Thomas Häber

• Dr. rer. nat.
• Researcher at Karlsruhe Institute of Technology

Falling film flows over rectangular corrugations can exhibit intense time-oscillatory interfacial motion. This is of considerable interest for heat and mass transfer applications, where structured surfaces play a crucial role in process intensification. Our contribution relies on high-speed imaging and image processing based on an internally refere...

Unsteady film flows play an important role in intensifying heat and mass transfer processes, with applications, e.g., in falling film absorbers or reactors. In this context, the influence of surface structure modification on the wave dynamics of falling film flows is experimentally investigated based on localized film thickness time series data. Ar...

This study investigates the NO reduction by H2 on a Pd/Al2O3 catalyst in a temperature range of 100–300 ◦C and NO/H2 ratios from 0.5–2, aiming to gain a deeper understanding of the reaction kinetics and its interaction with mass transfer. Planar laser-induced fluorescence (PLIF) is used to visualize the NO distributions over the catalyst, supplemen...

Detailed numerical simulations of stoichiometric premixed methane/air flames have been conducted for a side-wall-quenching (SWQ) setup, in order to study the effect of transient motion of the flame on flame-wall interaction (FWI). A W-shaped plane-jet (2D) flame is considered, which is bounded in its lateral direction by walls. The left wall oscill...

This work presents direct numerical simulations (DNS) of a circular turbulent jet impinging on rough plates. The roughness is once resolved through an immersed boundary method (IBM) and once modeled through a parametric forcing approach (PFA) which accounts for surface roughness effects by applying a forcing term into the Navier–Stokes equations wi...

Planar laser-induced fluorescence with laser synchronized flow control is employed as a non-invasive in situ technique to investigate a NOx storage catalyst, especially to grant a deeper insight into the...

The objective of this study is to derive morphological and nanostructural properties of soot as well as the reactivity against low-temperature oxidation by O2 from easily measurable optical properties. First, ex-situ experiments utilizing thermogravimetric analysis (TGA) and high-resolution transmission electron microscopy (HRTEM) serve to evaluate...

The numerical investigation of quenching distances in laminar flows is mainly concerned with two setups: head-on quenching (HOQ) and side-wall quenching (SWQ). While most of the numerical work has been conducted for HOQ with good agreement between simulation and experiment, far less analysis has been done for SWQ. Most of the SWQ simulations used s...

The two‐dimensional (2D) temporal evolution of the NO‐concentration over a NOx‐storage catalyst is investigated in situ with planar laser‐induced fluorescence (PLIF) in an optically accessible parallel wall channel reactor. Signal accumulated phase‐correlated 2D‐recordings of repetitive adsorption/desorption cycles are obtained by synchronizing the...

Highly-resolved numerical simulations employing detailed reaction kinetics and molecular transport have been applied to flame-wall interaction (FWI) of laminar premixed flames. A multiple plane-jet flame (2D) has been considered, which is operated with premixed methane/air mixtures at atmospheric conditions and with different equivalence ratios. Fr...

Recently we demonstrated the simultaneous detection of the chemiluminescence of the radicals OH* (310 nm) and CH* (430 nm), as well as the thermal radiation of soot in laminar and turbulent methane/air diffusion flames. As expected, a strong spatial and temporal coupling of OH* and CH* in laminar and moderate turbulent flames was observed. Taking a...

In recent years, the tomographic visualization of laminar and turbulent flames has received much attention due to the possibility of observing combustion processes on-line and with high temporal resolution. In most cases, either the spectrally non-resolved flame luminescence or the chemiluminescence of a single species is detected and used for the...

Planar laser-induced fluorescence is employed as noninvasive in situ technique to investigate the oxidation of formaldehyde over platinum. Two-dimensional absolute HCHO concentration distributions over a catalyst-coated plate are visualized in a parallel wall channel. The experimental results are compared with corresponding numerical simulations us...

Side-wall quenching (SWQ) is investigated numerically with steady-state 2D and 3D simulations of an experimental flame setup [1, 2]. The simulations fully resolve the flame and employ detailed reaction mechanisms as well as molecular diffusion models. Quenching distances are determined based on different markers: chemiluminescent species, temperatu...

