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Performance analysis of the partial evaporating organic Rankine cycle (PEORC) using zeotropic mixtures

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Abstract

A new organic Rankine cycle (ORC) architecture: partial evaporating organic Rankine cycle (PEORC) with the zeotropic mixture R245fa/R227ea as working fluid is presented in this paper. The thermodynamic first law analysis as well as the second law analysis were applied to evaluate the system performance. A techno-thermodynamic evaluation on heat exchangers and the expander was also performed in this research. The mass fraction of R227ea (corresponding to zeotropic mixture) and the expander inlet vapor quality (corresponding to PEORC) are chosen as the independent variables. The results showed that both the new cycle architecture: PEORC and zeotropic mixture working fluid can improve the thermodynamic performance and more importantly they can be combined together to further enhance the system. The optimized PEORC with R245fa/R227ea is able to generate about 24.7% more power than the traditional subcritical organic Rankine cycle (SCORC) with R227ea as working fluid. However, the heat exchanger economy may become worse, which should be considered. The results also revealed that the mixture working fluid mainly reduces the exergy loss in the condenser because of the temperature glide characteristic while the PEORC mainly reduces the exergy loss in the evaporator by improving the temperature matching between heat source and working fluid.

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... Li et al. [19] also performed comparative analyses of a basic ORC system and a TLC system at different evaporation temperatures, and concluded that the TLC system achieved a maximum net power output which was 37% higher than that of the ORC system for a case study with an evaporation temperature of 152 °C. Zhou et al. [20] analysed the performance of a PEC system and found that employing optimal operating parameters for such a system can lead to a higher net power output by close to 25% compared to a conventional subcritical ORC system. An in-depth thermodynamic comparison of PEC and subcritical ORC systems was also performed by Lecompte et al. [21], who showed a ~10% increase in the annual energy production by the PEC system relative to the ORC system. ...
... (2) The pump efficiency is assumed to be 0.7, which has also been used in similar studies [20,54]. ...
Article
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In this paper, results from comprehensive thermoeconomic assessments of small-scale solar organic Rankine cycle (ORC) systems are presented based on weather data in London, UK, which is taken as representative of a temperate climate with modest temperature changes, mild winters and moderate summers. The assessments consider a range of: (i) solar collector types (flat-plate, evacuated-tube, and evacuated flat-plate collectors); (ii) power cycle configurations (basic/recuperative, partial/full evaporating, and subcritical/transcritical cycles); (iii) expander types (scroll, screw, and piston) and designs; and (iv) a set of suitable working fluids. All possible solar-ORC system designs are optimised by considering simultaneously key parameters in the solar field and in the power cycle in order to obtain the highest electricity generation, from which the best-performing systems are identified. A representative number of selected designs are then subjected to detailed, annual simulations considering the systems' operation, explicitly considering off-design performance under actual varying weather conditions. The results indicate that, among all investigated designs, solar-ORC systems based on the subcritical recuperative ORC (SRORC), evacuated flat-plate collectors (EFPCs), a piston expander, and isobutane as the working fluid outperforms all the other system designs on thermodynamic performance, whilst having the highest annual electricity generation of 1,100 kW· h/year (73 kW· h/year/m 2) and an overall thermal efficiency of 5.5%. This system also leads to the best economic performance with a levelised cost of energy (LCOE) of ~1 $/kW· h. Apart from the specific weather data used for these detailed system simulations, this study also proceeds to consider a wider range of climates associated with other global regions by varying the solar resource available to the system. Interestingly, it is found that the optimal solar-ORC system design remains unchanged for different conditions, however, the LCOE can drop below 0.35 $/kW· h and payback times can be shorter than 16 years in high solar-resource regions, even in the absence of incentives that would otherwise lead to even better economic performance. This work complements previous efforts in the literature by considering the full design and operational features of solar-ORC systems, thereby providing valuable guidance for selecting appropriate cycle configurations, components, working fluids and other characteristics and, for the first time, presents a comprehensive comparison of such systems in small-scale applications. Nomenclature Abbreviations a1, a2 solar collector coefficients, W/(m 2 •K), W/(m 2 •K 2) A area, m 2 Bo boiling number c1, c2 heat transfer correction factors for evaporation process c3, c4 pressure correction factors for evaporation process c5, c6 heat transfer correction factors for condensation process c7, c8 pressure correction factors for condensation process cel electricity price, $/(kW·h) C cost, $ fp, f0, f1 correction factor for pressure G solar irradiance, W/m 2 Gp mass velocity, kg/(s⋅m 2) h specific enthalpy, J/kg hlg specific enthalpy of vaporisation, J/kg id discount rate iF inflation rate L length, m ṁ mass flow rate, kg/s M mass, kg N plant lifetime, year Nu Nusselt number P pressure, Pa or bar Pr Prandtl number q̇ heat flux density, W/m 2 Q̇ heat flow rate/thermal load, W Re Reynolds number Sp passage cross-sectional area, m 2 t time, s T temperature, K or °C u velocity, m/s U overall heat transfer coefficient, W/(m 2 •K) v kinematic viscosity, m 2 /s V̇ volumetric flow rate, m 3 /s V volume, m 3
... They revealed that the combined cycle with R152a has the best performance among R124, R152a, and R134a fluids [10]. Zou et al., 2016 [11] analyzed the performance of the partial evaporating ORC with zeotropic mixtures. They proposed a partial evaporating ORC with R245fa/R227ea, which can outperform the traditional subcritical ORC with R227ea by generating 24.7% more power [11]. ...
... Zou et al., 2016 [11] analyzed the performance of the partial evaporating ORC with zeotropic mixtures. They proposed a partial evaporating ORC with R245fa/R227ea, which can outperform the traditional subcritical ORC with R227ea by generating 24.7% more power [11]. Wang et al., 2017 [12] enhanced the performance of ORC with two-stage evaporation based on energy and exergy analysis. ...
Article
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Waste heat recovery plays an important role in energy source management. Organic Rankine Cycle (ORC) can be used to recover low-temperature waste heat. In the present work a sample power plant waste heat was used to operate an ORC. First, two pure working fluids were selected based on their merits. Four possible thermodynamic models were considered in the analysis. They were defined based on where the condenser and evaporator temperatures are located. Four main thermal parameters, evaporator temperature, condenser temperature, degree of superheat and pinch point temperature difference were taken as key parameters. Levelized energy cost values and exergy efficiency were calculated as the optimization criteria. To optimize exergy and economic aspects of the system, Strength Pareto evolutionary algorithm II (SPEA II) was implemented. The Pareto frontier solutions were ordered and chose by TOPSIS. Model 3 outperformed all other models. After evaluating exergy efficiency by mixture mass fraction, R245fa[0.6]/Pentane[0.4] selected as the most efficient working fluid. Finally, every component’s role in determining the levelized energy cost and the exergy efficiency and were discussed. The turbine, condenser and evaporator were found as the costliest components.
... In recent studies, zeotropic mixtures are preferred instead of pure refrigerants used in ORC systems [22][23][24][25][26][27][28][29]. Zhou et al. [28] examined the thermodynamic performance of the partial evaporating ORC cycle using the R245fa/R227ea zeotropic fluid mixture as the working fluid. ...
... In recent studies, zeotropic mixtures are preferred instead of pure refrigerants used in ORC systems [22][23][24][25][26][27][28][29]. Zhou et al. [28] examined the thermodynamic performance of the partial evaporating ORC cycle using the R245fa/R227ea zeotropic fluid mixture as the working fluid. They determined that this cycle was produced approximately 25% more power than a subcritical cycle using refrigerant R227ea. ...
Article
In the literature, energetic and exergetic performance of Organic Rankine Cycle (ORC) were investigated by various researchers. The working parameters affecting the cycle's performance were determined but the impact weights and the order of importance of these parameters were not discussed with a statistical approach. In this context, nine fundamental process parameters such as working fluid type, pinch point temperature differences in the evaporator and condenser, superheating temperature, evaporation and condensation temperatures, heat exchanger effectiveness, turbine and pump efficiencies have been selected for the statistical evaluation. A comprehensive statistical analysis has been carried out to observe the effect of the parameters on the first and second law efficiencies of the ORC. The impact ratios and order of importance of these parameters on the sys-tem's performance indicators have been determined. While Taguchi method is performed to determine the optimum levels of each parameter, ANOVA method is used to obtain the impact weights of the parameters on objective functions. In addition to these methods, Grey Relational Analysis (GRA) method is used to optimize the multi-objective function. Evaporator temperature, turbine efficiency, effectiveness of heat exchanger, condenser temperature are obtained as main process parameters on the multiple performance characteristics of ORC and the impact ratios of these parameters are calculated as 31.37%, 19.53%, 16.64%, and 16.61%, respectively. The best condition for the multiple performance characteristics is determined as A 1 B 1 C 3 D 3 E 3 F 3 G 1 H 3 I 3 and under these operating conditions, the first and second law efficiencies of the system are found as 18.1% and 65.52%, respectively.
