3. According to the shrinking particle model for gas-solid reaction, namely: A(G)+bB(s)Products The gas film resistance at the surface of a solid particle is dependent on several factors. (a) List three of these factors. [3 marks] (b) As the solid particle reduces in size during reaction, does the gas-film mass transfer coefficient, kA(G), increase or decrease with i. gas velocity [3 marks] ii. particle size? [3 marks] Justify your answer to both parts. (c) For small spherical particles (in the Stokes law regime) show that the time, , for complete disappearance of the particle is: =2bCA(G)DCBR0 where R0 is the particle radius, CB is the particle concentration, CA(G) is the concentration of the reactant in the gas phase and D is the diffusion coefficient. [10 marks] (d) For this first order gas-solid reaction, assume a surface reaction with gas film diffusion control is in place, then calculate the solid holdup (W) required in a reactor for a fractional conversion, B, of 0.8 with a feed flowrate, FB0, of 50 kgmin1 and time for complete conversion, , is 1.5 hours. Hint: according to Stokes law kA(G)=dp2D=RD and for gas film diffusional control: t=1(1B)1/3 [6 marks] [Total 25 marks]