Working Fluid Research Articles

Simulation study of R1234ze and its mixed working medium in TEG‐ORC combined cycle

AbstractThermoelectric generation (TEG) and organic Rankine cycle (ORC) technologies both have their respective limitations in recovering waste heat from ships. However, the combination of TEG and ORC is an effective approach to achieve cascaded waste heat recovery and improve heat utilization efficiency. There has been some progress in research on waste heat recovery in maritime applications based on TEG‐ORC combined cycles. The selection of a working medium is a crucial element that directly influences the design and performance of the entire system, but there is limited research on the impact of different working fluids on combined cycle systems. In this study, a simulation model of a TEG‐ORC combined cycle system was established to examine its output potential using two different working fluids R1234ze and a mixture of R245fa/R1234ze. The results demonstrate that compared to employing the R1234ze working medium, the combined cycle system with the mixed working medium achieved a 13% increase in maximum output power, a 102% improvement in optimum thermal efficiency, and a 53% reduction in optimum power production cost. Additionally, the power output distribution in the system utilizing the mixed working fluid was more uniform compared to the system employing a single working medium. This confirms the great potential of using a mixed working fluid in a combined cycle system.

Stable Droplet Manipulation in Multiple Directions on a Magnetically Responsive Micropillar Array Surface

AbstractDroplets constitute an essential discrete form of liquids and are prevalent in both natural and industrial fields. Droplet manipulation technologies have broad application prospects in various fields, including biomedical devices, chemical engineering, water collection, and so on. The manipulation of surfaces with magnetic responsiveness has emerged as a pivotal technique in droplet control owing to its flexibility and precision in remote operations. In this study, the dynamic rolling behavior of low‐surface‐tension working fluids and water droplets on a superhydrophobic magnetically responsive micropillar array (SMMA) is investigated, with a focus on the mechanisms that generate instabilities during the directional rolling motion of droplets. The factors influencing these instabilities are studied using data analysis. Moreover, techniques for capturing and releasing droplets are investigated, offering significant insights into the efficient handling of minute amounts of liquids in experiments and the automation of intricate chemical processes.

Efficiency enhancement of a combined cycle power plant by thermal integration of multiple waste heat streams with organic Rankine cycle

AbstractThe study investigated the efficiency improvement of a 9.5 MW gas engine‐based combined cycle power plant utilizing multiple waste heat streams in an organic Rankine cycle. Four different waste heat sources were considered: I) boiler stack gas, II) engine jacket water, III) boiler steam, and IV) engines' exhaust gas. Besides, three different organic fluids; R245fa, R134a, and R1234ze(Z) were employed to find the best working fluid in the given operating conditions. The performance analysis of the ORC revealed that R245fa is a suitable potential fluid for cases I and II, whereas R134a performs better for cases III and IV. Integrating the ORC with the boiler stack using R245fa at 8 barg provided an additional 16.5% waste gas heat recovery. It increased the net electric efficiency of the existing plant by 0.7%. The jacket water heat recovery further improved the net electric efficiency by 2.1%. By integrating both streams with the ORC in the existing system, the net electrical efficiency was increased from 42.6% to 45.3%. The estimated payback period for the jacket water heat recovery scenario utilizing Chinese ORC equipment was 9.3 years. However, this period was significantly reduced to 4.6 years for general industry applications, rendering it economically viable.

Simultaneous Optimization of Exergy and Economy and Environment (3E) for a Multistage Nested LNG Power Generation System

The study introduces an innovative three-stage nested power generation system that enables the cascading utilization of LNG cold energy. It makes the most of wasted energy by using ship jacket cooling water (JCW) and exhaust gas (EG) as heat sources, a trans-critical carbon dioxide cycle as internal circulation, and utilizing the pressure exergy of LNG. We choose two azeotrope mixing fluids that match the requirements and create four cases for the outer and middle cycle working fluids in the three-stage nested system. To discover the ideal system performance from the perspectives of exergy (E), economy (E), and environment (E), four cases were subjected to multi-objective optimization using the multi-objective particle swarm optimization technique (MOPSO). Finally, the optimal solution was found by applying the TOPSIS decision-making method. Through comparative analysis, the optimal system is selected among the four optimization results. R170 (22.66%) and R1150 (77.34%) are used as the outer circulating working medium, while R170 (90.86%) and R1270 (9.14%) are utilized as the inter-cycle working fluid. The net output work is 575.75 kW, the optimal exergy efficiency is 46.09%, the optimal electricity production cost is $0.04009 per kWh, the carbon dioxide emissions can be reduced by 36,910 tons, and the payback period is 2.548 years. After optimization, a more energy-efficient and environmentally friendly power generation system is obtained.

