Thermodynamic optimization of tree-shaped flow geometries

Zimparov, Ventsislav D.; Silva, A.K. da; Bejan, Adrian

doi:10.1016/j.ijheatmasstransfer.2005.11.016

Cited by 62 publications

(31 citation statements)

References 17 publications

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“…Entropy generation minimisation (EGM) has been used in various internal flow optimisation studies such as: the optimum tube diameter or Reynolds number for a tube [4,6]; the optimal Reynolds number for single-phase, fully developed, laminar and turbulent flow with constant heat flux [20]; and the optimum channel geometries with constant wall temperature or constant heat flux [21][22][23]. A rectangular channel with aspect ratio of eight, gives the minimum entropy generation in laminar flow and turbulent flow according to Ratts and Raut [20].…”

Section: Introductionmentioning

confidence: 99%

“…Various authors have emphasised the importance of the optimisation of the global performance of a system, by minimising the sum of the irreversibilities from all the different components or processes of the system (spreading the entropy generation rate through the system by optimally sizing the hardware, instead of optimising components individually) [6,9,21,23,28,30,39]. For the open and direct solar thermal Brayton cycle, an optimisation of this kind is not available from the literature.…”

Section: Introductionmentioning

confidence: 99%

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Thermodynamic optimisation of the integrated design of a small-scale solar thermal Brayton cycle

Roux

Bello‐Ochende

Meyer

2011

Int. J. Energy Res.

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SUMMARYThe Brayton cycle's heat source does not need to be from combustion but can be extracted from solar energy. When a black cavity receiver is mounted at the focus of a parabolic dish concentrator, the reflected light is absorbed and converted into a heat source. The second law of thermodynamics and entropy generation minimisation are applied to optimise the geometries of the recuperator and receiver. The irreversibilities in the recuperative solar thermal Brayton cycle are mainly due to heat transfer across a finite temperature difference and fluid friction. In a small-scale open and direct solar thermal Brayton cycle with a micro-turbine operating at its highest compressor efficiency, the geometries of a cavity receiver and counterflow-plated recuperator can be optimised in such a way that the system produces maximum net power output. A modified cavity receiver is used in the analysis, and parabolic dish concentrator diameters of six to 18 metres are considered. Two cavity construction methods are compared. Results show that the maximum thermal efficiency of the system is a function of the solar concentrator diameter and choice of micro-turbine. The optimum receiver tube diameter is relatively large when compared with the receiver size. The optimum recuperator channel aspect ratio for the highest maximum net power output of a micro-turbine is a linear function of the system mass flow rate for a constant recuperator height. For a system operating at a relatively small mass flow rate, with a specific concentrator size, the optimum recuperator length is small. For the systems with the highest maximum net power output, the irreversibilities are spread throughout the system in such a way that the internal irreversibility rate is almost three times the external irreversibility rate.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Thermodynamic optimisation of the integrated design of a small-scale solar thermal Brayton cycle

Roux

Bello‐Ochende

Meyer

2011

Int. J. Energy Res.

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“…Various studies have stressed the significance of the optimisation of the global performance of a system, by minimising the sum of the irreversibilities from all the different components or processes of the system (distributing the entropy generation rate through the system by optimally sizing the hardware, instead of optimising components independently) [1,17,18,38,108,121,122]. For future work it is recommended that geometry optimisation studies be done on especially intercoolers and reheaters (a second solar receiver) in the solar thermal Brayton cycle, as the inclusion of these components can largely increase the efficiency of such a system.…”

Section: Other Entropy Generation Mechanismsmentioning

confidence: 99%

A review on the thermodynamic optimisation and modelling of the solar thermal Brayton cycle

Roux

Bello‐Ochende

Meyer

2013

Renewable and Sustainable Energy Reviews

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Many studies have been published on the performance and optimisation of the Brayton cycle and solar thermal Brayton cycle showing the potential, merits and challenges of this technology. Solar thermal Brayton systems have potential to be used as power plants in many sun-drenched countries. It can be very competitive in terms of efficiency, cost and environmental impact. When designing a system such as a recuperative Brayton cycle there is always a compromise between allowing effective heat transfer and keeping pressure losses in components small. The high temperatures required in especially the receiver of the system presents a challenge in terms of irreversibilities due to heat loss. In this paper, the authors recommend the use of the total entropy generation minimisation method. This method can be applied for the modelling of a system and can serve as validation when compared with first-law modelling. The authors review various modelling perspectives required to develop an objective function for solar thermal power optimisation, including modelling of the sun as an exergy source, the Gouy-Stodola theorem and turbine modelling.With recommendations, the authors of this paper wish to clarify and simplify the optimisation and modelling of the solar thermal Brayton cycle for future work. The work is applicable to solar thermal studies in general but focuses on the small-scale recuperated solar thermal Brayton cycle.2

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“…In particular, there are several research works of Constructal Law on heat exchangers [4][5][6][7][8][9][10] and on the optimal shaping of fins with application to heat exchangers [11].…”

Section: Introductionmentioning

confidence: 99%

Constructal law optimization of a boiler

Gulotta¹,

Guarino²,

Cellura³

et al. 2017

IJHT

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The paper aims at the optimization of the design of a biomass boiler under the inspiration of the Constructal Law by Bejan. The boiler is of the smoke tubes typology, fuel being biomass pellets. The smoke tubes are 16 and are placed in a staggered configuration. A model is built in MATLAB environment, based on empirical correlations and the mean log temperature methodology. The analysis is based on the development of a wide parametric analysis that involves variations of diameters, numbers and positioning of the tubes. Results are based on the concept of the overall performance coefficient methodology and investigate both the pressure drops variation and the thermal power generated in the different configurations' boiler. However, since the aim of the boiler is to guarantee a fixed thermal power output to the users, results are also presented by fixing the thermal power output and adding as variable the volume of tubes adopted as an indicator to quantify materials required to achieve the same output. While from the point of view of pressure losses there is a clear best solution, this is not the case if the material uses minimization and pressure drops minimization are jointly analyzed. This leads to the need to a trade-off in performance to identify a best case.

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Thermodynamic optimization of tree-shaped flow geometries

Cited by 62 publications

References 17 publications

Thermodynamic optimisation of the integrated design of a small-scale solar thermal Brayton cycle

Thermodynamic optimisation of the integrated design of a small-scale solar thermal Brayton cycle

A review on the thermodynamic optimisation and modelling of the solar thermal Brayton cycle

Constructal law optimization of a boiler

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