Flash-back of laminar methane/air flames on slit and tube burners in a wide range of burner widths and with equivalence ratios between 0.9 and 1.2 is investigated. A comparison between measured and calculated values of the critical gradients shows that the critical gradients predicted by the numerical model do not deviate more than 10 from the measured critical gradients for burners with a width/diameter ranging from 4 to 10mm and with equivalence ratios between 0.9 and 1.1. The maximum difference between the computed critical gradients of the slit and the tube burner flames is approximately 10 at a width/diameterof 4mm. The differences are not visible in the experimental data because of experimental inaccuracies. For burners sizes larger than 6 mm the differences almost vanish. An analytical model which described the decrease of the critical gradient as a function of the burner width/diameter shows that this increase is mainly caused by the curvature of the parabolic velocity profile near the burner wall.
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