Optimization of Organic Rankine Cycle for Hot Dry Rock Power System: A Stackelberg Game Approach

Due to its simple structure and stable operation, the Organic Rankine Cycle (ORC) has gained significant attention as a primary solution for low-grade thermal power generation. However, the economic challenges associated with development difficulties in hot dry rock (HDR) geothermal power systems have necessitated a better balance between performance and cost effectiveness within ORC systems. This paper establishes a game pattern of the Organic Rankine Cycle with performance as the master layer and economy as the slave layer, based on the Stackelberg game theory. The optimal working fluid for the ORC is identified as R600. At the R600 mass flow rate of 50 kg/s, the net system cycle work is 4186 kW, the generation efficiency is 14.52%, and the levelized cost of energy is 0.0176 USD/kWh. The research establishes an optimization method for the Organic Rankine Cycle based on the Stackelberg game framework, where the network of the system is the primary optimization objective, and the heat transfer areas of the evaporator and condenser serve as the secondary optimization objective. An iterative solving method is utilized to achieve equilibrium between the performance and economy of the ORC system. The proposed method is validated through a case study utilizing hot dry rock data from Qinghai Gonghe, allowing for a thorough analysis of the working fluid and system parameters. The findings indicate that the proposed approach effectively balances ORC performance with economic considerations, thereby enhancing the overall revenue of the HDR power system.

Heat transfer in a non-uniformly heated enclosure filled by NEPCM water nanofluid

Purpose This paper aims to focuses on by investigate the heat transmission and free convective flow of a suspension of nano encapsulated phase change materials (NEPCMs) within an enclosure. Particles of NEPCM have a core-shell structure, with phase change material (PCM) serving as the core. Design/methodology/approach The enclosure consists of a square chamber with an insulated wall on top and bottom and vertical walls that are differently heated. The governing equations are investigated using the finite element technique. A grid inspection and validation test are done to confirm the precision of the results. Findings The effects of fusion temperature (varying from 0.1 to 0.9), Stefan number (changing from 0.2 to 0.7), Rayleigh number (varying from 103 to 106) and volume fraction of NEPCM nanoparticles (changing from 0 to 0.05) on the streamlines, isotherms, heat capacity ratio and average Nusselt number are investigated using graphs and tables. From this investigation, it is found that using a NEPCM nano suspension results in a significant enhancement in heat transfer compared to pure fluid. This augmentation becomes more important for the low Stefan number, which is around 16.57% approximately at 0.2. Secondary recirculation is formed near the upper left corner as a result of non-uniform heating of the left vertical border. This eddy expands notably as the Rayleigh number rises. The study findings indicate that the NEPCM nanosuspension has the potential to act as a smart working fluid, significantly enhancing average Nusselt numbers in enclosed chambers. Research limitations/implications The NEPCM particle consists of a core (n-octadecane, a phase-change material) and a shell (PMMA, an encapsulation material). The host fluid water and the NEPCM particles are considered to form a dilute suspension. Practical implications Using NEPCMs in energy storage thermal systems show potential for improving heat transfer efficiency in several engineering applications. NEPCMs merge the beneficial characteristics of PCMs with the enhanced thermal conductivity of nanoparticles, providing a flexible alternative for effective thermal energy storage and control. Originality/value This paper aims to explore the free convective flow and heat transmission of NEPCM water-type nanofluid in a square chamber with an insulated top boundary, a uniformly heated bottom boundary, a cooled right boundary and a non-uniformly heated left boundary.

