TWO PHASE STUDY OF POLLUTANT DISPERSION IN WATER FLOW IN CANAL

Abstract

Canals are the artificial channels for water navigation, to fulfil slack of water for irrigation needs. However, at many places there are several lateral entries of pollutant into the canal from household and industrial wastes. It is always desirable to acknowledge the canal water suitability for irrigation and other purposes. The present dissertation work is focused to investigate the flow and diffusion of domestic sewage pollutant in the continuous flowing canal water. Hence, a portion of Upper Ganga Canal at Roorkee (Uttarakhand) has been considered for the numerical investigation. The investigation has been carried out by developing three-dimensional model of the canal using computational tool ANSYS Fluent 16.0. The dimensions of the computational domain is taken equal to section of the canal considered for investigation (Old Ganga canal bridge to Ganeshpur bridge), with appropriately positioning the inlet of pollutant from sewages. For the investigation, two different models are used for tracing the pollutant in the canal. Species transport model is used to predict the amount of pollutant which is not mixed with canal water or the amount of pollutant get diffused in the canal water. Mixture model is used to predict the mixing of pollutant into the canal water, without diffusion. The turbulence in the flow field is calculated using standard k-ɛ turbulence model. Maximum mass fraction of pollutant left after diffusion in water obtained at the outlet is 0.012 (unit) and maximum mass fraction of pollutant without diffusion is 0.12 for 0.4 m/s sewage velocity. It was found that due to inclusion of successive sewage discharge the mass fraction of pollutant increases at Ganeshpur Bridge in Roorkee. Also, the mass fraction of pollutant is negligible in the middle portion of the canal throughout the depth and along the length of the canal, and pollutant free zone at outlet was found to be 20 m from the either side of the canal side wall. Fraction of pollutant increases with increase in sewage velocity since the diffusion rate reduces for the fixed length of the canal. Mass fraction of pollutant in species transport model is 10 % less than that in mixing model. Further, these two models can be used to provide information about the mass fraction of diffused sewage pollutant in two phase fluid flow in canal