Expander Inlet Pressure Research Articles

Energy, exergy, exergoeconomic, economic, and environmental analyses and multi-objective optimization of a novel combined cooling and power system with dual-pressure Kalina cycle-absorption refrigeration

A novel combined cooling and power system, the dual-pressure Kalina cycle-absorption refrigeration (DPKC-AR-CCP), is proposed for the cascade utilization of waste heat from high-temperature flue gas and jacket water from internal combustion engines. A pneumatic booster pump unit is employed to increase the inlet pressure of the low-pressure expander, with heat generated during the compression process utilized for preheating the ammonia/water mixture, and exhaust gas from the low-pressure expander is combined with driving gas for absorption refrigeration. By integrating the first and second laws of thermodynamics with the SPECO Methodology, models for energy, exergy, exergoeconomy, economy, and environment of the DPKC-AR-CCP system are developed. A multi-objective optimization model is formulated with maximum exergy efficiency, minimum total exergy cost rate, and maximum annual equivalent carbon dioxide (CO2) emission reduction as objective functions. MATLAB software (combined with REFPROP software) is utilized for simulation and multi-objective optimization. The performance of each component under specific conditions is assessed, and a comparison with the simple absorption refrigeration/Kalina cogeneration system (AR/KC) highlights the advantages of the DPKC-AR-CCP system; an investigation into the effects of different operating parameters on performance is conducted. The results indicate that, under identical operational parameters, the DPKC-AR-CCP system exhibits a substantial increase in net output power (230.2 %), cooling capacity (98.7 %), and exergy efficiency (148.8 %) compared to the simple AR/KC system; payback period is reduced by 64.8 %; and annual equivalent CO2 emissions are decreased by 202.2 %. However, there is an increase in the total exergy cost rate by 90.5 %. The optimal concentration of ammonia/water is determined to be 0.816/0.184, with a heat exchanger outlet temperature of 341.07 K, driving pressure of 0.654 MPa, and low-pressure expander inlet pressure of 5.064 MPa. Correspondingly, the optimal exergy efficiency is 87.2 %, the annual reduction in CO2 emissions is 5.53 × 107 kg, and the total exergy cost rate is 288.48$/h.

Thermodynamic analysis of power generation thermal management system for heat and cold exergy utilization from liquid hydrogen-fueled turbojet engine

Hydrogen propulsion is generally treated as the ultimate net zero-emission option for aviation, therein liquid hydrogen storage appears to provide the only feasible solution for aircraft with the constraints imposed by aircraft weight and volume. Hydrogen liquefaction consumes a great amount of energy, which significantly boosts the cost of hydrogen as an aviation fuel. Besides the H2 chemical exergy for combustion to provide thrust, the H2 physical exergy in the form of cold energy is also a kind of high-quality clean energy to produce power output, which offers great opportunities to achieve cost-effective use of hydrogen fuel. Thus, this paper presents a Rankine cycle and H2 direct expansion cycle (RC-DEC) combined power generation thermal management system for the simultaneous utilization of exhaust gas heat exergy and hydrogen fuel cold exergy from the liquid hydrogen-fueled turbojet engine. In the Rankine cycle, the transcritical mode is applied on the hot side while the liquid separation condensation concept is adopted on the cold side to achieve better thermal matchings with heat and cold sources. The hydrocarbon/inert gas binary mixture is proposed as the working fluid of the Rankine cycle. The effects of key thermodynamic parameters and the influence of Para-Ortho hydrogen conversion on system performance are discussed, then a comparison of the mixture working fluid is conducted. Results show that there exists an optimal separation temperature ratio and condensation pressure of RC to obtain maximum total net power output. As the DEC expander inlet pressure increases, the total net power output first increases and then levels off. The introduction of the Para-Ortho hydrogen conversion has a negligible impact on net power output but leads to a significant reduction in the exergy efficiency, which is attributed to the cold energy release nature of Para-Ortho hydrogen conversion. The results of the working fluid comparison indicate that the optimal inert gas retardant for CH4 is Kr, while those for C2H6 and C3H8 are Xe to achieve the maximum net power output and exergy efficiency of the proposed power generation system. Among them, C2H6/Xe(0.6/0.4) obtains the maximum net power output of 2717.9 kW and maximum exergy efficiency of 33.1%, which suggests an opportunity to provide megawatts of electrical power for the aircraft in place of the APU.

