Consider the overall driving force in Whitman's two-film theory of mass transfer. (a) Draw the suggested concentration profiles on both sides of the interface for three special cases: (i) the mass transfer film in the gas phase controlling the rate process; (ii) the mass transfer film in the liquid phase controlling the rate process; (iii) both films controlling the rate process and show the overall driving force. [3 marks] (b) Show that the overall mass transfer coefficient, Ky, can be related to the individual gas and liquid film mass transfer coefficients, ky and kx, respectively, by the following equation: Ky1=ky1+kxm where m is Henry's constant. [3 marks] (c) In a trial on an absorption tower to characterise the mass transfer coefficients, the gas flow rate is varied and the following conditions prevail for the molar gas flow rate, G, and the overall mass transfer coefficient based on the gas phase driving force, KG : (i) Discuss why KG varies with the gas flow rate. [5 marks] (ii) If the gas film coefficient varies linearly with G, the liquid film coefficient is independent of G, Henry's law constant, m, is 5.5 and the prevailing pressure is 100kPa, determine the individual film coefficients. The supplied graph paper may be used for his purpose. [9 marks] Consider the overall driving force in Whitman's two-film theory of mass transfer. (a) Draw the suggested concentration profiles on both sides of the interface for three special cases: (i) the mass transfer film in the gas phase controlling the rate process; (ii) the mass transfer film in the liquid phase controlling the rate process; (iii) both films controlling the rate process and show the overall driving force. [3 marks] (b) Show that the overall mass transfer coefficient, Ky, can be related to the individual gas and liquid film mass transfer coefficients, ky and kx, respectively, by the following equation: Ky1=ky1+kxm where m is Henry's constant. [3 marks] (c) In a trial on an absorption tower to characterise the mass transfer coefficients, the gas flow rate is varied and the following conditions prevail for the molar gas flow rate, G, and the overall mass transfer coefficient based on the gas phase driving force, KG : (i) Discuss why KG varies with the gas flow rate. [5 marks] (ii) If the gas film coefficient varies linearly with G, the liquid film coefficient is independent of G, Henry's law constant, m, is 5.5 and the prevailing pressure is 100kPa, determine the individual film coefficients. The supplied graph paper may be used for his purpose. [9 marks]