Comparative and optimal study of energy, exergy, and exergoeconomic performance in supercritical CO2 recompression combined cycles with organic rankine, trans-critical CO2, and kalina cycle

The bottom cycle in supercritical carbon dioxide (sCO2) recompression Brayton combined cycle (RCBC) effectively recovers substantial waste heat for electricity generation, enhancing energy utilization. The recovery efficiency is significantly influenced by the bottom cycle configurations and specific working conditions. Besides, implementing these bottom cycles introduces challenges related to increased system dimensions and design complexity. The present study aims to understand and evaluate the characteristics and optimal trade-offs of various bottom cycles, including trans-critical, subcritical, and non-azeotropic mixed working fluids, by establishing 3E (energy, exergy and Exergoeconomic) models for sCO2/tCO2, sCO2/ORC, and sCO2/KC combined cycle systems. To analysis and enhance interpretability, statistical Global Sensitivity Analysis (GSA) alongside unsupervised learning-based Self-Organizing Map (SOM) techniques and parametric analysis are employed. These methods identify key parameters and discern system patterns. Subsequently, the Non-Dominated Sorting Whale Optimization Algorithm (NSWOA) and entropy weight-based Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) are applied to establish a Pareto-optimal decision space and identify compromised ideal design points for each combined cycle. The results quantitatively rank sensitivity for objective variables within the design space in different combined cycles and visually represent system nonlinearity and coupling relationships in 2D weight planes using SOM. The TOPSIS trade-off points based on the Pareto frontier for the three combined cycles are ηth = 45.08 %, cp,tot = 8.5199 $/GJ, ηth = 45.13 %, cp,tot = 8.3739 $/GJ, and ηth = 48.97 %, cp,tot = 8.4783 $/GJ, respectively. Integrating machine learning techniques provides a comprehensive understanding of system patterns, offering valuable insights for decision-makers in the design and optimization of combined cogeneration cycles.

Thermo-economic investigation and comparative multi-objective optimization of dual-pressure evaporation ORC using binary zeotropic mixtures as working fluids for geothermal energy application

This contribution performs an energy, exergy, and exergoeconomic (3E) analysis of a dual-pressure evaporation organic Rankine cycle system employing twenty different binary zeotropic mixtures as working fluids for power production from a geothermal field. To this end, the designed system is modeled, invoking the mass and energy conservation laws and the exergy and cost balance analyses. Specific Exergy Costing (SPECO) procedure is utilized to provide practical insights into the exergoeconomic aspect of the system. Comparative optimization based on the multi-objective genetic algorithm is accomplished for each mixture in order to simultaneously maximize the exergy efficiency and minimize the total cost rate using the design variables of pressure factor in low-pressure and high-pressure stages, mixture fraction, pinch point temperature differences in low-pressure and high-pressure heat exchangers, and degree of superheat in the high-pressure heat exchanger. In this regard, the Pareto frontiers are drawn for the system with all twenty different binary zeotropic mixtures. The optimal point for each mixture is obtained via the decision-making technique of LINMAP. Subsequently, the LINMAP is re-utilized to find the preferred mixture. The optimization results suggest the R123/C2Butene (96.89/3.11) mixture for this system as the optimum working fluid, considering a trade-off between a low-cost rate of $88.0651 per hr and a high exergy efficiency of 64.07 %. Finally, the exergy flow diagram is plotted to provide the exergy flow rate and the amount of exergy destruction in each segment of the system considering the optimal working fluid. In the proposed system, exergy destruction chiefly occurs within the low-pressure preheater with a value of 1061 kW, followed by the low-pressure turbine and condenser with magnitudes of about 669 kW and 266 kW, respectively.

