Report On Dispersion Models -Gaussian Plume Modelling

Added on -2020-02-05

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INTRODUCTIONAtmospheric dispersion is termed to imply the transport of the effluent by winds and theconcurrent diffusion by atmospheric turbulence. Atmospheric dispersion models relate thequantity of effluent release and the distribution of its concentration in the atmosphere. Theserelations affected by properties of atmospheric motions. Also it may include effects ofprocesses such as radioactive decay etc. Development of these dispersion models has beenmotivated through the needs of controlling radiation hazards and air pollution. Currently alarge number of dispersion models has been developed for varies studies such as to determinewind and temperature profiles, turbulence spectra and precipitation scavenging etc. Applications of dispersion models To assess the environmental impacts due to nuclear installations- to assess the radiological risk to members from predicted routine releases- to prepare off-site emergency plans.To assess the environmental effects from industrial works where gases release as the waste to the atmospheric environment.Although there are several dispersion models that currently available for such modelingwhich discussed above widely applicable “Gaussian Plume Modelling” used here for thisreport.THEORYThe Gaussian model can be obtained as a solution of the diffusion equationC(x,y,z)=Q2Πσyσz ́uey22σy2{e(zH)22σZ2+e(z+H)22σz2}This is applicable for the situation when the wind velocity and the diffusion coefficient are independent of distance or from statistical theory.Here C(x,y,z) – concentration at the particular point in kg/m3Q – mass flow rate of release in kg/s σy , σz – dispersion parameters in y, z directions in mH – total height of release in mU is the wind speed in m/sTo calculate dispersion parameters various models has been developed and Pasquill – Giffordcharts used here.
Sourcehttp://www.iaea.org/inis/collection/NCLCollectionStore/_Public/17/072/17072243.pdfTable 1- identifying stability classֿ;
Figure 1 – charts for determining dispersion parameters
MODEL DEVELOPMENTData provide for the modelQ = 0.1 kg/s H = 30m U = 1 m/sDifferent height levelsZ = 0m, 15m, 40mAnd in each level, X distance vary from 100m to 5000m Y distance vary from 0m to 200mThis model is calculating concentration values at points of 50m intervals. σy , σz at each x distance determined from pasquill charts.Wind velocity < 2m/s and due to cloud cover day time insolation is taken taken as slight. Then pasquill stability chart for day time Class BAt night time with clear sky, there is no class defined for wind velocity < 2m/s. Due to further increase stability with less wind speeds, class F taken for night time which is for the very stable case.Table 2 – Determination of dispersion parameters for y,z direction from chartsDistance(X)in mσy fordaytimeσy fornighttimeσz fordaytimeσz fornighttime100174112.4150256173.3200348.321425045112853005013315.93506016396.6400701842745080195085008420558.455090236296009925689.8

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