Temperature Organic Rankine Cycle Research Articles

Enhancing thermodynamic performance with an advanced combined power and refrigeration cycle with dual LNG cold energy utilization

Utilizing waste heat to drive thermodynamic systems is imperative for improving energy efficiency, thereby improving sustainability. A combined cooling and power systems (CCP) utilizes heat from a temperature source to deliver both power and cooling. However, CCP systems utilizing LNG cold energy suffers from low second law efficiency due to significant temperature differences. To address this, an “Advanced Power and Cooling with LNG Utilization (ACPLU)” system is proposed, integrating a cascaded transcritical carbon dioxide (TCO2)-LNG cycle with an Organic Rankine cycle (ORC) for improved power generation and an absorption refrigeration system (ARS) for simultaneous cooling. This study evaluates the second law efficiency, net work output, and exergy destruction performance through a sensitivity analysis, optimizing variables such as heat source temperature, superheater temperature difference, ORC and CO2 turbine inlet and condenser pressures, evaporator temperature, and pinch point temperatures of heat exchangers and generator. Compared to previous studies on CCP systems, the ACPLU shows a superior performance, with a second law efficiency of 27.3 % and a net work output of 11.76 MW. Cyclopentane as an ORC working fluid resulted in the highest second law efficiency of 29.06 % and net work output of 12.27 MW. Parametric analysis suggested that heat source temperature significantly impacts net power output. The exergy analysis concluded that a high-pressure ratio and good thermal match between the heat exchangers enhance overall performance. Utilizing artificial neural network (ANN) to produce a multiple-input-multiple-output (MIMO) objective function and performing multi-objective optimization (MOO) using genetic algorithm (GA), an improved second law efficiency and net power output by 28.11 % and 14.16 MW respectively, with pentane as the working fluid, is demonstrated. An average cost rate of 9.121 $/GJ was observed through a thermo-economic analysis. The ACPLU system is promising for medium temperature waste heat recovery, such as, pharmaceutical manufacturing plants.

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 %.

Silicon Tetrachloride as innovative working fluid for high temperature Rankine cycles: Thermal Stability, material compatibility, and energy analysis

Silicon Tetrachloride (SiCl4) is proposed as a new potential working fluid for high-temperature Rankine Cycles. The capability to overcome the actual thermal stability limit of fluids commercially employed in the state-of-the-art Organic Rankine Cycles (ORC) is demonstrated by static thermal stability and material compatibility tests. Experimental static test proves its thermo-chemical stability with a conventional stainless-steel alloy (AISI 316L) up to 650 °C. A preliminary material compatibility analysis performed with optical microscope on the AISI 316L cylinder, after exposure of 300 h to SiCl4 at temperature higher than 550 °C, confirms the potentiality of this fluid when coupled with high-grade heat sources. A thermodynamic analysis has been carried out accounting for the effect of operating conditions on the axial turbine efficiency. A comparison with fluids adopted in medium–high temperature ORCs is performed, evidencing that the proposed fluid could achieve more than + 10 % points as thermal efficiency gain compared to any commercial solutions when coupled with high-temperature sources such as solar, biomass, waste heat from industrial processes and prime movers. A 2 MW SiCl4 cycle operating full-electric at 550 °C reaches a thermal efficiency of 38 %, exceeding values attainable by any other working fluid under similar conditions and power size.

Thermal decomposition mechanism and thermal stability prediction of n-pentane/n-butane mixture

Mixtures appear to hold more promise in organic Rankine cycle (ORC) system than pure working fluids due to their better performance. The key limiting factor for the screening of mixture in the medium- and high temperature ORC system is its thermal stability. ReaxFF reactive molecular dynamic simulations and density functional theory calculations are performed in this study to investigate the thermal decomposition mechanism of n-pentane/n-butane mixture and predict its thermal stability. The results show that the presence of n-butane improves the thermal stability of n-pentane. According to the initial decomposition time, decomposition rates and apparent activation energies of mixture and pure working fluids, n-pentane/n-butane mixture has a better thermal stability than n-pentane and worse than n-butane. Based on the decomposition temperature ranges of n-pentane and n-butane, it can be determined that the n-pentane/n-butane mixture is stable at 280 °C. Therefore, the safe use temperature of the mixture can be roughly predicted based on the thermal stability data of the known working fluids and comparing the thermal decomposition of the mixture with these known working fluids. This paper provides a simple, economical and fast way for the safe use temperature prediction of mixture.

