Publications
54 results found
White M, Oyewunmi OA, Haslam A, et al., 2017, Incorporating Computer-Aided Working-Fluid Design in the System Optimisation of an Organic Rankine Cycle Using the SAFT-γ Mie Equation of State, SAFT 2017 Conference
White MT, Oyewunmi OA, Haslam AJ, et al., 2017, High-efficiency industrial waste-heat recovery through computer-aided integrated working-fluid and ORC system optimisation, The 4th Sustainable Thermal Energy Management International Conference (SusTEM 2017)
In this paper, we develop a mixed-integer non-linear programming optimisation framework that combines working-fluid thermodynamic property predictions from a group-contribution equation of state, SAFT- Mie, with a thermodynamic description of an organic Rankine cycle. In this model, a number of working-fluids are described by their constituent functional groups (i.e., -CH3, -CH2, etc.), and integer optimisation variables are introduced in the description of the structure of the working-fluid. This facilitates combining the computer-aided molecular design of novel working-fluids with the power system optimisation into a single framework, thus removing subjective and pre-emptive screening criteria, and simultaneously moving towards the next generation of tailored working-fluids and optimised organic Rankine cycle systems for industrial waste-heat recovery applications. The thermodynamic model is first validated against an alternative formulation that uses (pseudo-experimental) thermodynamic property predictions from REFPROP, and against an optimisation study taken from the literature. Furthermore, molecular feasibility constraints are defined and validated in order to ensure all feasible working-fluid candidates can be found. Finally, the optimisation problem is formulated using the functional groups from the hydrocarbon family, and applied to three industrial waste-heat recovery case studies. The results demonstrate the potential of this framework to drive the search for the next generation of organic Rankine cycles, and to provide meaningful insights into which working-fluids are the optimal choices for a targeted application.
Oyewunmi OA, Kirmse CJW, Markides CN, 2016, HEAT EXCHANGER ANALYSIS OF AZEOTROPE MIXTURES IN ORGANIC RANKINE CYCLES, UK Heat Transfer Conference
Oyewunmi OA, Simó Ferré-Serres, Steven Lecompte, et al., 2016, An assessment of subcritical and trans-critical organic Rankine cycles for waste-heat recovery, The 8th International Conference on Applied Energy – ICAE2016, Publisher: Elsevier, ISSN: 1876-6102
Organic Rankine cycle (ORC) systems are increasingly being deployed for waste-heat recovery and conversion in industrial settings. Using a case study of an exhaust flue-gas streamat a temperature of 380 °C as the heat source, an ORC system power output in excess of 10MW is predicted at exergy efficiencies ranging between 20% and 35%. By comparison with available experimental data, the thermodynamic properties (including those in the supercritical region) of working fluids are shown to be reliably predicted by the SAFT-VR Mie equation of state; this verification is quite important as this is the first time that the SAFT-VR Mie equation of state is used forthermodynamic property predictionof working fluids in their supercriticalstateintrans-critical ORC systems.Various cycle configurations and the use of working-fluid mixtures are also investigated. ORC systems operating on trans-critical cycles and those incorporating an internal heat exchanger(IHE)are seen to be beneficial from a thermodynamic perspective, they are,however,more expensive than the simpleORC system considered (subcritical cycle with no IHE).Furthermore, ORC systems using pure working fluids are associated withslightly lower costs than those with fluid mixtures. It is concluded thatabasicORCsystem utilizingpure working fluidsshowsthe lowest specific investment cost(SIC)in the case study considered.
