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Oscillation and creep experiments have been performed with Semi-Solid Material (SSM) AlSi7 with 35% solid fraction to investigate the early visco-elastic properties after shearing of the material in a Searle Rheometer. The preparation of the SSM has been done in situ using a standard procedure to guarantee for all experiments the same initial properties of the material. First, oscillation experiments at low amplitude allowed to study the evolution of material structure with time. Subsequently, creep experiments have been performed changing the resting period based on previous results. Creep experiments are characterized by exposing the material to a sudden increase of shear stress. The resolution in time has been 0.01 seconds, which allows observing the dynamics of the development of visco-elastic properties.The material exhibits viscoelastic properties that are becoming more pronounced with longer resting time. This is in accordance with previous experiments where the ratio between elastic and viscous properties increases with increasing resting time. The development of the elastic properties follows the increase of the yield stress due to the creation of an internal structure of the material, which starts immediately after stopping shearing. The investigation of the short-term response of SSM can be particularly relevant for industrial practice, where material deformation during die filling is very fast and the material flow does not take place in steady-state condition.

An oxygen transport membrane module capable of total 596 Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) membranes was constructed and tested under various capacities. The module is designed to operate with up to 20 bar feed pressure and a vacuum on the permeate side. The separation performance was tested with of up to 96 membranes tubes. A maximum oxygen purity of 98.9% was obtained and a maximum oxygen flux of 2.8 ml cm−2 min−1 was measured under a feed pressure of 10 bar. The maximum permeate oxygen flow rate achieved was 22 l min−1. The performance is lower than expected, for which an inhomogeneous module temperature and suboptimal flow distribution can be accounted for, as CFD simulations show. A lot of membrane breakages occurred during operation. Some reasons for that could be identified and the module could be optimized throughout the 2 years of testing. Within that time, three long term tests were performed and a maximum continuous operational time of 1800 h was achieved.

Dynamic Mechanical Analysis (DMA) of semisolid aluminum alloys was performed in a rheometer of Searle type. DMA was applied on a binary AlSi7 alloy to demonstrate the advantages of the method for the investigation of the behavior of alloys in semi-solid state and it was compared to classical shear experiments. Frequency sweeps, amplitude sweeps as well as constant condition experiments (CCE) were performed. It became obvious that elastic properties are getting more dominant with increasing resting time without shearing. The shift from a more viscous to more elastic nature of the material can be quantified. Interestingly, it was found that the semi-empirically based Cox-Merz rule, usually applied for polymers, holds for the semisolid material as well. This allows investigating the shear viscosity under different relevant conditions - important to improve material models for die-filling simulation of semisolid alloys.

Screw press processing of biomass can be considered as a suitable mechanically based pretreatment for biofuel production since it disrupts the structure of lignocellulosic biomass with high shear and pressure forces. The combination with chemical treatment has been suggested to increase the conversion of lignocellulosic biomass to fermentable sugars. Within the study, the synergetic effect of alkaline (sodium hydroxide, NaOH) soaking and screw press pretreatment on wheat straw was evaluated based on, e.g., sugar recovery and energy efficiency. After alkaline soaking (at 0.1 M for 30 min) and sequential screw press pretreatment with various screw press configurations and modified screw barrel, the lignin content of pretreated wheat straw was quantified. In addition, the structure of pretreated wheat straw was investigated by scanning electron microscopy and measurement of specific surface area. It could be shown that removal of lignin is more important than increase of surface area of the biomass to reach a high sugar recovery. The rate constant of the enzymatic hydrolysis increased from 1.1 × 10−3 1/h for the non-treated material over 2.3 × 10−3 1/h for the alkaline-soaked material to 26.9 × 10−3 1/h for alkaline-assisted screw press pretreated material, indicating a nearly 25-fold improvement of the digestibility by the combined chemo-mechanical pretreatment. Finally, the screw configuration was found to be an important factor for improving the sugar recovery and for reducing the specific energy consumption of the screw press pretreatment.

Rheological properties of liquid metals are difficult to investigate experimentally because of the extreme border conditions to consider. One difficulty is related to the low viscosity of liquid metals. Surface tension effects can cause forces that can be considerably higher than the viscous forces in the liquid metals. Evaluating the experimental data without considering these effects leads to an apparent shear thinning behavior of the material. In the present study, experiments were performed by means of a Searle rheometer changing the dimension of the measuring system with metals of high surface tension, as mercury and tin. It became evident that surface tension plays a significant role in the effects that falsify measurements at low shear rate. Conclusions can be drawn to what extent measurements of semi-solid metals are affected.

