Working Fluid Research Articles

Thermodynamic and economic analysis of ocean thermal energy conversion system using zeotropic mixtures

Zeotropic mixtures offer a promising strategy for enhancing the thermodynamic efficiency and economic feasibility of ocean thermal energy conversion (OTEC) systems. This study investigates two binary mixtures containing R32: R32/R125 and R32/R134a. Through the development of comprehensive thermodynamic and economic models, the research examines the impact of mass fraction and evaporation temperature on the efficiency and cost-effectiveness of the OTEC system. The results indicate that, especially at high evaporation temperatures, the R32/R134a mixture—characterized by significant temperature glide—substantially increases the total energy production capacity of the OTEC system. Compared to pure R32, the OTEC with R32/R134a (mass fraction of R32 is 0.55) has a net output power increase of 9.87kW and a reduction in LCOE of about 61.4 %. In addition, the advantages of R32/R125 mixtures over pure working fluids are not significant due to the small glide temperature. Ultimately, this investigation enhances the overall performance of OTEC systems, thereby supporting sustainable energy solutions for island communities.

Investigation of vapor liquid equilibria for HFO-1336mzz(E) + HFC-1234ze(E) binary system by a novel developed cyclic-analytical apparatus

Hydrofluoroolefins (HFOs), which have excellent thermophysical properties and environmental performance, are considered as the most promising environmentally friendly alternatives to the currently used refrigerants. The vapor-liquid equilibrium (VLE) properties of fluids are the basis for the design and optimization of chemical separation and refrigeration systems. In this work, a high-precision and visual VLE experimental apparatus was developed based on the cyclic-analytical method. which mainly includes thermostatic bath, VLE cell, temperature and pressure measurement system, and gas chromatograph, etc. The expanded uncertainties of temperature, pressure, and composition measurement are 0.06 K, 0.0086 MPa, and 0.056 mole fraction, respectively. By measuring the VLE data of the known binary system and comparing it with the literature, the reliability and accuracy of the experimental apparatus were verified. The VLE data of HFO-1336mzz(E) + HFC-1234ze(E) were measured in the temperature range of 293.15 to 358.15 K. The experimental data were correlated with the Peng Robinson (PR) equation of state (EoS) combined with Mathias-Copeman alpha function (MC) and van der Waals (vdW) mixing rule (PRMC-vdW model) in order to adjust the binary interaction parameters (BIP). The VLE data was also compared with the PPR78 predictive model. The VLE investigation provides a basis for further research on the cycle performance of the mixed working fluid.

Impact of working fluid properties on heat transfer and flow characteristics of two-phase loop thermosyphon with high filling ratios

The two-phase loop thermosyphon (TPLT), known for its excellent heat transfer performance, simple and compact structure, and lack of need for a pump, effectively addresses heat transfer challenges in confined spaces under high heat loads.Compared to TPLT with low filling ratio, high-filling-ratio TPLT not only exhibit a higher maximum heat transfer capacity but also has a more complex heat and mass transfer process, leading to increased sensitivity to the working fluid's properties. Therefore, studying the impact of the working fluid on the operational state of high-filling-ratio TPLTs is crucial for understanding their heat transfer mechanisms. In this paper, comprehensive experiments were conducted on TPLT filled with H2O and R134a as working fluids in a wide filling ratio range (30 % -90 %), and their heat transfer performance and flow characteristics were compared. Heat transfer diagram, two-phase flow pattern diagram, and the distribution of gas-liquid two-phase of the TPLT was established with different filling ratio and heat input. Due to differences in latent heat of vaporization, the maximum heat transfer capacity of the H2O-TPLT (390 W/cm2) is greater than that of the R134a-TPLT (270 W/cm2). In the H2O-TPLT, the predominant large-volume slug flow leads to significant flow resistance. Whereas in the R134a-TPLT, the flow pattern is primarily dominated by small-volume bubbly flow and churn flow, resulting in low resistance. High viscosity and flow pattern in the H2O-TPLT cause oscillation phenomena, leading to significant temperature and pressure fluctuations. Under high filling ratio, both types of TPLT experiences geyser boiling phenomena causing periodic temperature and pressure fluctuations and flow pattern changes. In summary, R134a is the preferred working fluid when heat transfer requirements are met, as it effectively reduces temperature fluctuations while dissipating heat. When exceeding the R134a-TPLT's maximum heat transfer capacity and less stringent temperature control is acceptable, H2O may serve as the working fluid.

