RHSFluidizedBed:

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   Model of a Fluidized bed.
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   Form:
   xDot = RHSFluidizedBed( x, t, d )
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   ------
   Inputs
   ------
   x           (4,1) State [concentration of A; concentration of B; temp]
   t           (1,1) Time
   d           (1,1) data structure
                     .lEA     (1,1) Lewis number
                     .lEB     (1,1) Lewis number
                     .betaHat (1,1) Residence time
                     .beta1   (1,1) Heat of reaction
                     .beta2   (1,1) Heat of reaction
                     .gamma1  (1,1) Activation energy
                     .gamma2  (1,1) Activation energy
                     .alpha1  (1,1) Rate constant factor
                     .alpha2  (1,1) Rate constant factor
                     .xAF     (1,1) Concentration of A in the feed stream
                     .xBF     (1,1) Concentration of B in the feed stream
                     .tF      (1,1) Inlet stream temperature
                     .u       (1,1) Control
   -------
   Outputs
   -------
   xDot        (4,1) State derivative

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   Reference: Henson, M. A. and D. E. Seborg. (1997.) Nonlinear Process
              Control, Prentice-Hall. p. 244.
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