Low-temperature Organic Rankine Cycle Research Articles

On the Viability of Hydrofluoroolefin-R245fa Mixtures as Organic Working Fluids in a Low-Temperature Solar-Powered Organic Rankine Cycle (ORC)

Abstract To address the intermittent nature of solar and other renewable energy (RE) sources, an organic Rankine cycle (ORC) can be employed to facilitate steady production of power. Organic working fluid (OWF) mixtures in ORCs are of interest due to the possibility of reducing irreversible losses in the system and having a better sense of control over its environmental impact while not compromising on the performance benefits when paired with conventional fluids such as R245fa. Hydrofluoroolefins (HFOs) are considered as one of the components due to their zero ozone depleting potential (ODP) and very low global warming potential (GWP). This study evaluates the performance of binary zeotropic mixtures of R245fa and HFOs with available thermodynamic properties (R1234yf, R1234zeE, and R1234zeZ) as OWFs in a simple low-temperature solar-powered ORC. Specifically, the optimal compositions of each pair of HFO-R245fa mixtures within the specified operating conditions are identified via the performance indicators (1 kW net power output; thermal efficiencies; and GWP); and are compared against their pure components and known conventional OWFs. The turbine power outputs and efficiencies of the mixtures, determined from ASPEN Plus simulations, were observed to be competitive as alternatives for the pure components, and conventional fluids. At optimal compositions, R245fa/R1234zeZ (0.2619 mass fraction R245fa) was shown to be the most viable OWF blend with peak efficiency at 7.5545% and GWP of 274.2, accomplishing the target 1kW turbine power output, followed closely by R245fa/R1234zeE (0.2678 R245fa; 1kW power output; 7.4824% peak efficiency; GWP = 281), and R245fa/R1234yf (0.3589 R245fa; 0.9595 kW power output; 7.4338% peak efficiency; GWP = 372.2). It is recommended that more HFO-R245fa mixtures, as well as other complex blends, be explored and be subjected to further studies.

Thermodynamic Analysis and Optimization of Binary CO2-Organic Rankine Power Cycles for Small Modular Reactors

Small nuclear power plants are a promising direction of research for the development of carbon-free energy in isolated power systems and in remote regions with undeveloped infrastructure. Improving the efficiency of power units integrated with small modular reactors will improve the prospects for the commercialization of such projects. Power cycles based on supercritical carbon dioxide are an effective solution for nuclear power plants that use reactor facilities with an initial coolant temperature above 550 °C. However, the presence of low temperature rejected heat sources in closed Bryton cycles indicates a potential for energy saving. This paper presents a comprehensive thermodynamic analysis of the integration of an additional low-temperature organic Rankine cycle for heat recovery to supercritical carbon dioxide cycles. A scheme for sequential heat recovery from several sources in S-CO2 cycles is proposed. It was found that the use of R134a improved the power of the low-temperature circuit. It was revealed that in the S-CO2 Brayton cycle with a recuperator, the ORC add-on increased the net efficiency by an average of 2.98%, and in the recompression cycle by 1.7–2.2%. With sequential heat recovery in the recuperative cycle from the intercooling of the compressor and the main cooler, the increase in efficiency from the ORC superstructure will be 1.8%.

To Get a Power Generation Using a Waste Heat Recovery from IC Engine

This Research paper aims to develop and design a low-temperature organic Rankine cycle (ORC) system, focusing on enhancing the performance of the expander and selecting optimal refrigerants and heat sources. The study begins with a comprehensive analysis of available expanders and refrigerants suitable for ORC applications. The research then progresses to the development and improvement of an expander utilizing a reverse scroll compressor configuration, a novel approach aimed at enhancing efficiency and performance. Dynamic tests are conducted to assess the performance of the scroll compressor in this new configuration, providing valuable data for further optimization. The same expander is then integrated into an ORC system to evaluate its performance within the overall setup. Various performance parameters of the scroll compressor and the ORC system are meticulously analyzed to gauge efficiency and identify areas for improvement. Furthermore, the research paper includes a detailed process of selecting the most appropriate refrigerant and heat source from the available options. This selection is critical in optimizing the ORC system's effectiveness and sustainability. Overall, this research contributes to advancing low-temperature ORC technology by improving expander design, optimizing component performance, and selecting suitable operating parameters for enhanced energy conversion efficiency.

