Diffusion of Three-Dimensional Slot Jets With Deep and Shallow Submergence

Demissie, Misganaw

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https://hdl.handle.net/2142/66874 Copy

Description

Title

Diffusion of Three-Dimensional Slot Jets With Deep and Shallow Submergence

Author(s)

Demissie, Misganaw

Issue Date

1980

Department of Study

Civil Engineering

Discipline

Civil Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Engineering, Mechanical
• Energy

Language

eng

Abstract

• To minimize the adverse effects of thermal discharges on the natural environment, several methods are utilized to mix heated discharges with colder receiving water thoroughly and quickly. By discharging the heated water with high initial velocity it behaves like a non-buoyant jet. The velocity discontinuity between the jet and the receiving water gives rise to strong shearing action generating turbulence, which diffuses the heated water into the colder water keeping the temperature rise within acceptable limits.
• This research investigated the diffusion of incompressible, non-buoyant, and turbulent three-dimensional slot jets with deep and shallow submergence experimentally and theoretically. Three slot dimensions with aspect ratios of 4, 13 and 26 were used in the experimental work. For the deeply submerged jets, centerline velocity, velocity profiles along the major and minor axes and complete cross-sectional velocity measurements were taken at several locations. For shallow submerged jets vertical velocity profiles, from which trajectories of the maximum velocity towards the free-surface were determined, were taken under three different submergences.
• An analytical model based on Reichardt's hypothesis for free turbulence has been developed. Since Reichardt's hypothesis linearizes the momentum equation in the flow direction, it was possible to superimpose particular solutions. The analytical solutions for three-dimensional slot jets was then developed by superimposing Reichardt's solution for a point source. Assuming a distribution of point sources over the area of the slot and integrating, a solution for uniform exit velocity was obtained. By subdividing the slot area into small square sources and superimposing the momentum flux for each source, it was possible to handle the common case of non-uniform exit velocity. For the shallow submerged three-dimensional slot jet, the analytical model was developed by placing an image jet above the free surface at a distance equal to that of the real jet from the free surface. Assuming the same linear momentum equation for the deeply submerged jet applies for both the real and the image jets, and ignoring the surface disturbances generated due to the deflection of the jet towards the free-surface, the momentum flux for the shallow submerged jet was obtained by superimposing the momentum flux of the real and image jets.
• Both experimental and analytical results show that there are three distinct regions for three-dimensional slot jets. Based on the centerline velocity decay comparison with plane and axisymmetric jets, the three regions were defined as the potential core, two-dimensional zone and axisymmetric zone. The centerline velocity is equal to the velocity at the exit in the potential core; decays as a plane jet in the two-dimensional zone and as an axisymmetric jet in the axisymmetric zone. The end of the two-dimensional zone and the start of the axisymmetric zone depend on the aspect ratio.
• The entrainment rate and the dissipation of energy by three-dimensional slot jets also behave similar to those of a plane jet in the two-dimensional zone and to an axisymmetric jet in the axisymmetric zone. However, the axisymmetric behavior with respect to entrainment and energy dissipation starts at shorter distance from the jet outlet than the axisymmetric decay of the centerline velocity.

Graduation Semester

1980

Type of Resource

text

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