Efficiency Of Organic Rankine Cycle System Research Articles

Organic rankine cycle systems with mixture of pure fluids: On infeasible fluid’s fractions due to the interaction between the mixture glide and the hexs pinchs

The Organic Rankine Cycle (ORC) is a promising technology for power generation from low-grade heat. The selection of working fluids is one of the important key points to improve the performance of an ORC system. Zeotropic mixtures show promising performances as working fluids. In fact, their temperature glide during phase change enables better match between the working fluid and the heat source/sink temperatures. In order to reveal the performance of mixture in ORC system, this paper deals with the thermodynamic model of the subcritical Organic Rankine Cycle (ORC) systems driven by low grade heat source while using zeotropic mixture working fluids with a special consideration to the interaction between phase change glides and the pinch value and their location in both the evaporator and the condenser (HEXs). Zeotropic mixtures of seven pure fluids are evaluated as working fluids for a subcritical ORC system. The mass fraction effects of mixtures on the thermal efficiency are analyzed. For given working conditions (working fluid mass flow, pressure and bubble temperature) the results show that for each considered zeotropic mixture there exist mass fraction ranges that are not consistent with the pinch values constraint in the HEXs and leads to so-called ‘infeasible zones’ with unreal HEXs dimensions. Results shows also that, out of these “infeasible fractions” zone, keeping unchanged the working conditions, the thermal performances of ORC system using zeotropic mixture are always better than the thermal performances of the same systems using the correspondent pure fluids. In addition, out of these highlighted “unfeasible zones” it was found that mixture with high temperature glide improve the thermal efficiency of ORC system.

Experimental evaluation of organic Rankine cycle using zeotropic mixture under different operation conditions

The zeotropic mixture is a feasible way to improve the thermodynamics performance of organic Rankine cycle (ORC). A small-scale ORC experimental apparatus with a scroll expander was established. Then, the system performance using different zeotropic mixtures (including 0.75R245fa/0.25R141b, 0.5R245fa/0.5R141b and 0.25R245fa/0.75R141b) was tested and compared with the pure fluid of R245fa and R141b to determine whether the mixture fluid can improve the system performance. The experimental results show that the thermal efficiency and exergy efficiency of ORC system gradually increase with the increase of cooling water flow rate and the decrease of expander rotational speed. Under different working conditions, mixture fluids can produce more shaft power and have lower condenser exergy destruction than pure fluids. The zeotropic mixture is not always better than the pure fluid, while it can improve the thermal efficiency and exergy efficiency of the ORC system with an appropriate mass fraction. In the experiment, the best mass fraction of R245fa/R141b is 0.25/0.75, and its thermodynamic performance is significantly higher than that of R141b and R245fa. The maximum thermal efficiency and exergy efficiency of 0.25R245fa/0.75R141b are 5.58% and 23.2% respectively.

Application of novel framework based on ensemble boosted regression trees and Gaussian process regression in modelling thermal performance of small-scale Organic Rankine Cycle (ORC) using hybrid nanofluid

This work examined the thermal performance of a small-scale solar organic Rankine cycle system, in which a flat plate solar collector was employed to supply heat to the organic Rankine cycle system. In the ORC system, WO 3 +MWCNT/water nanofluid was employed for the solar collector, while MWCNT/R141b nano-refrigerant was used in the ORC system. In the first stage, the thermal and exergy efficiency of the ORC system was experimentally examined at different flow rates and concentrations of nanofluid. As a result, the peak thermal efficiency of 73.21% was attained at 3 L per minute (lpm) of nanofluid flow rate and 1.5 vol% of nanofluid concentration. Moreover, a significant increase in energy and exergy efficiency by 8.52% and 6.30%, respectively, was observed for 0.5 vol% of nanofluid concentration and 3 lpm of nanofluid flow rate in the collector. In the second stage, the experimental data was utilized to develop contemporary ensemble machine learning algorithms such as boosted regression trees (BRT) and Gaussian process regression (GPR) aiming to predict the solar collector's energy efficiency and the ORC system's energy-exergy efficiency. The GPR-based models performed exceptionally well as Pearson's coefficient (R), coefficient of determination (R 2 ), mean squared error (MSE), and root mean squared error (RMSE) were 0.9999, 0.9998–0.9999, 0.0015–0.0524, and 0.0124–0.0723, respectively. For BRT-based model the R, R 2 , MSE and RMSE were 0.9604–0.9949, 0.97–0.99, 0.0969–0.8783, and 0.3113–0.9372. Theil's U2 was employed to calculate the uncertainty in the prediction framework, which was determined to be in the range of 0.002–0.00369 for GPR and 0.00228–0.1414 for the BRT-based model. Overall, both machine learning algorithms performed well, although GPR did better than BRT across the board. • Thermal performance of a solar-aided ORC system was modeled with GPR and BRT. • Peak thermal efficiency of ORC system reached 73.21% at 3 lpm of nanofluid flow rate. • Energy and exergy efficiency were increased by 8.52% and 6.30% as using nanofluid. • GPR-based models worked with exceptionally good indicators of R, R 2 , MSE, and RMSE. • Nanofluid flow rates were the most influential factor on ORC system performance.