... Results showed that zeotropic mixtures do have higher thermal efficiency and lower exergy losses than pure fluids, at a certain mixture ratio. Combining zeotropic mixture with PEORC, Zhou et al.(2016) reported 24.7% more output for PEORC with zeotrope over SORC. Very few studies consider the thermo-economic performance and optimization of high latent heat alkanes blended with refrigerants in partial evaporating mode for low temperature heat recovery applications. ...
... The range of optimizing parameters along with the cycle design constraints are shown in Table 4. For mixtures and pure R245fa, the maximum evaporating bubble point temperature is restricted to 0.9 T c of R245fa (Zhou et al., 2016). For pure cyclopentane, this constraint is set to 0.9 T c of cyclopentane. ...
Conference Paper
For low-temperature ORC applications, maximum heat recovery and power output are critical. Hydrocarbons used in medium to high-temperature applications present excellent heat absorbing characteristics but are limited by their flammability. Combining partial evaporation with a zeotropic blend of alkane-refrigerant as the working fluid that combines high-temperature glide and high latent heat could enhance system performance. In this study, a partial evaporating ORC (PEORC) using a zeotropic mixture of R245a/Cyclopentane is presented. Influence of vapor fraction and mass fraction on system performance is analyzed and optimized performances for a range of heat source temperatures are obtained.PEORC with mixtures achieves the highest heat source utilization at lower vapor fractions. Thermal efficiency and net power output of PEORC using mixtures are higher than that of constituent pure fluids. PEORC with mixtures also minimize the exergy destruction in the evaporator and achieves the highest internal and external second law efficiencies. For heat source temperatures ranging from 363K-423K, the performance of PEORC is optimized using Genetic Algorithm and is compared with a standard ORC (SORC). Under optimum operations, PEORC with mixtures outputs 36-65% more power output than SORC with pure R245fa. As heat source temperature increases, PEORC with mixtures and pure R245fa show a decrease in the relative improvement of power output over SORC with R245fa. Furthermore, PEORC with mixtures presents only 3-5% higher power output than PEORC with pure R245fa. From a thermo-economic standpoint, PEORC using R245fa presents excellent system performance.
... Recently a new organic Rankine cycle with partial evaporation using the zeotropic mixture R245fa/R227ea as working fluid is proposed [12]. It was reported that the heat exchanger economy may become worse but the partial evaporation and zeotropic mixture working fluid can improve the thermodynamic performance and more importantly they can be combined together to further enhance the system. ...
... It can be observed from the figure that the peak value of the second-law efficiency with respect to the ammonia mass fraction becomes the maximum when the fluid quality is 0.8. For the efficient recovery of finite low-grade heat source, the partial evaporation and the zeotropic mixture working fluid can improve the exergetic performance of the system, and furthermore, they can be combined together to further enhance the system [12]. ...
Article
The power generation cycle using zeotropic mixture as working fluid has several advantages for recovery of low-grade finite heat sources. In this paper an exergetic analysis is carried out for regenerative partial-evaporation Rankine cycle with ammonia-water mixture. Based on the first and second laws of thermodynamics, the effects of the important system parameters on the exergetical performance of the system were theoretically investigated. The results showed that the second law efficiency has an optimum value with respect to the fluid quality at expander inlet as well as the ammonia mass fraction. © 2018, Engineering and Technology Publishing. All rights reserved.
... Other industrial process waste heat utilization and energy conversion methods were also discussed. [2][3][4][5][6][7][8] At the same time, we should also recognize that the rational utilization of resources alone is no longer sufficient to slow down the release of CO 2 in China's steel plants. Only by carbon capture and storage (CCS), climate change caused by large amounts of CO 2 can be mitigated in a short time. ...
... The equilibrium constant is calculated by Equation 6. ...
Article
Carbon capture and storage adopted by power plants has been extensively studied in recent years. However, little attention has been paid to carbon capture and storage for steel plants. After considering the differences between steel and power plants, a carbon capture system of reheating furnace flue gas is designed, based on the sensible heat of continuous casting slabs. As a result, a significant amount of waste heat resource from rolling mills can be effectively reused. By using Aspen Plus to optimize parameters of the capture system, such as regeneration pressure and reflux ratio, the regeneration energy consumption is obtained and the result is verified by comparing the data with that of other research. Under the constraint condition of 90% CO2 capture rate, simulation results show that the purity of CO2 obtained is 98.4%, and the annual CO2 capture capacity is about 70 000 tons. Finally, main parameters of continuous casting slabs and the heat recovery boiler are calculated. The heat load of the steam supplied for the reboiler is 8.5 MW, indicating that this steam generation method matches the carbon capture system.
... Wu et al. [11] studied the performance of ORC system by using RC318/HFC-245fa, Butane/HFC-245fa, HFC-227ea/HFC-245fa, and the pure working fluids, they found that the exergy efficiencies, power outputs, and cycle efficiencies of mixtures were higher than that of the corresponding pure working fluids. A partial evaporating ORC system was built by Zhou et al. [12], the results indicated that the use of HFC-245fa/HFC-227ea mixture in the condenser can reduce the exergy loss compared with pure working fluids. ...
Article
Density functional theory calculations and ReaxFF reactive molecular dynamic simulations are employed to investigate the decomposition and interaction of HFC-245fa/HFC-227ea mixture. The impact of HFC-245fa to HFC-227ea ratio, temperature and pressure on the decomposition of HFC-245fa/HFC-227ea mixture, and the interaction mechanism between HFC-245fa to HFC-227ea in mixture are studied. The results indicated that the main decomposition products of HFC-245fa/HFC-227ea mixture are HF, H2, CF4, CH2F2, CHF3, C2F2 and C3F8. H2 is the earliest molecular product generated during the decomposition process, Thus, H2 can be used as the decomposition indicator of HFC-245fa/HFC-227ea mixture. The hydrogen bond is generated between HFC-245fa and HFC-227ea in the HFC-245fa/HFC-227ea mixture, resulting in the thermal stability of HFC-245fa is improved. Thus, the thermal stability of HFC-245fa/HFC-227ea mixture is better than that of pure HFC-245fa. This study is conducive to the screening of HFC-245fa/HFC-227ea mixture used in the field of organic Rankine cycle.
... The partial evaporating organic Rankine cycle (PEORC) can be considered as a combination of an ORC and a TFC [28]: for a TFC, the fluid is heated to the boiling point, whereas for the PEORC the fluid starts to evaporate. Studies show that this cycle can reduce energy losses [29,30]. In fact, when compared to a traditional ORC system, PEORC exhibits a better match between the temperature profiles of the heat source and the working fluid. ...
Article
Full-text available
The organic Rankine cycle (ORC) technology is an efficient way to convert low-grade heat from renewable sources or waste heat for power generation. The partial evaporating organic Rankine cycle (PEORC) can be considered as a promising alternative as it can offer a higher utilization of the heat source. An experimental investigation of a small ORC system used in full or partial evaporation mode is performed. First characterized in superheated mode, which corresponds to standard ORC behavior, a semi-empirical correlative approach involving traditional non-dimensional turbomachinery parameters (specific speed, pressure ratio) can accurately describe one-phase turbine performance. In a second step, two-phase behavior is experimentally investigated. The efficiency loss caused by the two-phase inlet condition is quantified and considered acceptable. The turbine two-phase operation allows for an increase in the amount of recovered heat source. The ability to operate in two phases provides a new degree of flexibility when designing a PEORC. The semi-empirical correlative approach is then completed to take into account the partially evaporated turbine inlet condition. The qualitative description and the quantitative correlations in the one-phase and two-phase modes were applied to different pure working fluids (Novec649TM, HFE7000 and HFE7100) as well as to a zeotropic mixture (Novec649TM/HFE7000).
... Based on the above advantages, the mixtures have attracted the attention of researchers. Zhou et al. [12] proposed a partial evaporating ORC architecture, the zeotropic mixture R245fa/R227ea was used as the working fluid, the results found that the exergy loss can be reduced by the mixture R245fa/R227ea than pure working fluid in the condenser. Radulovic et al. [13] studied the potential of the mixtures of R-143a with other working fluids in supercritical ORC by using geothermal energy as heat source, they found that the cycle efficiency of ORC system using zeotropic mixtures can be increased by 15% than that of pure R-143a at the same conditions. ...
Article
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.
... These mixtures have variable phase change temperatures (non-isothermal). In recent years, several studies investigated the effects of using different mixtures on the performance of ORC [23,24]. For example, Miao et al. [25] studied the mixture selection criteria for ORC. ...
