Rankine Cycle Working Fluid Research Articles

Optimal multicomponent working fluid of organic Rankine cycle for exergy transfer from liquefied natural gas regasification

A hybrid optimization methodology is proposed for the working fluid selection of an organic Rankine cycle (ORC). First, a stochastic global solver is used to select the chemical species of the working fluid; then, a deterministic global solver is used to optimize the composition. The first step is a mixed integer nonlinear programing (MINLP) and the second a nonlinear program (NLP). The methodology is applied to the recovery of cryogenic energy during the evaporation of liquefied natural gas (LNG), which is a promising way to produce electricity with relatively high efficiency from the large amount of otherwise wasted heat. Seawater or low-grade heat sources can be used as heat source. Multicomponent working fluids have advantages compared to pure fluids because of the nonisothermal evaporation of LNG. Herein, a ternary mixture is considered. A mixture of CF4, CHF3, n-pentane is identified as an optimum ternary working fluid. It produces about 1.1 MJ/kmol LNG with a simple organic Rankine cycle using seawater as heat source. The optimization results are quantitatively compared with the literature in terms of power generation and are shown to have substantially higher electricity generation.

Expansion of organic Rankine cycle working fluid in a cylinder of a low-speed two-stroke ship engine

Electricity and power produced from waste heat is particularly relevant in shipping because fuel expenses constitute the majority of the cost of operating the ships; however, the cost-benefit aspect limits the widespread implementation of waste heat recovery power units on ships. This paper presents the thermodynamic analysis of a concept that aims at reducing the cost of an organic Rankine cycle unit by using one of the cylinders in a large diesel engine as expansion device. Numerical models were used to optimise the process parameters and thereby determine the power potential for this concept. The evaluation of 104 working fluids points to cyclopropane, R245fa and R1234ze(z) as the most promising. The results suggest that the power produced by the organic Rankine cycle cylinder is at least equivalent to that of the cylinders operating with the diesel process. This enables potential fuel savings and emissions reductions of about 8.3% in the studied scenario.

Experimental flow boiling characteristics of R134a/R245fa mixture inside smooth horizontal tube

The flow boiling characteristics were experimentally studied in smooth horizontal tube for pure R245fa and one of its mixtures, R134a/R245fa with 0.82/0.18 in mass fraction, which was regarded as a promising working fluid for Organic Rankine Cycle (ORC). The flow boiling heat transfer coefficient and pressure drop for the two fluids were measured under different vapor quality, mass flux, tube wall heat flux and evaporating pressure. Correlation for predicting the flow boiling heat transfer coefficient was developed for the selected mixture based on the experimental data. The results indicated that the flow boiling heat transfer coefficients of the two working fluids went up with mass flux, heat flux and evaporating pressure under the experimental conditions. The mixture of R134a/R245fa with 0.82/0.18 in mass fraction had less pressure drop, but higher heat transfer coefficient than that of the pure R245fa. The absolute errors of 89% experimental data are within 10% of prediction of the present developed correlation for the mixture. The results may benefit the potential utilization of R134a/R245fa in ORC.

Thermo-Economic Analysis of Zeotropic Mixtures and Pure Working Fluids in Organic Rankine Cycles for Waste Heat Recovery

We present a thermo-economic analysis of an Organic Rankine Cycle (ORC) for waste heat recovery. A case study for a heat source temperature of 150 °C and a subcritical, saturated cycle is performed. As working fluids R245fa, isobutane, isopentane, and the mixture of isobutane and isopentane are considered. The minimal temperature difference in the evaporator and the condenser, as well as the mixture composition are chosen as variables in order to identify the most suitable working fluid in combination with optimal process parameters under thermo-economic criteria. In general, the results show that cost-effective systems have a high minimal temperature difference ΔTPP,C at the pinch-point of the condenser and a low minimal temperature difference ΔTPP,E at the pinch-point of the evaporator. Choosing isobutane as the working fluid leads to the lowest costs per unit exergy with 52.0 €/GJ (ΔTPP,E = 1.2 K; ΔTPP,C = 14 K). Considering the major components of the ORC, specific costs range between 1150 €/kW and 2250 €/kW. For the zeotropic mixture, a mole fraction of 90% isobutane leads to the lowest specific costs per unit exergy. A further analysis of the ORC system using isobutane shows high sensitivity of the costs per unit exergy for the selected cost estimation methods and for the isentropic efficiency of the turbine.

