Effect of changes in pipe direction across surcharged manholes on dispersion and head loss.

Abstract

From the water quality perspective, looking at a sewer system as a reactor whose effluent should be regulated in terms of water quality, solute tracer studies need to be undertaken to define the retention and spread of temporally varying concentrations. Focussing on a manhole, its aspects such as shape, ratio of pipe and manhole diameter, and pipe direction all affect the transport of the solute through the sewer system. The aim of this study is to quantify the magnitude and changes in dispersive fraction (y) used in the ADZ technique, and head loss coefficient (K) due to changes in pipe direction across a manhole. Under surcharge conditions, solute transport along plane angles such as 0°, 30°, 60° and 90°, of an inlet and an outlet pipes with/without benching was investigated for a range of surcharge and discharge. Additionally, the head losses due to such an angle were also measured. From data analysis, both the dispersive fraction and the head loss coefficient were properties of each plane angle. For example, at the angle of 300 -unbenched, the dispersive fraction was constant at approximately 0.7 and the head loss coefficient was constant at about 2.22. Moreover, these comprehensive processed data were beneficial to basic knowledge of solute mixing. First, the square root of the ratio of head loss and residence time, represented by energy dissipation, was found to be linear to flow rate. Hence, it might be used as a conversion of a head loss to residence time. Second, two cell ADZ technique was developed to enhance the travel time prediction of a downstream concentration profile. The two cell technique was able to predict the concentration profile very well, but due to difficulty in application, a single cell ADZ technique was more useful in general