Article
ORC is a common power generation system that is driven by different heat source temperatures. Boiler pressure and working fluid are effective factors on the cycle performance. The use of mixtures can improve performance. Selecting a proportionate mixture is a great challenge. In this paper, the waste heat recovered from an industrial complex was utilized to generate power by an ORC. A large number of binary mixtures were considered as the working fluid. Based on the optimization algorithms such as Genetic Algorithm and Particle Swarm Optimization, the effects of various components and their concentrations in the mixture and boiler pressure were simultaneously optimized. The optimal conditions including components of the binary mixture, mixture concentration, and boiler pressure were presented for different heat source temperatures in the range of 80-190°C. R32-R290 with a concentration of 0.69-0.31 at the pressure of 37.06 bar had the highest net power and exergy efficiency for heat source temperature of 80˚C. For temperatures of 100˚C and 130˚C, R290-R143a and R290-R152a with concentrations of 0.2-0.8 and 0.57-0.43 were the most appropriate mixtures at their optimal pressures, respectively. The optimum binary mixtures for heat source temperatures of 160˚C and 190˚C were R600-R21 (0.31-0.69) and R600-R245fa (0.33-0.67), respectively.
... Another element of novelty compared to the state of the art is the numerical investigation of the effects that a variation of the expander built-in volume ratio has on the machine performance and the overall power recovery. This work also expands recently published work on Trilateral Rankine Cycles and partial-evaporating cycles, such as [32,33] and [34] respectively. ...
Article
Full-text available
This research work presents a numerical chamber model of a two-phase twin-screw expander and its further integration in a one-dimensional model of a Trilateral Flash Cycle (TFC) system for low-grade heat to power conversion applications. The novel feature of the expander is the capability of changing the built-in volume ratio (BIVR) of the machine through a sliding valve in the casing that opens an additional suction port. Lowering the BIVR from 5.06 to 2.63 results in an improvement of the volumetric efficiency from 53% to 77% but also in a reduction of the specific indicated power from 4.77 kJ/kg to 3.56 kJ/kg. Parametric analysis on several degrees of freedom of the full TFC system concluded that expander speed and BIVR are the variables that mostly impact the net power output of the unit. An optimisation study enabled the power output of the TFC system, at design point, to increase from 83 kW to 100kW.
... Deethayat, Kiatsiriroat, and Thawonngamyingsakul (2015) investigated the performance of a 50 kW ORC with an internal heat exchanger, using a mixture of R245fa/R152a as the refrigerant. Tiwari, Sherwani, and Kumar (2019) investigated the thermo-economic performance of the non-recuperated ORC driven by solar energy Zhou, Zhang, and Yu (2016) examined the thermodynamic performance of the partial evaporating ORC cycle using the R245fa/R227ea zeotropic fluid mixture as the working fluid. They determined that this cycle was produced approximately 25% more power than a subcritical cycle using refrigerant R227ea. ...
Article
In this study, the performance of organic Rankine cycle (ORC), which produces electrical energy, was examined by using a geothermal resource with a temperature of 145°C. The fluids used in the system were determined as dry type fluids, and R142b, R227ea, R245fa, R600, and R600a were preferred as a working fluid. Within the scope of this study, energy and exergy analysis of the system was performed for different evaporator pressures (1000-2000 kPa). With the help of these analyses, the performances of the cycle elements were examined and the first and second law efficiencies of the system were compared for different refrigerants. Considering the selection of refrigerant, and evaporator pressure within the scope of this study, the first and second law efficiencies of the cycle have enhanced maximum of 4.86% and 19.78%, respectively.
... Many researchers researched the working fluids for ORC systems [7][8]10,17,19,[27][28][29][30][31][32][33][34]. Zhou et al. [35] analyzed a partial evaporating organic Rankine cycle (PEORC) using zeotropic mixtures. The optimized PEORC with R245fa/R227ea is able to generate about 24.7% more power than the traditional subcritical organic Rankine cycle (SCORC) with R227ea. ...
Article
Studies and applications of organic Rankine cycle (ORC) systems are increasing in recent years because of the advantages of them on the recovery of low temperature heat sources. The choice of working fluids, system design methods, equipment, and applications of ORC systems were researched by many researchers. Expansion devices are the key equipment for ORC systems. The review of expansion devices for ORC systems was presented in this paper. The devices of scroll, screw, piston, vane, turbine, and ejector for ORC systems are involved. It is expected that the review presented here can summarize what was done before and will provide the investigator with the knowledge and ideas about how to choose and improve the performance of expansion devices for ORC systems.
... It was concluded that the TFC was able to achieve a higher net power output compared to the KC and the ORC, and the product cost of the TFC was greatly affected by the isentropic efficiency of the expander. Moreover, other researchers [18,19] pursued the idea of Partial-Evaporating Organic Rankine Cycle (PEORC) with pure fluids or zeotropic mixtures to improve the heat source temperature match with respect to the conventional ORC and to achieve a higher thermal efficiency and smaller heat transfer area requirements in comparison to the TFC. ...
Article
Two-phase expansion is of great interest to enhance the efficiency of conventional sub-critical organic Rankine cycle (ORC). However, the design of highly-efficient expanders to handle two-phase expansion is still an open topic in the literature. In this paper, an experimentally validated thermodynamic model was employed to investigate the two-phase expansion process in a reciprocating expander with a flash chamber for Trilateral Flash Cycle (TFC) applications. An intake ratio, ε, defined as the intake time to the expansion time has been proposed to analyze the suction process of saturated liquid and the corresponding intake losses. The evolutions of temperature, pressure, and quality during the expansion process have been simulated, and the intake losses have been quantified from the indicated diagrams. Moreover, parametric analyses on the influence of the intake ratio for different rotational speeds, mean inlet flow velocities, inlet port diameters, and intake mass values have been performed. The isentropic efficiency and the power output of the expander have been calculated and discussed under different operating conditions. Finally, a correlation for estimating the intake losses has been developed.
... • The pressure reduction and heat loses are neglected in evaporator (collector), expander and condenser (Geng, Du, and Yang 2016;Zhou, Zhang, and Yu 2015). • The kinetic and potential energy changes have been neglected (Wang and Zhao 2009). ...
Article
Full-text available
In current work, analytical expressions have been coded in MATLAB 9.0 linked with REFPROP 9.0, for solar powered ORC system integrated with conventional compound parabolic concentrator using environmental friendly hexane/R1234yf zeotropic mixture in order to calculate hourly (8 AM to 4 PM) combined performance of solar power ORC, based on experimental data. It has been observed that maximum heat gain in the collector is 5.132 × 10⁵ W at 1 PM for the mass fraction (0.7/0.3). Moreover , maximum overall thermal efficiency 17.65% is attained at 1 PM for the mass fraction 0.3/0.7 whereas overall exergetic efficiency 49.23% is achieved at the same time for the mass fraction 0.3/0.7.
... They also reported that the temperature glide has a negative effect on the net power output when the condenser bubble temperature is fixed, whereas the temperature glide increases the net power output when the cooling water temperature increases. Zhou et al. [25] proposed a novel partial evaporating ORC with zeotropic mixtures. The proposed ORC generated power, which is 24.7% higher than the one generated by the basic ORC using R245fa/R227ea as working fluids. ...
Article
Organic Rankine cycle (ORC) is a promising thermal-to-power technology that uses low-temperature heat from various sources including renewable energy and waste heat. A zeotropic fluid ORC offers thermodynamic-performance advantages over pure fluid ORC because of the relatively low irreversibility during the heat transfer process. Nonetheless, zeotropic fluid ORC may incur higher cost than pure fluid ORC because the former has high mass transfer resistance and small temperature difference in the heat exchanger. Limited research has been carried out to enhance thermo-economic performance of zeotropic ORC. In the present study, an ORC that uses zeotropic fluids and undergoes liquid–vapor separation during condensation is proposed. A thermo-economic analysis is developed based on a new optimization model for the proposed ORC. The objective function of the optimization model is the minimization of the specific investment cost. A genetic algorithm is used to solve the optimization model. A case study is then solved to illustrate the advantages of the proposed ORC and validate the proposed thermo-economic optimization method. The results of the thermodynamic analysis show that the condenser area of the proposed ORC is 17.6% lower than that of the conventional ORC under the same working conditions. Thermo-economic optimization results show that the specific investment cost of the proposed ORC is 13.3–18.4% lower than that of the basic ORC. Meanwhile, the second law efficiency of the proposed ORC is 4.2% higher than that of the conventional ORC. A sensitivity analysis is carried out to assess the dependence of the ORC performance on the temperatures of the heat source and the surrounding environment.
... [10][11][12]. Furthermore, Zhou et al. [13] investigated working-fluid mixtures operating within partially evaporated ORC systems. Whilst many of these studies report higher power outputs and higher exergy efficiencies, they also report larger heat exchanger costs. ...
