Compressor Inlet Pressure Research Articles

Multi-objective optimization and 4E analyses of the solar energy assisted direct-heated sCO2 power cycle for low-temperature applications

ABSTRACT The aim of this study is to investigate the performance of the intercooling and reheating supercritical CO2 Brayton cycle (SCBC) for low-temperature solar applications. Thermodynamic, exergo-economic, and exergo-environmental analyses of SCBC are examined. Furthermore, parametric research is performed to assess the effects of operating parameters on plant performance. Finally, multi-objective optimization (MOO) of the solar energy-based integrated plant is conducted for optimum operating conditions, taking into account the main parameters affecting the system performance. Considering the analyses, the generated power is calculated as 0.380 kW, while the system’s energetic and exergetic efficiencies are found as 3.91% and 4.20%, respectively. According to the exergo-economic analysis results, exergo-economic analysis, the total cycle’s cost rate is 0.889 $/h, the total cost rate of exergy destruction is 0.274 $/h, the total exergo-economic factor value is 69.14%, and the total purchase cost of the plant is 31,422$. Moreover, the total collector number is 23, the compressor inlet pressure is 8067.57 kPa, and the system’s entire purchase cost is 41,031 $, according to the MOO results. The exergy efficiency of the system improved by 20.53%, as an outcome of the optimization analysis.

Dynamic Performance and Control Analysis of a Supercritical CO2 Recuperated Cycle

Abstract Supercritical CO2 (sCO2) power cycles represent a promising technology for driving the energy transition. In fact, various research projects around the world are currently studying the possible applications of this technology, which is characterized by high efficiency, competitive costs, compact machinery, and enhanced flexibility with respect to competing systems, such as steam-based power cycles. Within this context, the European Union (EU)-funded SOLARSCO2OL project aims to build a MW-scale sCO2 pilot facility coupled with a concentrated solar power (CSP) plant. A transient model of the demonstration plant was previously developed in the transeo simulation tool by the Thermochemical Power Group (TPG) of University of Genoa to study the operational envelope of the cycle. In the present work, the model is upgraded to take into account all the relevant fluid-dynamic and thermodynamic phenomena affecting the transient behavior of the plant. In particular, a detailed crossflow sCO2–air cooler model is now included, which is crucial for assessing the compressor inlet temperature (CIT) behavior and controllability. The system has to comply with several constraints, such as compressor surge margin, turbomachinery inlet temperatures, and compressor inlet pressure (CIP). The desired net power output should also be guaranteed. The dynamic responses of the system to step variations in various input variables were recorded and used to design and tune the main operational controls. The input variables considered include: (1) compressor rotational speed, (2) anti-surge valve (ASV) fractional opening, (3) mass flowrate of air through the cooler, (4) mass flowrate of the molten salts through the heater, and (5) CO2 inventory for injection and extraction of working fluid. The implemented control structure includes proportional–integral–derivative (PID) controllers, feedforward action, and their combinations. The controllers are tuned using a mix of established methods, such as Cohen–Coon response-based PID tuning and adjustments from feedforward controls. The feedforward controls were designed taking into account the steady-state values from off-design simulations, as well as the interactions between each controller and the other controlled variables. The final control setup is tested on various power ramps to assess the capability of the prototype cycle in load following and disturbance rejection, showing very good performance in set-point tracking.

Investigation of control strategies for the hydrogen fueled R-Graz cycle

In the context of large-scale hydrogen power generation, the Graz cycle and its improved version, the R-Graz cycle, exhibits excellent performance and technological feasibility. For such semi-closed, split cycles, apart from the conventional adjustments of fuel consumption and compressor IGV angle, compressor inlet pressure and split ratio are two additional crucial control parameters. In this study, six control strategies are firstly formulated and compared. The results indicate that the control strategy aiming to maintain the turbine inlet temperature outperforms the strategy aiming to maintain the exhaust temperature in terms of efficiency. Among them, the inventory control strategy demonstrates superior efficiency compared to the split ratio and IGV control strategies. Taking into account the advantages of various strategies, a hybrid inventory control strategy suitable for the R-Graz cycle is proposed. Based on this strategy, at 40% load and the ambient temperature of 19 °C, the efficiency reaches 87.06% of the design point, surpassing conventional F-class gas-steam combined cycle units. When the ambient temperature varies, under winter conditions of 10 °C and summer conditions of 30 °C, the full load net efficiency of the cycle reaches 72.06% and 69.60%, respectively. This research holds practical guidance value for the engineering application of the R-Graz cycle and the efficient utilization of hydrogen energy.

