Pinch Point Temperature Research Articles

Study and application of the shift-temperature of heating fluid for zeotropic mixtures in organic Rankine cycle

The theoretical formulations of the shift-temperature of the heating fluid for zeotropic mixtures (Tshift) were derived when the pinch point was located at the evaporating bubble point and the working fluid inlet of the evaporator, respectively, which were applicable to dry, wet, and isentropic zeotropic mixtures. Tshift was corrected by the impact factor analysis and calculated exactly using the Dragonfly algorithm. The optimal zeotropic mixture was matched by comparing the heat source temperature(Tg, in) and Tshift. The results indicate that Tshift is a property of every zeotropic mixture and is related to the critical temperature, the evaporation bubble point temperature, and the condensation dew point temperature. When the pinch point is at the evaporation bubble point, the zeotropic mixture with Tshift lower than Tg, in is selected and then combined with the thermal efficiency for a comprehensive evaluation. When the pinch point is at the working fluid inlet of the evaporator, Tshift is also affected by the pinch point temperature difference and the temperature glide of the condensation process, Tshift is significantly lower than Tg, in, all zeotropic mixtures are applied. Among the matched zeotropic mixtures, R227ea/R22 with the lowest Tshift has the best thermal performance in the ORC system.

Thermodynamic, exergoeconomic and exergoenvironmental analyses and optimization of a solid oxide fuel cell-based trigeneration system

This study proposes a trigeneration system based on solid oxide fuel cell (SOFC) for generating power, cooling and heating simultaneously. The system mainly contains a SOFC, a gas turbine (GT), an organic Rankine cycle (ORC), a steam ejector refrigerator (SER) and a heat exchanger. The thermodynamic, exergoeconomic and exergoenvironmental models of proposed trigeneration system are developed, and the effects of design parameters on system performances are analyzed. The results indicate that the system average product cost and environmental impact per unit of exergy increase with SOFC inlet temperature and working pressure, the pinch point temperature difference and evaporating pressure of Generator, while decrease with the current density of fuel cell. Finally, optimization is performed to achieve the optimal exergy-based performance. It is revealed that though the system exergy efficiency is decreased by 7.64% after optimization, the system average product cost and environmental impact per unit of exergy are significantly reduced.

Thermo-economic assessment of sub-ambient temperature pumped-thermal electricity storage integrated with external heat sources

Thermally integrated pumped-thermal electricity storage (TI-PTES) offers the opportunity to store electricity as thermal exergy at a large scale, and existing studies are primarily focused on TI-PTES systems based on high-temperature thermal energy storage. This paper presents a thermo-economic analysis of a “cold TI-PTES” system which converts electricity into cold energy using a vapor compression refrigeration (VCR) unit and stores it at sub-ambient temperatures during the charging process, and generates electricity by using an organic Rankine cycle (ORC) working between the sub-ambient temperature and an external low-grade heat source during the discharging process. The effects of key parameters, i.e., mass flowrate and temperature of the storage medium, ORC evaporation temperature, component efficiencies, and pinch-point temperature differences, on the system performance are evaluated based on a whole-system thermo-economic model. The results reveal that the roundtrip efficiency and levelized cost of storage (LCOS) of the system increases while the electrical energy storage capacity decreases as the temperatures of the two cold storage tanks approach each other. When the temperature of the cold storage tank 1 rises from 1 °C to 8 °C while the cold storage tank 2 remains as 13 °C, there is an increase of 25% and 20% in the roundtrip efficiency and LCOS respectively while the energy storage capacity decreases by 69%. A roundtrip efficiency of 0.74 and LCOS of 0.32 $/kWh are achieved with a heat source temperature of 85 °C, using a mass flowrate and temperature of the cold storage medium of 50 kg/s and 1 °C. Furthermore, any change in cold storage medium mass flowrate changes both electrical energy storage capacity and power output by the same proportions. With a continuous high-flowrate external heat source, the LCOS can be as low as 0.17 $/kWh. By providing sufficient heat from an external heat source, the proposed system possesses a high potential for medium-to-large scale energy storage with a unique hybrid nature for electricity storage and thermal integration.

