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Gao X.,Tianjin University of Science and Technology | Wang J.,Tianjin University of Science and Technology | Wang S.,Tianjin University of Science and Technology | Li Z.,Tianjin University of Science and Technology | Li Z.,On-Line Monitoring
Drying Technology | Year: 2016

Modeling of particulate or thin-layer drying of materials is necessary to understand the fundamental transport mechanism and a prerequisite to successfully simulate or scale up the whole process for optimization or control of the operating conditions. Simple models with a reasonable physical meaning are effective for engineering purposes. Thin-layer drying of green peas was carried out in a fluidized bed with a newly developed slotted gas distributor. Based on the reaction engineering approach, a drying model of green peas was well established, in which relative activation energy (ΔEv/ΔEv,b) was correlated with reduced moisture content (X − Xb) at a drying air temperature of 80°C. The drying kinetics of green peas was discussed in terms of activation energy. In addition, activation energy based on a simplified material surface temperature profile was recalculated to evaluate the temperature sensitivity to the model establishment. © 2016, Copyright © Taylor & Francis Group, LLC.

Hao L.,Tianjin University of Science and Technology | Hao L.,On-Line Monitoring | Guan S.,Chiba University | Lu Y.,Chiba University | And 3 more authors.
Surface and Coatings Technology | Year: 2016

Mechanical coating followed by thermal oxidation in the atmosphere was used to prepare TiO2/SnO2 composite coatings. The coatings were characterized by X-ray diffraction (XRD), scanning electronic spectroscopy (SEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and so on. Results show that continuous rutile TiO2 coatings decorated with discrete SnO2 particles were formed during thermal oxidation at the temperature range of 873-1073 K. Through the temperature range, a small quantity of SnO was formed. However, tiny amount of Ti2O3 was formed only when oxidation temperature was 1073 K. The surface topography evolution of rutile TiO2 crystals during the thermal oxidation and relevant mechanism was also examined. Equiaxed, rod, columnar and needle TiO2 crystals with nanoscale were formed at temperatures from 873-1073 K. The topography evolution indicates that the diffusion of oxygen species into the formed rutile TiO2 layer was predominant at 873 K. It favored the growth of equiaxed crystals in the tangent plane rather than radial direction of Al2O3 ball substrate at the early stage of the thermal oxidation. However, the diffusion of Ti cations became prevailing compared with oxygen species at 1073 K. The reaction of Ti and oxygen species occurred at the external surface of the formed TiO2 layer where rutile TiO2 needles were formed. During thermal oxidation at 973 K, both the Ti cations and oxygen species were involved in the diffusion process and clusters of paired/parallel rutile TiO2 nanorods were formed. The addition of metallic Sn remarkably affected the surface topography and the grain size of rutile TiO2 crystals through regulating the diffusion of Ti cations and changing the local oxygen concentration surrounding Ti coatings. A proper additive amount refined the grains of rutile TiO2. © 2016 Elsevier B.V.

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Tian W.,Tianjin University of Science and Technology | Tian W.,On-Line Monitoring | Choudhary R.,University of Cambridge | Augenbroe G.,Georgia Institute of Technology | Lee S.H.,Lawrence Berkeley National Laboratory
Building and Environment | Year: 2015

Statistical energy modelling & analysis of building stock is becoming mainstream in the context of city or district scale analysis of energy saving measures. A common aspect in such analyses is that there is generally a set of key explanatory variables - or the main inputs - that are statistically related to a quantity of interest (end-use energy or CO2). In the context of energy use in buildings, it is not uncommon that the explanatory variables may be correlated. However, there has been little discussion about the correlated variables in building stock research. This paper uses a set of campus buildings as a demonstrative case study to investigate the application of variable importance and meta-model construction in the case of correlated inputs when quantifying energy demand of a building stock. The variable importance analysis can identify key factors that explain energy consumption of a building stock. To this end, it is necessary to apply methods suitable for correlated inputs because the observational data (inputs) of buildings are usually correlated. For constructing statistical energy meta-models, two types of regression models are used: linear and non-parametric models. The results indicate that the linear models perform well compared to the complicated non-parametric models in this case. In addition, a simple transformation of the response, commonly used in linear regression, can improve predictive performance of both the linear and non-parametric models. © 2015 Elsevier Ltd.

Li Z.,Tianjin University of Science and Technology | Li Z.,On-Line Monitoring | Wang S.,Tianjin University of Science and Technology | Wang J.,Tianjin University of Science and Technology | And 2 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2016

Gas distributor is a key component in fluidized beds. Various gas distributors for practical application have been successfully developed and studied in depth. Fluidization of coarse particles is still a challenge for good gas-solid contacting. In this study, a slotted gas distributor with simple structure was proposed for the fluidized bed processing coarse particles. The fluidization characteristics of the Geldart D type large particles (2-2.8 mm walnut shell) were investigated experimentally in a 285 mm × 190 mm × 700mm fluidized bed with the slotted gas distributor whose opening rate was 5.6%. The experimental results were compared with the ones obtained from the traditional perforated distributor. It was found that the bed expansion ratio increased by about 5% and the minimum fluidization velocity reduced by about 8% when using the slotted gas distributor, indicating that the slotted gas distributor had better fluidization characteristics for the large-sized particles. To explain the better fluidization performance of the slotted gas distributor, a computational fluid dynamics (CFD) model was developed based on the Eulerian-Eulerian model, the particle kinetic theory, the standard k-ε turbulence model and the SIMPLE algorithm. The CFD model was used to simulate the behaviors of the gas particle flow in the fluidized bed of walnut shell particles with slotted gas distributor or traditional perforated distributor, and the results of experiment and simulation were agreed well. The simulations were conducted under such operation conditions: The physical two-dimensional model of the rectangular fluidized bed was 285 mm × 700 mm with slotted gas distributor or traditional perforated distributor in which the opening rate was 5.6%. Particles packed in the fluidized bed had the volume fraction of 0.6 and the height of the bed was 200 mm. The superficial gas velocity of inlet was selected as operation parameter, which ranged from 0.615 to 1.128 m/s. The simulation results were compared on the bed pressure fluctuations due to bubble formation, the coalescence and eruption, the maximum bed expansion radio, the transient particle volume fraction distribution, the gas/particle velocity vector distribution and so on between the fluidized beds of these two distributors. It was observed that small bubbles first formed close to the gas distributor, coalesced when rising up, and finally erupted near the bed surface, which resulted in periodic fluctuations of bed pressure with different amplitudes and frequencies. Compared with the traditional perforated distributor, the frequency and amplitude of the bed pressure drop fluctuation caused by the slotted gas distributor were bigger and the bed expansion ratio was higher. The change of the particle concentration in the bed was scattered in the fluidized bed with slotted gas distributor, which was beneficial to the fluidization of particles near the bed wall. Also, the dead zone and recirculation area formed near the wall area were reduced. The V-shaped structure of the slotted gas distributor generated strong upward flow jets. The strong jets could deeply reach the material particle bed and easily bring the formation of bigger bubbles. The bigger bubbles caused more intensive disturbance inside the material bed, and thereby the bed pressure drop fluctuation and the bed expansion ratio were improved. Four small circulations were observed to form within the fluidized bed with slotted gas distributor, which was beneficial to the better mixing of gas and particle. Therefore, coarse particles of walnut shell can be well fluidized with the slotted gas distributor. The study provides a reference for the design and selection of fluidized bed distributor in the process of coarse particle processing in fluidized bed. © 2016, Chinese Society of Agricultural Engineering. All right reserved.

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