Performance analysis and prediction of a modified precompression transcritical CO2 power generation cycle

The efficient utilization of biomass energy and the optimal operation of integrated renewable energy sources in virtual power plants have become critical issues to achieve carbon neutrality targets in rural areas. In the rural areas of Northeast China, a large amount of electricity can be generated from biomass. It is very important to develop biomass power generation equipment for this rural area. Due to the high thermal efficiency and its compact system without freezing process like water, CO2 thermal cycle is an appropriate option for this kind of power generation equipment. According to whether the flow is separated, CO2 cycles can be divided into the single flow layouts and split flow layouts. Compared to the single flow layouts, split flow layouts have higher efficiency, but more complex structures and lower heat transfer power per unit area. Considering the climatic characteristics of Heilongjiang Province and the seasonality of straw biomass utilization, this study proposes a modified scheme for the precompression transcritical CO2 cycle in the single flow layout to meet the simple structure requirement of the small power plants in cold areas like Northeast China. Through energy analysis, the study calculates the thermal efficiencies of the two cycles when the inlet pressure of the main compressor is 5 MPa, the turbine inlet temperature is 550 °C and the pressure ratios of the main compressor are in the range of 4.5–5.5. The optimal efficiency of the traditional precompression cycle is 43.55 % when the main compressor pressure ratio is 5.5, while the modified precompression cycle is 44.86 % when the pressure ratio is 5.0266. The modified precompression cycle has a higher efficiency than the traditional precompression cycle at a lower pressure ratio of the main compressor.

Development of multilevel cascade layouts to improve performance of SCO2 Brayton power cycles: Design, simulation, and optimization

The multilevel cascade SCO2 Brayton cycles are developed based on the conventional recompression-reheat cycle to enhance thermodynamic performances using the multilevel cascade scheme. Mathematical models are proposed to characterize their thermal cycle efficiency. The results show that for three typical cases, the proposed multilevel cascade cycle with 3 compressors × 3 reheats × 2 turbines improve cycle efficiency by 2.56 %, 3.17 %, and 3.44 % in absolute change, while the other with 3 compressors × 3 reheats × 3 turbines further enhance by 3.17 %, 4.19 %, and 4.17 % in absolute change over the conventional cycle. The latter cycle as the optimal layout is chosen to perform the key parametric analysis. The cycle efficiency increases with increasing high-pressure turbine inlet temperature, while the main compressor inlet temperature has the opposite effect. It increases and then decreases with the high-pressure turbine inlet pressure, the main compressor inlet pressure, and the split ratio of the recompressor, respectively. Finally, the parametric global optimization is conducted to improve the cycle performance more deeply. It is demonstrated that the absolute efficiency can be further increased by 2.62 %, 1.81 %, and 1.09 % for the responding cases. The integrated configurations are also suggested for power generation systems with different applications.

