660MW切圆燃烧塔式锅炉烟温偏差机理数值模拟

降低烟温偏差是塔式锅炉的特性之一,但实际运行过程中其烟温偏差仍存在,目前还缺乏其偏差形成机理的深入研究。以一台660 MW四角切园燃烧的塔式锅炉为对象,研究了额定工况下的屏式受热面区域烟气流场偏斜与温度偏差特性;设计了3种不同的烟道结构和屏式受热面布置工况,研究其烟温偏差机理。结果表明:模拟值和烟温偏差特性与试验值和实际运行偏差特性一致。屏式受热面区域存在明显的烟气流动偏斜和温度偏差,左侧区域的速度和温度明显高于右侧区域;随着高度增加,左右两侧的流动和烟温偏差先增后减,在标高68 m的三级过热器入口附近烟温偏差达到最大值。引起烟气流动和烟温偏差的原因有两方面:一是在受热面管屏分割约束的作用下,旋转上升进入屏区的烟气垂直于管屏方向的速度分量被迫发生转向,导致靠近左侧区域烟气主要向前墙流动,而右侧区域烟气主要向后墙流动。二是由于炉膛顶部烟气出口不对称布置在后墙,在引风机的抽吸作用下,左侧区域的烟气流动先向前墙倾斜,而后转向后墙,在整个屏式受热面区域分布较居中;而右墙区域的烟气先向后墙倾斜,后沿后墙区域被抽走;左右两侧不同的烟气流动偏差导致温度偏差。

Deviation of Carbon Dioxide-Water Gas-Liquid Balance from Thermodynamic Equilibrium in Turbulence h Experiment and Correlation

The carbon dioxide-water system was used to investigate the flowing gas-liquid metastable state. The experiment was carded out in a constant volume vessel with a horizontal circulation pipe and a peristaltic pump forced CO2 saturated water to flow. The temperature and pressure were recorded. The results showed that some CO2 escaped from the water in the flow process and the pressure increased, indicating that the gas-liquid equilibrium was broken. The amount of escaped CO2 varied with flow speed and reached a limit in a few minutes, entitled dy- namic equilibrium. Temperature and liquid movement played the same important role in breaking the phase equilib- rium. Under the experimental conditions, the ratio of the excessive carbon dioxide in the gas phase to its thermody- namic equilibrium amount in the liquid could achieve 15%.

Asymmetric breakup of a droplet in an axisymmetric extensional flow

The asymmetric breakups of a droplet in an axisymmetric cross-like microfluidic device are investigated by using a three-dimensional volume of fluid(VOF) multiphase numerical model. Two kinds of asymmetries(droplet location deviation from the symmetric geometry center and different flow rates at two symmetric outlets) generate asymmetric flow fields near the droplet, which results in the asymmetric breakup of the latter. Four typical breakup regimes(no breakup, one-side breakup, retraction breakup and direct breakup) have been observed.Two regime maps are plotted to describe the transition from one regime to another for the two types of different asymmetries, respectively. A power law model, which is based on the three critical factors(the capillary number,the asymmetry of flow fields and the initial volume ratio), is employed to predict the volume ratio of the two unequal daughter droplets generated in the direct breakup. The influences of capillary numbers and the asymmetries have been studied systematically in this paper. The larger the asymmetry is, the bigger the oneside breakup zone is. The larger the capillary number is, the more possible the breakup is in the direct breakup zone. When the radius of the initial droplet is 20 μm, the critical capillary numbers are 0.122, 0.128, 0.145,0.165, 0.192 and 0.226 for flow asymmetry factor AS= 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5, respectively, in the flow system whose asymmetry is generated by location deviations. In the flow system whose asymmetry is generated by two different flow rates at two outlets, the critical capillary numbers are 0.121, 0.133, 0.145, 0.156 and 0.167 for AS= 1/21, 3/23, 1/5, 7/27 and 9/29, respectively.

Stability Analysis of Closed-loop Water System

Aiming at closed-loop water system, by the method that shutting certain subcircuit, and solving the piping network, computing flow deviation of other subcircuits, then analyzing the rules of variation of stability with various factors, following conclusions are obtained： When reducing the resistance in main pipes, increasing resistance of subcircuits, system stability can be improved. Centralized regulation by changing power has no influence on system stability; centralized regulation by changing resistances will decrease system stability. Pump characteristics curve influences system stability, stability of the flat characteristic is superior to the steep one. For direct return system （DRS）, the stability of subcircuit which is farthest from the heat source is the worst. For reverse return system （RRS）, the stability of subcircuit in the middle of the pipe-network has the worst stability. Overall, stability of RRS is inferior to that of DRS.

A disposable cobalt-based phosphate sensor based on screen printing technology

Screen printing is a promising technology because of its simplicity, low-cost, high reproducibility, and efficiency in large-scale production. In this work, a cobalt-based phosphate sensor was successfully fabricated using the screen printing technology for the determination of phosphate concentration in the aqueous solution. The disposable sensor consists of a fully integrated cobalt （Co） electrode, which is a layer of carbon conductive ink （C） physically doped with Co powder, and Ag/AgCI reference electrode. The SEM images show that the morphology of the Co electrode changes after exposure to the phosphate solution, indicating that the expendable reaction exists during the measurement. At the Co/C ratio of 1：99, the cobalt-based phosphate sensor shows phosphate-selective potential response in the range of 10-4 to 10-1 mol/L, yielding a detection limit of lxl0-5 mol/L and a slope of over 30 mV/decade in acidic solution （pH 4.5） for HzPO4-. The proposed screen-printed sensor also ex- hibited significant reproducibility with a small repeated sensing deviation （i.e., relative standard deviation （R.S.D.） of 0.5%） on a single sensor and a small electrode-to-electrode deviation （i.e., R.S.D. 〈 3.2%）. The recovery study of HzPO4- in real wastewater samples gave values from 95.4% to 101.8%, confirming its application potential in the measurement of phosphate in real samples. Apart from its high selectivity, sensitivity, and stability comparable with a conventional bulk Co-wire electrode, the proposed phosphate sensor still yields many other advantages, such as low price, compactness, ease of use, and the possibility of integration with other analytical devices such as flow injection analysis.