In recent years, the tomographic visualization of laminar and turbulent flames has received much attention. In most cases, either the integral flame luminescence or the chemiluminescence of a single species is detected and used for the tomographic reconstruction. In this work, we present a novel 2D emission tomographic setup that allows for the sim...

Side-wall quenching (SWQ) is investigated with 2D and 3D simulations of an experimentally measured flame setup. Quenching distances are identified by different markers, based on OH, OH* and CH* concentration profiles as well as temperature, which show qualitatively good agreement with measurements for two flames at different equivalence ratios. 3D...

This study is focused on the characterization of wall heat fluxes and its influence upon CO formation/oxidation within atmospheric flames in a side-wall quenching geometry. The influence of different wall temperatures ranging between 330 K and 670 K is compared for stoichiometric methane and dimethyl ether (DME) flames. Coherent anti-Stokes Raman s...

Detailed numerical simulations have been performed to study the ignition behavior of hot spherical particles at atmospheric conditions. The particles move relative to a combustible gas with a velocity of 0–30 m s , which spans different flow regimes, from creeping flow to unsteady vortex shedding. The temperature of the particles’ surface increases...

We investigate the flame-wall interaction of laminar, premixed methane/air and propane/air flames in a stationary, sidewall-quenching configuration over a wide range of equivalence ratios. Both, the wall material (stainless-steel, cast iron, aluminum), the type of thermal-barrier coating (soot, zirconium dioxide, titanium dioxide) and its thickness...

This study presents the simulation and detailed analysis of the ignition of initially quiescent fuel/air mixtures by small, stationary, laser-heated spherical particles. Our simulations cover a wide parameter space by varying the kind of fuel, stoichiometry, heating rate, radical surface destruction efficiencies as well as particle size. The result...

Mechanical sparks as ignition sources play an important role in safety-related assessments of the ignition of combustible mixtures. In this study, we use laser heated, small bearing balls made from silicon nitride as a model of non-combustible mechanical sparks. Fuel/air mixtures made from methane, ethane, propane, n-butane, ethylene, acetylene, hy...

This research investigates the concentration effect of the thermal release of adsorbed polyaromatic hydrocarbons (PAHs) from commercial carbon black nanoparticles (CBNP) by using thermogravimetric analysis (TGA). Pyrene was used for this study as a representative of PAHs and Printex 90 as representative of commercial CBNP. The thermal desorption oc...

To broaden the knowledge concerning ignition processes, small, hot, metal/ceramic particles were heated in a quiescent mixture of hydrogen/synthetic air mimicking the behavior of mechanical sparks, for example, from grinding processes. Materials under investigation were silicon nitride, tungsten carbide, and steel types 1.3505, 1.4034, and 1.3541....

The ignition of hydrogen/air and ethylene/air gas mixtures by laser-heated, sub-millimeter sized particles has been studied. Ignition temperatures strongly depend on particle material and size as well as on the type of fuel. As a general trend, surface temperatures at the time of ignition increase with decreasing particle diameter and are well abov...

Isomer- and mass-selective UV and IR-UV double resonance spectra of the BA(3) , B(2) A, and B(2) A(2) clusters of benzene (B) and acetylene (A) are presented. Cluster structures are assigned by comparison with the UV and IR spectra of benzene, the benzene dimer, as well as the BA, BA(2) , and B(2) A clusters. The intermolecular vibrations of BA are...

Das Verbundprojekt „Photokatalytische CO2-Reduktion mit Farbstoff-sensibilisierten Halbleitern (Solar2Fuel)“ gehört zum Bereich der Optischen Technologien, wobei es im Spitzenclusterwettbewerb im Cluster „Forum Organic Electronics“ aufgehängt ist. In diesem Projekt haben sich die industriellen Partner BASF SE (67056 Ludwigshafen am Rhein) und EnBW...

High-resolution gas-phase spectroscopy of biomolecules allows us to distinguish between the intrinsic properties of biomolecules and those properties that are induced by solvation or by the geometrical restrictions of the environment. In the gas phase, we can study the isolated biomolecules and their water clusters under size-controlled conditions....

