Question

The minimum fluidization height of 1.20 m is maintained during fluidized bed drying of carrots. The bed diameter of the fluidized bed dryer is 0.6 m. If mass and solid density of carrots are 250 kg and 1040 kg/m\(^3\), respectively, then the porosity of the bed at the minimum fluidization condition is \underline{\hspace{3cm}} (rounded off to 3 decimal places, \(\pi = 3.14\)).

Hint:

Porosity in fluidized beds is determined from bulk volume minus solid volume divided by bulk volume.

Answer 1

Step 1: Volume of bed. Bed volume: \[ V_{bed} = \pi \frac{D^2}{4} H \] \[ = 3.14 \cdot \frac{0.6^2}{4} \cdot 1.2 = 0.339 \, m^3 \]

Step 2: Volume of solids. \[ V_s = \frac{M}{\rho_s} = \frac{250}{1040} = 0.240 \, m^3 \]

Step 3: Porosity formula. \[ \varepsilon = \frac{V_{bed} - V_s}{V_{bed}} \] \[ = \frac{0.339 - 0.240}{0.339} = 0.099/0.339 \] \[ \varepsilon = 0.800 \] \[ \boxed{0.800} \]