3. Glauber's salt, Na2SO4.10H20, is to be produced in a Swenson-Walker crystalliser by cooling to 290 K a solution of anhydrous Na2SO, which saturates between 300 K and 290 K. If cooling water enters and leaves the unit at 280 K and 290 K respectively and evaporation is negligible, how many sections of crystalliser, each 3 m long, will be required to process 0.25 kg/s of the product? The solubilities of anhydrous Na2SO4 in water are 40 and 14 kg/100 kg water at 300 K and 290 K respectively, the mean heat capacity of the liquor is 3.8 kJ/kg K and the heat of crystallisation is 230 kJ/kg. For the crystalliser, the available heat transfer area is 3 m/m length, the overall coefficient of heat transfer is 0.15 kW/m K and the molecular masses are Na2SO4.10H30 = 322 kg/kmol and Na2SO4 = 142 kg/kmol. 4. A solution of 500 kg of Na2SO4 in 2500 kg water is cooled from 333 K to 283 K in an agitated mild steel vessel of mass 750 kg, At 283 K, the solubility of the anhydrous salt is 8.9 kg/100 kg water and the stable crystalline phase is Na2SO4 10H20. At 291 K, the heat of solution is -78.5 MJ/kmol and the specific heat capacities of the solution and mild steel are 3.6 and 0.5 kJ/kg deg K respectively. If, during cooling, 2 per cent of the water initially present is lost by evaporation, estimate the heat which must be removed. (use both methods)