In the summers of 2003 and 2004, size-separated suspended particulate matter (SPM) samples were collected with a high-volume Andersen air sampler at a site adjacent to Saitama Prefectural Route 57 in Saitama City. This sampling site is in an atmospherically polluted area that is also one of the “Specified Areas concerning Special Measures for Total Emission Reduction of Nitrogen Oxides and Particulate Matter from Automobiles” established in October 2002. We investigated carbonaceous compounds in the SPM before and after the Regulation on Diesel Vehicle Exhaust came into effect in October 2003 in Tokyo Metropolis and Saitama, Chiba, and Kanagawa prefectures. At the sampling site, elemental carbon (EC) in the fine particles (< 2µm) was derived mainly from diesel vehicle exhaust emissions, and crustal metals such as Al, Fe, and Mg in the coarse particles (> 2µm) were generated as road dust by vehicular traffic and wind. Correlations among chemical components generated by heavy-duty diesel vehicles suggest that the air quality is improving at the sampling site as a result of the enforcement of the Regulations on Diesel Vehicle Exhaust.
Jakarta city has serious air pollution problems which largely affected by transportation activities. In this paper, a comparative analysis of ambient roadside air pollution patterns in Jakarta city was conducted by using time series data at the existing roadside monitoring stations in 2003. The complex cause-effect relationships between meteorology and pollutants, thus, differ from one season to another. This paper attempts to apply structural equation models with latent variables, which represents the above-mentioned cause-effect relationships. The effectiveness of the established models is empirically confirmed that the goodness-of-fit indices are 0.783 for the weekday wet, 0.845 for the weekday dry, 0.775 for the weekend wet, and 0.822 for the weekend dry. The models give us a better way to analyze urban air pollution due to the results of the significant interactions among meteorological factors, wind and primary pollutants, and also their different influences on surface ozone for each season.
With increase in traffic volume and change in travel related characteristics, vehicular emissions and energy consumption have increased significantly since two decades in India. Current models are not capable of estimating vehicular emissions accurately due to inadequate representation of real-world driving. The focus of this paper is to understand the level of Indian Driving Cycle (IDC) in representing the real-world driving and to assess the impact of real-world driving on vehicular emissions. The study has revealed that IDC does not represent the real-world driving. Irrespective of road classes, about 30%of time is spent below 20km/h and the speed too exceeds IDC’s maximum limit of 42km/h. Emissions are estimated for different driving patterns using International Vehicle Emission (IVE) model. Emission rates vary significantly from one class of road to another and the largest effect is on local streets.
Vertical distribution of traffic-related pollutants inside an open street-canyon were observed in Suzhou, P.R. China, in 2005. The aim was to explore transfer and diffusion characteristics of vehicular exhaust emissions, as well as monitoring constraints associated with street canyons, courtyards and enclosed spaces. Vertical wind speed was found to strongly affect the fluctuation of all the pollutants. Daily average concentrations of NOx, NO2 and NO, as well as NO2/NOx ratio, were found to vary significantly alongside the vertical, proportionate to different average daily trends. Oxidation processes and photochemical activity are discussed to explain these phenomena. Daily CO trends were found to track closely with both NOx and Benzene, while the corresponding ratios were different relative to other published works. Different emission factors and driving conditions, as well as other emission sources types (especially for Benzene) are used to explain this point.
Passive sampling technique was used to preliminary assess the spatial and temporal distribution of air pollution in Suzhou (P.R. China) in 2003, with the aim to determine the representativeness of zones where to monitor air quality. 100 sites were selected to measure 15-days average concentrations of SO2, NOx, NO2, O3, NH3, Benzene, Toluene and Xylene in winter and summer. The distribution trend of NO and NO2, as well as the ratio of NO2/NOx was used to identify the heavy traffic polluted zones and design a network of monitoring stations (macrositing). NO2/NOx ratios varied throughout the two selected seasons and from site to site clearly demonstrating the different extent and completeness of NO → NO2 oxidation processes in time and space. The exceedance frequencies of pollutants was used to design the type of monitoring equipment to be installed at each station (micrositing). An air quality monitoring network composed by 9 monitoring stations has been finally established in 2004 according to the result of this survey and is now currently running.