Life cycle assessment of enhanced geothermal systems with CO2 as a working fluid—polish case study

AbstractLife-cycle assessment (LCA) is a methodology used to quantify the sustainability of a product, system, or process over its lifetime. The approach allows us to determine energy and material consumption at all life cycle stages, from raw material extraction to the end of a product's life, including the design, production, operation, and end-of-life stages. The LCA aims to assess the overall environmental impact of a facility, consider its strengths and weaknesses, and identify possible solutions to reduce the environmental burden sustainably. This research focuses on a novel approach to using carbon dioxide (CO2) as a working medium. The following research combines two key aspects of electricity production and carbon dioxide sequestration, a solution that can contribute to producing clean energy and reducing CO2 in the atmosphere. This paper aimed to assess the impact of enhanced geothermal systems (EGS) through a life-cycle analysis carried out under Polish conditions for the Gorzow block. It includes differentiating the main impact categories and key system components that indicate the most vulnerable areas. A framework available in the literature and the modelling results performed within the EnerGizerS project were adapted to carry out the study. Calculations were performed using SimaPro software. The work was performed for EGS with supercritical CO2 (sCO2-EGS) as the working fluid in a configuration involving direct expansion in a turbine for electricity production. An environmental impact assessment was conducted, including estimating the carbon footprint for such an installation and different working fluid mass flows. The main objective of the environmental analysis is to examine how the project will affect the various environmental elements (air, water, soil) or forms of nature conservation and to identify ways to prevent, reduce or minimise the effects of the planned investment. The study results show that the construction phase, which includes well drilling and hydraulic fracturing, has the most significant impact on the environment with climate change values for different working fluid mass flows. This phase dominates the indicators obtained, which are considered typical for renewable energy sources. Graphical Abstract

Development of an efficient cross-scale model for working fluid selection of Rankine-based Carnot battery based on group contribution method

Rankine-based Carnot battery is promising system with outstanding performances in addressing the challenges of local consumption of renewable energy generation and utilization of low-grade waste heat. A suitable working fluid is fundamental to the Rankine-based Carnot battery cycle and profoundly influences system performance. However, studies on working fluid selection for the Rankine-based Carnot battery are limited to a predefined database. This approach fails to study or design novel working fluids. Therefore, the nine molecular groups used as a set of molecular groups in this paper can cover most organic working fluids in Rankine-based thermodynamic cycle systems. Developing an accurate cross-scale model based on the group contribution method is used in working fluid selection for Rankine-based Carnot battery. Meanwhile, for the sake of testing the accuracy of the proposed model, twenty-one promising organic working fluids were selected to be compared and analyzed with the results calculated by the REFPROP under the typical working conditions of the Rankine-based Carnot battery. The results show that the absolute average relative deviation of the boiling temperature prediction using the multiple linear regression model proposed in this study is only 3.9 %, while the absolute average relative deviation of the critical temperature based on the proposed boiling temperature model is 5 %. Finally, the present work demonstrates excellent accuracy in predicting the thermodynamic performance of this system. The absolute average relative deviation of the coefficient of performance, generation efficiency and power-to-power-efficiency is 4.6 %, 2.0 %, and 6.4 %, respectively.