Lecompte S, Oyewunmi OA, Markides C, et al., 2016, Preliminary experimental results of an 11 kWe organic Rankine cycle, The 8th International Conference on Applied Energy – ICAE2016, Publisher: Elsevier, ISSN: 1876-6102
The organic Rankine cycle(ORC)is considered a viable technology forconvertinglow-and medium-temperature heat to electricity. However,many of ORC systems in practical applications operate in off-design conditions. In order to characterize thisoperation, experimental data is needed. In this paper, the commissioning of an 11 kWe ORC is described with special attention to the processingof the data. A filtering algorithm is introduced to isolate steady-state working points. This filter is thenappliedtothe raw experimental data. In addition,the reliability of the experimental data is evaluated by investigating the heat balancesover the heat exchangers and error propagation of the measurementuncertainties. The result of this work is a test-setup which is fully ready for high-accuracyand reliablemeasurements,including the post-processingsteps. In the future, off-design models will be validatedwith the acquired experimental dataand especially two-phase expansion will be further investigated.
White MT, Oyewunmi OA, Haslam AJ, et al., 2016, Integrated working-fluid design and ORC system optimisation for waste-heat recovery using CAMD and the SAFT-γ Mie equation of state, 3rd Annual Engine ORC Consortium Workshop
Freeman J, Guarracino I, Unamba CK, et al., 2016, Developing a test bed for small-scale ORC expanders in waste-heat recovery applications, 3rd Annual Engine ORC Consortium Workshop
Oyewunmi OA, Ferré-Serres S, Markides C, 2016, Supercritical organic Rankine cycles in waste-heat recovery using SAFT-VR Mie, 3rd International Meeting of Specialists on Heat Transfer and Fluid Dynamics at Supercritical Pressure (HFSCP2016)
Kirmse CJW, Oyewunmi, Taleb A, et al., 2016, A two-phase single-reciprocating-piston heat conversion engine: Non-linear dynamic modelling, Applied Energy, Vol: 186, Pages: 359-375, ISSN: 0306-2619
A non-linear dynamic framework is presented for the modelling of a novel two-phase heat engine termed ‘Up-THERM’, which features a single solid moving-part (piston). When applied across the device, a constant temperature difference between an external (low- to medium-grade) heat source and an external heat sink is converted into sustained and persistent oscillations of pressure and volumetric fluid displacement. These oscillations are transformed in a load arrangement into a unidirectional flow from which power is extracted by a hydraulic motor. The Up-THERM engine is modelled using a system of first-order differential equations that describe the dominant thermal/fluid processes in each component of the device. For certain components where the deviations from a linear approximation are non-negligible (gas spring in the displacer cylinder, check valves and piston valve, and heat exchangers), a non-linear description is employed. A comparison between the linear and non-linear descriptions of the gas spring at the top of the displacer cylinder reveals that the non-linear description results in more realistic predictions of the oscillation frequency compared to experimental data from a similar device. Furthermore, the shape of the temperature profile over the heat-exchanger surfaces is modelled as following a hyperbolic tangent function, based on findings from an experimental investigation. Following the validation of these important device components, a parametric study is performed on the Up-THERM engine model with the aforementioned non-linear component descriptions, aimed at investigating the effects of important geometric parameters and of the heat-source temperature on key performance indicators, namely the oscillation frequency, power output and exergy efficiency of the engine. The results indicate that the geometric design of the displacer cylinder, including the height of the gas spring at the top of the cylinder, and the heat-source temperature hav
Kirmse CJW, Oyewunmi OA, Haslam AJ, et al., 2016, Comparison of a novel organic-fluid thermofluidic heat converter and an organic Rankine cycle heat engine, Energies, Vol: 9, ISSN: 1996-1073
The Up-THERM heat converter is an unsteady, two-phase thermofluidic oscillator that employs an organic working fluid, which is currently being considered as a prime-mover in small- to medium-scale combined heat and power (CHP) applications. In this paper, the Up-THERM heat converter is compared to a basic (sub-critical, non-regenerative) organic Rankine cycle (ORC) heat engine with respect to their power outputs, thermal efficiencies and exergy efficiencies, as well as their capital and specific costs. The study focuses on a pre-specified Up-THERM design in a selected application, a heat-source temperature range from 210 °C to 500 °C and five different working fluids (three n-alkanes and two refrigerants). A modeling methodology is developed that allows the above thermo-economic performance indicators to be estimated for the two power-generation systems. For the chosen applications, the power output of the ORC engine is generally higher than that of the Up-THERM heat converter. However, the capital costs of the Up-THERM heat converter are lower than those of the ORC engine. Although the specific costs (£/kW) of the ORC engine are lower than those of the Up-THERM converter at low heat-source temperatures, the two systems become progressively comparable at higher temperatures, with the Up-THERM heat converter attaining a considerably lower specific cost at the highest heat-source temperatures considered.
