Performance Of Organic Rankine Cycle Research Articles

Impact of turbine characteristics on low temperature organic Rankine cycles operating with zeotropic and azeotropic mixtures

The urgent need to mitigate the environmental impacts of fossil fuel combustion has spurred interest in renewable energy sources for electricity generation, particularly solar organic Rankine cycles (ORCs). This study investigates the potential of fluid mixtures in low-temperature ORCs, focusing on a radial turbine. While fluid mixtures have shown promise for heat recovery in low-temperature applications, previous research often overlooked turbine characteristics by assuming constant efficiencies. This study set out to examine the impact of turbine characteristics on the ORC performance when adapting fluid mixtures by coupling a cycle-turbine model incorporated with real gas analysis. The outcomes of the turbine model are exported to the cycle model to evaluate its performance. Results reveal significant variations in cycle performance due to turbine power and efficiency, outweighing the effects of temperature glide in fluid mixtures. Although fluid mixtures enhance thermal compatibility with heat sources, certain pure fluids exhibit superior cycle performance owing to better turbine characteristics. Moreover, the assumption of constant turbine efficiency compromises result accuracy by up to 45 % compared to dynamic turbine efficiency. Notably, the isobutane/isopentane mixture (0.7/0.3) emerges as the most favourable, achieving a turbine power of 48.90 kW, turbine efficiency of 71 %, and thermal efficiency of 12.29 %.

Role of CO2-based mixtures in the organic Rankine cycle using LNG cold energy

Organic Rankine cycle (ORC) is an attractive method for recovery of liquefied natural gas (LNG). Zeotropic mixtures are optimal working fluids for improving the ORC power generation performance. In this study, eight CO2-based binary mixtures were selected as alternative working fluids for the utilization of medium-temperature LNG cold energy for ORC. The effect of CO2-based binary mixture on thermodynamic performance of ORC was presented and investigated. The genetic algorithm was applied to optimize the thermodynamic performance of ORC so as to determine the optimal working fluid among CO2-based binary mixtures. The results indicate that CO2-based binary mixtures significantly improve the thermodynamic performance of ORC in the recovery of LNG cold energy when compared with pure-CO2 ORC. There is a specific CO2 mass fraction that leads to the highest net power output of the ORC, and the mass fraction of CO2 increases with higher condensation temperatures (For CO2/Propane, the condensation temperatures are −55 °C, −40 °C, and −30 °C, and this CO2 mass fraction is 0.35, 0.65, and 0.8, respectively). Furthermore, the ORC using CO2/R134a exhibits the highest net power output at 13.50 kW among the eight alternative CO2-based binary mixtures.

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

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.

Experimental and simulation study on a zeotropic ORC system using R1234ze(E)/R245fa as working fluid

Organic Rankine Cycle (ORC) is a highly promising technology for converting heat to power, which has a widespread application in renewable energy utilization and waste heat recovery. Zeotropic working fluids are widely investigated to enhance the performance of ORC. In the present study, an experimental study on zeotropic mixture R1234ze(E)/R245fa is conducted under specified operating conditions and the operating behaviors of the ORC system are evaluated. An ORC simulation model (BP-ORC) based on a back propagation neural network and heat exchanger simulation modules is developed. The contribution factors that trigger the differences in heat transfer and system performance among the various working fluids are investigated. The operating behaviors of the heat exchangers and system are simulated for the working conditions beyond the experimental study. R1234ze(E)/R245fa (0.25:0.75 and 0.50:0.50) features a wider operating range of mass flowrate than R245fa due to their relatively lower density. The net power output of R1234ze(E)/R245fa (0.50:0.50) is 4.63 % higher than that of R245fa at a mass flow rate of 0.164 kg/s due to its relatively higher heat transfer performance. The variation of density and operating pressure plays a significant role in influencing the heat transfer behaviors and system performances.

Selected Aspects of Performance of Organic Rankine Cycles Incorporated Into Bioenergy With Carbon Capture and Storage Using Gasification of Sewage Sludge