Article
Full-text available
A mixed-integer non-linear programming optimisation framework is formulated and developed that combines a molecular-based, group-contribution equation of state, SAFT-γ Mie, with a thermodynamic description of an organic Rankine cycle (ORC) power system. In this framework, a set of working fluids is described by its constituent functional groups (e.g., since we are focussing here on hydrocarbons: CH3, CH2, etc.), and integer optimisation variables are introduced in the description the working-fluid structure. Molecular feasibility constraints are then defined to ensure all feasible working-fluid candidates can be found. This optimisation framework facilitates combining the computer-aided molecular design of the working fluid with the power-system optimisation into a single framework, thus removing subjective and pre-emptive screening criteria, and simultaneously moving towards the next generation of tailored working fluids and optimised systems for waste-heat recovery applications. SAFT-γ Mie has not been previously employed in such a framework. The optimisation framework, which is based here on hydrocarbon functional groups, is first validated against an alternative formulation that uses (pseudo-experimental) thermodynamic property predictions from REFPROP, and against an optimisation study taken from the literature. The framework is then applied to three industrial waste-heat recovery applications. It is found that simple molecules, such as propane and propene, are the optimal ORC working fluids for a low-grade (150°C) heat source, whilst molecules with increasing molecular complexity are favoured at higher temperatures. Specifically, 2-alkenes emerge as the optimal working fluids for medium- and higher-grade heat-sources in the 250–350°C temperature range. Ultimately, the results demonstrate the potential of this framework to drive the search for the next generation of ORC systems, and to provide meaningful insights into identifying the working fluids that represent the optimal choices for targeted applications. Finally, the effects of the working-fluid structure on the expander and pump are investigated, and the suitability of group-contribution methods for evaluating the transport properties of hydrocarbon working-fluids are considered, in the context of performing complete thermoeconomic evaluations of these systems.
... A method to determine the optimal condensation pressure was presented. Zhou et al. [85] analysed an ORC with partial evaporation, i.e. the expander received a stream in twophase flow. The results indicated that the optimized partial evaporation ORC configuration produced 24.7 % more power than the subcritical ORC configuration. ...
Article
The use of zeotropic fluid mixtures in refrigeration cycles and heat pumps has been widely studied in the last three decades or so. However it is only in the past few years that the use of zeotropic mixtures in power generation applications has been analysed in a large number of studies, mostly with low grade heat as the energy source. This paper presents a review of the recent research on power cycles with zeotropic mixtures as the working fluid. The available literature primarily discusses the thermodynamic performance of the mixture power cycles through energy and exergy analyses but there are some studies which also consider the economic aspects through the investigation of capital investment costs or through a thermoeconomic analysis. The reviewed literature in this paper is divided based on the various applications such as solar energy based power systems, geothermal heat based power systems, waste heat recovery power systems, or generic studies. The fluid mixtures used in the various studies are listed along with the key operation parameters and the scale of the power plant. In order to limit the scope of the review, only the studies with system level analysis of various power cycles are considered. An overview of the key trends and general conclusions from the various studies and some possible directions for future research are also presented.
Article
The exergy efficiency improvement potential of dual-phase expansion (trilateral and partial evaporation) Organic Rankine Cycles (ORC) with zeotropic mixtures of R1233zd(E), R1234ze(E) and R1234yf as well as isobutane and propane for waste heat temperatures from 80 °C to 200 °C is investigated. For each fluid pair, standard ORCs are compared to trilateral and partial evaporation cycles (T-ORC and P-ORC) of mixtures (T-Z and PE-Z) and pure fluids. For isobutane-propane and R1233zd(E)-R1234ze(E), PE-Z and T-Z cycles result in the highest exergy efficiency for most temperatures. For R1233zd(E)-R1234yf, PE-Z and T-Z cycles are superior below 140 °C. For R1234ze(E)-R1234yf, PE-ORCs and standard ORCs with R1234ze(E) are most efficient at temperatures below and above 140 °C, respectively. PE-Z cycles of R1233zd(E)-R1234ze(E) exhibit the highest efficiency at all temperatures except for 100 °C, at which T-Z cycles are superior. Generally, PE-Z cycles have slightly higher exergy efficiency compared to PE-ORCs with pure fluids of high critical temperature. Given the technical challenges of zeotropic cycles, the latter could be more appealing. For expansion isentropic efficiencies around 60%, dual-phase expansion cycles remain competitive against saturated vapor zeotropic (S-Z) and saturated ORCs at lower temperatures. However, isentropic efficiencies above 50% are necessary for them to be competitive against S-Z cycles.
Article
The waste heat from a geothermal-driven organic flash cycle has an outstanding potential to be recuperated. The present research is an effort to recover the thermal losses of a geothermal-based organic flash cycle to a feasible extent by employing a configuration that has not been studied in the literature. In this respect, the energy losses in the high-temperature and low-temperature throttling stages of the organic flash cycle are recuperated in a screw expander and an LiCl-H2O absorption chiller, correspondingly. Moreover, the heat loss in the condenser of the organic flash cycle is recovered in a Seebeck power generator, and the electricity produced in the expander and Seebeck generator is transmitted to a proton exchange membrane electrolyzer to generate hydrogen. In addition, a heat exchanger is embedded to produce hot water utilizing the residual energy of the geothermal water before reinjection. The proposed system is analyzed by the engineering equation solver from energy, exergy, and exergoeconomic standpoints. The exergoeconomic analysis is performed by employing the specific exergy costing method, and multi-objective optimization is carried out utilizing MATLAB software. The optimized thermo-economic performance of the system reveals that the heat loss recovery enhances the useful exergy of the system by producing 178 kW of exergy rate for cooling, heating, and hydrogen. Thus, the exergy efficiency of the polygeneration system is obtained as 30.3%, which is 10.5% points higher than the case of electricity generation by the turbine of the flash cycle. Above all, the low unit cost of polygeneration and payback period, respectively equal to 7.3 $GJ-1 and 1.4 years, make the designed system superior when is compared with similar geothermal-based polygeneration systems.
Article
Compared to pure fluids, zeotropic mixtures have the potential to lower the irreversibilities in low temperature Rankine cycles by better temperature profile matching of the working fluid with the heat source/sink. However, having a gliding temperature does not guarantee performance boost over pure fluids, as many factors influence the exergy efficiency of the cycle. In this study, 25 pure fluids and 104 binary mixtures of natural working fluids are analyzed in subcritical ORCs with heat source temperature range of 125–300 ℃ and different condensing conditions and the results are investigated within two frameworks: (1) comparing the mixtures to their pure constituents, (2) comparing the mixtures to the best performing pure fluid. In one behavior type, the performance of the mixture falls between the performance of its pure constituents for all evaporator pressure range, and the mixture provides no benefit. However, some mixtures could provide performance boost in a specific evaporator range. Therefore, the maximum allowable evaporator pressure plays an important role in the performance comparison of zeotropic mixtures to their pure constituents. Mixtures which outperform their pure constituents in the first perspective, are further analyzed in the second perspective. Finally, a screening method is presented to map the binary mixtures with performance boost compared to their pure constituents and high absolute exergy efficiency. This method is based on the key thermophysical properties of the fluids including critical temperature and normal boiling point, as well as working conditions such as heat source and heat sink temperature and PPTD in the evaporator and the condenser.
Article
The trilateral cycle (TLC) has been viewed as a promising technology for low grade heat to power conversion, while its application in reality is greatly limited by the low efficiency of two-phase expander and high volume flow rate at the expander outlet. This paper suggests a novel thermosyphon based trilateral cycle (TTLC), which uses hydraulic turbine for power generation instead of two-phase expander, avoiding problems in traditional TLC systems and also providing a chance for utilization of pump-as-turbine (PAT) technologies. Thermodynamic model of the novel system is developed, as well as the two-phase flow model for the riser. The system performance of TTLC is investigated based on the first law analysis and the second law analysis, and the results are compared with those of traditional TLC and organic Rankine cycle (ORC). It is found that the extra gravitational pressure drop is the main contributor to the riser efficiency. The working fluids with smaller density ratio and specific heat are more suitable for the proposed system, such as R502, R218, R125 and R115. Increasing heat source temperature is more efficient in energy conversion than decreasing sink temperature for the TTLC system, which generates marginally more power than TLC when the heat source temperature is less than 50 °C, and less power than TLC within the deviation of 10% for the heat source temperature in the range of 50-75 °C. The traditional ORC has the worst performance due to its bad temperature matching. Moreover, the volume flow rate at the turbine outlet of TTLC is only 2-17% of those for TLC and ORC, indicating a much smaller turbine size.
Article
Conventional exergoeconomic analysis suffers from a lack of solid conceptual meaning behind its auxiliary cost equations defined for the needed components. To provide a logical relation between auxiliary cost equations, here a modified exergoeconomic analysis is used, which integrates the energy level of each stream with the conventional exergoeconomic analysis. Since the energy level of a component stems from a temperature (known as thermal term) and pressure (known as mechanical term) difference between its inlet and outlet streams, modifying the unit cost of the streams by their energy level significantly affects the overall unit cost of product. Hence, in this study, a new integral micro-CCHP (combined cooling, heating, and power) system driven by geothermal source and working with different zeotropic mixtures is proposed and evaluated economically by employing the recommended modified exergoeconomic approach. Later, due to the existing conflicting trend between energy efficiency, exergy efficiency, and modified total unit cost associated with the products, a multi-objective optimization tool is used to merge several optimal design points into an equilibrium point as the final optimal point. Several similar benchmarks (in terms of applications or sketch) are selected and the superiorities of the devised micro-CCHP system over them in terms of thermodynamics and thermoeconomics have been demonstrated. After optimization, the net power, cooling load, and heating load are improved by 106.77%, 142.83%, and 49.78%, respectively. This improvement in all products has led to a meaningful enhancement of 24.91% in energy efficiency, 15.42% in exergy efficiency, and 9% in the total unit cost of product (TUCP) (in both modified and conventional cost approaches). The best representative optimal point has the optimal energy efficiency, exergy efficiency, and TUCP of 61.61%, 44.46%, and 0.63 $/kWh, respectively.