We investigated the self-aggregation of 2'-deoxy-3',5'-bis(tert-butyldimethylsilyl)-cytidine dC(TBDMS)(2) in CDCl(3) solutions by Fourier transform infrared (FT-IR) spectroscopy and report the formation of larger aggregates than dimers in this solvent for the first time. The hydrogen bonding patterns in these complexes, which occur with increasing...

We reinvestigated the self-aggregation of 1-cyclohexyluracil (1CHU) in CDCl3 solutions. Wavelength dependent absolute extinction coefficients of the monomer and of dimers are presented on the basis of a simple deconvolution method. Two isomeric dimer structures coexist in a solution with similar abundance. Our results are supported by RI-B3LYP/TZVP...

We present size- and isomer-selective IR–UV double resonance spectra of two pyrazine dimer isomers. The most stable isomer has a planar structure, stabilized by two CH⋯NCH⋯N contacts. The other isomer has a stacked, cross-displaced structure. Our assignment is supported by B3LYP-D calculations. RI-MP2 calculations tend to overestimate the stability...

Die grundlegendenStrukturmotiveder Elementarzellen knnten im Prinzip mit der Struktur vonNanokristallen verglichen werden, die bei der adiabatischenAbkhlung in berschallexpansionen entstehen. Allerdingsknnen kooperative Effekte zu isomeren Kristallstrukturenfhren, die nicht notwendigerweise den globalen Mini-mumsstrukturen der Cluster entsprechen....

(Figure Presented) Crystallization seeds in supersonic jets? T-shaped structures dominate the isomer-selective IR-UV double-resonance spectra of benzene-acetylene clusters in supersonic jets. The double T-shaped motif is also present in the 1:1 cocrystal (see picture).

Electronic and vibrational gas phase spectra of 1-methylthymine (1MT) and 1-methyluracil (1MU) and their clusters with water are presented. Mass selective IR/UV double resonance spectra confirm the formation of pyrimidine-water clusters and are compared to calculated vibrational spectra obtained from ab initio calculations. In contrast to Y. He, C....

We reinvestigated the self-association of 9-substituted adenine derivatives in CDCl3 solutions and present the infrared spectra of 9-ethyladenine and N-methyl-9-ethyladenine and its aggregates in the spectral regions between 1500 and 1800 cm(-1) and between 2700 and 3600 cm(-1). Wavelength dependent absolute extinction coefficients of the monomer a...

We present infrared-UV double resonance spectra and quantum chemical calculations of the natural di-peptide H-Trp-Ser-OH. Two conformers are present in the supersonic expansions. They have a compact folded structure with two hydrogen bonds and with the serin residue stacked above the indole ring and an unusual NH(Trp)...O=C interaction in the lowes...

We reinvestigated the assignment of the three major guanine conformers detected via resonance enhanced two-photon ionization (R2PI) in supersonic expansions and present IR/UV double resonance spectra in the spectral region between 1500 and 1800 cm(-1). Comparison with B3LYP/TZVPP and RI-MP2/cc-pVQZ calculations shows that both conformers B and C ar...

We present near- and mid-infrared-UV double resonance spectra of the natural dipeptide H-Pro-Trp-OH. Two conformers are present in the supersonic expansion: a stretched conformer with fully extended backbone and a folded conformer with an OH...OCpep hydrogen bond. Both conformers are stabilized by dispersion interaction between indole ring and pept...

2,2,2-Trifluoroethanol molecules synchronize their transiently chiral gauche configurations upon dimerization in supersonic jet expansions, while they avoid an energetically competitive heteroconfigurational hydrogen bonded dimer topology predicted by extensive quantum chemical calculations.

First high-resolution infrared spectra are presented for jet-cooled CH2 35Cl and CH2 37Cl radicals in the symmetric (nu1) CH2 stretching mode. A detailed spectral assignment yields refined lower and upper state rotational constants, as well as fine structure spin-rotation parameters from least-squares fits to the sub-Doppler line shapes for individ...

Isolated 2-fluoroethanol exists predominantly as a pair of enantiomeric all-gauche conformations, which are stabilized by an intramolecular O-H center dot center dot center dot F interaction. Its most stable OH center dot center dot center dot OH hydrogen-bonded dimers differ in their relative monomer configuration and in their network of weak inte...

