Analysis On The Two-phase Characteristics Of Sewage Flowing

With the rapid development of national economy and the acceleration of urbanization, industrial and domestic consumption, irrigation requirement in our country have increased enormously. Although the sewage disposal proportion has been improved a lot, discharge of the untreated sewage is still increasing due to the enlarging sewage amount, therefore it is still too early to be optimistic about the prospect of the hydro-environment. Therefore we must strengthen the management power of water pollution control in the long run.Now, most of the design of the sewage is according to gravity flow and we looks on the flow as water flow. Obviously, this means ignoring the multi-phase characteristics of the wastewater which is imperfect theoretically.In this paper, wastewater is looked on as solid-liquid two-phase flow. Firstly,the sedimentation of the particles in fluid was analyzed, and some equations was induced under different flow conditions. This set a base for the velocity in the next chapters. Secondly, the paper tells about how the two-phase theory was used in the analysis of the distribution of the velocity of two-dimension open channel flow and the general model of the flow with pushing layer. An equation of the distribution of velocity was get from this analysis and was proved to be reasonable. Within the framework of two-phase flow theory,an analysis is carried out based on the momentum and continuity equations of fluid mechanics. Corresponding to the physical process of the interaction of the solid and fluid phase, a perturbation analysis is systematically developed. Consequently, the generalized suspended sediment concentration profile suggested by Ni (1989) is derived directly from the basic governing equations.Finally, the equations of the velocity when the particles start to move, suspend and stop were gotten from the rule of silt sediment movement. The velocity with no depositting was gotten from a equation of silt sediment movement in drainage. And the relation between these velocity was analyzed at last. This is the conclusion:(1) The distribution of the velocity and concentration are get in the open channel flow and as the sewage flow is gravity flow, the equations is fit for this too.(2) Generally speaking, the self-cleaning velocity should be the starting velocity, and it could fit for the self-cleaning target in limited sense theoretically, but when facing some higher requirement, it is not large enough.