Air pollution caused by atmospheric particulate and gaseous pollutants has drawn broad public concern globally. In this paper, the spatial-temporal distributions of major air pollutants in Shenzhen from March 2013 to February 2014 are discussed. In this study, ground-site monitoring data from 19 monitoring sites was used and spatial interpolation and spatial autocorrelation methods were applied to analyze both spatial and temporal characteristics of air pollutants in Shenzhen City. During the study period, the daily average concentrations of Particulate Matter (PM 10 and PM 2.5 ) ranged from 16-189 µg/m 3 and 10-136 µg/m 3 , respectively, with 13 and 44 over-limit days, indicating that particulate matter was the primary air pollutant in Shenzhen. The highest PM occupation in the polluted air was observed in winter, indicating that fine particulate pollution was most serious in winter. Meanwhile, seasonal agglomeration patterns for six kinds of air pollutants showed that Guangming, Baoan, Nanshan, and the northern part of Longgang were the most polluted areas and PMs were their primary air pollutants. In addition, wind scale and rainfall played an important role in dissipating air pollutant in Shenzhen. The wind direction impacted the air pollution level in Shenzhen in multiple ways: the highest concentrations for all air pollutants all occurred on days with a northeast wind; the second highest ones appeared on the days with no wind. The concentrations on days with north-related winds are higher on average than those of days with south-related winds.

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This paper presents a hybrid methodology to analyze the commercial measures of changing stator windings and adjusting air gap length to upgrade efficiency of typical three-phase direct-on-line induction motors with die-cast copper rotor (DCR). The calculation is carried out through combining the time-stepping and time-harmonic finite element analysis (FEA) and the circuit equivalent circuit model. Typical full-load performance of stator windings with different air gap lengths are computed by MATLAB invoking the 2D transient and eddy current field analysis in ANSYS/MAXWELL. Then, MATLAB scripts about post-processing of the FEA results are used to obtain the full-load running performance including the loss distribution and circulating current. The MATLAB scripts of circuit model built based on the FEA results is used to compare the overload and starting performance. After that, four stators with the four windings and three DCRs with different air gap of an 11 kW motor are fabricated and tested to validate the calculations. By comparing results from both calculations and measurements, it is shown that the factors of stator windings and air gap length can effectively improve the efficiency of the 11 kW DCR induction motor without the addition of extra materials. The motor with the 11/12 pitch Y-∆ series winding and 0.6 mm air gap has the best performance, in terms of efficiency, overloading capability and starting performance. Its efficiency can increase from 90% to the highest 92.35% by sole adjustment of stator winding and air gap length.Many technical measures have been investigated for improving the efficiency of induction motors. The higher efficiency can usually be achieved by increasing the active materials, such as increasing the stack length [5,6], in induction motors. Another measure of upgrading materials such as premium electrical grade lamination steel is used for decreasing core losses and Ohmic losses [6][7][8].The efficiency can also be improved by enhancing the performance of cooling and bearing systems to reduce the mechanical losses [7] and improving cooling performance to make Ohmic losses less significant [9]. These methods either rise the raw material cost or increase manufacturing complexity. Although geometry optimization techniques [10][11][12][13][14][15][16] can be used to increase the efficiency of induction motors without increasing the active materials, this technique ends up producing a different design from the original one. Consequently, a new stator and rotor punching mold is required and additional cost results. It can be seen that in practice these measures can only be used to design a new motor, therefore many manufacturers have paid more attention to ways of increasing the efficiency of their induction motors with the least cost. That means the techniques should change construction or parameters of the existing motors as little as possible. Die-cast copper rotor (DCR) technology that involves the development of heated nickel-base alloy dies presents a potential route to design hi...

To investigate the performance of the heat and mass transfer of ammonia water during the process of falling film evaporation in vertical tube evaporator, a mathematical model of evaporation process was developed and solved based on stream function. Then an experimental study of falling film evaporation was carried out in order to validate the mathematical model. A series of parameters, such as velocity, film thickness and concentration, etc., were obtained from the mathematical model. The calculated results show that the average velocity and the film thickness change sharp at the entrance region when x \ 100 mm, while they vary slightly in the fully developed region when x [ 100 mm. The film thickness depends largely on the flow rate of solution. It is observed that the heating power and mass flow of solution significantly affect the concentration difference between the inlet and outlet of evaporation tube. The calculated results reveal that the tube length has a significant impact on the amounts of ammonia vapor evaporated. It is suggested that the roll-worked enhanced tube should be used in order to decrease the concentration gradient in the film thickness direction and enhance the heat and mass transfer rate. Furthermore, the experimental and calculated results indicate that the inlet solution concentration has a great influence on the heat exchange capacity, the amounts of ammonia vapor evaporated and the evaporation pressure. AbbreviationsC P Specific heat, J kg -1 K -1 D Tube diameter, m D m Diffusion coefficient, m 2 /s H Specific enthalpy, J/kg L Tube length, m m Solution mass flow, kg/h mE The amount of evaporated ammonia vapor, kg/h _ m Evaporation rate, kg/s/m 2 N Sequence number of experiment P Evaporating pressure, kPa PE Percent of evaporated ammonia vapor, % Q Heat exchange capacity between hot water and solution, kW T Temperature,°C u Film velocity of x direction, m/s v Film velocity of y direction, m/s V Volumetric flow of water, L/h DH Enthalpy difference, J/kgGreek symbols n Mass concentration of solution, kg/kg d Film thickness, m U Spray density, kg m -1 s -1 l Dynamic viscosity, N s/m 2 q Density, kg/m 3 k Thermal conductivity, W m -1 K -1