Recently, because of the regulatory enhancement together with the technology development, concentration of pollutants in emission sources are decreasing significantly. Nitrogen oxides concentrations in stack gases of electric power plants are around 10ppm, and for gas combined power plant it is less than that for facilities constructed in city areas. Therefore, the concentrations at emission sources are less than one hundred times of the ambient concentrations in urban areas or for some cases almost ten times of them. The ventilation towers for automobile tunnels in urban areas are an another typical example. For such kind of low concentration sources, particularly, for nitrogen oxides dispersion, the inert gas assumption of usual plume dispersion model is not suitable, since the dispersion and chemical reactions took place together in the atmosphere. They are the major controlling factors of the diffusion in the atmosphere. We developed an Integrated Plume Dispersion Model of NOx with Chemical Reactions and examined the performance of the model. The model is based on Gaussian plume dispersion model in integrated forms, and atmospheric diffusion and chemical reactions of NO, NO2, O3, O in the plume and ambient atmosphere are described by a set of ordinary differential equations. The model was solved for different emission conditions and back ground concentrations, and reasonable results were obtained.
A numerical simulation method has been developed to predict atmospheric flow and stack gas diffusion under a neutral stratification condition, considering the buildings and complex terrain located near and relatively far from a stack, respectively. The turbulence closure technique was used for flow calculation, some calculation grids on the ground within a plant area were treated as buildings, and stack gas diffusion was predicted using the Lagrangian particle model. The calculated flow and stack gas diffusion results were compared with those obtained by wind tunnel experiments under a neutral stratification condition, and the features of surface concentration, such as the occurrence of downdraft phenomena behind the buildings, were reproduced by both calculations and wind tunnel experiments. Furthermore, effective stack heights were estimated by the comparison of the surface concentration along the plume axis with those under a flat-plate condition, and it was apparent that the effective stack heights estimated by calculations were almost the same as those obtained by wind tunnel experiments.
In the metropolitan areas of Taiwan with high population density, heavy traffic, and/or zones of heavy industries, serious air pollution episodes may occur during stable weather conditions. The information of mixing height is therefore essential to the air pollution control in this area. In this study, diurnal variation of the mixing height derived using the newly established EPA-Taiwan microwave temperature profiler (MTP-5HE) and that obtained through the CWB soundings are compared. The relationships between the air quality and the diurnal variation of the mixing height is discussed during different air pollution episodes.
We evaluated the performance of the newly developed atmospheric mesoscale model, WRF, for the simulation of urban-scale weather in the Tokyo metropolitan area during a high photochemical Oxidant event. The simulation clearly shows that WRF represents the spatial distribution of surface air temperature during the daytime, although the model temperature is lower than the observations in the late afternoon to evening in the urban area. The wind system can be well reproduced in WRF. Simulated convergence zone moves toward the inland areas located to the northwest of the coastal area during the three hours. These results are consistent with the observations of temperature and Photochemical Oxidant, indicating that WRF has enough potential to predict the ongoing Oxidant concentration.
Carbon-free fuel is effective in preventing global warming. Hydrogen has no carbon and can be made also from nuclear energy or reproducible energies other than fossil fuels. However, hydrogen lacks portability because of its difficulty in liquefying, but ammonia can easily be liquefied at a room temperature and dissociated into high-content hydrogen and nitrogen using a suitable catalyst. An ammonia dissociation system for fuel cells is proposed in this paper. The residual ammonia by 13ppm or more in the dissociated gas (H2+ N2) causes a decrease in the output of fuel cells. To separate residual ammonia, it should be sent to an ammonia separator and then to an ammonia distiller. In the experiment, the authors examine the concentrations of ammonia after dissociation at various temperatures, pressures and space velocities. The ammonia separator uses the fact that ammonia dissolves well in water. Then the ammonia water is distilled in the distiller. Thereby, the authors have proposed an ammonia circulation system that is a clean energy system.
