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Special Issue "Entropy in Computational Fluid Dynamics"

A special issue of Entropy (ISSN 1099-4300).

Deadline for manuscript submissions: 31 May 2017

Special Issue Editor

Guest Editor
Priv.-Doz. Dr. Yan Jin

Hamburg University of Technology, Institute of Thermofluid Dynamics, Building K, Room 2542, D-21073 Hamburg, Germany
Website | E-Mail
Interests: fluid mechanics; heat/mass transfer; direct numerical simulation; turbulence modeling; optimization with the SLA; skin friction reduction

Special Issue Information

Dear Colleagues,

Losses in a flow and heat transfer process, from a thermodynamics point of view, are due to irreversible processes. In order to better understand the physics of these loss-producing mechanisms, fluid mechanic and heat transfer considerations might be complemented by some thermodynamic concepts with respect to the irreversible processes involved. Basically, these are concepts that assess energy by its value in terms of its convertibility from one form to another.

The second law analysis (SLA) is often used in thermodynamics in order to assess an irreversible process. According to the SLA, the quality of a flow and heat transfer process, and how reversible it is can only be assessed by the entropy generation rate. However, this concept is still not widely used to assess flow and heat transfer problems although they are often irreversible. The SLA may help to indicate where the losses occur and determine their strength, which is important for understanding a flow and heat transfer process. With the knowledge about the mechanisms of irreversibility, one may know how to reduce entropy generation, overall or locally, and thus improve the efficiency of a fluid machine.

Analysis of the irreversibility in flow or heat transfer processes, in particular for turbulent flows, is welcome. Papers about modelling the entropy generation due to turbulence are encouraged. Optimization of flow and heat transfer processes, e.g., reducing skin friction and enhancing heat transfer, with the SLA is of special interest.

Dr. Yan Jin
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Entropy is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

•    Entropy generation in a flow.
•    Entropy generation in a heat/mass transfer process.
•    Assessing the irreversibility with high accuracy methods, e.g., DNS.
•    Modeling the entropy generation due to turbulence.
•    Optimization with the second law of thermodynamics (SLA).
•    Skin friction reduction and heat transfer enhancement.

Published Papers (5 papers)