Analysis of the quantitative correlation between the heat source temperature and the critical temperature of the optimal pure working fluid for subcritical organic Rankine cycles

Organic Rankine cycles can use various working fluids. Different heat sources and working conditions lead to very different optimal working fluids. This paper presents a new quantitative criterion for selecting the optimal working fluid for open type heat sources with temperatures from 150 to 350 °C. The heat source recovery exergetic efficiency is used as the evaluation indicator. Over 30 working fluids with critical temperature from 71.87 to 357.65 °C are under evaluation. The working fluid critical temperature's influence on the heat source utilization, cycle efficiency and exergetic loss in the evaporator and condenser is analyzed to show that the critical temperature is the key parameter for selecting the optimal working fluid. The critical temperature of the optimal working fluid is determined by the heat source temperature, the pinch point temperature difference and the condensation temperature. When the cooling fluid outlet temperature is between 30 and 60 °C, which covers the most common natural cooling condition and the requirement of combined heat and power system, the correlation between the critical temperature of the optimal working fluid and the heat source temperature with different pinch point temperature difference is given. This correlation provides concise guidance for the optimal pure working fluids selection and mixture design.

Рабочее тело цикла Ренкина для утилизации холода регазификации

Рабочее тело цикла Ренкина для утилизации холода регазификации

On the use of SAFT-VR Mie for assessing large-glide fluorocarbon working-fluid mixtures in organic Rankine cycles

By employing the SAFT-VR Mie equation of state, molecular-based models are developed from which the thermodynamic properties of pure (i.e., single-component) organic fluids and their mixtures are calculated. This approach can enable the selection of optimal working fluids in organic Rankine cycle (ORC) applications, even in cases for which experimental data relating to mixture properties are not available. After developing models for perfluoroalkane (n-C4F10+n-C10F22) mixtures, and validating these against available experimental data, SAFT-VR Mie is shown to predict accurately both the single-phase and saturation properties of these fluids. In particular, second-derivative properties (e.g., specific heat capacities), which are less reliably calculated by cubic equations of state (EoS), are accurately described using SAFT-VR Mie, thereby enabling an accurate prediction of important working-fluid properties such as the specific entropy. The property data are then used in thermodynamic cycle analyses for the evaluation of ORC performance and cost. The approach is applied to a specific case study in which a sub-critical, non-regenerative ORC system recovers and converts waste heat from a refinery flue-gas stream with fixed, predefined conditions. Results are compared with those obtained when employing analogue alkane mixtures (n-C4H10+n-C10H22) for which sufficient thermodynamic property data exist. When unlimited quantities of cooling water are utilized, pure perfluorobutane (and pure butane) cycles exhibit higher power outputs and higher thermal efficiencies compared to mixtures with perfluorodecane (or decane), respectively. The effect of the composition of a working-fluid mixture in the aforementioned performance indicators is non-trivial. Only at low evaporator pressures (<10bar) do the investigated mixtures perform better than the pure fluids. A basic cost analysis reveals that systems with pure perfluorobutane (and butane) fluids are associated with relatively high total costs, but are nevertheless more cost effective per unit power output than the fluid mixtures (due to the higher generated power). When the quantity of cooling water is constrained by the application, overall performance deteriorates, and mixtures emerge as the optimal working fluids.

Selection of Optimum Working Fluid for Organic Rankine Cycles by Exergy and Exergy-Economic Analyses

The thermodynamic performance of a regenerative organic Rankine cycle that utilizes low temperature heat sources to facilitate the selection of proper organic working fluids is simulated. Thermodynamic models are used to investigate thermodynamic parameters such as output power, and energy efficiency of the ORC (Organic Rankine Cycle). In addition, the cost rate of electricity is examined with exergo-economic analysis. Nine working fluids are considered as part of the investigation to assess which yields the highest output power and exergy efficiency, within system constraints. Exergy efficiency and cost rate of electricity are used as objective functions for system optimization, and each fluid is assessed in terms of the optimal operating condition. The degree of superheat and the pressure ratio are independent variables in the optimization. R134a and iso-butane are found to exhibit the highest energy and exergy efficiencies, while they have output powers in between the systems using other working fluids. For a source temperature was equal to 120 °C, the exergy efficiencies for the systems using R134a and iso-butane are observed to be 19.6% and 20.3%, respectively. The largest exergy destructions occur in the boiler and the expander. The electricity cost rates for the system vary from 0.08 USD/kWh to 0.12 USD/kWh, depending on the fuel input cost, for the system using R134a as a working fluid.

