminant removal of heavy metals from water by electrospun PVDF/TiO<Subscript>2</Subscript> hybrid membranes

Electrospun hybrid membranes were synthesized using electrospinning of Poly (vinylidenefluoride) - titanium tetraisopropoxide (PVDF-TTIP) sol. Asymmetric post-treatment of membrane conducted for deprotonation of titanate and making hydrophilic/hydrophobic dual characteristics. The membranes were characterized by various methods such as wettability, scanning electron microscopy, infrared spectroscopy, X-ray diffraction and liquid entry pressure tests. For evaluating the separation performance, these membranes were applied in the VMD process to treat water heavy metal contaminants. The effects of operating parameters such as flow rate, temperature and membrane properties as porosity, on contaminant removal and producing ultra-pure water have been studied.