Study on the key parameters of closed-loop free-piston Brayton generator

The escalating energy crisis and environmental issues have compelled countries worldwide to advance energy transitions and vigorously develop green and clean energy technologies. External combustion devices can effectively utilize hydrogen-based fuels, biomass, solar energy, and other sources, playing a critical role in achieving carbon reduction. As a type of external combustion device, the free-piston Brayton generator, with its strong energy adaptability, stands as a highly promising power generation device. Therefore, the design optimization methods and operational characteristics of the free-piston Brayton generator system are worthy of thorough investigation. This paper introduces a novel method for constructing and structurally optimizing a free-piston Brayton generator model. Sage software is utilized to construct a closed-loop free-piston Brayton generator system in the time domain, followed by numerical analysis. The results show that within the frequency range of 35 ∼ 80 Hz, the system maintains a thermal-to-electric efficiency exceeding 40.00 %, demonstrating the system’s ability to operate efficiently at high frequencies. The piston diameter influences the dynamic behavior of the system’s piston, emphasizing the necessity of gradually adjusting the piston diameter to achieve optimal efficiency during structural parameter optimization. System efficiency and power can be balanced by adjusting the compressor inlet pressure. Under design conditions, the system can output 2046 W of electrical power. The thermal efficiency and thermal-to-electric efficiency are 46.84 % and 41.36 %, respectively. Additionally, an innovative analysis of the temperature distribution of the system and the distribution of exergy losses in major components under conditions of high frequency and small piston displacement is conducted. This work provides a new method and guidance for the subsequent design and optimization of free-piston Brayton generators.

Thermodynamic, exergoeconomic evaluation and optimization of S–N2O/t-N2O nuclear power cycle for the construction of the lunar base

With the continuous development of deep space exploration, many planetary exploration schemes and development plans regard the construction of planetary bases as an essential goal, especially the exploration of the Moon. Supercritical and transcritical nitrous oxide (N2O) cycles are compact, low-cost, efficient, and lightweight for nuclear reactors to supply power to the bases on other planets. This paper presents the thermodynamic, exergoeconomic, and mass analyses of a combined cycle consisting of a supercritical N2O recompression Brayton cycle and a transcritical N2O cycle (S–N2O/t-N2O). It is shown that under the optimal conditions, the combined thermal efficiency and exergy efficiency are 45.52 % and 60.13 %, respectively. Based on the exergy analysis, the exergy destruction mainly occurs in the reactor and main compressor. A sensitivity study shows that the split ratio, pressure ratio in the supercritical N2O cycle, main compressor inlet pressure, turbine2 inlet temperature, and turbine2 inlet pressure have significant effects on the net output work, thermal efficiency, specific mass, and levelized cost of electricity. Furthermore, multi-objective optimizations are considered to obtain the Pareto frontier solutions for different multi-objectives, and the optimal design condition is found. These findings could improve the power cycle performance for the construction of the Lunar Base.

Study on inherent mechanism between thermodynamic performance and mass evaluation of MW-class nuclear powered spacecraft

Nuclear powered spacecraft (NPS) with multiple Brayton loops (NPS-MBL) exhibit high efficiency, compact size, low weight, and operational stability, making them promising candidates for future deep space exploration and planetary bases. Optimizing NPS design requires an in-depth understanding of the relationship between thermodynamic performance and mass. In this study, comprehensive models were developed to evaluate the thermodynamic performance and mass of NPS-MBL. The influences of key parameters on thermodynamic performance and mass were analyzed. The results indicated that increasing the turbine inlet temperature and turbomachine efficiency enhanced the thermodynamic performance and reduced the total mass of NPS. The optimal specific mass was achieved by increasing the compressor inlet temperature, recuperator effectiveness, pressure ratio, and helium molar fraction. Additionally, theoretical upper limits for power generation and specific mass of NPS-MBL were obtained. For an NPS with quadruple Brayton loops and a reactor power of 5 MW, schemes maximizing power generation at 1.6 MW with a specific mass of 10.91 t∙MW-1 and minimizing specific mass at 5.52 t∙MW-1 with a power generation of 1.32 MW were identified. This study serves as a valuable reference for NPS design and optimization.

