Answer Happy

Question 2 (a) A diluted suspension of minerals with density p. 2200 kg m³, in water with density p= 1000 kg m³, and viscosity = 1 mN s m², is to be separated on plant by centrifuge. Pilot tests conducted at 10000 rpm with a throughput Q₁= 5x10 m³ s¹ provide a clarified overflow. The test machine has height H= 0.4 m, radius R= 0.03 m, and overflow weir, ro 0.015 m, while the plant machine has height H= 1 m, radius R= 0.1 m, and overflow weir, ro 0.05 m, and operates at 5000 rpm. (i) Calculate the volumetric holdup of liquid V' in the bowl, for the test and plant machines. [3 marks] (ii) Define, and calculate the capacity factor, Σ, for the test and plant machine. [3 marks] (iii) Calculate the throughput Q₂ that will provide the same quality of overflow for the plant machine. [3 marks] (iv) Determine the cut size, d, of the separation. [3 marks] (v) Calculate the residence time for the particles to settle. [3 marks] (b) 2500 kg of an aqueous solution containing 30% by weight of solids of Fe(NO3)2 is slowly cooled to T= 25° to form crystals of Fe(NO3)2 6H₂O. The solubility of crystals is 20% in mass ratio relative to solvent. The molecular mass of the anhydrous and hydrated salt is 179.8 kg kmol¹ and 287.84 kg kmol¹, respectively. Assume the evaporation of solvent to be negligible. (i) Calculate the amount of water of crystallisation. [5 marks] (ii) Calculate the crystal yield. [3 marks] (iii) If the same operation is carried out by evaporating 10% of the solvent, re-calculate the parameters in (i) and (ii) and comment your answer. [7 marks]