Lagrangian simulation of deposition of CO gas-solid sudden expansion flow

Freezing and blockage resulting from the deposition of solid CO₂ formed because of sudden expansion of the downstream pipe during the release of CO₂ through safety valves, will endanger the protected equipment. To overcome this problem, the characteristics of the CO₂ gas-solid sudden expansion flow are studied by using the disperse Lagrangian model. A comparison of the calculated deposition of the solid CO₂ with the experimental results shows that they are in reasonable agreement. The simulation results show that the size of the solid CO₂ formed should not be in the range of 0.04–0.07 mm (St number 3.2–9.8). This can be achieved by using an appropriate flow cross section of the safety valve.     

Hydrogen production from co-gasification of coal and biomass in supercritical water by continuous flow thermal-catalytic reaction system

Hydrogen is a clean energy carrier. Converting abundant coal sources and green biomass energy into hydrogen effectively and without any pollution promotes environmental protection. The co-gasification performance of coal and a model compound of biomass, carboxymethylcellulose (CMC) in supercritical water (SCW), were investigated experimentally. The influences of temperature, pressure and concentration on hydrogen production from co-gasification of coal and CMC in SCW under the given conditions (20–25 MPa, 650°C, 15–30 s) are discussed in detail. The experimental results show that H₂, CO₂ and CH₄ are the main gas products, and the molar fraction of hydrogen reaches in excess of 60%. The higher pressure and higher CMC content facilitate hydrogen production; production is decreased remarkably given a longer residence time. Translated from Journal of Xi’an Jiao Tong University, 2005, 39(5): 454–457 [译自: 西安交通大学学报]     

NOx control in large-scale power plant boilers through superfine pulverized coal technology

Superfine pulverized coal technology can effectively reduce NO _x emission in coal-fired power plant boilers. It can also economize the cost of the power plant and improve the use of the ash in the flue gas. Superfine pulverized coal technology, which will be widely used in China, includes common superfine pulverized coal technology and superfine pulverized coal reburning technology. The use of superfine pulverized coal instead of common coal in large-scale power plants will not only reduce more than 30% of NO _x emission but also improve the thermal efficiency of the boiler. __________ Translated from Journal of Shanghai University of Electric Power, 2006, 22(4): 333–337 [译自: 上海电力学院学报]     

Analysis of flow and heat transfer characteristics of porous heat-storage wall in greenhouse

The flow and heat transfer characteristics of porous heat-storage wall in greenhouse are studied by using the one-dimensional steady energy two-equation model for saturated porous medium. The results show that the heat exchange between the air and the solid matrix of the porous heat-storage wall depends upon the inlet air velocity, the porosity and the permeability of porous medium, and the thermal conductivity of the solid matrix. Because the incidence of solar radiation on the porous heat-storage wall is not uniform, the new composite porous solar wall with different porosity is proposed to reduce the disadvantageous effect. __________ Translated from Journal of Engineering Thermophysics, 2008, 29(2): 284–286 [译自: 工程热物理学报]     

Application of rapid thermal processing on SiNx thin film to solar cells

Rapid thermal processing (RTP) of SiN _x thin films from PECVD with low temperature was investigated. A special processing condition of this technique which could greatly increase the minority lifetime was found in the experiments. The processing mechanism and the application of the technique to silicon solar cells fabrication were discussed. A main achievement is an increase of the minority lifetime in silicon wafer with SiN _x thin film by about 200% after the RTP was reached. PC-1Dsimulation results exhibit an enhancement of the efficiency of the solar cell by 0.42% coming from the minority lifetime improvement. The same experiment was also conducted with P-diffusion silicon wafers, but the increment of minority lifetime is just about 55%. It could be expected to improve the solar cell efficiency if it would be used in silicon solar cells fabrication with the combination of laser firing contact technique. __________ Translated from Journal of Shanghai Jiaotong University, 2008, 42(1): 152–155 [译自: 上海交通大学学报]     

Experimental study of humid air reverse diffusion combustion in a turbulent flow field

