Development of a methodology for measuring axial and radial dispersion coefficients in multiphase apparatus using volumetric flow modulation (VOLMOD)
Motivation:
Bubble columns and trickle bed reactors are widely used contact apparatuses for heterogeneous catalysis, bioprocesses, exhaust gas, wastewater treatment and many more. The influence of hydrodynamics on the mass and heat transport processes taking place in them is very large but difficult to model completely because the processes involved are nonlinear and cross-scale. In such contactors, the most widely used theoretical approach to describe the gas and fluid phases is the Axial Dispersion Model. Successful implementation of this model requires accurate knowledge of the axial dispersion coefficient of both the liquid and gas phases. Conventional approaches to determine axial dispersion coefficients are based on experimental studies with tracer substances. However, such methods are unlikely to be universally applicable, cause harmful product contamination or process failures and alter the physical properties of the system.
Objectives:
The project aims to further develop and comprehensively apply the methodology of measuring axial dispersion coefficients using volumetric flow modulation for both bubble columns and trickle bed reactors. The proposed methodology is completely non-invasive and does not require any tracer substance.
Methods and results:
Instead of using a tracer substance, a marginal sinusoidal modulation is superimposed to the gas inlet flow rate and used as a virtual tracer. This modulation causes a sinusoidal variation of the gas holdup in time, called gas density wave. Dispersion causes amplitude attenuation and phase shift of the gas density wave along the column. Amplitude damping and phase shift can be measured and related to the value of the axial dispersion coefficient. Sinusoidal-resolved gamma-ray densitometry is used to investigate the amplitude damping and phase shift.
Sketch of the working principle and experimental setup of the gas flow modulation