Figure 6. Comparison of \(U_{\text{mf}}\) obtained from measurements and
predictions based on Eq. (13) for different temperature.
4.4 Fluidization transition from Geldart B to
A
According to Geldart, fluidization of Geldart B and A particles has
typical features as8:
- Group B: Bubbles occur when the bed of particles starts to be
fluidized, which is featured by\(\ {U_{\text{mf}}/\ U}_{\text{mb}}\) =
1.
- Group A: A homogeneous fluidization regime, in which no obvious
bubbles appear between \(U_{\text{mf}}\) and \(U_{\text{mb}}\),
leading to \(U_{\text{mb}}\)/\(U_{\text{mf}}\) > 1.
Based on the above measurement results,\(U_{\text{mb}}/U_{\text{mf}}\) is shown in Figure 7. As can be seen,
at ambient condition (T= 20°C), silica particles indeed manifest
Geldart B fluidization behavior, i.e.\({U_{\text{mf}}/\ U}_{\text{mb}}\) = 1. When the temperature is
increased to 200oC, the occurrence of first bubble
happens at \(1.164U_{\text{mf}}\), i.e. an interval of homogeneous
fluidization between \(U_{\text{mf}}\sim 1.164U_{\text{mf}}\) was
observed. This is typical Geldart A fluidization behavior. Further
increase in temperature to 400oC leads to an
enlarged interval of homogeneous fluidization
between\(\ U_{\text{mf}}\) and \(1.209U_{\text{mf}}\), which then
levels off to \(U_{\text{mf}}\sim 1.201U_{\text{mf}}\) at T= 600°C.
Thus, it can be obtained that \(U_{\text{mb}}/U_{\text{mf}}\)increases from 1.00 at 20°C to 1.201 at 600°C, suggesting that the
fluidization transits from Geldart B to A when the operating
temperature is increased from ambient to 600°C .