Abstract The study aims to investigate the application of the organic Rankine cycle (ORC) in the bioenergy with carbon capture and storage (BECCS) using gasification of sewage sludge. The tool used in the investigation is the aspen plus software with refprop property methods for calculating fluid properties. The reason for this study is that a detailed analysis of the proposed BECCS process flow diagram indicates that a certain amount of waste heat is available in the exhaust gas from the high-to-intermediate pressure gas turbine. Some of this energy can be used by applying expansion in a low-pressure turbine, optionally by applying regenerative water heating, which is then redirected to the combustion chamber, or finally by incorporating the ORC into the main cycle. For the ORC cycle, different configurations are studied, with regeneration and using different working fluids. For the highest efficiency of the cycle, the regenerative heating of high-pressure water is applied and a suitable ORC working fluid with optimal saturation parameters and mass flow is selected. Such modified proposed BECCS power plant hybrid systems with ORC are compared to the reference case with lower pressure expansion. A study of the heat duty and temperature distribution in heat exchangers is carried out. Five ORC fluids were investigated, namely ethanol, refrigerants R236ea, R245fa, R1233zd(E), and water, which gave a net efficiency of the whole power plant of 39.71%, 40.02%, 40.26%, 40.34%, and 39.35% respectively, while the proposed BECCS reference case gave 38.89%.

Investigation of the geothermal flash cycle developed by a thermoelectric generator and PEMFC: 3E analysis and optimization

Investigations have revealed that geothermal organic Rankine cycles (ORCs) have a low efficiency and high exergy destruction rate, especially in the heat exchangers network, which drastically reduces the whole system's performance. To tackle this problem, in the present research, the effects of employing thermoelectric generators (TEG) and proton exchange membrane fuel cell (PEMFC) on the performance of a geothermal ORC will be discussed from thermodynamic and economic points of view. In this study, three geothermal flash cycles are investigated. The first system, GFC, is a geothermal flash cycle. The second system is the GFC boosted by a TEG thermoelectric generator, which is applied instead of the condenser (GFTC). The third system is GFTC, developed using a PEMFC (GFTPC) before the evaporator. These systems are compared from energy, exergy, and economic perspectives. Parametric analysis is conducted for the system with the best performance and the effects of the evaporator temperature, evaporator quality, flash temperature, and PEMFC temperature on the system performance. Based on the results, the net power outputs of the GFTC and GFTPC are 10.21 % and 40.49 % higher than those of the GFC, respectively. GFTC and GFTPC have higher energy and exergy efficiencies and lower LCOE and payback period than GFC. In the GFTPC, a 32.86 % increase in the net power output, 20.81 % enhancement in the energy efficiency, and 0.22 % increase in the exergy efficiency are observed with an increase in the PEMFC temperature from 75 to 115 °C. Moreover, The PEMFC temperature increment reduces the LCOE and payback period of the GFTPC system. Also, the multi-objective optimization for GFTPC design with three decision variables has been done.

Energy, Exergy and Environmental Analysis of ORC Waste Heat Recovery from Container Ship Exhaust Gases Based on Voyage Cycle

Recovering the waste heat of a marine main engine (M/E) to generate electricity was an environmental way to minimize the carbon dioxide emissions for ships, especially with organic Rankine cycle (ORC) technology. The M/E had variable loads and operating times during voyage cycle, which directly affected the ORC thermodynamic potential. In this paper, a voyage cycle-based waste heat utilization from the M/E was introduced to provide reliable evaluation for proposing and designing ORC. The effect of various M/E loads and operating times on ORC performance among three dry-type substances was analyzed. The environmental impact was presented based on the data from one voyage cycle navigation of objective container ship. The results showed that Cyclohexane was capable of net power while Benzene was more suitable for thermal efficiency. The evaporator and condenser were the main irreversible components of the ORC system and required further optimization. Taking the operational profile into consideration, the evaporation pressures were 922–1248 kPa (Cyclohexane), 932–1235 kPa (Benzene) and 592–769 kPa (Toluene), respectively. During the voyage cycle, the carbon dioxide emissions were 99.68 tons (Cyclohexane), 96.32 tons (Benzene) and 60.99 tons (Toluene), respectively. This study provided certain reference for the design and investigation of ORC application to further improve the energy efficiency for container ship.

Development of 180 kW Organic Rankine Cycle (ORC) with a High-Efficiency Two-Stage Axial Turbine

The design of turbines used to convert thermal energy into electrical energy in an organic Rankine cycle (ORC) is crucial. A high-speed turbine requires high-performance bearings, which increases turbine manufacturing costs. In this study, a high-efficiency two-stage axial turbine at a low rotational speed was developed, and the ORC performance was presented. We designed a 180-kW axial turbine of 12,000 rpm. To increase turbine efficiency, the number of turbine stages was set to two, and turbine blades were designed to reduce pressure losses. One-dimensional design parameters of blades that minimized the total pressure loss were selected using an in-house code based on a generalized reduced gradient (GRG) nonlinear algorithm. Three-dimensional turbine blade modeling and numerical analysis were performed using commercial software. The total-to-static isentropic efficiency and output of the two-stage axial turbine were predicted to be 85.1% and 176 kW, respectively. ORC performance was assessed using the predicted turbine performance results. Assuming the temperature of the condenser outlet working fluid to be 25 °C, the ORC thermal efficiency and exergy efficiency were found to be 7.40% and 34.49%, respectively. Our findings highlight the applicability of various rotational speeds and number of stages for an axial turbine in an ORC.

