Mechanical Operation: Filtration and Fluidization Questions

1.      A constant pressure filtration test gave data that can fit an expression dt/dV = 9.3 V + 8.5; (t in seconds, V in liters). If the resistance of the filter medium is assumed unaffected with pressure drop and the compressibility coefficient of the cake is 0.3, what will be the time taken for the collection of 3.5 liters of filtrate at a filtration pressure twice that used in the test.     

2.      A pressure filter is operated in the constant rate mode to yield 10 m³ in the first ten minute, as the pressure increases from zero. In the next 20 minutes the filtration was continued at constant pressure, after which it was stopped. Assume filter medium resistance is negligible and the cake is incompressible.

a) Estimate the total volume of filtration obtained.

           b) Determine washing time if the volume of wash liquid equals the volume of filtrate obtained.

3.      Solid particles having a size of 0.12 mm, sphericity 0.88 and a density of 1000 kg/m³ are to be fluidized using air at 2 atm abs and 25°C. The voidage at minimum fluidizing conditions is 0.42. The cross section of the empty bed is 0.3 m² and the bed contains 300 kg of solid. Take viscosity of air 0.0185 cP.

a) Calculate the pressure drop across the bed.

b) Calculate the minimum fluidization velocity using Ergun’s equation for calculating pressure drop.                                  

   4.    A packed bed is composed of cylinders having a diameter of 0.02 m and height = 1.5 Diameter.           The density of the packed bed is 980 kg/m³ and the density of the solid cylinder is 1500 kg/m³.           Calculate the porosity of the bed, effective diameter and sphericity of the particle.