Rheological properties, crystallization and ripening phenomena have been investigated for three different steel grades in the semi-solid state. For each steel grade detailed investigation has been performed via differential scanning calorimetry to quantify the solid fraction as a function of temperature. The experimental procedure for all samples has been as follows: the completely liquid samples were cooled with a constant rate under constant shearing to temperatures corresponding to solid fractions of 30 and 40%. Tracking the viscosity during this procedure allowed analyzing the crystallization kinetics and final ripening process, which differ for the different steel grades. Evaluating the viscosity data on the base of a combination of convection dominated ripening model and a modified Krieger-Dougherty equation gives valuable information of the microstructural evolution. This is validated by additionally quenching samples.

The application of CCS technology involves considerable efficiency losses and significant additional investments. The aim is therefore to reduce these efficiency losses and to cut costs. Against this background, membrane-based carbon capture routes for the post-combustion, oxyfuel and pre-combustion technology lines will be analyzed in the following for hard-coal-fired power plants. To the best knowledge of the authors, this paper is the first one comparing membrane based capture routes on common technical and economic boundary conditions. The post-combustion process involves a cascade arrangement of polymer membranes. In the optimum case, the efficiency losses for this concept amount to 9.6 percentage points. In comparison, efficiency losses for the other two membrane-based concepts, i.e. oxyfuel (oxygen transport membrane (OTM) with vacuum pump) and pre-combustion (water-gas shift reactor—WGSMR), are considerably lower (5.3/5.5 percentage points). The main goal of this paper is to assess levelized cost of electricity (LCOE) for the process routes under consideration and their sensitivity on CO2 allowance costs, yearly operating hours, membrane costs and membrane lifetime. The specific investment costs for the capture plants are 2410 €/kW h (oxyfuel), 2572 €/kW h (post-combustion) and 2660 €/kW h (pre-combustion). This is 66% (post-combustion), 55% (oxyfuel) and 33% (pre-combustion) above the specific investment costs for the corresponding reference case without carbon capture. Allowance prices in a range from €20 (pre-combustion) to €39 (post-combustion) per tonne of CO2 would be necessary to compensate for the additional investments. Since it can be assumed that the membranes have a limited lifetime, the influence on electricity generation costs was calculated for different lifetimes. The results show that a technical service life of more than 3 years does not have a significant impact on generation costs. This applies to all the technological concepts investigated. In terms of LCOE and CO2 avoidance costs ( € / t CO 2 ) it turns out that oxyfuel and pre-combustion based membrane power plants are favorable compared to the post-combustion route. However, it has to be kept in mind that the uncertainty in membrane costs are higher for the oxyfuel membranes (ceramic oxygen transport membranes) and the pre-combustion membranes (microporous ceramic membranes) compared to the polymeric post-combustion membranes which already have achieved a commercial level.

To convert lignocellulose into transportation fuels and chemical products, pretreatment of the biomass, leading to the separation of the main components (cellulose, hemicellulose, and lignin), is a crucial and still challenging first step. Within this study, the screw press pretreatment of lignocellulosic biomass and its effect on the subsequent chemical pretreatment steps were evaluated. Macroscopic disruption and defibration of reed straw after screw press pretreatment were confirmed by scanning electronic microscopy and dye adsorption studies, showing an enhancement of the accessible surface area. Alkaline and dilute acid hydrolysis was tested to study the release of phenols or sugars from screw-press-treated and non-treated straw materials. To showcase a realistic subsequent chemical pretreatment step, kinetics of enzymatic hydrolysis after a biogenic and biphasic fractionation (OrganoCat) process was tested to evaluate the release of glucose from cut and pressed reed straw. Pretreatment by a screw pr...

The improvement of mathematical models for semisolid alloy flow properties requires profound understanding of the underlying physical nature. To date, it is commonly accepted that the shear thinning behaviour of these suspensions is caused by the solid phase microstructure, while the liquid phase is assumed to be Newtonian with a viscosity in the lowermPas-range. Recent measurements however, demonstrate non-Newtonian behaviour of fully liquid metals with pronounced shear thinning and high viscosities (multiplePas) in the low shear-rate range. By gathering and analysing rheological measurement data of various alloys (Sn14.2%Pb, A356 and X210CrW12), the relevance of the new findings for semisolid metals is investigated. The results indicate that the previously unexamined non-Newtonian flow behaviour of the liquid matrix has, besides the solid fraction, the most dominant influence on the shear thinning behaviour of semisolid alloys. The influences of shear-rate and solid fraction are nearly independent of each other which allow the construction of master-curves; a general flow curve for the suspension where the solid fraction is considered by a scaling factor. Consequently, a modelling approach is suggested in which the dependency of solid fraction is considered independently of the shear-rate.

