Figure 4. Standard deviation of average solids concentration versus
superficial gas velocity at temperature:
(a) T = 20 °C, (b) T = 200 °C, (c) T = 400 °C, and (d) T = 600 °C.
In fact, the pressure-drop versus superficial gas velocity curves can
also be used to determine \(U_{\text{mb}}\) according to Rapagnà et
al.42, in which \(U_{\text{mb}}\) is the point where a
shallow minimum occurs, as shown in Figure 5. The minimum bubbling
velocity \(U_{\text{mb}}\) obtained from the pressure-drop versus
superficial gas velocity curves is 3.6 cm/s for T =20°C, 3.4 cm/s for T
= 200°C, 3.0 cm/s for T = 400°C, and 2.9 cm/s for T = 600°C. This again
verified the reliability of high-temperature ECT in measuring the
minimum bubbling point in fluidized beds. In conclusion,
high-temperature ECT can provide a direct and accurate approach to
detecting the minimum bubbling velocity from the reconstructed images of
solids concentration of a fluidized bed.