Drag Characteristics Of Sewage Flowing As Two-Phase Fluid In Pipe

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. Thus constructing regional drainage is one of the main goals in future considering its advantages as economic, stability of operation and land saving .Sewage pipe flow is hypothesized as single-phase and uniform flow,and we are used to applying the Chezy formulas for designing sewer systems. But now it's urgent to adopt new methods for calculating the head loss of regional drainage due to some factors such as long length, large flow quantity and probable strong topographic change. It's the aim of this paper to find a new method.In this paper, sewage is regarded as liquid-solid two-phase fluid. It begins by analyzing turbulent pipe flow to know about the structure of turbulence; Then it precedes to make a general impression of the velocity and concentration distribution in two-phase pipe flows based on complex findings of the predecessors, mainly digesting and retaining their essence. Finally, it proposes the method and formulas of calculating the flow resistance of sewage in pipe viewing from the point of two-phase flows, which are associated with empirical equations used in practice at present. Through analyzing and calculating the typical sewage quality data at the moment, it reaches conclusions as follows.â‘ There are two patterns(patternâ… and patternâ…¡) for velocity profiles in flows mingled with particle. In patternâ… ,the velocity distribution still corresponds with the logarithmic formula except that the value of k is smaller than that in non-particle flows. As for pattern â…¡,the logarithmic formula is also effective either in core region or in surface layer ,and the values of k in both cases become smaller but differ to each other.â‘¡There are two patterns for vertical concentration distribution too. In pattern â… ,the concentration rises from the surface to the bottom(in open channel flows).As forpattern â…¡,it rises from the surface toward the bottom, until on certain point it comes to the maximum, and after that, it decreases.â‘¢The linear loss of sewage flowing in pipe is approximately equal to that of water pipe flow. So it's feasible to accept the method in use at present.â‘£The local resistance of sewage flows as two-phase fluid is larger than that of water flows under the same conditions. The accrual is variable according to different concentration, properties and size composition of contamination. In general, the accrual is too obvious to be ignored in design, especialy when the flow quantity is large and there are many elbows(for example, in regional drainage).