Rankine Cycle Working Research Articles

Innovative Approaches for Improving ORC Performance: A Review of Pure Fluids, Zeotropic Mixtures, and Nanoparticles

Although the organic Rankine Cycle (ORC) is said to effectively capture low-grade heat, its commercialization has been limited because of working fluid constraints and inefficiencies resulting from operating at low temperatures. This study reviews the working fluids used in organic Rankine cycles and examines how nanoparticles could enhance the efficiency of the ORC, by enhancing the thermophysical properties of the working fluids. Results from this review showed that zeotropic mixtures of pure fluids, provide a viable approach to improving the thermophysical characteristics of organic working fluids and have the potential to achieve thermo-economic performance superior to that of individual pure fluids. Research results on the relative effectiveness of zeotropic mixtures and pure fluids, however, are conflicting and call for further study. Although nanofluids have shown potential as heat transfer fluids, there has not been much research done on them as organic Rankine cycle working fluids. In comparison to typical nanoparticles, metal-organic heat carriers have been recognized as having substantial potential to improve organic Rankine cycle thermodynamic efficiency. Future study on nanofluids, particularly in zeotropic mixtures, is crucial for the creation of new working fluids for developing ORCs that could achieve a balance between thermodynamic, economic, and environmental performance required to recover low-grade heat and the generation of electricity.

Optimizing trigeneration energy systems: Biogas-centric methanol production via direct CO2 hydrogenation with advanced integration of PEM electrolyzer and LNG cold technology

Biogas, a sustainable alternative to fossil fuels, addresses issues of non-renewability and accessibility. Its structural similarity to fossil fuels makes it a potent option for energy systems. With this in mind, this paper discusses a novel trigeneration system that utilizes biogas and Liquefied natural gas cooling to produce methanol, electricity, cold water, hot water, oxygen, and natural gas. The system integrates various components such as a biogas burner, Kalina cycle, organic Rankine cycle, liquefied natural gas liquid gasification cycle, proton exchange membrane electrolyzer, and methanol synthesis unit. Simulation via Aspen HYSYS software includes an analysis of energy, exergy, economic, and environmental aspects. Efficiency assessment in single generation, cogeneration, trigeneration, and chemical trigeneration modes concludes chemical trigeneration as most efficient, with the proton exchange membrane electrolyzer being the most efficient subsystem. Key variables like Kalina cycle evaporator temperature, gas flow rate to the methanol reactor, and organic Rankine cycle working fluid pressure are assessed. Predictions on thermodynamic, environmental, and economic behaviors, along with their fluctuations, are made. Using a thermoeconomic approach, the economic analysis determines an exergy unit cost of 59.79 $/GJ and a total cost rate of 2764 $/h. Overall, this work presents a novel and efficient chemical trigeneration system that utilizes biogas and LNG cooling to produce multiple products.

Dry-Cooled Rankine Cycle Operated With Binary Carbon Dioxide Based Working Fluids

The dry-cooled Rankine cycle working with a zeotropic mixture of CO2+C6F6 is influenced by the ambient temperature as air is used as the heat sink. Varying heat sink temperatures allow for operating the cycle under sliding condensation pressure which may benefit a hybrid PV-CSP plant. The study demonstrates the effect of this operation mode on composition shift and condensation pressure and investigates the cycle performance. The results show that defining the turbine design conditions significantly impact whether the system´s thermodynamic performance behaves acceptably in off-design conditions. Operating the turbine which was designed for a big pressure ratio in part-load especially if both, inlet and outlet pressure are at off-design conditions, is not favorable and leads to deteriorated efficiencies. Under some constraints for turbine and heat exchanger design, the proposed cycle enhances the hybrid PV-CSP system.