Sensitivity analysis and multi-objective optimization of the energy, exergy and thermo-economic performance of a Brayton supercritical CO2-ORC configurations

The following research compared some energy, exergetic and thermo-economic indicators of a supercritical CO2 simple Brayton cycle integrated with a simple organic Rankine cycle (SORC), and a regenerative organic Rankine cycle (RORC). A thermodynamic model was developed to determine the net power, thermal efficiency, the fuel consumption, and the exergy destruction of all the components of the system. Also, a thermo-economic model was developed to determine some economic indicators such as the levelized cost of energy (LCOE), the payback period (PBP) and specific investment cost (SIC). A sensitivity analysis was carried out to study the influence of the primary turbine inlet temperature (TIT), the high-pressure in the compressor (PHigh), the evaporator pinch point temperature difference (PPT), and the pressure ratio (Pr) on the indicators performance. Three different working fluids were selected in this study: acetone, toluene and cyclohexane. The results showed that cyclohexane had the best energy performance giving an efficiency of 48.02% for the RORC system. Besides, it presented the best thermo-economic results for the LCOE (0.26 USD/kWh), SIC (2626.75 USD/kWh), and a PBP (11.2 years). Finally, a multi-objective optimization was developed based on energy, exergy and thermo-economic performance parameters as objective functions to obtain a technical and economic feasible solution able to implement them in industrial applications.

Parametric analysis and multi-objective optimization of biomass-fired organic Rankine cycle system combined heat and power under three operation strategies

Biomass-fired organic Rankine cycle (ORC) systems for combined heat and power (CHP) generation are a feasible technology to provide carbon-neutral power production. In this study, the parametric analysis and multi-objective optimization of a biomass-fired ORC-CHP system under three operation strategies are conducted. The thermodynamic, exergoeconomic, environmental and sustainability models are established, while the effects of seven operation parameters on exergy efficiency (ηex), unit cost of exergy (UCE), equivalent carbon emission (ECE) and ecological life cycle cost (ELCC) are examined. A further four-objective optimization problem is addressed using NSGA-II and the Pareto-optimal solutions for the three operation strategies are derived and compared. The results indicate that evaporation temperature, condensation temperature and heat source inlet temperature present positive effects on ηex and UCE, whereas opposite effects are imposed by degree of superheat and pinch point temperature difference. System B yields a 0.21% higher ηex and a 0.41 tons higher CO2,eq than system C. The Pareto-optimal solutions of ηex, UCE, ECE and ELCC for system A using TOPSIS decision-making are 12.380%, 0.183 $/kWh, 10.250 tons CO2,eq, and 13.677 × 10−3 $/kWh, respectively. System A may be regarded as the preferred operation strategy for biomass-fired ORC-CHP systems due to its moderate performance.

Multi-aspect investigation and multi-criteria optimization of a novel solar-geothermal-based polygeneration system using flat plate and concentrated photovoltaic thermal solar collectors

This study investigates different aspects of an innovative multi-heat recovery-based solar-geothermal polygeneration system, acclaiming the exergetic, exergoeconomic, and energetic concepts. Principally, using two renewable energy sources, the whole framework of the system encompasses Concentrated PhotoVoltaic Thermal (CPVT) solar collectors, Flat Plate Solar Collectors (FPSCs), geothermal wells, an Ejector Refrigeration Cycle (ERC) Organic Rankine Cycle (ORC) integrated with a Solid Oxide Electrolyzer Cell (SOEC), heating production units, an air dryer, and an Organic Rankine Cycle (ORC) unit. Afterward, the sensitivity analysis utilized for the parametric study makes a multi-aspects optimization in diverse scenarios in which NSGA-II, as well as, fuzzy TOPSIS and fuzzy VIKOR decision makings, are handled to designate the optimal solution. The suggested system has professionally been devised thanks to the characteristic of maximum use of energy of the streams circulated. Hence, crucial variables evaluated are more influenced by the variation in the geothermal heater pinch point temperature gradient. Also, in the optimization scenario based on unit cost of products / exergy efficiency, the TOPSIS selects the optimal objectives of 4.29%/1.13 $/GJ, while the VIKOR selects 4.06%/1.07 $/GJ, respectively.