Thermal stability of linear siloxanes and their mixtures

The working fluid thermal stability is one of the crucial features of an effective organic Rankine cycle. Hexamethyldisiloxane (MM - C6H18OSi2) and octamethyltrisiloxane (MDM - C8H24O2Si3) are siloxane fluids currently exploited in high temperature organic Rankine cycles. However, data about their thermal stability are scarce or absent in literature. This manuscript presents a study of their behavior and decomposition at operating temperatures in the range 270–420°C.The assessment of thermal stability can be performed with several methods, which are either based on pressure anomalous variation in isothermal stresses or on the deviation of the saturation curves experimentally obtained before and after the fluid is thermally stressed. An enhanced method is proposed here, based on chemical analysis of both vapor and liquid phases of the sample before and after it is subjected to thermal stress. A comparison of the pre- and post-stress vapor–liquid equilibrium curve complements the analysis.Results proved a higher stability for MM than for MDM. Moreover, due to the current interest in applying mixtures in organic Rankine cycles, an equimolar mixture of MM and MDM was also tested, which exhibit a behavior that appears to be different from the simple superimposition of pure fluid ones.

PVTx properties of the R600a/R245fa for low temperature organic rankine cycle

The gaseous PVTx properties of the mixtures of 2-methylpropane(R600a) + 1,1,1,3,3-pentafluoropropane(R245fa) are measured by the Burnett isothermal expansion method while the temperatures are 300.2 K to 335.9 K and the corresponding pressures are 144.09 kPa to 895.20 kPa. The mass fraction of R600a ranges from 0.15 to 0.40. The uncertainties of the experimental equipment are estimated as: the temperature uncertainty is ±8.1 mK, the pressure uncertainty is ±1.7 kPa, and the mass fraction uncertainty is ±0.003. The results of the experiment are rectified by the virial equation of state (EOS) and the fitting virial coefficients of the virial EOS are obtained. The pressures obtained by virial EOS agree well with the experimental pressures with the relative deviations within ±0.9 %. This study provides the meaningful information for the further studies on the Organic Rankine Cycle using these novel mixed refrigerants.

Effect Of Climatic Conditions On Performance Of ORC Using Environment-Friendly Working Fluids – Special Reference To India

<p>Efficient heat recovery from low-grade heat sources is an achievable scientific frontier in the coming decade. One of the promising technologies in waste heat recovery is the organic Rankine cycle (ORC) system. Major obstacles to low-grade heat recovery include economic viability, scale, system efficiency, and exergy efficiency. In low temperature ORC systems, the cost of condenser becomes significant and hence air-cooled condenser is a feasible option. However, the performance of the air-cooled condenser is sensitive to the variation in ambient air conditions. India, being a tropical country, have villages and cities whose average temperature varies from -2oC in winter to 50oC in summer. The present work involves the study of heat transfer effects on the condenser using common organic working fluids and quantifying the consequences of environmental temperature variations. The constant thermal evaporator load is supplied with a medium-enthalpy heat source at 100 and 150oC. The atmospheric temperature associated with heat rejection from the condenser is varied from 273K to 313K for 5 working fluids. A MATLAB model of the ORC system is developed to study the effect of condenser performance on the first and second law efficiency of the ORC system. The MATLAB model is used to investigate the effect of varying inlet temperatures of the working fluid on the performance of ORC system to choose an organic working fluid suitable for Indian climatic conditions. R365 mfc, and R1233zd exhibit higher expander work and show higher heat rejection. At higher heat source temperatures of 150oC, the simulation shows a higher second law efficiency for the working fluid R1224yd(Z), which has critical temperature closed to the heat source temperature.</p>

Pneumatic system for pressure probe measurements in transient flows of non-ideal vapors subject to line condensation

