Slip length of the tribo system steel-polyalphaolefin-steel determined by a novel tribometer

Nowadays sealing systems are commonly designed by means of hydrodynamic and elastohydrodynamic theories. Although the analytical as well as the computational approaches have improved in meaning full manner since the last decades: For small sealing gaps, in the order of micrometers and below, a discrepancy between experimental investigated and theoretically predicted leakage flows occur. As a cause for the discrepancy a breakdown of the no slip boundary condition is suspected. Since in small sealing gaps the continuum hypothesis is violated and molecular effects have to be considered. One fundamental quantity to take molecular affects into account is the slip length. Within this paper a new measurement apparatus to evaluate the slip length for hydraulic applications is presented. The adjustable gaps between two planar surfaces are in the order of magnitude of 1 μm. In a first step the slip length for the system steel-oil –steel is investigated at three different temperatures: 18°C, 22°C and 25°C. The measured slip lengths are in the order of magnitude of ~100 nm

Training of YOLO Neural Network for the Detection of Fire Emergency Assets

Building assets surveys are cost and time demanding and the majority of current methods still rely on manual procedures. New technologies could be used to support this task. The exploitation of Artificial Intelligence (AI) for the automatic interpretation of data is spreading throughout various application fields. However, a challenge with AI is the very large number of training images required for robustly detect and classify each object class. This paper details the procedure and parameters used for the training of a custom YOLO neural network for the recognition of fire emergency assets. The minimum number of pictures for obtaining good recognition performances and the image augmentation process have been investigated. In the end, it was found that fire extinguishers and emergency signs are reasonably detected and their position inside the pictures accurately evaluated. The use case proposed in this paper for the use of custom YOLO is the retrieval of as-is information for existing buildings. The trained neural networks are part of a system that makes use of Augmented Reality devices for capturing pictures and for visualizing the results directly on site

A Similarity based Efficiency Model of Spindle Screw Pumps

Spindle screw pumps are used in numerous different applications and industrial sectors. When selecting a suitable spindle screw pump for a specified application, manufacturers are often confronted with a lack of comparable measurement data for the desired combination of operating conditions and pumping fluid. Consequently, the volumetric and mechanical-hydraulic efficiency of a pump under the operating conditions of the application need to be estimated. In this context, this paper discusses the application of similarity for three-spindle screw pumps and introduces a similarity based efficiency model. The model is validated by means of a measured pump characteristic at different operating conditions varying pressure, rotational speed and the viscosity of the pumping fluid. The validation results prove that a pump characteristic can be represented over a wide operating range based on similarity. An estimation of the volumetric and the mechanical-hydraulic efficiency at a changed viscosity is achieved with high accuracy. Furthermore, a new approach to monitor and to evaluate manufacturing uncertainty based on the model parameter relative gap is presented. Finally, the paper gives an outlook on future experimental investigations at TU Darmstadt on model series of three-spindle screw pumps containing pumps of different displacement volume

Slip length of the tribo system steel-polyalphaolefin-steel determined by a novel tribometer

Nowadays sealing systems are commonly designed by means of hydrodynamic and elastohydrodynamic theories. Although the analytical as well as the computational approaches have improved in meaning full manner since the last decades: For small sealing gaps, in the order of micrometers and below, a discrepancy between experimental investigated and theoretically predicted leakage flows occur. As a cause for the discrepancy a breakdown of the no slip boundary condition is suspected. Since in small sealing gaps the continuum hypothesis is violated and molecular effects have to be considered. One fundamental quantity to take molecular affects into account is the slip length. Within this paper a new measurement apparatus to evaluate the slip length for hydraulic applications is presented. The adjustable gaps between two planar surfaces are in the order of magnitude of 1 μm. In a first step the slip length for the system steel-oil –steel is investigated at three different temperatures: 18°C, 22°C and 25°C. The measured slip lengths are in the order of magnitude of ~100 nm

Ähnlichkeitsbeziehungen bei Verdrängermaschinen - eine einheitliche Wirkungsgradmodellierung