PvT Property of HFE 7100 in the Gaseous Phase

HFE 7100 (C4F9OCH3) is a promising working fluid for organic Rankine cycles (ORC). However, there are no available published experimental gaseous pvT data. Thus, pvT data of HFE 7100 in the gaseous phase were measured with a Burnett apparatus. High purity helium was used to calibrate the cell constant of the Burnett apparatus. Then, the gaseous pvT data of HFE 7100 were measured from (363 to 431) K for pressures from (148 to 878) kPa. The temperature measurement standard uncertainty was estimated to be 2.3 mK, the pressure standard uncertainty was estimated to be 240 Pa, and the density relative standard uncertainty was estimated to be 0.0006. A truncated virial equation of state (EOS) for HFE 7100 was used to correlate the experimental data with a relative root-mean-square deviation of 0.00042.

Comparison of Parabolic Trough and Linear Fresnel Collectors Based Concentrating Solar Power Plants Using Organic Rankine Cycle

Concentrating solar power (CSP) plants with parabolic trough collector (PTC) using thermal oil as heat transfer fluid (HTF) and conventional steam Rankine cycle (SRC) as power generating cycle is the most commercially developed technology. Direct steam generating linear Fresnel reflector (LFR) systems are developed as a cheaper alternative to PTC systems. The major drawbacks of LFR systems are low optical efficiency and production of saturated steam. These result in higher solar field area requirement compared to PTC based plants of same capacity. Organic Rankine cycle (ORC) based power block, with dry working fluids, offers higher cycle efficiency as well as improved part-load turbine efficiency compared to SRC in modular scale plants with heat sources up to 400 °C. ORC is more suitable to LFR based CSP plants. In this paper, thermo-economic analysis of PTC and LFR based CSP plants with ORC has been presented. An approximate selection methodology, for LFR and PTC based CSP plants, is proposed and the selection diagram generated using the proposed methodology can be used for LFR and PTC based CSP plants with any working fluid of Rankine cycle. The applicability of the selection diagram is demonstrated using case studies of n-Pentane, Octamethyltrisiloxane (OMTS) and water working fluids based plants. Selection diagram captures the variations of power generating cycle efficiency, and costs of collector fields.

Selection of organic Rankine cycle working fluids in the low-temperature waste heat utilization

In the current study, simulations based on the engineering equation solver (EES) software are performed to determine the suitable working fluid for the simple organic Rankine cycle system in different temperature ranges. Under the condition of various temperatures and a constant thermal power of the flue gas, the influence of different organic working fluids on the efficiency of the subcritical organic Rankine cycle power generation system is studied, and its efficiency and other parameters are compared with those of the regenerator system. It is shown that the efficiency of the subcritical organic Rankine cycle system is the best when the parameters of the working fluid in the expander inlet are in the saturation state. And for the organic Rankine cycle, the R245fa is better than other working fluids and the efficiency of the system reaches up to 10.2% when the flammability, the toxicity, the ozone depletion, the greenhouse effect and other factors of the working fluids are considered. The R601a working fluid can be used for the high-temperature heat source, however, because of its high flammability, new working fluid should be investigated. Under the same condition, the efficiency of the organic Rankine cycle power generation system with an internal heat exchanger is higher than that of the simple system without the internal heat exchanger, but the efficiency is related to the properties of the working fluid and the temperature of the heat source.