Thermo-economic assessment of sub-ambient temperature pumped-thermal electricity storage integrated with external heat sources

Thermally integrated pumped-thermal electricity storage (TI-PTES) offers the opportunity to store electricity as thermal exergy at a large scale, and existing studies are primarily focused on TI-PTES systems based on high-temperature thermal energy storage. This paper presents a thermo-economic analysis of a “cold TI-PTES” system which converts electricity into cold energy using a vapor compression refrigeration (VCR) unit and stores it at sub-ambient temperatures during the charging process, and generates electricity by using an organic Rankine cycle (ORC) working between the sub-ambient temperature and an external low-grade heat source during the discharging process. The effects of key parameters, i.e., mass flowrate and temperature of the storage medium, ORC evaporation temperature, component efficiencies, and pinch-point temperature differences, on the system performance are evaluated based on a whole-system thermo-economic model. The results reveal that the roundtrip efficiency and levelized cost of storage (LCOS) of the system increases while the electrical energy storage capacity decreases as the temperatures of the two cold storage tanks approach each other. When the temperature of the cold storage tank 1 rises from 1 °C to 8 °C while the cold storage tank 2 remains as 13 °C, there is an increase of 25% and 20% in the roundtrip efficiency and LCOS respectively while the energy storage capacity decreases by 69%. A roundtrip efficiency of 0.74 and LCOS of 0.32 $/kWh are achieved with a heat source temperature of 85 °C, using a mass flowrate and temperature of the cold storage medium of 50 kg/s and 1 °C. Furthermore, any change in cold storage medium mass flowrate changes both electrical energy storage capacity and power output by the same proportions. With a continuous high-flowrate external heat source, the LCOS can be as low as 0.17 $/kWh. By providing sufficient heat from an external heat source, the proposed system possesses a high potential for medium-to-large scale energy storage with a unique hybrid nature for electricity storage and thermal integration.

Power, cooling, freshwater, and hydrogen production system from a new integrated system working with the zeotropic mixture, using a flash-binary geothermal system

The current paper proposes a new hybrid system based on a binary-geothermal system to generate power, cooling capacity, freshwater, and hydrogen. This system includes an internal integration of the organic Rankine cycle and ejector refrigeration cycle with zeotropic working fluids, proton exchange membrane electrolyzer, and reverse osmosis desalination unit. The system is analyzed by developing a precise model in the Matlab software, and then a multi-objective grey wolf optimization is employed to optimize the proposed system performance. The net present value, payback period, and sum unit cost of products are considered the system's economic performance criteria to study the system's feasibility for investment. Results indicate that the Isobutene-R114 provides the best net output power, and the R12-R114 combination has the best cooling performance. Also, the R12-R114 reports the best overall performance as the organic Rankine cycle working fluid. Based on optimization results, the exergy and thermal efficiency reached 17.84% and 34.24%, respectively. The system could provide 856.06 kW net output power, 2410.54 kW cooling capacity, 0.743 kg/h hydrogen, and 40.22 kg/s freshwater with a sum unit cost of 25.5 $.GJ−1, and the total profit and payback period of 6.82 $M and 3.76 years.

Determination of optimum organic Rankine cycle parameters and configuration for utilizing waste heat in the steel industry as a driver of receive osmosis system

The existence of the waste heat from the exhaust of steel industry with the temperature of 227 °C and water evaporation in the cooling process, the limitation of the water sources with high quality, the sharp decline of the groundwater, and access to the saline water are the reasons to study and analyze the ORC-RO system in this paper. This investigation is based on energy analysis (1E), exergy analysis (2E), economic analysis (3E), and environmental impacts (4E). The environmental analysis is conducted considering three aspects: (1) The effects of the ORC system depending on the selection of the working fluid. (2) The impacts of RO system on the brine, which depends on the brine stream density (introduced by the non-dimensional function Ω), showing the span of the RO system brine dilution. (3) The decline in the removal of the groundwater happens when the fresh water increases. In this comparison, four types of cycles consist of basic configuration, basic configuration with recuperator, basic configuration with regenerative, and basic configuration with the combination of regenerative and recuperator are investigated. The trade-off between exergy and thermal efficiency parameters and TAC (total annual cost) are the reason for using the Genetic Algorithm (GA) as the optimization algorithm. The main optimization parameters are: (1) configuration of ORC, (2) the optimized design of RO system, (3) Rankine cycle working fluid based on thermal source, (4) membrane selection among company membranes DOW, (5) determining the approach and pinch temperatures of WHR for maximum recovery, according to the limitation of acid dew point. These parameters are obtained based on two objectives; reducing the price of produced water and increasing the system’s exergy efficiency. Production of freshwater reduces water withdrawal from groundwater resources, and the working fluid with low ODP and GWP reduces the environmental impacts of the cycle. The results show that the cycle with basic configuration and the cycle with recuperator are the two optimum cycles in the Pareto curve. The working fluid R245ca (GWP = 640; ODP = 0) is chosen as optimum fluid in each of the two cycles. The exergy efficiency, total cost and Ω in basic cycle and the cycle with recuperator are 32.51%, 2.84 $/m3, 16.94% and 32.49%, 2.64 $/m3, 12.74% respectively. Also, the production of freshwater reduces 2.5% of water withdrawal from groundwater resources.

