Optimal Working Fluid Research Articles

Optimization of thermodynamic performance and mass evaluation for MW-class space nuclear reactor coupled with noble gas binary mixtures Brayton cycle

Space exploration technology is an important indicator of society's technological level. A space reactor coupled with a Brayton cycle is preferable for megawatt-scale space power systems. Noble gas binary mixtures have high chemical stability, heat transfer performance, and compressibility, making them the principal choice of working fluid for the space reactor Brayton cycle, which is also the key factor affecting the thermodynamic performance and mass of the system. This study developed thermodynamic performance and mass evaluation models for the space nuclear Brayton cycle and discovered the inherent relationship between system thermodynamic performance and mass. The effects of noble gas binary mixtures on system performance and mass were investigated. The results indicated that the elevated molar mass of noble gas binary mixtures reduced the aerodynamic load and mass of the turbomachines and increased the mass of the recuperator. There are optimal values of the total mass, specific mass of the system, and working fluid composition. Helium-xenon mixture is the optimal working fluid because it can achieve the highest thermodynamic efficiency and lowest mass. Furthermore, the optimal scheme of the helium-xenon Brayton cycle for a space nuclear power system was obtained by multi-objective optimization. Its power generation efficiency, specific mass, and helium molar fraction in the helium-xenon working fluid are 29.04%, 5.65 t∙MW−1 and 77.5%, respectively. This study provides a reference for the design and optimization of space nuclear power systems.

Using advanced exergy analysis to select an optimal working fluid pair in an absorption refrigeration cycle

Using advanced exergy analysis to select an optimal working fluid pair in an absorption refrigeration cycle

Molecular modelling of energy storage performance on metal organic frameworks/ethane nanoparticles nanofluids mixtures and derivatives

Through the utilization of optimum working fluids, thermodynamic cycles may perform more effectively. In this study, we used molecular modeling approaches to conduct computational studies on nanofluids of ethane and its derivatives with metal organic frameworks (ZIF-8). DMol3 was used to investigate the structure and electrical behavior of nanomaterials prior to as well as following fluid adsorption. The adsorption behavior of the refrigerant gases ethane (R-170), fluroethane (R-161), and difluroethane (R-152a) on ZIF-8 was investigated using grand canonical Monte Carlo simulations at various temperatures. Additionally, R-170/ZIF-8, R-161/ZIF-8, and R-152a/ZIF-8 nanofluids' stability and thermal energy storage traits were assessed. The outcomes demonstrate a decrease in the order of R-170 > R-152a > R-161 in the adsorption of the fluids on ZIF-8. Additionally, adding ZIF-8 nanomaterial to R-170, R-161 and R-152a fluids improved their ability to store energy, but improvements at higher ZIF-8 concentrations revealed sensitive dependence on the pressure and temperature conditions, particularly the fluid under consideration's critical temperature. To validate the computational findings, they were contrasted with previously collected experimental data.

Performance analysis, multiobjective optimization and working fluid selection for a DPORC system with geothermal source shunting

A dual-pressure ORC system with geothermal source shunting (GSS-DPORC) is proposed. The geothermal source at the outlet of the high-pressure evaporator is shunted so that one portion of it heats the high-pressure preheater and the other portion heats the low-pressure evaporator. Thermodynamic, economic, and environmental performance of the GSS-DPORC system are examined and contrasted with those of the DPORC system under different working fluids and conditions. Further, the EW-GRA-TOPSIS comprehensive evaluation method, which picks the optimal working fluid while attaining the best working conditions, is proposed. It fully assesses the working fluid based on the multiobjective optimization results generated by NSGA-II. The results indicate that the performance metrics of the GSS-DPORC system are superior to those of the DPORC system when the geothermal source inlet temperature is in the range of 373–423 K, the evaporation pressure of high-pressure stage ranges from 740 kPa to 1610 kPa, and the evaporation pressure of low-pressure stage ranges from 540 kPa to 1020 kPa. R227ea has better thermodynamic and economic performance, and R245fa has better economic performance. The R227ea has the best overall performance following a thorough review using the EW-GRA-TOPSIS method, while the R245fa has the poorest performance.