Deep learning-based forecasting modeling of micro gas turbine performance projection: An experimental approach

Performance forecasting of aeroengines is crucial for achieving better operational efficiency, ensuring safety, reducing costs, and minimizing environmental impact in the aviation industry. It enables engineers and researchers to make informed decisions, leading to advancements in technology and the overall evolution of aviation. This study is focused on the effects of flight conditions on the performance of a turbojet, which in consequence affects the environmental aspect of operation. By investigating the relationships between aeroengine efficiency and performance indicators such as thrust, shaft speed, and exhaust gas temperature (EGT), and flight characteristics expressed in terms of environmental and operational conditions, the study seeks to elucidate these connections. The article's significance lies in its successful application of Long Short-Term Memory (LSTM) networks to predict thrust, shaft speed, and EGT variations in turbojet engines under varying flight conditions. Experimental data from a turbojet test bench is processed with deep learning, specifically LSTM recurrent neural networks that are developed based on Matrix Laboratory (MATLAB). The model inputs are free stream air speed, compressor inlet pressure, combustor inlet temperature, combustor inlet pressure, turbine inlet temperature, turbine inlet pressure, nozzle inlet pressure and fuel flow, and the outputs are thrust, shaft speed and EGT. Predicted thrust closely aligns with actual thrust values, though with minor discrepancies. Shaft speed predictions exhibit a similar trend, while EGT predictions showcase a comparable pattern with slight variations. Despite the prediction errors, a thorough evaluation of median values, box plots, and probability density functions confirms that the models effectively capture available information, though discrepancies may arise from measurement inaccuracies and initial engine conditions. These results show that it is possible to accurately predict turbojet performance using LSTM recurrent neural network. This research paves the way for enhanced aeroengine performance prediction, particularly in scenarios requiring off-board or high-performance applications.

Thermodynamic feasibility and multiobjective optimization of a closed Brayton cycle-based clean cogeneration system

The present research has analyzed the energy and exergy of a combined system of simultaneous power generation and cooling. To provide a comprehensive data sheet of this system, the system has been investigated in the temperature range of 300–800 °C, and 6 working fluids, including air, carbon dioxide, nitrogen, argon, xenon, and helium, have been investigated. The parameters affecting the performance of the system, namely the compressor inlet pressure, the compressor pressure ratio, and the intermediation pressure ratio were investigated. The power produced by the Brayton cycle at a pressure ratio of 5.2 is the highest due to the increase in compressor power consumption and turbine power generation. The results of the parametric study showed that the exergy efficiency of the system has the maximum value at the pressure ratio of 4.73. The results of the parametric study showed that increasing the pressure of the compressor does not have a significant effect on the electricity consumption and the temperature of the working fluid due to the constant pressure ratio. The input energy to the heat exchanger of the absorption chiller decreases with the increase in the Brayton cycle pressure ratio, and as a result, the cooling created by the chiller also decreases. In this method, three objective functions of exergy efficiency, energy efficiency, and total production power are considered as objective functions. The most optimal value of intermediation pressure ratio was obtained after the optimization process of 1.389. Also, the most optimal value of the pressure ratio of high-pressure and low-pressure turbines was reported as 2.563 and 1.845, respectively.

Single-Flow Supercritical CO2 Brayton Cycles: A Performance Comparison of the Different Layouts

Supercritical CO2 Brayton cycle (sCO2-BC) has been frequently used in power generation applications in recent years due to its high efficiency, compact size, and low-cost advantages. In this study, performances of different configurations of single-flow sCO2-BCs, such as recuperation, intercooling, reheating, pre-compression, inter-recuperation, and split expansion, are examined. Firstly, thermodynamic analyzes of six different single-flow sCO2-BCs were conducted. Secondly, parametric analyses based on the system performance-influencing parameters, such as turbine input temperature, turbine inlet pressure, and compressor inlet pressure, were carried out. Engineering Equation Solver (EES) computer software was used in the analysis. According to the initially accepted design parameters, the highest energy efficiency was calculated as 39.25 % in the reheating cycle, and the lowest efficiency was found as 29.62 % in the split expansion BC. Moreover, it has been determined that the energy and exergy efficiencies of cycles increase with rising turbine input temperature and turbine input pressure.

