No abstract

The crystal layer growth rate is governed by the heat transfer in a layer melt crystallization process and is essential to the separation efficiency. Herein, a numerical model was proposed to predict the solid−liquid (S-L) interface temperature and the growth rate of the crystal layer. The heat transfer equation was taken as the governing equation, combining crystal layer growth kinetics, mass balance, and heat balance in the model which were solved using the finite volume method. The calculation results provided details of temperature distribution in the crystal layer, temperature of the moving S-L interface, and the layer growth rate. The simulated results were validated by experiments using P-xylene as the model substance. Finally, the crystal layer growth rate was found to be very sensitive to the seeding supercooling, especially at the early stage right after seeding. The proper seeding supercooling could be optimized by this model according to both the optimized crystal layer growth rate and productivity.

In a one-way road tunnel with a sidewalk for pedestrians (total length: 667 m, 2 lanes: 7 m width, sidewalk: 3.5 m width), size-fractionated particles that were suspended in the air were sampled and tested for the potential health risks to pedestrians. These particles were predominantly emitted from motorized traffic. Particles down to the nano-size range were collected using a PM 0.07 sampler based on the "inertial filter" technology, which can be applied for the separation of nano-size particles. PM 10 and fine particles less than 1 μm were simultaneously monitored online by a tapered element microbalance (TEOM), a condensation particle counter (CPC) and scanning mobility particle sizer (SMPS), and a video camera was used to monitor the amount of traffic and the wind velocity inside the tunnel. Concentrations of mass and polycyclic aromatic hydrocarbons (PAHs) in each size range of particles were discussed relative to the total traffic amount, the types of motorized vehicles, and the sampling duration, and then compared with other data that had been either simultaneously or separately obtained at different sampling locations outside the tunnel.The correlation was clear between PM 0.1 and heavy traffic involving large diesel vehicles, such as buses and trucks. The mass concentrations and fractions of PAHs in the road tunnel became larger than at the mouth of the tunnel and the rural sampling site. PM emissions could be classified into fine particles smaller than 0.5 μm and coarse particles larger than 2.5 μm, which referred to exhaust and road dust, respectively. PM 0.07 particles from vehicle exhaust might have contained a higher component of PAHs.

To analyze the relationship between nanoparticles and the chemical forms in an urban atmospheric environment, metallic particles with different diameters were collected using a nanoparticle sampling system and analyzed for chemical and morphological characteristics, bioactivity, and the risk of carcinogenic and non-carcinogenic effects. The source of the atmospheric particles was analyzed based on the enrichment factor method, and the carcinogenicity of the atmospheric particles was analyzed using the health risk model. The partition contents of metals extractable by a weak acid, including As, Ca, Cd, Cs, Pb, Sr, and Zn, were in a range of 32.17–71.4%, with an average value of 47.07%. The content of oxides and reducible metals of all of the elements was generally low. Potassium was distributed mainly in the residual and weak-acid-extractable fractions. Barium had a high proportion of the oxidation state. Each fraction of Zn was basically the same, while the content of the weak-acid-extractable fraction was slightly higher. We found bio-access potential to be positively correlated with a high proportion of the weak acid extracts such as Mg, Sr, and Zn. We also found there to be a large weak-acid-extractable fraction (F1) and residual fraction (F4) and relatively enriched elements and strongly enriched elements, which means F1 and F4 may be the cause of enrichment. The hazard index (HI) and the total cancer risk (TCR) were far beyond the safety threshold when the diameter of the particle was in the range of 0.1–0.5 μm, indicating that the residents in Dongguan city were experiencing obvious non-carcinogenic and carcinogenic risks.