Oyewunmi OA, Kirmse CJW, Haslam AJ, et al., 2016, Working-fluid selection and performance investigation of a two-phase single-reciprocating-piston heat-conversion engine, Applied Energy, Vol: 186, Pages: 376-395, ISSN: 0306-2619
We employ a validated first-order lumped dynamic model of the Up-THERM converter, a two-phase unsteadyheat-engine that belongs to a class of innovative devices known as thermofluidic oscillators, which containfewer moving parts than conventional engines and represent an attractive alternative for remote or off-gridpower generation as well as waste-heat recovery. We investigate the performance the Up-THERM withrespect to working-fluid selection for its prospective applications. An examination of relevant working-fluidthermodynamic properties reveals that the saturation pressure and vapour-phase density of the fluid play importantroles in determining the performance of the Up-THERM – the device delivers a higher power outputat high saturation pressures and has higher exergy efficiencies at low vapour-phase densities. Furthermore,working fluids with low critical temperatures, high critical pressures and exhibiting high values of reducedpressures and temperatures result in designs with high power outputs. For a nominal Up-THERM designcorresponding to a target application with a heat-source temperature of 360 ◦C, water is compared withforty-five other pure working fluids. When maximizing the power output, R113 is identified as the optimalfluid, followed by i-hexane. Fluids such as siloxanes and heavier hydrocarbons are found to maximize theexergy and thermal efficiencies. The ability of the Up-THERM to convert heat over a range of heat-sourcetemperatures is also investigated, and it is found that the device can deliver in excess of 10 kW when utilizingthermal energy at temperatures above 200 ◦C. Of all the working fluids considered here, ammonia, R245ca,R32, propene and butane feature prominently as optimal and versatile fluids delivering high power over awide range of heat-source temperatures.
Oyewunmi OA, Markides C, 2016, Thermo-Economic and Heat Transfer Optimization of Working-Fluid Mixtures in a Low-Temperature Organic Rankine Cycle System, Energies, Vol: 9, ISSN: 1996-1073
In the present paper, we consider the employment of working-fluid mixtures in organicRankine cycle (ORC) systems with respect to thermodynamic and heat-transfer performance,component sizing and capital costs. The selected working-fluid mixtures promise reduced exergylosses due to their non-isothermal phase-change behaviour, and thus improved cycle efficienciesand power outputs over their respective pure-fluid components. A multi-objective cost-poweroptimization of a specific low-temperature ORC system (operating with geothermal water at 98 ◦C)reveals that the use of working-fluid-mixtures does indeed show a thermodynamic improvementover the pure-fluids. At the same time, heat transfer and cost analyses, however, suggest that it alsorequires larger evaporators, condensers and expanders; thus, the resulting ORC systems are alsoassociated with higher costs. In particular, 50% n-pentane + 50% n-hexane and 60% R-245fa + 40%R-227ea mixtures lead to the thermodynamically optimal cycles, whereas pure n-pentane and pureR-245fa have lower plant costs, both estimated as having ∼14% lower costs per unit power outputcompared to the thermodynamically optimal mixtures. These conclusions highlight the importanceof using system cost minimization as a design objective for ORC plants.
