In this article, comprehensive comparisons are made between the SIMPLER and IDEAL algorithms for four application examples. It is found that the IDEAL algorithm is efficient and stable not only for the simple, low-Re/...
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In this article, comprehensive comparisons are made between the SIMPLER and IDEAL algorithms for four application examples. It is found that the IDEAL algorithm is efficient and stable not only for the simple, low-Re/Ra or coarse-mesh flow cases, but also for the complex, high-Re/Ra or fine-mesh flow cases. For the low-Re/Ra, coarse-mesh flow cases, the ratio of CPU time of IDEAL to that of SIMPLER ranges from 0.029 to 0.7. For the high-Re/Ra, fine-mesh flow cases, the IDEAL algorithm can obtain convergent results but the SIMPLER algorithm cannot, even though the underrelaxation factors are adjusted. [ABSTRACT FROM AUTHOR]
Gasification is a clean technique that converts coal into syngas, which can be cleaned much more easily than the coal itself. The raw sysgas exiting the gasifier is usually at a very high temperature. To protect the r...
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ISBN:
(纸本)189097725X
Gasification is a clean technique that converts coal into syngas, which can be cleaned much more easily than the coal itself. The raw sysgas exiting the gasifier is usually at a very high temperature. To protect the rearward equipment, the raw syngas needs to be cooled to allow appropriate cleaning of particulates, ashes, and sulfur before it exits the gasifier. Cooling of the syngas can be performed by employing heat exchangers or direct spray cooling. This paper focuses on conducting a 3-D CFD parametric study to aid in the design of an effective water spray cooling deployment. The studied parameters include water droplet sizes (100400m) and water injection angles. The goal is to cool the syngas from 1550C to 800C using the shortest spray section. The gasifier is designed to produce methanol at a full load condition, so the amount of sprayed water is fixed to ensure the syngas composition meets the specifications for methanol production. The gasifier is steam-oxygen blown with dry coal feed using approximately 960 tons per day. The results reveal that smaller droplets are effective in reducing the cooling section length. Moreover, using three water injection angles show that inclining the spraying angle upward 45 degrees could shorten the effective cooling length. This study provides a guide for cutting the cost of manufacturing a gasifier cooling section.
Slug flow is a highly intermittent flow regime in which large bubble slugs flow alternately with liquid slugs at randomly fluctuating frequency. A one-dimensional model for the interfacial structure in bubble slug was...
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Slug flow is a highly intermittent flow regime in which large bubble slugs flow alternately with liquid slugs at randomly fluctuating frequency. A one-dimensional model for the interfacial structure in bubble slug was developed based on mass and momentum conservation for bubble nose, body and tail as well as for a hydraulic jump at the rear of the bubble. The model can reproduce experimental results accurately. The results indicate that the interfacial structure is strongly dependent on the Froude number defined by gas/liquid mixture velocity, pipe inclination, and bubble length.
Slug initiation and subsequem evolution along a 5.0 cm ID, 16m long horizomal pipe are experimentally studied. The transient characteristics of interfacial structures are described by using simultaneous measuremeres o...
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Slug initiation and subsequem evolution along a 5.0 cm ID, 16m long horizomal pipe are experimentally studied. The transient characteristics of interfacial structures are described by using simultaneous measuremeres of the liquid height at multiple locations along the pipe. Various effects of superficial gas and liquid velocities and pressure oscillation on the slug initiation and evolution along the pipe are illustrated. It is found that the slug is initiated by a deterministic orocess with reolenishmem and deoletion of liquid near the inlet for the superficial gas velocity USG〈3.0m·s^-1 and by a stochastic process with wave coalescence along the pipe for USG〉3.0m·s^-*** evolution of the slugs is strongly attected by superhclal gas and liquid veloclties for USG〈3.0m·s^-1 but weakly affected by the superficial gas velocity for USG〉3.0 m·s . The suppression of pressure oscillation at the pipe inlet significantly delays the onset of slugging, with slugs forming postponed further downstream. The slug frequency at the outlet is, however, not affected by the variation in the pressure oscillation.
Considering the fact that proton exchange membrane (PEM) fuel cell has different impedance performances under different discharge currents, a PEM fuel cell with single serpentine flow field was investigated with elect...
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Considering the fact that proton exchange membrane (PEM) fuel cell has different impedance performances under different discharge currents, a PEM fuel cell with single serpentine flow field was investigated with electrochemical impedance spectroscopy, and the R (QR) equivalent circuit was used to calculate the circuit element parameters. The experimental results show that water in the fuel cell increases from insufficient to sufficient and then excessive with the increasing discharge current. Accordingly, the electrochemical reaction rate on the electrodes increases first and then decreases, thus the charge transfer resistance decreases and then increases. The impedance of PEM fuel cell increases obviously for high discharge currents due to the accessional impedance produced by double-layer effect, while the impedance reaches minimum at medium discharge current (5 A).
Biodiesel is generally produced by the transesterification of vegetable oils or animal fats com- posed of C-C fatty acid triglycerides with methanol under the presence of a catalyst. The conventional biodiesel product...
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Biodiesel is generally produced by the transesterification of vegetable oils or animal fats com- posed of C-C fatty acid triglycerides with methanol under the presence of a catalyst. The conventional biodiesel production technology use base or acid *** are several
Pb2+ doped Cd0.2Zn0.8S and Cd0.8Zn0.2S were prepared with coprecipitation method. The results indicate that the valence band of Cd0.2Zn0.8S solid solution with wide band gap is heightened by the Pb 6s level hybridizat...
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Pb2+ doped Cd0.2Zn0.8S and Cd0.8Zn0.2S were prepared with coprecipitation method. The results indicate that the valence band of Cd0.2Zn0.8S solid solution with wide band gap is heightened by the Pb 6s level hybridization with valence band, and the photocatalytical hydrogen evolution ability is improved. When Pb2+ is doped in Cd0.8Zn0.2S solid solution with narrow band gap, it acts as a recombination center and is unable to improve water splitting activity of the catalyst. So the doping of Pb2+ is effective only for the semiconductor with wide band gap.
The numerical simulation technique was employed to study the flow and heat transfer performance of the rotating cooling channel with feed chamber and impingement chamber. The discharge coefficient of the impingement h...
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The numerical simulation technique was employed to study the flow and heat transfer performance of the rotating cooling channel with feed chamber and impingement chamber. The discharge coefficient of the impingement holes and the average Nusselt number of the impingement target surface in the blade leading edge in rotating were obtained. The result shows that the Coriolis force induced by the rotation effect can change the discharge coefficient of the impingement holes. With the increase of the rotating speed, the Coriolis force effect becomes more obvious. The discharge coefficient increases with the increase of rotating Reynolds number and outflow ratio, and decreases with the increase of the inlet Reynolds number. The influence of the rotation on the average Nusselt number of the impingement target surface is not obvious. With the increase of the rotating speed, Nusselt number increases slightly only at high rotating speed.
The processing of interference fringe is the most important step in holographic interferometric technique. The interference fringe of mass diffusion were gathered and proposed, and 3 key steps in the process which red...
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The processing of interference fringe is the most important step in holographic interferometric technique. The interference fringe of mass diffusion were gathered and proposed, and 3 key steps in the process which reduce the precision mostly were improved in this paper. The improvements include the following steps: wavelet de-noise, frequency-domain wave filtering, phase unwrapping. The categories of noise were analyzed and some specific methods were used to reduce the noise. The improvements increased the precision greatly, and established a solid foundation for the using of laser holographic interferometric technique.
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