A study of the optimal conditions for organic Rankine cycles coupled with vapour compression refrigeration using a rigorous approach based on the Helmholtz energy function

VCR-ORC systems combine an organic Rankine cycle (ORC) to produce energy from low-moderate temperature sources and a standard refrigeration cycle (VCRC). Accurate objective functions for the optimal performance of the system are developed based on the Helmholtz energy function and its derivatives. Moreover, the utility of two objective functions is analysed in the search for the optimal conditions of a VCR-ORC system. Finally, it presents a comparative analysis of several working fluids to give the directives in selecting an optimal working fluid and its operation optimal conditions. The method described above uses a set of refrigerants and the PC-SAFT EOS as the prediction model. The results presented in this work show that variables such as the condenser temperature, T1, are fundamental for the optimisation of VCR-ORC systems. Pentane and R1233zd have the best performance for this system. However, the fourth-generation refrigerant shows the best operational condition in all the indicators among the studied fluids despite its wet expansion in optimal operation. In the idealised VCR-ORC cycle, the optimal ORC efficiency links with the optimal COP of the cycle while the extracted heat links with the optimal mechanical work produced by the ORC.

The effects of different working fluids on the performance characteristics of the Rankine and Brayton cycles

In this study, 143 different working fluids have been analyzed for Rankine and Brayton cycles in terms of performance characteristics such as power, thermal and exergy efficiency, and EFECWOD. The selection of working fluid is a significant consideration in the design of both these cycles, as it can importantly affect the performance and efficiency of the system. As of late, there has been growing interest in investigating the effects of various working fluids on the performance characteristics of these cycles. This article aims to determine the ten best among different working fluids according to the determined criteria using the Technique for Order of Preference by Similarity to Ideal Solution, which is a multi-criteria decision method. In the decision-making process, the importance scale of the analytical hierarchy process was used to determine the weight values of the criteria to be used in the TOPSIS analysis to obtain more accurate results. Artificial Neural Network method is employed to identify the optimal working fluid as well. As a conclusion of this thermodynamic analysis of the performance characteristics for Rankine and Brayton cycles using various working fluids, the Rankine cycle achieved the maximum power of 12,277 kW, the maximum efficiency of 93 %, and the maximum EFECWOD value of 9962 kJ/m3 with hydrogen, helium, and dimethylcarbonate as the respective working fluids. Furthermore, hydrogen exhibits the highest power output of 2493 kW in the Brayton cycle. Nitrogen demonstrates the highest efficiency at 44 %, while R141b achieves the highest exergy efficiency at 98 %. Lastly, the fluid with the highest EFECWOD value is R13, with a measurement of 4932 kJ/m3.

On mixtures as working fluids of air-cooled ORC bottoming power plants of gas turbines

The use of mixtures as working fluids of organic Rankine cycle (ORC) waste heat recovery (WHR) power plants has been proposed in the past to improve the matching between the temperature profile of the hot and the cold streams of condensers and evaporators, thus to possibly increase the energy conversion efficiency of the system. The goal of this study is to assess the benefits in terms of efficiency, environmental (GWP) and operational safety (flammability) that can be obtained by selecting optimal binary mixtures as working fluids of air-cooled ORC bottoming power plants of medium-capacity industrial gas turbines. Furthermore, two thermodynamic cycle configurations are analyzed, namely the simple recuperated cycle and the so-called split-cycle configurations. The benchmark case is a combined cycle power plant formed by an industrial gas turbine and an air-cooled recuperated ORC power unit with cyclopentane as the working fluid. The results of this study indicate that binary mixtures provide the designer with a wider choice of optimal working fluids, however, in the case of the recuperated-cycle configuration, no improvement in terms of combined cycle efficiency over the benchmark case can be achieved. The split-cycle configuration leads to an increase of combined cycle efficiency of the order of 1.5%, both in case of pure and blended working fluids. Furthermore, for this cycle configuration the use of Novec 649 as working fluid is advantageous because it is environmentally and operationally safe, and it does not involve any penalty in terms of combined cycle efficiency if compared to the benchmark case. Additionally, the use of this fluid would lead to a more compact turbine, as the corresponding thermodynamic cycle would determine a turbine volume flow ratio that is half of the value of the benchmark case and a specific enthalpy difference over the expansion that is one fifth.