The benefits of a recuperative layout of an ORC-based unit fed by a solar-assisted reservoir operating as a micro-cogeneration plant

Organic Rankine Cycle -based microcogeneration systems that exploit solar sources to generate electricity and domestic hot water simultaneously are promising solutions for reducing CO2 emissions in the residential energy-intensive sector. Such systems can be assisted by thermal energy storage reservoirs in which water is heated by solar energy and cooled by the direct use of thermal energy for domestic hot water production and acting as heat source of the power plant. An interesting plant layout optimisation involves the adoption of a recuperative heat exchanger to preheat the working fluid before it enters the heat recovery vapour generator, which is fed with the same working fluid leaving the expander. Despite the positive effect of recuperative heat exchanger adoption on the efficiency of the entire plant, the impact on electrical energy production at this microscale is not straightforward to assess as the heat source is represented by the water inside the reservoir and it is not a continuous high- or medium-temperature stream. The lack of experimental analyses in the literature on these applications makes this a debatable question.Thus, to fill this gap and quantitatively assess the benefits introduced by the adoption of a recuperative stage, a wide experimental comparison between recuperative and not-recuperative Organic Rankine Cycle-based power unit layout was performed. To support the experimental analysis, a comprehensive theoretical model of the Organic Rankine Cycle-based plant was developed and validated against experimental data.The experimental campaign demonstrated that the recuperative Organic Rankine Cycle-based unit required a lower working fluid flow rate for a given expander inlet temperature and pressure ratio. Consequently, a higher electrical power can be produced, requiring lower thermal power from a heat source. The reduction in the thermal power absorbed from the heat source, produced by a higher temperature incoming working fluid entering the Heat Recovery Vapor Generator, had a positive effect, allowing a longer-in-time working condition with a higher conversion efficiency intrinsically produced by the recuperative heat exchanger. Considering the annual electricity consumption of 2700 kWh of a family living in a city in central Italy, the contribution given by the recuperative Organic Rankine Cycle plant operating with a reservoir fed by 15 m2 of flat solar panels was 330 kWh, whereas without the recuperative stage, the production was 240 kWh. The cost of electricity saved justified the adoption of a recuperative heat exchanger.

Thermo-Economic Performance of Organic Rankine Cycle-Based Waste Heat Recovery for Power Generation at a Wide Range of Operating Conditions

This study assesses the performance of organic Rankine cycle-based waste heat recovery systems under different working fluids and operating conditions. The basic ORC (BORC) and ORC with recuperator (RORC) are investigated for power generation and economy using toluene and benzene. Thermodynamic and economic indicators are studied at various expander inlet temperatures, expander inlet pressure, evaporation temperature, and condensation temperature. RORC achieves higher ηth by reducing heat source in the evaporator whereas BORC recovers more waste heat and improves Pnet. With toluene, BORC improves Pnet when increasing the expander inlet temperature and pressure. The lowest LCOE of 0.0532 US$/kWh is from BORC operated with toluene at a Pnet of 349 kW and decreases with an increase in expander inlet temperature. The addition of a recuperator adds to the costs of initial investment and LCOE and slightly improves the performance of the ORCs for waste heat recovery.

Experimental validation of a 0.3 kW ORC for the future purposes in the study of low-grade thermal to power conversion

Organic Rankine cycle (ORC) is a promising development direction for energy conservation and environmental protection, as it can effectively convert low-temperature waste heat into mechanical work. This article focuses on the experimental performance study of what is likely the world's smallest scroll expander used in a 0.3 kW micro-ORC system. The system uses R1233zd-E as the working fluid, and the expander is repurposed from a scroll compressor of an air conditioner, with a displacement of 11.1 mL/rev. In the first part of the experiments, the influence of the system pressure difference and the expander rotational speed on the system performance is investigated while keeping the expander inlet superheating fixed. The maximum system efficiency, expander efficiency, and power output were 5.46 %, 72.4 %, and 0.266 kW, respectively. In the second part of experiments, the effect of changing the heating source temperature on the system is explored while keeping the expander rotational speed and inlet pressure fixed. As the superheat increased, both the expander and cycle efficiency increased. In addition, this study combines the experimental results with previous data on small-scale ORC systems and discusses the similar trends, indirectly demonstrating that the 0.3 kW micro-ORC can achieve similar behavior as predicted in a large-scale ORC.