High-resolution IR absorption spectra of supersonically cooled ethyl radicals (Trot approximately 20 K) have been obtained in a slit supersonic jet discharge expansion, revealing first rotationally resolved data for CH-stretch excitation of the methyl group. Three different vibrational bands are observed, one parallel (k=0<--0) and two perpendicula...

An apparatus for detailed study of quantum state-resolved inelastic energy transfer dynamics at the gas-liquid interface is described. The approach relies on supersonic jet-cooled molecular beams impinging on a continuously renewable liquid surface in a vacuum and exploits sub-Doppler high-resolution laser absorption methods to probe rotational, vi...

We present resonant two-photon ionization (R2PI), IR-UV, and UV-UV double resonance spectra of jet-cooled 2-aminopurine (2AP) as well as Fourier transform infrared (FTIR) gas phase spectra. 2AP is a fluorescing isomer of the nucleobase adenine. The results show that there is only one tautomer of 2AP which absorbs in the wavelength range 32,300-34,5...

We present the first gas-phase Fourier transform infrared (FT-IR) spectra of uncapped (natural) amino acids using a fast thermal heating technique up to around 570 K. The experimental spectra of phenylalanine, proline, valine, leucine and isoleucine in the range 900–3700 cm−1 show no sign of decomposition and are in good agreement with ab initio ca...

To understand the intrinsic properties of peptides, which are determined by factors such as intramolecular hydrogen bonding, van der Waals bonding and electrostatic interactions, the conformational landscape of isolated protein building blocks in the gas phase was investigated. Here, we present IR-UV double-resonance spectra of jet-cooled, uncapped...

For Abstract see ChemInform Abstract in Full Text.

Presented are the ragout-jet FTIR spectra of isolated (HBr)n clusters (n≤4) in pulsed slit-jet expansions. These are the first gas phase infrared spectra of (HBr)3 and (HBr)4 reported so far. The assignment is based on a direct comparison with hydrogen chloride and MP2/6-311++G(d,p) ab initio calculations. Despite the well known difficulties of sta...

Infrared OH stretching spectra of hydrogen bonded 2-methyl-propan-2-ol (t-butyl alcohol) clusters are investigated by ragout-jet FTIR spectroscopy. A spectral difference technique is used to discriminate approximately between neighbouring cluster sizes. Dimers, trimers and cyclic tetramers can be detected along with larger clusters, which exhibit a...

Direct absorption supersonic jet Fourier transform spectroscopy provides a panoramic view of the dynamics of molecular clusters over the entire IR spectral range. The new and generally applicable ragout-jet technique compensates for the sensitivity limits inherent in the incoherent FTIR approach by the use of synchronized giant gas pulses expanding...

Supersonic jet FTIR spectra of the OH-stretching bands of glycidol monomers and clusters are presented. Chiral discrimination leads to marked differences in the absorption patterns of RR (SS) s. RS glycidol dimers. The dominant absorption peaks are located at 3492 (RR, SS) and 3488 cm−1 (RS) within a rich line spectrum with sizeable variations betw...

Fourier transform infrared (FTIR) spectra at thermal equilibrium and in seeded, pulsed slit jet expansions of 2-propanol (IP), 1,1,1-trifluoro-2-propanol (TFIP), and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) reveal dimers, oligomers, and large clusters as well as conformational isomerism of the monomers. The assignments are supported by hybrid densi...

The influence of eucalyptol, a bicyclic ether, on the hydrogen bond aggregation of methanol (MeOH) and 2-methyl-2-propanol (BuOH) is investigated by ragout-jet FTIR techniques. O–H stretching bands of supersonic jet cooled binary complexes are identified and compared to spectra of liquid mixtures and quantum chemical predictions. Experimental O–H s...

A new approach to the Fourier transform infrared (FTIR) absorption spectroscopy of molecular clusters in pulsed supersonic jets is developed to the point where it is competitive with high-sensitivity laser absorption techniques for intermediate and large molecular systems. A combination of rapid spectral acquisition and of a buffered jet chamber en...

Zugl.: Göttingen, Universiẗat, Diss., 2000.