**5. Conclusions and prospective**

**Figure 26.** The change of pressure drop, the change of combination factor φ and combination factor *k* during succes‐

Through the above process, a convenient method for on-line monitoring the fluidized state of the particles in a high-temperature coating process can be proposed. The pressure drop change before and after coating can be used effectively as real-time analysis of particle flow conditions. The combination factor *φ* can be calculated on the basis of design values of coating layer, the pressure drop change can be obtained from the experimental results, so *k* can be calculated in four coating process, then a constant *k* should be obtained. One can compare *k* values to estimate the fluidization state at different coating process of four coating layers. If an abnormal value is found, which indicates the poor quality of particle fluidization state during the coating process, and then the quality of the coated layer will be affected. Additionally, *k* can also be estimated firstly by a series of experiments, the pressure drop changes can be calculated by Eq.(4) in the same spouted bed coating furnace according to the design value of the coated layer, and then real-time comparative analysis with the experimental results of pressure drop changes can be performed to monitor the fluidized state of the particles on-line in the coater.

The multiscale study of the coating technology of nuclear fuel kernels are discussed above,

sive (TRISO) coating on UO2 micro-spheres

180 Modern Surface Engineering Treatments

**4. Brief summary**

and the brief summary can be given as follows:

In this chapter, the multiscale study concept of the coating technology is stated and validated as an effective and necessary method to develop the coating technology of nuclear fuel kernels from the lab to the factory. It should be indicated that the application of the coating technology for other usages rather than nuclear industry is extensive, such as CNT preparation and suface modification of catalyst particles. The multiscale study of the coating technology can be seen as a universal methodology in the R&D of the coating process, especially in the field of fluidized bed chemical vapor deposition (FB-CVD).

The FB-CVD method is a suitable technique for preparing various kinds of films/layers on the spherical materials by initiating chemical reaction in a gas. This technique can be used for many purposes, such as synthesizing carbon nanotube composite photocatalyst ((CNT)/Fe-Ni/ TiO2). Also, some modified method based on FB-CVD, such as plasma-enhanced FB-CVD, has been used to prepare the transparent water-repellent thin films on glass beads in modern surface engineering treatment. So the investigation of FB-CVD method is helpful and impor‐ tant for modern surface treatments.

This multiscale study should be developed in the future, especially in the the mutual coupling reasearch in micro-, meso- and micro- scales, such as the effect of fluidized state on the homogeneity and compactness of coating materials. Also, this method should play an important role in the study of the scale-up methodology in the field of FB-CVD.