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Research

Open AccessArticle Entropy Generation of Double Diffusive Forced Convection in Porous Channels with Thick Walls and Soret Effect
Entropy 2017, 19(4), 171; doi:10.3390/e19040171
Received: 14 March 2017 / Revised: 13 April 2017 / Accepted: 13 April 2017 / Published: 15 April 2017
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Abstract
The second law performance of double diffusive forced convection in a horizontal porous channel with thick walls was considered. The Soret effect is included in the concentration equation and the first order chemical reaction was chosen for the concentration boundary conditions at the
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The second law performance of double diffusive forced convection in a horizontal porous channel with thick walls was considered. The Soret effect is included in the concentration equation and the first order chemical reaction was chosen for the concentration boundary conditions at the porous-solid walls interfaces. This investigation is focused on two principal types of boundary conditions. The first assumes a constant temperature condition at the outer surfaces of the solid walls, and the second assumes a constant heat flux at the lower wall and convection heat transfer at the upper wall. After obtaining the velocity, temperature and concentration distributions, the local and total entropy generation formulations were used to visualize the second law performance of the two cases. The results indicate that the total entropy generation rate is directly related to the lower wall thickness. Interestingly, it was observed that the total entropy generation rate for the second case reaches a minimum value, if the upper and lower wall thicknesses are chosen correctly. However, this observation was not true for the first case. These analyses can be useful for the design of microreactors and microcombustor systems when the second law analysis is taken into account. Full article
(This article belongs to the Special Issue Entropy in Computational Fluid Dynamics)
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Open AccessArticle Entropy Generation Analysis and Performance Evaluation of Turbulent Forced Convective Heat Transfer to Nanofluids
Entropy 2017, 19(3), 108; doi:10.3390/e19030108
Received: 21 January 2017 / Revised: 26 February 2017 / Accepted: 8 March 2017 / Published: 11 March 2017
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Abstract
The entropy generation analysis of fully turbulent convective heat transfer to nanofluids in a circular tube is investigated numerically using the Reynolds Averaged Navier–Stokes (RANS) model. The nanofluids with particle concentration of 0%, 1%, 2%, 4% and 6% are treated as single phases
[...] Read more.
The entropy generation analysis of fully turbulent convective heat transfer to nanofluids in a circular tube is investigated numerically using the Reynolds Averaged Navier–Stokes (RANS) model. The nanofluids with particle concentration of 0%, 1%, 2%, 4% and 6% are treated as single phases of effective properties. The uniform heat flux is enforced at the tube wall. To confirm the validity of the numerical approach, the results have been compared with empirical correlations and analytical formula. The self-similarity profiles of local entropy generation are also studied, in which the peak values of entropy generation by direct dissipation, turbulent dissipation, mean temperature gradients and fluctuating temperature gradients for different Reynolds number as well as different particle concentration are observed. In addition, the effects of Reynolds number, volume fraction of nanoparticles and heat flux on total entropy generation and Bejan number are discussed. In the results, the intersection points of total entropy generation for water and four nanofluids are observed, when the entropy generation decrease before the intersection and increase after the intersection as the particle concentration increases. Finally, by definition of Ep, which combines the first law and second law of thermodynamics and attributed to evaluate the real performance of heat transfer processes, the optimal Reynolds number Reop corresponding to the best performance and the advisable Reynolds number Read providing the appropriate Reynolds number range for nanofluids in convective heat transfer can be determined. Full article
(This article belongs to the Special Issue Entropy in Computational Fluid Dynamics)
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Open AccessArticle An Entropy-Assisted Shielding Function in DDES Formulation for the SST Turbulence Model
Entropy 2017, 19(3), 93; doi:10.3390/e19030093
Received: 12 November 2016 / Revised: 7 February 2017 / Accepted: 23 February 2017 / Published: 27 February 2017
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Abstract
The intent of shielding functions in delayed detached-eddy simulation methods (DDES) is to preserve the wall boundary layers as Reynolds-averaged Navier–Strokes (RANS) mode, avoiding possible modeled stress depletion (MSD) or even unphysical separation due to grid refinement. An entropy function fs is
[...] Read more.
The intent of shielding functions in delayed detached-eddy simulation methods (DDES) is to preserve the wall boundary layers as Reynolds-averaged Navier–Strokes (RANS) mode, avoiding possible modeled stress depletion (MSD) or even unphysical separation due to grid refinement. An entropy function fs is introduced to construct a DDES formulation for the k-ω shear stress transport (SST) model, whose performance is extensively examined on a range of attached and separated flows (flat-plate flow, circular cylinder flow, and supersonic cavity-ramp flow). Two more forms of shielding functions are also included for comparison: one that uses the blending function F2 of SST, the other which adopts the recalibrated shielding function fd_cor of the DDES version based on the Spalart-Allmaras (SA) model. In general, all of the shielding functions do not impair the vortex in fully separated flows. However, for flows including attached boundary layer, both F2 and the recalibrated fd_cor are found to be too conservative to resolve the unsteady flow content. On the other side, fs is proposed on the theory of energy dissipation and independent on from any particular turbulence model, showing the generic priority by properly balancing the need of reserving the RANS modeled regions for wall boundary layers and generating the unsteady turbulent structures in detached areas. Full article
