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The thickness of downward-flowing annular wall layers in circulating fluidized bed risers has been determined in the literature based on measured radial profiles of both local particle velocity and solids flux. The thickness of the wall layer is shown to be larger based on solids flux profiles than when based on particle velocity profiles, because fluctuations in local instantaneous particle velocity are correlated with fluctuations in local solids concentration. A new correlation is developed to predict the time-average thickness of the downflowing particle streamer layer based on solids flux measurements as a function of the cross-sectional average voidage. It successfully accounts for the variation of the wall layer thickness with axial location and solids circulation rate. 相似文献
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保温层经济厚度的确定 总被引:5,自引:0,他引:5
于明 《化学工业与工程技术》1998,19(2):12-14
将传热方程与经济核算相结合,导出了单层和双层保温层经济厚度的计算公式,介绍了有关参数的确定方法,对于合理选择绝热材料和确定保温层的厚度具有重要意义。 相似文献
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The rheological characterization of highly filled suspensions consisting of a Newtonian matrix (hydroxyl-terminated polybutadiene), mixed with two different sizes of aluminum powder (30% and above by volume) and two different sizes of glass beads (50% and above by volume), was performed using a parallel disk rheometer with emphasis on the wall slip phenomenon. The effects of the solid content, particle size, type of solid particle material, and temperature on slip velocity and slip layer thickness were investigated. Suspensions of small particles of aluminum (mean diameter of 5.03 μm) did not show slip at any concentration up to the maximum packing fraction. However, suspensions of the other particles exhibited slip at the wall, at concentrations close to their maximum packing fraction. In these suspensions, the slip velocity increased linearly with the shear stress, and at constant shear stress, the slip velocity increased with increasing temperature. The slip layer thickness increased proportionally with increasing size of the particles for the glass beads. Up to a certain value of (filler content/maximum packing fraction), ϕ/ϕm, the slip layer thickness divided by the particle diameter, δ/DP, was 0, but it suddenly increased and reached a value that was independent of ϕ/ϕm and the temperature. On average, the ratio of δ/DP was 0.071 for aluminum and 0.037 for glass beads. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 515–522, 1998 相似文献
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The Marangoni instability in the non-steady-state absorption of a gas by a liquid layer with a finite thickness is considered. The critical time of reaching the unstable convective regime as a function of the physical characteristics of the process and the thickness of the liquid layer is studied. The dependence of the critical Marangoni number on the Lewis number is obtained numerically. 相似文献
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Saif Matar 《Electrochimica acta》2010,56(1):600-606
The effects of cathode catalyst layer (CCL) thickness on the detrimental effect of methanol cross-over in a direct methanol fuel cell (DMFC) under various operating conditions are studied. Three membrane electrode assemblies (MEAs) with different CCL thicknesses but identical catalyst loading and identical anode catalyst layer are used. The results show that, when a thicker CCL, approximately twice the thickness of the base case, is used, the fuel cell performance increases significantly. The increase in performance with a thicker CCL is attributed to the oxidation of the methanol crossed-over in part of the catalyst layer and leaving the rest of the catalyst layer free from methanol contamination, leading to mitigations of the effects of mixed potentials. The results of electrochemical impedance spectroscopy (EIS) show that the charge transfer resistance for the fuel cell with twice the thickness of CCL is 30% lower compared to that for the base case, indicating that the active catalyst area available for oxygen reduction reaction (ORR) is indeed greater. The results of the electrochemical active surface areas (ECA) show that without methanol contamination, the ECA of the thicker CCL is actually lower, indicating that the better performance and the lower charge transfer resistance are not caused by a higher original ECA, but a higher active area for ORR. A much thicker CCL, about 5 times of that for the base case, is also used and the cell performance is also higher than that for the base case. The experimental results show that there exists an optimum cathode catalyst layer thickness and the thickness of cathode catalyst layer has a significant effect on DMFC performance. 相似文献
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《Ceramics International》2022,48(1):711-719
Cu2ZnSnS4 (CZTS) is a good candidate for cost-effective perovskite solar cells (PSCs) due to its direct bandgap with a value of 1.4–1.5 eV. In this study, we investigate CZTS ink as an inorganic hole-transport-layer (HTL) in CsMAFAPbIBr mixed halide PSCs. We study the cell efficiency and hole extraction from the perovskite layer for different thicknesses of HTL. The optimized device exhibits better hole selectivity, and the best efficiency of the device (12.84%) is achieved for the CZTS layer with a thickness of 159 nm. The prepared samples were also tested by open-circuit voltage decay analysis and electrochemical impedance spectroscopies. Results show that the optimized device effectively prohibits the electrons-holes recombination with a charge transfer resistance of 9.38 Ω cm2. This work suggests that the optimal thickness of CZTS as an HTL in triple-cation PSC is about 159 nm by giving short-circuit current density of 23.69 mA cm?2. 相似文献
