Hydraulic and Structural Analysis of Complex Cross-Section Reinforced Concrete Pipes to Improve Sewage Flow in a Combined Sewer System

A complex cross-section reinforced concrete pipe that combines a sub-pipe for the flow of sewage in dry weather and a main pipe for the flow of rainwater was developed to reduce sedimentation of the combined sewer system in dry weather. The sub-pipe was designed, considering the flow velocity, constructability, and maintenance. By fitting the sewage data in the dry weather to the normal distribution, the ratio of the cross-sectional area of sewage flow to that of the pipe was determined to be approximately 0.418, which could cover 99.85% of the sewage volume of the target site. Based on this ratio, the diameter of the sub-pipe corresponding to the combined sewer system with a pipe diameter between 450 and 1300 mm was determined. The hydraulic performance analysis results showed that the flow velocity increased by 11 to 12% compared to the circular pipe based on the full sub-pipe and by more than 15% depending on the water level. The shear stress increased by more than 16.5%, and higher tractive force was observed. Structural safety was determined as the crack load and failure load far exceeded the minimum criteria, thereby verifying the feasibility and field applicability of the complex cross-section reinforced concrete pipe.

Analysis of the Flow Performance of the Complex Cross-Section Module to Reduce the Sedimentation in a Combined Sewer Pipe

The difference in the amount of stormwater and sewage in a combined sewer system is significantly large in areas where heavy rainfall is concentrated. This leads to a low water level and slow flow velocity inside the pipes, which causes sedimentation and odor on non-rainy days. A complex cross-section module increases the flow velocity by creating a small waterway inside the pipe for sewage to flow on non-rainy days. While considering Manning’s equation, we applied the principle where the flow velocity is proportional to two-thirds of the power of the hydraulic radius. The flow velocity of a circular pipe with a diameter of 450 mm and the corresponding complex cross-section module was analyzed by applying Manning’s equation and numerical modeling to show the effects of the complex cross-section module. The tractive force was compared based on a lab-scale experiment. When all conditions were identical except for the cross-sectional shape, the average flow velocity of the complex cross-section module was 14% higher while the size of the transported sand grains was up to 0.5 mm larger. This increase in flow velocity can be even higher if the roughness coefficient of aging pipes can be decreased.

High-Throughput Particle Concentration Using Complex Cross-Section Microchannels

High throughput particle/cell concentration is crucial for a wide variety of biomedical, clinical, and environmental applications. In this work, we have proposed a passive spiral microfluidic concentrator with a complex cross-sectional shape, i.e., a combination of rectangle and trapezoid, for high separation efficiency and a confinement ratio less than 0.07. Particle focusing in our microfluidic system was observed in a single, tight focusing line, in which higher particle concentration is possible, as compared with simple rectangular or trapezoidal cross-sections with similar flow area. The sharper focusing stems from the confinement of Dean vortices in the trapezoidal region of the complex cross-section. To quantify this effect, we introduce a new parameter, complex focusing number or CFN, which is indicative of the enhancement of inertial focusing of particles in these channels. Three spiral microchannels with various widths of 400 µm, 500 µm, and 600 µm, with the corresponding CFNs of 4.3, 4.5, and 6, respectively, were used. The device with the total width of 600 µm was shown to have a separation efficiency of ~98%, and by recirculating, the output concentration of the sample was 500 times higher than the initial input. Finally, the investigation of results showed that the magnitude of CFN relies entirely on the microchannel geometry, and it is independent of the overall width of the channel cross-section. We envision that this concept of particle focusing through complex cross-sections will prove useful in paving the way towards more efficient inertial microfluidic devices.