Yaxin Su

Evolution and comparative assessment of ambient air quality standards in China

Abstract Ambient air pollution has become one of the key issues in China because it is highly associated with economic development, energy consumption, the atmospheric environment, and public health. Ambient air quality standards are guidelines of environmental management and fundamentals of air pollution emission control. To adapt to the changing environmental situation, China’s ambient air quality standard GB 3095 was established in 1982, amended in 1996, again in 2000, and most recently in 2012. This article presents a historical analysis on the evolution of China’s ambient air quality standards focusing on the critical pollutants and their concentration thresholds, as well as a comparative analysis that illustrates the differences to important developed countries and international organizations. The results show that the ambient air quality standard in China features a progressive update in pollutant items, more stringent concentration thresholds, and more scientific planning. Although there are differences in the economic, technological, and environmental development levels, China’s latest ambient air quality standard GB 3095-2012 is found to be comparable with other important standards. However, the support of macro policies and technical measures are necessary to ensure the standard is implemented more effectively.

Cyclone performances depend on multiple factors: comments on "A CFD study of the effect of cyclone size on its performance parameters" by Mehdi Azadi et al. (2010).

In the manuscript published by Azadi et al. [1], the authors invesigated the effect of cyclone size on its performance parameters. n their work, the authors used the CFD approach to simulate the as-particle flow inside cyclones with three different sizes, and hen determined the effect of cyclone size on the particle cut-off iameter and pressure drop. As interested yet critical readers of the article, we would like to hare some understanding and comments on the effects of cyclone imensions and physical properties of particles on the particle cutff diameter, the effect of cyclone size on the pressure drop, and herefore the major conclusions derived from their work.

Effect of calcium oxide (CaO) and sawdust on adhesion and cohesion characteristics of sewage sludge under agitated and non-agitated drying conditions

Stickiness phenomenon is widely observed in sewage sludge drying practices. This paper is aimed at demonstrating and comparing the sticky properties of sewage sludge through non-agitated and agitated drying tests specially designed for sewage sludge. Special attentions were paid to the effects of additives, i.e. CaO, fine sawdust (FSD) and coarse sawdust (CSD), on the adhesive and cohesive characteristics of sewage sludge. The results indicated that the sticky properties of the sludge were markedly different under the different testing methods, and was also greatly influenced by CaO or sawdust addition. For instance, in the non-agitated drying tests, CaO can significantly enhance the maximum adhesive and cohesive stresses of the sludge, whereas in the agitated drying tests, the torque of agitation, which strongly correlated with the cohesive stress of the sludge, was lowered by CaO addition. During agitated drying process, sludge lump with CaO addition started to break up at higher moisture content than that of original sludge. On the other hand, sawdust also affected the sticky properties of sludge in a way that was totally different with CaO. After sawdust addition (at 5-10%WS (wet sludge basis)), the cohesive stress of the sludge was markedly increased due to strengthening of mechanical interlocking inside the sludge, whereas the adhesiveness of the sludge was lowered by sawdust addition. The influencing mechanisms of CaO and sawdust under the different testing methods were detailedly discussed in the paper.

Numerical modelling of effect of channel width on heat transfer and ventilation in a built-in PV-Trombe wall

The heat transfer and air flow rate in a built-in PV-Trombe wall with vertical inlet were numerically simulated based on CFD method. Effect of channel width on heat transfer and air flow rate was discussed. As the channel width increased, the natural convective heat transfer was enhanced and the PV surface was better cooled by the air which improved the PV electricity efficiency slightly. The ventilation rate through the built-in PV-Trombe wall reached its maximum at an optimal ratio of the channel width to the channel height, (b/H)opt=1/5. Dimensionless expressions to calculate the averaged heat transfer coefficient, Nusselt number, and the air flow rate in term of a Reynolds number were correlated according to a modified Rayleigh number by multivariable regression analysis.

Second Law Optimization of Pin Fin Heat Exchangers with Lateral Ejection Holes

The authors theoretically studied the entropy generation during heat transfer of a pin fin array in channels with lateral ejection holes for a turbine blade. The entropy generation model was established based on the second-law analysis. The distribution of the entropy generation due to heat transfer and fluid friction irreversibility respectively was analyzed and a comparison was made for three typical short pin fin channels. The entropy generation number component due to heat transfer decreases while Red increases, while the component due to fluid friction increases with the increase of Red. The entropy generation number takes its minimum value when the two components meet and the corresponding Reynolds number is optimal. The ejection holes influence the energy lost of the working fluid. For the three cases studied in the paper, case b with short ejection holes gives the best comprehensive thermal performance with comparison to cases with no and long ejection holes. The results would be helpful for the design of the heat dissipation of pin fin heat exchangers.

Numerical Study of Effect of Burner Jet Parameters on High Temperature Air Combustion of Coal Gas

A numerical simulation was carried out on the High Temperature Air Combustion of coal gas in an industrial furnace with a multi-jet burner. The effect of jet parameters on NOx emission, temperature and oxygen distribution was investigated. A Beta function PDF(Probability Density Function) combustion model was selected to simulate the gas combustion combined with the standard k-ƒÕ model to simulate the turbulent flow. The radiation was simulated by a Discrete Ordinates method. The NOx emission was simulated by thermal NOx model. The effect of jet parameters, i.e., the velocity ratio of fuel jet and air jet and the fuel jet inclined angle on the combustion characteristics was discussed. The simulated results showed that the jet parameters changed the recirculation of flue gas in the furnace leading to different mixing of the fuel, air and hot flue gas which determined the local temperature, oxygen concentration and NOX production. As the velocity ratio of fuel jet and air jet and the fuel jet inclined angle increased, the flue gas recirculation was enhanced and the low oxygen zone enlarged. The maximum and mean temperature both decreased and NOX emission decreased.