Thermal Analysis of Tungsten Targets for High-Power X-ray Tubes

Sammanfattning

In cost-sensitive industries, the performance and reliability of commercial X-ray tubes are often limited by overheating, which causes component degradation and shortens operational lifespan. Although imaging systems have advanced, the core design of commercial X-ray tubes—especially regarding thermal management—has seen minimal innovation. This thesis addresses this gap by examining the thermal performance and durability of tungsten (W) and tungsten–rhenium (W–Re) targets in stationary X-ray tubes, emphasising heat transfer optimisation and cooling system design. A comprehensive literature review established the theoretical basis, highlighting the principles of conduction, convection, radiation, and fluid dynamics relevant to forced convection. Monte Carlo simulations (CASINO®) and finite element analysis (COMSOL Multiphysics®) were employed to model heat transfer under natural and forced convection scenarios. A primary aim was to develop a predictive thermal model capable of estimating temperature behaviour across varying operational conditions. Validation against experimental data from monoblock testing revealed an error of less than 5% in copper temperature measurements. The temperature difference in copper between W and W–Re targets was less than 1%, indicating similar heat conduction properties. Target surface temperatures varied by up to 21%, depending on whether the backscattering factor was modelled using realistic or idealised assumptions—though the BSF itself remained nearly identical for both materials. Simulated temperatures approached the recrystallisation thresholds of the materials, confirming the model's reliability.Cooling simulations conducted under laminar flow conditions revealed that doubling the oil flow rate resulted in only a 3% reduction in the target temperature and an 18% decrease in the copper temperature. This implies that substantial thermal improvements necessitate transitioning into turbulent flow regimes, such as those achieved through jet impingement or the use of turbulators. Long-term testing revealed that W–Re targets maintained their structural integrity after 150 hours, whereas pure W targets experienced erosion, demonstrating their superior resistance to thermal fatigue.