Research on mass transfer mechanisms due to short-term water-rock interactions between granite cuttings and alkaline NaCl solution and their patterns

Water-rock interactions induced by working fluids in hot dry rock (HDR) reservoirs lead to reservoir damages through mass transfer. Therefore, investigating the mass transfer mechanisms due to the interactions between working fluids and reservoir rocks contributes to minimizing HDR reservoir damages. Drilling fluid is an important working fluid, yet the interactions between drilling fluids and HDR reservoir rocks lack understandings. Here, interaction experiments were conducted using a high-temperature and high-pressure flow reactor under temperatures of 180 °C and 240 °C, a pressure of 24 MPa, and a flow rate of 0.05 mL/min for 7 days. Pure water and an alkaline NaCl solution, which is referred to a HDR reservoir drilling fluid, were prepared to interact with granite cuttings from the HDR reservoir at Qiabuqia site in Gonghe Basin, Qinghai Province, China. Mineral characteristics, mass and chemical changes in the cuttings, solution element content concentrations, micro-morphology and element contents on the cuttings surface, as well as the size of suspending fines in the solutions were determined to reveal the mass transfer mechanisms. The results indicate that the mass transfer mechanisms include mineral reactions and fines migration, and fines migration is the dominating mechanism. The mineral reactions, including feldspar dissolution, quartz dissolution and feldspar alteration, are strong at the front section, while are weak at the end section. At the middle section, the released element contents by mineral reactions form various precipitates, mainly including aluminosilicate, silicate and silica. Strong mineral reactions at the front section lead to fines migration, while the precipitation of Na-bearing minerals at the middle section inhibits fines migration through a coating effect. Suspending fines are identified in the solutions, with a diameter of 100–300 nm, and settled fines are observed at the end section, with a diameter of hundreds of nanometers to a few microns. Simulations of reaction equilibrium show that the precipitation of quartz and biotite increases with a higher NaCl concentration and a lower temperature, while albite changes from dissolution to precipitation as NaCl concentration rises from 6 wt% to 12 wt%. The formation of halite by simulations supports the coating effect. This study provides theoretical basis to minimize HDR reservoir damage induced by working fluids.

Experimental investigation on the influence of lubricant oil on CO2 nucleate pool boiling heat transfer characteristics

As a natural working fluid, CO2 is considered the most promising alternative refrigerant to hydrofluorocarbons. In the fields of automotive air conditioning and commercial heat pumps, transcritical CO2 cycles show significant potential for performance enhancement. Although there are many studies on CO2 flow boiling in the open literature, few studies involve CO2 nucleate boiling heat transfer, which is the dominant mechanism of CO2 flow boiling heat transfer process. This study is proposed to conduct experimental investigations of CO2 nucleate boiling heat transfer. The influences of evaporation temperature, heat flux and lubricant oil addition on boiling heat transfer performance and bubble dynamic characteristics are discussed. The results show that in pure CO2 nucleate boiling, heat flux increase leads to higher bubble density and bubble diameter in bulk liquid, which in turn enhances boiling heat transfer. The effect of evaporation temperature increases on bubble diameter is significant. The reduction in bubble diameter weakens the convective heat transfer caused by bubble motion, which leads to less variation in the CO2 nucleate boiling heat transfer coefficient with evaporation temperature. Lubricant oil addition significantly changes the bubble dynamics of CO2 nucleate boiling process, leading to larger bubble density and smaller bubble diameter. Moreover, the oil diffusion at the phase interface notably affects the heat transfer performance, resulting in greater differences in the boiling heat transfer characteristics of the mixtures compared to that of pure CO2. The mixture boiling heat transfer coefficient is collectively influenced by evaporation temperature, heat flux and oil concentration. The experimental results suggest that the heat transfer coefficient of the mixture with an oil concentration of 0.5 % increases by an average of 25 % compared to pure CO2 at an evaporation temperature of 0 °C. At higher evaporation temperatures and high oil concentrations (>1%), oil addition leads to heat transfer deterioration. Findings from this work can provide a better understanding of oil effect on refrigerant boiling heat transfer and a fundamental basis for heat exchanger design of CO2 systems.

