The Gas-Liquid Mass Transfer Coefficient (k La) in the Gas-Liquid Multi-stage Agitated Contactor (MAC)

Abstract

Data on the volumetric liquid-side gas-liquid mass transfer coefficient, k(L)a, in a Multi-stage Agitated Contractor (MAC) are reported for three gas-liquid systems (air-water, helium-n-octane, and air-Monoethylene Glycol (MEG)). k(L)a (s(-1)) was determined using a dynamic method with moderately soluble gaseous tracers (acetylene for water and MEG and methane for n-octane). The observed response curves could be described accurately by coupling the single phase residence time distribution models for gas and liquid phase (Breman et al., (1,2)), via interfacial gas-liquid mass transfer. All k,a data could be correlated with an average relative deviation of 11.3% by a combination of Calderbanks' relation(3) for k(L) (m s(-1)) and a modified type of Calderbanks' relation(3) for the interfacial area, a (m(-1)), which takes a combined effect of the superficial gas velocity (u(G)) and the liquid viscosity (eta(L)) on a into account: a = 51.1(P/V)(0.286) sigma(-0.19)(u(G)/v(b))((0.127+21.1 eta L)) with g = acceleration of gravity (= 9.81 m(2) s(-1)), P/V = volumetric power input (W/m(-3)), v(b) = bubble rise velocity (m s(-1)) and the experimental conditions ranging from: superficial gas velocity u(G) = 0.01-0.09 m s(-1), stirring speed (N) = 10-36.7 rev s(-1), eta(L) = 0.00041-0.021 N m(-2) s, surface tension (sigma) = 0.02-0.073 N m(-1), liquid density (rho(L)) = 684-1113 kg m(-3), gas density (rho(G)) = 0.16-1.205 kg m(-3) and liquid diffusion coefficient (L-L) = 1.3 x 10(-10)-3.5 x 10(-9) m(2) s(-1). The overall influence of u(G) on k(L)a in this relation is such that k(L)a is hardly affected by u(G) both for water and n-octane, whereas, in contrast, k(L)a is predicted to increase significantly with increasing u(G) for the more viscous monoethylene glycol, The general applicability of the proposed relation for a has to be confirmed by measurements for other liquids and by measurements on a larger scale.