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Item type:Publication, Access status: with files , How to Teach Heat Transfer More Systematically by Involving EntropyIn order to teach heat transfer systematically and with a clear physical background, it is recommended that entropy should not be ignored as a fundamental quantity. Heat transfer processes are characterized by introducing the so-called “entropic potential” of the transferred energy, and an assessment number is based on this new quantity.Publicationtype: Journal ArticleScopus© Citations 5 355 442 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , What exactly is the Nusselt Number in convective heat transfer problems and are there alternatives?The often used Nusselt number is critically questioned with respect to its physical meaning. Based on a rigorous dimensional analysis, alternative assessment numbers are found that in a systematic way separately account for the quantitative and qualitative aspect of a heat transfer process. The qualitative aspect is related to the entropy generated in the temperature field of a real, irreversible heat transfer. The irreversibility can be quantified by referring it to the so-called entropic potential of the energy involved in the transfer process.Publicationtype: Journal ArticleScopus© Citations 27 469 913 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , 190 235 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , The misleading use of “enthalpy" in an energy conversion analysisThe frequently used thermodynamic state quantity enthalpy H turns out to be very problematic when applied in an energy conversion analysis. Due to the fact that H combines two terms, the internal energy U and the product pV, the interpretation of what H means in physical terms is often obscure and leads to various misinterpretations. Several examples are given and interpreted twice, i.e. with and without referring to enthalpy.Publicationtype: Journal Article148 250 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , How to determine losses in a flow field: A paradigm shift towards the second law analysis(Multidisciplinary Digital Publishing Institute (MDPI), 2014-05-26); 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.Publicationtype: Journal ArticleScopus© Citations 51 532 715 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , The entropic potential concept: a new way to look at energy transfer operationsEnergy transfer operations or processes are systematically analyzed with respect to the way they can be assessed. It turns out that the energy transfer should not only be characterized by the operation or process itself but that it should be seen in a wider context. This context is introduced as the entropic potential of the energy that is transferred. It takes into account the overall transfer from the energy in its initial and finite states, <em>i.e.</em>, starting as pure exergy when it is a primary energy, for example, and ending as pure anergy when it has become part of the internal energy of the ambient. With this concept an energy devaluation number can be defined which has several properties with a reasonable physical background. Two examples of different complexity of the process assessed are given and discussed with respect to the physical meaning of the new energy devaluation number.Publicationtype: Journal ArticleScopus© Citations 38 546 524 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Diffuser and nozzle design optimization by entropy generation minimization(Multidisciplinary Digital Publishing Institute (MDPI), 2011-07-20); 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.Publicationtype: Journal ArticleScopus© Citations 32 363 586