Study of Heat Transfer during Preheating for Piercing of Oxyfuel Gas Cutting

Abstract

The heat input parameters, the local heat transfer coefficient, , and the gas temperature right on the plate, T G , are nearly unchanged with time during preheating for Oxyfuel gas cutting. A genetic algorithms (GA)-based identification technique for and T G 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 and T G 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 followings 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 Hydrogen-LP mixed gas flame around the preheating gas ejection hole is 40% larger than that of LPG flame while the total calorific value of Hydrogen-LP mixed gas is 25% smaller than that of LPG. This result shows that it is not appropriate to evaluate the thermal effect of preheat flame only from the total calorific value alone.3) The calculated time until the plate face temperature to exceed the steel's kindling temperature almost agrees with the minimum piercing time observed in piercing tests. It becomes possible to anticipate the piercing time by numerical simulation for the first time.

Experimental and numerical characterisation of heat flow during flame cutting of thick steel plates

“…They proposed a model of heat input that take into account the preheating flame, the oxidation reaction and dross but no thermal heat flow analysis has be performed. Osawa et al (2012) studied the transient heat transfer during oxyfuel gas piercing by using genetic algorithms. They determined the heat input by comparing the measured and calculated plate back face temperatures during spot heating tests and found out heat power for 6 mm steel plates between 7 and 9.25 kW depending on the gas mixture used for piercing.…”

Study on the Influence of the Preheating Flame Characteristics and the Oxy-fuel Gas Cutting Performance

“…and can be identified by a linear regression on the relation between and . Osawa et al 5) , proposed a direct identification technique for and based on genetic algorithms. The validity of this technique was demonstrated by comparing the identified with the one measured by LIF.…”

“…However, one of the side effects of mixing fossil gases in the preheating flame is the reduction of cutting performance. Several studies [2][3][4][5] have shown a deterioration of the cutting performance (e.g., cutting speed, kerf quality, thermal distortion) while adding fossil gases in the preheating flame. In this regard, the precise deterioration mechanism of the process has not been fully clarified yet.…”

“…In order to automate the preheating flame adjustment, clarification on the relationship of the preheating flame conditions and the cutting performance needs to be addressed. Osawa et al 5) developed a method to study the thermal effects during the piercing process. In their study, the distributions of the heat transfer parameters ( and ) were identified by performing an inverse heat conduction analysis of a thin circular plate during spot heating tests.…”

“…In the present work, the influence of the CO2 on the cutting performance is studied by estimating and by performing three-dimensional heat conduction analyses developed by Osawa et al 7) . The heat input parameters , and of the preheating gases H2 and H2-CO2 are determined by performing spot heating tests using a method developed by Osawa et al 5) . The cutting groove geometry (e.g., cutting front shape, the curvature of the cutting front, plate thickness) are measured by performing gas cutting tests for the selected preheating gases.…”