A rigorous approach for characterising the limiting optimal efficiency of working fluids in organic Rankine cycles

González, Johan; Llovell, Fèlix; Garrido, José Matías; Quinteros-Lama, Héctor

doi:10.1016/j.energy.2022.124191

Cited by 7 publications

(6 citation statements)

References 49 publications

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“…The second scenario imposes the condition of a completely dry expansion after the turbine, where the limiting efficiency of the fluids is obtained. In this case, no other combination of temperature and pressures can provide a larger efficiency without regard to heat and head losses [ 22 ].…”

Section: Methodsmentioning

confidence: 99%

“…The problem of analytically obtaining and expressing the optimum operation of both the maximum efficiency and the maximum net power output of an ORC is reduced to describe the derivatives of each phase in operation. The details of the derivatives and their application of a generic equation of state are described in previous work [ 22 ]. The systematic comparison of both approaches yields a suitable range of pressure for the boiler.…”

Section: Methodsmentioning

confidence: 99%

“…The

-function represents the condenser and boiler temperature values for an ORC expanding from a saturated vapor from the boiler outlet to a saturated vapor in the turbine outlet. The above function represents an optimal condition of an ORC that reaches the global limit of the efficiency of a working fluid [ 22 ]. Similar to the

-function, the

-function represents the temperature values of the condenser and boiler for an ORC that expands from a saturated vapor from the boiler outlet until a saturated vapor in the turbine outlet with maximum net power output, determining an optimal condition of an ORC that reaches the limit of the net power output of a working fluid.…”

Section: Methodsmentioning

confidence: 99%

“…This work develops an accurate mathematical structure to determine the maximum net power of a single-stage ORC. The cited structure is compared with the maximum efficiency function [ 22 ] and the geometry of the saturated entropy curve [ 23 ]. The comparison sheds light on the correct methodologies to obtain the best ORC performance in different circumstances of operation.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of the Maximum Efficiency and the Maximum Net Power as Objective Functions for Organic Rankine Cycles Optimization

González

Garrido

Quinteros-Lama

2023

Entropy

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Maximum efficiency and maximum net power output are some of the most important goals to reach the optimal conditions of organic Rankine cycles. This work compares two objective functions, the maximum efficiency function, β, and the maximum net power output function, ω. The van der Waals and PC-SAFT equations of state are used to calculate the qualitative and quantitative behavior, respectively. The analysis is performed for a set of eight working fluids, considering hydrocarbons and fourth-generation refrigerants. The results show that the two objective functions and the maximum entropy point are excellent references for describing the optimal organic Rankine cycle conditions. These references enable attaining a zone where the optimal operating conditions of an organic Rankine cycle can be found for any working fluid. This zone corresponds to a temperature range determined by the boiler outlet temperature obtained by the maximum efficiency function, maximum net power output function, and maximum entropy point. This zone is named the optimal temperature range of the boiler in this work.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…The

-function, the

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Analysis of the Maximum Efficiency and the Maximum Net Power as Objective Functions for Organic Rankine Cycles Optimization

González

Garrido

Quinteros-Lama

2023

Entropy

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“…[12][13][14] Preferences may change the key factors slightly, yet fundamental properties influencing the outcomes are easily identifiable, regardless of the circumstances. Even though the optimum behavior of an ORC is not directly connected to the isentropic behavior of the fluids, 15 the shape of the saturated vapor line of the selected fluid in the T-s diagram plays an important role 16 when the purpose is to maximize the power output or when cycle efficiency is to be improved. 17,18 Namely directly affecting the layout and indirectly affecting the investment and operational costs.…”

mentioning

confidence: 99%

Simultaneous working fluid and expander selection method for reaching low‐threshold technology organic Rankine cycle (ORC) design

Groniewsky

Kustán

Imre

2023

Energy Science & Engineering

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Maximizing the utilization of an available source serves as the ideal approach, provided that only technical factors are considered. For sources with low heat flux, however, cost‐effective solutions are more suitable due to the minimal net power generated, regardless of the effectiveness of the energy conversion. In such cases, utilizing low‐threshold technology may be the most fitting solution, the layout of these cycles should be simple and inexpensive. In the case of organic Rankine cycles (ORCs)‐based power cycles, this means the omission of superheaters or recuperative heat exchangers and the use of simple expanders and small heat exchangers. Simplifying the design, however, requires additional considerations about the elementary steps of the cycle. This work presents a procedure to select favorable working fluids for ORC while considering the expander's internal efficiency. The criteria for favourability is to have a nonideal expansion process starting and ending in (or very near) saturated vapor states to avoid problems related to wetness/dryness between the given maximal and minimal expansion temperatures. It is demonstrated that the design can be simplified under the simultaneous working fluid and expander selection method presented in this study, regardless of the type and isentropic efficiency of the expander. The resulting methodology applies the novel classification of working fluids using the sequences of their characteristic points on temperature‐entropy space. The proposed approach is illustrated with a case study finding optimal working fluid for an ORC system fitted to industrial waste heat, a low‐temperature geothermal, and a cryogenic heat source.

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Wet-to-dry transition description in the mixture of working fluids

Ahmed,

Imre

2024

Discov Appl Sci

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The organic rankine cycle performance and some similar processes depend on many factors. One of them is the category of the working fluid, influencing the performance through the phase/phases during and at the end of the expansion process. Droplet formation for wet fluids and superheated for dry fluids motivated the researchers to seek isentropic working fluids, where expansion could proceed and terminate in a saturated vapour state. The shape of the T-s diagram is a material property; it cannot be changed for real pure fluids, but small jumps can be initiated by replacing one working fluid with a chemically very similar one, like Propane (a wet one) with Butane (a dry one). Our study presents a much smoother transition, using mixed working fluids prepared from chemically similar materials to obtain almost ideal zeotropic mixtures. The main point of our study is to show the wet-to-dry transition for mixtures and prove or disprove the existence of compositions where the fluid can show T-s diagram resembling the ones for ideal isentropic working fluids. For this purpose, Propane was mixed with other alkanes, such as Butane, Pentane, and Hexane, in various compositions, and the thermophysical properties of fluids were calculated by using the REFPROP software program. Wet-to-dry transitions were shown for the Propane/Hexane mixture at (0.6584 + 0.3416 mass fraction), while (0.5823 + 0.4177 mass fraction) and (0.6436 + 0.3564 mass fraction) was the transition mixture for Propane/Butane and Propane/Pentane respectively. Consequently, when exceeding the mentioned composition range, the fluids switch from wet to dry without forming a composition showing ideal isentropic properties. Therefore, isentropic working fluid (showing an infinite slope for the saturated vapour branch in a finite, nonzero temperature range) was not found during this transition.

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A rigorous approach for characterising the limiting optimal efficiency of working fluids in organic Rankine cycles

Cited by 7 publications

References 49 publications

Analysis of the Maximum Efficiency and the Maximum Net Power as Objective Functions for Organic Rankine Cycles Optimization

Analysis of the Maximum Efficiency and the Maximum Net Power as Objective Functions for Organic Rankine Cycles Optimization

Simultaneous working fluid and expander selection method for reaching low‐threshold technology organic Rankine cycle (ORC) design

Wet-to-dry transition description in the mixture of working fluids

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