The objective of this study is to improve the exit flow uniformity of a gas torch with multiple exit holes for effective heating of a steel plate. The torch was simulated, and combustion experiments were performed for validation. Based on a basic model, three different revised models were designed and analyzed with the software ANSYS FLUENT 18.2. The flow uniformity (γ) of the velocity distribution at the multiple exit holes was investigated with the pressure drop ranging from 100 to 500 Pa. The basic model had flow uniformity ranging from 0.849 to 0.852, but the three new models had γ1 = 0.901–0.912, γ2 = 0.902–0.911, and γ3 = 0.901–0.914, respectively. The maximum percentage difference of the flow uniformity index between the three new models and the basic model was 7.3%. The basic model with nonuniform flow distribution made a temperature difference of the back side of the steel plate from the center to the edge of around 229 °C, while the modified model with uniform flow distribution had a smaller temperature difference of 90 °C. The simulation results showed good agreement with our experimental results for both the basic model and the modified model. The modified gas torch made a wider and more uniform temperature distribution on a preheated steel plate than the basic one. The results revealed that a trade-off between cost and flow uniformity, as well as the new gas torch, could be applied to a steel-plate preheating process before welding.
The temperature distribution on a steel plate during a preheating process was comparedusing gas torch models with and without guide vanes. Numerical simulations were done usingANSYS FLUENT software, and experiments were done using thermal images obtained by aTVS-200EX infrared thermal camera. Liquefied petroleum gas (LPG) was used as fuel for the gastorch in the simulation and experiment. The temperature distribution on the steel plate and theflame region were first compared. The temperature increase caused by the flame concentrationwith the guide vanes was 65 C. The transient and steady-state temperature distribution on theback side of the steel plate were then examined. The results showed good agreement between thesimulation and experimental results. At steady state, the back-side temperature deviation of thesteel plate between the numerical simulation and experimental results was approximately 4.9%.The effects of the equivalence ratio (Φ), Reynolds number (Re), and the downstream distance ratioof the combustion gas from the torch outlet to the steel plate (H/d) on the temperature distributionwere also investigated. The highest temperature distribution was found in stoichiometriccombustion. The temperature of the plate increased as the Reynolds number increased from 2368 to4876 but decreased as the distance ratio (H/d) increased from 25 to 75. The guide vane angles at thegas torch outlet were from 30 to 60 degrees, and the angle of 40 degrees resulted in the highesttemperature of the steel plate.
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