Techno-economic analysis of a foil-based solar collector driven electricity and fresh water generation system

For medium-scale dispatchable (on demand) power and fresh water generation, a concentrated solar energy powered system with thermal energy storage is an attractive option. However, currently used concentrated solar power technologies (parabolic trough collector, solar power tower, linear Fresnel reflector) use heavy and very expensive glass mirrors and receivers. Recently, a novel micro-structured polymer foil-based concentrating solar collector system, with the advantages of a low installation cost and a low operation and maintenance cost, has been proposed. This system, which generate heat by focusing sunlight like magnifying glasses, can be effectively used for applications with temperatures up to about 350 °C. Techno-economic analysis and optimization of a micro-structured polymer foil-based concentrating solar collector powered organic Rankine cycle based electricity and multi-effect distillation based fresh water generation system is presented in this paper. The proposed system has a lot of potential for the places with electricity and water crisis. The results indicate that cyclopentane is the most appropriate organic Rankine cycle working fluid for the plant, achieving a levelized cost of electricity of 0.116 €/kWhe and levelized cost of fresh water of 1.13 €/m3 for Antofagasta, Chile and 0.163 €/kWhe and 1.62 €/m3 for Cape Town, South Africa.

Design and dynamic simulation of a photovoltaic thermal-organic Rankine cycle considering heat transfer between components

Photovoltaic thermal systems concept is very attractive for two reasons; Firstly, using the coolant fluids decreases the temperature of the photovoltaic modules. Secondly, the heat, gathered from photovoltaic modules, can be employed in a thermal or energy conversion system. Hence, the efficiency of a photovoltaic is enhanced from both sides. In this study, a combination of an organic Rankine cycle with photovoltaic modules is proposed. Despite previous works, which considered such schemes for a limited environmental conditions, dynamic model of heat transfer for varying radiation and temperature throughout a typical year is employed. A detailed model of the heat transfer between the photovoltaic-thermal components is utilized to investigate the combination's thermal behavior. Also, for the first time, the optimum photovoltaic array area is calculated based on the heat transfer between photovoltaic modules and the Rankine cycle working fluid. Considering design conditions, 80 m2 area of photovoltaic arrays are needed to preheat the working fluid before entering the evaporator. The round trip efficiency of the system is equal to 22.62%, using HFO-1234yf as the working fluid. Besides, the effect of changing pressure of evaporator and condenser along with using different coolants is investigated. Four pure refrigerant and two fluid mixture are used to find the effect of working fluid on the performance of the system. The parametric analysis shows that using isobutane results in the highest achievable round trip efficiency (22.81%), among the selected fluids. Cost analysis showed that the levelized cost of electricity is 0.05 $/kW h, which is slightly higher than the electricity price for the same installed capacity of PV without cooling.

Comparison of different optimized heat driven power-cycle configurations of a gas engine