Case study: Repowering of ORC system by means of experimental test bench with supercritical carbon dioxide, proposal, and field experience improvements

Although organic Rankine cycles (ORCs) have cornered the small-scale energy harvesting market, the generation capacities produced by sCO2 cycles far exceed those of ORCs, reaching higher powers and efficiencies. This paper analyzes the results of the field tests performed in 2022 at the Grupo Dragón, Nayarit, Mexico, facilities, in which the objective was to validate the operation of the ORC IDEA-10 system with a capacity of up to 10 kWe. The thermodynamic states reached during the test time lapses in which there was full operational stability and with direct loads are analyzed. The results obtained together with proposals for improvement led to compare the performance of ORCs with sCO2 systems for low temperature geothermal sources. The efficiencies of simple sCO2 cycles (5.32%) turned out to be lower than that of ORC at the same temperatures (9.7%), however, the efficiency of the sCO2 cycle improved notably in a regenerative configuration, given the properties of CO2 near its critical point, reaching efficiencies above 25% even at low temperatures compared to conventional ORCs with efficiencies below 10%. Finally, the basis for the implementation of sCO2 in low enthalpy geothermal applications was established, designing an experimental circuit with results obtained in the literature.

Molecular dynamics simulation of homogeneous condensation and thermophysical properties of R245fa/R141b

The use of zeotropic mixture is an effective way to improve the thermodynamic performance of organic Rankine cycle. The thermophysical properties and homogeneous condensation of zeotropic mixtures are of great significance for the design of condensers. This work conducted molecular dynamics (MD) simulation to investigate the homogeneous condensation and thermophysical properties of R245fa/R141b at various oil concentrations and mixing ratios. MD simulations provided thermophysical properties such as liquid density, specific heat capacity, internal potential energy, radial distribution function, mean squared distribution and cluster formation. The results show that simulated density and specific heat capacity of R245fa/R141b under different R245fa ratios agree well with the data from Nist Refprop 9.1. The condensation rate of R245fa/R141b is lower at higher oil concentrations or lower R245fa ratios. During condensation, the total potential energy of the system decreases rapidly, and the van der Waals energy is the main factor for the reduction. In addition, the internal molecule structure of the fluids does not change during condensation.

Optimizing Solar Energy Harvesting through Integrated Organic Rankine Cycle–Reverse Osmosis Systems: A Techno–Economic Analysis

When it comes to seawater desalination in the small- to medium-electricity ranges, the organic Rankine cycle (ORC) powered by solar energy stands out as the most energy-efficient technology currently available. Various solar techniques have been developed to capture and absorb solar energy. Among them, the parabolic trough collector (PTC) has gained recognition as a low-cost solar thermal collector with a long operating life. This study investigates the thermodynamic performance and economic parameters of a PTC-powered ORC using Dowtherm A and toluene as working fluids for the solar cycle and ORC cycle, respectively. Thermo-economic multi-objective optimization and decision-making techniques are applied to assess the system’s performance. Four key parameters are analyzed for their impact on exergy efficiency and total hourly cost. Using TOPSIS decision-making, the best solution from the Pareto frontier is identified, featuring an ORC exergy efficiency of 30.39% and a total hourly cost of 39.38 US$/h. The system parameters include a mass flow rate of fresh water at 137.7 m3/h, a total output net power of 577.9 kJ/kg, and a district heating supply of 1074 kJ/kg. The cost analysis reveals that the solar collector represents approximately 68% of the total hourly cost at 26.77 US$/h, followed by the turbine, thermoelectric generator, and reverse osmosis (RO) unit.

