Effect of subsurface thermocouple installation on the discrepancy of the measured thermal history and predicted surface
- PDF / 1,106,599 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 26 Downloads / 178 Views
I. INTRODUCTION
INCREASINGLY, computational modeling of industrial metallurgical and materials manufacturing processes is becoming an integral part of enhancing final product quality. The modeling, design, and control of many of these operations hinges, in part, on being able to accurately quantify the heat transfer occurring at the boundary of the products being processed. In many cases, water is used as the medium to cool these components to the desired temperatures before further processing occurs. Quantification of the heat-transfer boundary conditions in these situations can be quite challenging, especially as rapid nonlinear changes in the heat flux or heat-transfer coefficient occur with the variation of the component surface temperature. Moreover, the boundary condition can also change dramatically depending on the properties of the water, the conditions under which the water is applied to the surface of the component, and the interaction of the water with the surface of the component. In light of the need for quantification of the boiling water heat transfer during the quench process and the challenges associated with this, researchers are increasingly turning to inverse heat conduction (IHC) methods to quantify surface heat fluxes based D.I. LI, Postdoctoral Fellow, and M.A. WELLS, Assistant Professor, are with the Department of Materials Engineering, University of British Columbia, Vancouver, BC, Canada V6T 1Z4. Contact e-mail: mary@ cmpc.ubc.ca Manuscript submitted March 1, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS B
on experimental data.[1–5] In these methods, the boundary heat flux is not initially known but is calculated based on accurate knowledge of the temperature-time history experienced at a known interior location in the material during the cooling process. Historically, thermocouples installed at an interior location in the sample have been the most common measurement technique to infer the heat flux at the surface of the sample as well as the sample surface temperature using an IHC model.[1–4] Figure 1 shows a schematic of a typical thermocouple used to measure the temperature history in a sample during a quench operation. Referring to Figure 1, a thermocouple is made up of two wires, and typically an insulating material such as MgO is used to separate the two TC wires from each other. The thermocouple assembly is then covered using a metal sheath. In situations where the temperature changes rapidly during the quench operation, the thermocouples are positioned within the sample so that the thermocouple tip is very close to the quench surface. This ensures that the detailed changes in the heat flux during the quench operation can be captured. It is important that the thermocouple bead, which is located at the temperature measurement point, has intimate contact with the sample so that the thermal resistance between the thermocouple and sample is reduced. Although there are many situations where the perturbing effect of the thermocouple hole on the heat propagation within the sample is ne