Experiments were performed to investigate the differences between the propane/air turbulent diffusion reactive flows past bluff-body and the propane/humid air turbulent diffusion reactive flows in the same conditions. The velocity distributions of the non-humid reactive flow fields and the humid reactive flow fields were measured by particle image velocimetry (PIV) techniques. The temperature fields were measured by high temperature thermocouples, and NO_x distributions were obtained by using gas detection instruments. The results show that although humid air reactive flow fields are similar to non-humid flow fields in general, there are some differences in the humid air combustion flow field comparing with the non-humid combustion flow field: the center of the reversed-flow region goes forward; the dimension of the reversed-flow region is smaller; the peak temperature and NO_x formation are reduced. It is suggested that humid air combustion is helpful to shorten the axial length of combustors, and reduce the formation of pollutants. __________ Translated from Journal of Shanghai Jiaotong University, 2006, 40(8): 1 287–1 292 [译自: 上海交通大学学报]     

Study on combustion characteristics of blended coals

Power plants in China have to burn blended coal instead of one specific coal for a variety of reasons. So it is of great necessity to investigate the combustion of blended coals. Using a test rig with a capacity of 640 MJ/h with an absolute milling system and flue gas online analysis system, characteristics such as burnout, slag, and pollution of some blended coals were investigated. The ratio of coke and slag as a method of distinguishing coal slagging characteristic was introduced. The results show that the blending of coal has some effect on NO _x but there is no obvious rule. SO _x emission can be reduced by blending low sulfur coal. Translated from Proceedings of the CSEE, 2005, 25(18): 97–103 [译自: 中国电机工程学报]     

Optimization and performance prediction of a new near-zero emission coal utilization system with combined gasification and combustion

In accordance with the new near-zero emission coal utilization system with combined gasification and combustion, which is based on the CO₂ acceptor gasification process, the product gas composition of the gasifier and the combustor was calculated by means of thermodynamic equilibrium calculation software FactSage 5.2. Based on these calculations, the whole system efficiency calculation method that complies with the mass and energy conservation principle was established. To enhance the system efficiency, the system pressure and the gasifier carbon conversion ratio were optimized. The results indicate that the system efficiency increases with increasing pressure and gasifier carbon conversion ratio. After taking into consideration the influence of the pressure and carbon conversion ratio on the performance of the system, the gasifier and the combustor were synthetically studied. The optimum system pressure and carbon conversion ratio were obtained as 2.5 MPa and 0.7, respectively. The system efficiency could reach around 62.1% when operated in these two optimum parameters. If the advanced ion transport membrane (ITM) air separation technology is used, there would be an increase of another 1.3%. Translated from Proceedings of the CSEE, 2006, 26(9): 7–13 [译自: 中国电机工程学报]     

Study of two-phase flow regime identification in horizontal tube bundles under vertical upward cross-flow condition using wavelet transform

A wavelet-transform based approach for flow regime identification in horizontal tube bundles under vertical upward cross-flow condition was presented. Tests on two-phase flow pattern of R134a were conducted under low mass velocity and flow boiling conditions over ranges of mass flux 4–25 kg/m²·s, vapor quality 0.02–0.90. Time series of differential pressure fluctuations were measured and analyzed with discrete wavelet transform. Different time-scale characteristics in bubbly flow, churn flow and annular flow were analyzed. The wavelet energy distributions over scales were found to be appropriate for flow regime identification. Based on the wavelet energy distribution over characteristic scales, a criterion of flow regime identification was proposed. The comparison with experiment results show that it is feasible to use the discrete wavelet transform as the tool of flow regime identification in horizontal tube bundles under vertical upward cross-flow condition. __________ Translated from Journal of Shanghai Jiaotong University, 2007, 41(3): 337–341, 346 [译自: 上海交通大学学报]     

Numerical analysis of aerodynamic noise radiated from cross flow fan

The flow field in a cross flow fan was simulated by solving the 2-D unsteady Reynolds-averaged Navier-Stokes equations. The calculated pressure fluctuations of the blades, the vortex wall, and the rear wall were then used as noise sources to calculate the sound field. The Ffowcs Williams-Hawkings (FW-H) equation was employed to predict the noise field caused by these sources. The predictions show that the rear wall and the vortex wall sources contribute significantly to the total noise and that both the predicted aerodynamic performance and noise agree well with the experimental results. __________ Translated from J Tsinghua Univ (Sci & Tech), 2007, 47(2): 236–239 [译自: 清华大学学报(自然科学版)]     

Theoretical analysis of deposition and melting process during throttling high pressure CO2 into atmosphere

Previous study has discovered that periodic solid CO₂ deposition and melting phenomena happen during releasing high pressure CO₂ through a safety valve from CO₂ refrigeration system into atmosphere, and that a longer duration of the deposition and a shorter duration of melting are advantageous for the system safety. In order to know the suitable parameters to get a longer duration of the deposition and a shorter duration of melting, a Lagrangian particle-trajectory model and a Nusselt-type model are presented for the deposition and melting, respectively. The validation of the models was done by comparison of the calculation results and experimental data. Calculation with the models shows that the diameter of the formed solid CO₂ should not be in the range of 0.04–0.07 mm in order to avoid a shorter duration of the deposition and that increase of the tube diameter can greatly prolong the melting process. It is also found that the tube diameter must be carefully chosen in order to maintain longer deposition and shorter melting process.     