This paper presents the design, construction and commissioning of a pneumatic system for pressure probe measurements in flows of organic vapors in non-ideal conditions, namely in the thermodynamic region close to the liquid–vapor saturation curve and the critical point where the ideal gas law is not applicable.Experiments were carried out with fluid siloxane MM (hexamethyldisiloxane, C6H18OSi2), commonly employed in medium/high temperature Organic Rankine Cycles (ORCs), in the Test Rig for Organic VApors (TROVA), a blow-down wind tunnel at the Laboratory of Compressible fluid dynamics for Renewable Energy Applications (CREA lab) of Politecnico di Milano. TROVA operation is intrinsically transient due to its batch nature, with a low frequency content (∼1Hz) related to the emptying of the high-pressure reservoir feeding the test section.The challenges linked to possible condensation in pneumatic lines, such as vapor–liquid menisci, hydrostatic head and mass-sink effects, were evaluated by means of theoretical calculation and experiments. To avoid these issues, a nitrogen-flushed pneumatic system for absolute and differential pressure measurements was designed and successfully tested with superheated MM vapor expanding in planar choked converging nozzles characterized by a portion with constant cross-sectional area yielding design Mach numbers of 0.2, 0.5 and 0.7. Commissioning of the complete system including a probe was performed with the first ever testing of an L-shaped Pitot tube in non-ideal subsonic flows of siloxane MM vapor at Mach numbers M=0.2 and 0.5. Measurement delay issues were identified and assessed through a dynamic testing procedure, and were solved by reducing the overall pneumatic lines volume including the one hidden within pressure transducers. The correct performance of the complete system was therefore verified for probe measurements of total, static and dynamic pressure in non-ideal flows of organic vapors. This sets the foundation for future directional pressure probes calibration and use in the characterization of such flows, as in direct measurement of total pressure losses across shocks and in testing of ORC turbine blade cascades.

Thermal decomposition and interaction mechanism of HFC-227ea/n-hexane as a zeotropic working fluid for organic Rankine cycle

Organic Rankine Cycle (ORC) is an effectively technology for the utilization of industrial waste heat and renewable energy. Zeotropic working fluids are more attractive than pure working fluids due to their lower exergy losses, higher cycle efficiencies and higher work outputs. The thermal stability is the major limitation factor for the selection of working fluid in the high temperature ORCs. This paper investigates the thermal decomposition and interaction mechanism of HFC-227ea/n-hexane as a zeotropic working fluid by using ReaxFF reactive molecular dynamic simulations and density functional theory calculations. The thermal decomposition process, the effects of temperature and HFC-227ea to n-hexane ratio on the thermal decomposition of HFC-227ea/n-hexane zeotropic working fluid, and the interaction between HFC-227ea to n-hexane for the thermal stability of zeotropic working fluid were investigated. The results showed that the hydrogen bond formed between HFC-227ea and n-hexane in HFC-227ea/n-hexane zeotropic working fluid improved the thermal stability of n-hexane and weakened the thermal stability of HFC-227ea. Therefore, the thermal stability of the HFC-227ea/n-hexane zeotropic working fluid is better than that of pure n-hexane and weaker than that of pure HFC-227ea.

Determination of Optimum Pinch Point Temperature Difference Depending on Heat Source Temperature and Organic Fluid with Genetic Algorithm

In this study, the effect of evaporator pinch point temperature difference (∆TPP,e) value in Organic Rankine Cycle (ORC) on system performance was determined. Under different applications of ORC, optimum ∆TPP,e value has been determined in ORC systems designed with different heat source temperatures. By changing the ∆TPP,e value, the heat input provided to the system, the mass flow of organic fluid, the evaporation pressure and the enthalpy drop in the turbine are affected. In thermodynamic optimization, the objective function is determined as turbine power maximization. Genetic algorithm optimization technique is used. Within the scope of low and high temperature ORC applications, the optimum ∆TPP,e value of different organic fluids under 10 different heat source temperatures (Low, 90-130 °C; High, 250-290 °C) has been determined. Low temperature organic fluids have been selected from dry, isentropic, wet and new-generation categories. High temperature organic fluids have been selected from the alkane, aromatic hydrocarbon, and siloxane categories. The effect of ∆TPP,e on fluids of different categories was determined for low and high temperature ORCs. It has been determined that taking the ∆TPP,e value constant regardless of the heat source temperature and organic fluid causes performance loss in ORC.