Self-sufficient power plant prototype composed by cascaded disruptive power units doing work by isothermal contraction and expansion

This research work aims at the design and development of a disruptive prototype for a Self-sufficient power plant (SSPP) prototype composed by cascaded disruptive power units (PUs) doing work by isothermal contraction-expansion processes. The innovative design integrates thermo-hydraulic actuators enabled to drive hydraulic pumps connected to a hydraulic motor-generator. The prototype's cascaded PUs operates on a double closed processes-based isochoric-isothermal-isochoric-isothermal (VTVT) thermal cycle, enabled to do useful work by contraction and expansion of a thermal working fluid (TWF), which is notable for its high specific work output and high thermal efficiency. This is due to a disruptive cascaded heat recovering technique associated to a heat upgrading strategy. Among the most relevant Key Features are its self-sufficient operation modes that challenge traditional limitations of second-kind perpetual motion machines (PMMs) The expected capabilities on the basis of the consistency of empirical analysis are summarized as: - Design based on the optimal number of cascaded power units, - Efficient generation of useful mechanical work through expansion and contraction of the TWF, - High specific useful work (kJ/kg of TWF), such as helium, - Low ratio of actuator volume and weight to specific work. Preliminary tentative validation: The prototype design model was validated through case studies using air and helium as real TWFs. Empirical results demonstrate the SSPP's exceptional performance under certain conditional restrictions. - The optimal SSPP completed with nine cascaded PUs each operating on a double-VTVT cycle per PU. - Helium: RIT value of 0.9 and 9 PUs coupled in cascade to give an SSI of 156.72and a SSEP yield of 922.23 kJ/kg.cy. - Air: RIT value of 0.9 and 9 PUs coupled in a shell to give an SSI of 27.41 and a SSEP production of 37.67 kJ/kg.cy. These findings highlight the prototype's potential to significantly advance energy production efficiency and self-sufficiency in power generation systems.

Reverse design of molecule‐process‐process networks: A case study from HEN‐ORC system

AbstractThe integrated design of the heat exchanger network (HEN) and organic Rankine cycle (ORC) system with new working fluids is a complex optimization problem. It involves navigating a vast design space across working fluid molecules, ORC processes, and networks. In this article, a new two‐stage reverse strategy is developed. The optimal HEN‐ORC configurations and operating conditions, and the thermodynamic properties of the hypothetical working fluid are identified by an equation of state (EOS) free HEN‐ORC model in the first stage. With two developed group contribution‐artificial neural network thermodynamic property prediction models, working fluid molecules are screened out in the second stage from a database containing more than 430,000 hydrofluoroolefins (HFOs). The presented method is employed in two cases, where new working fluids are found. The total annual cost of Case 1 is 12%–22% lower than the literature, and the power output of Case 2 is 5%–8% higher than the literature.

Experimental Investigation of Heat Pipe Flow Dynamics and Performance

Due to their safety, efficiency, and passive operation, heat pipes have found diverse applications that include nuclear microreactors. Heat pipes enable increased reliability in microreactors, as they eliminate the need for reactor coolant pumps and their associated auxiliary systems while resulting in a greatly reduced spatial footprint. Experimental work is needed to support and expedite the design and licensing of heat pipe microreactors, especially the validation of heat pipe performance, as key heat transfer components. The present work develops a comprehensive heat pipe experimental database covering a wide range of heat pipe operating conditions. In addition, two-phase thermosyphon experiments are conducted to serve as a benchmark for performance. The operating conditions are determined based on previously developed scaling laws for heat pipes and two-phase thermosyphons using low-temperature working fluids. The tested heat pipe is about 2 m long and equipped with in-house-developed annulus screen wicks. To allow for the investigation of heat pipe flow dynamics, various instruments are incorporated to acquire heat pipe pressures, pressure drops, and temperatures. In particular, a fiberoptic sensor is implemented to measure temperatures along the centerline of the entire heat pipe. The results can be directly applied to the advancement of numerical tools currently under development for heat pipe microreactor analysis.

