Uncertainty assessment in friction factor measurements as a tool to design experimental set-ups

The promising performance of microchannels has given rise to intensive research on pressure drop and heat transfer characteristics of flows at the small scale. To check the classical models and to validate new ones, experiments need to be conducted, which are particularly difficult given the characteristic dimensions involved and the magnitude of the fluxes to be measured. Although more care has been devoted lately to the design of experiments in terms of control of the geometry and of the boundary conditions, the uncertainties which inevitably affect each measurement do not seem to have been given the proper consideration. Correctly calculating uncertainties not only allows a correct assessment of the experimental data obtained, but can also be used to decide which measurements need to have the highest precision to achieve a certain accuracy, thus saving money on the others. In this paper, a quantitative criterion is given to assess the accuracy achievable in the determination of the friction factor in the laminar regime for the flow of a fluid in a circular microtube. The influence of the six quantities (pressure drop, outlet pressure, temperature, length, diameter and volume flow rate) measured to determine f in the laminar regime are studied separately and when combined. It is found that at low Reynolds numbers flow rate and pressure drop measurements are determinant for the final value of the uncertainty, while at larger Reynolds numbers the influence of the accuracy in measuring the hydraulic diameter prevails and also limits the minimum value that the total uncertainty can take.     

Ein Bemessungsmodell für durchlaufende Verbundträger mit großen Stegöffnungen

A design model for continuous composite beams with large web openings. Continuous composite beams can be designed according to the plastic hinge theory. The plastic reserves of the cross section and of the system are used to full capacity with this method. The treatment of large web openings was not clarified for the appliance of the plastic hinge theory until now. At the Institute for Concrete Structures and Structural Design at the Kaiserslautern University of Technology a research project, which was supported by the Deutsche Forschungsgemeinschaft (DFG), was executed. Within this project continuous composite beams with openings were experimentally and numerically investigated. Furthermore a design model for calculating those beams according to the plastic hinge theory was developed. In this paper the design model is presented.     

Pressure analysis of the hydromechanical fracture behaviour in stimulated tight sedimentary geothermal reservoirs

Hydromechanical phenomena in fractured sediments are complex. They control the flow in stimulated tight sediments and are crucial for the exploitation of geothermal energy from such rocks. We present the analysis of a cyclic water injection/production (huff–puff) process, a promising method to extract geothermal energy from tight sedimentary reservoirs. It uses a single borehole, which considerably reduces investment costs. A huff–puff test was performed in a 3800-m deep sedimentary formation (borehole Horstberg Z1, Lower Saxony, Germany). The analysis presented herein explains the downhole pressure measurements by a simplified reservoir model containing a single vertical fracture. The model addresses the flow behaviour between the fracture and the rock matrix in a layered formation, and the coupling between fluid flow and the mechanical deformation of the fracture. The latter aspect is relevant to predict the efficiency of the geothermal reservoir because cooled regions resulting from a particular injection/production scheme can be identified. The analysis methods include: (1) the curve-fitting code ODA used for a determination of different flow regimes (radial or linear), (2) an analytical solution for the calculation of the injection pressure, assuming a time-dependent fracture area, and (3) the simulator ROCMAS, which numerically solves the coupling between fluid flow and fracture deformation. Whereas each single approach is insufficient to explain the complete test data, a combination of the results yields an understanding of the flow regimes taking place during the test.     

Untersuchungen zur Homogenität von Bauwerksteilen mit Lasertechniken

Investigations concerning homogeneity of building parts by laser techniques. The subproject B1 “Diagnostics and Quality Control by Non‐Destructive, Contactless Testing Techniques” is working within the CRC 524 on the procedural and measurement technological evolutionary development of the conventional ultrasonic through‐transmission method towards an optical measuring method by application of laser technologies. The aim is the determination of the distribution of elastic characteristic parameters for the evaluation of laboratory test specimens in investigations on durability of concrete and for the actual state of construction elements in the course of revitalising buildings. In this case, a laser induced sound excitation takes place by means of an Nd:YAG‐laser. The sound waves that have been influenced by the investigation object are detected by a laser vibrometer. By applying these methods, both a high lasing rate and a high achievable data density are to be expected since the laser beams in both systems can be deflected optically by means of scanners. Furthermore, a surveying‐technological approach for sound path determination at each pair of measuring points has been developed, which can also be used for the conventional application of the ultrasonic through‐transmission method.     

