Extending the allowable exposure time of rotating X-ray anodes via an embedded lithium pulsating heat pipe: A ۳D multiphase analysis

Thermal management of high-power X-ray rotating anodes is strictly constrained by the intense, localized heat fluxes generated during brief exposure times. This study proposes the integration of a lithium-based rotating pulsating heat pipe (RPHP) into the anode and investigates its transient thermal-hydraulic performance using a volume of fluid (VOF) multiphase model, which is heavily influenced by both extreme centrifugal forces and the intense heat flux applied during the exposure time. The results reveal a fundamental thermodynamic trade-off governing the optimal rotational speed: while higher rotational speeds enhance internal fluid circulation as well as latent and sensible heat transport, they simultaneously generate massive hydrostatic pressures that cause a significant transient delay in the phase-change (boiling) process. Consequently, the maximum allowable exposure time exhibits a non-monotonic dependence on the rotational speed. A case study based on the RAD-۱۴ X-ray tube was investigated with a heat input of ۲۰ kW on a minimum focal spot size (۰.۳ mm). A critical temperature limit of ۲۲۰۰ K was defined to evaluate and compare the allowable exposure times across different configurations. Compared to a conventional solid anode (which is limited to an exposure time of ۰.۴۳۶ s), the RPHP integration at ۸۵۰۰ rpm achieves optimal thermal performance, extending the allowable exposure time to ۰.۷۰۶ s (a ۶۲ % increment). However, further increasing the speed to ۱۰۰۰۰ rpm exacerbates the pressure-induced boiling retardation, leading to an exposure time of ۰.۶۱۹ s (a ۴۲ % increment relative to the solid base, but a ۱۲ % reduction compared to the ۸۵۰۰ rpm peak).

کلیدواژه ها:

Rotating anode X-ray tube ، Rotating Pulsating Heat Pipe (RPHP) ، Volume of fluid (VOF) ، Thermal Management