Théorie et application de la distribution normale de θ1/3 aux temps de séjour des fluides dans les réservoirs agités en régime continu

Statistical models of residence time distributions in ideal stirred tanks in series are well approximated by a normal distribution of θ^1/2, θ^1/2 or θ according as the number of tanks is > 15, > 50 and very large respectively. For one stirred tank, the normal distribution of θ^1/3 approximates well the residence time distribution for both ideal and nonideal mixing. For ideal mixing, the mean x_m and standard deviation σ of the θ^1/2 distribution assume values of 8/9 and 1/3 respectively. For nonideal mixing, x_m is < 8/9 while σ is > 1/3. At constant fluid viscosities, when the rotational speed of the agitator increases, x_m increases gradually to reach its upper limiting value of 8/9 whilst σ decreases to reach its lower limiting value of 1/3. At fixed rotational speeds, if the viscosity increases, x_m decreases whilst σ increases. A simple mixing efficiency criteria derived from the normal distribution of θ^1/3 is proposed and is compatible with Danckwerts' segregation concept.