Kirmse CJW, Oyewunmi OA, Haslam AJ, et al., 2016, A thermo-economic assessment and comparison of the Up-THERM heat converter and an organic Rankine cycle engine, Heat Powered Cycles Conference 2016
In this paper we present a thermodynamic and economic comparison of a recently proposed two-phasethermofluidic oscillator known as the Up-THERM heat converter and the more established organic Rankine cycle(ORC) engine, when converting heat at temperatures below 150 °C using the refrigerant R-227ea as the workingfluid. The Up-THERM heat converter is being considered as a possible prime mover for small- to medium-scalecombined heat and power (CHP) applications. Using suitable thermodynamic models of both systems, it is foundthat the power output and thermal efficiencies of a pre-specified Up-THERM design are generally lower thanthose of an equivalent ORC engine. The Up-THERM, however, also demonstrates higher exergy efficiencies andis associated with lower capital costs, as expected owing to its simple construction and use of fewer and morebasic components. Interestingly, the specific costs (per rated kW) of the ORC engine are lower than those of theUp-THERM converter at lower heat source temperatures, specifically below 130 °C, whereas the Up-THERMbecomes a more cost effective alternative (in terms of the specific cost) to the ORC engine at higher temperatures.
Kirmse CJW, Oyewunmi OA, Haslam A, et al., 2016, A THERMO-ECONOMIC COMPARISON OF THE UP-THERM HEAT CONVERTER AND AN ORGANIC RANKINE CYCLE HEAT ENGINE, 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics
In this paper we compare a recently proposed two-phase thermofluidicoscillator device termed ‘Up-THERM’ to a basic(sub-critical, non-regenerative) equivalent organic Rankine cycle(ORC) engine. In the Up-THERM heat converter, a constanttemperature difference imposed by an external heat source andsink leads to periodic evaporation and condensation of the workingfluid, which gives rise to sustained oscillations of pressureand volumetric displacement. These oscillations are convertedin a load arrangement into a unidirectional flow, which passesthrough a hydraulic motor that extracts useful work from the device.A pre-specified Up-THERM design is being considered in aselected application with two n-alkanes, n-hexane and n-heptane,as potential working fluids. One aim of this work is to evaluatethe potential of this proposed design. The thermodynamic comparisonshows that the ORC engine outperforms the Up-THERMheat converter in terms of power output and thermal efficiency,as expected. An economic comparison, however, reveals that thecapital costs of the Up-THERM are lower than those of the ORCengine. Nevertheless, the specific costs (per unit power) favourthe ORC engine due to its higher power output. Some aspects ofthe proposed Up-THERM design are identified for improvement
Oyewunmi OA, Kirmse CJW, Pantaleo AM, et al., 2016, Performance of working-fluid mixtures in an ORC-CHP system for different heat demand segments, 29th international conference on Efficiency, Cost, Optimisation, Simulation and Environmental Impact of Energy Systems
Organic Rankine cycle (ORC) power systems are being increasingly deployed for waste heat recovery andconversion to power in several industrial settings. In the present paper, we investigate the use of working-fluidmixtures in ORC systems operating in combined heat and power mode (ORC-CHP) with shaft power providedby the expander/turbine and heating provided by the cooling-water exiting the condenser. The waste-heatsource is a flue gas stream from a refinery boiler with a mass flow rate of 560 kg/s and an inlet temperature of330 °C. When using working fluids comprising normal alkanes, refrigerants and their subsequent mixtures, theORC-CHP system is demonstrated as being capable of delivering over 20 MW of net shaft power and up to15 MW of heating, leading to a fuel energy savings ratio (FESR) in excess of 20%. Single-component workingfluids such as pentane appear optimal at low hot-water supply temperatures, and fluid mixtures becomeoptimal at higher temperatures, with the combination of octane and pentane giving an ORC-CHP systemdesign with the highest efficiency. The influence of heat demand intensity on the global system conversionefficiency and optimal working fluid selection is also explored.