For thixoforming (semi-solid processing) it is necessary to have a fine globular microstructure in a semi-solid range. Here this has been obtained for 7075 aluminium alloy by addition of modifying agents: 0.5 weight % of scandium and zirconium. The thixoforming process was carried out at 632 °C which gave about 23 volume % of liquid phase. The microstructure of the thixo-formed part (a rotor) consisted of globular grains surrounded by precipitates of secondary phase. The average hardness of thixo-formed parts was 105 HV 5 and the tensile strength 300 MPa. T6 heat treatments were performed with solutionisation at 450 °C for 30 min and 10 h. In both cases the ageing time was set as 18 h at 120 °C. The heat treatments led to an increase in average tensile strength up to 495 MPa. Transmission Electron Microscopy (TEM) analysis enabled the identification of precipitates of the metastable dispersoids of L1 2 –Al 3 (Zr, Sc) and η′ (MgZn 2 ) phases in the alloy after the thixoforming and T6 treatment. The measurements of rheological properties of 7075Al alloy with Sc and Zr additions in the semi-solid range indicated an increase of particle size and spheroidization leading to an observable decrease of viscosity during isothermal shearing. A shear rate jump experiment showed that with increasing shear rate the viscosity rapidly falls.

An important aspect of the rheological characterization of semi-solid metals is the determination of the materials ability to exhibit yield stress. The yield stress is the stress level at which the material cease from purely elastic to plastic deformation. In semi-solid metal suspensions the yield stress is not a constant value, but depends on the transient state of the material. The investigation of yield stress in semi-solid metal alloys has been initiated in previous works, however, a profound understanding of the influence of the material history on the yield stress is so far lacking. In semi-solid metal suspensions, the physical cause of the yield stress is generally described by the formation of a particle "skeleton" structure which can hold a certain stress level without being subject to irreversible deformation. The yield stress in alloy suspensions can be described as a function of structural properties i.e. the solid fraction and the particle size, form and spatial distribution. It has been observed in previous works that the yield stress of semi-solid metals depends on the duration of resting time. It is generally assumed that this is due that as the material is resting, the particle network build up over time leading to an increase in the yield stress. In addition, we assume that the yield stress is also a function of the shear history as this affects the particle spatial distribution. The goal of the proposed work was to investigate the yield stress in semi-solid alloys including its dependency on the materials shear history and resting time. This was investigated both from a structural and a rheological point of view. The yield stress of the semi-solid alloys was measured with shear stress ramp and oscillation tests. Structural imaging measurements of quenched samples were performed to correlate structural parameters with the value of the yield stress. However, in semi-solid alloys, the experiments performed at a long time scale are influenced by aging of the material (Ostwald ripening). Therefore, rheological experiments were also performed with synthetic suspensions to investigate the long term yield stress dependencies without errors caused by the aging effects.

In this work, the effect of stirring conditions on agglomeration and coalescence-coarsening in isothermal, globulitic, semisolid AlCu10%wt was investigated. It is shown that for the investigated system, a shear rate regime exists which promotes crystallographic alignment of the agglomerated grains, leading to a rapid coalescence process, thereby the formation of rosettes. It is also experimentally validated that for lower shear rates, the size and porosity of aggregates are increased compared to that at higher level of shear.

Rheometrical analysis of steel slurries in rotational rheometers requires a range of operating temperatures of about 1300 to 1600 °C, leading to a delicate device-related challenge with respect to the applied materials on the one hand and a suitable constructional set-up gaining unbiased measurements on the other hand. Accordingly, a new high-precision rotational rheometer for temperatures up to 1700 °C has been developed as an improvement on an existing rheometer previously developed at the Chair of Mechanical Process Engineering (AVT) of RWTH Aachen University. First measurements on the tool steel X210CrW12 in the mushy state with solid fractions of 20% to 40% demonstrate a remarkable improvement on the preciseness of torque gain which broadens the area of possible experimental operations on steel slurries in order to reliably characterize transient behavior of the material by e.g. creep, relaxation and oscillation experiments.

Rheological properties of semi-solid alloys are closely knit to the solid-phase microstructure. Parameters such as particle size distribution are commonly determined by 2D cross section analysis. The determination of mechanisms such as particle deagglomeration with increasing shear rate however, requires information on the 3D spatial distribution. By means of synchrotron radiation tomography and SEM on AlCu samples, particle size distributions and the not yet microscopically observed interrelation of shear rate and particle agglomeration in thixo-material is investigated.