Verdrängermaschinen zeichnen sich durch ihr breites Einsatzspektrum aus. Dies zeigt sich in der Vielzahl zum Einsatz kommender Medien und in der Vielfalt konstruktiver Ausführungen. Aufgrund dieser Vielfalt ist eine einheitliche Wirkungsgradmodellierung, die für eine konsistente energetische Bewertung von Maschinen notwendige Voraussetzung ist, bisher nur in Ansätzen gelungen. Die hier vorgestellte dimensionsanalytische Modellierung ermöglicht nunmehr eine kompakte und typenunabhängige Beschreibung des Wirkungsgrads anhand lediglich folgender vier dimensionslosen Kenngrößen: (i) Spezifischer Druck, (ii) Reynoldszahl, (iii) spezifische Nachgiebigkeit und (iv) relativer Spalt. Im Modell unterscheiden sich die Maschinentypen allein durch den relativen Spalt. Maschinen gleichen Typs ordnen sich zu einer Spaltklasse. Dies ist das Ergebnis der Modellanwendung auf vier verschiedene Maschinentypen mit 155 unterschiedlichen Größen und über 2680 Betriebspunkten. 1.Kernaussage: Die energetische Effizienz von Verdrängermaschinen lässt sich typunabhängigvon nur vier dimensionslosen Größen darstellen. 2.Kernaussage: Unterschiedliche Maschinentypen unterscheiden sich im Rahmen des Modellsallein im relativen Spalt. Die Spaltklasse ψ/ψref wird als neue charakteristische Größe für dieverschiedenen Maschinentypen eingeführt

Slip length in narrow sealing gaps – an experimental approach

For narrow sealing gaps in average smaller ca. 1 μm it is expected that the no-slip boundary condition does not yield anymore. As a consequence the friction is reduced and the leakage is increased compared to the no-slip design case. Though the concept of slip length was introduced by Navier and Maxwell already in the 19th century, it is up to now costly to measure the slip length. This is due to the required measurement precision. Today the slip length is measured in laboratories for glass, silicium or sapphire wafers while using fluorescence methods to determine the flow velocity and is thus far from sealing applications. The present paper introduces an alternative method to measure the slip length for typical materials that are used in sealing technologies. A key advantage of the presented method is that the slip length can be evaluated while measuring the physical quantities torque and gap setting. Within the paper the design of the apparatus including the measurement equipment is discussed in detail

Influence of Temperature and Shear Rate on the Slip Length in the Hydrodynamic Lubrication for a Polyalphaolefin

Generally sealing systems are designed by means of elasto-hydrodynamics. In this case, the no slip boundary condition is applied to the solid walls for solving the Reynolds equation. Nowadays engineers apply the no-slip boundary condition with the most matter of course. But in the 19th century the behaviour of fluids close to the solid wall was discussed by personalities as Stokes, Poisson, Maxwell or Navier. Navier [1] e.g. introduced a slippage factor in his derivation of the Navier-Stokes equations. In the middle of the 19th century Stokes was commissioned by the Royal Society, to discuss the issue regarding the slipping behaviour of fluids close to solid walls. And he concluded in [2] & [3] that the effect of slippage on solid walls, if it exists, was up to his time too small to measure and could be neglected. Hence for sufficiently large flow geometries the effect of wall sliding was neglected. Even today measuring the slip velocity close to solid walls is a challenging task and no general approach has figured out. This conclusion yields up to now and is sometimes treated like a principle. But in the case of sealing systems where commonly gaps are in the order of some microns and below the effect of wall slippage has to be taken into account. Experimental investigations of sealing manufacturers show that the leakage behav- iour of geometrically identical sealing systems depends on the material paring and hence on the surface energy. As a cause for the discrepancy between calculations and experimental investigations a breakdown of the no slip boundary condition is suspected

