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Effects of buoyacy on jets in crossflow: application to the kraft recovery boiler Aghdasi, Fariba F.


This thesis investigates the effect of buoyancy forces on jets in a crossflow, with specific application to kraft recovery furnaces. Both experimental and numerical studies are presented. Experiments were conducted to investigate the concentration profiles of variable density slot jets issuing into a confined crossflow. A recently-developed multigrid computational fluid dynamics code is used to find the flow pattern of variable density jets in a crossflow. The governing equations of motion for non-isothermal flow, i.e. mass continuity, Navier-Stokes equations, and energy equation, are discretized using the control volume technique. The turbulence phenomena are modelled using modified k -- ∈ equations. The validity of the code for variable density conditions is verified by comparison with experimental results. Numerical modelling of two-dimensional slot jets in crossflow, simulating the primary air jets in the kraft recovery furnace, is carried out. The effect of buoyancy force on the penetration and spread of these jets is investigated. It is found that, for horizontal jets being issued into an upwards crossfiow, excluding the buoyancy force from the momentum equation results in under prediction of the jet penetration and spread. The effect of buoyancy force on the penetration of the jet is found to be significantly affected by the orientation of the jet and the crossifow. The effects of buoyancy force on the flow field of three-dimensional single jets and a row of jets issuing into a crossflow, which simulates the tertiary air jets in a kraft recovery furnace, are investigated. The penetration of the row of jets is found to be more significantly affected by buoyancy than is the penetration of a single jet. Numerical simulation of the flow field inside the full kraft recovery furnace is carried out. The gross features of the gas flow fields inside the furnace for cases both with and without the buoyancy force are similar.

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