Virendra Sethi

Multicomponent Aerosol Dynamics of the Pb-O2 System in a Bench Scale Flame Incinerator

A study was carried out to understand the formation and growth of lead particles in a flame incinerator. A bench scale flame incinerator was used to perform controlled experiments with lead acetate as a test compound. A dilution probe in conjunction with real-time aerosol instruments was used to measure the evolution of the particle size distribution at different locations in the flame region. A multicomponent lognormal aerosol model is developed accounting for the chemistry of the lead-oxygen system, and various aerosol dynamic phenomena such as nucleation, coagulation, and condensation. Reasonable agreement is obtained between the predictions of the model using appropriate kinetic parameters and the experimental results.

Particle impaction patterns from a circular jet

The surface distributions of particles that have impacted from a circular jet have been measured by optical microscopy and image analysis. Monodisperse, 3-μm ammonium fluorescein particles were impacted onto greased surfaces at various velocities from the nozzle. The spot radius is approximately equal to the nozzle radius at √St = 0.8. At √St = 1.6, the spot radius is about half of the nozzle radius; convergence of the flow into the nozzle results in a focusing effect. The surface density has a peak which moves out to larger radius with decreasing Stokes number, reaching the nozzle radius at about √St = 0.5. The radii enclosing 10.5% and 70.3% of the particles as a function of √St are in good agreement with the theoretical predictions of Marple (1970); however, the upturn of the experimental data for √St 0.5 is somewhat sharper. Empirical formulas were fitted to the data

Aerosol and carbon monoxide emissions from low-temperature combustion in a sawdust packed-bed stove

Low-temperature combustion in biomass-burning stoves used for cooking results in poor thermal efficiency and high emissions. A sawdust packed-bed stove has been shown to give more stable combustion at higher temperatures than woodstoves. The study examines pollutant emissions from this stove and their dependence on stove dimensions, specifically the vertical port radius and the stove-pot spacing. Emission rates of particulate matter (PM)—along with size resolution—and of carbon monoxide (CO) were measured during steady-state combustion. The stove power increased with increased spacing and vertical port radius. However, the air-flow rate, combustion temperature, and air-fuel ratio showed complex variations with stove dimensions from the described coupling among the pyrolysis, combustion, induced air flow, and mixing. Emission rates of PM (0.21–0.36 gh−1 and CO (3–8 gh−1 and were a factor of ten lower than those previously measured from woodstoves. Emission rates of CO decreased, while PM increased, with increasing combustion temperature. Aerosol size distributions were unimodal with mass median aerodynamic diameters (MMAD) of 0.24–0.40 𝛍 a factor of two smaller than from woodstoves. Cool combustion at 534–625°C gave lower PM emission rates but particles of larger MMAD, while hot combustion at 625–741°C gave higher PM emission rates with smaller particle MMAD. The OC/EC ratio obtained for cool combustion was higher (1.20) than that for hot combustion (0.96). Greater elemental carbon formation was seen at the higher temperatures. PM and CO emission rates followed opposite trends with combustion temperature and stove configuration, resulting in no single configuration at which both CO and PM emissions were minimized. However, its superior thermal efficiency and significantly lower emissions than wood stoves should motivate further study of this device to optimize thermal and emissions performance.

Modeling of Particle Formation and Dynamics in a Flame Incinerator

A model has been developed to predict the formation and growth of metallic particles in a flame incinerator system. Flow fields and temperature profiles in a cylindrical laminar jet flame have been used to determine the position and physical conditions of the species along the flame. The size distribution of the particles formed was approximated by a unimodal lognormal function to describe the aerosol behavior in the flame. The effects of inlet metallic vapor feed concentrations, initial seed sizes and seed concentrations on the resultant particle size distribution are presented. The model has potential for further development to be used as a predictive technique for applications in design and operation of incinerator systems.

Breakup of Latex Doublets by Impaction

The breakup by impaction of a simple agglomerate consisting of two identical spherical particles has been studied. The agglomerates were doublets produced by nebulizing suspensions of latex particles. The doublet concentrations before and after impaction were determined from the particle size spectra obtained with an optical particle counter. Preliminary experiments showed that the latex doublets did not break up in the acceleration nozzle of the impactor. The doublet fraction (DF) is defined as the doublet/singlet concentration ratio after impaction to that before impaction. The DF of 2.99-μm Dow latex measured at √Stk = 1.62 decreased by about a factor of 2 as the relative humidity (RH) was varied from 8% to 85%. The remaining experiments were made at low RH with seven different surfactant-free suspensions of polystyrene latex stabilized by the addition of charged surface functional groups. All of the data, for particle sizes ranging from 1.62 to 4.07 μm and impact velocities from 10 to 80 m/s, could be...

