Novel method for measuring temperature-dependent diffusion coefficient of radon in porous media

Radon exhalation behavior and determination of diffusion migration parameters in spherical porous emanation media

There is a significant impact of the radon diffusion coefficient and the free radon production rate on the exhalation of radon from porous materials that can be regarded as spheres, hexahedrons, or cylinders. To understand this effect, the radon exhalation rules of spherical porous media with different radii were studied according to the radon diffusion migration theory. A specialized method for simultaneous determination of the radon diffusion coefficient and the free radon production rate of the spherical porous media was proposed, and applied to determine the above two parameters for two hemispherical test blocks with different radii. The results show that:(1) For spherical porous media with a certain radon diffusion length (Ld), as the radius (r0) of the sphere increases, the radon exhalation rate first increases, and tends to stabilize at r0≥6Ld; The free radon release share gradually decreases from approximately 1, and drops to a steady state at r0≥18Ld. (2) Compared with conventional methods, the relative error of the free radon production rate determined by the proposed method is within 3.9%, which verifies the reliability of the new method.

Design on intermittent ventilation strategy for radon removal in underground space

Ventilation to reduce radon was one of the most widely used, important, and effective means to reduce radon concentration in underground engineering. The largest energy consumption of underground buildings was the building ventilation system. Taking the radon migration process in a room as an example, this paper built a numerical model that accounted for the mechanism of radon production, exhalation, and diffusion process, by proposing a novel intermittent ventilation strategy to mitigate radon concentration in underground space. Three ventilation strategies (no ventilation, continuous ventilation, and intermittent ventilation) were compared under various wind speeds and fresh air ratios. Under the same safe duration of radon concentration, when intermittent ventilation was operated with the same wind speed, the startup time was reduced by 79.4%, 86.0%, 90.8%, 92.8%, 91.25%, with compared with continuous ventilation. The higher the fresh air ratio, the lower the radon concentration limit, and the faster the dynamic equilibrium state of radon concentration will be reached. During intermittent ventilation, reducing the fresh air ratio can greatly increase the recovery and utilization of the return air heat, thereby reducing the power of the air conditioning unit. Considering the comprehensive energy-saving benefits of the ventilation system, the appropriate intermittent ventilation plan should be made to meet radon reduction requirements in the range of low wind speed. If low wind speed was selected, there existed advantages of low ventilation noise and more comfortable, as well.