Among different technologies in internal combustion engines, waste heat recovery from the lost energies has great potential to improve fuel economy and reduce CO2 emission. In the present work, to achieve the optimal design parameters for a waste heat recovery system of a gas engine, a multi-objective optimization evolutionary algorithm is employed. The system consists of different types and combinations of the Organic Rankine/Kalina cycle as the waste heat recovery system of gas engine exhaust gas and the waste heat of cooling water is recovered by the trilateral flash cycle. The objective functions are chosen to maximize exergy efficiency and minimize the specific investment cost of the system. Cyclohexane, Toluene, and Benzene have been investigated and compared to the organic Rankine cycle working fluid. To evaluate different cycle configurations and working fluids, the Pareto front solutions related to 18 studied cases are compared. Meanwhile, the “Linear Programming Technique for Multidimensional Analysis of Preference” decision-making approach has been used as an optimal point in all cases. This work is aimed to compare the optimal design operating conditions of the studied configurations to choose the best configuration for waste heat recovery from a gas engine. The results reveal that, among the decision parameters, the organic Rankine cycle turbine inlet temperature is the most important in terms of the specific investment cost of the system. Also, considering the exergy and energy efficiency of the system, organic Rankine cycle turbine inlet temperature as well as organic Rankine cycle and trilateral flash cycle turbine isentropic efficiencies are of great importance. The Pareto front comparison for each configuration indicates that toluene is the most suitable fluid for the organic Rankine cycle in all configurations. Comparing the selected optimal points in different combinations reveals that, the configuration of organic Rankine cycle with internal heat exchanger-trilateral flash cycle, due to its lower payback period and specific investment cost as well as the higher exergy efficiency and net power output in optimal point, is the prominent compared to the other combinations. Furthermore, the optimized configuration of the organic Rankine cycle with the internal heat exchanger-trilateral flash cycle shows a 14.31% increase in the exergy efficiency and an 8.2% decrease in the specific investment cost of the system compared to the base case. Employing the optimized configuration of the organic Rankine cycle with internal heat exchanger-trilateral flash cycle as waste heat recovery of the gas engine leads to a 7.8 kW increment of net power output, equivalent to an increase of 18.85% exergy efficiency of the whole system including engine and bottoming cycle. On the other hand, additional equipment to the engine, impose 3061$/kW specific investment cost which takes 2.2 years to be paid back.

Techno-economic analysis of combined inverted Brayton – Organic Rankine cycle for high-temperature waste heat recovery

Many practical cases with waste heat recovery potential such as exhaust gases of reciprocating engines, cement kilns or heat-treating furnaces, are nowadays often integrated with organic Rankine cycle to convert waste heat to the mechanical power. However, when dealing with high-temperature waste heat, organic Rankine cycle faces efficiency limit due to the physical properties of the working and thermal fluids. That gives room for further enhancement of the waste heat recovery technologies via the investigation of different non-conventional schemes as one of the possible ways. In the present work, a system introducing the combined inverted Brayton plus organic Rankine cycle is under investigation. Aspen Hysys models of both conventional organic Rankine cycle and combined cycle were designed, orienting on waste heat recovery from the heavy-load gas-fueled reciprocating engine exhaust. In this way, the performance of the combined scheme was benchmarked versus the conventional organic Rankine cycle. An assessment of the organic Rankine cycle working fluids was provided, and pentane has shown the best thermodynamic performance. The study on inverted Brayton cycle defined the remarkable effect of the water condensation in the gas duct on the inverted Brayton cycle performance. Finally, both thermodynamic and economic optimizations of the models were conducted, setting the stage for the comparison of solutions. Results have shown the 10% advantage of the combined scheme over organic Rankine cycle in generated power and system efficiency. The levelized-cost-of-energy-based optimization for variable capacity factors has highlighted above 6% advantage of the investigated solution. The analysis of the sensitivity from machines’ efficiencies and heat exchangers’ pinches has shown that with some sets of parameters, the studied scheme may concede to the organic Rankine cycle.

A feasibility study of CO2‐based solar‐assisted Rankine cycle: a comparative case study for Isparta, Turkey

AbstractIn this study, a feasibility analysis of a solar‐assisted transcritical Rankine cycle working with carbon dioxide (CO2) is performed for Isparta, Turkey, in comparison with Kyoto, Japan, conditions. For the analyses, the characteristics of the system are adapted from the actual experimental research conducted at Doshisha University, Kyoto, Japan. In order to evaluate the performance of the CO2‐based integrated system, a mathematical model is established for the evacuated solar collectors. Energy and exergy analyses are carried out using the solar energy data of both cities. According to the simulation results, the average turbine power capacities are determined as 0.415 and 0.396 kW, while the average heat recovery capacities are calculated as 2.10 and 1.89 kW for Isparta and Kyoto, respectively. The yearly electricity generation for Isparta conditions is found to be about 40% higher than the Kyoto conditions with 1138.09 kWh. The results of second law analyses are showed that the highest exergy destruction rate occurs in August for Isparta conditions with 8.18 kW due to the higher solar radiation rates. From the results, it appears that the CO2‐based next‐generation solar‐assisted power and heat generation system can be established and utilized in Isparta more effectively. The future research should, therefore, concentrate on moving the actual experimental setup to Isparta for field test experiments. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Experimental investigation of solar‐assisted transcritical CO 2 Rankine cycle for summer and winter conditions from exergetic point of view