Cycle analysis and environmental assessments of cascade organic rankine cycle on diesel engine ships

This study investigates the application of organic Rankine cycle (ORC) on ships to reduce fuel oil consumption and assess improvements in the Energy Efficiency Existing Ship Index (EEXI), and carbon intensity indicator (CII). A cascade ORC(C-ORC) configuration is designed to utilize the exhaust gas from a diesel engine.Thermodynamic simulation identified a combination of toluene and R1233zd as the optimal working fluids for the C-ORC. Exergy analysis was conducted to evaluate the performance difference between the C-ORC system and a version with an internal heat exchanger (C-IHX ORC). The results showed a maximum exergy efficiency of 56.78 % for the C-IHX ORC, compared to 49.33 % for the C-ORC. Further evaluations of the C-IHX ORC, including fuel savings, energy generation, EEXI, and CII, demonstrated that average vessel fuel consumption decreased by 1.02 %, and average attained EEXI improved by 0.93 %. Additionally, the attained CII value was enhanced by 0.98 % on average, depending on operating loads and traveled distances. Although the improvements of EEXI, and CII offered were modest, they present the potential for further enhancement through the utilization of additional waste heat sources, such as economizer steam, and jacket cooling water.

Multi-objective optimisation of ORC–LNG systems using the novel One-shot Optimisation method

Optimisation is drawing more and more attention in the organic Rankine cycle (ORC) research field. However, as the complexity of the ORC scenarios increases, it poses challenges on operational parameter, working fluid, and configuration optimisation levels. This work first proposes an improved optimisation method, termed the One-shot Optimisation (OSO) method, which can simultaneously optimise the working fluid and configuration. Then, a two-objective optimisation is performed using the OSO method in combined ORC–LNG systems, considering up to eight operational parameters, 11 working fluids, and 16 system configurations to maximise energy efficiency and minimise the electricity production cost (EPC). Finally, the result of the optimisation is divided according to the thermodynamic weight (W1), and two typical conditions are analysed in detail: the maximum case (W1 = 1) and the balanced case (W1 = 0.5). The results show that the OSO method is capable of identifying the optimal working fluid and optimal configuration within a single optimisation process. The basic ORC configuration is preferred when W1 is lower while the recuperative ORC is preferred when W1 is higher. The balanced case can achieve an energy efficiency comparable to that of the maximum case but with a significantly lower EPC. The balanced case can achieve as much as 87. 48% of energy efficiency, requiring only 19.77% of the EPC compared to those of the maximum case.

Performances Study of Eco-friendly Binary Azeotropic Mixtures Used as Working Fluid in Three Refrigeration Cycles

According to the European (F-gas) regulation, all refrigerants with a global warming potential (GWP) above 150 will be out by 2030. Searching for alternative refrigerants that are environmentally friendly has become an urgent challenge for the refrigeration and air-conditioning sector. Based on their environmental advantages and good thermo-physical properties, azeotropic mixtures have recently gained special interest as substitutes for conventional refrigerants. This study aims to compare the performance of three eco-friendly azeotropic mixtures with the common refrigerant R134a in three refrigeration cycles: the basic cycle (BC), the ejector-expansion refrigeration cycle, and the ejector sub-cooled cycle. The mixtures under study are R1234ze+R600a, R1234yf+R600a, and R1234yf+R290. These mixtures have global warming potential (GWP) of 5.668, 3.8688, and 3.2865 respectively, whereas R134a has a GWP of 1430. To reach this objective a numerical program was developed using MATLAB software to evaluate the coefficient of performance (COP), and the cooling capacity of the three refrigeration cycles using the studied eco-friendly mixtures and were compared with those of the commonly used R134a refrigerant. The entrainment ratio was also compared for the two ejector cycles using these refrigerants. The simulation was realized for condensing temperatures (Tc) selected between 30 and 55°C and evaporation temperatures (Te) ranging between -10 and 10°C. The results have shown that the eco-friendly azeotropic mixture R1234yf+R290 (GWP=3.51) has the best performances compared to the two other mixtures and they are close to those of R134a. On the other hand, the ejector expansion refrigeration cycle has exhibited a high coefficient of performance compared to the basic cycle and ejector sub-cooled cycle, and a high entrainment ratio compared to the ejector sub-cooled cycle for all used refrigerants. However, the ejector sub-cooled cycle gave a better cooling capacity than the other cycles. According to the obtained results, the azeotropic mixture R1234yf+R290 apart from its excellent environmental properties yields better performances in most of cases, this confirms that it could be a suitable substitute for conventional working fluid R134a which has a great global warming potential.

