Study of Heattransfer During Piercing Process of Oxyfuel Gas Cutting

Abstract

The heat transfer parameters, the local heat transfer coefficient, α, and the gas temperature adjacent to the plate, TG, are nearly unchanged with time during preheating for oxyfuel gas cutting. A genetic algorithm (GA)-based identification technique for α and TG is proposed. The validity of the proposed technique and the accuracy of the identified parameters are examined by comparing the measured and calculated plate back face temperatures during spot heating tests. Hydrogen-LP mixed gas and LPG are used as preheating gases in these tests. It is considered that the plate temperatures during preheating for piercing can be calculated by using α and TG identified in spot heating tests. The minimum piercing time is estimated by calculating the time until the plate heating face temperature reaches the kindling temperature. The validity of the above assumption is examined by comparing the estimated and measured minimum piercing times for hydrogen-LP mixed gas and LPG. As a result, the following are found: 1) The plate temperatures during spot heating tests calculated by using the identified heat input parameters agree well with the ones measured. This demonstrates the accuracy of the identified parameters and the validity of the proposed heat transfer simulation technique. 2) The heat flux of a hydrogen-LP mixed gas flame around the preheating gas ejection hole is 40 % greater than that of a LPG flame, while the total calorific value of hydrogen-LP mixed gas is 25 % lower than that of LPG. This result shows that it is not appropriate to evaluate the thermal effect of the preheat flame only from the total calorific value alone. 3) The calculated time for the plate face temperature to exceed the steel’s kindling temperature almost agrees with the minimum piercing time observed in piercing tests. For the first time, it is possible to anticipate the piercing time by numerical simulation.