Experimental study on hydraulic performance and cavitation characteristics of a R134a refrigerant self-lubricating centrifugal pump

As the primary power equipment in pump flooding cooling systems, the efficiency and performance of mechanical pumps play a crucial role in two-phase cooling systems. A high-speed centrifugal pump with self-lubricating working fluid was designed with a speed of 7500 rpm and a flow coefficient of 0.0506. The hydraulic and cavitation performance of the pump were tested with R134a as the working fluid. The results show that the working fluid pump is capable of efficiently pumping R134a with an efficiency of 40.3% and a head coefficient of 0.988 under the design condition. Within the tested range of inlet temperature from 5°C to 15°C, the flow coefficient from 0.01 to 0.105, and the height of the refrigerant tank from 1.4 m to 5 m, lower net positive suction heads available at the same flow rate will reduce the pump head, increase power consumption, and decrease efficiency. Increasing the pump speed from 3000 rpm to 7500 rpm can improve the pump's performance. At 6000 rpm, the critical cavitation number of the working fluid pump increases with the increase in flow coefficient. At 7500 rpm, the critical cavitation number has a minimum value when the flow coefficient φ = 0.0434. At the design speed and flow rate, both the critical cavitation coefficient and fracture cavitation number increase as the inlet temperature decreases. The inducer can significantly reduce the critical cavitation number of the pump. Finally, an empirical correlation considering the thermodynamic effects is proposed to predict the increase in the critical cavitation number.

Optimisation of Brayton cycle CO2-based binary mixtures: An application for waste heat recovery of marine low-speed diesel engines exhaust gas

The energy-saving capabilities and efficient operation of marine low-speed diesel engines (MLDE) is a key emphasis for the main power source for ocean transportation. The purpose of the supercritical carbon dioxide recompression Brayton cycle (SCRBC) is to capture and utilise waste heat emitted by the engine's exhaust gas. However, the SCRBC performance will be severely affected by the large temperature fluctuations of ocean-going vessels during operation and high ambient temperatures in the cabin. A SCRBC model was built using the exhaust gas test data as the boundary conditions and validated using the Sandia National Laboratory (SNL) test data. The physical characteristics of the working fluids were evaluated by adding other fluids to CO2 in specific proportions to modify the critical point and increase cycle efficiency. The results demonstrated that employing CO2-based binary working fluids with low alkane and hydrogen sulfide (H2S) enhanced the recovery power, with the most significant increase obtained by the addition of 16.48 % H2S, which increased the power by 9.72 kW and improved the Brayton cycle efficiency by 3.31 %. Compared to the MLDE at 100 % load, the total efficiency increased by 1.77 % and the BSFC decreased by 6.76 (g kW−1 h−1) using CO2-H2S as the working fluid. The analysis of the SCRBC system component exergy losses showed that the cooler had the highest exergy losses. Adding other fluids to CO2 reduced the exergy losses of each component with the SCRBC system exergy losses decreasing from 162.97 to 129.90 kW and the exergy loss efficiency decreasing from 24.24 % to 22.65 %. The use of CO2-based binary working fluids specifically designed for ambient temperature may be expanded to other engines to enhance the efficiency of waste heat recovery.

Finite-time optimization of a quantum Szilard heat engine

We propose a finite-time quantum Szilard engine (QSE) with a spin-1/2 quantum particle as the working substance (WS) to accelerate the operation of information engines. We introduce a Maxwell's demon (MD) to probe the spin state within a finite measurement time tM to capture the which-way information of the particle, quantified by the mutual information I(tM) between WS and MD. We establish that the efficiency η of QSE is bounded by η≤1−(1−ηC)ln2/I(tM), where I(tM)/ln2 characterizes the ideality of quantum measurement, and approaches 1 for the Carnot efficiency reached under ideal measurement in quasistatic regime. We find that the output power of QSE scales as PO∝tM3 in the short-time regime and as PO∝tM−1 in the long-time regime. Additionally, considering the energy cost for erasing the MD's memory required by Landauer's principle, there exists a threshold time that guarantees QSE to output positive work. Published by the American Physical Society 2024

Utilization of cryogenic phases of helium as “magic” working fluids in laboratory experiments: Pushing the boundaries of fluid dynamics

A surprisingly large part of the valuable scientific contributions of K. R. Sreenivasan—known to his friends and coworkers as Sreeni—to fluid dynamics is directly connected with precisely controlled benchmark experiments with cryogenic phases of helium. These experiments have been performed in a number of leading low temperature laboratories using conventional viscous 4He and 3He gases, normal liquid 4He (He I), as well as liquid 3He–4He mixtures and superfluid phases of 4He (He II) and 3He-B. We review their extraordinary physical properties and describe selected experiments, focusing on various forms of thermal convection, which push the boundaries of classical and quantum fluid dynamics.

