Characterization of the Boundary Condition in Heat Treatment Operations Using an Inverse Heat Conduction Algorithm

The accurate determination of the heat transfer boundary condition is a crucial component of mathematical models aimed at predicting the evolution of the thermal, microstructural and stress fields in heat treatment operations. However, the direct measurement of surface heat flux, heat-transfer coefficient or surface temperature, is a very difficult task. Therefore, the application of algorithms that solve the inverse heat conduction problem of estimating the surface heat flux together with surface temperature, based on experimentally determined subsurface temperatures, has rapidly gained importance as a tool for process modelling. A widely used algorithm is the sequential function specification technique. In this paper, the sequential function specification algorithm has been applied to estimate the surface heat flux and heat-transfer coefficient at the surface of interstitial-free steel bars subjected to forced convective quenching. A quenching apparatus was specially built to measure the temperature response in the bars under controlled laboratory conditions. The geometry of the test section used ensured one-dimensional heat flow. It was found that filtering the raw data prior to the inverse analysis greatly improved the estimates of surface heat flux and heat-transfer coefficient. The characterization of the critical heat flux (CHF) was also significantly improved by pre-filtering the data. An important advantage of inverse heat conduction techniques like sequential function specification (compared with the sequential exact matching approach) is that over-responses to sudden changes in the measured temperatures can be reduced; this becomes particularly important for rapidly varying temperature responses.