Article
Organic Rankine cycle (ORC) is an effective approach for low-grade energy utilization. It is important to improve the efficiency of an ORC when the heat source temperature varies. In this study, a method of selecting zeotropic mixture for a bottoming ORC with changeable heat source temperature is presented. The effects of the operation conditions of the marine engine and the ambient temperature are investigated. First, the optimal performances of the ORC using 40 pure working fluids are determined and compared. Then, two zeotropic mixtures benzene/m-xylene and cyclopentane/toluene are selected and the mechanism of temperature match with the heat source and sink is explored. Finally, the performance improvement with benzene/m-xylene using the composition adjustment method is evaluated. The results indicate that the suitable pure working fluids are isopentane and R245ca for a low exhaust temperature while toluene and m-xylene are the best when the exhaust temperature is high. Using the zeotropic mixtures benzene/m-xylene and cyclopentane/toluene can obtain a high performance over the operation range of the marine engine. When the exhaust temperature is 225 °C, the net power and exergy efficiency of benzene/m-xylene are improved by 6.9%–21.9% and 6.5%–22.0%, respectively, compared with the pure fluids benzene and m-xylene. When the exhaust temperature increases to 380 °C, these improvements decrease to 1.9%–6.8%. If a zeotropic mixture is used, the critical temperature of the component with a high-boiling point should be close to the maximum operation temperature of the heat source, and the temperature glide should first match with the temperature increase of the heat sink. If the heat sink temperature is fixed, it is impossible to enhance the ORC performance using the composition adjustment method. However, the composition adjustment method is effective when the temperature of the heat sink varies with the ambient temperature. The net power and exergy efficiency of the ORC are improved by up to 21.9% and 22% in winter using benzene/m-xylene. However, these improvements are less than 6.8% in summer.
Article
Geothermal energy is an important renewable energy. Oilfields in high water cut stage are also geothermal fields. We propose a geothermal cascade utilization system, including organic Rankine cycle (ORC) power generation, Li-Br absorption refrigeration, oil gathering and transportation heat tracing (OGTHT) and heat. Associated geothermal water from abandoned oil wells is used as a renewable heat source. The thermodynamic and economic analysis of the cascade utilization system is carried out by establishing a mathematical model. In ORC system, we use two-stage series evaporation to reduce irreversible losses. The results show that there is an optimum evaporation temperature to maximize the net output power, thermal efficiency and exergy efficiency. It is found that the mass flow of the working fluid has a great impact on the system performance. In economic analysis, we find that both cost and benefit increase with the increase of geothermal water temperature (Tgw in) and driving heat source temperature. We use the payback period (PBP) as a comprehensive evaluation index of economy. The results show that there is an optimal temperature combination to minimize PBP. The smallest payback period occurs at the Tgw in is 383 K and the driving heat source temperature is 363 K, which is 3.07 years.
Article
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.
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In the present study, a cascade power generation system, consisting of a partial evaporation Rankine cycle (PERC), and an organic Rankine cycle (ORC) with a parabolic trough solar collector (PTSC) as the driver coupled with a storage tank, has been studied and optimized from energy and exergoeconomic viewpoints. Instead of using conventional steam turbine, a screw expander has been utilized in PERC, in order to facilitate coupling the PERC with the PTSC and the storage tank, operating near the recommended temperature of 300 °C, as well as to avoid producing superheated vapor in the upper Rankine cycle. This configuration is appropriate specifically because of the pressure limit at the inlet of expander (4 MPa), corresponding to a saturation temperature of 250 °C for steam. With toluene as the selected organic fluid among 4 candidates, parametric analysis was performed to investigate the effect of variations in solar radiation intensity, collector aperture area, PERC evaporation and condensation temperatures, and expander inlet steam quality on the thermoeconomic performance of the system, followed by a tri-objective optimization using genetic algorithm considering net power output, exergy efficiency and total cost rate as objective functions. The obtained results show that for the optimum design point, the studied solar power plant with aperture area of 5540 m2 and storage tank volume of 184.7 m3 can produce 782 kW of power with exergy efficiency of 18.61% and total cost rate of 228 $.h-1. The optimum design case indicates an improvement in net power output, exergy efficiency, and unit cost of electricity by 65%, 2.9%, and 27.26%, respectively, compared to the base case. Furthermore, at the optimal point, the power output of ORC (440.6 kW) is higher than that of PERC (349.2 kW). However, the unit cost of electricity production is lower for PERC (22.82 $.GJ-1) compared to ORC (37.19 $.GJ-1).
Article
When organic Rankine cycles (ORC) are employed to convert waste heat into work, the thermal efficiency is not recommended as a key performance metric because waste heat recovery and power output are not generally maximized at the point of peak efficiency. In such an application, maximization of the net power output should be the objective. Two alternative cycle configurations that can increase the net power output from a heat source with a given temperature and flow rate are analyzed and compared to a baseline ORC. These cycle configurations are: an ORC with two-phase flash expansion (TFC) and an ORC with a zeotropic working fluid mixture (ZRC). A design-stage ORC model allowed a consistent comparison of multiple ORC configurations with finite capacity of the source and heat sink fluids. Simulation results indicated that the TFC offered the most improvement over the baseline ORC, but required a highly efficient two-phase expansion. The ZRC shows improvement over the baseline as long as the condenser fan power requirement is not negligible. At the highest estimated condenser fan power, the TFC is no longer beneficial. Finally, a partial-evaporating ZRC (PE-ZRC) has also been considered to reduce the volume ratio requirements of a flash expansion.
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The Organic Rankine Cycle (ORC) system is a rather promising technology for waste heat recovery. However, waste heat source generally presents a fluctuating behavior, which is a big challenge to the security and efficiency of the ORC. An improved dynamic model of ORC system with zeotropic mixture is firstly developed, which can be better adapted to the phase change process of working fluid. Accordingly, dynamic behavior of the ORC and dynamic distribution of evaporation stages are investigated. Besides, three control strategies are proposed to improve the performance of steadiness with external controllable conditions. Results show that a sudden abnormal change occurs in specific enthalpy of working fluid at the evaporator outlet when different disturbances are imposed to the system. It is found that the proposed control strategies are adapted to different heat source fluctuation. The control strategies with feedforward control system work well with low frequency variation of heat source temperature.
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This paper proposed a gas turbine and organic Rankine cycle (GT-ORC) combined cycle to further improve the energy efficiency of gas turbines. Alkanes, linear siloxanes, and aromatics were selected as working fluids for the bottoming organic Rankine cycle. Based on the mathematical model and solution procedure proposed, a thermodynamic comparison of GT-ORC combined cycle was conducted with pure and mixture working fluids. Simulation results showed that the mixtures made the combined cycle achieve higher efficiency than pure fluids. Compared with conventional steam Rankine cycles, the organic Rankine cycle had larger potential in recovering exhaust heat from gas turbines. The thermodynamic analysis showed that the thermal efficiency of the bottoming cycle increased with the rise of turbine inlet pressure. Besides, the ORC net power was maximum at the optimum turbine inlet pressure. Four commercial gas turbines with different exhaust temperatures (553-778 K) were also examined, and results indicated that the Trent 60 combined cycle achieved the highest thermal efficiency of 56.48%. For gas turbine of different power levels, the toluene/benzene mixture was more suitable in recovering waste heat from small and medium size gas turbines, while the cyclopentane was more applicable for microgas turbines.
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In this research work, the computer code is written in MATLAB 9.0 which is interfaced with Refprop 9.0. in order to develop a thermodynamic model of solar driven organic Rankine cycle. A novel glazed reverse absorber conventional compound parabolic concentrator integrated with recuperated organic Rankine cycle {case (ii)} using low global warming potential and zero ozone depletion potential working fluid cyclohexane/R245fa has been proposed. The coding has been done to evaluate hourly concentrator fluid outlet temperature, heat gain in concentrator, expander output, overall thermal efficiency, overall exergetic efficiency and exergy destruction. The performance of the glazed reversed absorber conventional compound parabolic concentrator integrated with recuperated organic Rankine cycle {case (ii)} has been compared with glazed reversed absorber compound parabolic concentrator with non recuperated organic Rankine cycle {case (i)}. It is observed that overall first law efficiency improves by 40.9% and exergetic efficiency 36.28% using recuperated organic Rankine ORC {case (ii)} in comparison of non-recuperated ORC {case (i)}. The system in case {ii} has been found to be self-sustainable system and gives better result in term of thermal efficiency, environmental, space heating, day lighting and electricity use.