Influence of thermal stability on organic Rankine cycle systems using siloxanes as working fluids

• An off-design model with fluid decomposition parameters was established. • The influence of MM thermal decomposition on the ORC system was evaluated. • MM decomposition reduced the net power and efficiency of ORC system obviously. • MM decomposition may lead to incomplete evaporation and evaporator acid corrosion. The organic Rankine cycle (ORC) is an efficient power generation technology that has been widely used in renewable energy utilization and industrial waste heat recovery. The thermal stability of working fluids has a significant effect on the fluid selection and system design of ORC systems. In this study, an off-design model of an ORC system was established with hexamethyldisiloxane (MM) as the working fluid, and the effects of the MM thermal stability on the system were analyzed. The results showed that the effect of MM thermal decomposition on the cold source and working fluid pump was limited. The outlet temperature of the evaporator decreased with MM decomposition, which might lead to incomplete evaporation of working fluids and possible damage to the expander. The outlet temperature of the heat source also decreased with MM decomposition, which led to lower outlet temperatures than the acid dew point limit temperature. Both of these results can affect the safe operation of ORC systems. The net power and thermal efficiency of the system decreased with increasing thermal decomposition ratios of MM. The net power and thermal efficiency decreased by 7.48% and 10.72% respectively in the model of this study with a 10% decomposition ratio.

Experimental investigation on steady and dynamic performance of organic Rankine cycle with R245fa/R141b under different cooling and expander speed conditions

A kW-scaled organic Rankine cycle (ORC) experimental apparatus with a modified scroll compressor as the expander was established to investigate its operation characteristics. The test rig uses steam with a temperature of about 110°Cfrom a 30 kW electric steam generator as the heat source. In this study, the steady-state performance and dynamic response of R245fa/R141b (mass ratio 0.5/0.5) and R245fa under variable cooling water flow rate and expander rotational speed are experimentally studied. In the steady-state experiments, system thermal efficiency decreases with the increase of expander rotational speed. The mechanical efficiency of scroll expander is in the range of 91%–99%. Additionally, the maximum shaft power and isentropic efficiency of the expander and thermal efficiency of ORC system with R245fa/R141b are 831 W, 58%, and 5.2%, respectively. Compared with R245fa, the maximum shaft power and thermal efficiency of R245fa/R141b are increased by 9.9% and 13.0%, respectively. In the dynamic experiment, the disturbance of rotational speed and cooling water flow rate has little influence on the inlet temperature of expander. Under the disturbance of the rotational speed, the response time of shaft power, torque and speed of expander is in the range of 1–5s. The dynamic response of the ORC system is mainly controlled by the condenser and pump. Under the disturbance of coolant flow rate, the response time of pump inlet temperature and outlet temperature is about 350s and 600s, respectively. The ORC system using R245fa and R245/R141b have the same response speed.

