Technical Papers and Presentations

This work presents a multiphysics simulation of a Pirani vacuum gauge using COMSOL Multiphysics. Pirani gauges infer pressure from the pressure dependence of gas thermal conductivity by measuring the steady‑state temperature of a resistively heated filament. Accurate modeling is challenging in the transition flow regime, where the gas mean free path becomes comparable to characteristic geometric dimensions and continuum assumptions lose validity. The model couples heat transfer in solids and fluids, laminar flow through nonisothermal flow coupling, and surface‑to‑surface radiation in a rotationally symmetric 3D geometry. Rarefied gas effects are approximated using a Knudsen‑corrected effective thermal conductivity for nitrogen. A tungsten filament supported by low‑conductivity Ti‑6Al‑4V wires is driven with a constant 100 mW heat input, and the surrounding housing is held at a fixed temperature. A parametric sweep from 10⁶ Pa to 1 Pa is performed. Results show a monotonic increase in filament temperature with decreasing pressure, yielding approximately 335 K sensitivity across six decades. The study demonstrates that reducing parasitic conductive losses and incorporating Knudsen corrections are essential for physically meaningful Pirani gauge simulations in the transition regime and provides a framework for geometry and material optimization.