Effect of resistive load characteristics on the performance of Organic Rankine cycle (ORC)

The effects of various organic Rankine cycle (ORC) components, such as evaporator, expander and condenser on the performance of the system have been extensively studied. However, only a handful of studies have focused on studying the influence of external load characteristics. A small-scale ORC test rig of 3 kWe was constructed to experimentally investigate the effect of resistive load on the performance of the system. In order to achieve this, the study combined the thermodynamic method with electrical analysis. The results showed that the increase in output power caused a simultaneous increase in rotational speed, torque and inlet pressure of the expander under constant load resistance conditions. However, the fluid mass flow rate only affected the expander's inlet pressure. The decrease in load resistance increased the expander's inlet pressure and torque, and reduced the superheating and rotational speed. The influences of load resistance on the isentropic efficiency and net efficiency were mainly thorough the expander's inlet pressure and superheating. The net efficiency also benefited from the ideal cycle efficiency due to that decreasing load resistance enlarged the enthalpy drop of expander. The effects of load resistance on performance parameters were restricted by the mass flow rate of the fluid.

Experimental investigation of solar organic Rankine cycle with parabolic trough concentrator using nitrate salt as heat transfer and storage fluid

Nitrate salt with low melting point as heat transfer and storage fluid simplifies the heat transfer, storage, and exchange processes, and organic Rankine cycle as heat and power conversion system can realize the distributed energy supply. This study experimentally investigated the solar organic Rankine cycle with parabolic trough concentrator using nitrate salt as heat transfer and storage fluid, and the main problems and phenomena during the operation process have been described and analyzed in detail. Experimental results showed that the temperature difference of collector tube changes with direct normal irradiation and lags behind the changes of direct normal irradiation. Molten salt heat storage system can effectively restrain the temperature fluctuation at the collector tube outlet. The abrupt temperature drop at the evaporator inlet was caused by the heat imbalance between R123 and nitrate salt and inappropriate design of the evaporator. The effects of expander inlet pressure and expansion ratio on the ORC electrical power output were obtained at different superheating degrees of the expander inlet. The researches on each component are instructive to the technology of the parabolic trough concentrated solar power generation system with molten salt as heat transfer and storage fluid and provide some guides for the subsequent research. Furthermore, the energy and exergy analyses on overall system were developed, and results indicated the system average efficiency can reach 1.5%. Novelty statement Experimental study on parabolic trough concentrated solar ORC system with nitrate salt as heat transfer and storage medium were firstly analyzed. Single screw expander was firstly applied in a real solar thermal power generation system and showed a stable performance. Dynamic changes on the temperatures of PTC, molten salt tanks, and ORC were shown, and energy and exergy analyses on overall system were carried on.

Exergy and exergoeconomic comparison between multiple novel combined systems based on proton exchange membrane fuel cells integrated with organic Rankine cycles, and hydrogen boil-off gas subsystem

A comparative study is applied to evaluate four combined power producing systems based on low-temperature and high-temperature proton exchange membrane fuel cells (LT-PEMFC and HT-PEMFC) with equal power generation of 1056 kW. Single-stage organic Rankine cycle (SORC) and cascade two-stage ORC (CTORC) are employed to recover the waste heat from the fuel cells as well as exploiting the hydrogen boil-off gas for generating excess power, and feeding to the fuel cells. The performance of the proposed systems is compared to energy, exergy, and exergoeconomic viewpoints. Also, a parametric analysis is carried out to assess the effects on the thermodynamic and economic performance of the investigated systems by considering main parameters such as current density, fuel cell operating pressure and temperature, turbine inlet pressure, and expander lead. The results obtained from the parametric analysis reveal that with increasing the fuel cell operating temperature the overall exergy efficiencies for the proposed combined systems based on LT-PEMFC and HT-PEMFC decreases and increases, respectively. Also, the net output power and the total product unit cost of the considered systems are optimized at a specific value of BOG expander inlet pressure. The results indicate that albeit the highest values of energy and exergy efficiencies among the considered systems (61.42% and 63.20%) are related to LT-PEMFC/CTORC but the lowest total product unit cost of 33.75 $/GJ is related to HT-PEMFC/SORC.