Possibility of optimal efficiency prediction of an organic Rankine cycle based on molecular property method for high-temperature exhaust gases

Working fluid selection is critical for the system design of an organic Rankine cycle (ORC). Computer-aided molecular design (CAMD) provides a new approach to search novel working fluids. In this study, the possibility of using molecular properties to predict the optimal system performance of an ORC is investigated. First, for a heat source of high-temperature exhaust gases, the influences of the molecular properties including the critical temperature and the specific heat capacity on the exergy efficiency of an ORC using 10 alkanes as working fluid are estimated. Then, the possibility of using the parameters of PC-SAFT to assess the optimal efficiency of the ORC is explored. The relation of the optimal temperature difference between the heat source and the molecular properties is determined. The prediction precision of PC-SAFT method is compared with the other four different molecular property methods. The results indicate that the parameters of PC-SAFT can be used to predict the optimal exergy efficiency of ORC system and the corresponding optimal heat source temperature. The average deviations of the exergy efficiency predicted is only 1.44% for the PC-SAFT method. The search range of the optimal working fluid can be decreased and the computation load is reduced significantly.

Thermodynamic analysis and optimization of a partial evaporating dual-pressure organic rankine cycle system for low-grade heat recovery

The organic Rankine cycle (ORC) has been proven as one of the most effective technologies for low-grade heat recovery. However, its efficiency is limited due to exergy losses caused by the large temperature difference between the heat source and working fluid in the evaporator. To enhance the ORC system efficiency, in this paper, a novel partial evaporating dual-pressure ORC (PEDORC) system is proposed. A mathematical model is developed to evaluate the system thermal characteristics and investigate the effects of key parameters (e.g. evaporating temperature, quality, superheat temperature, energy distribution) on the system performance. Results show that an optimal evaporating temperature in the evaporators exists to achieve the maximum net power output and exergy efficiency. However, the system thermal efficiency increases as the evaporating temperature increases. Furthermore, the best thermal performance occurs when the thermal energy is properly distributed in the evaporators I and II. The performance of the proposed PEDORC system is further compared with the simple ORC (SORC) and basic dual-pressure ORC (BDORC) systems. The results show that the net power output and exergy efficiency of the proposed PEDORC system are increased by up to 27% and 4.6%, respectively, in comparison to the SORC system. By comparing with the BDORC system, the net power output and exergy efficiency of the proposed system are increased by up to 9.2% and 4%, respectively, and the Levelized Cost of Electricity is reduced by up to 4%. These analyses demonstrate that the proposed PEDORC system is an effective means to recover low-grade thermal energy.

Influence of Superheated Vapour in Organic Rankine Cycles with Working Fluid R123 Utilizing Low-Temperature Geothermal Resources

An organic Rankine cycle (ORC) system with R123 working fluid has been utilised for generating electricity from low-temperature geothermal resources. The degree of superheated vapour warrants attention to be studied further. This is because the degree of superheated vapour is the last point to absorb heat energy from geothermal heat sources and influence the amount of expansion power produced by the expander. Therefore, achieving high ORC system efficiency requires a parameter of superheated vapour degree. This paper presents an experimental study on a binary cycle, applying R123 as the working fluid, to investigate the effect of variation in superheated vapour degree on the ORC efficiency. Geothermal heat sources were simulated with conduction oil as an external heat source to provide input heat to the ORC system. The temperature high inlet (TH in) evaporator was designed to remain at 120 °C during the experiment, while mass flow rate was adjusted to make superheated vapour variations, namely set at 278, 280, 282, 284, and 286 K. Furthermore, the effect was observed on heat transfer inlet, pinch, heat transfer coefficient, expander work output, isentropic efficiency, expander shaft power, power generation, thermal efficiency, and ORC efficiency. The experimental results showed that the mass flow rate nearly remained unchanged at different degrees of superheated vapour. The ranges of heat transfer inlet, pinch temperature, and heat transfer coefficient were 25.34–27.89 kJ/kg, 9.35–4.08 °C, 200.62–232.54 W/m2·K, respectively. In conclusion, ORC system efficiency can be triggered by various parameters, including the temperature on the exit side of the evaporator. The superheated vapour of R123 working fluid to higher temperatures has caused a decrease in ORC system efficiency due to the decrease in heat transfer inlets, although theoretically, the work total increased. Further investigation has found that the magnitude of the mass flow rate affects the behaviour of the components of the ORC system.