Comparison Of The Electricity Generation Potentials Of Solar ORC Designed With Different Fluids Depending On Instantaneous Solar Radiation In Four Districts Of Türkiye

In this study, the solar Organic Rankine Cycle (ORC) system was analyzed to meet some of the electrical energy needed in large and medium-sized buildings and large enterprises such as hotels from solar energy. A simulation study was conducted for different districts in Türkiye that are rich in solar energy potential. These counties and the provinces they are affiliated with; Silifke-İçel, Alanya-Antalya, Bodrum-Muğla, Çeşme-İzmir. The power value transferred to the ORC was determined by considering the instantaneous radiation values and sunshine durations for the districts. The performance of solar ORC was determined by comparing fluids from three different organic fluid types. Organic fluids and types used in design; benzene-aromatic hydrocarbon, cyclohexane-alkane, octamethylcyclotetrasiloxane (D4)-siloxane. Considering the maximum electrical energy values obtained from Solar ORC in the summer months, it was seen that 205 MWh electricity generated was obtained for Silifke with benzene at a heat source temperature of 223 oC in July. Maximum solar parabolic trough collector (PTC) specific electric power value was determined as 59.52 W/m2 in Alanya district with benzene in June. When the four districts are evaluated together, it has been determined that benzene performs better than cyclohexane by 3.8% on average and 23% better than D4. When the annual electrical energy values are examined, the highest production was determined as 1625 MWh with benzene fluid in Alanya district.

Small-Scale Organic Rankine Cycle Performance Using an Additional Heat Exchanger

Small-Scale Organic Rankine Cycle Performance Using an Additional Heat Exchanger

Experimental investigation of a zeotropic organic Rankine cycle system with liquid-separation condensation for composition adjustment

Organic Rankine cycle (ORC) systems often experience a decline in operating performance when subjected to off-design conditions. To address this issue, an emerging method for improving the ORC performance under variable operating conditions is the use of composition adjustment through liquid-separation condensation. In the present study, an experimental facility of a 1 kW zeotropic ORC system that allows for composition adjustment based on liquid-separation condensation is developed. A composition adjustment strategy based on the proposed composition adjustment system is developed, and the stability and effectiveness of the composition adjustment system are experimentally investigated. An experimental comparison is conducted to demonstrate the superiority of the composition-adjustable ORC over the conventional composition-fixed ORC under variable operating conditions. The results indicate that the proposed composition adjustment system can effectively separate mixtures at different compositions within a short period of time. Under variable operating conditions, the composition of R134a/R245fa in the ORC is effectively adjusted from 0.300/0.700 to 0.172/0.828 using the proposed composition adjustment system. As a result, the net power output of the composition-adjustable ORC is found to be 4.79–9.71% higher than that of the composition-fixed ORC.

Study on performance evaluation framework and design/ selection guidelines of working fluids for subcritical organic Rankine cycle from molecular structure perspective

Organic Rankine cycle (ORC) is a promising power cycle to convert low-grade thermal energy. The quick and easy evaluation of the potential working fluids lacking thermophysical property data is important for the working fluid selection of ORC. This paper proposes a systematic framework of working fluid evaluation from the molecular structure perspective, which couples the quantitative structure property relationship (QSPR) and universal equations of state. The thermodynamic performance of ORC is first correlated with four key thermophysical properties based on universal equations of state. Then, these thermophysical properties are obtained from the corresponding QSPR models based on the molecular structure of working fluids. The influence factors of ORC performance at a micro level are investigated using the QSPR models. Moreover, the effects of molecular characteristics on thermal efficiency are analyzed. The criteria for working fluid design/selection are recommended aiming at the improvement of thermal efficiency. The proposed framework shows sufficient accuracy with the relative errors of −0.41 - 15.85% and mean absolute error of 8.29% compared with the results based on REFPROP. It is found that the cyclization of carbon chain is an ideal method for the working fluid design based on alkanes and alkenes. This work can provide new insights for the evaluation, selection, and design of working fluids on the molecular structure level.

Theoretical and experimental study on the selection of pure and mixed refrigerants for a power-cooling system driven by ultra-low-grade heat

This study theoretically and experimentally evaluates the performance of a system that combines an organic Rankine cycle (ORC) and a vapor compression cycle (VCC) driven by ultra-low-grade heat (ULGH). A systematic method is developed for the selection of pure refrigerants for the efficient performance of ORC over a temperature range between 50°C to 100°C. Binary and ternary mixtures are developed followed by sensitivity analyses and composition optimization to determine the optimal performance of these mixtures. Several experimental tests are conducted to ensure the operability of the system with the developed refrigerants. The results show that the use of ternary and binary mixtures enhances the performance of the system with lower GWP and ODP compared to pure refrigerants. Several mixtures are developed with energy efficiencies higher than 9% at a heat source temperature of 75°C. A mixture of R142b/R152a/R600 improves the energy efficiency of the system by 22.80%, reduces the back work ratio by 19.40% with an increase in the evaporation capacity by 13.25%. The methodology and results presented herein will be useful in the development, design, and optimization of power and cooling systems driven by ULGH with pure and mixed refrigerants.