Design and experimental validation of a high capacity loop heat pipe for avionics cooling

With the rapid development of modern aviation industry, the power of avionics has been increasing continuously, bringing great challenge to thermal management. As an efficient two-phase heat transfer device, loop heat pipe (LHP) holds great application potential in avionics cooling. To address the issue of inadequate heat transfer capability, a set of kW-class LHP was specially designed and experimentally validated considering the airborne environment. A detailed introduction covering the entire design process was presented, in which some targeted design criteria were provided. Ammonia was chosen as the optimal working fluid, and stainless steel envelope with a nickel wick was adopted. Experimental validation showed that, at a heat sink temperature of 20 ℃, the designed LHP could achieve a maximum heat transfer capacity of 1021 W, confirming the efficacy of the design method. The average heat flux at the evaporator could reach 12.04 W/cm2. The LHP exhibited a maximum and minimum thermal resistance of 0.16 and 0.054 ℃/W, respectively, achieved at heat loads of approximately 50 W and 600 W. The maximum temperature fluctuation at the center of the saddle surface was no more than ±1.40 ℃. A method for estimating the heat leak between the evaporator and the compensation chamber was also developed, and the maximum heat leak rate was calculated to be approximately 5.2%. Moreover, the designed LHP also manifested excellent startup performance and operation stability.

Multi-criteria thermo-economic analysis of solar-driven tri-generation systems equipped with organic Rankine cycle and bottoming absorption refrigeration and Kalina cycles

Optimal thermo-economic integration of renewable energy sources with multi-generation energy systems is a prime research topic today. The present study proposes a multi-criteria evaluation method of such integration, based on combined heating and power (CHP), and combined cooling and power (CCP) scenarios, for three different solar intensities. Three novel solar-driven tri-generation systems are selected. They include different organic Rankine cycle (ORC) architectures and a Kalina cycle system (KCS) and a double-effect absorption refrigeration cycle as bottoming cycles. Evaluation of the tri-generation systems, both with and without the KCS system, indicates a performance improvement of up to 23% in various thermoeconomic characteristics when the KCS system is present. Selection of the suitable tri-generation system for each condition and optimization of the working fluid are carried out based on a multi-attribute decision-making method. P-xylene is found as the optimal organic working fluid for ORC and ORC (ORC integrated with internal heat exchanger) based systems, and benzene for the regenerative ORC-based system in both CHP and CCP scenarios. Multi-criteria analysis shows that ORC-based system outperforms other systems with net outranking flow of 0.44 (0.39) for CHP (CCP) application. The optimal configuration gives 95.6 M$ and 1.99 years for net present value and dynamic payback period, and 83.03% and 34.55% for energy and exergy efficiencies, respectively.

Performance prediction and design of CO2 mixtures with the PR-VDW model and molecular groups for the transcritical power cycle

Nowadays, CO2 mixture has been widely considered as the working fluid of power cycle. However, how to select appropriate fluid from the numerous organic fluids has to be solved, so as to achieve the high-efficient power cycle. Thus, in this work, PR-VDW and GCM-PR-VDW models are respectively developed to predict the properties of CO2 mixture. Under the given operating conditions, the prediction deviations of cycle performance are obtained and the influences of cycle temperature, pressure and mixing ratio on prediction accuracy are explored. The results show that PR-VDW model has high prediction accuracy for the thermal properties and cycle performance of CO2 mixtures. The prediction deviations of cycle efficiency and net work are 11.38% and 6.88%, respectively. For the GCM-PR-VDW model, cycle efficiency and net work have deviations 15.65% and 8.65%, respectively. On this basis, with the maximum output power as the optimization objective, the optimal organic working fluid and its ratio in CO2 mixture are determined by employing GCM-PR-VDW model. Under the given heat source conditions, it is found that CO2+R32 (0.23/0.78, molar ratio) is the optimal mixture for the transcritical power cycle, and the corresponding cycle efficiency and net work are 16.48% and 1148.04 kW, respectively.

