The Thermal Hydraulics and Irradiation Engineering (THIE) Group at Oak Ridge National Laboratory (ORNL) designs and builds capsules in which to irradiate advanced fuels and materials that are typically inserted into ORNL’s High Flux Isotope Reactor. Experiments are designed to achieve a target temperature that ranges from 250°C to 1200°C. Most capsules do not have active temperature measurement or control, which puts an imperative on accurate temperature simulation. Temperature control in these capsules is accomplished by designing specific gaps between adjacent parts and filling the capsules with an inert gas: helium, neon, or argon.

Most any finite element solver will do an excellent job estimating temperatures within individual parts, but the simulation challenge for these complex, multi-body systems is to accurately predict the heat transfer through contact surfaces or interstitial gas gaps. The gas gaps are on the order of 150 μm, so accurate simulation must include thermal expansion of the adjacent parts, the thermal jump effect on the part surfaces, and the possibility the parts will touch or break contact during expansion. This paper will discuss the limitations in thermal contact modeling in finite element modelers and the algorithms the THIE Group uses to overcome these limitations.

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