الفهرس 
Coaxial jets with Axis -Switching
COMPUTATIONAL METHODOnly 14 pages are availabe for public view
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Abstract
Reactants mixing has a great effect on the combustion efficiency, and the use of sharp corners in nozzles has recently been investigated as an approach to obtain better mixing conditions for inverse jet diffusion flames and to generate a fully developed flame with a low percentage of unburned hydrocarbons. The present work examines the effect of using nozzles with sharp corners on inverse jet diffusion flames experimentally, as well as by numerical simulations. This research has been held for reacting flow, using nine different sharp corners nozzles with an approximate equivalent diameter of 12.38 mm. A circular nozzle is adopted as a reference value for comparison. The experiments were held at a constant air to fuel ratio of 50.30. The results showed that increasing the number of sharp corners led to an increase of 38.54 % in the temperature fluctuations. Consequently, there was a reduction of 13.78 % in the peak temperature using the cross nozzle and an increase of 30% for the octagon nozzle. The triangular nozzle showed an effective enhancement in the fuel to air mixing rates such that the flame length was shortened by 50 %.
In the numerical simulations three different nozzle shapes, which are circle, square and triangle, have been examined. The commercial Package ANSYS-FLUENT 16.0 finite-volume solver has been used for the numerical modelling of the reacting flow field using a mixture fraction non-premixed model. The numerical model results have been validated with experimental data and its result showed an agreement in trend line with an approximate shift of 10% from the experimental result. The numerical results showed a favourable effect of sharp corners and direct influence of both the number of sharp corners and sharpness of angles on the stability of the inverse flame. The numerical results showed that increasing the number of these sharp corners led to increasing the turbulent kinetic energy at a range of 35 to 50%, accompanied by a decrease in peak temperature by about 23% which is in a good agreement with the experimental results. In addition, decreasing the vertex angle of these sharp corners enhances the mixing rates of reactants and increases vortices by 40%.