In thixo casting and forming processes, the forming alloy is in a semi solid state - a suspension of solid particles in a liquid matrix. As known from suspension rheology, the solid fraction, particle size distribution, particle shape, surface properties, state of agglomeration etc. determine the complex flow behaviour of the material. In thixo forming, the flow behaviour determines the quality of the produced parts, and it is essential to quantify the flow behaviour to optimize the process route. The goal of the present work was to evaluate the effect of particle size and state of agglomeration on the flow properties in a thixo material-analogue suspension, and to establish an easily applicable model to describe the non-Newtonian behaviour of a thixo material. For this purpose, experiments were conducted applying synthetic suspensions (built up of mono-disperse glass spheres in silicone oil) with behaviour analogue to thixo material. The advantage of synthetic suspensions is that parameters such as particle size and shape can be controlled in a simple manner and hence the number of unknown parameters is decreased. The experimental results show influence of shear rate, solid fraction, particle size and liquid viscosity. A model to determine the shear dependent viscosity was set up. This model was based on the Krieger-Dougherty equation for the relation between viscosity and solid fraction, and on the generally accepted theory that the state of agglomerations is influenced by shear. The model could successfully display the degree of shear thinning and takes into account the influence of particle size. However, it was found that the relation of the viscosity of the suspension and the liquid viscosity was non-linear. This does not correspond to the Krieger-Dougherty equation.

Heavy metals enter an incineration plant as trace components in the fuel and are inhomogeneously distributed into the ash streams exiting the plant. Their concentration in the respective ash streams mainly depends on their chemical properties, especially on their volatility. Several authors already modelled the chemical state within an incinerator by one single thermochemical equilibrium calculation and achieved qualitative characterization of the heavy metals’ behavior. In the work at hand, a multizonal thermochemical process model of an incineration plant is developed. The chemical reactions within the incinerator are modelled as a sequence of thermochemical equilibria. Reaction kinetic as well as mass transport related inhibitions are accounted for by choosing a proper model structure. Test calculations for a waste and a biomass fired incinerator show that the model is capable of simulating the distribution of As, Cd, and Sn into the ash streams with better quantitative accuracy compared to the abovementioned single-equilibrium approach. The distribution of Cu and Pb is found to be closely coupled to the volatility of Cl on the grate.

A rigorous one-dimensional dynamic model of a rotary kiln for calcination of titanium dioxide white pigment is developed. The regenerative heat transfer in the kiln wall is described by a new mixed numerical/analytical approach. The model is validated by means of a dynamic test case representing a 15-day period of plant operation. The required process data are captured within a measurement campaign on a kiln run by TRONOX Pigments GmbH, Krefeld-Uerdingen, Germany. The predictive accuracy of the model is estimated by means of a sensitivity analysis considering uncertainties of model parameters and measured input values. The actual agreement between simulation and measurement results is significantly better than indicated by the sensitivity analysis.

Calcination is the last process step of the sulphate method for production of titanium dioxide. The chemical reactions that occur during calcination are analysed by means of simultaneous DTA-TG-MS-measurements in order to provide a 5-step reaction schematic. The corresponding enthalpies of reaction are determined calorimetrically by means of the reversed drop method. The developed schematic is suitable for process modelling purposes.

MIEC membranes (mixed ion-electron conducting membranes) are attracting increasing interest for industrial applications in which oxygen-enriched air or pure oxygen is used. One of these applications is the oxyfuel power plant process. High oxygen permeability and adequate chemical stability under operating conditions, especially with respect to CO 2 and SO 2 , are therefore essential. In the work described here, permeation and chemical stability tests were performed with tubular membranes made of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3− δ (BSCF), Sr 0.5 Ca 0.5 Mn 0.8 Fe 0.2 O 3− δ (SCMF) and La 2 NiO 4+ δ . To investigate the effects on the materials, microstructure analysis were performed before and after each experimental run by means of energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the highest permeability can be reached with BSCF membranes, but BSCF displays instability with respect to CO 2 . The other materials show higher chemical stability without any significant degradation effects caused by CO 2 , but they do display instability if the sweep gas contains 360 ppm SO 2 . Furthermore, poisoning of the membrane materials by chromium evaporated from the steel was detected in the case of BSCF and SCMF membranes.