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The aim of this study is to investigate the thermo-economic performance of the transcritical organic Rankine cycle (TORC) system using R1234yf/R32 mixtures as the working fluids for the lower-grade waste heat recovery (WHR). The components of R32 and R1234yf are selected due to their zero ozone depletion potential, lower global warming potential and complementary thermodynamic properties. The influences of the mass fractions of R1234yf/R32 mixtures, isentropic efficiencies of the expander, condensation temperature, turbine inlet pressure and temperature on performances have been investigated. The results show that R1234yf/R32 at optimal mass fraction is superior to pure R1234yf and pure R32 by 1.46% and 4.88% in thermo-economic performance, respectively. The optimal compositions of mixtures and the optimal temperature entropy diagrams are obtained to fit the various isentropic efficiencies possessed by the different types of expanders. In thermo-economic evaluation, the lower the condensation temperature is, the larger the optimal mass fraction of R32 in the mixtures will be. The increase of optimal expander inlet pressure and temperature are proportional to that of mass fraction of R32 in mixtures. The relationships among mass fraction, optimal expander inlet pressure and temperature and performance are expressed as the correlations for convenient design in lower-grade WHR.
Article
Purpose The purpose of this paper is to investigate the effect of four controllable parameters (fuel mixture, evaporation bubble point temperature, expander inlet temperature and condensation dew point temperature) of a solar-driven organic Rankine cycle (ORC) on the first-law efficiency, the exergetic efficiency, the exergy destruction and the volume flow ratio (expander outlet/expander inlet). Design/methodology/approach Nine experiments as per Taguchi’s standard L9 orthogonal array were performed on the solar-driven ORC. Subsequently, multi-response optimization was performed using grey relational and principal component analyses. Findings The results revealed that the grey relational analysis along with the principal component analysis is a simple as well as effective method for solving the multi-response optimization problem and it provides the optimal combination of the solar-driven ORC parameters. Further, the analysis of variance was also employed to identify the most significant parameter based on the percentage of contribution of each cyclic parameter. Confirmation tests were performed to check the validity of the results which revealed good agreement between predicted and experimental values of the response variables at optimum combination of the input parameters. The optimal combination of process parameters is the set with A3 (the best fuel mixture in the context of optimal performance is 0.9 percent butane and 0.1 percent pentane by weight), B2 (evaporation bubble point temperature=358 K), C1 (condensation dew point temperature=300 K) and D3 (expander inlet temperature=370 K). Research limitations/implications In this research, the Taguchi-based grey relational analysis coupled with the principal components analysis has been successfully carried out, whereas for any optimized solution, it is required to have a real-time scenario that may be taken into consideration by the application of different soft computing techniques like genetic algorithm, simulated annealing, etc. The results generated are purely based on theoretical modeling, and, for further research, experimental analyses are required to consolidate the generated results. Originality/value This piece of research work will be helpful to users of solar energy, academicians, researchers and other concerned persons, in understanding the importance, severity and benefits obtained by the application, implementation and optimization of the cyclic parameters of the solar-driven ORC.
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This paper communicates detailed energy and exergy analysis of low-grade energy resource of solar powered ORC integrated with both the internal heat exchanger and open feed water heater, ORC incorporated with the internal heat exchanger, with open feed water heater and basic ORC respectively. Results highest first law (11.9%) and exergetic efficiency (51.88%) and lowest exergy destruction (1749kW) of ORC integrated with both the internal heat exchanger and regenerator among other considered ORCs. Moreover, zeotropic mixture (butane/R1234yf) shows better first law and exergetic efficiency and lower exergy destruction than pure fluid.
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The growing cost for energy production and distribution as well as problems related to environmental pollution have induced an increasing interest in the research of alternative solutions and in particular innovative technologies capable of compromising energy production cost, optimization and guaranteeing environmental sustainability. One of the technologies of increasing interest in recent years is the Organic Rankine Cycle (ORC). These systems are generally suitable for the recovery of low grade heat at low pressure this is a major advantage of the system in terms of safety and management. Furthermore, they enhance simple operation, low maintenance, and the use of a working fluid that is environmentally friendly. This paper presents a comprehensive and current literature overview of micro generation systems up to 100kWe. A working fluid screening criteria has been discussed taking into account the environmental impact as well as the thermo-physical properties of various potential working fluids. From the analyses it emerges that the fluid most used in installed ORC systems is the R245fa also confirmed by means of a computational code developed for micro-systems of the size range. Components and expander selection has also been examined, the study reveals that the most suitable expander for the applications of these plant size ranges are the scroll for small installations and the vane or screw expanders for larger installations. Finally a detailed list of characteristics of both industrial and experimental prototype application is presented with references to their manufacturers.
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Based on the thermoeconomic multi-objective optimization and decision makings, considering both exergy efficiency and LEC (levelized energy cost), the performance comparison of low-grade ORCs (organic Rankine cycles) using R245fa, pentane and their mixtures has been investigated. The effects of mass fraction of R245fa and four key parameters on the exergy efficiency and LEC are examined. The Pareto-optimal solutions are selected from the Pareto optimal frontier obtained by NSGA-II algorithm using three decision makings, including Shannon Entropy, LINMAP and TOPSIS. The deviation index is introduced to evaluate different decision makings. Research demonstrates that as the mass fraction of R245fa increasing, the exergy efficiency decreases first and then increases, while LEC presents a reverse trend. The optimum values from TOPSIS decision making are selected as the preferred Pareto-optimal solution for its lowest deviation index. The Pareto-optimal solutions for pentane, R245fa, and 0.5pentane/0.5R245fa in pairs of (exergy efficiency, LEC) are (0.5425, 0.104), (0.5502, 0.111), and (0.5212, 0.108), respectively. The mixture working fluids present lower thermodynamic performance and moderate economic performance than the pure working fluids under the Pareto optimization.
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This paper presents the analysis and results of a supercritical Waste Heat Recovery (WHR) Organic Rankine Cycle (ORC) modelling study. The study focuses on multiple series heat sources from vehicles and the potential of WHR ORC's to convert this into useful work. The work presented is generally applicable to any waste heat recovery system, either stationary or mobile and, with careful consideration, is also applicable to single heat sources. The simulation model simultaneously calculates WHR ORC performance for multiple circuit layouts related to the position of the regenerator. The work presented details the optimisation of WHR ORC performance with regard to fluid selection from a distinct pool of preselected fluids and from an operational parameter perspective at realistic drive cycle related heat boundary conditions. The paper also looks at WHR ORC performance with regard to condenser pressure and atmospheric conditions for different fluids. The paper concludes with estimated WHR ORC vehicle fuel consumption improvement figures.
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An Organic Rankine Cycle (ORC) system was built to test the performance of a scroll expander with organic working fluid R123. The output performance of the scroll expander was tested under different conditions with various electric loads and pump capacity. Meanwhile, based on the geometric structure of the scroll expander and using thermodynamic method integrated with force balance analysis, the working process of the scroll expander was simulated. The simulation results were compared with the experimental data. The scroll expander modified from a scroll compressor worked stably in the ORC system. The maximum output power, maximum isentropic efficiency, and maximum rotation speed was 1540W, 86%, and 2165r/min respectively in the experiments. The average deviation between the simulation and the experimental results was 18.9%. The numerical model developed in this paper could predict the output performance of the scroll expander and state parameters in expansion chambers.
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The ORC (organic Rankine cycle) is an established technology for converting low temperature heat to electricity. Knowing that most of the commercially available ORCs are of the subcritical type, there is potential for improvement by implementing new cycle architectures. The cycles under consideration are: the SCORC (subcritical ORC), the TCORC (transcritical ORC) and the PEORC (partial evaporation ORC). Care is taken to develop an optimization strategy considering various boundary conditions. The analysis and comparison is based on an exergy approach. Initially 67 possible working fluids are investigated. In successive stages design constraints are added. First, only environmentally friendly working fluids are retained. Next, the turbine outlet is constrained to a superheated state. Finally, the heat carrier exit temperature is restricted and addition of a recuperator is considered. Regression models with low computational cost are provided to quickly evaluate each design implications. The results indicate that the PEORC clearly outperforms the TCORC by up to 25.6% in second law efficiency, while the TCORC outperforms the SCORC by up to 10.8%. For high waste heat carrier inlet temperatures the performance gain becomes small. Additionally, a high performing environmentally friendly working fluid for the TCORC is missing at low heat carrier temperatures (100 C).