Model based control of the inlet pressure of a sliding vane rotary expander operating in an ORC-based power unit

• Experimental analysis on Sliding Vane Rotary Expander in ORC plant. • Development of a new approach for volumetric losses calculation. • Inlet pressure control strategy based on expander speed variation. • Effectiveness assessment of the proposed control strategy. • Performance optimization through the proposed regulation strategy. Sliding vane rotary expanders (SVREs) are widely used in organic Rankine cycle (ORC)-based power units for low-grade heat recovery because of their capability to deal with severe off-design working conditions. In particular, the speed of SVREs is a very effective operating parameter, together with the speed of the pump, to regulate the recovery unit and to lead the involved components in an acceptable operating behaviour when they are far from the design conditions. In this study, a control strategy based on the variation in revolution speed of a SVRE was developed, where the inlet pressure of the expander is the main controlled property, which must be verified when the flow rate of the working fluid is changed to match the thermal power recovery at the hot source. In fact, pressure level control is a key point of the recovery unit for thermodynamic reasons and for the safety and reliability of the expander and, more generally, of the whole recovery unit. The proposed control strategy is based on an original theoretical procedure that relates the expander speed, inlet pressure, volumetric efficiency, and working fluid mass flow rate in an analytical form. This analytical formulation is widely nonlinear and is simplified for use as a tool for the model-based control of the inlet expander pressure. An experimental activity performed on a SVRE operating in an ORC-based power unit, fed by the exhaust gases of a supercharged diesel engine, was the base of the analytical formulation. This provided the possibility of deriving a simplified model-based control of the expander inlet pressure and assessing its effectiveness and limits during off-design conditions. Higher expander global efficiencies were obtained (up to 45%), allowing a greater mechanical energy recovery (up to 2 kW).

Effects of evaporation parameters on recuperative transcritical organic Rankine cycle using binary mixture fluids

Abstract In this study, thermodynamic analysis was performed on basic and recuperative transcritical organic Rankine cycles by using five pure and six mixed fluids. The effects of evaporation parameters on the first- and second-law efficiencies (ηI and ηII) as well as power output were investigated. The results indicate that a recuperator had a positive effect on the ηI and ηII and negative effects on the specific power. The total irreversibility of the system was improved by the recuperator. However, the total irreversibility considerably increased with an increase in the expander inlet temperature (Texp,in) due to the significant increase in irreversibility in the condenser, particularly for working fluids with low critical temperatures, namely R134a, R1234yf and R290, and low proportions of R245fa and R600a in mixed fluids. For both the pure and mixed fluids, the specific power linearly increased with an increase in the expander inlet pressure (Pexp,in) and Texp,in. However, with an increase in Pexp,in, the ηI and ηII first increased and then decreased. Finally, for ηI and ηII, the effect of the recuperator increased with an increase in Texp,in even though the recuperator had a relatively small effect on the working fluids with high critical temperature, especially when Pexp,in was high.

Thermodynamic Analysis for Supercritical Carbon Dioxide Brayton Cycle by Considering Both Thermal Efficiency and Cooler Area

Abstract The performances of the supercritical carbon dioxide (sCO2) Brayton cycle with the recuperator were investigated by the simulation method. Evaluation criteria were proposed for system performance optimization. The calculation and analysis of the system thermal efficiency and the length of the cooler were performed. The effects of the inlet and outlet pressure of the expander, the heat transfer coefficient and the logarithmic mean temperature difference (LMTD) on the system thermal efficiency and the length of the cooler were investigated. The system thermal efficiency has a peak value with the increase of the expander inlet pressure. The peak value varies from 45% to 45.4% with different expander outlet pressures. The average heat transfer coefficient and the length of the cooler decrease with the increase of the inlet pressure, but the LMTD is on the contrary. When the expander inlet pressure is in the low-pressure stage (22–26 MPa), the thermal efficiency of the lower outlet pressure (8 MPa) is higher, which ranges from 44.3% to 45.4%. However, the length of the cooler is also larger (6.7–10.9 m). As the expander inlet pressure rises to the high-pressure stage (26–30 MPa), the higher outlet pressure (9.5 MPa) has a greater advantage in the thermal efficiency, and the range of efficiency is 44.7–45%. Similarly, the length of the cooler is the largest (4.5–8 m). Therefore, both the thermal efficiency and the length of the cooler should be fully considered in the design of the system operating conditions.