(This article belongs to the Special Issue Entropy in Computational Fluid Dynamics)
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Open AccessArticle Local Entropy Generation in Compressible Flow through a High Pressure Turbine with Delayed Detached Eddy Simulation
Entropy 2017, 19(1), 29; doi:10.3390/e19010029
Received: 11 November 2016 / Revised: 3 January 2017 / Accepted: 9 January 2017 / Published: 11 January 2017
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Abstract
Gas turbines are important energy-converting equipment in many industries. The flow inside gas turbines is very complicated and the knowledge about the flow loss mechanism is critical to the advanced design. The current design system heavily relies on empirical formulas or Reynolds Averaged
[...] Read more.
Gas turbines are important energy-converting equipment in many industries. The flow inside gas turbines is very complicated and the knowledge about the flow loss mechanism is critical to the advanced design. The current design system heavily relies on empirical formulas or Reynolds Averaged Navier–Stokes (RANS), which faces big challenges in dealing with highly unsteady complex flow and accurately predicting flow losses. Further improving the efficiency needs more insights into the loss generation in gas turbines. Conventional Unsteady Reynolds Averaged Simulation (URANS) methods have defects in modeling multi-frequency, multi-length, highly unsteady flow, especially when mixing or separation occurs, while Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) are too costly for the high-Reynolds number flow. In this work, the Delayed Detached Eddy Simulation (DDES) method is used with a low-dissipation numerical scheme to capture the detailed flow structures of the complicated flow in a high pressure turbine guide vane. DDES accurately predicts the wake vortex behavior and produces much more details than RANS and URANS. The experimental findings of the wake vortex length characteristics, which RANS and URANS fail to predict, are successfully captured by DDES. Accurate flow simulation builds up a solid foundation for accurate losses prediction. Based on the detailed DDES results, loss analysis in terms of entropy generation rate is conducted from two aspects. The first aspect is to apportion losses by its physical resources: viscous irreversibility and heat transfer irreversibility. The viscous irreversibility is found to be much stronger than the heat transfer irreversibility in the flow. The second aspect is weighing the contributions of steady effects and unsteady effects. Losses due to unsteady effects account for a large part of total losses. Effects of unsteadiness should not be neglected in the flow physics study and design process. Full article
(This article belongs to the Special Issue Entropy in Computational Fluid Dynamics)
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Open AccessArticle Determining the Optimum Inner Diameter of Condenser Tubes Based on Thermodynamic Objective Functions and an Economic Analysis
Entropy 2016, 18(12), 444; doi:10.3390/e18120444
Received: 1 October 2016 / Revised: 3 December 2016 / Accepted: 6 December 2016 / Published: 10 December 2016
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Abstract
The diameter and configuration of tubes are important design parameters of power condensers. If a proper tube diameter is applied during the design of a power unit, a high energy efficiency of the condenser itself can be achieved and the performance of the
[...] Read more.
The diameter and configuration of tubes are important design parameters of power condensers. If a proper tube diameter is applied during the design of a power unit, a high energy efficiency of the condenser itself can be achieved and the performance of the whole power generation unit can be improved. If a tube assembly is to be replaced, one should verify whether the chosen condenser tube diameter is correct. Using a diameter that is too large increases the heat transfer area, leading to over-dimensioning and higher costs of building the condenser. On the other hand, if the diameter is too small, water flows faster through the tubes, which results in larger flow resistance and larger pumping power of the cooling-water pump. Both simple and complex methods can be applied to determine the condenser tube diameter. The paper proposes a method of technical and economic optimisation taking into account the performance of a condenser, the low-pressure (LP) part of a turbine, and a cooling-water pump as well as the profit from electric power generation and costs of building the condenser and pumping cooling water. The results obtained by this method were compared with those provided by the following simpler methods: minimization of the entropy generation rate per unit length of a condenser tube (considering entropy generation due to heat transfer and resistance of cooling-water flow), minimization of the total entropy generation rate (considering entropy generation for the system comprising the LP part of the turbine, the condenser, and the cooling-water pump), and maximization of the power unit’s output. The proposed methods were used to verify diameters of tubes in power condensers in a200-MW and a 500-MW power units. Full article
(This article belongs to the Special Issue Entropy in Computational Fluid Dynamics)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Electro-Osmotic Flows in Varying-Section Channels
Author: Paolo Malgaretti
Affiliation: Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569 Stuttgart, Germany
Website: http://www.is.mpg.de/dietrich/malgaretti

Tentative title: Entropy Generation of Double Diffusive Forced Convection in Porous Channels with Thick Walls and Soret Effect
Authors: G.P. Peterson and Mohsen Torabi
Affiliation: The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA

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