Oxyfuel combustion is considered to be an energy efficient process for carbon capture and storage in power plants. Compared to cryogenic air separation, oxygen supply by means of an oxygen transport membrane (OTM) is more energy efficient. This paper describes possible implementations of an OTM into an oxyfuel process, in particular that is three-end and four-end integration of the membrane whereby the focus is put on overall cycle efficiency and possible measures to improve cycle efficiency. Starting from a simple conservative integration of the membrane, several steps for improvement of the process efficiency are shown. With a three-end integration the maximum achievable efficiency is 40.1%, with a four-end integration of the membrane an overall efficiency of 40.7% including CO 2 compression with 90% capture can be achieved for a hard coal fired power plant of 1210 MW th compared to 45.9% efficiency for a reference power plant without carbon sequestration. In this case the effective energy demand for oxygen production can be reduced to 26 kWh/ t O 2 . In a process variant in which the expansion turbine for the oxygen depleted air is co-fired, the combined efficiency reaches 46.1%. Although OTM operation in four-end design is preferable due to higher achievable net efficiencies, OTM operation in three-end design is likely to be technically viable at first since up to now no membrane material is available which withstands contact with flue gas.

A novel gas purification system employing membrane contactors with dense membranes in the absorption as well as the desorption unit has been tested concerning the separation efficiency of CO 2 . The separation efficiency of potassium carbonate (K 2 CO 3 ) promoted by piperazine (PZ) as absorption medium has been tested in the absorption unit. Since the absorbent will be regenerated in the desorption unit, the influence of temperature, sweep flow rate and absorbent type (0.5 M K 2 CO 3 and 0.5 M K 2 CO 3 /0.5 M PZ) on the separation efficiency of CO 2 in the desorption unit has been investigated. Desorption by vacuum has been considered as well. In addition experimental results of the coupling of a bioreactor producing hydrogen by anoxygenic photosynthesis (low and fluctuating product gas flow rates and fluctuating compositions) with a membrane contactor for gas purification are reported. This was done in order to show the applicability of this system to processes producing biogases.

In the contribution at hand two main concepts of photobioreactors are considered: the flat-panel reactor and the tubular reactor. Both reactors are investigated under outdoor conditions in Germany in the summer time for their applicability for H2 production by means of purple non-sulphur bacteria Rhodobacter capsulatus. The experiments are performed as fed batch. The performance of a photobioreactor is evaluated in terms of H2 productivity per IRS (illuminated reactor surface). It is demonstrated that both reactors could be operated stable for several weeks with comparable H2 productivities. The mean hydrogen productivity for the panel and the tubular reactor is 3690 ml H2/(mIRS2 d) and 3350 ml H2/(mIRS2 d) respectively. While approximately 8 m2 of the illuminated reactor surface of the panel reactor can be installed on 1 m2 of ground space, the relation of the illuminated reactor surface to the ground area for the tubular reactor is approximately 1–1.

Oxyfuel processes represent a promising technique for carbon capture and storage since the related energy penalty is considered to be comparatively low. A possibility to separate the O 2 from air is the use of mixed ion electron conducting (MIEC) membranes. A favored membrane material is Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3− δ since its permeation rate is high. In the work at hand this membrane material has been studied experimentally to determine the coefficients of the Wagner equation. The experiments have been performed with membrane tubes considering the use of tubular membrane systems for industrial application in future oxyfuel power plants. 3- and 4-end operating conditions have been applied to provide an additional degree of freedom for the integration of the membrane module into the power plant process. Wagner constants C = 1.004 × 1 0 − 8 mol/(cm s K) and K = 6201 K have been determined. A membrane model for Aspen Plus has been developed, which allows to calculate the heat and mass transfer in an oxygen membrane module. Calculations were performed based on data from oxyfuel membrane power plant simulations found in the literature. Compared to the 3-end concept the 4-end concept shows a higher net-efficiency together with a lower demand on membrane area. Depending on the operation mode and boundary conditions, the estimated specific membrane area is between 0.22 and 0.59 m 2 / kW th .

The application of semisolid process was investigated on Pb-Sb alloys that are normally used for metallic parts in car batteries, in order to increase their mechanical properties and corrosion resistance. The semisolid behaviour of a Pb-4%Sb alloy was analysed by means of rheological and calorimetry differential scanning experiments. The alloy was melted, treated by ultrasound to obtain the semisolid state and then poured into permanent moulds. Some of these samples were also heated in semisolid temperature range and injected in thixo-casting apparatus. Both poured and injected samples were characterized by metallographic analysis, mechanical test and electrochemical corrosion experiments. The results show an improvement of mechanical and corrosion resistance

Shear stress ramp experiments were performed in order to analyze the yield stress of the aluminium alloys AlSi5 and AlSi5Cu03Mg05Ag06 in the semi-solid state with regard to its dependency on time, solid fraction and particle size in the slurry. The experimental results were not influenced by the different chemical compositions of the alloys.