Determination of Chopped Fruits Freshness with High Accuracy by Using Electronic Nose

In this study, the effect of evaporator pinch point temperature difference (∆TPP,e) value in Organic Rankine Cycle (ORC) on system performance was determined. Under different applications of ORC, optimum ∆TPP,e value has been determined in ORC systems designed with different heat source temperatures. By changing the ∆TPP,e value, the heat input provided to the system, the mass flow of organic fluid, the evaporation pressure and the enthalpy drop in the turbine are affected. In thermodynamic optimization, the objective function is determined as turbine power maximization. Genetic algorithm optimization technique is used. Within the scope of low and high temperature ORC applications, the optimum ∆TPP,e value of different organic fluids under 10 different heat source temperatures (Low, 90-130 °C; High, 250-290 °C) has been determined. Low temperature organic fluids have been selected from dry, isentropic, wet and new-generation categories. High temperature organic fluids have been selected from the alkane, aromatic hydrocarbon, and siloxane categories. The effect of ∆TPP,e on fluids of different categories was determined for low and high temperature ORCs. It has been determined that taking the ∆TPP,e value constant regardless of the heat source temperature and organic fluid causes performance loss in ORC.

Design and Optimization of a Radial Inflow Turbine for Use with a Low Temperature ORC

This study aims to design and optimize an organic Rankine cycle (ORC) and radial inflow turbine to recover waste heat from a polymer exchange membrane (PEM) fuel cell. ORCs can take advantage of low-quality waste heat sources. Developments in this area have seen previously unusable, small waste heat sources become available for exploitation. Hydrogen PEM fuel cells operate at low temperatures (70 °C) and are in used in a range of applications, for example, as a balancing or backup power source in renewable hydrogen plants. The efficiency of an ORC is significantly affected by the source temperature and the efficiency of the expander. In this case, a radial inflow turbine was selected due to the high efficiency in ORCs with high density fluids. Small scale radial inflow turbines are of particular interest for improving the efficiency of small-scale low temperature cycles. Turbines generally have higher efficiency than positive displacement expanders, which are typically used. In this study, the turbine design from the mean-line analysis is also validated against the computational fluid dynamic (CFD) simulations conducted on the optimized machine. For the fuel cell investigated in this study, with a 5 kW electrical output, a potential additional 0.7 kW could be generated through the use of the ORC. The ORC’s output represents a possible 14% increase in performance over the fuel cell without waste heat recovery (WHR).

Effect of ambient temperature organic Rankine cycle geothermal power plant with Aspen plus

This study concerns a thermodynamic analysis of the Organic Rankine Cycle for energy conversion from geothermal resources. Some thermodynamic variable was simulated by using Aspen plus. The equation of state is expressed by the Peng-Robinson formulation. Analysis carried out considering the variance of ambient temperature (27°C, 30°C, 33°C, 35°C, and 40 °C) on air-cooled in the condenser. Result is obtained for several set operating parameters, such as the evaporation and condensation pressure for the variance of ambient temperature, the mass flow rate of the geothermal fluid. From results, the ambient temperature has affected for power generated of ORC. The lower ambient temperature then will increase the power generate of the system.

Assessment of a District Trigeneration Biomass Powered Double Organic Rankine Cycle as Primed Mover and Supported Cooling

This study presents a combined cooling, heating, and power system powered by biogas, suitable for small scale communities in remote locations. To run such a system, in order to obtain the daily life essentials of electricity, hot water, and cooling, municipal waste can be considered as an option. Furthermore, the organic Rankine cycle part of the organic Rankine cycle powered vapor compression chiller can be used in times of need for additional electric production. The system comprises a medium temperature organic Rankine cycle utilizing M-xylene as its working fluid, and the cooling was covered by an Isobutane vapor compression cycle powered by an R245fa employing organic Rankine cycle. The system analyzed was designated to provide 250 kW of electricity. The energetic and exergetic analysis was performed, considering several system design parameters. The impact of the design parameters in the prime mover has a much greater effect on the whole system. The system proposed can deliver cooling values at the rate between 9.19 and 22 kW and heating values ranging from 879 up to 1255 kW, depending on the design parameter. Furthermore, the second law efficiency of the system was found to be approximately 56% at the baseline conditions and can be increased to 64.5%.