Cogeneration system based on large temperature difference heat transfer with stepwise utilization

Organic Rankine cycle (ORC) plays a critical role in systems such as waste heat recovery, cogeneration, renewable energy generation and energy storage. No matter which field ORC is applied in, the evaporator side of ORC has an extremely poor utilization of the thermal energy from heat source, resulting in the outlet temperature of hot side fluid being much higher than the inlet temperature of cold side fluid. In order to fully capitalize on the thermal energy, this study introduces the two-stage absorption heat exchanger (AHE) and integrates it into ORC to obtain an original high-efficiency cogeneration system (AHEORC-CHP), which is parametrically analyzed by constructing and operating thermo-economic model in terms of the expansion pressure ratio and working fluid of ORC, the type and flow rate of heat source, and the inlet temperature of generator in AHE. Due to the existence of pinch point temperature difference, conventional ORC design can only reduce the outlet temperature of the heat source with an inlet temperature of 130 °C to about 70 °C under the condition of ideal heat transfer. The AHEORC-CHP configuration proposed in this work can achieve a significant reduction in the final outlet temperature of waste heat source (as low as 24.69 °C) and realize heat exchange with large temperature difference and efficient utilization of the heat source. Besides, the thermoelectric efficiency and temperature effectiveness can reach 90.9% and 1.2 respectively, while the profit ratio of investment rises to 8.46. Further improving the performance of AHEORC-CHP system requires optimizing the design of the pressure in absorption heat pump (AHP) cycle as well as the concentration and flow rate of LiBr-H2O solution. This study can provide a simulation pathway for the application of two-stage AHE in ORC, and likewise for future experimental investigations.

Thermo-economic and environmental optimization using PSO of solar organic Rankine cycle with flat plate solar collector

The use of solar energy is considered a potential strategy for the production of electrical energy through thermal heat sources. This article portrays a study framed to be energetic, economic, and environmental fields. This study was carried out in two thermal configurations: the Regenerative Rankine Cycle (RORC) and the Simple Organic Rankine Cycle (SORC), which use solar energy to supply electrical power to a building. The thermodynamic and economic models were proposed for each subsystem of the thermal process, allowing hourly simulations to know the economic indicators such as the payback period (PBP), the levelized cost of energy (LCOE), the specific investment cost (SIC), and the initial investment cost (CInv). The effect of operational variables such as the pressure ratio (rp), the evaporator pinch point temperature (Ap), the condensation pinch point temperature (Tcond), and the solar collector area (Ac) on the Relative Annual Benefit (RAB) were studied. Finally, the Particle Swarm Optimization (PSO) algorithm was implemented to optimize the economic indicators and the environmental impact of the thermal configurations. Results showed that the RORC configuration presented a better performance in terms of generation, purchase, and hourly sale of energy. However, in terms of RAB, the SORC (39,833 USD/year) showed better results in contrast to the RORC (39,604 USD/year) for an evaporator pinch point temperature of 35 °C. Finally, the application of the PSO optimization algorithm allowed the reduction of the LCOE (11.64%), SIC (11.67%), and PBP (11.81%) thermo-economic indicators from the base condition for the SORC, and the reductions obtained in the RORC were LCOE (18.11%), SIC (10.67%), and PBP (11.11%). However, the decrease in environmental Impact for both systems was less than 1% as a consequence of the high contribution of thermal oil in the construction phase of the system.

Advanced exergy, economic, and environmental evaluation of an Organic Rankine Cycle driven dual evaporators vapour-compression refrigeration system using organic fluids