Selection of organic Rankine cycle working fluid based on unit-heat-exchange-area net power

To improve energy conversion efficiency, optimization of the working fluids in organic Rankine cycles (ORCs) was explored in the range of low-temperature heat sources. The concept of unit-heat-exchange-area (UHEA) net power, embodying the cost/performance ratio of an ORC system, was proposed as a new indicator to judge the suitability of ORC working fluids on a given condition. The heat exchange area was computed by an improved evaporator model without fixing the minimum temperature difference between working fluid and hot fluid, and the flow pattern transition during heat exchange was also taken into account. The maximum UHEA net powers obtained show that dry organic fluids are more suitable for ORCs than wet organic fluids to recover low-temperature heat. The organic fluid 1-butene is recommended if the inlet temperature of hot fluid is 353.15–363.15 K or 443.15–453.15 K, heptane is more suitable at 373.15–423.15 K, and R245ca is a good option at 483.15–503.15 K.

화력발전소 폐열에 따른 작동유체별 액-증기 이젝터를 적용한 1MW급 ORC의 성능 분석

Abstract: In this paper, suitable working fluid of 1MW Organic Rankine Cycle(ORC) with liquid-vapor ejector using effluent from power plant is selected. The results of comparison performance of 5 refrigerants are as follows; R600a, R134a, R1270, R236fa, R235fa. The operating parameters considered in this study include the condensation capacity evaporation capacity and efficiency. As a result of comparison of basic ORC system and with liquid-vapor ejector, with ORC system presents the higher system efficiency since the ejector makes the turbine outlet pressure lower than condensation pressure through its pressure recovery. Also, this ejector ORC system is advantageous in miniaturizing the size of components owing to decrease of evaporation capacity and condensation capacity. Key Words ：Organic Rankine Cycle(ORC), Liquid-Vapor Ejector, Working Fluid, Power Plant Effluent **†윤정인(교신저자) : 부경대 냉동공조공학과 E-mail : yoonji@pknu.ac.kr, Tel : 051-629-6180 *김현욱 : 부경대 냉동공조공학과 대학원**손창효 : 부경대 냉동공조공학과**†Jung-In Yoon(corresponding author) : Department of Refrigeration and Air Conditioning Engineering, Pukyoung University.E-mail : yoonji@pknu.ac.kr, Tel : 051-629-6180 *Hyeon-Uk Kim : Graduate school of Refrigeration and Air Conditioning Engineering, Pukyoung University.**Chang-Hyo Son : Department of Refrigeration and Air Conditioning Engineering, Pukyoung University.

Selecting working fluids in an organic Rankine cycle for power generation from low temperature heat sources

This paper presents a thermodynamic study carried out on the use of low-temperature heat sources for power generation through a subcritical Rankine cycle with organic working fluids. An analysis of the state of the art of this technology shows the selection of the working fluid as an open research line, since until now there is no fluid that can meet all environmental and technical aspects to be considered in these cycles. Hence, we have developed a series of simulations that allow us to study the behavior of the Rankine cycle with different configurations and fluids (wet, dry and isentropic) which has led us to observe the influence on the overall cycle efficiency when we change the type of fluids used (refrigerants, hydrocarbons and water) as well as the conditions of temperature, pressure, flow, etc. With the work realized, the viability of this type of processes is demonstrated for the recovery of heat in industry and/or the use of renewable sources of low and medium temperature for the production of electricity.

냉매(R245fa)를 이용한 유기랭킨 사이클에 관한 연구

The organic Rankine cycle has been widely used to convert the renewable energy such as the solar energy, the geothermal energy, or the waste energy etc., to the electric power. Some previous studies focused to find what kind of refrigerant would be a best working fluid for the organic Rankine cycle. In this study, R245fa was chosen to the working fluid, and the cycle analysis was conducted for the output power of 30kW or less. In addition, properties (temperature, pressure, entropy, and enthalpy etc.) of the working fluid on the cycle were predicted when the turbine output power was controlled by adjusting the mass flowrate. The configuration of the turbine was a radial-type and the supersonic nozzles were applied as the stator. So, the turbine was operated in partial admission. The turbine efficiency and the optimum velocity ratio were considered in the cycle analysis for the low partial admission rate. The computed results show that the system efficiency is affected by the partial admission rate more than the temperature of the evaporator.

