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Ceramic microstructure devices in form of counterflow and crossflow microchannel heat exchangers have been manufactured to be used in thermal and chemical process engineering. The performance has been tested using water as a test fluid with maximum flow rates of 120 kg/h. The results of the measurements are compared with global estimations using standard correlations for heat exchangers and a more detailed simulation using a local porous body approach of the micro structured region. The devices show stronger heat transfer and pressure loss than predicted by theoretical considerations. This result is mainly explained by effects of channel blockages arising from the joining process.

A numerical tool to simulate micro-channel flow and heat transfer in compact heat exchangers is developed. The method is based on a forced convection porous body approach combined with conventional pipe flow closure correlations. The proposed technique aims to provide developers of micro-channel heat exchangers with a fast efficient tool to estimate the thermodynamic behaviour dependent on geometry and operation conditions. The program calculates outlet temperatures, pressure losses and vapour volume fractions, if boiling occurs. In addition the thermohydraulic conditions inside the heat exchanger can be determined. First results are compared to experiments with cross flow and counter flow heat exchangers for single-phase flow and with an electrical evaporator for boiling conditions.

The small non-adiabaticity associated with the slow collision of a 450 eV to 3 keV O 2 + beam incident at 5° to a carefully flattened Si(001) surface was used to probe the adiabatic potential energy surface for the O 2 /Si(001) adsorption/reaction system in the limit of low coverage. The scattering products include O 2 − and O − . From the observation of efficient O 2 − formation and th dependence of the negative-ion yields on beam energy, we infer that O 23 − is an intermediate or precursor in the dissociative chemisorption of O 2 on Si(001). The total yield of negative ions (O 2 − and O − ) is high in comparison with similar experiments on th O 2 /Ag(111) system. This may be explained by a reduced reneutralisation probability on the exit trajectory due to the band gap of Si.

A 450 eV−3 keV O2+ beam incident at 5° to a carefully flattened Si(001) surface was used to probe the adiabatic potential energy surface for the O 2 Si(001) adsorption/reaction system in the limit of low coverage. Over the full incident energy range, O2- an are formed as scattering products. We argue that the O2− product correlates with an O2−-like region on the potential energy surface and therefore propose that an O2−-like species is an intermediate or precursor in the dissociative adsorption of O2 on Si(001). Classical trajectory calculations indicate that a large amount of collision induced dissociation occurs at all energies.

Molecular ions of CO, and O 2 CO 2 are scattered at grazing incidence with an energy of 400 eV from clean Ni(111) and Ni(111) + K. Most of the scattered particles are neutralized molecules and neutral dissociation products. With increasing K-coverage the yield of negative ions and the dissociation of O 2 and CO 2 increases. In the case of Co and K adsorption has little influence on the electronic interaction with the surface. The CO 2 − ions observed are identified with corresponding negative molecular ions in chemisorption experiments, the O 2 − ions are possibly related to short lived intermediates in chemisorption.

The Balmer series of hydrogen was studied in the reflexion of hydrogen atoms from clean and cesiated nickel. We observe an enhancement of the line intensity with the decrease of the work function induced by the Cs over layer up to n = 7. For higher main quantum numbers n the series is depressed in comparison to the excitation from the clean Ni surface.

The scattering of CO + and CO + 2 at grazing incidence from Ni(111) +K and clean Ni(111), Ni(110) surfaces produces CO, CO 2 and dissociated species. The observation of negative species O - and CO - 2 is strongly dependent on the K coverage or work function of the surface. The dissociation of CO + (CO) is weakly changed by the presence of K, whereas in the CO + 2 (CO 2 ) case dissociation via CO - 2 a CO + O - is strongly increasing with K coverage.

The reflection of nitrogen molecular ions from a nickel surface has been studied at energies between 200 eV and 4400 eV. In the scattered beam neutral atoms and molecules and atomic and molecular ions are detected. From the energy spectra of the atoms the relative kinetic energy distributions of the fragments are obtained. These give information on the processes leading to dissociation. The main mechanism for dissociation at low primary energies is charge capture. At higher energies vibrational and rotational excitation dominates.

The influence of the symmetry of molecular states on the neutralization and dissociation of molecular ions is demonstrated experimentally for O 2 + and N 2 + scattered from Ni(111).

Neutralization and harpooning leading to negative molecular ions has been observed in collisions of O2+ at 1400 eV from clean Ag(111). The experiments are performed for specular scattering at grazing angles of incidence (85°). Scattered positive ions are not observed. O, O2, O− and O2− products are observed using time-of-flight techniques. The degree of dissociation for the neutral molecules is large, and in contrast to the small degree for negative ions. The results show that grazing incidence high energy beams can be used to probe chemical interactions at surfaces.