The current research combines a dual evaporator vapour-compression refrigeration system with an organic Rankine cycle. The integrated system is a renewable energy-based technology that can provide refrigeration at different refrigeration temperatures and capacities. The system's performance is compared using five different organic working fluids: butane, pentane, isopentane, hexane, and R245fa, to recommend the most suitable fluid for the system. Coefficient of performance (COP), exergy efficiency (ηex), total cost (Ctot), and payback period (PB) are taken as the performance parameters. Moreover, the system's exergy performance is analysed using advanced exergy analysis (AEA), and sensitivity analysis to determine the optimal operating condition for system components. The result indicates that butane is the optimal fluid for improving energy, exergy, economical, and environmental performance. The system has a COP of 0.377, an exergy efficiency of 10.91%, a total cost of $33,091, and a payback period of 5.8 years. Boiler, compressor, condenser, and EPG make up 31% of the total exergy destruction that can be avoided by adequately selecting their operating condition. The optimal condition for boiler temperature, condenser temperature, the pinch-point temperature difference in condenser and boiler, and compressor efficiency is 120 °C, 40 °C, 3 °C, 10 °C, and 0.7, respectively.

Numerical study on dynamic performance of low temperature recuperator in a S-CO2 Brayton cycle

Transient response of the pinch point is crucial to the evaluations of the recuperator efficiency. A reheat and recompression cycle dynamic simulation system for supercritical CO2 is built, and a transient segmented model is developed to explore the dynamic characteristics of the recuperators. The operating conditions including inlet mass flowrate, temperature and pressure of the low temperature recuperator (LTR) change dramatically with the withdraw-mass variation, which causes different response characteristics of the pinch point. The pinch point gradually transfers from the cold end to the hot end of the LTR as the mass flowrate decreases. The higher pinch-point temperature difference leads to lower heat exchanger effectiveness, and the internal pinch point greatly weakens the recuperator performance. A new prediction model is proposed to quickly determine the pinch point location and analyze the operating conditions prone to cause internal pinch point. The range of split ratio in which the internal pinch point exists in the LTR is obtained. The lower-limit of split ratio variation is sensitive to the high- and low-pressures, the isentropic efficiency of the compressor, and the outlet temperature of the precooler, while the upper-limit of split ratio is only related to the pressures of the recuperator.

Thermodynamic and Heat Transfer Performance of the Organic Triangle Cycle

Compared to the organic Rankine cycle (ORC), the organic triangle cycle (TC) is simpler in structure and is not limited by pinch point temperature differences. TC has been studied to some extent by previous researchers, such as the selection of working fluid, application, and the design of the expander. However, system optimization and parameter analysis of TC are still rare. The thermodynamic performance of TC internal circulation and TC heat recovery systems are investigated by theoretical analysis and numerical simulation, respectively. The results indicate that the expander inlet temperature T3 and heater inlet temperature T2 are key elements impacting the thermodynamic performance of the TC internal circulation. For the TC heat recovery system, an optimal value of the average heat-capacity flow rate of working fluid Cwf is discovered to output the maximum net power output Wnet. Moreover, the total heat transfer coefficients for the heater (kA)h and condenser (kA)c are discussed in relation to Cwf variations. The findings will provide critical guidance for system investment and optimization.

Energy and exergy performance evaluation of a novel low-temperature physical energy storage system consisting of compressed CO2 energy storage and Kalina cycle

To improve the overall performance of the Compressed CO2 Energy Storage (CCES) system under low-temperature thermal energy storage conditions, this paper proposed a novel low-temperature physical energy storage system consisting of CCES and Kalina cycle. The thermal energy storage temperature was controlled below 200 °C, and the Kalina cycle was used to optimize the reuse of the stored thermal energy. A thermodynamic model of the integrated system was constructed, and the system performance was analyzed from the energy and exergy perspectives. Several evaluation indicators, such as system exergy efficiency (SEE), round trip efficiency (RTE), system energy density (SED), Kalina exergy efficiency (KEE), and Kalina energy efficiency (KEnE), were defined to evaluate system performance. In addition, the influences of several core parameters (e.g., split ratio (r), storage pressure (ps), turbine efficiency (te), pinch point temperature difference (pt) of heat exchangers, and ambient temperature (T0)) on the system performance were analyzed. The results of the base condition showed that SEE, RTE, SED, KEE, and KEnE were 58.17 %, 59.38 %, 6.32 kWh/m3, 38.62 %, and 8.64 %, respectively. The exergy destruction in heat exchanger 3 was the largest, accounting for 71.7 % of total exergy destruction. The sensitivity analysis results showed that increasing r could increase the SEE of the system, increasing ps could lead to a decrease in the RTE of the system, and increasing T0 could cause the RTE and SED to increase. The increase in te could improve all evaluation indices, while the increase in pt could reduce the system's overall performance. This study provides a new solution for the integrated application and optimal design of CCES systems under low-temperature thermal energy storage conditions.