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 %.

Proposal and simulation of a geothermal-driven water electrolysis unit integrated with a CO2 methanation process toward a novel sustainable framework

This paper presents a novel multigeneration structure powered by geothermal energy, featuring a geothermal power plant, water electrolyzer unit, methanation reactor, fuel and utility production unit, supercritical-carbon dioxide cycle, and both high-temperature and low-temperature organic Rankine cycles. Simulated in Aspen HYSYS software and analyzed from energy, exergy, economic, and environmental (4E) perspectives, the process, under base operating conditions, is capable of producing 20,940 kW of power, 620.70 kg/h of hydrogen, 4,913 kg/h of oxygen, 12.35 kg/s of domestic hot water, 5.293 kg/s of chilled water, and 2.659 kg/s of carbon dioxide with over 99% mole purity. Efficiency assessments reveal energy, exergy, and electrical efficiencies of 10.69%, 48.53%, and 3.73%, respectively, with a total unit product cost of $3.11/GJ and a net present value of $67.40 million. The water electrolyzer unit, with an 88.94% exergy efficiency and a 10% contribution to total system irreversibility, is identified as the most efficient subsystem. The geothermal power plant accounts for the highest system irreversibility at 61%, while the combustor in the fuel and utility production unit contributes 11,250 kW of irreversibility. Environmentally, the system operates with zero emissions and significantly reduces annual CO2 emissions compared to coal, oil, biomass, and natural gas power plants by 453.14 × 106, 576.80 × 106, 111.92 × 106, and 344.10 × 106 kg, respectively.

Multi-aspect analysis of an innovative environmentally friendly process integrated into a gas turbine power plant using a multi-heat recovery approach

This study presents a novel heat integration model for a gas turbine power plant that enables sustainability through efficient utility generation and production of fresh water. Significant advantage of proposed system lies in its utilization of a novel thermal matching method between integrated combined processes, leading to development of an environmentally sustainable multi-generation structure. Consequently, the integrated system includes a Kalina cycle, high- and low-temperature organic Rankine cycles, an absorption chiller, a heating provision unit, and a water desalination subsystem. The simulated procedure utilizes the Aspen HYSYS software and follows with a comprehensive analysis to assess its energy, exergy, economic, and environmental characteristics. The study's findings exhibited net power output, cooling load, heating load, and desalination energy output of 23,924.06 kW, 3486 kW, 6671 kW, and 230.9 kW, respectively. The system's energy efficiency improves from 47.81 % to 68.58 % when operating in single-generation and multi-generation modes. Likewise, the exergy efficiency improves from 45.55 % to 52.42 %. The study also illustrates the carbon dioxide emission intensity associated with both mentioned modes at 0.4187 kg/kWh and 0.2641 kg/kWh, respectively. Besides, the economic evaluation reveals total annual cost, cost of energy, and total cost of products of 147.65 M$/year, 0.5783 $/kWh, and 10.71 $/GJ, respectively.

Comprehensive assessment and sustainability improvement of a natural gas power plant utilizing an environmentally friendly combined cooling heating and power-desalination arrangement

Considering the significant waste heat generated by existing natural gas power plants, it is imperative to implement eco-friendly combined process designs to ensure their long-term sustainability. The present paper introduces and investigates a novel integrated process aimed at achieving multiple generational advantages within an environmentally friendly framework, with the ultimate goal of enhancing sustainability. The new structure incorporates a natural gas power plant, high-temperature and low-temperature organic Rankine cycles, a combined cooling and power subsystem, and a water desalination unit to produce power, heating, cooling, and freshwater simultaneously. This system is simulated within the Aspen HYSYS software and examined from energy, exergy, economic, environmental, and sustainability perspectives. Furthermore, parametric studies evaluate the impact of the overall system's various environmental, economic, and operational conditions. It is found that the production capacities of power, hot water, chilled water, and freshwater are 179,265.17 kW, 387.8 kg/s, 563.6 kg/s, and 21.4 kg/s, respectively. Hence, the overall energy and exergy efficiencies improve to 66.06% and 42.95%, respectively. The financial estimation also reveals a cost of energy of 0.1084 $/kWh and a total net present value of 818.67 M$. It is also determined that the cost per unit of destroyed exergy is equal to 7.156 $/GJ.

