Amélioration du transfert de chaleur et de la dynamique d’écoulement dans des dispositifs de refroidissement pour IRM sans hélium liquide : modélisation physique.

Cryocooler contact cooling methods partially mitigate the challenges of liquid helium use in medical Magnetic Resonance Imaging (MRI), where resource constraints and costs are critical. However, these systems still face challenges, including mechanical vibrations, limited cooling capacity, prolonged pre-cooling times, and thermal overload originating from copper leads. This study presents a liquid helium-free MRI cooling device that maintains a temperature of 4 K through natural convection in a helium circuit. A three-dimensional multiphysical model was developed to investigate cool-down times for both single and double pipe configurations and to quantitatively assess their thermal performance. The cooling process was optimized by varying pipe diameters and the integration of copper foam inserts. Increasing porosity and particle diameter significantly reduced cooldown time. The single pipe device achieved a 25 % reduction in cool-down time (from 40 h to 30 h), while the double pipe configuration showed a 72.5 % decrease (from 40 h to 11 h). As the pipe diameter increased from 5 mm to 45 mm, performance markedly improved. The double pipe device’s cool-down time dropped from 38.1 h to 11.3 h (70.1 % improvement), and the single pipe device reduced from 395.7 h to 13 h (96.7 % reduction). To further enhance heat transfer and minimize vortex formation, baffles were introduced, resulting in a significant improvement in the cooling efficiency of the 40 mm diameter single pipe device. Increasing the bottom baffle
length (D2) led to 60 mm reduced the cool-down time by 28.7 % matching the performance of double pipe configurations. This optimized design and the developed models provide a framework for advancing sustainable, cost-effective liquid helium-free MRI systems.