Optimization of Venturi tube design for pipeline pulverized coal flow measurements

A Venturi flow meter was designed to accurately measure the mass flow rate of pulverized coal in power plant pipelines. Numerical simulations of the dilute turbulent gas-solid two-phase flow in a horizontal Venturi tube were used to study the effects of Venturi tube geometry on the pressure distribution in the mixture. The results show that Venturi tube geometry strongly influences the metering of the dilute gas-particle two-phase flow. The geometry can be optimized to improve the precision of the measurement and ensure stable measurements. Furthermore, the geometries of three types of Venturi tubes were optimized for an experimental study of pulverized coal mass flow rate measurements. __________ Translated from Journal of Tsinghua University (Sci & Tech), 2007, 47(5): 666–669 [译自: 清华大学学报( 自然科学版)]     

Experimental research on catalysts and their catalytic mechanism for hydrogen production by gasification of peanut shell in supercritical water

Peanut shell, mixed with sodium carboxymethyl-cellulose, was gasified at a temperature of 450°C and a pressure range from 24 to 27 MPa with the presence of different catalysts, including K₂CO₃, ZnCl₂ and Raney-Ni. The experimental results show that different catalysts have greatly different effects on the reaction. Gasification efficiency (GE), hydrogen gasification efficiency (GHE), carbon gasification efficiency (GCE), yield of hydrogen production and potential yield of hydrogen production are applied to describe the catalytic efficiency. From the result of gaseous components, ZnCl₂ has the highest hydrogen selectivity, K₂CO₃ is lower, and Raney-Ni is the lowest, but Raney-Ni is the most favorable to gasify biomass among the three catalysts, and its G _E, G _HE, G _CE reach 126.84%, 185.71%, 94.24%, respectively. As expected, hydrogen selectivity increased and CH₄ reduced rapidly when the mixture of ZnCl₂ and Raney-Ni is used under the same condition. The optimization mixture appeared when 0.2 g of ZnCl₂ was added to 1 g of Raney-Ni, 43.56 g·kg⁻¹ of hydrogen production was obtained. In addition, the catalytic mechanisms of different catalysts were analyzed, and the possible reaction pathway was brought forward, which helped to explain the experiment phenomena and results correctly. __________ Translated from Journal of Xi’an Jiaotong University, 2006, 40(9): 1 263–1 267 [译自: 西安交通大学学报]     

Supersonic flows over cavities

The characteristics of supersonic cold flows over cavities were investigated experimentally and numerically, and the effects of cavities of different sizes on supersonic flow field were analyzed. The results indicate that the ratio of length to depth L/D within the range of 5–9 has little relevance to integral structures of cavity flow. The bevel angle of the rear wall does not alter the overall structure of the cavity flow within the range of 30°–60°, but it can exert obvious effect on the evolvement of shear layer and vortexes in cavities. __________ Translated from Journal of National University of Defense Technology, 2007, 29(3): 1–5 [译自: 国防科技大学学报]     

Numerical simulation of laminar premixed combustion in a porous burner

Premixed combustion in porous media differs substantially from combustion in free space. The interphase heat transfer between a gas mixture and a porous medium becomes dominant in the premixed combustion process. In this paper, the premixed combustion of CH₄/air mixture in a porous medium is numerically simulated with a laminar combustion model. Radiative heat transfer in solids and convective heat transfer between the gas and the solid is especially studied. A smaller detailed reaction mechanism is also used and the results can show good prediction for many combustion phenomena. Translated from Journal of Combustion Science and Technology, 2006, 12(1): 46–50 [译自: 燃烧科学与技术]     

