UBC Theses and Dissertations
Multiple jet interactions with special relevance to recovery boilers Tse, Daniel C.M.
The problem of multiple turbulent jet interactions is investigated with special attention to applications in kraft recovery boilers. The phenomena due to turbulence are simulated with the k-ε turbulence model, and a multigrid numerical technique is applied to solve the time-averaged Navier-Stokes equations governing the flows. Investigations carried out include a study on the simulation of primary level jets and on the characteristics of a row of jets discharging into a confined crossflow. For the primary level jets, the interaction and merging of the jets are investigated. The jets merge rapidly and a suitable open slot representation gives an adequate description of the velocity field. For jets in a row interacting with a confined crossflow, the effects of varying the jet spacing on flow characteristics are investigated. At moderate spacing, the penetration decreases as the spacing is reduced. It is also observed that the vorticity structures of a jet within the row can be substantially different from those of an isolated jet. The penetration of rectangular jets from orifices having different aspect ratios is then studied. A quantitative analysis is carried out to examine the extent of mixing between the jets and the crossflow. The applicability of a correlation by Holdeman and his co-workers is extended to rectangular jets. The correlation yields information on the penetration at various values of jet spacing, confinement size, and jet-to-crossflow momentum ratio. Holdeman’s correlation is also found to be applicable to a crossflow having a peaked non-uniformity in the velocity profile. The use of Holdeman’s correlation indicates that, for a given mass flow from the jets, large jets at a low momentum can penetrate as far as smaller jets at a higher momentum. Furthermore, because of their low momentum, these large jets introduce a lower degree of flow non-uniformity in the mainstream.
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