Analysis of the Effects of Blade Installation Angle and Blade Number on Radial-Inflow Turbine Stator Flow Performance

Organic Rankine cycle (ORC) is a reliable technology to recover low-grade heat sources. The radial-inflow turbine is a critical component, which has a significant influence on the overall efficiency of ORC system. This study investigates the effects of the blade installation angle and blade number on the flow performance of radial-inflow turbine stator. R245fa and toluene were selected as the working fluids in the low and high temperature range, respectively. Two-dimensional stator blades model for the two working fluids were established, and numerical simulation was conducted through Computational Fluid Dynamics (CFD) software. The results show that for low temperature working fluid R245fa, when the installation angle is 32° and blade number is 22, the distribution of static pressure along the stator blade has no obvious pressure fluctuation, and the flow loss is least. Meanwhile, the stator blade obtained the optimal performance. For high temperature working fluid toluene, when the installation angle is 28° and blade number is 32, the average outlet temperature is the lowest, while the average outlet velocity is the largest. The flow state is well and smooth, and the remarkable flow separation and shock wave are not present. Moreover, the stator blade for R245fa has a larger chord length, cascade inlet diameter, and cascade outside diameter but a lower blade number compared to toluene.

Effect of radial turbo-expander design on off-highway vehicle organic Rankine cycle system efficiency

Effect of radial turbo-expander design on off-highway vehicle organic Rankine cycle system efficiency

Effect of radial turbo-expander design on off-highway vehicle organic Rankine cycle system efficiency

Compared to other waste heat recovery (WHR) technologies, organic Rankine cycle (ORC) system is regarded as the most candidate technology due to its simplicity, low cost and small back pressure impact. Expanders are crucial components of an ORC system along with working fluid. In this simulation study, an in-house code has been developed to explore the effect of various working fluids on optimum radial expander geometry. In addition, an off-design turbine analysis has been employed in order to evaluate the performance of the calculated expander geometry under various engine operating conditions. Finally, the effect of various expanders' designs on fuel consumption and emissions of an off-highway vehicle is presented. Compared to conventional diesel powertrain systems, the WHR system showed an up to 5.7% increase in brake torque and brake power and a 5.4% reduction in BSFC. The results also showed that working fluid and expander speed are critical parameters on the performance of the proposed powertrain configuration.

Improving energy recovery efficiency by retrofitting a PCM-based technology to an ORC system operating under thermal power fluctuations

Energy-intensive industrial processes, such as those occurring in steel billet reheating furnaces, usually release waste heat characterised by a fluctuating and/or intermittent nature, which limits the efficiency of current waste heat recovery systems. In fact, current waste heat recovery systems are usually designed for one single operating point, which forces them to operate at off-design conditions when subjected to power fluctuation of the waste heat.This paper investigates the impact of retrofitting a technology based on high temperature phase change materials (PCM-based technology) in an existing waste heat recovery system – composed of an air preheater and an Organic Rankine Cycle (ORC) system – installed downstream of a steel billet reheating furnace. The analysis was carried out by using real data from a billet reheating furnace and ORC system to develop and validate a model in Modelica language; a comparison between the ORC system efficiency and capacity factor with and without the PCM-based technology was then performed.The results showed that the introduction of the PCM-based technology allows the capacity factor to increase from 38% to 52% and the average thermal efficiency to increase from 15.5% to 16.4%. The cost-benefit analysis shows that electric energy priced between 83 and 120 €/MWh could guarantee a payback period between 3 and 5years.

Exergy and economic analysis of organic Rankine cycle hybrid system utilizing biogas and solar energy in rural area of China

ABSTRACTDue to the existing huge biogas resource in the rural area of China, biogas is widely used for production and living. Cogeneration system provides an opportunity to realize the balanced utilization of the renewable energy such as biogas and solar energy. This article presented a numerical investigation of a hybrid energy-driven organic Rankine cycle (ORC) cogeneration system, involving a solar ORC and a biogas boiler. The biogas boiler with a module of solar parabolic trough collectors (PTCs) is employed to provide heat source to the ORC via two distinct intermediate pressurized circuits. The cogeneration supplied the power to the air-condition in summer condition and hot water, which is heated in the condenser, in winter condition. The system performance under the subcritical pressures has been assessed according to the energy–exergy and economic analysis with the organic working fluid R123. The effects of various parameters such as the evaporation and condensation temperatures on system performance were investigated. The net power generation efficiency of the cogeneration system is 11.17%, which is 25.8% higher than that of the base system at an evaporation temperature 110°C. The exergy efficiency of ORC system increases from 35.2% to 38.2%. Moreover, an economic analysis of the system is carried out. The results demonstrate that the profits generated from the reduction of biogas fuel and electricity consumption can lead to a significant saving, resulting in an approximate annual saving from $1,700 to $3,000. Finally, a case study based on the consideration of typical rural residence was performed, which needs a payback period of 7.8 years under the best case.