Cavitation in semi-open centrifugal impellers for a miniature pump

Cavitation in miniature pumps was investigated experimentally for two semi-open centrifugal impellers. Although both impellers had the same blade cross-section, one impeller had a two-dimensional blade, while the other had a leaned blade. The flows were also analyzed using a numerical model of the three-dimensional turbulent flow in the pumps near the peak efficiency point using the k-ɛ turbulence model and the VOF cavitation model. The average cavitation performance of each impeller was satisfactorily predicted by the numerical simulations. The results show that the miniature pumps have similar cavitation performances as an ordinary-size pump, with the cavitation performance of the semi-open impeller reduced by increased axial tip clearances. Also, both the hydraulic and cavitation performance of the semi-open impeller were improved by the leaned blade. The results also show that uniform flow upstream of the impeller inlet will improve the cavitation performance of a miniature pump. __________ Translated from J Tsinghua Univ (Sci & Tech), 2006, 46(8): 1451–1454 [译自: 清华大学学报(自然科学版)]     

Control of homogeneous charge compression ignition combustion in a two-cylinder gasoline direct injection engine with negative valve overlap

Homogeneous charge compression ignition (HCCI) has challenges in ignition timing control, combustion rate control, and operating range extension. In this paper, HCCI combustion was studied in a two-cylinder gasoline direct injection (GDI) engine with negative valve overlap (NVO). A two-stage gasoline direct injection strategy combined with negative valve overlap was used to control mixture formation and combustion. The gasoline engine could be operated in HCCI combustion mode at a speed range of 800–2 200 r/min and load, indicated mean effective pressure (IMEP) range of 0.1–0.53 MPa. The engine fuel consumption is below 240 g/(kW⁻¹·h⁻¹), and the NO _x emission is below 4 × 10⁻⁵ without soot emission. The effect of different injection strategies on HCCI combustion was studied. The experimental results indicated that the coefficient of variation of the engine cycle decreased by using NVO with two-stage direct injection; the ignition timing and combustion rate could be controlled; and the operational range of HCCI combustion could be extended. Translated from J Tsinghua Univ (Sci & Tech), 2006, 46(5): 720–723 [译自: 清华大学学报]     

Study on the NOx release rule along the boiler during pulverized coal combustion

Numerical simulation and experimental study on NO _x release along the boiler during pulverized coal combustion have been conducted. With the increase of temperature the NO _x emission increased and the peak value of NO _x release moved forward. But when the temperature increased to a certain degree, NO _x emission began to reduce. NO _x emission increased with the increase of nitrogen content of coal. The peak value of NO _x release moved backwards with the increase of coal rank. NO _x emission increased obviously with the increase of stoichiometric ratio. There existed a critical average diameter of the pulverized coal (d _c ). If d ⩽ d _c , NO _x emission reduced with the decrease of pulverized coal size. If d > d _c , NO _x emission reduced with the increase of the pulverized coal size. The results showed that the simulation results are in agreement with the experimental results for concentration distribution of NO _x along the axis of the furnace. Translated from Proceeding of the CSEE, 2006, 26(1): 35–39 [译自: 中国电机工程学报]     

Experimental study on the temperature dependence of ultraviolet absorption cross-sections of sulfur dioxide

The photoabsorption cross-sections of sulfur dioxide were measured in the spectral regions of 200–230 nm and 275–315 nm at 298–415 K, using a grating monochromator with a resolution of 0.2 nm. The discrete absorption cross-section is directly correlated with the number of quantum excited from the base state. The absorption cross-sections at the peaks of discrete bands decreased linearly with the increase of temperature, which corresponded to the decrease in the population of vibrational and rotational transitions from the base level to higher excitation levels. The absorption cross-section peaks decreased linearly when the temperature increased from 298 to 415 K, with relative drops of 74.0% and 75.8% at 200–230 nm and 275–315 nm, respectively. Another distinctive feature of sulfur dioxide absorption spectra in the above two spectral regions was the quasiperiodic structure of the absorption peaks, whose equal wavelength intervals were 1.53 nm and 1.95 nm, respectively. Red and blue shifts were not found at the absorption peak positions. __________ Translated from Journal of Zhejiang University (Engineering Science), 2007, 41(2): 329–332 [译自: 浙江大学学报(工学版)]     

Characteristics of force acting on adjustable axial flow pump blade

The internal three-dimensional turbulent flow of adjustable axial-flow pump arrangement was simulated, and the force acting on the blade surface was calculated under different operating conditions. Based on the calculated results, finite element method (FEM) was adopted to analyze stress and strain distributions of the adjustment blade in different operations. Hydraulic moment, centrifugal moment and friction moment which must be conquered by adjusting the blades were also calculated. __________ Translated from Journal of Shanghai University (Natural Science), 2007, 13(3): 314–319 [译自: 上海大学学报]