Modeling of an Organic Rankine Cycle Waste Heat Recovery system for automotive engine applications

The remarkable investments made by manufacturers over the last few decades have contributed to improving the performance of internal combustion engines in every aspect: lower polluting emissions, greater specific power and thermal efficiency. Despite this, on an average, about 40% of the thermal power theoretically available from the combustion of the fuel is still stored in the exhaust gases and therefore dispersed in the environment. In this work the modeling and validation of a waste heat recovery (WHR) plant will be described, combining the engine with a low temperature Organic Rankine Cycle (ORC) system, in order to investigate the feasibility of this system on board of a vehicle, analyzing the quantity of thermal power recovered and made available in the form of electrical power. The ORC plant is modeled using a 0D/1D thermo-fluid dynamic approach. Starting from experimental tests, a map-based model for the piston pump and the scroll expander has been developed. The model has been validated through the use of a vector optimization technique, exploiting a genetic algorithm (MOGA). Subsequently, this system has been coupled to a spark ignition engine for automotive applications, adapting its speed range to comply with the ORC experimental tests. To have an accurate control over the expander inlet temperature, a bypass circuit and two throttles actuated by a PI controller have been implemented. The simulations were performed by considering 18 engine points at maximum load and different rpm. An average thermal efficiency increase of the system of 2.6% was obtained by introducing the recovery plant, and wide improvement chance can be foreseen in the case of ORC full-power use.

Experimental investigation on heat transfer characteristics of hexamethyldisiloxane (MM) at supercritical pressures for medium/high temperature ORC applications

The supercritical organic Rankine cycle (ORC), with favorable thermo-economy, has been considered as one of the most promising solutions to convert medium/high temperature renewable energy or waste heat into electricity. Hexamethyldisiloxane (MM) has relatively high thermostability and low critical parameters, rendering it suitable for the medium/high temperature supercritical ORC system. Since the abnormal heat transfer phenomenon caused by the sharp change of the thermal properties around the pseudo-critical temperature at supercritical pressures of MM in the heating tube, the heat exchanger design becomes one of the most challenging aspects related to the supercritical ORC modeling. To fill this gap, the present work experimentally investigates the heat transfer to MM at supercritical pressures in a smooth vertically upward tube with an inner diameter of 2.4 mm. The effects of key heat transfer conditions, predictions of heat transfer deterioration (HTD), applicability of existing heat transfer correlations and the development of a new correlation are analyzed based on the experimental data. The results show that the heat transfer process at supercritical pressures can be divided into three stages according to the wall temperature, bulk temperature and pseudo-critical temperature. The higher heat flux, lower pressure and mass flux lead to the more serious HTD. The non-dimensional heat flux gives a better prediction of HTD than the buoyancy parameter and flow acceleration parameter. Among the existing correlations, Bishop correlation can get a more accurate predicted result with the mean absolute relative deviation (MAD) of 8.5%. Fitted by 900 experimental points of MM, the proposed correlation considering the non-dimensional heat flux shows a lower MAD of 4.6%.

Experimental investigation of a cascaded organic Rankine cycle plant for the utilization of waste heat at high and low temperature levels

A power plant with two cascaded organic Rankine cycles (CORC) to exploit waste heat from a 800 kWe combined heat and power plant, fueled by biogas, is designed and tested. Heat from the exhaust gas is utilized with a high temperature organic Rankine cycle (HT-ORC), where toluene is employed as a working fluid. The heat discharged from the HT-ORC as well as heat from the engine coolant and additional heat from the exhaust gas is supplied to a low temperature ORC (LT-ORC) with the working fluid Solkatherm SES36. The design of the CORC and the selection of working fluids is presented, aiming at a maximum plant efficiency, but also complying with environmental, safety and practical issues. Furthermore, plant components and construction details are described. After manufacturing, initial tests are carried out, obtaining thermodynamic conditions that are close to the design of the HT-ORC, where a maximum electrical turbo-generator output of 17.5 kW is measured. The cascading of the low temperature heat sources and the transfer to the LT-ORC is shown as well as the basic operation of the LT-ORC. However, several problems occurred, such as a turbo-generator damage in the HT-ORC, a too high condensation pressure and a low working fluid mass flow rate in the LT-ORC, which are discussed together with proposed optimization measures.

Thermal stability and material compatibility for hexamethyldisiloxane as the working fluids of organic Rankine cycle

