Particle motion in mixed flow dryers

Differences in flow rates of this nature have a significant effect on the unevenness of the moisture content of the dried material, since the material which remains in the drying chamber for an unnecessarily long time is over-dried and the under-drying is a problem for the material remaining in the dryer for too short a time. In this article, I analyzed the effect of increasing particle-wall friction on the unevenness of the particle flow velocity field. The research has shown that dead zones are formed in the vicinity of the rough walls, which reduce the uniformity of the flow. The results show that the tribological properties of the inner wall surfaces of the dryers can have a very significant effect on the efficient operation of the dryers.

Numerical Simulation of the Burning Process in a King-Size Cigarette Based on Experimentally Derived Reaction Kinetics

Summary A comprehensive two-dimensional (2D) mathematical model has been proposed to simulate the burning process of a king-size cigarette. The characteristics of this model are including: 1) the use of kinetic models for the evaporation of water, the pyrolysis of tobacco and the oxidation of char, 2) the application of mathematical relationships between the release amounts of certain products (i.e., “tar” and CO) and different reaction variables (i.e., temperatures and oxygen concentrations), 3) the introduction of mass, heat and momentum transports, 4) the consideration of filtration effects of the cigarette filter on “tar”. These characteristics were expressed in a set of coupled equations that can be solved numerically by FLUENT. The information about the char density field, temperature field, flow velocity field, “tar” and CO density fields and the filtration efficiency could be obtained from the model. This model was validated by comparing the predictions with experimental data on puff number, the temperatures at specific locations, the filtration efficiency and the yields of “tar” and CO under different puff intensities. The calculated results show a good agreement with the experimental data. The predicted puff number was 7.3, and the experimental puff number was 6.8. The standard root mean square error (NRMSE) between the experimental and the predicted temperatures at specific locations is < 18%. The predicted filtration efficiency for “tar” was 46.1%, and the experimentally determined filtration efficiency for nicotine was 44.5%. The maximum relative deviations of the yields of “tar” and CO under different puff intensities were 8.9% and 10.6%, respectively.

Determination of Dynamic Drainage Volume in Water-Flood Operations Based on Fluid Flow Velocity Field Delineation

Dynamic drainage volume is a useful measure in evaluating well completions, well spacing, and water-flood operations. It is usually approximated with a two-dimensional circle or a three-dimensional (3D) box that encloses a well using empirical correlations and production/injection volumes. While this approximation may be convenient, it certainly is not a good estimation for the effective and dynamic drainage volume, which is key for improved recovery. This paper proposes a new method to compute dynamic drainage volumes based on reservoir simulation results. A 3D fluid flow velocity field is first generated and then visualized as a function of time. Through velocity thresholding, one can delineate flow regions, and accurately and parsimoniously determine well drainage in water-flood operations. Our new method was proven to be more efficient and practical as demonstrated in a field-based synthetic model with nine injectors and 16 producers formed as an inverted five-spot water-flood pattern commonly used in the field, and a benchmark SPE 9 model. The novelty of the method lies in that a 3D fluid velocity field is generated to determine dynamic drainage volume. Our new method could be applied to optimize well placement and improve well operation, and finally increase the production in a heuristic, instructive, and cost-effective manner to maximize the estimated ultimate recovery.

The Hemodynamics of Aneurysms Treated with Flow-Diverting Stents Considering both Stent and Aneurysm/Artery Geometries

Flow diverting stents are deployed to reduce the blood flow into the aneurysm, which would thereby induce thrombosis in the aneurysm sac; the stents prevent its rupture. The present study aimed to examine and quantify the impacts of different flow stents on idealized configurations of the cerebral artery. In our study, we considered a spherical sidewall aneurysm located on curved and tortuous idealized artery vessels and three stents with different porosities (70, 80 and 90%) for deployment. Using computational fluid dynamics, the local hemodynamics in the presence and absence of the stents were simulated, respectively, under the assumption that the blood flow was unsteady and non-Newtonian. The hemodynamic parameters, such as the intra-aneurysmal flow, velocity field and wall shear stress and its related indices, were examined and compared among the 12 cases simulated. The results illustrated that with the stent deployment, the intra-aneurysmal flow and the wall shear stress and its related indices were considerably modified depending on both stent and aneurysm/artery geometries, and that the intra-aneurysmal relative residence time increased rapidly with decreasing stent porosity in all the vessel configurations. These results also inform the rationale for selecting stents for treating aneurysms of different configurations.

FEM-Analysis of 2D Micromachined Flow Transduers based on aGe-Thermistor Arrays and a Double Bridge Readout

This paper reports on a design and simulation study aiming at high-accuracy 2D micromachined thermal flow transducers. The scope is restricted to micromachined devices featuring a square-shaped membrane incorporating central symmetric thin-film devices. A microthermistor array probed spatial excess temperature variations while the main heat supply was alternatively established by optional heating resistors or by pronounced self-heating of the thermistor devices. Proper device designs enable leading edge transducer performance without sophisticated signal conditioning schemes. We found that a high azimuthal uniformity of flow magnitude transduction is tantamount to a precise azimuthal accuracy. The most advanced result gave a maximum azimuthal aberration of 0.17 and 1.7 degrees for 1 m/s and 10 m/s, respectively, while the corresponding magnitude uniformity amounted to 0.07% and 0.5%. Such excellent specifications exceed the need of ordinary meteorological applications by far. However, they are essential for, e.g., precise non-contact measurements of 2D relative movements of two quasi-planar surfaces via the related Couette flow in intermediate air gaps. The simulations predicted significantly better device characteristics than achieved by us in first experiments. However, this gap could be attributed to imperfect control of the flow velocity field by the measurement setup.

Flow Velocity Field Measurement of Vertical Upward Oil–Water Two-Phase Immiscible Flow Using the Improved DPIV Algorithm Based on ICP and MLS

Flow velocity field measurement is important for analyzing flow characteristics of oil–water two-phase immiscible flow in vertical well. Digital particle image velocimetry (DPIV) is an effective velocity field measurement method that has overcome single point measurement limitation of traditional instruments. However, multiphase flow velocity fields generated by DPIV are often accompanied by local false vectors caused by image mismatching, which leads to measurement results with low accuracy. In this paper, the reasons for oil–water two-phase immiscible flow image mismatching in inner diameter 125 mm vertical pipe is identified by studying the DPIV calculation process. This is mainly caused by image noise and poor window following performance that results from poor deformation performance of the interrogation window. To improve deformation performance of the interrogation window, and thus improve the accuracy of the algorithm, iterative closest point (ICP) and moving least squares (MLS) are introduced into the window deformation iterative multigrid algorithm in DPIV postprocessing algorithm. The simulation showed that the improved DPIV algorithm had good matching performance, and thus the false vector was reduced. The experimental results showed that, in light of the present investigation, on average, the improved DPIV algorithm is found to yield an accuracy improvement of ~6%; the measurement uncertainty and reproducibility of the improved DPIV algorithm were 0.149 × 10−3 m/s and 1.98%, respectively.

Experimental setup to study two phase flows for environmental applications

The air water mix is a major concern for the environmental application. This paper proposes an experimental method to accede simultaneously at the water flow velocity field and at the void fraction. Instantaneous and mean fields, as well as the evolution with the flow parameters variation are obtained in cavitation or aerated flows. This method allows a good accuracy for the flow velocity fields (2%) and void (vapours or air) contours (4%).