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The organic Rankine cycle (ORC) is commonly accepted as a viable technology to convert low temperature heat into electricity. Furthermore, ORCs are designed for unmanned operation with little maintenance. Because of these excellent characteristics, several ORC waste heat recovery plants are already in operation. Although the basic ORC is gradually adopted into industry, the need of increased cost-effectiveness persists. Therefore, a next logical step is the development of new ORC architectures. Even though there has been a strong renaissance towards ORC research in the last decade, ORC architectures have received relatively little attention. Several barriers can be listed. First, there is the difficulty in assessing the additional complexity of the system. While several advanced cycle designs appear promising from a thermodynamic viewpoint, it is not clear that these represent viable economic solutions. Secondly, there is a lack of experimental data from open literature. Additionally, there is the challenge of coping with various boundary conditions from literature, which makes an objective comparison difficult. In this article an overview is presented of ORC architectures. The performance evaluation criteria and boundary conditions are clearly stated. As well, an overview of the available experimental data is given.
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Scroll expander has demonstrated high efficiency at low power range. In this paper, a generic model of a scroll expander hasbeen developed. It can calculate the ideal expander parameters to give the optimalefficiency and prevent under- orover-expansionat any given operating conditions or fluids. The dynamic model was validated bypredictingthe ideal volumetric expansion ratio with ideal expansion ratio of 4.03 at 0.7MPa pressure,and showed agreement with experimental data. The results suggested thatthe rate of scroll increase K in the geometric model has little effect on volumetric expansion ratio or ideal scroll length of the expander, but whenexpansion ratio is kept constant, lower K value results inlower leakage losses.
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Power production from low grade heat and waste heat does not only mitigate environmental impact but also improve energy efficiency and reduce energy cost. The type and design of expander for a low grade heat engine are critical and affect the performance, efficiency and cost of low grade heat and waste heat recovery system. The choice of expansion machine is strongly correlated with operating conditions, working fluid and size of the system. Low grade heat and waste heat recovery systems for electricity production are usually smaller in size. Turbines cannot be used due to their high rotational speed and high cost for waste heat and low grade heat recovery systems less than 50kWe. Therefore, volumetric expanders are more suitable in low grade heat and waste heat engines for a smaller size. The current article provides a comprehensive review of volumetric expanders including vane expander, screw expander, scroll expander, and piston expander applications for low grade heat and waste heat recovery using organic Rankine cycle. The operational performance, design optimizations, leakage and frictional losses, modeling techniques for each type of expander has been investigated in detail. Technical constraints and operational performance of expanders have been analyzed followed by the comparative assessment based on their performance, current market status, and economics. The comparative assessment shows that screw expander and scroll expander are most suitable having a relative score of 73.6 and 70.4 respectively on a scale of 100. The vane expanders have the lowest score of 47.2 due to low power range, leakage and frictional losses, and technical complexities.
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In order to reveal the performance of mixture in Organic Rankine Cycle (ORC), this paper presents the performance of ORC using hot air as heat resource. The zeotropic mixture fluids studied are R227ea/R245fa, Butane/R245fa and RC318/R245fa. The first law efficiency, the second law efficiency, exergy loss distributions and net power output of zeotropic mixture fluids are calculated and compared with corresponding pure fluids. By using the counter flow heat exchangers, the system's economic performance is analyzed based on the net power output per unit UA. The result indicates that better thermal performance can be achieved when the temperature difference of cooling water is near the temperature glide of zeotropic mixture in the condenser; cycle efficiency, exergy efficiency and net power output increase compared to corresponding pure fluid cycles, but the net power output per unit UA decreases; in other words, the economic performance of this system becomes worse in some degree.
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Based on the thermoeconomic multi-objective optimization, simultaneously considering exergy efficiency and levelized energy cost (LEC), the thermoeconomic comparisons between pure and mixture working fluids of organic Rankine cycles (ORCs) have been investigated. Four models are proposed based on the different location of evaporating bubble point temperature or condensing dew point temperature for mixture working fluids. The effects of mass fraction and four key parameters (evaporator temperature, condenser temperature, pinch point temperature difference and degree of superheat) on exergy efficiency and levelized energy cost (LEC) are examined. Pareto-optimal solutions of four models using 0.7R245fa/0.3R227ea are obtained and compared. Taking mass fraction into account, the thermoeconomic comparisons between pure and mixture working fluids have been studied. Research demonstrates that the mixtures don't always present better thermodynamic performance and economic performance than pure working fluids. Model 2 (T7=TE,T3=TC) is the favorable operation condition for its highest thermodynamic performance and relatively low economic factor. Taking mass fraction as decision variable, Pareto-optimal solutions for models 1, 2, 3 and 4 in pairs of (exergy efficiency (%), LEC ($/kW h)) are (56.71, 0.188), (57.67, 0.192), (57.11, 0.194), and (56.91, 0.192), respectively. Compared with pure working fluids, the mixture working fluids present better exergy efficiency but worse LEC except model 1.
Article
The detailed experimental investigation of an organic Rankine cycle (ORC) is presented, which is designed to operate at supercritical conditions. The net capacity of this engine is almost 3 kW and the laboratory testing of the engine includes the variation of the heat input and of the hot water temperature. The maximum heat input is 48kWth, while the hot water temperature ranges from 65 up to 100°C. The tests are conducted at the laboratory and the heat source is a controllable electric heater, which can keep the hot water temperature constant, by switching on/off its electrical resistances. The expansion machine is a modified scroll compressor with major conversions, in order to be able to operate with safety at high pressure (or even supercritical at some conditions). The ORC engine is equipped with a dedicated heat exchanger of helical coil design, suitable for such applications. The speeds of the expander and ORC pump are regulated with frequency inverters, in order to control the cycle top pressure and heat input. The performance of all components is evaluated, while special attention is given on the supercritical heat exchanger and the scroll expander. The performance tests examined here concern the variation of the heat input, while the hot water temperature is equal to 95°C. The aim is to examine the engine performance at the design conditions, as well as at off-design ones. Especially the latter ones are very important, since this engine will be coupled with solar collectors at the final configuration, where the available heat is varied to a great extent. The engine has been measured at the laboratory, where a thermal efficiency of almost 6% has been achieved, while supercritical operation did not show superior performance, due to the oversized expander. A smaller expander would allow operation at even higher pressures for higher speed with increased electric efficiency, which would probably reveal the full potential of the supercritical operation, even at the kW scale.
Article
The ORC (organic Rankine cycle) system is an effective technology to generate electricity from low temperature heat sources. The twin-screw expander is a key component that is commonly used in the small-to-medium capacity ORC system to convert thermal energy into work. In this paper, the performance of a twin-screw expander is theoretically and experimentally studied. A mathematical model is developed and subsequently validated using experimental data. The effect of several important factors including expander speed, suction pressure and inlet superheat on the expander performance is investigated. Results indicate that the expander speed and suction pressure have large influences on the expander performance, while the inlet superheat has relatively small effect. The isentropic efficiency of the expander decreases from 0.88 to 0.6 and the expander volumetric efficiency decreases from 0.88 to 0.7 as the expander rotational speed increases from 1250 to 6000 rpm. The results further show that the expander volumetric efficiency decreases from 0.91 to 0.85 as the expander suction pressure increases from 0.33 to 0.47 MPa. Furthermore, the energy conversion efficiency of the studied ORC system using the twin-screw expander is as high as 7.5% under the site conditions.
Article
The Organic Rankine Cycle (ORC) has been demonstrated to be a promising technology for the recovery of engine waste heat. Systems with hydrocarbons as the working fluids exhibit good thermal performance. However, the flammability of hydrocarbons limits their practical applications because of safety concerns. This paper examines the potential of using mixtures of a hydrocarbon and a retardant in an ORC system for engine waste heat recovery. Refrigerants R141b and R11 are selected as the retardants and blended with the hydrocarbons to form zeotropic mixtures. The flammability is suppressed, and in addition, zeotropic mixtures provide better temperature matches with the heat source and sink, which reduces the exergy loss within the heat exchange processes, thereby increasing the cycle efficiency. Energetic and exergetic analysis of ORC systems with pure hydrocarbons and with mixtures of a hydrocarbon and a retardant are conducted and compared. The net power output and the second law efficiency are chosen as the evaluation criteria to select the suitable working fluid compositions and to define the optimal set of thermodynamic parameters. The simulation results reveal that the ORC system with cyclohexane/R141b (0.5/0.5) is optimal for this engine waste heat recovery case, thereby increasing the net power output of the system by 13.3% compared to pure cyclohexane.
Article
Twin screw expanders are widely used for power generation in small scale Organic Rankine Cycles (ORC). In order to increase the efficiency and maximize the generated power, an optimized design and appropriate operating conditions should be used. The use of Computational Fluid Dynamics (CFD) allows the analysis of the flow inside these machines which is impossible to investigate experimentally but which is influencing the performance of the expander. Some of the challenges when performing CFD analysis in these machines are the complexity of the rotors' motion and the properties of the refrigerant. In this paper a 3D CFD analysis of a twin screw expander is presented. The 3D block-structured grid for the twin screw expander is constructed from the solution of Laplace problems in two-dimensional sections on an unstructured grid of the same geometry. During the transient calculations, grid nodes are moved while keeping the mesh topology. The properties of the refrigerant R245fa have been evaluated using the ideal gas Equation of State (EoS), the Aungier Redlich-Kwong EoS and the CoolProp. 3D CFD analysis of the screw expander showed that the difference in power output between the ideal gas EoS and the Aungier Redlich-Kwong EoS is 8% and between Aungier Redlich-Kwong EoS and CoolProp is negligible for operating conditions of interest. To investigate the performance of the expander, different pressure ratios and rotational speeds were studied for two different designs of the twin screw expander. The flow analysis inside the clearances that are forming leakage paths gives more insight in the performance of the expander. It is concluded that the biggest pressure drop is caused by a throttling loss at the inlet port and therefore an optimized design of the inlet port is necessary.
