Pure Fluids Research Articles

Comparative research of flow in tube bundle: Source term method and pressure drop method

There are two methods for calculating fluid in porous materials, namely the pressure drop method (PDM) and the source term method (STM), which are widely utilized in their respective fields. Although in principle, the two methods can be applied interchangeably in each other's fields under certain conditions, this situation is extremely rare. This paper conducts a comparative study from various aspects to illustrate the advantages and disadvantages of each method. From a comparison of mathematical equations, PDM does not have the momentum equation, resulting in lower computational costs and better computational performance. From the simulation results of single porous media, STM has more sources of error, and the error in PDM mainly originates from the fitting method. Except for low Reynolds numbers, PDM is generally superior to STM. Both methods yield consistent results when the flow field is uniform. From the perspective of the coupling between porous media and pure fluid, STM captures flow details better. At low Reynolds numbers, STM's computation results are closer to experimental results. While at high Reynolds numbers, PDM aligns better with experimental results. Theoretically, PDM has higher computational efficiency, but it is difficult to achieve efficient coupling with the momentum equation. The computational efficiency of both methods is usually almost the same. In summary, both methods have their advantages and can be employed interchangeably under some conditions to achieve higher computational efficiency, accuracy, and convenience.

Wet-to-dry transition description in the mixture of working fluids

The organic rankine cycle performance and some similar processes depend on many factors. One of them is the category of the working fluid, influencing the performance through the phase/phases during and at the end of the expansion process. Droplet formation for wet fluids and superheated for dry fluids motivated the researchers to seek isentropic working fluids, where expansion could proceed and terminate in a saturated vapour state. The shape of the T-s diagram is a material property; it cannot be changed for real pure fluids, but small jumps can be initiated by replacing one working fluid with a chemically very similar one, like Propane (a wet one) with Butane (a dry one). Our study presents a much smoother transition, using mixed working fluids prepared from chemically similar materials to obtain almost ideal zeotropic mixtures. The main point of our study is to show the wet-to-dry transition for mixtures and prove or disprove the existence of compositions where the fluid can show T-s diagram resembling the ones for ideal isentropic working fluids. For this purpose, Propane was mixed with other alkanes, such as Butane, Pentane, and Hexane, in various compositions, and the thermophysical properties of fluids were calculated by using the REFPROP software program. Wet-to-dry transitions were shown for the Propane/Hexane mixture at (0.6584 + 0.3416 mass fraction), while (0.5823 + 0.4177 mass fraction) and (0.6436 + 0.3564 mass fraction) was the transition mixture for Propane/Butane and Propane/Pentane respectively. Consequently, when exceeding the mentioned composition range, the fluids switch from wet to dry without forming a composition showing ideal isentropic properties. Therefore, isentropic working fluid (showing an infinite slope for the saturated vapour branch in a finite, nonzero temperature range) was not found during this transition.

Thermo-Fluidic Analysis of Pulsating Heat Pipes Charged with Water-Based Immiscible Fluid Pairs

Immiscible fluids may provide operational flexibility for pulsating heat pipes (PHPs) due to thermo-hydrodynamic diversity lead by each pure component. In this regard, present paper focuses on the thermo-fluidic analysis of non-uniform pulsating heat pipes charged with water-based immiscible fluid pairs. Research parameters cover gravity effect via the inclination angles (IA) of 0o and 90o, and fluid pair effect via two different water-based immiscible binary fluids as Water (W) – Hexane (H), and Water (W) – Pentane (P). The volumetric mixing ratios are W:H=1:1, 1:4, 4:1, 1:0, 0:1, and W:P=1:1, 1:4, 4:1, 1:0, 0:1; and the non-uniform flat plate type pulsating heat pipe (FP-CLPHP) has alternating-sequence parallel channels. The experiments are performed at the filling ratio of 40% (FR=40%), and flow phenomena is visualized. As some conclusions; at vertical orientation, the FP-CLPHPs having binary fluids of water-pentane show better thermal performance compared to the pure counterparts. Especially, the heat transfer characteristics of W:P=1:1 are the best ones among all the pure and binary fluids. On the other hand, as a conclusion of combination of non-uniform design and suitable thermophysical properties, the FP-CLPHPs charged with pure pentane, pure hexane or binary fluid of W:P=1:4 can work independent from gravitational force.

Utilization of H2O/CuO and Syltherm 800/CuO Nanofluids in a Concentrating Solar Collector with Photovoltaic Elements

This study examined the performance of a concentrating solar collector with an asymmetric reflector. Two receivers were investigated, differing in the presence of photovoltaic cells. The first one was equipped with cells on both sides while the other was without cells. The analysis was performed using a numerical model that integrates a combination of three-dimensional optical and thermal analyses developed in COMSOL. The investigation included studying the influence of CuO/water and CuO/Syltherm 800 nanofluids on the thermal performance for the receiver without photovoltaic elements, as well as on both thermal and electrical efficiencies for the hybrid receiver. Two volumetric concentrations of CuO in water and Syltherm 800, 3% and 5%, were explored with varying inlet temperatures, ranging from 20 °C to 80 °C for the hybrid solar unit and from 20 °C to 140 °C for the thermal solar unit. The outcomes of the examination were compared between the nanofluids and the pure base fluid. Properly pressurized water was considered in the case without photovoltaic elements.