Exergoeconomic optimization of a proposed novel combined solar powered electricity and high-capacity cooling load production system for economical and potent generation via utilization of low-grade waste heat source

A novel system for combined electricity and cooling generation was introduced, integrating Flat Plate Solar Collectors (FPSC), Absorptional Heat Transformer (AHT), Organic Rankine Cycle (ORC), and Absorption Cooling Cycle (ACC) systems to utilize low-grade solar energy. The ability to use low-grade waste heat sources (70 °C–90 °C) via FPSC system for high-capacity integrated cooling and electricity generation in a more economical way, a feature not commonly addressed in conventional systems and previous literature studies, was a key advancement. The need for additional generators, boilers, and high-temperature heat sources was eliminated, resulting in substantial cost savings and a simplified system design. The FPSC-AHT integration, identified as having significant advantages over separate electricity and cooling load production, was comprehensively evaluated for its combined exergoeconomic and environmental benefits in multigeneration system design. The modeling was performed using Engineering Equation Solver (EES) and Transient System Simulation Software (TRNSYS) in Izmir, Turkey, with the aim of achieving the heightened economic efficiency and superior Coefficient of Performance (COP) values without high-temperature waste heat sources. Three configurations were examined, with the third demonstrating superior technoeconomic performance due to the increased thermal efficiency of solar hybrid photovoltaic-thermal (PV-T) systems. The higher cost per unit area in the PV-T system was effectively offset by the substantial electricity consumption, contributing to energy savings. Economic indicators for the third configuration included an initial investment of US$9.91 million, annual operational costs of US$1.29 million, a payback period of 4.2 years, an annual energy cost gain of US$9.25 million, a levelized cost of cooling (LCC) of US$0.014/kWh, and an electricity cost (LCE)of US$0.015/kWh. Through exergy analysis, toluene was identified as the optimal working fluid, revealing a total exergy destruction rate of 13245.46 kW. The performance of the proposed system was tested under different operation conditions, and based on these results, a sensitivity analysis and a comparison with the real-word studies were performed. In comparison to real-world data, the proposed system exhibits superior performance metrics, especially in terms of COP and exergy efficiency values. The optimal configuration, established using single and multiobjective optimization approaches based on exergoeconomic parameters, indicated annual electricity and cooling load production of 40,000 MWh and 300 GWh, respectively. The system’s efficiency in producing 1000 kW of electricity power and 4000 kW of cooling load at a comparable cost to systems generating only one output was highlighted. To determine the technoeconomic performance improvement of the proposed integrated system, the optimal configuration of the novel integrated system was compared to a reference plant for similar-scaled integrated power and cooling generation (UCI Trigeneration Plant). Compared to the UCI Trigeneration Plant, the proposed system demonstrated significant improvements in technoeconomic performance. Specifically, the proposed system achieved a 164.13 % increase in annual electricity production, a 97.38 % increase in annual cooling duty, a 60.36 % reduction in initial investment, a 57 % reduction in annual operational costs, and a 47.5 % reduction in payback period. Additionally, the levelized costs of electricity and cooling were 40 % and 22.22 % lower, respectively. Significantly higher electricity and cooling output highlights the system’s ability to meet demanding energy needs. Lower initial investment and operational costs, coupled with a reduced payback period, make the system financially attractive. Lower levelized costs for electricity and cooling increase the system’s competitiveness and affordability. The innovative integration of technologies provides new insights into the design of multigeneration systems, setting a new benchmark for sustainable energy solutions