The scattering of molecular ions from surfaces has in general the same aspects as atomic scattering: nuclear and electronic interactions. For the nuclear or elastic part we have with molecules the additional channels of vibrational and rotational excitation, which are very important for the scattering of molecules at thermal energies, and may contribute to the dissociation of fast molecules. For the electronic or “inelastic” part molecules provide an additional channel for charge exchange processes, i.e. neutralization into dissociative states known as dissociative attachment in gas phase interaction. Experimental and theoretical results of the interaction of diatomic molecules with clean and Cs covered surfaces show that further improvements of present day charge exchange theories are needed. The results include the influence of the molecular axis orientation on the neutralization in the case of H + 2 and the influence of work function changes on the molecular survival and neutralization in case of H + 2 , N + 2 and O + 2 .

We apply the technique of specular scattering of energetic beams from carefully flattened surfaces to investigate the dynamics of the O2Ag(111) adsorption/reaction system. The experiments were performed using 100–3000 eV beams of O+2 incident at 85° to the surface normal. The scattering products, O, O2, O− and O−2 were observed using time-of-night techniques. Part of the incident O+2 beam dissociates via charge transfer to dissociative or predissociative states of O2. Charge transfer to the ground electronic state of O2, if accompanied by the transfer of a second electron, results in O−2 formation. Above a threshold energy of 180 eV, the probability of formation of vibrationally cold O−2 is high (> 5%), indicating a large charge transfer probability at the surface and efficient access of the O−2 region of the adsorption/reaction potential energy surface (PES). At an incident beam energy of 2000 eV a threshold for O− production is observed. Classical trajectory calculations performed for the scattering of O2 from Ag(111) indicate that below 2000 eV no dissociation of the molecule occurs and that even about a fraction of a third of the molecules is vibrationally cold. Above 2000 eV collision induced dissociation of the O2 molecule is observed in the calculations that bears a striking resemblance to the experimentally observed O− yield. Therefore we propose that O−2 dissociates as a result of the impulsive collision with the surface, resulting in the observed O− production. We conclude from our results that O−2 is a precursor to dissociative adsorption and that the O− region of the PES is not readily accessible in our experiment, despite the presence of sufficient translational energy to overcome all activation barriers along the reaction coordinate.

A direct correlation is established between the results of 480 eV CO + 2 -, N + 2 -, CO + + -, and 490 eV O + 2 -Ni(110) specular scattering experiments and known adsorption behaviour of the corresponding neutral molecules on Ni(110). Most importantly, we observe CO − 2 and O − 2 ions in our scattered product distributions. This observation demonstrates that negative ions that are precursors to dissociative chemisorption can be exposed and directly observed using high energy beam scattering techniques.

During the interaction of molecular ions with a metal surface charge exchange processes occur which change the status of the molecule. One of the processes causes the dissociation of the molecule. The process is identified as dissociative attachment by capture of electrons from the conduction band of the metal.

A description of the charge exchange between energetic diatomic molecular ions and metal surfaces is presented, which includes in a semiclassical way the coupling between the available exit channels. Explicit results for resonant electron capture during the scattering of ${\mathrm{H}}_{2}$${\mathrm{}}^{+}$ from Al(110) are given. For low incident energies, capture to both the X ${}^{1}$${\ensuremath{\Sigma}}_{g}^{+}$ and b ${}^{3}$${\ensuremath{\Sigma}}_{u}^{+}$ states occurs on the incident portion of the trajectory. Capture to the singlet state predominates for molecule-axis orientations nearly parallel to the surface, and to the triplet state for near-normal orientations. The axis-orientation dependence of the triplet occupation probability and the dissociation-fragment relative kinetic-energy distribution are calculated, as is the vibrational population distribution of the singlet ground state.

We provide a parameter-free perturbation treatment of the resonant electronic coupling between a simple diatomic molecule (${\mathrm{H}}_{2}$) and a jelliumlike metal surface [Al(110)]. Assuming the unperturbed molecular and metallic states to be orthogonal (which is a good approximation), the matrix element simplifies to the form 〈${\ensuremath{\psi}}_{f}$\ensuremath{\Vert}H\ensuremath{\Vert}${\ensuremath{\psi}}_{i}$〉, where ${\ensuremath{\psi}}_{f}$ is the neutral free-molecule final state, ${\ensuremath{\psi}}_{i}$ the product of the unperturbed metallic and molecular-ion wave functions, and H the Coulomb interaction of the metal electron with the nuclei and 1\ensuremath{\sigma} electron in ${\mathrm{H}}_{2}$${\mathrm{}}^{+}$. Using scaled linear-combination-of-atomic-orbitals ${\mathrm{H}}_{2}$${\mathrm{}}^{+}$, scaled Heitler-London ${\mathrm{H}}_{2}$, and jellium wave functions, this matrix element, including its spin dependence, is evaluated. With use of the golden-rule expression, the transition rates for charge transfer to the ${\mathrm{H}}_{2}$ X ${\mathrm{}}^{1}$${\mathrm{\ensuremath{\Sigma}}}_{\mathrm{g}}^{+}$ and b ${}^{3}$${\ensuremath{\Sigma}}_{u}^{+}$ states are calculated. The dependence of these transition rates on molecule-axis orientation, distance from the surface, resonance energy, and internuclear separation, is investigated.