The cooperative project OXYCOAL-AC aims at the development of a zero-CO2-emission coal combustion process for power generation. The scope of the research comprises a multitude of aspects. This article focuses on membrane-based air separation modules and their design for oxycoal conditions, the specifics of coal combustion in a CO2/O2 atmosphere including related burner design as well as the cleaning of hot flue gas from oxycoal combustion.

The aim of the MEM-BRAIN project is the development and integration of gas separation membranes for zero-emission fossil power plants. This will be achieved by selective membranes with high permeability for CO2, O2 or H2, so that high-purity CO2 is obtained in a readily condensable form. The project is being implemented by the “MEM-BRAIN” Helmholtz Alliance consisting of research centres, universities and industrial partners.The MEM-BRAIN project focuses on the development, process engineering, system integration and energy systems analysis of different gas separation membranes for the different CO2 capture process routes in fossil power plants.

When analysing semi-solid metal alloys or any other suspension in rheometers a major problem is related to wall slip effects which lead to an underestimation of the suspensions viscosity. Using smooth rotating rods in rotational rheometry for analysing suspensions a thin particle free layer of liquid is formed at the surface of the rod due to near-wall segregation. Thus, mainly the viscosity of this layer is measured which is much lower than the one of the bulk phase. Kiljanski [1] proposed a method for rotational rheometers to recalculate such measurements to get viscosity values without slip effects. A device-related change to minimize wall slip is the use of rotating rods with grooved surfaces. Therewith near-wall mixing is produced to destroy the particle free layer. Alternatively, the use of multiple blade vanes is proposed in the literature to avoid wall slip. The differences of the two measuring devices (grooved, vane) are discussed at the example of measurements for a low melting tin-lead alloy in the semi-solid state. It is figured out whether a vane geometry is also suitable to be applied for rheological measurements on metallic suspensions.

The direct analysis and the inverse parameter fitting are methods for determination of unknown material parameters in rheometry. In this paper the efficiency of the both methods is examined on the case of a semi-solid alloy. The difference between the obtained material parameters is studied and the necessity of inverse parameter fitting is discussed.

Relatively low and frequently changing flow rates and compositions in biohydrogen production require a highly efficient and low energy consuming gas cleaning technology to let this process become a competitive alternative in hydrogen production. Membrane contactors with non-porous polymeric membranes were selected to be suitable since they do not only absorb the by-product carbon dioxide effectively but they also supply sterile conditions, they withstand high feed pressures and they prevent a contamination of the gas products by the liquid phase. The latter even allows the use of harmful substances such as mono ethanol amine (MEA) as liquid carriers. By testing different membrane materials and liquid carriers the contactors have been optimized and the applicability of this technology in biohydrogen production processes has been proven.

Heat transfer in falling liquid film systems is enhanced by waviness. Comprehension of the underlying kinetic phenomena requires experimental data of the temperature field with high spatiotemporal resolution. Therefore a non-invasive measuring method based on luminescence indicators is developed. It is used to determine the temperature distribution and the local film thickness simultaneously. Results are presented for the temperature distribution measurement in a laminar-wavy water film with a liquid side Reynolds number of 126 flowing down a heated plane with an inclination angle of 2° at two positions in flow direction. The measured temperature distributions are used to calculate the local heat transfer coefficient for solitary waves at two positions in flow direction.

Wasserstoff wird aufgrund seines emissionsarmen Oxidationsprozesses als einer der moglichen Energietrager der Zukunft angesehen. Um eine nachhaltige Wirkung auf den Treibhauseffekt zu erzielen, muss aber auch der Energiebedarf des Produktionsprozesses moglichst gering gehalten werden. Das integrierte Projekt Hyvolution, das im 6. Forschungsrahmenprogramm unter dem Schwerpunkt nachhaltiger Energiesysteme der Europaischen Komission gefordert wird, hat es sich deshalb zum Ziel gemacht, einen zweistufigen Bioprozess zu entwickeln, der zukunftig in dezentralen Kleinanlagen Wasserstoff aus Biomasse freisetzt.

Vorgestellt wird eine optische Messmethode, mit der erstmalig Temperaturverlaufe in einer Einzelwelle einer laminar-welligen dunnen Filmstromung experimentell ermittelt werden konnten. Mit den ermittelten Temperaturverteilungen wird der Verlauf des lokalen Warmeubergangskoeffizienten erhalten. Dieser gibt genaueren Aufschluss, in welchen Bereichen der Wellen eine Transportverbesserung auftritt. Mit der Variation der Betriebsbedingungen lassen sich die Transportverhaltnisse gezielt beeinflussen. Ebenso lassen sich kritische Zustande, wie Aufreisen der Filmstromung aufgrund lokaler Uberhitzung, genauer abschatzen.

