TUHH Open Research (TORE)https://tore.tuhh.deTORE captures, stores, indexes, preserves, and distributes digital research material.Fri, 09 Jun 2023 05:54:42 GMT2023-06-09T05:54:42Z50121- Loss coefficients for compressible flows in conduit components under different thermal boundary conditionshttp://hdl.handle.net/11420/6266Title: Loss coefficients for compressible flows in conduit components under different thermal boundary conditions
Authors: Schmandt, Bastian; Herwig, Heinz
Abstract: Losses in flows through conduit components of pipe systems are usually accounted for by head loss coefficients K. For incompressible flows they are often determined based on measurements of total head in different cross sections. If, however, the flow is compressible but still subsonic, the physical interpretation of this method is problematic, since then the difference in total head does neither exactly correspond to dissipation nor to an exergy loss, i.e. the loss of available work. As an alternative, a method is presented, which makes use of the local entropy generation in order to determine the loss of available work instead of the loss of total head induced by a conduit component. Furthermore, a method for a meaningful visualization of the loss distribution within the component and its adjacent flow field is introduced. Based on this visualization the spatial extent of the additional losses due to the component can be quantified leading to a nondimenional length of impact.
The procedure is illustrated for the special case of ideal gas flow through a 90deg bend of square cross section in the laminar flow regime which prevails in mini and micro flow situations. Nondimensional values for the loss coefficient K, now based on entropy generation, are shown for various Mach and Reynolds numbers and for different thermal boundary conditions. They are a constant wall heat flux for heating or cooling, respectively, compared to the case of adiabatic walls.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11420/62662014-01-01T00:00:00Z
- Strömungsmechanik : Physik - mathematische Modelle - thermodynamische Aspekte (3., ergänzte Auflage)http://hdl.handle.net/11420/6224Title: Strömungsmechanik : Physik - mathematische Modelle - thermodynamische Aspekte (3., ergänzte Auflage)
Authors: Herwig, Heinz; Schmandt, Bastian
Abstract: Probleme in der Strömungsmechanik werden immer häufiger durch den Einsatz von kommerziellen Computerprogrammen gelöst. Eine solche Vorgehensweise setzt aber voraus, dass die Physik des Problems wirklich verstanden ist. Das Buch trägt zum grundlegenden Verständnis der Zusammenhänge bei, indem es die Physik verschiedener Strömungsformen anschaulich darstellt.
· Die mathematischen Grundgleichungen, insbesondere die Navier-Stokes-Gleichungen und der Energiesatz, werden zunächst in allgemeiner Form bereitgestellt und in ihrer mathematischen Bedeutung erläutert.
· Die physikalisch/mathematische Modellierung einzelner wichtiger Strömungen bzw. Strömungsformen wird anschließend konsequent aus diesen Grundgleichungen abgeleitet. Die Autoren verfolgen dabei systematisch das Konzept der deduktiven Herleitung.
· Thermodynamische Überlegungen werden herangezogen, insbesondere um Verluste bei Strömungen physikalisch interpretieren zu können.
Dimensionsanalytische Überlegungen spielen eine wichtige Rolle. Das Buch enthält zahlreiche Beispiele und Übungsaufgaben mit vollständigem Lösungsweg.
Neu an der 3. Auflage ist das Kapitel „Strömungen aus thermodynamischer Sicht“. In diesem Teil wird gezeigt, wie wichtige strömungsmechanische Größen (z.B. die Verlustbeiwerte) mit thermodynamischen Überlegungen ermittelt und interpretiert werden können.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/11420/62242015-01-01T00:00:00Z
- Strömungsmechanik : physikalisch-mathematische Grundlagen und Anleitung zum Lösen von Aufgaben (4., erweiterte Auflage)http://hdl.handle.net/11420/4846Title: Strömungsmechanik : physikalisch-mathematische Grundlagen und Anleitung zum Lösen von Aufgaben (4., erweiterte Auflage)
Authors: Herwig, Heinz; Schmandt, Bastian
Abstract: Probleme in der Strömungsmechanik werden immer häufiger durch den Einsatz von kommerziellen Computerprogrammen gelöst. Eine solche Vorgehensweise setzt aber voraus, dass die Physik des Problems wirklich verstanden ist. Das Buch trägt zum grundlegenden Verständnis der Zusammenhänge bei, indem es die Physik verschiedener Strömungsformen anschaulich darstellt. Die mathematischen Grundgleichungen, insbesondere die Navier-Stokes-Gleichungen und der Energiesatz, werden zunächst in allgemeiner Form bereitgestellt und in ihrer mathematischen Bedeutung erläutert.