Pinch and exergy assessment of an innovative hydrogen and methane purification process configuration based on solar renewable energy

Energy recovery from waste sources and developing new high-performance systems are essential to minimize energy consumption. A novel purification structure is developed to produce hydrogen and liquid natural gas (LNG) using exhaust gases from various industries, mixed refrigeration system, organic Rankine cycle (ORC), and solar energy sources. Solar parabolic trough collectors are used to supply energy in the low-temperature ORC. The proposed system produces 1.922 kg/s hydrogen with purity of 94.25 mol% and 1.777 kg/s LNG as the main product by consuming 10.56 kg/s crude hydrogen feed gas. The LNG and pure hydrogen specific power consumption (SPC) are 0.4111 and 0.3803 kWh/kg, respectively. The SPC of the sum of both products is obtained at 0.1975 kWh/kg. The methane and hydrogen recovery factors are 94.80% and 98%, respectively, indicating maximum methane and hydrogen absorption of the crude hydrogen feed gas. The exergy analysis indicates that the total exergy destruction of the integrated system is calculated at 5561 kW, and its exergy efficiency is obtained as 28.56%. The heat exchanger networks for the HE1, HE2, HE3, HE4, and HE6 multi-stream heat exchangers are extracted through the pinch strategy. The multi-stream heat exchangers have 8, 13, 6, 8, and 2 simple heat exchangers. The outcome results obtained from the parametric study is a 25.88% increase in the production rate of the main products (LNG and pure hydrogen). In addition, when the ratio of LNG to fuel gas increases by 48.08%, the ratio of main product to by-product increases from 54 to 62 mol%. By performing parametric analysis, it can be concluded that increasing the hydrogen content of the crude feed improves the performance of the system.

Enhancing sustainable energy conversion: Comparative study of superheated and recuperative ORC systems for waste heat recovery and geothermal applications, with focus on 4E performance

This study investigates the 4E performance of small-scale (<100 kW), low-temperature (<179 °C) Organic Rankine Cycle (ORC) technology, comparing two distinct configurations using different working fluids and heat sources. The work utilizes experimental methods to analyse the efficiency of the ORC systems, focusing on variables such as evaporation temperature and pressure drop across the heat exchanger. Various working fluids and heat sources are tested to evaluate their impact on performance using CoolProp libraries.The results reveal that the ideal evaporation temperature for maximizing overall performance and efficiency is between 140 and 150 °C. Higher pressure drop across the heat exchanger improves heat transfer, thermal efficiency, and power output, but increases pumping requirements and reduces overall effectiveness. Among the tested heat sources, the Dynalene SF exhibits the best performance, followed by therminol T72, T66, geothermal water, and Paratherm HE. The most suitable working fluids for commercial ORC units are R245fa and hexamethyldisiloxane (MM), providing excellent thermodynamic properties and low environmental impact. Comparatively, the superheated ORC system using R245fa outperforms the MM, achieving higher net efficiency (7.29%), greater network generation (20.29%), and improved exergy efficiency (20.54%). The economic viability of the recuperative system is evident from the Levelized Cost of Electricity (LCOE) range of 12.4–14.5 (cents/kWh), with an average Total Installed Cost (TIC) of 354.5 k$. These results showcase the system's competitiveness in providing cost-effective electricity generation, reaffirming its potential as a financially viable option for sustainable energy solutions.The objective is to explore the use of Organic Rankine Cycle (ORC) technology as an alternative to steam Rankine cycle for low-power and lower-temperature applications. Specifically, the study focuses on ORC systems with external heat sources, including geothermal, solid fuels and waste heat recovery (WHR).The novelty of this article lies in its updated analysis of the techno-economic-environmental feasibility of ORC systems for different applications, which goes beyond previous studies. It provides a systematic evaluation and comparison specifically tailored to small-scale and low-temperature operating conditions. The aim is to promote the integration of these two systems in various sectors, particularly for countries undergoing an energy transition. This emphasis on the technical aspects and the specific focus on small-scale and low-temperature conditions make this study unique and valuable in advancing the understanding and application of ORC technology.

