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Quantifying Boundary Impingement of Inclined Negatively Buoyant Jet

Author(s): A. Ramakanth; M. J. Davidson; R. I. Nokes

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Keywords: Desalination; Negatively buoyant jets; Boundary impingement; LIF

Abstract: Discharges from desalination plants are a primary environmental concern surrounding this technology and their behaviour can be represented by an inclined negatively buoyant jet (INBJ). Existing experimental results pertaining to the flow configuration have shown a distinct lack of consistency due to the inclusion of a lower boundary in the corresponding experimental setup. Conceptually it is expected that a boundary would inhibit the mixing achieved near the boundary, because the amount of clean ambient fluid able to be entrained is reduced. This issue has been investigated through a series of the source height (represented in non-dimensional form as H/F! d) was varied between 0.058 and 1.84. experiments where inclined negatively buoyant jets are discharged onto a raised horizontal platform placed within the vicinity of the initial discharge location. Experiments were conducted using Laser induced fluorescence (LIF) to produce time-averaged concentration fields. The source angle was 60o and Geometric and dilution results are presented in the context of the non-dimensional source height. For comparative purposes an additional set of experiments was conducted where the lower boundary was removed from the recording area. Changes in the flow behaviour have been assessed by comparing flow statistics between the two sets of experiments at the maximum rise height (maximum height achieved by the discharge) and the return point (where the flow returns to its original discharge height). The analysis suggests a reduction in the dilution at the return point and the extent of this reduction is dependent on the proximity of the lower boundary to the source. The dilution recorded at the impact point has also been highlighted and its variation with the source height is presented. Finally comparisons with previous studies are performed using the dilution ratio in order to resolve the well documented discrepancies.


Year: 2016

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