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61.
Chul-Kun Cho Kil Sang Chang Timothy S. Cale 《Korean Journal of Chemical Engineering》1993,10(4):195-202
Magnetic crystallite thermometry has been used to measure the average nickel crystallite temperature in packed bed reactors
during ethane hydrogenolysis, an exothermic reaction. The technique is based on the temperature dependence of the magnetic
moment of dispersed nickel catalysts. Measurement of the average catalyst temperature is very useful for reactor control because
of its shorter time constant compared with exit fluid temperature. Bed temperature control based on the exit fluid temperature,
which has often been used as a control variable, is too slow to protect thermal runaway of the bed. The advantage of short
time constant by measuring the average catalyst temperature has been incorporated with enhanced feedback control system to
control the bed temperature and prevent the thermal runaway of the catalyst bed. An enhanced feedback control structure with
supervisory action performed better than the classical proportional-integral control in runaway prevention when the two control
schemes were compared with each other on the basis of the trippoint (incipient thermal runaway). 相似文献
62.
Jin Sung Choi Sang Hyuk Im Min Young Song O Ok Park Hansol Cho Jin Taek Hwang 《应用聚合物科学杂志》2005,95(5):1100-1104
A gradient refractive index rod was successfully prepared by a new fabrication method using laminar shear mixing, and a graded index polymer optical fiber that satisfied IEEE1394b was obtained from the method. To fabricate the gradient refractive index rod, a liquid monomer mixture with a relatively low refractive index was placed in a prepared cylindrical glass reactor and a transparent polymer rod with a higher refractive index was introduced at the center of the reactor. The reactor and the polymer rod were then rotated concurrently with a small rotating speed difference to generate a Couette flow in the liquid phase. The centrifugal force generated by rotation and the polymer diffusion into the liquid monomer mixture developed a graded concentration profile in a radial direction. The Couette flow could reduce the concentration fluctuation in a tangential direction. In addition, the graded index profile could be controlled by the copolymer composition of the rod and its diameter. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1100–1104, 2005 相似文献
63.
Dissipative structures of autocatalytic reactions with initially uniform concentrations are studied in tubular flow reactors. A unique steady state exists in a continuous stirred tank reactor. Linear stability analysis predicts either a stable node, a focus or an unstable saddle-focus. Sustained oscillations around the unstable focus can occur for high values of Damköhler number. In distributed parameter systems, travelling, standing or complex oscillatory waves are detected. For low values of Damköhler number, travelling waves with pseudo-constant patterns are observed. With intermediate values of Damköhler number, single or multiple standing waves are obtained. The temporal behavior indicates also the appearance of retriggering or echo waves. For high values of Damköhler number, both single peak and complex multipeak oscillations are found. In the cell model, both regular oscillations near the inlet and chaotic behavior downstream are observed. In the dispersion model, higher Peclet numbers eliminate the oscillations. The spatial profile shows a train of pulsating waves for the discret model and a single pulsating or solitary wave for the continuous model. 相似文献
64.
Yinfeng Liu Lai Chen Bei Su Aiming Huang Jiadong Hua Wenbin Sang Jiahua Min Zhongyan Meng 《应用聚合物科学杂志》2002,84(6):1263-1268
In this article nano‐sized CdS crystal embedded in a PEO matrix was successfully prepared by a complex transformation method that is universal for preparing nanosized compounds containing transition metals. The size of embedded CdS particles was in the nanoscale from 2 to 10 nm determined by X‐ray diffusion. The nanosized CdS displayed the expected blue shift of the onset absorbance in the UV spectrum. The amount of blue shift depends upon the dipping time of the PEO–cadmium complex film in a sodium sulfide solution as well as its concentration. The most effective means for adjusting the size of CdS nanocrystals is to change the ratio of the oxygen along with the PEO chain to the cadmium ion in the complex film. The alkali salt in the film would contribute to the conductivity of the composite film. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1263–1268, 2002; DOI 10.1002/app.10459 相似文献
65.
To understand the smart (i.e., good memory) characteristics of hybrid composites of carbon fibers (CFs) and glass fibers (GFs) with epoxy resin as a matrix, the changes in the electrical resistance of composites with tension and on bending were investigated. The electrical resistance behavior of composites under tension changed with the composition of the CF/GF, as well as with the applied strain. The fractional electrical resistance increased slowly with increasing strain within a relatively low strain region. However, with further loading it increased stepwise with the strain according to the fracture of the CF layers. The strain sensitivity of the samples increased with increasing CF weight percentage, and the samples incorporating more than 40 wt % CF showed a strain sensitivity higher than 1.54 for a single CF. The changes in the fractional electrical resistance with bending were not so dominant as those with tension. This difference was attributed to the action of two cancelling effects, which are the increasing and decreasing fractional electrical resistance due to tension and compression with bending, respectively. On recovery from a large applied bending, the fractional electrical resistance decreased slowly with unloading because of the increase of contacts between the fibers that resulted from the reorganization of ruptured CFs during the recovery. Even the composites incorporating a relatively small CF content showed an irreversible electrical resistance with both tension and bending. However, the strain sensitivity being larger with tension than with bending is ascribed to the difference in their mechanical behaviors. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2447–2453, 2002 相似文献
66.
67.
The infrared reflectance and transmission spectra of amorphous CdGe
x
As2 were investigated to study the amorphous structure with varying Ge content. The mid-infrared optical absorption edges of amorphous CdGe
x
As2 with 0<x<1.2, were observed in the range 1.6–1.7 m, indicating a structural similarity in short-range order throughout. Comparing the reflectance and transmission spectra of amorphous and devitrified crystalline phases established that the structures of amorphous CdGe
x
As2 transformed from the CdAs2 basic structure to the chalcopyrite (CdGeAs2) structure, as one progressed fromx=0 tox=1.2. The infrared spectra were interpreted interactively with radial distribution function, magnetic susceptibility, density measurements, and crystallization studies. The crystallization behaviour of amorphous CdGe
x
As2 that was heat treated at different temperatures was investigated using far-infrared transmission spectra. 相似文献
68.
The effects of winglet offset distance, winglet coverage, and winglet cross section on the over-tip leakage loss for the plane tip have been investigated experimentally in a turbine blade cascade for a tip gap height-to-span ratio of h/s = 1.36 %. The results show that the over-tip leakage loss for the full coverage winglet increases steeply with increasing the winglet offset distance. This loss generation is attributed to flow disturbances over the forward-facing and backward-facing steps within the tip gap. The winglet flush mounted to the tip surface provides the best result. With the leading edge winglet portion or without it, the both-side winglet always provides better aerodynamic performance than the corresponding pressure-side winglet or suction-side winglet. Longer coverage of the both-side winglet leads to lower loss. Therefore, the full coverage winglet performs best in the loss reduction for the plane tip. In general, thinner winglet leads to better aerodynamic result, and the winglet cross section having a slant bottom surface with the smallest thickness at its outer end is recommended. 相似文献
69.
采用浸渍还原法(I-R法)在Nafion离子膜上镀覆纳米Ag,并就AgNO3浓度对SPE电极镀覆纳米银的影响作了研究.研究表明采用I-R法可制得细致Ag镀层,有效增加Ag的分散度及电极的真实面积.在还原剂浓度为0.1mol·L-1,浸渍还原温度均为50℃及浸渍还原时间分别为40 min,60 min的条件下,调节浸渍液AgNO3浓度至3.5 mmol·L-1时,可获得致密、均匀的纳米级Ag/SPE电极.同时验证砂纸糙化的预处理有利于增加Ag的负载和附着力,有利于提高Ag催化层的有效面积. 相似文献
70.