Experimental Study on the Influence of Wind Speed on the Start-Up Characteristics and Thermoelectric Generation Characteristics of Gravity Heat Pipe in Gangue Dump

As an efficient heat exchange component, the gravity heat pipe can effectively control the accumulated temperature inside gangue dumps and enable reuse of transferred heat. This study establishes a similar simulation experimental platform for gravity heat pipes to control gangue dumps and thermoelectric generation. The influence of wind speed on the start-up performance and isothermal performance of gravity heat pipes is analyzed, along with the impact of wind speed on their thermoelectric generation performance. Initially, the optimal working fluid height and heating height are determined, followed by a comparison and analysis of the isothermal performance, start-up performance, and thermoelectric generation performance of the gravity heat pipe under different wind speeds. The results indicate that at a wind speed of 1.0 m/s, the gravity heat pipe exhibits better start-up and isothermal performance. At a wind speed of 2.0 m/s, the thermoelectric power generation reaches its peak. In the range of 1.0~2.0 m/s wind speeds, the curve of thermoelectric generation exhibits the most fluctuations.

Study on strengthening power generation by using LNG cold energy with multi-stream heat exchange

The utilization of cold energy released during the liquefied natural gas vaporization to enhance power generation is an efficient method for energy conservation and emission reduction. In this study, a novel multi-stream cascade combined cycle (MS-CCC) is proposed, which integrates multi-stream heat exchange into the power generation system. In contrast to the cycles of the previous research, MS-CCC improves the utilization efficiency of cold exergy while simultaneously recovering the cold exergy of the working fluid without the need for additional heat exchangers in the system. The thermodynamic performance and economic benefits of MS-CCC were evaluated by comparing them with traditional combined cycle (CC), parallel combined cycle (PCC) and cascade combined cycle (CCC) by genetic algorithm, and the study also investigated the influence of operating parameters and cycle structure on the performance of MS-CCC. Compared to the CC, PCC and CCC, the exergy efficiency of MS-CCC can be higher by 88.6 %, 63.1 % and 12.4 % respectively when the same working fluid is employed. Additionally, the net annual income with the optimal working fluids can be increased by 1.039, 1.036 and 0.405 M$, respectively. The maximum net annual income of MS-CCC reaches 1.225 M$ with an exergy efficiency of 17.46 % when employing the optimum working fluid group of ethane + R32. The exergy efficiency of MS-CCC can be maximized at certain condensing temperatures, and it increases with the decline of the natural gas exhaust pressure of the system. Furthermore, the removal of direct expansion has minimal effect on the system efficiency, and by adding one stage of Rankine cycle, the exergy efficiency can be increased by more than 24.4 %.

Working fluid design and performance optimization for the heat pump-organic Rankine cycle Carnot battery system based on the group contribution method

Among various energy storage technologies, the heat pump-organic Rankine cycle (HP-ORC) Carnot battery technology exists comparably long-life cycles, geographical independence, high energy density and efficient storage energy at low temperatures, which shows the potential of application in large-scale energy storage. As the core of the heat pump and organic Rankine cycles, the employed working fluid significantly influences component design, system performance, its stability and safety. Thus, this paper proposes a novel method for evaluating the HP-ORC Carnot battery performance using different working fluids based on the group contribution method. It is beneficial for improving the designed efficiency of working fluids and the performance optimization of this presented system at the molecular scale. In this study, the basic thermophysical properties of 70 working fluids were first estimated based on the group contribution method and then the power-to-power-efficiency of the proposed system was calculated under the given boundary conditions. Finally, the working fluids with power-to-power-efficiency in the top 20% were evaluated by the entropy weighting method, taking into account thermodynamic, environmental and safety properties, and the optimal working fluids of the proposed system were obtained. The results show that the proposed system was accurately predicted according to the group contribution method, where the average absolute deviation of generation efficiency is 0.61%. Besides, the proposed system with R272fa had the highest power-to-power-efficiency of 57.5%. Finally, R272ea, R272fa, R1261zf and R1243zc were recommended as optimal candidates. Their corresponding total evaluation scores are 0.528, 0.592, 0.667 and 0.526, respectively.