Tue, 31 Jul 2018 00:00:00 GMThttp://hdl.handle.net/11420/48462018-07-31T00:00:00Z
- Diffuser and nozzle design optimization by entropy generation minimizationhttp://hdl.handle.net/11420/1412Title: Diffuser and nozzle design optimization by entropy generation minimization
Authors: Schmandt, Bastian; Herwig, Heinz
Abstract: Diffusers and nozzles within a flow system are optimized with respect to their wall shapes for a given change in cross sections. The optimization target is a low value of the head loss coefficient K, which can be linked to the overall entropy generation due to the conduit component. First, a polynomial shape of the wall with two degrees of freedom is assumed. As a second approach six equally spaced diameters in a diffuser are determined by a genetic algorithm such that the entropy generation and thus the head loss is minimized. It turns out that a visualization of cross section averaged entropy generation rates along the flow path should be used to identify sources of high entropy generation before and during the optimization. Thus it will be possible to decide whether a given parametric representation of a component’s shape only leads to a redistribution of losses or (in the most-favored case) to minimal values for K.; Diffusers and nozzles within a flow system are optimized with respect to their wall shapes for a given change in cross sections. The optimization target is a low value of the head loss coefficient K, which can be linked to the overall entropy generation due to the conduit component. First, a polynomial shape of the wall with two degrees of freedom is assumed. As a second approach six equally spaced diameters in a diffuser are determined by a genetic algorithm such that the entropy generation and thus the head loss is minimized. It turns out that a visualization of cross section averaged entropy generation rates along the flow path should be used to identify sources of high entropy generation before and during the optimization. Thus it will be possible to decide whether a given parametric representation of a component’s shape only leads to a redistribution of losses or (in the most-favored case) to minimal values for K.
Wed, 20 Jul 2011 00:00:00 GMThttp://hdl.handle.net/11420/14122011-07-20T00:00:00Z
- How to determine losses in a flow field: A paradigm shift towards the second law analysishttp://hdl.handle.net/11420/1414Title: How to determine losses in a flow field: A paradigm shift towards the second law analysis
Authors: Herwig, Heinz; Schmandt, Bastian
Abstract: Assuming that CFD solutions will be more and more used to characterize losses in terms of drag for external flows and head loss for internal flows, we suggest to replace single-valued data, like the drag force or a pressure drop, by field information about the losses. These information are gained when the entropy generation in the flow field is analyzed, an approach that often is called second law analysis (SLA), referring to the second law of thermodynamics. We show that this SLA approach is straight-forward, systematic and helpful when it comes to the physical interpretation of the losses in a flow field. Various examples are given, including external and internal flows, two phase flow, compressible flow and unsteady flow. Finally, we show that an energy transfer within a certain process can be put into a broader perspective by introducing the entropic potential of an energy.; Assuming that CFD solutions will be more and more used to characterize losses in terms of drag for external flows and head loss for internal flows, we suggest to replace single-valued data, like the drag force or a pressure drop, by field information about the losses. These information are gained when the entropy generation in the flow field is analyzed, an approach that often is called second law analysis (SLA), referring to the second law of thermodynamics. We show that this SLA approach is straight-forward, systematic and helpful when it comes to the physical interpretation of the losses in a flow field. Various examples are given, including external and internal flows, two phase flow, compressible flow and unsteady flow. Finally, we show that an energy transfer within a certain process can be put into a broader perspective by introducing the entropic potential of an energy.