Particulate Respiratory Dose to Indian Women from Domestic Cooking

Particulate mass size distributions were measured during cooking and non-cooking periods in three Indian urban household kitchens with Liquefied Petroleum Gas as fuel. Based on the measured mass size distributions, fraction of particulate deposition in the respiratory system were calculated for a healthy Indian female using a deterministic lung deposition model. Respiratory physiological data of Indian women were collected from the published data. These physiological parameters were incorporated in the model to determine the particulate deposition in the respiratory system. The cooking generated very high concentration of particles 4 to 5 times more than the non-cooking background periods. Particulate size distributions in both cooking and non-cooking periods showed bimodal characteristics. Cooking process generated particles predominantly in accumulation mode (0.1–0.3 μ m) whereas during non-cooking periods particulates are found in coarse mode (1.0–2.0 μ m). Also, during frying process, the particulates were found to have a predominant coarser/droplet mode 0.7–1.0 μ m. The highest deposition was observed in pulmonary region during cooking periods. The study shows that the daily particulate dose to the urban Indian women from domestic cooking is comparable with the dose resulting from outdoor particulate exposure.

Threshold for Resuspension by Particle Impaction

The threshold velocity for the resuspension of 8.6-μm diameter ammonium fluorescein particles from a Tedlar surface by impaction of 3-μm ammonium fluorescein particles has been measured to be 9.3 ± 4.3 m/s. The resuspension rate, observed with an optical particle counter, has a wide variability. Image analysis of the particle patterns on the surface suggests that particle resuspension takes place at a radius somewhat smaller than that of the nozzle of the impactor used in the experiments. Exposure of some test surfaces to laboratory air for several days prior to the measurements did not change the results significantly. A theoretical model has been shown to predict a threshold velocity within a factor of 2 of the experiment. The major uncertainty involves the value of the surface energy parameter, a difficulty encountered previously in a study of particle bounce. The model is based on the transfer of vertical momentum to the struck particle which is subsequently compressed against the surface. Elastic reb...

Sustainability Assessment of Biomass Gasification Based Distributed Power Generation in India

Access to energy is a precursor to sustainable development. In India, at present, the number of people without access to electricity remains high, despite several efforts by the government. Non-feasibility of grid extension is one of the major reasons for this poor energy access. Even in the areas with grid connectivity, reliable electricity supply still remains a challenge. Biomass gasification based renewable distributed power generation sources may provide electricity access by generating it at the point of consumption using locally available resources. Most of the prior studies have evaluated biomass gasification system based on cost of electricity generation neglecting its impact on environment and society. Instead, sustainability aspects including social, technical, environmental, and resource should be an integral part of this practice along with economic aspect and compared in transparent way. This not only necessitates identification of appropriate indicators to reflect relevant sustainability dimensions, but also requires development of general framework comparing different qualitative and quantitative indicators. Framework should bring out various trade-offs and bounce associated with indicators. This paper analyses different indicators and assessment methodologies including single-criterion and multi-criteria decision methods discussed in the literature for sustainability assessment of power generation systems followed with specific focus on sustainability assessment methodologies suggested for biomass gasification systems. Research gaps with scope for conceptual contributions in the prevailing sustainability assessment process from selection of appropriate indicator to assessment methodologies are discussed. Based on the literature review, this article identifies appropriate criteria and indicators to be considered for assessing the sustainability of biomass gasification based power generation systems. A total of 18 indicators representing economic, technical, environment, resource, and social aspect of sustainability along with their relevance and importance for sustainability assessment are discussed. The set of indicators identified may be used for comparing sustainability of possible distributed power generation systems in Indian context.

Managing Water Quality and Quantity under Drought Conditions

It is common practice to select the most pristine available water source when choosing a drinking water supply. However in many parts of the world and some parts of the United States both the quality and quantity of available source water is declining. This trend together with increasing populations in urban areas is making it increasingly difficult for drinking water utilities to find adequate water sources. Compounding this problem is the tightening of drinking water standards throughout the world. One consequence of this trend is the need to explore various options, including mixing and blending of water from several sources or the installation of advanced treatment in order to provide water of acceptable quality to consumers.