Design and Assessment of the Solar Energy Based Direct Steam Generation Supercritical CO2 Brayton Cycle

The aim of this study is to examine the performance of the supercritical CO2 Brayton cycle (sCO2-BC)with intercooling and reheating for low-temperature solar energy application. The heat required for the sCO2-BC is supplied from an evacuated tube solar collector. Energy and exergy analyses of the solar energy-assisted sCO2-BCwith intercooling and reheating are investigated. In addition, the effects of operating parameters like solar radiation, collector number, compressor, and turbine input pressure on system performance are examined parametrically.According to the findings of the analysis, the net power production is found to be 0.2687 kW. In addition, the solar energy-based sCO2-BC's energy and exergy efficiencies are found to be 3.68% and 3.95%, respectively. Moreover, it has been determined that the sCO2-BC's energy and exergy efficiencies reduce with the increase of solar irradiation, the collector number, and the compressor inlet pressure, while the system's energy and exergy efficiencies rise with the increase of the turbine input pressure.

Comparative assessment of the various split flow supercritical CO2 Brayton cycles for Marine gas turbine waste heat recovery

Supercritical CO2 Brayton cycle (sCO2 BC) can become easily utilized in marine gas turbine waste heat recovery applications due to their high efficiency, compact size, and low-cost advantages. In this study, the performance of the three different split flow sCO2 BCs, including turbine split flow-1 (TSF-1), turbine split flow-2 (TSF-2), and turbine split-3 (TSF-3), for the recovery of marine gas turbine waste heat is compared. The Engineering Equation Solver (EES) application is used to compare the three different split flow sCO2 BCs' performances. Moreover, to investigate the influence of important thermodynamic parameters on cycle performance, a parametric analysis is carried out. The effect of variable exhaust gas temperature, turbine input pressure, and compressor inlet pressure on net power, the energy efficiency of the system, system's exergy efficiency, and exergy destruction are examined. The results suggest that the energy efficiencies of the TSF-1 sCO2 BC, the TSF-2 sCO2 BC, and the TSF-3 sCO2 BC are calculated by 28.71%, 34.5%, and 29.42%, respectively. The TSF-2 sCO2 BC has more advantages in efficiency among all the cycle layouts while the TSF-3 sCO2 BC layout has better performance in the net power. In addition, the TSF-3 sCO2 BC has the highest exergy destruction at 99.71 kW, followed by the TSF-1 sCO2 BC at 91.83 kW and the TSF-2 sCO2 BC at 41.75 kW. It has been determined that the cycle's net power increases with rising exhaust gas temperature and turbine input pressure and decreases with compressor input pressure. Exhaust gas temperature and turbine inlet pressure have a positive effect on the performance of all split flow sCO2 BCs.

Preliminary design and optimization of a solar-driven combined cooling and power system for a data center

Aiming at the demand of reducing cost, increasing efficiency and green low-carbon development in data center, a novel solar-driven combined cooling and power system is constructed by coupling supercritical power cycle with transcritical refrigeration cycle. The heliostat field is designed, and the models on thermal, economic, environmental and comprehensive performances are established. On this basis, system performances under design conditions are studied, and the system parameters are analyzed. Thereafter, optimal system performances at typical days in four seasons are compared based on genetic algorithm. The results indicate that: under design conditions, the system energy and exergy efficiencies are 29.47% and 16.21% respectively. The total system capital cost is $1.2576 × 108. The carbon emissions are reduced by 257,420 kg per day. The comprehensive performance evaluation index (CPEI) can reach up to 47.63%. CPEI increases with the increase of turbine inlet pressure. With the increase of high-pressure compressor (HPC) inlet pressure and evaporation temperature, CPEI increases first and then decreases. Furthermore, CPEI shows a continuous downward trend as the load rate of data center increases. The system performances at autumn equinox and spring equinox are more similar, while those at summer solstice and winter solstice are quite different from those of spring equinox.