This study deals with energy and exergy analysis of the experimental solar-assisted Rankine cycle working with an environmentally friendly working fluid transcritical CO2. The experimental system consists of evacuated solar collectors, a heat recovery system, condenser, a pump, and an expansion valve to simulate the realistic turbine operation. The system was designed for electricity production and the heat supply for various applications. The experiments were made funder typical winter and summer days to evaluate seasonal system performance in Kyoto, Japan. According to the obtained results, the turbine capacity was calculated as 0.118 kW and 0.177 kW for winter and summer seasons. From the exergetic point of view, solar collectors were found to be the major contributor to the total exergy destruction with 96.32% for summer and 93.58% for the winter season. Therefore, the efforts should be focused on the collectors. Thus, any attempt for improving the system performance should be focused on solar collectors first. Furthermore, the exergetic efficiency of the overall system was calculated as 7.63% for the winter season and 4.08% for the summer season. As a result, the utilization of CO2 in the energy conversion cycle can be sustainably developed and extended by providing a glimpse into the carbon-free clean energy future.

WITHDRAWN: Techno-economic analysis of combined inverted Brayton - Organic Rankine cycle for high-temperature waste heat recovery

Abstract Many practical cases with waste heat recovery potential such as exhaust gases of reciprocating engines, cement kilns or heat-treating furnaces, are nowadays often integrated with organic Rankine cycle to convert waste heat to the mechanical power. However, when dealing with high-temperature waste heat, organic Rankine cycle faces efficiency limit due to the physical properties of the working and thermal fluids. That gives room for further enhancement of the waste heat recovery technologies via the investigation of different non-conventional schemes as one of the possible ways. In the present work, a system introducing the combined inverted Brayton plus organic Rankine cycle is under investigation. Aspen Hysys models of both conventional organic Rankine cycle and combined cycle were designed, orienting on waste heat recovery from the heavy-load gas-fueled reciprocating engine exhaust. In this way, the performance of the combined scheme was benchmarked versus the conventional organic Rankine cycle. An assessment of the organic Rankine cycle working fluids was provided, and pentane has shown the best thermodynamic performance. The study on inverted Brayton cycle defined the remarkable effect of the water condensation in the gas duct on the inverted Brayton cycle performance. Finally, both thermodynamic and economic optimizations of the models were conducted, setting the stage for the comparison of solutions. Results have shown the 10% advantage of the combined scheme over organic Rankine cycle in generated power and system efficiency. The levelized-cost-of-energy-based optimization for variable capacity factors has highlighted above 6% advantage of the investigated solution. The analysis of the sensitivity from machines’ efficiencies and heat exchangers’ pinches has shown that with some sets of parameters, the studied scheme may concede to the organic Rankine cycle.

An innovative integrated system concept between oxy-fuel thermo-photovoltaic device and a Brayton-Rankine combined cycle and its preliminary thermodynamic analysis

This study summarizes the guidelines for the quality-splitting utilization of the radiation and thermal energy after a brief review of the thermo-photovoltaic (TPV) technology and the power cycles. Based on this, an innovative concept of a system that integrates TPV technology and the Brayton-Rankine combined cycle (TBRC) is first proposed. The basic structure of the new system was modeled and a preliminary thermodynamic analysis was performed. The effects of the working conditions including the combustion conditions of different combustion atmospheres, the oxygen concentrations and fuels, and the cycle conditions of different pressures and working fluids on the TBRC system were investigated. It was found that the optimal pressure of the Brayton cycle in the system increased with the combustion oxygen concentration. The system output power was proportional to the combustion oxygen concentration. The system efficiency was similar under 21% O2/N2 conditions and 30% O2/CO2 conditions. The system efficiency was slightly higher for fuel oil than for methane. After considering the efficiency and environmental impacts, n-pentane was selected as the preferred organic Rankine cycle working fluid. Finally, we discuss the application and development prospects of the new system. It is determined that the oxy-fuel TBRC system with flue gas recycle and the integration between the cascade TPV technology and complex power cycles are future research directions.