Evaluation of carbon dioxide blends with isopentane and propane as working fluids for organic Rankine cycles

The main theme of this paper is to study the flammability suppression of hydrocarbons by blending with carbon dioxide, and to evaluate these mixtures as possible working fluids in organic Rankine cycle for medium temperature concentrated solar power applications. The analysis takes into account inevitable irreversibilities in the turbine, the pump, and heat exchangers. While the isopentane + CO2 mixture suffers from high irreversibility mainly in the regenerator owing to a large temperature glide, the propane + CO2 mixture performs more or less the same as pure propane albeit with high cycle pressures. In general, large temperature glides at condensing pressures extend the heat recovery into the two-phase dome, which is an advantage. However, at the same time, the shift of the pinch point towards the warm end of the regenerator is found to be a major cause of irreversibility. In fact, as the number of carbon atoms in alkanes decreases, their blend with CO2 moves the pinch point to the colder end of the regenerator. This results in lower entropy generation in the regenerator and improved cycle efficiency of propane + CO2 mixtures. With this mixture, real cycle efficiencies of 15–18% are achievable at a moderate source temperature of 573 K. Applicability for a wide range of source temperatures is found to be an added advantage of this mixture.

Selection of the Optimum Working Fluids in Organic Rankine Cycles Using Topsis

Organic Rankine Cycles (ORC) can be used to convert low-grade waste heat to electricity. The working fluid employed in the ORC has a strong influence on the thermal efficiency of the system. Until now, methods for the selection of working fluids have been based on trial and error approaches which are not very effective. As a result, the motivation for the work reported in this paper is to remedy this using decision-making techniques such as TOPSIS (technique for order preference using similarity to ideal solution), which can help identify an optimal working fluid at the preliminary stage.

Exergoeconomic analysis and optimization of an evaporator for a binary mixture of fluids in an organic Rankine cycle

This paper focuses on the research of an evaporator with a binary mixture of organic working fluids in the organic Rankine cycle. Exergoeconomic analysis and performance optimization were performed based on the first and second laws of thermodynamics, and the exergoeconomic theory. The annual total cost per unit heat transfer rate was introduced as the objective function. In this model, the exergy loss cost caused by the heat transfer irreversibility and the capital cost were taken into account; however, the exergy loss due to the frictional pressure drops, heat dissipation to surroundings, and the flow imbalance were neglected. The variation laws of the annual total cost with respect to the number of transfer units and the temperature ratios were presented. Optimal design parameters that minimize the objective function had been obtained, and the effects of some important dimensionless parameters on the optimal performances had also been discussed for three types of evaporator flow arrangements. In addition, optimal design parameters of evaporators were compared with those of condensers.

Thermal Stability of Cyclopentane as an Organic Rankine Cycle Working Fluid

Laboratory experiments were performed to determine the maximum operating temperature for cyclopentane as an organic Rankine cycle working fluid. The thermochemical decomposition of cyclopentane was measured in a recirculation loop at 240, 300, and 350 °C at 43 bar in a glass-lined heated tube. It was determined that, in the absence of air at the two lower temperatures, decomposition was minor after more than 12 days of continuous operation. At 240 °C, the total cyclopentane decomposition products were approximately 65 ppm, and at 300 °C, the total decomposition products were on the order of 270 ppm at the end of the experiment. At 350 °C, the decomposition products were significantly higher and reached 1500 ppm. When the feed was saturated with air under prevailing atmospheric conditions, the decomposition rate increased dramatically. Residues found in the reactor after the decomposition experiments were examined by a number of different techniques. The mass of the residues increased with experimental temperature but was lower at the same temperature when the feed was saturated with air. Analysis of the residues suggested that the residues were primarily heavy saturated hydrocarbons.

A Thermodynamic Similarity Framework for Assessment of Working Fluids for Solar Rankine Power Generation

Numerous studies have compared the merits of different working fluids for use in Rankine power systems. Most often, however, these have considered a limited number of specific fluids for which the thermodynamic properties are known. In the investigation summarized here, the Redlich–Kwong fluid model was used to develop a thermodynamic similarity framework that can be used as a comparative model for evaluating the performance of Rankine cycle working fluids. This can be viewed as a reduced order model that, based on thermodynamic similarity, quantifies the characteristics of the working fluids in terms of a single dimensional coordinate space defined by the choice of critical temperature. The advantage of this framework is that it allows exploration of the performance advantages of working fluids for which full thermodynamic properties are not yet available. Predictions of the model for common fluids were examined and conclusions regarding optimal fluids for solar Rankine systems are discussed.