How do you understand that the fluidized bed bed resistance has little to do with the material layer?

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2.3 Determination of material layer resistance To measure the material layer resistance, a material layer of a certain thickness is laid on the air distribution board. In the same way as the resistance of the air distribution board is measured, the static pressure of the air chamber with different air volumes is measured. Every time the thickness of the material layer is changed in the future, the measurement of the relationship between the air volume and the static pressure of the air chamber is repeated. The static pressure of the air chamber is equal to the sum of the resistance of the air distribution plate and the resistance of the material layer, that is,: 　　Material layer resistance = air chamber static pressure - air distribution plate resistance. The three values ​​in the above formula all correspond to the values ​​under the same air volume. 　　Based on the results measured in the above two tests, the relationship between material layer resistance and air volume under different material layer thicknesses can be obtained, and the material layer resistance-air volume relationship curve can also be drawn. A large amount of statistical data shows that the resistance of the fluidized bed is roughly equal to the difference between the weight of the bed material on the air distribution plate per unit area and the buoyancy of the fluid. That is, ΔP== =hfg(ρp-ρf)(1-ε) (2) where: △P—resistance of fluidized bed, Pa ； 　　　G — the mass of the material in the fluidized bed, kg; g — the acceleration of gravity, m/s2 ； 　　　hf —Height of fluidized bed, m ； 　　　Fb —fluidized bed area, m2 ； 　　　ρp, ρf - the actual density of the material and the air density, kg/m3; ε - the average void ratio of the fluidized bed. 　　Because ρp?ρf, the influence of ρf can be ignored in the calculation, so △Ρ=hfgρp (1-ε). Further simplified through experiments, the bulk density of the fixed bed material before fluidization is used to express it as: △Ρ=Ahgρd g (3) where: hg—height of static material layer, m ； 　　ρd—Pack density of material layer, kg/m3 ； 　 A—Proportional coefficient determined by coal type, see Table 2. 　　When the thickness of the static material layer hg>0.3m, the calculated results are very close to the experimental data. From formula 3, we can see that the resistance of the material layer is directly proportional to the thickness of the static material layer. The thicker the material layer, the greater the resistance. For simplicity, Table 3 can be used to estimate the material layer thickness through the material layer resistance.