Oxidation And Heat Transfer Analysis Of Heat Resisting Stainless Steel In High Temperature And High Pressure Water Vapor

Under high temperature and pressure, the oxidation rate of stainless steel in water vapor is quicker than that in air. Based on the water vapor high temperature oxidation mechanism, the oxidation physical model of heat resisting steel 1Cr18Ni9Ti in high temperature water vapor was obtained. Oxidation film structure was composed of outer layer and inner layer. The main ingredient of outer layer is Fe3O4 and inner layer is (Fe,Ni,Cr)3O4.External oxidation model and internal oxidation model of 1Cr18Ni9Ti were built individually. According to Wagner theory, oxidation film thickness controlled by diffusion grows with parabolic rule. Through simplified hypothesis, external oxidation model is built by uniderectional diffusion of oxygen, and internal oxidation is built by bidirectional diffusion reaction model of oxygen and Cr. Oxidation rate is influenced mostly by gas'temperature and pressure, water vapor concentration,gas flow rate, and so on. By calculating and verifying, all these factors will pick up the oxidization process, especially temperature. By means of concentration calculation of diffusion elements, oxygen in external and internal oxidation film is approximately in linear distribution, after long-time oxidation. At internal oxidation foreland, oxygen and Cr react completely, the concentration of which approximate zero. Infiltration depth of oxygen grows with oxidation time.Oxidation film gets great influence to the heat-transfer performance of nozzle. By means of heating calculation and flow field calculation, thermal boundary condition of nozzle is confirmed. By calculation with finite element method, the conclusion is that total thermal resistance of stainless steel increasing after oxidation, instant heat flux intensity diminishing, slope of temperature rise curve decreasing. The roughness of oxidation film improves the performance of thermal transmission. However because of relative importance of the thermal resistance of oxidation film, the heat transfer capability of stainless steel after oxidation is deteriorated.