Gas-solid fluidized beds have historically been employed in a variety of fields owing to the excellent mixing they provide, which can enhance chemical reaction rates and make the control of the reactor temperature easier than other technologies. Due to this wide application, heuristic knowledge of their functioning has been accumulating over the years. This knowledge, however, is not always backed by a deep understanding of the physical phenomena occurring in such systems. While this heuristic knowledge is sufficient to operate fluidized beds, operation optimization and scale-up are much harder to perform. A range of diagnostic techniques have been applied over the years to draw information about the inner workings of fluidized beds. Among these, x-ray imaging techniques, especially x-ray digital radiography and x-ray computed tomography, stand out for the kind and quality of information they can provide. Their high penetrating power enables visualization of phenomena taking place in the bulk of a fluidized bed, without disturbing the bed hydrodynamics. Furthermore, x-rays are generated by a source that can be switched off, making them inherently safer than other imaging techniques relying on radioactive sources, such as γ-ray computed tomography. This work gives an overview of the techniques themselves, of the quantities they can measure, and of some modern applications of gas-solid fluidized beds they have been applied to, such as waste treatment and thermochemical conversion of biomass. Overall, x-ray digital radiography and x-ray computed tomography are better suited for process understanding than for process monitoring and are extremely useful in the study of voidage distribution and macro structures, such as bubbles and jets.

气固流化床历史上因其提供的良好混合而被应用于多种领域，与其他技术相比，它可以提高化学反应速率并使反应器温度更容易控制。由于这种广泛的应用，多年来关于其功能的启发式知识不断积累。然而，这种知识并不总是得到对此类系统中发生的物理现象的深刻理解的支持。虽然这种启发式知识足以操作流化床，但操作优化和扩大规模却更难执行。多年来，已经应用了一系列诊断技术来获取有关流化床内部运作的信息。其中，X 射线成像技术，尤其是 X 射线数字射线照相和 X 射线计算机断层扫描，因其可提供的信息种类和质量而脱颖而出。它们的高穿透力能够使流化床主体中发生的现象可视化，而不会干扰流化床的流体动力学。此外，X 射线是由可以关闭的源产生的，这使得它们本质上比其他依赖放射源的成像技术（例如 γ 射线计算机断层扫描）更安全。这项工作概述了这些技术本身、它们可以测量的数量以及它们所应用的气固流化床的一些现代应用，例如废物处理和生物质的热化学转化。总体而言，X 射线数字射线照相和 X 射线计算机断层扫描比过程监控更适合过程理解，并且在研究空隙分布和宏观结构（例如气泡和射流）时非常有用。