The organic Rankine cycle (ORC) is one of the most suitable methods to generate electricity for renewable energy and industrial waste heat recovery systems. High temperature ORCs have recently attracted much interest because of the improved theoretical thermal efficiency. For high temperature ORCs, the working fluids need high critical temperature, low flammability and good thermal stability. Siloxanes are considered as the promising working fluids for high temperature ORCs in previous studies because of their high critical temperature, low flammability and environmental friendliness. The thermal stability and material compatibility of working fluid is the primary limitation for the working fluid selection at high temperatures. However, the results about thermal stability and material compatibility of siloxanes are scarce in previous studies. In this paper, the thermal stability and material compatibility of siloxanes were studied with hexamethyldisiloxane (MM) as a representative fluid. A test system and an experimental method were designed to identify the compositions of decomposition products. The masses of liquid samples were measured before and after tests to confirm the mass fractions of gaseous and liquid compositions in decomposition products. Liquid decomposition products, such as octamethyltrisiloxane (MDM) and tetramethylsilane, were found to be the main decomposition products of MM. The possible decomposition paths of MM were analyzed by the results of decomposition product composition analysis. The decomposition ratios of MM at 220, 240, 260, 280 and 300°C were measured after decomposition for 24 h. The decomposition could be detected at 240°C, which was lower than the critical temperature of MM. Thus, the thermal stability of MM should be emphasized for supercritical ORCs if the decomposition of MM is unacceptable in ORC systems. The air was confirmed to have big effects on MM decomposition and could change the reaction paths of MM decomposition. Thus, air dissolved in the liquid working fluid should be removed before filling the working fluid into ORC systems. The material compatibility of MM with metal samples was measured experimentally. 304 stainless steel and copper were chosen as test metal materials and the metal samples were processed into the shapes for the tensile experiments. The experimental temperature was 220°C, which was considered as a thermal stable temperature for MM. The material compatibility experimental periods in this study were 10 days, which were long enough in previous studies. The experimental results showed that the mass and hardness relative changes in both metal samples were very small and could be negligible. However, the tensile strength changes in the copper samples were obviously bigger than those in 304 stainless steel samples. Thus, 304 stainless steel has better compatibility with MM than copper as the metal material in systems at 220°C. The material compatibility of n-pentane with metal samples at 220°C was also measured using the same test system and method to be a comparison. The results showed that the tensile strength changes in metal samples with n-pentane were much bigger than those with MM. Thus, MM exhibited better compatibility with metal materials than n-pentane at 220°C as ORC working fluids.

HCFO-1224yd(Z) as HFC-245fa drop-in alternative in low temperature ORC systems: Experimental analysis in a waste heat recovery real facility

The organic Rankine cycle (ORC) has been growing in importance as a technology for producing electricity from low temperature waste and renewable heat sources. In small-scale applications, the most used working fluid has been HFC-245fa, although this is being substituted for low GWP alternatives. A new HCFO working fluid, HCFO-1224yd(Z), has appeared as a possible alternative for HFC-245fa. In this study, this alternative working fluid is analysed and, finally, the working fluid is experimentally tested as drop-in alternative in a commercial ORC system. The main purpose is to determine the feasibility of using HCFO-1224yd(Z) as a drop-in replacement for HFC-245fa in a real facility that was initially designed to operate with HFC-245fa. The results show how the use of HCFO-1224yd(Z) offers power output that ranges from 7.5% to 17.4% lower than that provided by HFC-245fa. Although HFC-245fa offers higher power output, the results show that HCFO-1224yd(Z) offers up to 7.7% higher cycle net efficiency; this is due to the higher input thermal rate required by HFC-245fa. Finally, HCFO-1224yd(Z) has been stated as a suitable alternative to HFC-245fa as a drop-in replacement in a small-scale, low-temperature ORC, which increases its attractiveness for heat source with higher temperatures.

Evaluation of working fluids for organic Rankine cycles using group-contribution methods and second-law-based models

The group-contribution (GC) methods suffer from a limitation concerning to the prediction of process-related indexes, e.g., thermal efficiency. Recently developed analytical models for thermal efficiency of organic Rankine cycles (ORCs) provide a possibility of overcoming the limitation of the GC methods because these models formulate thermal efficiency as functions of key thermal properties. Using these analytical relations together with GC methods, more than 60 organic fluids are screened for medium-low temperature ORCs. The results indicate that the GC methods can estimate thermal properties with acceptable accuracy (mean relative errors are 4.45%–11.50%); the precision, however, is low because the relative errors can vary from less than 0.1% to 45.0%. By contrast, the GC-based estimation of thermal efficiency has better accuracy and precision. The relative errors in thermal efficiency have an arithmetic mean of about 2.9% and fall within the range of 0–24.0%. These findings suggest that the analytical equations provide not only a direct way of estimating thermal efficiency but an accurate and precise approach to evaluating working fluids and guiding computer-aided molecular design of new fluids for ORCs using GC methods.