One way to produce fuel gases is using bioreactors producing CH4/CO2, H2/CO2 and CH4/H2/CO2 gas mixtures. This method has many advantages; for example, low energy consumption, high ecological efficiency, utilization of organic wastes, accessibility and simplicity of hardware implementation. The results of organic waste bioconversion into methane and hydrogen by using an active membrane system integrated with aerobic and anaerobic bioreactors are presented. The suggested biomembrane system includes three types of fermenters: an aerobic phototrophic biomass producing reactor for CO2 consumption and O2 production from Anabaena variabilis, an anaerobic methane bioreactor for biomass transformation into biogas by using the methanogenic community, and Rhodobacter capsulatus immobilized in a polymeric matrix. The latter system was used for lactate or other low organics decomposition. The combination of the biosystem with membrane contactors and a selective membrane valve achieves a continuous process for energy production and total removal of CO2 from microbial gas mixtures, which can be fed back into the first aerobic productive reactor. In total, the developed system obtains energy from sunlight in the form of combustive gases (CH4 and H2) with a net CO2 consumption.

The investigation of the flow behavior of semi-solid steel alloys poses a great challenge by reason of high operation temperatures and the need of ceramic components for the measuring system. A high-temperature Couette rheometer has been developed to analyze flow properties of semi-solid alloys up to temperatures of 1500°C. In the present work the alloy under investigation is X210CrW12. Differently performed experiments clearly show its shear-thinning and time-dependent flow properties with a yield stress. This flow behavior is modeled using a Herschel-Bulkley approach where the experimental results achieved serve to identify model parameters.

Alloys of a specific microstructure exhibit a shear-rate history-dependent flow behaviour in the semi-solid state. Rheological studies have been carried out using various experimental techniques such as concentric cylinder rheometers of Couette or Searle type as well as capillary rheometers and parallel plate compression tests. With the Searle type rheometer and the capillary rheometer two different approaches of rheological measurement techniques are discussed and compared regarding advantages, potentials and its distinct characteristics. Experiments using the Searle type rheometer have been conducted under steady-state or oscillating conditions and have been used to verify time-dependency of step responses due to discontinuous or linear variances of the shear rate. These experiments provide all types of flow curve parameters as implemented in the numerical simulation. However the variances of the commonly used Couette and Searle type rheometers are limited to shear-rates which are significantly lower than that appearing in the technical thixo- or rheocasting processes. For that reason an additional experimental set-up with a horizontal slot capillary integrated in a shot-controlled high-pressure die-casting machine is used in order to examine flow properties at shear rate conditions similar to those in real thixocasting processes. After an initial examination of low temperature model alloys, such as PbSn15, the experimental set-up is then adjusted in order to obtain rheological data for light metal alloys such as Aluminium AlSi7Mg0.3. The Aluminium alloy is processed within each rheometer either as partially solidified or partially remelted in order to represent conditions of both, the conventional thixocasting and the lately introduced rheocasting process. Finally the appearance of physical phenomena which affects the accuracy of rheological experiments such as wall slip is considered for both types of rheometers.

Oscillation experiments, creep tests and shear stress ramps have been performed to analyze the yield stress and its time dependency. It has to be distinguished between iso-structural, dynamic and static yield stress. The iso-structural yield stress occurs immediately after shearing. Since the slurry structure remains unchanged, it is equivalent to the structure during shearing. At rest an internal structure builds up, this leads to an increase of the yield stress, which is referred to as the dynamic yield stress. It increases until its maximum value, the static yield stress, is reached.

Zur numerischen Simulation der Transportverhaltnisse und der chemischen Reaktionen im Zementdrehrohrofen wird eine CFD-Software mit einem Werkzeug zur Berechnung komplexer thermochemischer Gleichgewichte kombiniert. Warme- und Stofftransportvorgange im Ofen werden mit der CFD-Software und einem vereinfachten Modell der Klinkerbildungsreaktionen ohne Berucksichtigung der Nebenkomponenten berechnet. Aus diesen Ergebnissen wird ein Prozessmodell entwickelt, in dem die chemischen Reaktionen als Abfolge thermochemischer Gleichgewichtszustande dargestellt sind. Mithilfe dieses Prozessmodells kann die Einbindung von Nebenkomponenten in den Klinker in guter Ubereinstimmung mit Messwerten berechnet werden. Die Ausbildung von Verdampfungs/Kondensationskreislaufen im Ofen wird qualitativ gut wiedergegeben.