Investigation on the relations of operating parameters of a thermodynamic cycle energy storage system

In the background of carbon neutrality targets, energy for power generation is being converted from fossil to renewable sources. Energy storage has become particularly more and more important because it is a key technology to solve the instability of renewable energy. An energy storage method coupled with a heat pump and power cycle named thermodynamic cycle energy storage, which uses a heat pump and power cycle to run alternately for energy storage and has attracted the attention of international researchers because of its characteristics of green development, flexible application and convenience for large scale. The relations of operating parameters of the thermodynamic cycle energy storage are very important for operating this system sufficiently. Therefore, an optimization model of thermodynamic cycle energy storage was established for the CO2 transcritical thermodynamic cycle, with hot water as a hot storage medium and NaCl brine as a cold storage medium. The relations of its operating parameters were analyzed by pinch point temperature difference and control variable method. The results showed that turning of some parameter curves occurs with changing the position of pinch point and largest temperature difference points. The round-trip efficiency generally increases firstly and then decreases with increasing the high-temperature side pressure of the power cycle. In the calculation range, when the evaporating pressure of the heat pump is 2.00 MPa, the high-temperature side pressure of the heat pump is 20.00 MPa, and the CO2 temperature of the air cooler outlet is 20 °C, the peak value of round-trip efficiency is the largest, the maximum round-trip efficiency is 56.9 %.

Mathematical modeling of a binary ORC operated with solar collectors. Case study—Ecuador

<abstract> <p>The present study is significant because it can contribute to developing sustainable energy strategies and expanding knowledge about renewable energies in Ecuador, specifically by modeling two modules: the thermal module (parabolic solar collectors and energy storage tank) and the Organic Rankine Cycle (ORC) module. The objective was to determine a region in Ecuador where the thermal module exhibits the highest efficiency for solar collectors. Subsequently, a detailed analysis of the ORC module was conducted, considering the working fluid, boiling temperature, condensation temperature, pinch point temperature, solar collector area, and the collector area-to-energy storage volume ratio (<italic>Ac/V</italic>). Finally, an economic analysis was performed based on the Net Present Value (NPV), Internal Rate of Return (IRR), and payback period of implementing this type of system. After conducting all the respective analyses in the thermal module, while considering the yearly average meteorological data of ten years (2012–2022), it was determined that due to its meteorological conditions, ambient temperature (14.7 ℃) and solar beam radiation (184.5 W/m<sup>2</sup>), the efficiency of the collectors in the Andean region of Ecuador is higher. This efficiency is further enhanced by using Therminol VP-1 as the thermal fluid, as it possesses better thermodynamic properties than the other fluids analyzed. Similarly, the ORC module analysis results determined that cyclohexane is the working fluid for the ORC, thereby leading to a higher ORC efficiency (25%) and overall system efficiency (20%). Finally, the system was optimized to maximize the IRR and minimize the <italic>A</italic>c/<italic>V</italic> of the collector for a nominal power of 92 kW. As a result, the optimal operating conditions of the system include a solar collector area of 1600 m<sup>2</sup>, an energy storage tank volume of 54 m<sup>3</sup>, an electricity production of 23757 MW/year, a total system efficiency of 22%, an IRR of 15.65% and a payback period of 9.81 years.</p> </abstract>

Thermo-economic performance comparison and advanced analysis using orthogonal experiment for organic Rankine cycle