Accurately measuring slowly propagating flame speeds: Application to ammonia/air flames

Environmental concerns have driven the development of alternative fuels and refrigerant working fluids with low global warming potential. Ammonia (NH3) is a potential zero-carbon fuel, while hydrofluorocarbons (HFCs) like R-32 and R-1234yf are being adopted as refrigerants. When mixed with air, these compounds can sustain slowly propagating flames with laminar flame speeds less than 10 cm/s. Unlike typical hydrocarbon-fueled flames, these slow flames are influenced by buoyancy-induced flow and radiation heat loss. In this study, we experimentally investigate the flame speeds of NH3/air mixtures using the constant-pressure spherically expanding flame method, while circumventing gravity-induced natural convection, and account for radiation-induced inward flow. To mitigate buoyant convection, a low-cost drop tower was built and used to study slow spherically expanding flames in free fall. A computational model (SRADIF) is utilized that combines thermodynamic equilibrium and finite rate optically thin limit radiation heat loss calculations to estimate the inward flow. The developed methodology is utilized to investigate slowly propagating NH3/air flames over a range of equivalence ratios. A systematic approach was undertaken to understand and quantify the errors that could arise when deriving the laminar flame speed. It was found that attempting to study slowly propagating flames in a static configuration, as opposed to in free fall, results in large differences in flame dynamics and subsequently all derived quantities. It is necessary to study slowly propagating flames in free-fall. Additionally, using experimental data that has not been corrected for radiation-induced flow leads to large errors in all derived quantities. Furthermore, direct comparisons of experimental measurements and detailed flame simulations are found to be necessary to determine if existing extrapolation approaches are applicable to these slowly propagating flames, which are challenging to study.

Heat transfer analysis of CuO-ZnO/water hybrid nanofluid in a Shell and tube heat exchanger with various tube shapes

Heat exchangers are widely used in various applications, including heating and cooling systems. Adding nanoparticles to the base working fluid can enhance the fluid's thermophysical properties, thereby increasing the thermal performance of heat exchangers. Further heat transfer enhancement can be done by using a hybrid nanofluid, which contains two or more different nanoparticles. The findings of the paper can be utilized to enhance the thermal efficiency of a shell and tube heat exchanger with different tube shapes and by using CuO-ZnO/ water hybrid nanofluid as a working fluid. Numerical simulations were conducted to model thermal heat exchangers with different configurations. Copper tubes of circular, hexagonal, and elliptical geometry were considered for the experiment. The model is solved using Ansys software with a finite volume approach. The solver employs an upwind-based multidimensional linear approach and upwind discretization schemes. The water inlet velocity in the Shell ranges from 0.5m/sec to 3.2 m/sec at a Reynold number of 10,000 to 15,000 whereas the velocity of cold fluid in the tube varies from 1.4 to 2 m/sec. All experiments were conducted with a 0.01–0.1 %vol % CuO-ZnO (80:20)/ water hybrid nanofluid. The hybrid nanofluid on the tube side is used to cool hot fluid (water) on the shell side. Hybrid nanofluid inlet temperature was maintained at 30°C to cool hot water at 60°C. Hexagonal tube geometry increases the contact surface area, resulting in a 22.11 % increase in heat transfer rate compared to round tubes and an 18.42 % increase compared to round tubes. Experimental and numerical results for the convective heat transfer coefficient, Nusselt number, and pressure drop were also reported.

