Extending the allowable exposure time of rotating X-ray anodes via an embedded lithium pulsating heat pipe: A 3D multiphase analysis

Amini, Mohsen; Sarhaddi, Faramarz; Azarkish, Hassan

doi:10.22104/jpst.2026.8247.1291

Extending the allowable exposure time of rotating X-ray anodes via an embedded lithium pulsating heat pipe: A 3D multiphase analysis

Document Type : Research Article

Authors

Mohsen Amini

Faramarz Sarhaddi

Hassan Azarkish

Department of Mechanical Engineering, University of Sistan and Baluchestan, Zahedan, Iran

10.22104/jpst.2026.8247.1291

Abstract

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-14 X-ray tube was investigated with a heat input of 20 kW on a minimum focal spot size (0.3 mm). A critical temperature limit of 2200 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 0.436 s), the RPHP integration at 8500 rpm achieves optimal thermal performance, extending the allowable exposure time to 0.706 s (a 62 % increment). However, further increasing the speed to 10000 rpm exacerbates the pressure-induced boiling retardation, leading to an exposure time of 0.619 s (a 42 % increment relative to the solid base, but a 12 % reduction compared to the 8500 rpm peak).

Graphical Abstract

Extending the allowable exposure time of rotating X-ray anodes via an embedded lithium pulsating heat pipe: A 3D multiphase analysis

Highlights

Novel application of a pulsating heat pipe for rotating anode X-ray tube cooling.
Extended X-ray exposure times and improved tube rating charts.
Precise VOF modeling of pressure-dependent phase change at extreme speeds.
Predicting nucleation delay from high centrifugal pressure at 10000 rpm.

Keywords

Rotating anode X-ray tube

Rotating pulsating heat pipe (RPHP)

Volume of fluid (VOF)

Thermal management

Subjects

Modelling and Simulation

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