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XPS测定减水剂吸附层厚度 总被引:10,自引:5,他引:5
通过XPS谱图和XPS信息深度的计算方法测定了减水剂在胶凝颗粒表面的吸附层厚度。结果显示,木质素磺酸盐减水剂(LS)、改性木质素磺酸盐减水剂(GCL1-T)、萘系减水剂(FDN)和氨基磺酸盐减水剂(ASP)在水泥颗粒表面的吸附层厚度分别为8.70、10.87、1.50、7.26 nm;GCL1-T和FDN在粉煤灰表面的吸附层厚度分别为6.76 nm和0.95 nm。此方法可较准确描述减水剂在胶凝颗粒表面吸附层厚度的相对大小。由测定结果可进一步推断,FDN的分散机理以静电斥力效应为主;而空间位阻效应在LS、GCL1-T和ASP的分散机理中不可忽略。 相似文献
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Pijush K. Mitra Prodyot K. Sarkar Dipti K. As Bimalendu Biswas Aditya B. Chakraborty Krishna Raja 《Fuel》1978,57(10):639-642
A study of the effect of ash yield on the maximum thickness of the plastic layer (MTPL) of some coking coals (as measured by the Sapozhnikov plastometer) has revealed that with an increase in the former the latter in general decre?es. A rectilinear relation approximately exists between the ash percentage (dry basis) and log MTPL values of coals. For the samples studied, a multiple correlation incorporating the rank factor was found to be unnecessary. Higher Fe2O3 and SO3 contents from the coal were found to be associated with higher MTPL values. 相似文献
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Rongbin Li Qiyu Huang Dongxu Zhang Xiangrui Zhu Jinxu Shan Zhimin Li 《American Institute of Chemical Engineers》2021,67(1):e17077
In this study, the thickness and wax content of wax deposits were found to be thinner and lower in the polyethylene (PE) pipe than in the stainless steel (SS) pipe using a flow loop apparatus. The diffusivity of wax, radial thermal gradient, and wax precipitation rate in the PE and SS pipes were calculated and compared. It was found the diffusivity of wax in the PE pipe was higher and tended to enhance the wax deposition in the PE pipe, while the radial thermal gradient and wax precipitation rate were lower in the PE pipe and had the opposite effects. These factors are shown to be comparable with each other and the effect of the thermal gradient dominates the mass flux of wax from bulk to the oil-deposit interface and into the deposits finally, thus causing differences in thickness and wax content of deposits between the PE and SS pipes. 相似文献
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Flow structure and thickness of annular downflow layer in a circulating fluidized bed riser 总被引:1,自引:0,他引:1
Sung Won Kim 《Powder Technology》2004,142(1):48-58
Flow structures were determined in a circulating fluidized bed (CFB) riser (0.203 m i.d.×5.9 m high) of FCC particles (dp=70 μm, ρs=1700 kg/m3). A momentum probe was used to measure radial momentum flux profiles at several levels and to distinguish between upward and downward flow regions. Time-mean dynamic pressure (ΔPm) decreases towards the wall in the range Ug=5-8 m/s, Gs=10-340 kg/m2 s. The thickness of the annular downflow layer based on ΔPm=0 reaches a maximum with increasing height. The annular downflow layer disappears locally with increasing solids mass flux (Gs) at a constant gas velocity, with achievement of the dense suspension upflow (DSU) regime. A new correlation is developed to predict the time-mean thickness of solids down-flowing layer based on solids mass flux and momentum flux. It successfully accounts for the variation of the annular layer thickness with height and Gs, and covers a wide Gs range right up to near the onset of the DSU regime. 相似文献
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P. M. Krishenik S. A. Rogachev K. G. Shkadinsky 《International Journal of Self-Propagating High-Temperature Synthesis》2012,21(2):83-88
Profile of combustion front in structurally unordered heterogeneous media was found to depend on the character of distribution in scale characteristics of burning media. In case of continuum distribution, dispersion markedly affects a front structure in the vicinity of transition from homogeneous to relay-race combustion. Dispersion also narrows the range of quasi-homogeneous combustion. In case of normal size distribution, oscillations of front amplitude become irregular upon increase in dispersion; this is also accompanied by an increase in the magnitude of forced vibrations caused by system inhomogeneity. Steadiness of combustion was found to depend not only on model parameters but also on the type of size distribution function. 相似文献
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Glass and Ceramics - 相似文献
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Zhongyan Hu Tianyun Zhao Wei Zhao Fang Yang Hongxun Wang Kaige Wang Jintao Bai Guiren Wang 《American Institute of Chemical Engineers》2021,67(4):e17148
Electroosmotic flows (EOFs) on insulated interfacial surface commonly exists as interfacial flows. Previously theoretical studies indicate that EOFs of Newtonian fluids on the insulated interfacial surface are steady in microchannels with symmetric zeta potentials (Suresh and Homsy, Physics of Fluids, 2004, 16, 2,349). Restricted by flow diagnostic methods in microfluidics, few velocity measurements of instantaneous EOFs have been reported, and the existence of unsteady EOFs on the insulated surface remains unclear. In this investigation, the velocity fluctuations of EOFs generated under AC electric field (named as ACFEOF) overlapped on a steady pressure-driven flow are measured by laser induced fluorescence photobleaching anemometer, at the diffuse electric double layer (EDL) on the bottom wall far from electrodes. Chaotic velocity fluctuations according to unsteady ACFEOF has been, for the first time, observed. Stokes number (St ) and electrical Reynolds number (ReE ) related to oscillation and electro-inertial effect are suggested to control chaotic ACFEOF. 相似文献