Experimental analysis of the R290 variable geometry ejector with a spindle

The aim of this work was to experimentally analyze the variable geometry gas ejector with a spindle designed for operation with the natural working fluid propane (R290). The performance of the ejector was evaluated based on the mass entrainment ratio and critical temperature, being the most crucial parameters for optimizing the cooling capacity in ejector refrigeration systems, as well as the ejector efficiency using common literature notation. Additionally, local pressure drop measurements allowed for the determination of pressure profiles inside for different spindle positions used for capacity regulation. The experimentally defined ejector efficiency curves demonstrated the ability to control the ejector capacity by means of the spindle, irrespective of the unfavorable operating conditions. By decreasing the effective throat area using spindle, the ejector mass entertainment ratio increased by 35%. Spindle movement allowed for the decrease of the motive nozzle flow rate by up to 65%, while still maintaining the suction of the secondary flow of the ejector. Moreover, the behavior of a slight increase in suction nozzle flow with a decrease in motive nozzle flow has been observed for the initial movement of the spindle followed by a huge drop for further reduction of the effective throat area, confirming the previous conclusions shown in the literature.

Effect of superheat degree on the performance of an organic Rankine cycle system that utilizes a wet working fluid

AbstractLimited experimental research has been conducted on organic Rankine cycle (ORC) systems that use wet working fluids. Therefore, the present study examined how the performance of an ORC system that uses a wet working fluid (R134a) was affected by the superheat degree ratio (SDR) under various scroll rotation speeds. The SDR is the dimensionless ratio between superheat degree and evaporation temperature at a given heat source temperature. Experimental results indicated that at scroll rotation speeds of 900, 1350, and 1800 rpm, the maximum output power of the aforementioned system was 1103, 1464, and 1537 W, respectively, with SDRs of 0.49, 0.49, and 0.54, respectively. The maximum net efficiencies at these speeds were 5.87%, 5.91%, and 5.32%, respectively, which occurred at SDRs of 0.61, 0.49, and 0.48, respectively. This level of system performance was attributable to the high enthalpy at the expander inlet and the high mass flow rate at the high evaporation pressure under an SDR of approximately 0.5. Although increasing the SDR did not enhance the scroll expander's isentropic efficiency, this efficiency decreased considerably when the SDR fell below 0.2. These findings emphasize the importance of optimizing the SDR of ORC systems to improve their performance.

Review of Reservoir Damage Mechanisms Induced by Working Fluids and the Design Principles of Reservoir Protection Fluids: From Oil–Gas Reservoirs to Geothermal Reservoirs

Various working fluids are applied during geothermal reservoir development, and geothermal reservoir damage induced by contacts between working fluids and reservoir formations are inevitable. Reservoir damage mechanisms, including solid and colloidal plugging, fluid sensitivity, stress sensitivity, and water locking, provide guidance for designing reservoir protection working fluids. In this paper, based on the design principles of reservoir protection working fluids applied in oil–gas reservoirs, four design principles of reservoir protection working fluids are proposed to eliminate potential geothermal reservoir damage for geothermal reservoirs, containing solid-free, facilitated flowback, temporary plugging, and inhibition. Solid-free is achieved by replacing solids with polymers in working fluids. Surfactant and materials with low affinity towards rock surfaces are applied for the facilitated flowback of working fluids from reservoir formations. Temporary plugging is achieved by using temporary plugging materials, some of which are polymers that also apply to solid-free working fluids. Besides, some of the temporary plugging materials, such as surfactant, are applicable for both the facilitated flowback and inhibition of working fluids. The inhibition of working fluids include the inhibition of clay minerals, which can be attributed to clay mineral inhibitors or activity regulators in working fluids, as well as the inhibition of mineral precipitations. This review aims to provide insights for geothermal reservoir protection working fluids, contributing to achieving an efficient development of geothermal resources.

Fluid dynamics in the Kalina cycle: Optimizing heat recovery for sustainable energy solutions

The Kalina cycle is well-known for its innovative energy conversion optimization, utilizing various working fluids such as butane, freon, isobutane, and pentane to evaluate efficiency and performance. This research explores the interaction of fluids in the Kalina cycle to enhance heat recovery by utilizing heat from road infrastructure. Our research focuses on analyzing thermodynamic intricacies and fluid dynamics to provide insights for improving sustainable energy technologies and enhancing heat utilization in various industrial applications. The performance of working fluids in the Kalina cycle has a notable impact on power generation or consumption, which can differ depending on the equipment configurations. One interesting observation is that certain cycles showed a net energy gain at the turbine, particularly the ammonia cycle running at 75 % working fluid, which generated a total net power of −1030.6048 kW. Two freon cycles were compared in terms of net power output: the pure freon cycle produced −125.493 kW, whereas the freon cycle with 90 % freon generated −375.1616 kW. Finally, the pentane cycle with a 50 % efficiency yielded a net power output of −137.6613 kW. This study offers a thorough understanding of how working fluids perform in the Kalina cycle, which can help improve energy conversion processes and promote sustainable energy solutions.