Design of Radial-Inflow Turbines for Low-Temperature Organic Rankine Cycle

This study presents the development of a design method that has been extended to the design of radial-inflow turbines operating in organic Rankine cycles (ORC). Both the conventional design method and the circulation method available in the literature have been reviewed. The two main limitations of the current circulation method that make it not suitable for the ORC turbine design are the lack of real gas capability and 3D blades with high stresses. Using the circulation method, the flow field is decomposed into a potential part and a rotational part. The mean velocity field and the periodic velocity field are solved separately. To model the thermodynamic properties of the real gas, NIST REFPROP or CoolProp are used. The blade geometry is then solved iteratively by assuming that the velocity vector is parallel to the blade surface. The blade boundary condition is modified to force the blade camber to be radial-fibred, which is helpful to reduce the centrifugal bending stress on the blade. All the formulations are derived step by step, and the numerical treatments, including grid generation, numerical differentiation, computational scheme, and convergence, are discussed in detail. This method is validated by designing a R245fa ORC turbine rotor. The performance of the rotor design is predicted by CFD and FEA simulations, and it is compared to the results using other methodologies in the literature.

4E Assessment of an Organic Rankine Cycle (ORC) Activated with Waste Heat of a Flash-Binary Geothermal Power Plant.

In this paper, the 4E assessment (Energetic, Exergetic, Exergoeconomic and Exergoenvironmental) of a low-temperature ORC activated by two different alternatives is presented. The first alternative (S1) contemplates the activation of the ORC through the recovery of waste heat from a flash-binary geothermal power plant. The second alternative (S2) contemplates the activation of the ORC using direct heat from a geothermal well. For both alternatives, the energetic and exergetic models were established. At the same time, the economic and environmental impact models were developed. Finally, based on the combination of the exergy concepts and the economic and ecological indicators, the exergoeconomic and exergoenvironmental performances of the ORC were obtained. The results show higher economic, exergoeconomic and exergoenvironmental profitability for S1. Besides, for the alternative S1, the ORC cycle has an acceptable economic profitability for a net power of 358.4 kW at a temperature of 110 °C, while for S2, this profitability starts being attractive for a power 2.65 times greater than S1 and with a temperature higher than 135 °C. In conclusion, the above represents an area of opportunity and a considerable advantage for the implementation of the ORC in the recovery of waste heat from flash-binary geothermal power plants.

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.

ANN-PSO aided selection of hydrocarbons as working fluid for low-temperature organic Rankine cycle and thermodynamic evaluation of optimal working fluid

Organic Rankine cycle (ORC) has been demonstrated to extract useful work output from low-grade heat sources like solar-thermal, biomass/biofuel combustion, geothermal, and waste heat. However, working fluid selection for ORC is a complex process and calls for careful optimization. To address this problem, the current work constitutes a design of experiments approach with a full-factorial design. A heat source temperature of 150 °C is selected, and a list of 11 possible candidates of working fluid mixtures (among hydrocarbons) is taken. Work output and efficiencies from each fluid are determined based on the design of experiments, and the results are used to model an artificial neural network (ANN). Equations for work output and first law efficiency are developed using tan sigmoid function and ANN constants which act as objective functions that are maximized using multi-objective particle swarm optimization (PSO). The results of the ANN-PSO model is validated with the values from thermodynamic analysis with less than 2% error. The optimal working fluid obtained for maximum work output is R600a operating at an evaporator pressure of 1.88 MPa without any superheating. The resulting maximum work output is 7.15 kW at 8.05% thermal efficiency and an exergy efficiency of 38.13%.