Design and evaluation of a dilute flow particle-to-air heat exchanger for energy storage applications

The use of inert and redox-active particles for high-temperature energy storage requires the development of components that can efficiently transfer energy to high-pressure working fluids like supercritical carbon dioxide (sCO2). Dilute flow reactors can enable high working fluid outlet temperatures and minimal parasitic losses compared to moving packed bed and fluidized bed reactors. This research uses both computational and experimental methods to explore the design trade-offs and practical challenges of a novel component for transferring energy from dilute flows of hot, reduced metal oxide (MOx) particles to sCO2 in tubes. A discretized thermal resistance network model, which accounts for particle hydrodynamics, multi-mode heat transfer, and reaction equilibrium, guides the design of a prototype device. This device is experimentally tested with a surrogate heat transfer fluids and inert particle temperatures up to 400 °C and a heat duty exceeding 1 kW. The data are used to validate the thermal hydraulic sub-models, allowing for the simulation of reacting particle scenarios. Under nominal design conditions, the flow rate of reactive particles is predicted to be 30 % lower than that of inert particles for the same energy recovered, with over 70 % of the stored particle energy transferred to the sCO2. These findings can inform the design of more efficient energy recovery reactors for particle-based systems and can be integrated into system-level concentrated solar power models with thermal storage to optimize operating conditions.

Theoretical analysis of organic Rankine cycle for maximum power generation in optimization operation conditions

The global critical issue in energy scarcity should be appropriately solved to realize a sustainable society. Effective use of Rankine cycle is one possible way since it provides most of worldwide electricity production. In this paper, theoretical analysis model of organic working fluids R717, R134a, R1234yf, R290, R245fa and R1233zd in Rankine cycle for maximum power generation in optimization operation using low-temperature heat sources are proposed and studied for development next generation green and zero-carbon energy generation system to promote the race to zero. Results show that temperatures of warm and cold water at inlet, mass flow rate of the warm water and performance of the evaporator play a key role to obtain the theoretical optimization operation conditions for maximum power generation. In the case of same initial conditions of temperatures of warm water (85 Celsius degree) and cold water (15 Celsius degree) at inlet, mass flow rate of the warm water (10 ​kg/s) and performance of the evaporator (100 ​kW/K), R717 has the best performance in terms of the maximum power output 56.0 ​kW with thermal efficiency of 8.6%, and the next is the R1233zd (54.4 ​kW, 8.3%), R245fa (54.0 ​kW, 8.2%), R134a (52.8 ​kW, 7.9%), R290 (52.7 ​kW, 7.9%), and R1234yf (51.7 ​kW, 7.7%). Here, it should be noticed that other optimization conditions are almost the same (mass flow rate of the cold water 9.1–9.2 ​kg/s; performance of the condenser 91∼92 ​kW/K) to get their maximum power output of ORC. In addition, it also known that low-GWP R1233zd (GWP: 1) can deserve the best option to replace R245fa (GWP: 950) and R1234yf (GWP: 4) also can replace r134a (GWP: 1430) since their optimization operation conditions are almost same.