The aim of this study was to evaluate energy saving in cases of introducing both a cogeneration system and an energy network in Kokubo Industrial Park. The industrial park has implemented zero emission activities since 1992. The energy data of 22 factories were classified into steam, hot water, heating, cooling and electric power on the basis of interviews. The author developed an energy network model based on linear programming, so as to minimize the total system cost. The industrial park was divided into a 10,000 square meter mesh in order to take steam transport into consideration. Three cases were investigated. The ratio of energy saving to demand reached 22% compared with the reference system. It was found that the energy network system could correspond to the energy demand seasonally. This is useful for the stable supply of energy, prevention of air pollution, and improvement of urban design.
Regarding sodium pool burning, ignition delay and ignitability are examined in order to obtain appropriate, comprehensive parameters that can correlate dominant system parameters influencing ignition. To this aim, theoretical work is first conducted, considering that the surface reaction exerts the main influence. It is found that both the ignition delay time and the limit of ignitability are closely related to the pool size and oxygen concentration, as well as the initial sodium temperature. Specifically, for ignition delay, a comprehensive parameter, defined as the ignition delay time multiplied by oxygen concentration and divided by pool depth, is identified. For the limit of ignitability, another comprehensive parameter, defined as the product of oxygen concentration and representative length for the heat transfer, is derived. In order to evaluate the appropriateness of the theory, experimental comparisons are conduced, using experimental data in the literature. It is demonstrated that there exists a fair degree of agreement between the experimental and analytical results, as far as the trend and approximate magnitude are concerned, in spite of differences in experimental conditions and several assumptions made in the present analysis. Because of the simple forms of the comprehensive parameters, they are expected to be useful in evaluating the ignitability of sodium prior to pool burning in an oxidizing atmosphere. Furthermore, it is found that an increase in the volume-to-surface-area ratio of the sodium pool prolongs ignition delay, and that a decrease in pool diameter suppresses ignition, both of which can be attributed to the reduced contribution of the surface reaction that supplies heat during the induction period.
This paper presents results of validation study of large eddy simulation (LES) that is applied to homogeneous isotropic turbulence in order to assess its spectral accuracy. The LES is performed by using a streamline-upwind finite element method with second order accuracy both in time and space and the results are compared with those from direct numerical simulation (DNS) based on the spectral method. The validation tests are done by using Standard Smagorinsky Model (SSM) and Dynamic Smagorinsky Model (DSM), and include following two cases: a low Reynolds number case and a higher Reynolds number case. In the former case, the Reynolds number is low enough that the computational grid is capable of resolving all the turbulence scales. In this case our interest is in whether any effects of the subgrid scale (SGS) model should appropriately be dampened out. In the latter case, a relatively large Reynolds number is selected where effects of turbulent eddies that are not resolved by the computational grid should be properly taken into account by the SGS model. It is confirmed that DSM performs better than SSM for both cases and it gives good agreement with DNS results in terms of both spatial spectra and decay of the turbulence statistics. Visualization of the computed flow fields by the DSM also reveals existence of distinct, coherent and tube-like vortical structures similar to those found in instantaneous flow fields computed by the DNS.
The simultaneous measurement of the velocities at two points with X-type hot wire probes has been performed in three regions of a plane jet (i.e., the potential core region, the interaction region and the self-preserving region). The Karhunen Loève (KL) expansion was applied to the velocity data, and the development of coherent structure was investigated by the eigenvalues and eigenfunctions as well as the spatial velocity correlations. It is found that in the potential core region the first and second modes are dominant in the kinetic energy with almost the same magnitude. The profiles of the eigenfunctions downstream of the interaction region show that the first mode of streamwise velocity u is asymmetrical about the jet centerline whereas that of cross-streamwise velocity v is symmetrical. These results are consistent with the feature of the two-point velocity correlation.