Oyewunmi OA, Kirmse CJW, Markides CN, 2016, Performance of working-fluid mixtures in an ORC-CHP system for waste-heat recovery
Organic Rankine cycle (ORC) power systems are being increasingly deployed for waste heat recovery and conversion to power in several industrial settings. In the present paper, we investigate the deployment of working-fluid mixtures in ORCs operating in combined heat and power mode (ORC-CHP) with shaft power provided by the expanding working fluid and heating provided by the cooling-water exiting the ORC condenser. Using the flue gas from a refinery boiler as the waste-heat source and with working fluids comprising normal alkanes, refrigerants and their subsequent mixtures, the ORC-CHP system is demonstrated as being capable of delivering over 20 MW of net shaft power and up to 15 MW of heating, leading to a fuel energy savings ratio (FESR) in excess of 20%. Single-component working fluids such as pentane appear to be optimal at low hot-water supply temperatures. Working-fluid mixtures become optimal at higher temperatures, with the working-fluid mixture combination of octane and pentane giving an ORC-CHP system design with the highest efficiency.
Oyewunmi OA, Kirmse CJW, Markides CN, 2016, Performance of working-fluid mixtures in an ORC-CHP system for waste-heat recovery
© 2016 University of Ljubljana. Organic Rankine cycle (ORC) power systems are being increasingly deployed for waste heat recovery and conversion to power in several industrial settings. In the present paper, we investigate the deployment of working-fluid mixtures in ORCs operating in combined heat and power mode (ORC-CHP) with shaft power provided by the expanding working fluid and heating provided by the cooling-water exiting the ORC condenser. Using the flue gas from a refinery boiler as the waste-heat source and with working fluids comprising normal alkanes, refrigerants and their subsequent mixtures, the ORC-CHP system is demonstrated as being capable of delivering over 20 MW of net shaft power and up to 15 MW of heating, leading to a fuel energy savings ratio (FESR) in excess of 20%. Single-component working fluids such as pentane appear to be optimal at low hot-water supply temperatures. Working-fluid mixtures become optimal at higher temperatures, with the working-fluid mixture combination of octane and pentane giving an ORC-CHP system design with the highest efficiency.
Oyewunmi OA, Markides CN, 2015, EFFECT OF WORKING-FLUID MIXTURES ON ORGANIC RANKINE CYCLE SYSTEMS: HEAT TRANSFER AND COST ANALYSIS, 3RD International Seminar on ORC Power Systems, Publisher: University of Liège and Ghent University
The present paper considers the employment of working-fluid mixtures in organic Rankine cycle (ORC)systems with respect to heat transfer performance, component sizing and costs, using two sets of fluidmixtures: n-pentane + n-hexane and R-245fa + R-227ea. Due to their non-isothermal phase-change behaviour,these zeotropic working-fluid mixtures promise reduced exergy losses, and thus improved cycleefficiencies and power outputs over their respective pure-fluid components. Although the fluid-mixturecycles do indeed show a thermodynamic improvement over the pure-fluid cycles, the heat transfer andcost analyses reveal that they require larger evaporators, condensers and expanders; thus, the resultingORC systems are also associated with higher costs, leading to possible compromises. In particular,70 mol% n-pentane + 30 mol% n-hexane and equimolar R-245fa + R-227ea mixtures lead to the thermodynamicallyoptimal cycles, whereas pure n-pentane and pure R-227ea have lower costs amounting to14% and 5% per unit power output over the thermodynamically optimal mixtures, respectively.