Article
A single-screw expander with 155 mm diameter screw has been developed. In order to investigate the performance of this prototype with different inlet vapor dryness, an organic Rankine cycle experimental system was built, and experiments were conducted at different inlet vapor dryness by adjusting the mass flow rate of working fluid into evaporator. The results indicated that with the increase of inlet vapor dryness, the power output and expansion ratio were increased,however, the volume efficiency and overall efficiency were decreased. The maximums of power output, expansion ratio, volumetric efficiency and total efficiency of single-screw expander were 5.12 kW, 4.55, 80.5% and 49.5%, respectively.
Article
The performance of the ORC (organic Rankine cycle) systems using zeotropic mixtures as working fluids for recovering waste heat of flue gas from industrial boiler is examined on the basis of thermodynamics and thermo-economics under different operating conditions. In order to explore the potential of the mixtures as the working fluids in the ORC, the effects of various mixtures with different components and composition proportions on the system performance have been analyzed. The results show that the compositions of the mixtures have an important effect on the ORC system performance, which is associated with the temperature glide during the phase change of mixtures. From the point of thermodynamics, the performance of the ORC system is not always improved by employing the mixtures as the working fluids. The merit of the mixtures is related to the restrictive conditions of the ORC, different operating conditions results in different conclusions. At a fixed pinch point temperature difference, the small mean heat transfer temperature difference in heat exchangers will lead to a larger heat transfer area and the larger total cost of the ORC system. Compared with the ORC with pure working fluids, the ORC with the mixtures presents a poor economical performance.
Article
Six zeotropic mixtures are proposed for conducting a parametric optimisation of supercritical Rankine cycle powered by low temperature geothermal heat source. Different mixing ratios of two types of zeotropic mixtures were studied and their performance evaluated in the range of process parameters. Optimal operational conditions were identified for each mixture and their advantages over pure fluids quantified. The results indicate that the choice of pressure and temperature at the turbine inlet can be tuned to the mixture properties. Thermal and exergy efficiencies of R-143a/R-124 mixtures were higher than for R-143a/R-C318 mixtures in the range of process parameters studied. Mixture R-143a(0.2)/-R124(0.8) yielded the highest thermal efficiency of 16% at evaporator pressure value of 10 MPa and maximum operational temperature 470 K. The highest exergetic efficiency of 47% was developed by R-143a(0.7)/R-124(0.3) at 3.9 MPa and 365 K. A comparative analysis between the zeotropic mixtures and pure R-143a shows that the cycle efficiency can be improved by 15% at the same operational conditions.
Article
The paper investigates the performance of high-temperature Organic Rankine cycle (ORC) with zeotropic mixtures as working fluid. A numerical model, which has been validated by comparing with the published data, is developed to predict the first law thermal efficiency of the cycle. The effects of mixture concentration, temperature gradient of the heat transfer fluid, pinch temperature difference, pressure ratio, and condensation pressure on the first law efficiency are presented firstly using a purposely designed program, and then the suitable conditions for the described ORC are suggested based on the results of the simulation. It is demonstrated that the use of zeotropic mixtures leads to an efficiency increase compared to pure fluids.
Article
The thermodynamic performance of non-superheated subcritical Organic Rankine Cycles (ORCs) with zeotropic mixtures as working fluids is examined based on a second law analysis. In a previous study, a mixture selection method based on a first law analysis was proposed. However, to assess the perfor-mance potential of zeotropic mixtures as working fluids the irreversibility distributions under different mixtures compositions are calculated. The zeotropic mixtures under study are: R245fa–pentane, R245fa–R365mfc, isopentane–isohexane, isopentane–cyclohexane, isopentane–isohexane, isobutane– isopentane and pentane–hexane. The second law efficiency, defined as the ratio of shaft power output and input heat carrier exergy, is used as optimization criterion. The results show that the evaporator accounts for the highest exergy loss. Still, the best performance is achieved when the condenser heat pro-files are matched. An increase in second law efficiency in the range of 7.1% and 14.2% is obtained com-pared to pure working fluids. For a heat source of 150 °C, the second law efficiency of the pure fluids is in the range of 26.7% and 29.1%. The second law efficiency in function of the heat carrier temperature between 120 °C and 160 °C shows an almost linear behavior for all investigated mixtures. Furthermore, between optimized ORCs with zeotropic mixtures as working fluid the difference in second law efficiency varies less than 3 percentage points.
Article
Mixture models explicit in Helmholtz energy have been developed to calculate the thermodynamic properties of refrigerant mixtures containing R-32, R-125, R-134a, R143a, and R-152a. The Helmholtz energy of the mixture is the sum of the ideal gas contribution, the compressibility (or real fluid) contribution, and the contribution from mixing. The independent variables are the density, temperature, and composition. The model may be used to calculate the thermodynamic properties of mixtures, including dew and bubble point properties, within the experimental uncertainties of the available measured properties. It incorporates the most accurate equations of state available for each pure fluid. The estimated uncertainties of calculated properties are 0.1% in density and 0.5% in heat capacities and in the speed of sound. Calculated bubble point pressures have typical uncertainties of 0.5%.
Article
Thermally activated systems based on sorption cycles, as well as mechanical systems based on vapor compression/expansion are assessed in this study for waste heat recovery applications. In particular, ammonia-water sorption cycles for cooling and mechanical work recovery, a heat transformer using lithium bromide-water as the working fluid pair to yield high temperature heat, and organic Rankine cycles using refrigerant R245fa for work recovery as well as versions directly coupled to a vapor compression cycle to yield cooling are analyzed with overall heat transfer conductances for heat exchangers that use similar approach temperature differences for each cycle. Two representative cases are considered, one for smaller-scale and lower temperature applications using waste heat at 60 °C, and the other for larger-scale and higher temperature waste heat at 120 °C. Comparative assessments of these cycles on the basis of efficiencies and system footprints guide the selection of waste heat recovery and upgrade systems for different applications and waste heat availabilities. Furthermore, these considerations are used to investigate four case studies for waste heat recovery for data centers, vehicles, and process plants, illustrating the utility and limitations of such solutions. The increased implementation of such waste heat recovery systems in a variety of applications will lead to decreased primary source inputs and sustainable energy utilization.
Article
The characteristics of evaporation heat transfer and pressure drop for refrigerant R134a flowing in a plate heat exchanger were investigated experimentally in this study. Two vertical counter flow channels were formed in the exchanger by three plates of commercialized geometry with a corrugated sine shape of a chevron angle of 60°. Upflow boiling of refrigerant R134a in one channel receives heat from the hot downflow of water in the other channel. The effects of the heat flux, mass flux, quality and pressure of R134a on the evaporation heat transfer and pressure drop were explored. The preliminary measured data for the water to water single phase convection showed that the heat transfer coefficient in the plate heat exchanger is about 9 times of that in a circular pipe at the same Reynolds number. Even at a very low Reynolds number, the present flow visualization in a plate heat exchanger with the transparent outer plate showed that the flow in the plate heat exchanger remains turbulent. Data for the pressure drop were also examined in detail. It is found that the evaporation heat transfer coefficient of R134a in the plates is quite different from that in circular pipe, particularly in the convective evaporation dominated regime at high vapor quality. Relatively intense boiling on the corrugated surface was seen from the flow visualization. More specifically, the present data showed that both the evaporation heat transfer coefficient and pressure drop increase with the vapor quality. At a higher mass flux the pressure drop is higher for the entire range of the vapor quality but the heat transfer is only better at high quality. Raising the imposed wall heat flux was found to slightly improve the heat transfer. While at a higher system pressure the heat transfer and pressure drop are both slightly lower.
Article
This paper studies refrigeration cycles in which plate heat exchangers are used as either evaporators or condensers. The performance of the cycle is studied by means of a method introduced in previous papers which consists of assessing the goodness of a calculation method by looking at representative variables such as the evaporation or the condensation temperature depending on the case evaluated. This procedure is also used to compare several heat transfer coefficients in the refrigerant side. As in previous works the models of all the cycle components are considered together with the heat exchanger models in such a way that the system of equations they provide is solved by means of a Newton–Raphson algorithm. Calculated and measured values of the evaporation and the condensation temperatures are also compared. The experimental results correspond to the same air-to-water heat pump studied in other papers and they have been obtained by using refrigerants R-22 and R-290.