The processing of semisolid metal alloys in the innovative Thixoforming process induces several problems in the design of new dies and process strategies. This is mainly caused by the fact that segregation occurs in flows of suspensions and that semisolid metal alloys show shear thinning thixotropic behaviour and exhibit a yield stress. Beyond this the flow behaviour is influenced by the solid fraction, which depends on the slurry temperature. One way to reduce the development costs for new Thixoforming processes is to apply computational fluid dynamics. To this end a non-isothermal two-phase model has been developed and implemented into a proprietary developed FEM software. The model is based on a modified Herschel–Bulkley approach and comprises the entire non-Newtonian behaviour of semisolid alloys. The model has been validated with the experimental results of a specially designed die filling experiment. This experiment allows the observation of the flow front during the filling process for different filling velocities and die temperatures. The die geometries used represent two characteristic flow conditions of industrial casting processes, like sudden changes in flow direction and abrupt changes of the free cross-section. The reference values for the numerical simulation are the contour of the flow front, the spatial solid fraction distribution and the filling pressure.

The competing effects of pentanol adsorption and ammonia absorption on the shape of axisymmetric oscillating water jets are studied experimentally and interpreted qualitatively. While there is no significant influence of the absorption process on pure water jets, considerable change in jet length and deviation from sinusoidal evolution of surface oscillation in presence of n-pentanol is observed, accompanied by an increase in absorption rate. Hence dependence of jet shape on interfacial convection is shown. The effects of pentanol adsorption, surface elasticity of a pentanol surface film and nonuniform velocity distribution on jet stability are discussed quantitatively.

Semi-solid metal alloys, as used in industrial thixoforming, have a special microstructure of globular grains suspended in a liquid metal matrix. The complex rheological properties are strongly influenced by the local solid fraction, particle shape, particle size and state of agglomeration. It was analysed how the microstructure develops in dependence of the shear rate and cooling rate during the solidification and it was observed that the average particle size increased with increasing shear rate and decreasing cooling rate. In order to account for those phenomena, the rate of crystal growth and the relationship between average particle diameter and viscosity was modelled by applying the Sherwood two-film model for the mass transport. The dependence of the viscosity from the particle size were modelled with a modified Krieger–Dougherty model. Based on the rheological and microstructural observations an evaluation method was elaborated that allows for the construction of objective master curves that are independent of the particle growth during the experimentation. The isothermal experiments for the characterisation of the rheological behaviour consisted of step-change of shear-rate and yield-stress experiments. From the experimental data the steady-state flow curves could be determined as well as the time-dependent relaxation of the shear stress after a change of shear rate. The steady-state rheological behaviour was found to be shear thinning. Nevertheless, immediately after a shear-rate change an overshoot was observed that resulted from a short-time shear-thickening behaviour. The yield stress was found to strongly depend on the microstructure and the degree of agglomeration of the solid phase. With increasing rest time the yield stress was increasing strongly, because of the agglomeration of the solid particles. Based on the step-change of shear-rate experiments a single-phase flow has been developed that consists of a modified Herschel–Bulkley approach and accounts for the thixotropic as well as for the yield-stress behaviour of the alloys.

The development of new, low-energy consuming and clean technologies can include the utilization of organic wastes with the production of high-quality fuel gases (methane, hydrogen). This paper presents the results of organic wastes’ bioconversion into hydrogen and of the respective H 2 /CO 2 gas mixtures’ separation by using active membrane systems (membrane contactors) with moving liquid carriers. Rhodobacter capsulatus was used for lactate or low organic decomposition to H 2 -containing gas mixture and Thermohydrogenium kirishi was used for hydrogen production from glucose. Active membrane system was used for the separation of H 2 /CO 2 gas mixtures with the production of high-purity hydrogen. The possibility of integration of gas separating membrane systems with aerobic or anaerobic bioreactors are considered as well.

A new modular process modelling tool has been developed to support the design and operation of metallurgical processes. A modelling concept was formulated and a flowsheeting software tool has been developed for the calculation of complex non-equilibrium phenomena. To test both the basic approach and software tool, the modelling and simulation of a LD converter process was undertaken. The validation of the simulation model shows good agreement of reported and calculated values for species concentration and temperature development in time. The aim of this approach is to achieve a high degree of accuracy in modelling and, at the same time, to correspond to the speed requirements of day to day design work. It is intended to extend the current research to obtain a tool not only for the design and simulation of established processes, but also for the computer-aided development of new process routes.