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

&lt;p&gt;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.&lt;/p&gt;

Solar driven micro-ORC system assessment for residential application

The purpose of this study is to estimate the electricity production obtainable by coupling an existing kW-size recuperated Organic Rankine Cycle (ORC) prototype with a commercial solar thermal collector to reduce the yearly electricity purchased by a single-family user. A detailed semi-empirical steady-state model, validated against experimental data, is employed for the power plant simulation. The optimal sizes of both the collector surface and the storage tanks were assessed considering that a solar collector surface larger than 32.25 m2 would lead the micro-ORC working in off-design conditions; while storage volumes higher than 6000 l become too large to be completely exploited.Then, different low global warming potential fluids and blends were simulated for comparison with HFC-134a, the reference fluid for low-temperature ORC. Results show that the integrated system working with R134a can cover approximately 39% of the yearly electricity demand, corresponding to more than 1150 kWh. The replacement of R134a with the alternative fluids results in a penalization in the output electric power, related to thermodynamic properties such as density, liquid viscosity, and latent heat. Indeed, with R1234yf barely 16% (466 kWh) of the yearly electricity demand is covered; whilst the blend R513A allows to reach only 17.5% (525 kWh).

Influence of Evaporator Superheating and Pressure on the Performance ORC with R134a

This research examines the heat sources using a low-temperature organic Rankine cycle thermodynamic analysis. The effect of increasing the temperature and pressure at the expander input is explored. The performance of an ORC system using R134a was investigated thermodynamically. The expander's input temperature ranged from 55 to 85 degrees Celsius. Pressures in the evaporator range from 0.4 to 0.6 MPa. The software used was Engineering Equation Solver. The temperature and pressure of evaporation have an impact on cycle characteristics including net power production, irreversibility, rotational speed, and thermal and exergy efficiency. At constant evaporator pressure of 0.6 MPa and rising temperature, the thermal efficiency drops to 3.907%, whereas at constant evaporator temperature and expander pressure of 0.4-0.6 MPa, the thermal efficiency rises to 3.907%. When the exergy efficiency is 0.6MPa at constant evaporator pressure, raising the temperature leads to an increase in exergy efficiency of 18.81% -18.89%. At 85℃ and a pressure of 0.4-0.6 MPa, the effect of increasing exergy efficiency was between 2.185% and -18.89% at constant evaporator temperature. The findings of the research reveal that the ORC power plant is a good choice for energy generation. R134a is suitable for the ORC system.

Experimental Flow Boiling Study of R245a at High Reduced Pressures in a Large Diameter Horizontal Tube

Evaporators used in organic Rankine cycles (ORC) are designed using existing flow boiling correlations that are mainly based on HVAC&amp;R data. However, the ORC evaporators employed in the industry typically have larger diameters and operational conditions at higher reduced pressures compared to the HVAC&amp;R applications. The present study presents the results of flow boiling heat transfer experiments in operational conditions that are representative for an industrial waste heat recovery low-temperature ORC’s evaporator tube, by being performed at high reduced pressures and in a large-diameter horizontal tube with R245fa as working fluid. The measurements are performed within a range of mass flux, saturation temperature and heat flux at 83–283 kg/m2s, 85–120 °C (8.9–19.2 bar) and 17–29 kW/m2, respectively. Test section is a round and plain horizontal carbon steel tube with 21 mm I.D., 2.5 m length. 513 local two-phase heat transfer coefficients are recorded. The experimental results are compared with each other to reveal heat transfer coefficient trends with respect to varying experimental conditions. Four distinctive heat transfer zones are observed, namely, the nucleate boiling dominant (NBD) zone, weakening nucleate boiling dominance (WNBD) zone, flow boiling zone (FBZ) and the dry-out zone (DOZ). Heat transfer coefficient vs vapor quality trends partly resembled CO2 flow boiling results reported in the literature. Two flow boiling correlations moderately predicted the data.

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).