Bi-objective optimization and environmental assessment of SOFC-based cogeneration system: performance evaluation with various organic fluids

Heat recovery offers multiple advantages, such as reducing energy consumption, promoting environmental sustainability, and enhancing productivity. Consequently, in this study, a bi-evaporator organic flash cycle (BEOFC) is utilized to recover heat from a solid oxide fuel cell (SOFC) and serves as a heat recovery unit. The BEOFC is a groundbreaking system that generates cooling and electricity. It boasts a dual-evaporator design that cools air at two distinct temperatures. Examining various organic fluids for better BEOFC performance entails evaluating their thermodynamic, environmental, and economic aspects. Based on the results, R227ea is selected as the optimal working fluid for BEOFC due to its superior performance. Subsequently, a parametric study is conducted and a bi-objective optimization of the proposed system is performed, where the objective functions comprise minimizing the total unit cost of products (TUCP) and maximizing the exergy efficiency. Optimized performance can be achieved when TSS1= 364.5 K, Teva1= 273.1 K, TSOFC= 897.3 K, and JSOFC= 5004 A/m2. At this point, the exergy efficiency and TUCP surge by 2.63%-point and 27.1% compared to the initial state. However, there is a rise of 7.26% in CO2 emission rate, 13.15% in sustainability index, and 8.8% in the total exergoeconomic factor when compared to the base case.

"THE POTENTIAL OF GEOTHERMAL SOURCES IN SOUTHERN KAZAKHSTAN FOR HEAT SUPPLY TO RURAL CONSUMERS, the case OF THE ZHAMBYL REGION"

"The article presents the characteristics of geothermal deposits in the south of Kazakhstan and the analysis of the potential of geothermal waters of the Zhambyl region. Moreover, the study carries out the review of various types and methods of using geothermal water for household and its needs. Consequently, it outlines information on thermal boreholes. During the elaboration, manufacture and testing of these combined power units, several scientific and technical issues, such as the choice of the optimal low-boiling working fluid for heat and hot water supply systems were solved. An overview of the refrigerants and vapor compression fluids currently available have been made. The classification and characteristics of secondary heat carriers of various types and temperatures of their use are given. Therefore, it is proposed to use non-azeotropic binary mixtures as working bodies of a closed heat-power circuit. Moreover, an analysis was carried out on the use of non-azeotropic mixtures for heat pumps. It is proposed to use mixtures of refrigerants as working bodies for the second circuit. The specific characteristics of refrigerants are outlined. As a result, a description of the operation scheme of a steam compression heat pump operating in the mode of heat and hot water supply is highlighted. "

Effect of critical temperature and category of zeotropic mixture working fluids on the thermal performance in subcritical ORC

Several thermodynamic properties are crucial in selecting the optimal working fluids and significantly affect the performance of the Organic Rankine cycle (ORC); one of them is the liquid-vapor critical temperature. Four different thermodynamic models were used; they differed by the definition of maximal (TEva) and minimal (TCond) temperatures. Three different scenarios were investigated in all models by picking components from different working fluid classes to prepare zeotropic mixtures. The main focus of our study was on the investigation of the effect of the critical temperature (Tcr) of the mixture and the class of the components (wet/wet, wet/dry, and dry/dry) on thermal efficiency (ηth) and net-work output (Wnet). Results indicate that occasionally, the zeotropic mixtures with higher critical temperatures (but not always) outperform other mixtures under given conditions. Consequently, it cannot be asserted that the higher thermal efficiency and net- work output are monopolized by the highest critical temperature of all mixed working fluids. Selecting a certain mixing ratio and the appropriate model (evaporator and condenser temperatures set as on the bubble and dew points) that matches the ORC application can assist in obtaining the highest thermal efficiency and net-work output.

Thermo-economic performance limit analysis of combined heat and power systems for optimal working fluid selections

