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Shuai Deng - One of the best experts on this subject based on the ideXlab platform.
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A preliminary approach to the 3D construction of thermodynamic cycle based on zeotropic Working Fluids
Chinese Science Bulletin, 2018Co-Authors: Shuai DengAbstract:Thermodynamic cycle is one of the important ways to convert energy. Improving the efficiency of thermodynamic cycle is still an important way to promote the efficient use of energy at the present stage, and it is also the efficient way to solve the energy crisis. Organic Rankine cycle (ORC), with advantages of simple structure, less maintenance and possibility of small scales, has been widely applied for various types of source in recent years. In exiting researches, the Working fluid, as the "blood" of ORC, is commonly considered to play a vital role in the cycle: (1) relative to ideal cycle, the actual power cycles in the engineering field cannot operate without Working fluid; (2) energy efficiency, considering the analysis of second-law efficiency, of actual cycle has a significant decrease due to the introduction of Working fluid. The thermos-physical properties parameters, transport parameters and other parameters of Working fluid could directly affect the efficiency, safety, stability and economy of ORC. With the increasing requirements on Working Fluids, it is difficult to find a pure Working fluid not only with satisfied thermodynamic performance but also permissible environmental protection and safety. In contrast, zeotropic Working fluid, which is mixed with two or more pure Working Fluids, is easier to meet the requirements of thermos-physical properties, environmental and safety. But at the present stage, the application of zeotropic Working Fluids in ORC still adapts or employs the methodology originated from what we learn from pure Working Fluids, which leads to the fact that the efficiency of the ORC using zeotropic Working Fluids is still low. This paper takes the Working fluid as the starting point and uses the characteristics of the component shift to break the limitation of the thermodynamic cycle performance of the single circulating Working Fluids by adding the mixing and separation processes of zeotropic Working Fluids. Firstly, the 3D construction method of ORC is proposed by adding the dimensionality of the zeotropic component on the basis of the transmission temperature entropy analysis. Subsequently, the 3D ORC is compared with the traditional 2D ORC, and the advantages of 3D construction of thermodynamic cycle are clearly defined: (a) analysis of variable mass system; (b) reveal the thermodynamic process of composition regulation; (c) explore new ways to reduce the loss of exergy. At last, in view of the utilization of waste heat of internal combustion engine, a component adjustable ORC is proposed, and the application and function of the 3D construction method are expounded. The preliminary exploration results are given for the advantages of the thermodynamic cycle in 3D space relative to the traditional 2D construction method.
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a new understanding on thermal efficiency of organic rankine cycle cycle separation based on Working Fluids properties
Energy Conversion and Management, 2018Co-Authors: Yongzhen Wang, Qingsong An, Guibing Chen, Shuai Deng, Jun Zhao, Junaid AlviAbstract:Abstract The pivotal of organic Rankine cycle (ORC) promotion and optimization is revealing the thermodynamic relationship between cycle configuration, condition and its Working fluid properties. Different from the traditional numerical calculation method (TNCM) of ORC, a new thermodynamic cycle separating method (TCSM) is introduced in this paper. Then, efficiency of ORC is conducted expediently by TCSM where Triangle cycle ( η TC ), Carnot cycle ( η CC ) and Brayton cycle ( η BC ) efficiencies are regarded as variables, that is, η SORC = f ( η TC , η CC , η BC ) . When comparing with TNCM, TCSM not only has the acceptable precision for all the investigated 21 Working Fluids, but also the influence of critical temperature, molecular complexity of the Working fluid and superheat degree as well as the reduced operating conditions of ORC can be revealed qualitatively and quantitatively. Finally, three conclusions are revealed: (1) Relationship between ORC limited efficiency (the reduced evaporating temperature of 0.9) and critical temperature of Working fluid is revealed; (2) When superheat degree increases, ORC efficiency of dry fluid decreases and wet fluid increases linearly, while the variation of isotropic Working fluid remains constant; (3) If the reduced temperatures of two different Working Fluids are equal, the corresponding efficiencies are equal too. The proposed thermodynamic cycle separating method provides an approach for Working Fluids selection and performance prediction of ORC.