The rate of circulating flow passing through the tongue division and the pressure recovery in the casing are investigated in a centrifugal blower, which has no diffuser and large tongue clearance. At the design point, the ratio of circulating flow rate to total flow rate at the scroll end is about 45 percent, and the pressure recovery in the scroll is about 45 percent. As the remaining 55 percent of the pressure recovery in the casing is recovered in the section between the scroll end and exit duct, this section acts as a high-performance diffuser. It is concluded that the centrifugal force produced by the secondary flow and boundary layer suction are the main causes of the large pressure recovery. Moreover, it is found that the flow conditions from the scroll toward the exit duct are closely related to the low flow rate characteristics of the blower.
The flow through the single-plate lock-up clutch in an automotive torque converter with a 250-mm nominal diameter was numerically investigated using a CFD code. The flow was computed under various clearances between the lock-up piston and the torque converter cover. The stable location of the lock-up piston was determined so that the thrust acting on it became zero. The computation results showed that the fluid flowed outwards in the narrow channel between the lock-up clutch facing and the converter cover, whereas the flow reversed inwards near the lock-up piston surface upstream and downstream of the narrow channel in most cases. Along the outer surface of the axial flow channel near the exit, the flow also reversed far upstream of the channel. The computation results well predicted the stable position of the lock-up piston. It is noteworthy that the sharp increase in clearance in the coupling range can be clearly captured with this method.
In the present paper, attention was focused on the relation between vortex shedding phenomena and acoustic resonance in staggered tube banks. As a result, three types of vortex shedding were found with different Strouhal numbers (St), 0.29, 0.22, and 0.19, in cases without resonance. When resonance was generated at the natural frequency of the duct, 342.5Hz, at a gap velocity of 39.2m/s, two types of vortex shedding were found with different frequencies, mainly about 342.5Hz (St=0.29) and 262.5Hz (St=0.22), inside the tube banks. The velocity fluctuation and periodicity of the vortex shedding were the most intense in the wake of the second row of tube banks. A short baffle plates was effective for preventing the generation of acoustic resonance of the transverse mode if it was installed at the correct place where velocity fluctuation and periodicity of vortex shedding were most intense.
This paper presents the response surface optimization method using three-dimensional Navier-Stokes analysis to optimize the shape of a forward-curved blades centrifugal fan. For numerical analysis, Reynolds-averaged Navier-Stokes equations with k-ε turbulence model are discretized with finite volume approximations. In order to reduce huge computing time due to a large number of blades in forward-curved blades centrifugal fan, the flow inside of the fan is regarded as steady flow by introducing the impeller force models. Three geometric variables, i.e., location of cut off, radius of cut off, and width of impeller, and one operating variable, i.e., flow rate, were selected as design variables. As a main result of the optimization, the efficiency was successfully improved. And, optimum design flow rate was found by using flow rate as one of design variables. It was found that the optimization process provides reliable design of this kind of fans with reasonable computing time.
A gas-fired directional radiant heater is proposed, and the irradiation characteristics were studied numerically. The heater is composed of a bundle of tubes set in front of a flat burner. The Monte-Carlo method is used to calculate the irradiation profiles on the surface of an object in front of the heater. The influence of the related parameters on the irradiation intensity and uniformity along the surface of the object are analyzed. The length-to-radius ratio of the tube bundle, the arrangement (aligned/staggered), and the distance between the burner and the object surface were the parameters in the analyses. The results show that, when a tube bundle is set in front of a conventional flat burner, the heat flux on the surface of an object facing the burner is almost uniform and the intensity is nearly independent of the distance between the surface and the burner.
Experiments at the Japan Microgravity Center (JAMIC) have investigated the interaction between diffusion flames and solid surfaces placed near flames. The fuel for the flames was C2H4 and the surrounding oxygen concentration 35%, with surrounding air temperatures of Ta=300 and 600K. The effects of these parameters on soot distribution in diffusion flames and soot deposition on solid walls were studied. Direct images of the whole flame and shadow images of the flame with back light were recorded and used to calculate the soot volume fraction by the Abel transformation method. Results show that at the higher surrounding air temperature the soot particle distribution region is closer to the wall and results in more deposition. Numerical simulation was also performed to determine the motion of soot particles in the flames and the soot deposition characteristics. The results are in good agreement with the observed soot behavior in microgravity.