Mon, 26 May 2014 00:00:00 GMThttp://hdl.handle.net/11420/14142014-05-26T00:00:00Z
- Losses due to the flow through conduit components in mini- and micro-systems accounted for by head loss/change coefficientshttp://hdl.handle.net/11420/6267Title: Losses due to the flow through conduit components in mini- and micro-systems accounted for by head loss/change coefficients
Authors: Schmandt, Bastian; Herwig, Heinz
Abstract: The definition of head loss/change coefficients should be based on the dissipation in the flow field or, in a more general sense, on the entropy generation due to a conduit component. When, in the simplest case, unbranched flow is considered, an entropy based approach is straight forward since the flow rate can be used as the general reference quantity. If, however, one mass flow rate is split or two partial flow rates are united like in junctions, a new aspect appears: There is an energy transfer between the single branches that has to be accounted for appropriately. It turns out that this energy transfer changes the total head in each flow branch in addition to the loss of total head due to entropy generation. Therefore, appropriate coefficients for junctions should be named head change coefficients. As an example, head change coefficients for dividing and combining flows due to T-shape micro-junctions are investigated and discussed with respect to their physical meaning. For combining flows, the special case of engulfment, leading to enhanced mixing in micro mixers, is considered in detail.
Fri, 01 Aug 2014 00:00:00 GMThttp://hdl.handle.net/11420/62672014-08-01T00:00:00Z
- The head change coefficient for branched flows : why "losses" due to junctions can be negativehttp://hdl.handle.net/11420/6227Title: The head change coefficient for branched flows : why "losses" due to junctions can be negative
Authors: Schmandt, Bastian; Herwig, Heinz
Abstract: In this study, the phenomenon of negative "loss"-coefficients reported in various studies about turbulent branched flows through combining junctions is investigated systematically. It turns out, that the "loss" for one branch of a junction and its adjacent ducts only in parts is due to devaluation of mechanical energy, which would be a real loss, so that the term energy change is more appropriate. The other part of the energy change which is not due to a loss is due to a mutual energy transfer between the two partial flows. As a consequence, non-dimensional coefficients should be called energy change coefficients rather than head loss coefficients whenever branching of flows occurs. Furthermore, a method is introduced by which losses and the energy transfer are determined directly in the flow field. The field values allow a quantification and visualization of the local loss and work transfer, while their integral values can be used to quantify the individual contributions of losses and energy transfer within the energy change of a flow through a junction.
Sat, 01 Aug 2015 00:00:00 GMThttp://hdl.handle.net/11420/62272015-08-01T00:00:00Z
- Determination of head change coefficients for dividing and combining junctions : a method based on the second law of thermodynamicshttp://hdl.handle.net/11420/6268Title: Determination of head change coefficients for dividing and combining junctions : a method based on the second law of thermodynamics
Authors: Schmandt, Bastian; Iyer, Vasudevan; Herwig, Heinz
Abstract: Losses due to the flow through conduit components in a pipe system can be accounted for by head loss coefficients K. They correspond to the dissipation in the flow field or, in a more general sense, to the entropy generation due to the conduit component under consideration. When only one single mass flow rate is involved, an entropy based approach is straight forward since the flow rate can be used as a general reference quantity. If, however, one mass flow rate is split or two partial flow rates come together like in junctions, a new aspect appears: there is an energy transfer between the single branches that has to be accounted for. It turns out that this energy transfer changes the total head in each flow branch in addition to the loss of total head due to entropy generation. Therefore, appropriate coefficients for junctions should be named as head change coefficients. As an example, the method is applied to laminar flows. Head change coefficients for dividing and combining flows in a T-shape micro-junction are determined for both branches and discussed with respect to their physical meaning. For the combining junction, the special case of engulfment, leading to enhanced mixing in micro-mixers, is also considered. Finally, it is shown, how the newly defined coefficients can be used for the design of a flow network.
Mon, 03 Mar 2014 00:00:00 GMThttp://hdl.handle.net/11420/62682014-03-03T00:00:00Z
- Losses Due to Conduit Components: An Optimization Strategy and Its Applicationhttp://hdl.handle.net/11420/5944Title: Losses Due to Conduit Components: An Optimization Strategy and Its Application
Authors: Schmandt, Bastian; Herwig, Heinz
Abstract: In the present study, we introduce a method which we call the glass box optimization (GBO) method as a strategy how to reduce flow losses whenever numerical data based on computational fluid dynamics (CFD)-results are available. Based on local values of the velocity and entropy generation fields, a systematic analysis of the loss mechanisms involved is used in order to develop control mechanisms for the reduction of losses due to a conduit component. Furthermore, it is shown how the losses are distributed between a component itself and the adjacent flow field. Since often a large amount of the losses occurs outside of the actual component, it is discussed under which circumstances an optimized component leads to improved efficiency of an entire fluid flow network. The method is exemplified for turbulent flow through a 90' bend.
