Ni Mingjiang

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.

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.

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.

A dielectric multilayer filter for combining photovoltaics with a stirling engine for improvement of the efficiency of solar electricity generation

In this Letter we outline a dielectric multilayer spectrally selective filter designed for solar energy applications. The optical performance of this 78-layer interference filter constructed by TiOx and SiO2 is presented. A hybrid system combining photovoltaic cells with a solar-powered Stirling engine using the designed filter is analyzed. The calculated results show the advantages of this spectrally selective method for solar power generation.

Development of an evaporation crystallizer for desalination of alkaline organic wastewater before incineration

A wastewater evaporation-desalination pretreatment method was introduced to remove the Na+ and K+ salts in volatile organic compounds (VOCs) wastewater before it was fed into the incinerator. VOCs in the wastewater were volatilized in the evaporation system and then the vapor was combusted in an incinerator. Simulated phenol wastewater containing sodium chloride was evaporated and concentrated and sodium chloride was crystallized in different parameters. The experimental results showed that the higher initial concentration of sodium chloride increases the ratio of volatilization of VOCs, which was due to the effect of “salting out” (a decrease in the solubility of the nonelectrolyte, in the solution, or more rigorously, an increase in its activity coefficient, caused by the salt addition (Furter and Cook, 1967)). When evaporation speed was increased from 1.67 ml/min to 2.73 ml/min, the total removal coefficient of sodium chloride was about 99.88%–99.99%. This pretreatment procedure eliminates the slag phenomenon caused by Na+ and K+ salts during wastewater incineration, so the incinerator could operate continuously, and the wastewater evaporation could increase the heat value of wastewater, and the operation cost, would be reduced.

Heat transfer in a large-scale circulating fluidized bed boiler

Heat transfer of a furnace in a large-scale circulating fluidized bed (CFB) boiler was studied based on the analysis of available heat transfer coefficient data from typical industrial CFB boilers and measured data from a 12 MWe, a 50 MWe and a 135 MWe CFB boiler. The heat transfer of heat exchanger surfaces in a furnace, in a steam/water cooled cyclone, in an external heat exchanger and in the backpass was also reviewed. Empirical correlation of heat transfer coefficient was suggested after calculating the two key parameters, solids suspension density and furnace temperature. The correlation approach agrees well with the data from the large-scale CFB boilers.

THE PREDICTION AND MEASUREMENT OF PARTICLE BEHAVIOR IN CIRCULATING FLUIDIZED BEDS

ABSTRACT A two-dimensional gas-particle flow numerical model is presented which accounts for particle fluctuation and particle-particle collisions in the circulating fluidized beds. This model treats fluctuation of particle movement as a random Fourier series based on gas-flow fluctuation spectrum and hence is known as the fluctuation-spectrum-random-trajectory (FSRT) model. The model is used to predict the velocity particle trajectory and concentration of the particle-phase in circulating fluidezed beds. Measurements of particle velocity and the concentration of the particle-phase in circulating fluidized bed are carried out and the predictions of the FSRT model are compared with the experimental results. Some aspects of the behavior of the particle movement in circulating fluidized beds are also predicted.

Combustion of electronic wastes using a drop tube furnace

High temperature combustion is a key during the pyrometallurgical recycling for electronic wastes. Former researches relating to thermal treatment concentrated on thermal decomposition during electronic wastes pyrolysis and oxidation, using e.g. thermogravimetric analysis (TGA) or lab-scale batch-feeding furnace. In the present research, a bench-scale incineration system was developed to study the combustion of electronic wastes and the emission characteristics. The system features a continuously-fed drop tube furnace. By using it, the combustion proceeds under comparable conditions and the emitted flue gas is steady & uniform, the thermodynamic equilibrium approach for conversions of inorganic halogen could be investigated. It also equips with a cooling & sampling unit for investigating the emission of post-combustion area. The effects of operating conditions on the completeness of combustion and the emission of inorganic Br for waste printed circuit boards were investigated systematically by using this furnace. Under the proposed conditions, the combustion is quiet complete and more than 99.89% organobrominated compounds contained in raw materials are destroyed and convert to HBr & Br2 in flue gas. The two forms of inorganic bromine seem reach thermodynamic equilibrium within 0.25 s. Further experiments could provide the datum for analyzing the combustion performance, the emission characteristics of organic pollutants and the mechanism of chlorinated dioxins (PCDD/Fs) & brominated dioxins (PBDD/Fs) formation by fly ash catalyzed de novo synthesis.

The Mechanism of Naphthalene Decomposition in Corona Radical Shower System by DC Discharge

Polycyclic aromatic hydrocarbons (PAHs) from coal-fired boilers and waste incinerators are regarded as some toxic and difficult decomposition pollutants. In this paper, it was studied how the applied voltage, the initial concentration and the catalyst affected the naphthalene decomposition characteristics using a corona discharge radical shower system. The emission spectrum of OH (A2Σ+ → X2П) was detected to understand the decomposition mechanism, of naphthalene better. In addition, the decomposition by-products and the decomposition process were also analyzed initially. The results show that the increasing applied voltage and humidity is helpful to the naphthalene decomposition because of the increasing OH radicals. High initial concentration of naphthalene can heighten the decomposition amounts and the catalyst can improve the naphthalene decomposition. The main decomposed by-product is CO2 and H2O. However, there are also little CO and small-molecule organic compounds to be found because of the incompletely oxidative reactions.