To improve the thermo-economic performance of organic Rankine cycle (ORC) systems, a multi-level analysis method is proposed in this study. In the first level, the optimal configuration is determined based on the thermo-economic optimization. The exergy efficiency and electricity production cost are selected as the objective functions of optimization for three ORC configurations, including simple ORC, TORC (two-stage ORC), and DORC (dual-loop ORC). In the second level, the real potential of performance improvement for the optimal configuration is revealed through advanced exergy analysis method. Finally, the order of operating parameters to different performance indicators of the optimal configuration is determined by orthogonal experiment method. The results show that the TORC system exhibits better thermo-economic performance. Although the low-temperature condenser in the TORC system has the highest exergy destruction, the LTT (low-temperature turbine) contributes the largest avoidable-endogenous exergy destruction. Thus, the LTT has the greatest potential for technical improvement. The condensation temperature and pinch point temperature difference in the low-temperature evaporator are the primary factors for the thermodynamic and economic performance of the TORC system, respectively. While the evaporation temperature of the high-temperature evaporator has the greatest effect on the potential of technical improvement for the LTT.

Simultaneous optimization of working fluid and temperature matching for heat pump assisted geothermal cascade heating system

The heat pump assisted geothermal cascade heating system (GCHS) has a promising prospect in space heating. In this paper, considering thermodynamic, economic and environmental performance, the optimal working fluid from four hydrocarbon candidates and temperature-matching for the GCHS are determined simultaneously based on multi-objective optimization and grey relational analysis. The results show that according to the optimal compromise solutions, the GCHS with R600 has the highest thermodynamic performance (COPtot) of 22.58 and the least annual carbon emission (ACE) of 2.80 × 103 ton while R290 has the largest net present value (NPV) about 45.83 × 106 CNY. Additionally, all temperature variables considered generally tend to reach their extreme value except for the temperature lift of middle circulation water in the secondary plate heat exchanger. The optimal working fluid based on comprehensive performance is considered to be R600 with the largest grey relational degree of 0.752. Besides, the global sensitivity analysis on the GCHS with R600 indicates that the pinch point temperature difference of condenser is the most important influential parameter for COPtot with total Sobol index about 0.918 and the geothermal tail water temperature plays a significant role for both NPV and ACE with total Sobol index up to 0.806 and 0.992, respectively.

Design, 3E scrutiny, and multi-criteria optimization of a trigeneration plant centered on geothermal and solar energy, using PTC and flash binary cycle

A hybrid solar-geothermal power plant for electricity, heating, and cooling is provided in this paper. A flash-binary geothermal cycle, parabolic trough solar collectors, auxiliary heater, single effect LiBr-water absorption chiller, and heat exchangers are all part of the planned integrated power plant. The plant provides steady electrical power as well as the necessary heating and cooling for the yeast industry. The solar-geothermal power plant's energetic and exergetic efficiencies for the proposed system under steady-state conditions with constant irradiation are 10.78 percent and 23.1 percent, respectively. The auxiliary heater is found to function in 85 percent of the year due to the inability of solar energy to increase the fluid temperature to the necessary amount throughout several periods of the year. The impacts of different performance factors on the system's exergetic efficiency and overall cost rate are also evaluated using parametric analysis. It was discovered that parameters such as the flash separator's inlet pressure and temperature, the pinch point temperature difference in the heat recovery steam generator (HRSG), and the geofluid outlet temperature in the heat exchanger 1 (HX1) have a significant impact on the system's exergetic efficiency and total cost rate. Furthermore, the effect of variations in sunbeam irradiance on assessment parameters is examined. In constant heat input to the cycle, increasing beam irradiance results in increased total exergy efficiency and a lower overall cost rate of the system. By raising the sunbeam irradiance, the proportion of the auxiliary heater in the plant's energy supply and the mass flow rate of the fuel would be reduced. Also, the optimization findings show that the exergy efficiency of 33.8 percent might be attained under ideal operating circumstances.