Tue, 01 Mar 2016 00:00:00 GMThttp://hdl.handle.net/11420/59442016-03-01T00:00:00Z
- Loss coefficients for periodically unsteady flows in conduit components : illustrated for laminar flow in a circular duct and a 90 degree bendhttp://hdl.handle.net/11420/6864Title: Loss coefficients for periodically unsteady flows in conduit components : illustrated for laminar flow in a circular duct and a 90 degree bend
Authors: Schmandt, Bastian; Herwig, Heinz
Abstract: Losses in a flow through conduit components of a pipe system can be accounted for by head loss coefficients K. They can either be determined experimentally or from numerical solutions of the flow field. The physical interpretation is straight forward when these losses are related to the entropy generation in the flow field. This can be done based on the numerical solutions by the second law analysis (SLA) successfully applied for steady flows in the past. This analysis here is extended to unsteady laminar flow, exemplified by a periodic pulsating mass flow rate with the pulsation amplitude and the frequency as crucial parameters. First the numerical model is validated by comparing it to results for unsteady laminar pipe flow with analytical solutions for this case. Then K-values are determined for the benchmark case of a 90 deg bend with a square cross section which is well-documented for the steady case already. It turns out that time averaged values of K may significantly deviate from the corresponding steady values. The K-values determined for steady flow are a good approximation for the time-averaged values in the unsteady case only for small frequencies and small amplitudes. © 2013 by ASME.
Fri, 22 Feb 2013 00:00:00 GMThttp://hdl.handle.net/11420/68642013-02-22T00:00:00Z
- Drag with external and pressure drop with internal flows : a new and unifying look at losses in the flow field based on the second law of thermodynamicshttp://hdl.handle.net/11420/6141Title: Drag with external and pressure drop with internal flows : a new and unifying look at losses in the flow field based on the second law of thermodynamics
Authors: Herwig, Heinz; Schmandt, Bastian
Abstract: Internal and external flows are characterized by friction factors and drag coefficients, respectively. Their definitions are based on pressure drop and drag force and thus are very different in character. From a thermodynamics point of view in both cases dissipation occurs which can uniformly be related to the entropy generation in the flow field. Therefore we suggest to account for losses in the flow field by friction factors and drag coefficients that are based on the overall entropy generation due to the dissipation in the internal and external flow fields. This second law analysis (SLA) has been applied to internal flows in many studies already. Examples of this flow category are given together with new cases of external flows, also treated by the general SLA-approach. © 2013 The Japan Society of Fluid Mechanics and IOP Publishing Ltd.
Fri, 30 Aug 2013 00:00:00 GMThttp://hdl.handle.net/11420/61412013-08-30T00:00:00Z
- Performance evaluation of the flow in micro junctions : head change versus head loss coefficientshttp://hdl.handle.net/11420/6044Title: Performance evaluation of the flow in micro junctions : head change versus head loss coefficients
Authors: Schmandt, Bastian; Herwig, Heinz
Abstract: Losses due to the flow through conduit components in a pipe system can be characterised by head loss coefficients. They basically account for the dissipation in the flow field or, in a more general sense, for the entropy generation due to the conduit component under consideration. When only one single mass flow rate is involved, an entropy based approach is straight forward and m can be used as a general reference quantity. If, however, the mass flow rate is split or united like in junctions, some new aspects appear. In our study the general approach for these kind of conduit components is discussed. Like for single mass flow rates losses are accounted for by determining the entropy generation rates. New aspects for the branchedflows are an additional parameter, the splitting ratio, and the fact that there is an energy transfer between the single branches that has to be accounted for appropriately. It turns out that this energy transfer changes the total head in each flow brach in addition to a sole loss of total head. Therefore, the coefficients should be named head change coefficients when this effect occurs. As an example the flow through a T-shaped junction is considered, for which head loss coefficients are determined for both branches and discussed with respect to their physical meaning. Copyright © 2013 by ASME.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/11420/60442013-01-01T00:00:00Z