Performance response to operating-load fluctuations for Sub-megawatt-scale recuperated supercritical CO2 Brayton cycles: Characteristics and improvement

The Sub-megawatt-scale supercritical CO2 Brayton cycles (SCBCs) have shown great potential in renewable energy and mobile power systems, but the response of technical performances to fluctuating operating load has not yet been completely known even for those basic cycle layouts. For this purpose, the present work investigated the performance characteristics of the global operating loads for the 0.1 and 1 MWe-scale recuperated SCBS systems. A thermodynamic model was proposed and demonstrated to be feasible to predict the cycle performance with 0.19%–9.59% relative error. Using the control-of-variables strategy, the response of cycle efficiency and net power were comprehensively examined to the 90%–110% reference load (namely ±10% fluctuations) of operating parameters, including the compressor inlet pressure, compressor inlet temperature, turbine inlet pressure, turbine inlet temperature, and mass flow rate. It was found that although the cycle performances depend upon the facility scale, the appropriate parameter matching can effectively improve the cycle efficiency and net power by 31.97% and 76.42% for the 0.1 MWe-scale cycle, and by 13.89% and 26.69% for the1 MWe-scale cycle respectively at a given the mass flow rate of CO2. The results provide a positive reference for the performance assessment and operation optimization of the small-scale recuperated SCBC systems.

Control strategies and dynamic experimental tests on the wide-range and rapid load regulation of a first pilot multi-megawatts fossil-fired supercritical CO2 power system

Supercritical CO2 (sCO2) power system is a research front in recent years due to its high efficiency and flexibility which is considered as a transformative power system in terms of consumption of the fluctuated and intermittent renewables. The merits of sCO2 power systems have been widely shown by small-scale test loops. However, it is still very lack of the investigations on the control strategies based on real-time dynamic operational data of large-scale multi-megawatts pilot power system, especially for wide-range and rapid load regulation to demonstrate the feasibility of large-scale utilization and commercialization. A worldwide first pilot multi-megawatts SMART (Supercritical CO2 Modular Advanced Research and Test) fossil-fired power system has been built and operated for more than 1000 h at TPRI (Thermal Power Research Institute), Xi’an, China with turbine inlet parameters of 20 MPa/600 °C/600 °C. The influence of key parameters on the dynamics of the system are experimental studied. In-depth tests of the wide-range load regulation and rapid load regulation of the SMART@TPRI power system are performed. The test results show that the key target parameters such as turbine inlet temperatures, compressor inlet temperature and pressure, sCO2 mass flow rate and exhaust flue gas temperature can be well regulated by a set of well-developed control modules to ensure an efficient and safe operation during load variations. The SMART@TPRI power system can run stably and flexibly within the whole range from 0 %Pe to 100 %Pe. The averaged load ramp and load reduction rate achieves 6.35 %Pe/min and −6.37 %Pe/min, respectively, which is almost 3 ∼ 4 times than that of steam power system, under the control strategy of sliding pressure with fixed turbine inlet temperature by a combination of several novel well-developed control modules.

Performance improvement potential of a PV/T integrated dual-source heat pump unit with a pressure booster ejector

• Ejector enhanced PV/T air dual-source heat pump is presented. • Optimum PV/T evaporation temperature is determined. • The COP of the heat pump can be improved by 22.6% when 15 m 2 PV/T collector is used. • Consumed electricity from the grid for heating can be reduced by 75% when 15 m 2 PV/T collector is used. Dual-source heat pump unit can utilize the evaporation of the refrigerant at two different pressures. By adopting an ejector, high-pressure refrigerant stream can be used to lift compressor inlet pressure which results in a higher coefficient of performance (COP). This study proposes a renewable energy sourced and high-efficiency heat pump system which can be easily building integrated to offer a renewable heating solution. The system is devised on the complementation of dual thermal sources; one is air and the other one is solar, to maximize the utilization of ambient energy for highly efficient operation of heat pump. Using the advantage of the relatively lower operating temperature in the solar collector line, the thermal efficiency of the collector would be sufficient in winter. Adaptation of photovoltaics in the collector as a PV/T unit, will benefit the system from the produced electricity for further reduction of the demand from the grid. Along with the use of PV/T collector, the system can be potentially carbon neutral for larger collector areas. In this study, the performance improvement potential of a dual-sourced heat pump unit with an ejector as a booster is investigated for different locations in Turkey which presents different solar and weather profiles. The optimum collector evaporation temperatures are determined, and COP improvement potentials are discussed for different conditions. For a heating supply of 5 kW, the COP of the system can be improved by 22.6% under 400 W/m 2 and 10°C ambient using 15 m 2 PV/T collector. Including the electricity generated from the PV, reduction of the electricity demand from the grid can reach to 75% for the same conditions.

