Cen Ke-fa

Dependence of Nanofluid Viscosity on Particle Size and pH Value

We investigate the viscosity of silicon dioxide nanofluid at different particle sizes and pH values considering nanoparticle aggregation. The experimental and simulation results indicate that nanoparticle size is of crucial importance to the viscosity of the nanofluid due to aggregation. As the nanoparticle size decreases, the viscosity becomes much more dependent on the volume fraction. Moreover, when the nanoparticle diameter is smaller than 20 nm, the viscosity is closely related to the pH of the nanofluid, and fluctuates with pH values from 5 and 7.

Mechanism study on cellulose pyrolysis using thermogravimetric analysis coupled with infrared spectroscopy

Based on the investigation of the polysaccharide structure of cellulose by using Fourier transform spectrum analysis, the pyrolysis behaviour of cellulose was studied at a heating rate of 20 K/min by thermogravimetric (TG) analysis coupled with Fourier transform infrared (FTIR) spectroscopy. Experimental results show that the decomposition of cellulose mainly occurs at the temperature range of 550–670 K. The weight loss becomes quite slow when the temperature increases further up to 680 K and the amount of residue reaches a mass percent of 14.7%. The FTIR analysis shows that free water is released first during cellulose pyrolysis, followed by depolymerization and dehydration. Glucosidic bond and carbon-carbon bond break into a series of hydrocarbons, alcohols, aldehydes, acids, etc. Subsequently these large-molecule compounds decompose further into gases, such as methane and carbon monoxide.

Dissolution rate of limestone for wet flue gas desulfurization in the presence of sulfite

Limestone dissolution rate was measured by a pH-stat method with CO(2) sparging and dissolved sulfite. The dissolution rate of limestone under these conditions was found to be controlled by mass transfer and surface kinetics. As can be seen from the results, in the presence of sulfite, limestone dissolution rate increases with increasing stirring speed, reaction temperature and CO(2) partial pressure. The crystallinity of limestone has a great impact on the dissolution rate: The lower the value of the crystallinity of limestone is, the higher the dissolution rate is. The presence of sulfite promotes the dissolution rate when pH value is below 5.5 but inhibits it when pH value is above 5.5.

Numerical simulation of tube erosion by particle impaction

Abstract Erosion of tubes by coal particles or coal ash impingement has caused serious problems for many pulverized coal energy conversion systems. This type of erosion has led to many experimental investigations. This paper presents the numerical results of an investigation of coal particle dynamics about a tube. The calculation of particle trajectories takes into account the effect of turbulence using a stochastic particle dispersion model. The results from this study include the frequency of particle impact and the erosion distribution on the tube surface. Good agreement is found between the numerical method and experiment.

Numerical simulation of the effects of turbulence intensity and boundary layer on separation efficiency in a cyclone separator

From the point of view of the influence of turbulence structure, this paper presents an elementary numerical analysis of the interaction between a particle and a gas phase. The effects of turbulence structure and the thickness of boundary layer on the separation efficiency in a cyclone separator have been investigated. The effects of the Saffman force on the particle trajectory are also analyzed. The results indicate that the separation efficiency decreases with an increase in turbulence intensity and increases with a decrease in the thickness of the boundary layer. The Saffman force can enhance the separation of small particles and also can shorten their residence time in the cyclone.

Numerical and experimental study of finned tube erosion protection methods

Abstract Erosion of tubes by coal particles or coal ash impingement has caused serious problems to many pulverized coal energy conversion systems (such as the circulating fluidized bed combustion system). It is important to study erosion protection methods for tubes undergoing erosion. In this paper we present the results of numerical and experimental investigation of a new type of erosion-protection method: the finned tube erosion protection method. An experimental investigation of finned tube erosion processes was made by placing erosionprone wax cylinders with fins in a bench-scale cold flow circulating fluidized bed to simulate the long-term erosion effect. A numerical study was conducted for the flow of a dilute particle-laden gas moving past a finned tube undergoing erosion. An orthogonal curvilinear coordinate system was used to calculate turbulent flow around the finned tube. The calculation of particle trajectories took into account the effect of the turbulence with a stochastic particle dispersion model. The results from this study show that the finned tube is a simple and efficient erosion protection method in most industrial two-phase systems where erosion occurs. The fin relative height, the fin number and the angle between two adjacent fins are three important parameters which affect finned tube erosion protection abilities.

Wavelet-based depth-of-field extension, accurate autofocusing, and particle pairing for digital inline particle holography

Depth-of-field extension and accurate 3D position location are two important issues in digital holography for particle characterization and motion tracking. We propose a method of locating the axial positions of both opaque and transparent objects in the reconstructed 3D field in the wavelet domain. The spatial-frequency property of the reconstructed image is analyzed from the viewpoint of the point spread function of the digital inline holography. The reconstructed image is decomposed into high- and low-frequency subimages. By using the variance of the image gradient in the subimages as focus metrics, the depth-of-field of the synthesis image can be extended with all the particles focalized, and the focal plane of the object can be accurately determined. The method is validated by both simulated and experimental holograms of transparent spherical water droplets and opaque nonspherical coal particles. The extended-focus image is applied to the particle pairing in a digital holographic particle tracking velocimetry to obtain the 3D vector field.

Experimental study of the influence of acid wash on cellulose pyrolysis

The analysis of microstructure and polymerization degree showed that acid wash altered the cellulose morphology and decreased the polymerization degree significantly. A series of experiments were done to study the effect of acid wash on cellulose rapid pyrolysis. Experimental results showed that under acid pretreatment, the yield of bio-oil decreased while the production of gas and char increased. With an increase in acid concentration, this trend would be further enhanced. Sulphuric acid limited the formation of bio-oil more effectively than hydrochloric acid and phosphoric acid. According to the GC-MS analysis of bio-oil, high-concentration acid wash restrained the formation of levoglucosan by catalyzing dehydration process and cross linking reaction.

Experimental study of a finned tubes impact gas-solid separator for CFB boilers

Abstract We present a finned tubes impact gas-solid separator with enhancing heat transfer behavior which can be used in circulating fluidized bed boilers (CFBB). Experimental results show that this separator has advantages such as high separation efficiency, low pressure drop and compact structure. Furthermore, it can also enhance heat transfer, and fins welded on the tubes can be cooled at the same time by the work medium in the tubes so that they can be made by common boiler steel. We describe the fluid dynamics characteristics, heat transfer and separation performance of the finned tubes separator through a series of experiments.

Study on mixing performance of municipal solid waste (MSW) in differential density fluidized beds (FBs)

Mixing performances of municipal solid waste (MSW) in differential density fluidized beds (FBs) have been investigated simulating five kinds of materials (plastic, wood, candle, coal and coal-stone). The results show that the differential density FB technology can realize good mixing performances for different MSW components. The density of MSW components has a conspicuous effect on the mixing characteristics of FB. Also, the size of the components has effects. The mixing index is adopted via a regression analysis to the experimental data, and a mixing expression formula is obtained, that will be beneficial for MSW incinerator design and operation.