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The performance of thermodynamic cycles based on the properties of Working Fluids
Chinese Science Bulletin, 2017Co-Authors: Li Zhao, Shuai DengAbstract:With the increase of global energy demand, themodynamic cycles, such as Rankine cycle, refrigeration or heat pump, have been widely employed to generate work or transfer heat. Since these cycles generally consist of a linked sequence of state points with physical properties variables, the physical properties of Working fluid are essential to the cycle analysis. They directly determine the design of components, the cycle performance, the cycle stability and safety. However, in the thermodynamic analysis, the determination of cycle performance and the calculation of required physical properties are usually seperated. The thermodynamic peroperties of Working Fluids are often obtained from the complex experimental equations, so that the relationship between the cycle performance and the Working Fluids has not been established yet. What′s more, due to the fact that Carnot efficiency doesn′t contain detailed information on the properties of Working Fluids, a nature idea emerges how to derive the efficiency limit under the constraint of Working Fluids. Thus, in this work, the influences of thermodynamic properties on power cycles are investigated and the limiting efficiencys are proposed. In order to derive the cycle performances from the physical properties of Working Fluids, a general cubic equation of state is employed to obtain the residual properties, such as residual enthalpy, residual entropy and residual internal energy. Thereafter, on the basis of the properties of ideal gas, thermodynamic parameters of Working Fluids at any state are determined. According to the thermodynamic general relationships, the required heat is obtained for four classical processes, namely isochoric, isobaric, isothermal and isentropic processes. Based on the derived expressions, the output work and cycle efficiency are obtained for power cycles including Carnot cycle, Rankine cycle, Brayton cycle and Sterling cycle. The relationship between the cycle performance and the temperature, the properties of Working Fluids is developed. As a theoretical upper bound of cycle efficiency, Carnot efficiency is only determined by temperatures of heat source and sink. While the output work of Carnot cycle is a function of temperatures and the properties of Working Fluids. For other power cycles, it can be concluded that the thermodynamic performances are related with temperatures and Working Fluids, based on the derived expressions from cubic equation of state. Furthermore, compared with the Carnot efficiency under the same heat source and sink, the thermodynamic perfections of cycles are very low in practical engineering. Therefore, performance limits of thermodynamic cycles are investigated on the basis of the characteristics of Working Fluids in this paper. Limiting performance is derived from the equation of state and the temperature-entropy diagram of Working Fluids. For Rankine cycle and Brayton cycle, a maximum isobaric slope in the temperature-entropy diagram is employed to cut out the unexploited area from the enclosed area of Carnot cycle, so that the limiting work and efficiency can be obtained from the cycle areas. For Sterling cycle, when the used Working fluid is ideal gas, the cycle efficiency is equal to Carnot efficiency. Although the proposed limiting performance can not be achieved by practical cycles, it can provide some theoretical guidance for the operating condition and the optimal design of thermodynamic cycles.
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simultaneous Working Fluids design and cycle optimization for organic rankine cycle using group contribution model
Applied Energy, 2017Co-Authors: Li Zhao, Shuai DengAbstract:The performance of Organic Rankine Cycle (ORC) is significantly influenced by the used Working fluid and the operating condition. Consequently, this paper presents a systematic model for the efficient design of Working Fluids and the optimization of cycle parameters at the molecular scale, so that optimal Working Fluids can be identified by simultaneously considering cycle parameters, environmental and safety properties. In the proposed model, Working Fluids are generated via the combination of groups. The required properties, which consist of thermodynamic, environmental and safety properties, are estimated by the published group contribution methods. Based on these estimated properties, cycle optimizations are performed to obtain the optimal performance of Working Fluids using an ORC model. Thereafter, optimal Working Fluids are identified, according to the cycle parameters, environmental and safety properties. Furthermore, Working Fluids design and cycle optimization for an example are conducted to demonstrate the proposed model. The optimal candidates, namely R254eb, R254cb, are found for the considered example through proposed methodology. The novel Working Fluids, which are firstly reported in ORC applications, are worth being studied in-depth through time-consuming and expensive experiments.
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new knowledge on the temperature entropy saturation boundary slope of Working Fluids
Energy, 2017Co-Authors: Wen Su, Li Zhao, Shuai DengAbstract:The slope of temperature-entropy saturation boundary of Working Fluids has a significant effect on the thermodynamic performance of cycle processes. However, for the Working Fluids used in cycles, few studies have been conducted to analyze the saturated slope from the molecular structure and mixture composition. Thus, in this contribution, an analytical expression on the slope of saturated curve is obtained based on the highly accurate Helmholtz energy equation. 14 pure Working Fluids and three typical binary mixtures are employed to analyze the influence of molecular groups and mixture compositions on the saturated slope, according to the correlated parameters of Helmholtz energy equation. Based on the calculated results, a preliminary trend is demonstrated that with an increase of the number of molecular groups, the positive liquid slope of pure Fluids increases and the vapor slope appears positive sign in a narrow temperature range. Particularly, for the binary mixtures, the liquid slope is generally located between the corresponding pure Fluids', while the vapor slope can be infinity by mixing dry and wet Fluids ingeniously. It can be proved through the analysis of mixtures' saturated slope that three types of vapor slope could be obtained by regulating the mixture composition.
