Study of axial mixing, holdup and slip velocity of dispersed phase in a pulsed sieve plate extraction column using radiotracer technique.
Axial mixing, holdup and slip velocity of dispersed phase which are parameters of fundamental importance in the design and operation of liquid-liquid extraction pulsed sieve plate columns have been investigated. Experiments for residence time distribution (RTD) analysis have been carried out for a range of pulsation frequency and amplitude in a liquid-liquid extraction pulsed sieve plate column with water as dispersed and kerosene as continuous phase using radiotracer technique. The column was operated in emulsion region and (99m)Tc in the form of sodium pertechnetate eluted from a (99)Mo/(99m)Tc generator was used to trace the dispersed phase. Axial dispersed plug flow model with open-open boundary condition and two points measurement method was used to simulate the hydrodynamics of dispersed phase. It has been observed that the axial mixing and holdup of dispersed phase increases with increase in pulsation frequency and amplitude until a maximum value is achieved while slip velocity decreases with increase in pulsation frequency and amplitude until it approaches a minimum value. Short lived and low energy radiotracer (99m)Tc in the form of sodium pertechnetate was found to be a good water tracer to study the hydrodynamics of a liquid-liquid extraction pulsed sieve plate column operating with two immiscible liquids, water and kerosene. Axial dispersed plug flow model with open-open boundary condition was found to be a suitable model to describe the hydrodynamics of dispersed phase in the pulsed sieve plate extraction column.
AXIAL-DISPERSION IN A RECIPROCATING PLATE EXTRACTION COLUMN
Axial dispersion coefficients have been measured in the continuous phase of a 5 cm diameter reciprocating plate extraction column. The measurements were made by observing the course of an instantaneous chemical reaction between acid and base in the continuous phase, using phenolphthalein as indicator. The data for single-phase operation have been correlated in terms of amplitude and frequency of reciprocation, and spacing between plates. A similar correlation applies for liquid-liquid operation under intense agitation. At low agitation rates, and for gas-liquid operation, the dispersion coefficient depends strongly on the flow rate of dispersed phase. 
 
 
 
On a mesure les coefficients de dispersion axiale dans la phase continue d'une colonne d'extraction munie de plateaux de 5 centimetres de diametre lesquels etaient donnes d'un mouvement de va et vient. On a fait les mesures en observant la marche d'une reaction chimique instantanee entre un acide et une base, dans la phase continue, et en employant la phenol-phtaleine comme indicateur. On a etabli une correlation entre les resultats obtenus pour une operation en phase simple, et ce, en fonction de l'amplitude et de la frequence du mouvement de va et vient et de l'espacement entre les plateaux. Une correlation semblable s'applique au cas d'une operation impliquant deux liquides soumis a une agitation intensive. Dans le cas de vitesses faibles d'agitation et d'une operation impliquant un gaz et un liquide, le coefficient de dispersion depend considerablement du debit de la phase dispersee.
Turbulent boundary layer wall‐pressure fluctuations downstream from an abrupt change in surface roughness
Spectra of wall‐pressure fluctuations beneath a turbulent boundary layer have been investigated immediately downstream from an abrupt change in surface roughness, from slightly rough to very rough. Over the measurable frequency band (400 Hz to 7 kHz), the spectra in the first 150 mm scale on wall variables. This indicates that the motions responsible for the pressure fluctuations measured in this region are very close to the wall. Farther downstream this scaling procedure breaks down. It is suggested that the initially thin internal layer behaves independently of the flow external to it until it has grown appreciably and only then interacts with the outer boundary layer. It was found that, for all frequencies measured, the dimensional spectral level decreases initially then rises to a maximum at 250 mm from the roughness change before decreasing once more. The position of the maximum is close to where the internal layer ceases to have a distinct edge.