Computer modeling of employing binary/ternary organic blends in integrated HP-assisted HDH desalination systems

The global demand for potable water is rising, prompting the development of various energy systems for distilled water production. However, the significance of utilizing multicomponent working fluids in these systems has been largely overlooked. This study presents computer modeling of three HDH-based distillation units powered by two conventional heat pump cycles, namely, the simple and vapor injection heat pumps (first and second models) and an innovative heat pump cycle with an ejector expander (third model). The significance of the research lies in its pioneering investigation of utilizing two- and three-component mixtures in heat pump-based desalination units, which has not been previously explored. The study's primary aim is to determine whether using multicomponent working fluids instead of pure fluids or introducing structural modifications can more effectively enhance the performance of heat pump-based distillation units. The proposed models are simulated using EES and MATLAB software, with the study focusing on energetic, exergetic, exergoeconomic, and heat exchanger modeling to evaluate the feasibility of the configurations. The findings revealed that the structural modifications in the third scenario using R134a resulted in the highest GOR, with improvements of 44 % and 26.03 %, respectively, compared to the other scenarios. However, utilizing binary blend R22/R142b with different compositions improved the GOR of the first to three scenarios by 41.26 %, 29.06 %, and 11.87 %, respectively. Furthermore, in this case, the unit cost of distilled water for the first, second, and third scenarios increased by 12.87 %, 14.32 %, and 12.70 %, respectively. Finally, the first scenario has the highest NPV of 4.40 M$ and the shortest PP of 8.13 years. Therefore, utilizing the blend in a simple heat pump proves to be more efficient and cost-effective than implementing structural modifications.

Research Progress on CO2 as Geothermal Working Fluid: A Review

With the continuous increase in global greenhouse gas emissions, the impacts of climate change are becoming increasingly severe. In this context, geothermal energy has gained significant attention due to its numerous advantages. Alongside advancements in CO2 geological sequestration technology, the use of CO2 as a working fluid in geothermal systems has emerged as a key research focus. Compared to traditional water-based working fluids, CO2 possesses lower viscosity and higher thermal expansivity, enhancing its mobility in geothermal reservoirs and enabling more efficient heat transfer. Using CO2 as a working fluid not only improves geothermal energy extraction efficiency but also facilitates the long-term sequestration of CO2 within reservoirs. This paper reviews recent research progress on the use of CO2 as a working fluid in Enhanced Geothermal Systems (EGS), with a focus on its potential advantages in improving heat exchange efficiency and power generation capacity. Additionally, the study evaluates the mineralization and sequestration effects of CO2 in reservoirs, as well as its impact on reservoir properties. Finally, the paper discusses the technological developments and economic analyses of integrating CO2 as a working fluid with other technologies. By systematically reviewing the research on CO2 in EGS, this study provides a theoretical foundation for the future development of geothermal energy using CO2 as a working fluid.

Effect of working fluid charging amount on system performance in an ocean thermal energy conversion system

In ocean thermal energy conversion (OTEC) systems, the initial working fluid charging amount is crucial as it relates to the system’s performance and economic cost. But currently, there is no clear standard for it, and as the working fluid circulating pump is the most direct and only means to regulate the working fluid flow, it is necessary to investigate the coupled effects of it and the working fluid charging amount on the system performance. To this issue, a corresponding experimental facility was established. The coupled effects were investigated by energy and exergy analysis under varying temperature difference. The results showed that varying working fluid charging amount changed the physical state of the working fluid, and the effect on the system varied under dissimilar temperature difference conditions. Compared to the standard charge (8 kg), 75 % of the standard charging amount diminished the system thermal efficiency by 17 % and exergy efficiency by 16 % at small temperature difference (20 °C), whereas a charging amount of more than 100 % resulted in improved thermal efficiency by 14 % and exergy efficiency by 13 %. At large temperature difference (28 °C), 75 %, 125 % and 150 % of the standard working fluid charging amount all improved system performance (thermal efficiency by maximum 16 %, exergy efficiency by maximum 21 %). Besides, an increase in circulating pump frequency improved system performance regardless of the temperature difference and working fluid charging amount. This research innovatively investigates the above problems in the application scenario of OTEC, and provides theoretical and data support for the development of OTEC technology.