M De Paepe - One of the best experts on this subject based on the ideXlab platform.
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exergy analysis of zeotropic mixtures as Working Fluids in organic rankine cycles
Energy Conversion and Management, 2014Co-Authors: Steven Lecompte, Bernd Ameel, Davide Ziviani, M Van Den Broek, M De PaepeAbstract:Abstract The thermodynamic performance of non-superheated subcritical Organic Rankine Cycles (ORCs) with zeotropic mixtures as Working Fluids is examined based on a second law analysis. In a previous study, a mixture selection method based on a first law analysis was proposed. However, to assess the performance potential of zeotropic mixtures as Working Fluids the irreversibility distributions under different mixtures compositions are calculated. The zeotropic mixtures under study are: R245fa–pentane, R245fa–R365mfc, isopentane–isohexane, isopentane–cyclohexane, isopentane–isohexane, isobutane–isopentane and pentane–hexane. The second law efficiency, defined as the ratio of shaft power output and input heat carrier exergy, is used as optimization criterion. The results show that the evaporator accounts for the highest exergy loss. Still, the best performance is achieved when the condenser heat profiles are matched. An increase in second law efficiency in the range of 7.1% and 14.2% is obtained compared to pure Working Fluids. For a heat source of 150 °C, the second law efficiency of the pure Fluids is in the range of 26.7% and 29.1%. The second law efficiency in function of the heat carrier temperature between 120 °C and 160 °C shows an almost linear behavior for all investigated mixtures. Furthermore, between optimized ORCs with zeotropic mixtures as Working fluid the difference in second law efficiency varies less than 3 percentage points.
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second law analysis of zeotropic mixtures as Working Fluids in organic rankine cycles
26th International Conference on Efficiency Cost Optimization Simulation and Environmental Impact of Energy System (ECOS - 2013), 2013Co-Authors: Steven Lecompte, M Van Den Broek, M De PaepeAbstract:To improve the thermal performance of the basic organic Rankine cycle (ORC) several modifications are proposed in literature. One of these modifications is the use of zeotropic mixtures as Working Fluids. Zeotropic mixtures as Working Fluids have the ability to better match the heating (cooling) temperature profiles of the heat source (heat sink). As a result the irreversibilities associated with a finite temperature thermal heat transfer are reduced. In a previous study a first law mixture selection method was proposed, considering most of the commonly used hydrocarbons and siloxane substances as components in various mixture concentrations. This paper extends the previous study by comparing the basic ORC and the ORC with zeotropic mixtures as Working Fluids based on a second law analysis. The zeotropic mixtures under study are: R245fa-pentane, R245fa-R365mfc, isopentane-isohexane, isopentane-cyclohexane, isopentane-isohexane, isobutane-isopentane and pentane-hexane. The exergetic efficiency, defined as the ratio of shaft power output and input waste heat exergy, is used as optimization criterion. Furthermore, the irreversibilities associated with the different components of the ORC are assessed under different mixture compositions. Next, the optimization potential when using zeotropic mixtures is thoroughly discussed. The results show that the evaporator amounts for the highest exergy loss. However, the best performance is achieved when the condenser heat profiles are matched. A relative increase of exergetic efficiency between 7.1% and 14.2% is found for a waste heat source at 150 °C. The ORC with isobutane-isopentane as Working fluid has the highest second law efficiency (32.05%) under optimal mixture concentration and evaporation pressure.
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potential of zeotropic mixtures as Working Fluids in organic rankine cycles
Energy, 2012Co-Authors: Michael Chys, M Van Den Broek, Bruno Vanslambrouck, M De PaepeAbstract:The effect of using mixtures as Working Fluids in organic Rankine cycles (ORCs) is examined with a simulation model of the cycle that includes all elements of an actual installation. We consider several of the commonly used pure ORC Fluids as potential components, discuss a mixture selection method, and suggest optimal concentrations. For heat sources at 150 °C and 250 °C, a potential increase of 16% and 6% in cycle efficiency is found. The electricity production at optimal thermal power recuperation can be increased by 20% for the low temperature heat source.
Attila R. Imre - One of the best experts on this subject based on the ideXlab platform.
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A Simple Method of Finding New Dry and Isentropic Working Fluids for Organic Rankine Cycle
Energies, 2019Co-Authors: Gábor Györke, Axel Groniewsky, Attila R. ImreAbstract:One of the most crucial challenges of sustainable development is the use of low-temperature heat sources (60–200 °C), such as thermal solar, geothermal, biomass, or waste heat, for electricity production. Since conventional water-based thermodynamic cycles are not suitable in this temperature range or at least operate with very low efficiency, other Working Fluids need to be applied. Organic Rankine Cycle (ORC) uses organic Working Fluids, which results in higher thermal efficiency for low-temperature heat sources. Traditionally, new Working Fluids are found using a trial-and-error procedure through experience among chemically similar materials. This approach, however, carries a high risk of excluding the ideal Working fluid. Therefore, a new method and a simple rule of thumb—based on a correlation related to molar isochoric specific heat capacity of saturated vapor states—were developed. With the application of this thumb rule, novel isentropic and dry Working Fluids can be found applicable for given low-temperature heat sources. Additionally, the importance of molar quantities—usually ignored by energy engineers—was demonstrated.