Thermal Modeling and Performance Analysis of U-Tube Evacuated Solar Collector using CO2

This study deals with the thermal modeling of U-tube evacuated solar collectors to investigate the heat transfer and performance characteristics. The U-tube evacuated solar collectors are integrated into solar-assisted new generation experimental organic Rankine cycle working with environmentally friendly supercritical CO2. For the modeling, one-dimensional heat transfer analysis is applied to the U-tube collectors for determining the heat transfer characteristics of the collectors as well as the CO2 exit temperature from the collectors for the steady heat transfer process. Additionally, heat loss coefficient and overall heat transfer coefficients are determined for the experimental U-tube collectors. The obtained results are also compared with the results of the experimental study.

Performance and operation of micro-ORC energy system using geothermal heat source

In the electricity production sector, geothermal energy is considered a reliable energy source because of its independence of seasonal, climatic and geographical conditions. Low-temperature geothermal wells present a huge potential of exploitation, as the development of binary cycles and the technological improvement in drilling make this heat source a competitive solution for electricity generated distribution and self-consumption. The Organic Rankine Cycle (ORC) is currently the best solution to convert heat into electricity using low enthalpy heat sources. The ORC technology is already mature and widespread for medium and large-scale power plants, applying for geothermal, solar, biomass or waste heat recovery exploitation. Micro-scale ORC applications are still not diffused in the market: the system layout, the working fluid selection and the expander architecture can significantly vary depending on the specific realization requirements, thus a standard configuration has not established yet.In this paper, a particular case study of a micro-ORC power system using a geothermal well is presented. The application in analysis is a plug-and-play ORC facility, currently installed and operating in a pool centre. The system layout and the main components are described. The heat source is a geothermal well, which continuously supplies (by pressure difference) liquid water at a temperature lower than 60 °C to a binary Rankine cycle working with R134a. The ORC system is driven by a prototypal radial-piston expander and adopts an external-gear feed pump and a recuperative cycle. It is developed for working continuously, delivering the generated electricity directly into the grid. The facility is provided with temperature, pressure and electric power sensors for monitoring the operation and for a preliminary evaluation of the performance. The global efficiency of expander and feed pump and the ORC net efficiency have been evaluated at the regular working conditions of the geothermal well, showing values equal to, respectively, 53 %, 41 % and 4.4 %.

Evaluation of transient characteristics of medium temperature solar thermal systems utilizing thermal stratification

System level transient moving boundary models are interesting in the context of advanced control of the solar thermal systems. However, development of control-oriented heat exchanger models faces the key challenges that these models should remain both reasonably accurate and mathematically tractable. In this paper, dynamic moving boundary model is developed for the medium temperature (∼200 °C) solar thermal power plant using a novel concept based on auxiliary pressurized water storage tank to enhance overall thermal efficiency, where the time varying pressure on the subcooled organic Rankine cycle working fluid (refrigerant) at the two-phase heat exchanger inlet is considered as the sole independent variable and all other thermodynamic variables are assumed to be dependent on the specified pressure. Modified idealized stratification model is adopted to analysis the thermal stratification in the storage tank. Small sinusoidal variation about the steady-state pressure level is considered to investigate its effect on the heat exchanger tube wall temperature and the length of different flow regimes. Additionally, the model incorporates a provision to capture the effect of transient changes in the bulk temperature of the heat transfer fluid (commercial thermic oil) on the moving phase change boundaries in the working fluid side of the heat exchanger. At an indicative solar radiation level of 450 W/m2, the primary energy transfer at the solar collector is found to be enhanced by about 11% by using an auxiliary pressurized water storage tank, compared to the case where commercial thermic oil is used in the collector loop. The overall thermal efficiency of the solar thermal system for a peak power level of 840 kWt is estimated as 20.75%.