Oyewunmi OA, Taleb A, Haslam A, et al., 2015, On the use of SAFT-VR Mie for assessing large-glide fluorocarbon working-fluid mixtures in organic rankine cycles, Applied Energy, Vol: 163, Pages: 263-282, ISSN: 1872-9118
By employing the SAFT-VR Mie equation of state, molecular-based models are developed from which the thermodynamic properties of pure (i.e., single-component) organic fluids and their mixtures are calculated. This approach can enable the selection of optimal working fluids in organic Rankine cycle (ORC) applications, even in cases for which experimental data relating to mixture properties are not available. After developing models for perfluoroalkane (n-C4F10 + n-C10F22) mixtures, and validating these against available experimental data, SAFT-VR Mie is shown to predict accurately both the single-phase and saturation properties of these fluids. In particular, second-derivative properties (e.g., specific heat capacities), which are less reliably calculated by cubic equations of state (EoS), are accurately described using SAFT-VR Mie, thereby enabling an accurate prediction of important working-fluid properties such as the specific entropy. The property data are then used in thermodynamic cycle analyses for the evaluation of ORC performance and cost. The approach is applied to a specific case study in which a sub-critical, non-regenerative ORC system recovers and converts waste-heat from a refinery flue-gas stream with fixed, predefined conditions. Results are compared with those obtained when employing analogue alkane mixtures (n-C4H10 + n-C10H22) for which sufficient thermodynamic property data exist. When unlimited quantities of cooling water are utilized, pure perfluorobutane (and pure butane) cycles exhibit higher power outputs and higher thermal efficiencies compared to mixtures with perfluorodecane (or decane), respectively. The effect of the composition of a working-fluid mixture in the aforementioned performance indicators is non-trivial. Only at low evaporator pressures (< 10 bar) do the investigated mixtures perform better than the pure fluids. A basic cost analysis reveals that systems with pure perfluorobutane (and butane) fluids are associated with rela
Kirmse C, Oyewunmi OA, Haslam AJ, et al., 2015, A two-phase single-reciprocating-piston heat conversion engine, 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics (HEFAT2015)
This paper considers an energy-conversion heat-engineconcept termed ‘Up-THERM’. This machine is capable ofconverting low- to medium-grade heat to useful positivedisplacementwork through the periodic evaporation andcondensation of a working fluid in an enclosed space. Thesealternating phase-change processes drive sustained oscillations ofthermodynamic properties (pressure, temperature, volume) as theworking fluid undergoes an unsteady thermodynamic heatenginecycle. The resulting oscillatory flow of the working fluidis converted into a unidirectional flow in a hydraulic loadarrangement where power can be extracted from the machine.The engine is described with lumped dynamic modelsconstructed using electrical analogies founded on previouslydeveloped thermoacoustic and thermofluidic principles, whichare extended here to include a description of the phase-changeheat-transfer processes. For some sub-components of the engine,such as the gas spring, valves and the temperature profile in theheat exchangers, deviations from the linear theory are nonnegligible.These are modelled using non-linear descriptions. Inparticular, the results of linear and non-linear descriptions of thegas spring are compared using three important performanceindicators — efficiency, power output and frequency.The non-linear description of the gas spring results in morerealisticpredictions of the oscillation frequency compared todirect measurements on an experimental prototype of a similarengine. Owing to its mode of operation and lack of moving parts,the Up-THERM engine does offer a much simpler and morecost-efficient solution than alternative engines for heat recoveryand solar applications. The results from this work suggest thatthis technology can be a competitive alternative in terms of costper unit power in low-power, small-scale applications, especiallyin remote, off-grid settings, for example in developing countrieswhere minimising upfront costs is crucial.
Oyewunmi OA, Haslam AJ, Markides CN, 2015, Towards the computer-aided molecular design of organic rankine cycle systems with advanced fluid theories, SusTEM 2015 International Conference, Pages: 180-189
Organic Rankine cycle (ORC) power-generation systems are increasingly being deployed for heat recovery and conversion from geothermal reservoirs and in several industrial settings. Using a case study of an exhaust flue-gas stream, an ORC power output in excess of 20 MW is predicted at thermal efficiencies ranging between 5% and 15%. The considerable influence on cycle performance of the choice of the working fluid is illustrated with alkane and perfluoroalkane systems modelled using the SAFT-VR Mie equation of state (EoS); in general, the more-volatile pure components (n-butane or n-perfluorobutane) are preferred although some mixtures perform better at restricted cycle conditions.The development of computer-aided molecular design (CAMD) platforms for ORC systems requires both cycle and working-fluid models to be incorporated into a single framework, for the purposes of whole-system design and optimization. Using pure alkanes and their mixtures as a case study, we test the suitability of the recent group-contribution SAFT- Mie EoS method for describing the thermodynamic properties of working fluids relevant to the analysis of ORC systems. The theory is shown to predict accurately the relevant properties of these fluids, thereby suggesting that this SAFT-based CAMD approach is a promising approach towards working-fluid design of ORC power systems.
