Master theses / Diploma theses / Student Assistant / Compulsory internship / Volunteer internship

Application of flow modulation technique to trickle bed reactors (Id 345)

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Trickle bed reactors are subjected to dispersion phenomena on both the gas and liquid phase. In the last decades, several models have been proposed to describe the hydrodynamics of trickle bed reactors, involving up to six parameters, as reviewed by Gianetto et al. (1978). However, the axial dispersion model remains the most practical, accepted and used one. This model assumes dispersion as a stochastic phenomenon and uses the axial liquid dispersion coefficient as the sole parameter.
Traditionally, axial dispersion coefficients are measured using the residence time behaviour of inserted tracer substances. However, such methods are hardly universally applicable considering also production units. Tracer substances can alter the physical properties of the system and may cause detrimental impurities or process downtimes.
The flow modulation technique (FMT) has been proposed by Hampel (2015) and was recently applied by Do ß et al. (2017) for measuring the axial gas dispersion coefficient in bubble columns. However, it has never been applied for measuring the axial liquid dispersion coefficient in trickle bed reactors. Using the FMT, no tracer substances are injected; instead, a marginal sinusoidal modulation is superimposed to the inlet flow rate and used as a virtual tracer. This way, the modulation introduces a sinusoidal variation of the liquid holdup in time, called holdup wave. Along the reactor, the holdup wave gets damped in amplitude and shifted in phase due to liquid dispersion. Amplitude damping and phase shift can be measured and related to the value of the axial liquid dispersion coefficient via the above mentioned dispersion model. A schematic sketch of the working principle of liquid flow modulation is shown in the figure below. The approach is a new, non invasive and easy to apply experimental approach.
The candidate (f/m/d) will experimentally test the applicability of the (liquid) flow modulation approach in trickle bed reactors of different sizes, using gamma ray densitometry as a measurement technique. For comparison purposes, conductivity based tracer measurements will be performed as well. Liquids of different viscosities will be tested and the impact of viscosity on the value of the liquid axial dispersion coefficient will be evaluated.

Department: Experimental Thermal Fluid Dynamics

Contact: Marchini, Sara


  • Studies in chemical engineering or comparable
  • Interest in experimental work
  • Good communication skills in both written and spoken English


  • Start in September/October 2022
  • Work in multidisciplinary and international environment
  • Compensation as for HZDR conditions