Thermodynamic Simulation in Eco-Friendly Aquadest Production Through Compression System Method Combined with Steam Power Plant as Heat Source

Access to clean water and sanitation is one of the Sustainable Development Goals (SDGs), a global action plan agreed upon by world leaders. Water demand is increasing every year. As much as 97% of the water on earth is seawater, which requires desalination technology to convert seawater into freshwater that will be used to meet daily human needs. It is necessary to continue to develop environmentally friendly clean water treatment technology to overcome the problem of freshwater crisis. Research related to clean water treatment technology needs improvement in order to have a high effectiveness value to be applied and developed in areas with clean water crisis. Therefore, this study aims to produce distilled water by utilizing heat from the condenser of a steam power plant. The cooling water from the condenser must first be throttled to allow the vapor and liquid extraction to occur. Next, the steam is compressed to raise the temperature. After the compression process, the steam must be condensed using a water-cooled condenser to produce the distilled water in order to get maximum distilled water yields and low energy consumption. In this study, the lowest SEC (Specific Energy Consumption) was -1194.02kJ/kg of distilled water with the mass flow rate of 0.996 kg/s. To overcome the environmental problems, the condenser temperature was lowered to 41.5°C, and the PPTD (Pinch Point Temperature Difference) by 10 made the temperature discharge to seawater drop to 31.5°C. The lowest energy consumption can be obtained by setting the temperature in the cyclone separator to 22°C and the mass of water discharged to the sea by 99%, which lowers compressor energy consumption.

Experimental investigation on micro-ORC system operating with partial evaporation and two–phase expansion

This paper presents an experimental analysis conducted on a low-temperature micro-ORC energy system, to assess its performance operating with partial evaporation (PE-ORC). Temperatures of the heat source in the range between 40 °C and 75 °C have been tested, and for each value, the vapour quality at the expander inlet has been varied by regulating the feed-pump rotating speed. The thermodynamic state of the working fluid in two-phase conditions has been estimated by means of a thermal balance at the heat exchangers, using the measured values of temperature, pressure and flow rate.Detailed experimental results are provided, with special focus on the performance of evaporator, expander and feed-pump, highlighting the difference in their behaviour compared with the regular operation with dry expansion of the same micro-ORC system. Relevant improvements have been observed in the evaporator effectiveness, mainly due to the reduction of the pinch point temperature difference. Also, the volumetric and total efficiencies of the feed-pump are improved substantially. On the other hand, the net power output and the expander efficiency resulted penalized by the operation with partial evaporation. The maximum power output obtained was close to 1.2 kW, with heat source temperature equal to 75 °C and fluid quality close to 1. The power output is reduced, at constant temperature, by decreasing the vapour quality at the expander inlet.The results suggest that operating a small-scale ORC system with partial evaporation may lead to some improvements to the performance of the cycle, especially regarding the evaporator performance. Moreover, with values of fluid quality at the expander inlet between 0.8 and 1, the penalization on the expander performance, compared to the dry expansion mode, is limited. However, a proper redesign of the power plant for the specific purpose is required in order to make partial evaporation an effective solution. Specifically, the expander and pump geometry and control require to be optimized for the particular working conditions, the recuperator must be removed, and the evaporator should be designed for the optimal exploitation of the heat source.

Pinch point determination and Multi-Objective optimization for working parameters of an ORC by using numerical analyses optimization method

In parallel with Kyoto, Paris and the green production agreements, the nowadays crucial subject is minimising energy consumption, increasing renewable energy usage and recovering waste heat. When it comes to waste heat, the organic Rankine cycle (ORC) technology comes fore. However, although the presence of many studies on the ORC in the literature, there is still an intense gap related to information on ORC working conditions, pinch point detection and numerical design and analysis methods. In this respect, the present paper suggests a multi-objective optimization model for an ORC by considering many parameters that affect the performance of the ORC like fluid type, thermodynamic properties of the organic fluids, pinch point temperature etc. For the analyses, experimentally recorded exhaust gas parameters for a reheat furnace located in the iron and steel plant were used. By considering all these, all performance-affecting parameters were included through the development of the multi-objective model. For the analyses, two wet types (ethanol, methanol), two isentropic (acetone, butene), and two dry types (cyclohexane, benzene) working fluids were selected to develop the multi-objective design and optimising method. After comprehensive analyses, it was seen that the developed mathematical model was valid for the designing and analysing of the ORC. In addition, it was observed that the system performance increases as the pinch point temperature difference decreases. In addition, it was seen that isentropic fluids have low efficiency in medium-temperature heat sources. Considering the system performance, initial investment cost and payback periods, it was seen that a waste heat recovery plant using Benzene, Methanol and Ethanol as working fluids is more feasible.