Kirmse C, Taleb AJ, Oyewunmi OA, et al., 2015, Performance comparison of a novel thermofluidic organic-fluid heat converter and an organic rankine cycle heat engine, 3rd International Seminar on ORC Power Systems (ASME ORC 2015)
The Up-THERM engine is a novel two-phase heat engine with a single moving part–a vertical solidpiston–that relies on the phase change of a suitable working fluid to produce a reciprocating displacementand sustained thermodynamic oscillations of pressure and flow rate that can be converted to useful work.A model of the Up-THERM engine is developed via lumped dynamic descriptions of the various enginesub-components and electrical analogies founded on previously developed thermoacoustic principles.These are extended here to include a description of phase change and non-linear descriptions of selectedprocesses. The predicted first and second law efficiencies and the power output of a particular Up-THERM engine design aimed for operation in a specified CHP application with heat source and sinktemperatures of 360 ○C and 10 ○C, are compared theoretically to those of equivalent sub-critical, nonregenerativeorganic Rankine cycle (ORC) engines. Five alkanes (from n-pentane to n-nonane) are beingconsidered as possible working fluids for the aforementioned Up-THERM application, and these arealso used for the accompanying ORC thermodynamic analyses. Owing to its mode of operation, lackof moving parts and dynamic seals, the Up-THERM engine promises a simpler and more cost-effectivesolution than an ORC engine, although the Up-THERM is expected to be less efficient than its ORCcounterpart. These expectations are confirmed in the present work, with the Up-THERM engine showinglower efficiencies and power outputs than equivalent ORC engines, but which actually approach ORCperformance at low temperatures. Therefore, it is suggested that the Up-THERM can be a competitivealternative in terms of cost per unit power in low-power/temperature applications, especially in remote,off-grid settings, such as in developing countries where minimising upfront costs is crucial.
Oyewunmi OA, Taleb AI, Haslam AJ, et al., 2014, An assessment of working-fluid mixtures using SAFT-VR Mie for use in organic Rankine cycle systems for waste-heat recovery, Computational Thermal Sciences, Vol: 6, Pages: 301-316, ISSN: 1940-2503
© 2014 by Begell House, Inc. Working-fluid mixtures offer an improved thermal match to heat source streams in organic Rankine cycles (ORCs) over pure (single) fluids. In the present work we investigate the selection of working-fluid mixtures and component mixing ratios for an ORC system from a thermodynamic and economic point of view. A mathematical model of a subcritical, nonregenerative ORC is constructed. We employ the SAFT-VR Mie equation of state, a state-of-the-art version of the statistical associating fluid theory (SAFT), to predict the thermodynamic state properties and phase behavior of the fluid mixtures. The effect of the working-fluid mixture selection on the efficiency and power output from the cycle is investigated, as is its effect on the sizes of the various components of the ORC engine. This is done in order to appreciate the role that the fluid mixtures have on the investment/capital costs attributed to the installation of such a unit, intended for waste-heat recovery and conversion to power. Results of an ORC using a binary decane–butane mixture as the working fluid demonstrate a significant improvement in the cost per unit power output compared to the two pure fluid components. Specifically, the added costs of the four main ORC system components (pump, expander, and two heat exchangers) were found to be as low as 120–130 £/kW, 20–30% lower compared to the pure fluids.
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