Dr.-Ing. Fabian Hagen

Students of chemical engineering/process engineering (or equivalent) interested in experimental work and with a preference for innovative diagnostic tools. Knowledge of aerosol/particle technology, optical diagnostics and/or physical chemistry may help you get started but is not required.

Location: CS

Motivation:

Cavity ring down spectroscopy (CRDS) is a non-intrusive, highly sensitive, laser-based diagnostics for measuring extremely low concentrations of trace gases and/or gas-borne particles. Within this thesis, the method is to be applied to determine the volume fraction of gas-borne carbon nanoparticles. CRDS utilizes the light absorption within a cavity, which consists of two highly reflective mirrors. Therefore, pulsed laser light is injected into the cavity. Simultaneously, the light transmitted through one of the mirrors is recorded by a detector. The temporal intensity of the laser light decreases exponentially, as each time the light passes between the mirrors, part of the light is absorbed by carbon nanoparticles moving between the mirrors. Therefore, the time constant for the decrease in measured intensity represents the particle volume fraction. Due to the high reflectivity of the mirrors, effective path lengths of several kilometers can be achieved, explaining the high sensitivity of the measurement method.

Task:

This thesis is dedicated to the conceptualization, design and testing of an optical setup enabling the non-intrusive measurement of volume fractions of carbon nanoparticles via cavity ring down spectroscopy (CRDS). The functionality of the developed CRDS system is to be demonstrated by measuring nanoparticle concentrations in a generic validation experiment, which is also to be designed and set up. The work concludes with the quantification of concentration profiles of carbon nanoparticles during their formation in counterflow flames of varying boundary conditions.

Responsible:

Prof. Dr.-Ing. Dimosthenis Trimis