Thermodynamic analysis of organic Rankine cycle using zeotropic mixtures

In recent years, more and more attention has been paid to organic Rankine cycle (ORC), which is simply structured, highly reliable and easily maintainable. In order to improve the efficiency of ORC systems, zeotropic mixtures whose phase change process is variable temperature, are used as working fluids to match the temperature profiles of the heat source and heat sink. In this paper, a thermodynamic model which mainly includes Jacob number and the ratio of evaporation temperature and condensation temperature is proposed to forecast the thermal efficiency, output work and exergy efficiency of ORC system with zeotropic mixture. Furthermore, the proposed model programmed by Mablab 2010a is verified by the theoretical data. Then, for different heat source inlet temperature, using different zeotropic mixture pairs, output work that is objective function is maximized by optimizing the evaporation temperature. The results show that if the other working conditions are fixed, the heat source inlet temperature has a significant influence on the best composition of zeotropic mixtures at the optimal evaporation temperature. With the increase of heat source inlet temperature, there exists a heat source inlet temperature that pure working fluid has better system performance than zeotropic mixture. The extent of ORC system performance improvement has a positive correlation with zeotropic mixture’s temperature glide.

Study of zeotropic mixtures of ORC (organic Rankine cycle) under engine various operating conditions

Aiming at the recovery of exhaust energy for a diesel engine, a set of ORC (organic Rankine cycle) system is designed. The characteristics of the exhaust gas under various operating conditions are studied through experiment. Based on experimental results and theoretical calculation, effects of eight kinds of zeotropic mixtures on the performance of ORC system for exhaust energy recovery are discussed for vehicle engine under various operating conditions. Variation of net power output, thermal efficiency, exergy efficiency of ORC system and mass flow rate of zeotropic mixture under various operating conditions of engine is investigated. Two concepts – WHRE (waste heat recovery efficiency) and POIR (power output increasing rate) – are defined and studied. The results show that when the evaporating pressure is 2.0 MPa, the net power output of ORC system can reach up to 24.65 kW. Using this ORC system, the maximum WHRE is 8.5% and engine power output can be increased by 10.63%.

Experimental Evaluation of the Regenerative and Basic Organic Rankine Cycles for Low-Grade Heat Source Utilization

AbstractThe present paper conducts the experimental evaluation of the performance of a regenerative organic Rankine cycle (ORC) system working with refrigerant R123 and generating 10-kW-level power. The ORC system consists of an axial-flow single-stage turbine, a regenerator, an evaporator, a condenser, and a pump. The regenerative ORC and the basic ORC system efficiency are evaluated under the same conditions. The degree of superheat of the turbine inlet vapor is controlled by the evaporating temperature. The cooling water flow rate is controlled by adjusting the opening of the valve. The experiment results show that the thermal efficiency of the regenerative ORC is higher than that of the basic ORC by about 25%. The thermal efficiency of basic ORC with saturated vapor at turbine inlet is higher than that with superheated vapor by 3.2%, and the thermal efficiency of the regenerative ORC with saturated vapor at turbine inlet is higher than that with superheated vapor by 4.36%. The enthalpy drop across the...

Analysis of Cogeneration System in Series Circuit Based on Regenerative Organic Rankine Cycle

In this paper thermodynamic performance of a combined heat and power cogeneration system driven by low-temperature source is investigated. The system consists of regenerative Organic Rankine Cycle (ORC) and an additional process heater as a series circuit. Seven working fluids of isobutene, butane, R11, R123, isopentane, normal pentane, and R113 are considered in this work. Special attention is paid to the effects of system parameters such as the turbine inlet pressure or source temperature on the characteristics of the system such as the ratio of mass flow rates, net work production as well as the efficiencies of the first and second laws of thermodynamics for various working fluids. This study finds that higher turbine inlet pressure leads to lower second law efficiency of ORC system but higher that of the combined system. Results also show that the optimum working fluid varies with the source temperature.