Über die Korrelation der ödometrischen und der “dynamischen” Steifigkeit nichtbindiger Böden

On the correlation of the oedometric and the “dynamic” stiffness of non‐cohesive soils. The “dynamic” shear modulus G_dyn of the soil, i.e. the secant stiffness of the shear stress – shear strain – hysteresis at very small strain amplitudes is often estimated my means of a diagram correlating the dynamic constrained elastic modulus E_s,dyn with the oedometric stiffness E_s for first loading. However, the assumptions and limits of this correlation are not clear. In the context of this paper the correlation E_s ↔ E_s,dyn is checked for four sands with different grain size distribution curves. For this purpose tests with oedometric compression and measurements of the compression wave velocity in a triaxial cell were performed. Partially, significant deviations of the measured data from the correlation approach actually used were obtained. On the basis of the wave velocity measurements and supplementing resonant column tests this paper also discusses the “dynamic” Poisson's ratio ν and presents a modified correlation E_s ↔ G_dyn.     

Analysis of Volatiles Induced by Oviposition of Elm Leaf Beetle Xanthogaleruca luteola on Ulmus minor

Egg deposition of the elm leaf beetle Xanthogaleruca luteola causes the emission of volatiles from its food plant, Ulmus minor. These volatiles are exploited by the egg parasitoid, Oomyzus gallerucae, to locate its host. In contrast to other tritrophic systems, the release of volatiles is not induced by feeding but by egg deposition. Previous investigations showed that the release is systemic and can be triggered by jasmonic acid. Comparison of headspace analysis revealed similarities in the blend of volatiles emitted following egg deposition and feeding. The mixture consists of more than 40 compounds; most of the substances are terpenoids. Leaves next to those carrying eggs emit fewer compounds. When treated with jasmonic acid, leaves emit a blend that consists almost exclusively of terpenoids. Dichloromethane extracts of leaves treated with jasmonic acid were also investigated. After separation of extracts of jasmonate induced elm leaves on silica, we obtained a fraction of terpenoid hydrocarbons that was attractive to the parasitoids. This indicates that jasmonic acid stimulates the production of terpenoid hydrocarbons that convey information of egg deposition to the parasitoid.     

Sonochemical Activation of Al/Ni Hydrogenation Catalyst

This paper proposes a sonochemical approach to the nanostructuring of Al/Ni catalyst with high content of accessible Ni centers and a high reusability. The surface and bulk composition as well as pore size distribution of this catalyst are controlled synergistically by adjusting the ultrasound intensity in aqueous solution. Sonochemical activation of Al/Ni alloy leads to formation of mesoporous Al/Ni metallic based frameworks with surface area up to 125 m² g^?1, and regular distribution of nickel active center in the porous matrix. One of the opportunities of porous Al/Ni catalyst is that due to a time‐resolved controllable formation of protective oxide layer it can be stored and handled under air in comparison to traditional Raney catalysts which need inert conditions. The Al/Ni catalyst is characterized by scanning electron microscopy (SEM), electron diffraction spectroscopy (EDS), X‐ray photoelectron spectroscopy (XPS), confocal scanning fluorescence microscopy (CSFM), solid‐state NMR experiments, and powder X‐ray diffraction analysis (PXRD). The catalytic activity was investigated for the hydrogenation of acetophenone.     

Thiol–Ene Clickable Gelatin: A Platform Bioink for Multiple 3D Biofabrication Technologies

Bioprinting can be defined as the art of combining materials and cells to fabricate designed, hierarchical 3D hybrid constructs. Suitable materials, so called bioinks, have to comply with challenging rheological processing demands and rapidly form a stable hydrogel postprinting in a cytocompatible manner. Gelatin is often adopted for this purpose, usually modified with (meth‐)acryloyl functionalities for postfabrication curing by free radical photopolymerization, resulting in a hydrogel that is cross‐linked via nondegradable polymer chains of uncontrolled length. The application of allylated gelatin (GelAGE) as a thiol–ene clickable bioink for distinct biofabrication applications is reported. Curing of this system occurs via dimerization and yields a network with flexible properties that offer a wider biofabrication window than (meth‐)acryloyl chemistry, and without additional nondegradable components. An in‐depth analysis of GelAGE synthesis is conducted, and standard UV‐initiation is further compared with a recently described visible‐light‐initiator system for GelAGE hydrogel formation. It is demonstrated that GelAGE may serve as a platform bioink for several biofabrication technologies by fabricating constructs with high shape fidelity via lithography‐based (digital light processing) 3D printing and extrusion‐based 3D bioprinting, the latter supporting long‐term viability postprinting of encapsulated chondrocytes.