Thermodynamic analysis and performance optimization of the supercritical carbon dioxide Brayton cycle combined with the Kalina cycle for waste heat recovery from a marine low-speed diesel engine

With the continuous rise in world oil prices and increasing environmental awareness, how to improve ship energy efficiency and reduce ship pollution emissions has become a common concern of the shipping industry. Waste heat recovery technology is an effective method to improve the fuel economy of ships and help the future ships to meet the increasingly stringent Energy Efficiency Design Index of the International Maritime Organization. Under the thermodynamic analysis results of the 8S90ME-C10.2 low-speed marine diesel engine, this paper proposed a waste heat recovery scheme that combined the supercritical carbon dioxide Brayton cycle power generation system with the Kalina cycle power generation system. According to the energy and exergy balances of the combined cycle system, a MATLAB program based on the REFPROP database was established. With the application of control variate method, the influence of the key operating parameters including the main compressor inlet temperature, the turbine inlet temperature, the main compressor outlet pressure, the expander inlet pressure, and the ammonia solution mass concentration on the system performance was thoroughly analyzed. Moreover, the multi-objective optimization matching between the diesel engine and the combined power generation system was carried out from the viewpoints of the thermodynamic performance and economic performance and the impact of the system on the fuel economy and the Energy Efficiency Design Index of the ship was calculated. The results showed that the combined power generation system was used to recycle the waste heat of diesel engine exhaust gas and bypass exhaust gas to generate electricity, which reduced the annual fuel consumption and the Energy Efficiency Design Index to 16.62% and 15.01%, respectively. Finally, this study provides a reference for researchers to study the combined use of supercritical carbon dioxide Brayton cycle and Kalina cycle to recycle the waste heat of the marine diesel engine.

Working Fluid Dependence on Source Temperature for Organic Rankine Cycles

Abstract This paper presents the results of numerical simulations of organic Rankine cycles (ORCs) for low-grade heat source temperature in the range of 373–653 K for 20 working fluids. The goal of the study is to determine the importance of the level of the source temperature in the selection of working fluids and operation conditions. As a performance indicator, a function of the net power, the internal and external exergy efficiencies, and the exergy efficiency of the evaporator is used. The results show that there is a strong correlation between the level of the source temperature and the critical temperature, between the expander inlet temperature and the source temperature, and between the expander inlet pressure and the critical pressure of the working fluids tested. The study shows that once the source temperature level is known, it is possible to select the working fluid and the conditions at the expander entrance.

Enhancing refrigeration capacity of turbo expander by means of multipoint design optimization

Turbo expander produces cold energy in cryogenic Air Separation Unit (ASU) to meet the requirement of liquefied air fractional distillation. The study is initiated by recent commissioning operation of a single-point designed turbo expander in the 1600 Nm3/h oxygen yield ASU, where the online measured cold energy at an off-design operation point is under the requirement. To enhance the expander refrigeration capacity over a wide-spread condition and support the ASU flexible operations, a novel multipoint design optimization method is proposed. Characterization of the ASU expander condition point is done by allowing for the expander real status in the operational ASU; a 3-factors and 5-levels’ uniform design experimentation scheme is proposed and used to identify the multiple design points in the 3D space (formed by the expander inlet pressure and temperature, and shaft speed) and they are used to establish the multipoint objective function; adaptive surrogate model-based optimization algorithms are incorporated to enable the aim-oriented global optimal searching with considerably reduced CFD computations. The multipoint optimized expander impeller is manufactured and used to replace the original. In the restarted ASU, the expander operates at a new condition point but produces high-level overall performance and sufficient cold energy for liquefied air fractional distillation.

Deep Water Cooled ORC for Offshore Floating Oil Platform Applications

Normal 0 21 false false false ES X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:Normal Tablo; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Times New Roman,serif; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} Due to global warming, environmental pollution and cost reduction, increasing efficiency of electricity conversion has become a key issue for the offshore market. This paper proposes an Organic Rankine Cycle (ORC), which uses heat waste from exhaust gases of an FPSO (Floating, Production, Storage and Offloading unit) as heating source, and deep ocean water as cooling source. A genetic algorithm optimization was conducted targeting maximization of net power output, by taking in to consideration of 23 working fluids. Expander inlet temperature and pressure were set as independent variables. The analysis encompasses subcritical or supercritical conditions and recuperation was included in a second version of the system as an option. The first configuration presented ethanol as optimal fluid, followed by toluene and the second configuration indicated cyclohexane followed by ethanol. Use of recuperation, when feasible, increased power output specially for cycles operating with dry and isentropic fluids, presenting an average contribution of 22.7%. Net power and efficiency results from ORC using deep sea water in condenser were presented and compared with ORC using shallow ocean water as cooling source and with Carnot efficiency operating under the same temperatures. Use of deep water raised net power output by 23.3% (cyclohexane recuperative ORC) and 12.5% (ethanol non-recuperative ORC) for the optimal configurations.

Thermo-economic analysis of the transcritical organic Rankine cycle using R1234yf/R32 mixtures as the working fluids for lower-grade waste heat recovery

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.

