Investigation of the structure of two-phase flow model-media in bubble-column bioreactors

Summary By applying photographic, electrical conductivity, and electrooptical methods, the transverse variation of bubble size and velocity, the local gas hold up, and the local specific gas/liquid interfacial area were estimated in a bench scale bubble-column bioreactor containing model cultivation media. The liquid velocity profile, the transverse turbulence intensity variations, and the turbulence energy dissipation scale were also measured by a hot film turbulence probe and constant temperature anemometer technique.A significant relationship was found between the two-phase flow fluid dynamical state and the transverse variation of the various properties.Symbols M mass - L length - T time - a gas/liquid interfacial area L² - specific gas/liquid interfacial area with regard to the bubbling layer volume L^–1 - D transverse coordinate (measured from the wall of the column) L - d bubble diameter L - d mean bubble diameter L - d_e dynamic equilibrium (maximum stable) bubble diameter L - d_p primary bubble diameter L - d_s Sauter bubble diameter L - E specific energy dissipation rate with regard to the volume of the liquid ML^–1T^–3 - EV_L energy dissipation rate ML²T^–3 - , since =1 g/cm³, E has the same numerical value as E. Therefore, the symbol E is used everywhere in the present paper for E for simplicity and called energy dissipation rate (S.s^–2=Stokes.s^–2) L²T^–3 - E_G or local relative gas holdup - f (r) cross correlation function - g acceleration of gravity LT^–2 - h longitudinal distance from the aerator L - relative turbulence intensity - N_O number of u and crossings T^–1 - n_B bubble frequency T^–1 - r distance between two points 1 and 2 of the cross correlation function L - t time - u instantaneous liquid velocity LT^–1 - mean liquid velocity LT^–1 - mean square fluctuation velocity L²T^–2 - turbulence intensity LT^–1 - w_SG superficial gas velocity LT^–1 - w_SL superficial liquid velocity LT^–1 - or E_G local relative gas holdup LT^–1 - energy dissipation scale L - kinematic liquid viscosity L²T^–1 - liquid density M L^–3 - surface tension M T^–2 - dynamic turbulence pressure M L^–1T^–2 Indices p primary (at the aerator) - e equilibrium (far from the aerator)