Control strategies of pumps in organic Rankine cycle under variable condensing conditions

The working medium pump and cooling water pump are important components in organic Rankine cycle system. However, they have not received as much attention as the expander and working medium. Simultaneously, the dramatic changes in condensing environment deviate the organic Rankine cycle working point from the designed operating conditions. Hence, this paper focused on the performance improvements and control strategies of working medium pump and cooling water pump in small-scale organic Rankine cycle under variable condensing conditions. A model was established to predict the performances of an organic Rankine cycle system with R245fa, especially the pumps in the system, under variable condensing conditions. The results showed that the overall efficiency of multi-stage centrifugal pump was between 14% and 39% at an estimated speed of approximately 1600 RPM to 2328 RPM. In winter conditions, the back work ratio increased from 0.05 to 0.19 with increasing evaporation pressure and decreasing mass flow rate. In other words, it is unnecessary to pursue excessively high evaporation temperature at low rotational speed of multi-stage centrifugal pump. As for the cooling water pump, it is feasible to reduce the power consumption of the cooling system through changing the rotational speed of water pump. The water pump can be operated with high efficiency (between approximately 58.4% and 65.3%, corresponding to an estimated speed range of 1374 RPM to 1813 RPM) when the system run in optimum operating conditions. It is also found that the performance of organic Rankine cycle was strongly influenced by fluctuating ambient temperature, with the net efficiency and net power increase of 3.36 % and 5.11 kW in winter compared to summer.

Deep Learning Based Prediction of axial turbine performance for Clean Organic Rankine Cycle system driven by low-temperature heat source

The big data performances of Organic Rankine Cycle (ORC) system is widely used in avariety of industrial applications. In some processes, the axial flow turbine at the low temperature heatsource is crucial. The goal of this work is to increase the high efficiency of a tiny axial turbine poweredby an Organic Rankine Cycle (ORC) utilizing numerical studies and deep learning method. To providethe best performance for the Organic Rankine Cycle (ORC) application, various turbine stages aresuggested. Three-dimensional RANS computations are recommended for five different rotational speedsand four mass flow rates ranging from 0.2 to 0.5 kg/s with an inlet temperature of 365 K in order todescribe the hydrodynamic and thermodynamic capabilities and get a big data. The analysis show that thetwo-stage turbine with a fixed rotational speed delivers the highest power output value of 10000W, hasthe highest turbine efficiency of 86%.In a three-stage turbine arrangement operating at steady state, theefficiency of the turbine and its output are 89% and 12000 W, respectively. The maximum values forturbine efficiency and power production are 88% and 12000W, respectively, as a result of the transientcomputational procedure. These results demonstrate the potential for exchanging low temperature heatsources using micro-three-stage axial turbines in Organic Rankine Cycle (ORC) systems .

Information theory-based dynamic feature capture and global multi-objective optimization approach for organic Rankine cycle (ORC) considering road environment

Efficient capture and global optimization of organic Rankine cycle (ORC) operating features in road environment is the key to obtain actual waste heat recovery potential. The complexity of time-varying characteristics intensifies the nonlinear coupling relationship between ORC performance and parameters. This paper first designs and builds an ORC experimental system for recovering waste heat from internal combustion engine (ICE). The experimental system includes ICE and its measurement subsystem, ORC subsystem, expander lubrication subsystem, cooling subsystem, and ORC measurement subsystem. R245fa is used as working fluid; The expander adopts a specially designed single screw expander. The performance of ORC waste heat recovery is tested by adjusting the operating conditions of the ICE, expander, pump, and valve opening. The temperature range of waste heat is 627–686 K. Subsequently, a dynamic feature capture and global multi-objective optimization approach for ORC is proposed. The results show that the precision of dynamic feature capture can be improved at least 41.78% with the introduction of information theory in complex environment. Frequent fluctuation of vehicle speed is not conducive to the improvement of evaporator inlet temperature at working fluid side. As the speed of the vehicle is greatly reduced, the evaporator inlet temperature drops sharply. The frequent fluctuation of speed will intensify the nonlinear correlation between operating parameters and system performance and make the system performance more dependent on the coupling correlation between operating parameters. The approach proposed in this paper can provide a new idea for efficient capture of dynamic characteristics and global multi-objective optimization of ORC in road environment.

Assessment of the Impact of using Zeotropic Mixture on the Thermodynamic Performance of Organic Rankine Cycle Integrated Vapor Compression Refrigeration System

Assessment of the Impact of using Zeotropic Mixture on the Thermodynamic Performance of Organic Rankine Cycle Integrated Vapor Compression Refrigeration System