Preliminary tests on dynamic characteristics of a CO2 transcritical power cycle using an expansion valve in engine waste heat recovery

CO2 has been proposed recently as working fluid for power generation from low grade heat sources due to its good thermodynamic properties and natural feature. CO2 transcritical power cycle (CTPC) is suitable for engine waste heat recovery since it has the advantage of miniaturization and better temperature matching. In this research, a constructed test bench of CTPC using an expansion valve was dynamically tested to recover exhaust energy from a heavy-duty diesel engine. CTPC system dynamic responses to mass flow rate and pressure ratio are presented in detail. Based on dynamic characteristics, a steady state detection method is proposed, which will give reference for experiments of waste heat recovery systems and make it more time-saving and economical. Results show that the CTPC system possesses good dynamic characteristics and the average transition time is less than 62 s. System high pressure or expander inlet pressure could be chosen as a representative indicator for steady state detection and experiment guidance. In addition, the test set-up is of high-accuracy and reliable after examining the heat balances over the heat exchangers and error propagation of the measurement uncertainties. CTPC is applicable for engine waste heat recovery although more efficiency improvements are needed.

Performance analysis of compressed air energy storage systems considering dynamic characteristics of compressed air storage

The compressed air storage connects charging and discharging process and plays a significant role on performance of Adiabatic Compressed Air Energy Storage (A-CAES) system. In this paper, a thermodynamic model of A-CAES system was developed in Matlab Simulink software, and a dynamic compressed air storage model was applied in the simulation, revealing the influence of time-varying temperature and pressure of air on performance indicators, e.g., roundtrip efficiency and energy density. The analysis results can be used as an explanation of the contradicting conclusions on system efficiency from other articles, as well as a reference in the design and operation of an A-CAES plant.There exists an optimal after-throttle-valve pressure when applying energy density as objective function with constant expander inlet pressure. A relatively higher heat transfer coefficient between atmosphere and air in storage tank results in more stored air in charging process and more released air in discharging process, which are of great benefit for A-CAES system in terms of energy density. The dynamic performance characteristic of compressed air storage can affect design capacity of first heat exchanger of expansion train and moreover, reduce roundtrip efficiency and energy density of A-CAES system.

Energetic and exergetic performance investigation of a solar based integrated system for cogeneration of power and cooling

Combining the ejector with organic Rankine cycle has shown potential improvements in the efficiency. However, a solar based combined power and cooling cycle is still a subject for further study. Evaluating the efficiency of this cycle is made difficult by the fact that there are two different simultaneous outputs, namely power and refrigeration. In this paper, the first and second laws of thermodynamics are used to assess the performance of a novel solar based integrated system which produces two different simultaneous outputs using R141b as a working fluid. A mathematical model based on exergy method is introduced to evaluate the local irreversibility in each component of the integrated system. It is shown that the central receiver and heliostat are the biggest source of irreversibility followed by the HRVG, ejector and condenser. Both energy and exergy efficiencies of the integrated system and exergy loss distributions of solar heat input are computed and compared with energy distribution. Parametric analysis of the results shows that expander inlet pressure, condenser temperature, evaporator temperature, and expander back pressure have a strong effect on the power output, refrigeration capacity, and on the energy and exergy efficiency of the proposed system.

Thermodynamic analysis of a Kalina-based combined cooling and power cycle driven by low-grade heat source

This paper investigates a Kalina-based combined cooling and power (CCP) cycle driven by low-grade heat source. The proposed cycle consists of a Kalina cycle and an absorption refrigeration cycle. By establishing the mathematical model, numerical simulation is conducted and parametric analysis is performed to examine the effects of five key parameters on the thermodynamic performances of Kalina-based CCP cycle. A performance optimization is conducted by genetic algorithm to obtain the optimum exergy efficiency. According to parametric analysis, an optimum expander inlet pressure can be achieved; exergy efficiency increases with expander inlet pressure and concentration of ammonia-water basic solution, but exergy efficiency decreases when terminal temperature difference of high-temperature recuperator and low-temperature recuperator increases. Refrigeration exergy increases with expander inlet pressure and decreases as expander inlet temperature and concentration of ammonia-water basic solution rise. However, the refrigeration exergy keeps constant as the terminal temperature difference of high-temperature recuperator and low-temperature recuperator vary. Furthermore, the optimized Kalina-based CCP cycle is compared with a separate generation system which is also optimized. The optimization results show that the exergy efficiency and net power output of Kalina-based CCP are higher than those of separate generation system.