Reduction of Bearing Load Capacity and Increase in Volume Flow Due to Wall Slip

Since the beginning of the 20th century, hydraulic sealings and journal bearings are designed employing Reynolds lubrication theory /1–3/. The Reynolds lubrication theory presumes the no slip boundary condition at the liquid-solid interface. Recent studies conducted by the authors show, that the assumed no slip boundary condition at the liquid-solid interface is not valid for most fluid power applications; cf. /4/. This effects the prediction of leakage flow and frictional behaviour of sealing systems as well as bearing capacity of journal bearings. Thus, considering slip at the liquid-solid interface is important for the design of hydraulic components. The concept of wall slip was already discussed by Navier /5/ and Stokes /6/, when deriving the momentum equation for Newtonian fluids in the 19th century. Stokes favours the no slip boundary condition and justifies his hypothesis by a good agreement of the theory with experimental investigations of Poiseuille /7/. In contrast, Navier /5/ formulates the slip boundary condition, with the slip velocity being the product of the shear rate and the slip length. Regardless of this discussion, the no slip boundary condition is established over the centuries, based on the insufficient measurement techniques. However, in many technically important applications of fluid power technologies wall slip is not negligible. This is the case if the quotient of slip length and typical flow geometry is less than 10E-3. Thus, for typical hydraulic systems is reasonable to consider slip, if the gap geometries are of the order of magnitude of 10 μm

Temperature-dependent wall slip of Newtonian lubricants

We discuss (i) the measurement, (ii) interpretation and (iii) technical impact of temperature-dependent wall slip and its activation energy for polar and non-polar hydrocarbon Newtonian fluids moving relative to machined metal surfaces. A newly developed apparatus, the slip length tribometer (SLT), overcomes the drawbacks of existing measurement devices in terms of characterising relevant rough surfaces by measuring the slip length at different temperatures over a sufficiently large wetted area. The experimental data show that the bulk viscosity and slip length at the fluid–metal interface is independent of the shear rate up to 10⁵ s⁻¹, being consistent with recent results from molecular dynamics simulations by Mehrnia & Pelz (J. Mol. Liq., vol. 336, 2021, 116589). Furthermore, the activation energies for wall slip and bulk shear determined by means of the SLT differ by a factor of two, i.e. Eλ ≈ 0.5Eμ for non-polar hydrocarbon molecules sliding relative to metal walls. This difference is explained by a generalised Eyring model applied to wall slip. The paper closes with the impact of wall slip on Sommerfeld’s similarity theory of tribology and the resulting Stribeck curve (Sommerfeld, Z. Math. Phys., vol. 50, 1904, pp. 97–155; Z. Tech. Phys., vol. 2. Jahrg., 1921; Mechanik der deformierbaren Medien, 1944, Akademische Verlagsgesellschaft Becker & Erler). For this purpose, Reynolds’ equation generalised for wall slip is solved in combination with the experimentally determined constitutive relations for bulk shear and wall slip to predict typical characteristics of journal bearings. The results show that, for a typical journal bearing, where the ratio of slip length to average bearing clearance is of the order of 10⁻², the influence of wall slip on both load-carrying capacity and dissipation is not negligible. This work combines nanofluidics and tribology in order to provide methods and knowledge for e.g. tailor-made fluids and interfaces

Leichtbautilger für Fahrwerke

Konventionelle, passive Fahrwerkskonzeple bestehen aus einem Feder- und einem Dämpferelement und das Systemverhalten ist mit der Abstimmung der Steifigkeils- und Dämpfungswerte fest vorgegeben. Bei der Fahrwerksabstimmung werden die Zielfunktionen Fahrsicherheit und -komfort für das jeweilige Fahrzeugkonzept ausgelegt. Jede optimale Lösung stellt ein Kompromiss zwischen Fahrsicherheit und -komfort dar, da die beiden Zielfunktionen gegenläufig sind. Alle optimalen Lösungen liegen im sogenannten Konfliktdiagramm auf einer Pareto-Linie. In dieser Arbeit wird gezeigt, wie ein hydraulisch übersetzter Leichtbautilger - Fluid Dynamic Absorber - in das Fahrwerk integriert und das Systemverhalten durch die Veränderung der Systemtopologie verbessert wird. Prinzip bedingt bringt ein Tilger immer zusätzliche Masse in das System ein. Dieses unerwünschte Verhalten wird durch die hydraulische Übersetzung (Prinzip der virtuellen Masse) minimiert. Hierzu wird der Leichtbautilger an das Chassis, das als Quasi-Inertialsystem dient, angebunden