In previous works, we have proposed the thermodynamic performance limit analysis methodology for the organic Rankine cycle for analyzing the impact of working fluid properties on system performance. Here the concept is extended to the thermo-economic performance limits, and is applied to a combined heat and power system based on an organic Rankine cycle. Working fluids are characterized with 8 characteristic thermodynamic and transport properties based on a corresponding state model and a residual entropy scaling approach. The 8 fluid characteristic properties along with 3 system operational parameters are optimized using a multi-objective genetic algorithm; a Monte Carlo algorithm is further adopted to avoid sub-optimal convergences. As the result, the performance limits could be well represented by the trade-off (Pareto front) between the maximized thermal efficiency and minimized payback period. The impact of the fluid characteristic properties on both thermodynamic and economic targets is investigated and ultimately guided the choice of working fluids: low molar mass, low thermal conductivity scaling factor, high viscosity scaling factor and high critical pressure are always preferred. "Wet" working fluid is preferred for a high thermal efficiency while "dry" working fluid is favored for a short payback period. Critical temperature has the most profound impact, while ideal gas isobaric heat capacity and acentric factor have negligible impacts. The choice of working fluid, system design (e.g., recuperative effectiveness) and system operational parameters (e.g., evaporation temperature) highly depends on the given hot sources and the preferences to the thermodynamic and economic targets.

Micro-grooved circular miniature heat pipe for thermal management: Experimental and analytical investigations

In this paper, thermal performance of a cylindrical micro-grooved heat pipe is experimentally and mathematically investigated. The experimental tests are conducted included the optimum working fluid filling ratio, heat pipe inclination, and input heat load. The new correlations of micro-grooved heat pipe condensation and evaporation heat transfer coefficients are proposed basing on the experimental data. A coupled thermal and hydraulic model is developed to predict the heat pipe local thermal resistances and operating temperature regarding the effect of the architectural size. The Experimental results show that the heat pipe thermal performance is not affected by the inclination angle. Whereas the heat pipe performance is better at horizontal position. It showed that the micro-grooved heat pipe could provide an efficient performance even if the condenser is longer that 40% of the total length and the heat pipe microgrooves aspect ratio higher than 37%.

Simultaneous working fluid and expander selection method for reaching low‐threshold technology organic Rankine cycle (ORC) design

AbstractMaximizing the utilization of an available source serves as the ideal approach, provided that only technical factors are considered. For sources with low heat flux, however, cost‐effective solutions are more suitable due to the minimal net power generated, regardless of the effectiveness of the energy conversion. In such cases, utilizing low‐threshold technology may be the most fitting solution, the layout of these cycles should be simple and inexpensive. In the case of organic Rankine cycles (ORCs)‐based power cycles, this means the omission of superheaters or recuperative heat exchangers and the use of simple expanders and small heat exchangers. Simplifying the design, however, requires additional considerations about the elementary steps of the cycle. This work presents a procedure to select favorable working fluids for ORC while considering the expander's internal efficiency. The criteria for favourability is to have a nonideal expansion process starting and ending in (or very near) saturated vapor states to avoid problems related to wetness/dryness between the given maximal and minimal expansion temperatures. It is demonstrated that the design can be simplified under the simultaneous working fluid and expander selection method presented in this study, regardless of the type and isentropic efficiency of the expander. The resulting methodology applies the novel classification of working fluids using the sequences of their characteristic points on temperature‐entropy space. The proposed approach is illustrated with a case study finding optimal working fluid for an ORC system fitted to industrial waste heat, a low‐temperature geothermal, and a cryogenic heat source.

Multi-criteria assessment of a new energy-saving and environmentally-friendly scheme for natural gas-fired power plants

Recently, natural gas-fired power plants have received wide attention for their environmental advantages. However, high-temperature waste gas causes a quantity of heat loss, and a large amount of carbon dioxide emissions exacerbate the greenhouse effect. In order to efficiently utilize the waste heat of flue gas and reduce the carbon dioxide emissions from power plants, a cascade system which combines waste heat recovery technologies, including the supercritical carbon dioxide (SCO2) cycle and trilateral organic cycle (TOC), with carbon dioxide capture device is proposed. After validating the accuracy of thermodynamic model, the optimum working fluid for the trilateral organic cycle is selected and some main factors affecting the thermodynamic performance are analyzed in detail. Finally, to test the feasibility of the design, this paper optimizes the economy performance of the cascade system and the amount of captured CO2. The results show that the maximum net output power, carbon dioxide capture and payback period of the system are 157.1 MW, 96.49 ton/h and 4.125 years. Moreover, compared with original power plant design, the net plant efficiency of the cascade system has a significantly increasing of 23.6%. Hence, the new scheme proposed in this paper is a feasible method to achieve the aim of energy conservation and emission reduction.