Hydraulic characteristics of siphonic roof drainage outlets

Rains, JP 2008, Hydraulic characteristics of siphonic roof drainage outlets , PhD thesis, University of Salford.

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Abstract

Siphonic roof drainage uses an innovative hydraulic design to increase the efficiency of rainwater disposal. The roof outlet is a critical component of the system and not only promotes and sustains priming of the system but also controls the depth of approach flow. This thesis investigates the hydraulic characteristics of an idealised roof outlet to improve outlet design. A literature survey was carried out and found that only a limited number of studies have been undertaken on single outlets on flat roofs. Therefore, the search was widened to include related subjects and the information was used to develop a programme of experimental testing. An idealised outlet was tested within a physical hydraulic model across a range of geometries to observe and measure the water flow rate, depth, pressure and the air flow. The relationships between the key parameters are presented and compared with the theoretical values. The study confirmed that a baffle plate is essential for stable priming of the outlet and that the idealised geometry is sufficient to provide a stable and efficient operation of the system. The maximum typical air flow rate during the priming sequence was approximately a third of the water flow rate and occurred at less than half of the maximum water flow rate. The outlet should be designed to ensure rapid and stable priming by creating a turbulent, well-mixed flow at the roof outlet. The depth of approach flow can be reduced by increasing the diameter of the baffle plate within practical limits and by reducing the height of the baffle. An empirical relationship was developed between the water radial velocity and the pulsing frequency of entrained air and is presented in the form of a modified Strouhal number. This relationship could be used to develop a non-intrusive flow measurement system in the air-regulated regime of operation. Tests were conducted on a small range of commercial outlets and the results compared well with those from the idealised outlet. The conclusions drawn from the idealised outlet would thus be useful in the development of commercial outlets.

Item Type: Thesis (PhD)
Contributors: Baker, R (Supervisor) and Yousif, S (Supervisor)
Schools: Schools > School of Computing, Science and Engineering
Funders: Engineering and Physical Sciences Research Council (EPSRC)
Depositing User: Institutional Repository
Date Deposited: 19 Aug 2021 08:25
Last Modified: 27 Aug 2021 21:57
URI: http://usir.salford.ac.uk/id/eprint/61638

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