Dynamics and control implementation of a supercritical CO2 simple recuperated cycle

Interest in supercritical CO2 power cycles is constantly increasing, showing good efficiency, and promising competitive costs and enhanced flexibility with respect to competing systems. Some project within the EU Horizon 2020 program have studied these systems and aim to demonstrate them in large scale, following the example of the STEP project in US. This work is part of the effort of the SOLARSCO2OL project to build a sCO2-CSP power demo plant at MW scale. A dynamic model of a simple recuperated sCO2 cycle is developed in TRANSEO, using miniREFPROP to compute fluid properties, and table of properties are implemented, when possible, to enhance the performance of the code. Control logics is described and simple controllers implemented. Finally, controllers are tested showing the response of the main parameters of the plant to a ramp variation of the load. Stable compressor inlet pressure is achieved with an inventory control, while a stable turbine inlet temperature allows a high efficiency in part-load operation.

Thermodynamic analysis and multi-objective optimization of a waste heat recovery system with a combined supercritical/transcritical CO2 cycle

This study firstly develops a novel combined cycle system consisting of a supercritical CO2 recompression Brayton cycle and a transcritical CO2 refrigeration cycle to recover waste heat from a marine turbine for both power generation and refrigeration. The pressure drop of the total heat exchanger in the whole cycle is considered in the thermodynamic and economic modeling process. Then, the influence of crucial system parameters on the system performance and economics is investigated through parametric sensitivity analysis. Finally, the system is optimized parametrically by multi-objective optimization. The results show that the higher inlet pressure of the high-pressure compressor helps to improve the thermal efficiency but reduces the exergy efficiency; the low-temperature heat exchanger plays a decisive role in the overall system exergy destruction; the HRHE accounts for a more significant proportion of the system cost, and the pressure drop has the most significant impact on the network of the system. The optimal solution is COP = 3.059, LCOE = 18.348$/(kW/h), and ηWhr = 0.651 when waste heat recovery efficiency, COP, and LCOE are considered optimization objectives.

Performance simulation of expander-compressor boosted subcooling refrigeration system

Many applications have made extensive use of refrigeration systems, which have a high energy requirement. Any improvement on the refrigeration systems can reduce the need for energy demand. A common method to improve the system performance is to subcool the condenser exit temperature and known as subcooling. An expander-compressor booster enhanced subcooling vapor compression cycle is proposed as an addition to the subcooling systems described in the literature. The refrigerant is split into two parts at the condenser exit: one portion expands in the expansion device to reach the necessary subcooling temperature, while the other part goes straight into a separate heat exchanger. Later, this additional refrigerant flows into the other expansion valve, the evaporator, and a booster expander-compressor to increase inlet pressure of compressor. As working fluids, six distinct refrigerants including low global warming potential (GWP) are used (namely R134a, R1234yf, R32, R290, R1270, and R600a) in simulations. The coefficient of performance (COP) and increment in COP values for each refrigerant are computed and graphically displayed for various evaporation temperatures between -10 °C and 5 °C. Furthermore, the heat exchanger analysis of subcooling heat exchanger is performed to compare heat transfer surface area and pressure drop for each refrigerant. Results indicate that R1234yf achieves the greatest performance with an increase in COP by 16.7, 19.1 and 21.8% depending on the mechanical efficiencies of the expander and compressors and as well as isentropic efficiency of the expander. By utilizing an expander-compressor with higher or lower mechanical and isentropic efficiencies, these enhancements can be raised or lowered. Heat exchanger analyses show that the pressure drop in the exchanger does not significantly affect the performance of the system.