Thermodynamic analysis of a cascade organic Rankine cycle power generation system driven by hybrid geothermal energy and liquefied natural gas

The combination of renewable energy and liquefied natural gas (LNG) cold energy can effectively improve energy utilization efficiency and achieve the goal of energy conservation and emission reduction, which is one of the important directions of future development. This work proposed a cascade organic Rankine cycle (ORC) driven by a geothermal heat source and an LNG heat sink. Seven organic fluids are chosen as candidates to form different working fluid pairs. The effects of the main design parameters on system performance are carried out through the thermodynamic analysis. Then, the optimal design conditions and fluid selection schemes are searched based on the single-objective optimization results. Finally, the exergy destruction study is conducted under the optimal design conditions and working fluid pair. Results showed that the cascade ORC system using the working fluid pair of R601/R290 had the highest exergy efficiency, which could reach 20.02%. At the same time, under the optimal design conditions, the secondary cycle condenser and LNG direct expansion brought high exergy destruction, which was respectively 29.3% and 25.8%, and followed by the two turbines in the cascade ORC system, which were 16.1%, 11.2% and 7.7%.

Investigation on Saturation Vapor Pressure of NH3–H2O–LiBr in Absorption Energy Storage System

Energy storage technology applied between building energy and renewable energy exhibits inherent characteristics of continuity, stability, and high efficiency of energy density. To improve the energy storage density and efficiency of solution absorption energy storage system, an innovative method is proposed by adding ammonia to regulate the saturated vapor pressure of Lithium Bromide solution, which is used as the energy storage working fluid for the absorption energy storage system. Based on the static method principle of vapor–liquid equilibrium of multiple working fluids, a testing platform for the vapor pressure of multiple working fluids was built. The pressure of the Lithium Bromide solution and the Lithium Bromide solution added Ammonia with a concentration of 58% were measured. The results show that the pressure of the Lithium Bromide solution added Ammonia is 2–5 times higher than that of the Lithium Bromide solution. The maximum relative deviations between the calculated value of the models fitted by Antoine equation and Peng Robinson state equation and the experimental value are 4.65% and 10.88%, respectively. That indicates that the model fitted by Antoine equation is more precise for the calculation of the equilibrium pressure of the ternary working fluid. The equilibrium pressure of the Lithium Bromide solution added Ammonia is predicted by the model fitted by the Antoine equation.

Performance assessment on a modified precision refrigeration cycle using low GWP mixtures

Recently, with the increasing worldwide demand for low-temperature freezers, applying natural working medium hydro-carbon refrigerants for them has been widely concerned. Auto-cascade refrigeration cycle (ARC), as an efficient refrigeration technology, has been widely applications. However, the low separation efficiency of the refrigerant mixtures of the conventional ARC leads to its poor performance. Therefore, this paper presents a modified auto-cascade refrigeration cycle (MARC) using low GWP hydro-carbon refrigerants R170 and R290 for low-temperature freezer applications. In MARC, the two auxiliary separators are applied to make more low-boiling working fluid into evaporator to improve the volumetric cooling capacity (qev) and COP. The characteristics of conventional ARC and MARC are evaluated with theoretical method. The important parameters such as evaporating temperature and intermediate temperature for MARC are also detailed discussed. The theoretical research results suggest the MARC is more energy-saving and feasible. The improved cycle offers significant improvements in qev, COP and exergy efficiency. In detail, for MARC, the qev can be lifted by 40.3–91.3 % and the COP can be improved by 30.6–70.4 % compared with the ARC system. Therefore, the modified MARC shows its potential advantages for low-temperature freezer applications.