Economic optimization of Organic Rankine cycle with pure fluids and mixtures for waste heat and solar applications using particle swarm optimization method

The optimization criterion for designing the thermodynamic layout of an organic Rankine cycle is often based on either achieving maximum thermodynamic efficiency or incurring minimum initial specific investment costs. Such designs, however, need not lead to the maximum utilization of waste heat potential or an optimal investment. For full potential utilization of a waste heat source, its temperature should be brought down to near ambient temperatures via transfer of enthalpy to the organic Rankine cycle working fluid. In the limit, however, pursuit of complete source utilization may lead to capital intensive organic Rankine cycle layouts that demand infinitesimal temperature gradients in heat exchangers leading to massive heat transfer areas. This paper defines a new objective function that reveals the tradeoffs between specific investment cost and the extent to which waste heat is utilized. A particle swarm optimization algorithm is used to optimize 7 and 8 dimensional search space for pure and mixture based working fluids, respectively, for case studies involving power capacities of 5, 50 and 500 kWe, waste heat source temperatures ranging from 75 to 275 °C and a number of working fluids. As a practical aid to designers, a methodology for generating high isentropic efficiency scroll geometries corresponding to optimized cycles is presented, and the optimization analysis is further extended to solar thermal applications.

Research on Performance Test Characteristics of Solar Energy ORC Generator Set

In order to study the performance of low-temperature solar-powered ORC generator sets, a solar-powered ORC power generation test bench was designed and built. In the experiment, R-123 was used as the organic Rankine cycle working fluid, and the solar ORC power generation system was experimentally studied. The research results show that when the direct solar radiation intensity is about 400W, the temperature of the heat transfer oil at the outlet of the collector can reach 140 °C. When the temperature of the heat transfer oil at the outlet of the collector is around 110°C, the collector efficiency of the collector can reach about 60%. Under the heat source condition, when the power cycle part is switched from the basic cycle to the regenerative cycle mode, the collector heat collection efficiency can reach about 60%. Under the heat source condition, when the power cycle part is switched from the basic cycle mode to the regenerative cycle mode, the measured efficiency is increased from 9.3% to 10.8%, and the measured cycle efficiency is increased from 1.57% to 1.67%, which is an increase of 6.07%. The measured cycle system efficiency is about 10%, and the heat recovery mode is slightly higher than the basic cycle mode. The organic Rankine cycle performance under different working fluid flows was also investigated in the experiment. The maximum measured average power was 386.27 W when the working fluid flow was 6.88 kg·s. At a certain heat source temperature, as the flow rate of the working fluid increases, the inlet pressure of the expander increases, and the circulating output work also increases. Under a certain working fluid flow rate, as the temperature of the heat source increases, the temperature of the inlet of the expander increases, and the inlet pressure increases. the cycle output work also increased.

Numerical study of using different Organic Rankine cycle working fluids for engine coolant energy recovery

Engine waste heat recovery technology especially Organic Rankine cycle (ORC) has been widely studied in order to achieve higher overall thermal efficiency, reduce the engine emissions and improve the fuel economy. The coolant energy occupies around 30% of the fuel energy can be used as the heat source for ORC system. This paper studies thermal status of the engine heated components when using different ORC working fluids as engine coolant to avoid the heat loos using heat exchanger to transfer coolant to the ORC fluid. A Solid-Liquid Conjugated Heat Transfer (SLCHT) calculation method is developed to calculate the heat transfer inside the engine, which can solve the temperature field of both solid zone and fluid zone. The simulation results have been validated by the experimental data from a 6-cylinder medium duty diesel engine, when water is the coolant in the system. The simulation model is then used to predict the temperature profile using different ORC working fluids and investigate the influence of different ORC working fluids on the cooling effects of the engine heated parts. The maximum temperature of the heated components has been selected as the evaluation parameters. The results reveals that applying selected ORC working fluids in engine as coolant is not practical under the designed conditions, which will make the engine overheated. Further investigation showed that increasing mass flow rate of the coolant can decrease the thermal status of the heated components but still cannot meet the cooling demands even under 200% of the original mass flow rate. The variations of the coolant outlet temperature and exergy were also analysed.