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Novel classification of pure Working Fluids for Organic Rankine Cycle
Energy, 2018Co-Authors: Gábor Györke, Ulrich K. Deiters, Axel Groniewsky, Imre Lassu, Attila R. ImreAbstract:Abstract Power generation from low-temperature heat sources (80–300 °C) like thermal solar, geothermal, biomass or waste heat has been becoming more and more significant in the last few decades. Organic Rankine Cycle (ORC) uses organic Working Fluids, obtaining higher thermal efficiency than with water used in traditional Rankine Cycles, because of the physical (thermodynamic) properties of these Fluids. The traditional classification of pure (one-component) Working Fluids is based on the quality of the expanded vapour after an isentropic (adiabatic and reversible) expansion from saturated vapour state, and distinguishes merely three categories: wet, dry and isentropic Working Fluids. The purpose of this paper is to show the deficiencies of this traditional classification and to introduce novel categorisation mostly to help in finding the thermodynamically optimal Working fluid for a given heat source.
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description of wet to dry transition in model orc Working Fluids
Applied Thermal Engineering, 2017Co-Authors: Axel Groniewsky, Gábor Györke, Attila R. ImreAbstract:Abstract Conventional steam power cycles have their limitations on recovering low grade waste heat, therefore other alternatives are required in these cases. Organic Rankine Cycle (ORC) is suitable for power generation based on various heat sources including solar, geothermal, biomass or waste heat. ORC Working Fluids can be characterized as wet, dry or isentropic. The aim of this paper is to give a method to find novel dry or isentropic Working Fluids based on simple physical properties, like degree of freedom and isochoric heat capacity.
Ibrahim Dince - One of the best experts on this subject based on the ideXlab platform.
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comparative performance analysis of low temperature organic rankine cycle orc using pure and zeotropic Working Fluids
Applied Thermal Engineering, 2013Co-Authors: S Aghahosseini, Ibrahim DinceAbstract:In this paper, a comprehensive thermodynamic analysis of the low-grade heat source Organic Rankine Cycle (ORC) is conducted and the cycle performance is analyzed and compared for different pure and zeotropic-mixture Working Fluids. The comparative performance evaluation of the cycle using a combined energy and exergy analysis is carried out by sensitivity assessment of the cycle certain operating parameters such as efficiency, flow rate, irreversibility, and heat input requirement at various temperatures and pressures. The environmental characteristics of the Working Fluids such as toxicity, flammability, ODP and GWP are studied and the cycle CO2 emission is compared with different fuel combustion systems. R123, R245fa, R600a, R134a, R407c, and R404a are considered as the potential Working Fluids. Results from this analysis provide valuable insight into selection of the most suitable Working Fluids for power generating application at different operating conditions with a minimal environmental impact.
Weifeng He - One of the best experts on this subject based on the ideXlab platform.
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thermal matching performance of a geothermal orc system using zeotropic Working Fluids
Renewable Energy, 2015Co-Authors: Wenhao Pu, Weifeng HeAbstract:The thermal matching performance analysis is conducted for a geothermal organic Rankine cycle system using zeotropic mixtures as Working Fluids. The constant isentropic efficiency is replaced by internal efficiency of an axial flow turbine with given size for each condition, and the zeotropic mixtures of isobutane and isopentane is used as Working Fluids of the organic Rankine cycle, in order to improve thermal match in evaporator and condenser. The results showed the use of zeotropic mixtures leads to the prominent thermodynamic first law and second law efficiencies, especially at high minimum temperature difference in evaporator (Δt1), and there exists an optimal thermal performance at some certain mole fraction of isopentane in zeotropic mixtures (x) and Δt1. The geothermal organic Rankine cycle with x of 0.2 and Δt1 of 16 K shows the maximal thermodynamic first law and second law efficiency in this research. The geothermal organic Rankine cycle system using zeotropic mixtures shows the optimal overall thermal performance at some certain x, which is not necessary to be the point with the maximal temperature glide. The use of zeotropic mixtures is not always lead to a high thermal to electricity efficiency compared to the pure Working fluid, and its overall net power output of PORC is even lower than the pure Working Fluids compositions at some certain x.