Enhanced conjugate natural convection in a corrugated porous enclosure with Ag-MgO hybrid nanofluid

Understanding the impact of hybrid nanofluids (NF) on natural convection (NC) within complex enclosures can significantly advance the efficiency of heat transfer (HT) mechanisms. These advancements play a crucial role in various engineering applications, such as thermal systems in electronics, energy conversion, and heat exchangers. This study numerically examined the NC taking place within a sinusoidal corrugated enclosure filled with an Ag-MgO hybrid NF. This system was heated differentially by a vertical solid wall. The vertical right wall of the solid is maintained at an isothermal at a high-temperature Th, while the left vertical wall of the cavity is kept at an isothermal at a low-temperature Tc. The vertical left wall of the solid is in contact with the porous medium (PM) saturated with the cavity's hybrid NF. In contrast, the top and bottom horizontal walls are maintained adiabatic. The governing equations were solved by employing the Galerkin weighted residual finite elements approach. The porous domain is modeled by employing the Darcy-Brinkman formulation. The parameters being studied encompass the Darcy number (10−5 ≤ Da ≤ 10−2), Rayleigh number (103 ≤ Ra ≤ 106), nanoparticle volume fraction (0 ≤ ϕ ≤ 0.04), amplitude of waviness (0.05 ≤ A ≤ 0.2), and number of undulations (1 ≤ N ≤ 4). The results highlighted that the introduction of hybrid nanoparticles into the pure fluid enhances the HT rate across the parameter spectrum. The highest average Nusselt number (Nuav) is attained at Ra = 106, Da = 10−2, A = 0.2 and N = 4. The findings of the current study have practical implications for current industrial applications, particularly in the cooling of electronic devices.

Aspects of Gas Storage: Confined Geometry Effects on the High-Pressure Adsorption Behavior of Supercritical Fluids.

During the last decades, major progress was made concerning the understanding of subcritical low-pressure adsorption of fluids like nitrogen and argon at their boiling temperatures in nanoporous materials. It was possible to understand how structural properties affect the shape of the adsorption isotherms. However, within the context of gas storage applications, supercritical high-pressure gas adsorption is important. A key feature here is that the experimentally determined surface excess adsorption isotherm may exhibit a characteristic maximum at a certain pressure. For a given temperature and adsorptive/adsorbent system, the surface excess maximum (and the corresponding adsorbed amount) is related to the storage capacity of the adsorbent. However, there is still a lack of understanding of how key textural properties such as surface area and pore size affect details of the shape of supercritical high-pressure adsorption isotherms. To address these open questions, we have performed a systematic experimental study assessing the effect of pore size/structure on the supercritical adsorption isotherms of pure fluids such as C2H4, CO2, and SF6 over a wider range of temperatures and pressures on a series of model materials exhibiting well-defined pore sizes, i.e., ordered micro- and mesoporous materials (e.g., NaY zeolite, KIT-6 silica, and MCM-48 silica). A fundamental result of our experiments is a unique fluid-independent correlation between the pressure of the surface excess maximum pmax (at a given temperature) and the pore size (by taking into account the kinetic diameter of the fluid and the underlying effective attractive fluid-wall interaction). Summarizing, our results suggest important structure-property relationships, allowing one to determine, for given thermodynamic conditions, important information related to the optimal operating conditions for supercritical adsorption applications. The insights may also serve as a basis for optimizing and tailoring the properties of nanoporous adsorbent materials for gas storage applications.

Thermophysical and Electrical Properties of Ethylene Glycol-Based Nanofluids Containing CaCO3

The thermophysical properties of various types of nanofluids are often studied to find more effective working fluids for heat transfer applications. In this paper, the mass density, isobaric heat capacity, thermal conductivity, dynamic viscosity surface tension, and electrical properties of calcium carbonate-ethylene glycol (CaCO3-EG) nanofluids were investigated. The samples with mass fractions of 0.01, 0.02, and 0.03 were prepared with a two-step method and studied as well as pure base fluid (ethylene glycol). The measurements were conducted at temperatures between 283.15 and 313.15 K and the obtained results show the impact of CaCO3 nanoparticles on the thermophysical and electrical properties of ethylene glycol.

System Size Dependence of the Diffusion Coefficients in MD Simulations: A Simple Correction Formula for Pure Dense Fluids.

A practical correction formula relating the self-diffusion coefficient of dense liquids from molecular dynamics (MD) simulations with periodic boundary conditions to the self-diffusion coefficient in the thermodynamic limit is discussed. This formula applies to pure dense fluids and has a very simple form D = D0(1 - γN-1/3), where D0 is the self-diffusion coefficient in the thermodynamic limit and N is the number of particles in the simulation. The numerical factor γ is dependent on the geometry of the simulation cell. Remarkably, γ ≃ 1.0 is the most popular cubic geometry. The success of this formula is supported by results from MD simulations, including very recent simulations with a "magic" simulation geometry.

THERMODYNAMICS ANALYSIS OF CASSON HYBRID NANOFLUID FLOW OVER A POROUS RIGA PLATE WITH SLIP EFFECT

The main objective of this work is to examine the nature of heat transfer and thermodynamics on Darcy-Forchheimer flow over porous Riga plate using Casson hybrid nanofluid. The impact of external forces, i.e., slip velocity and magnetic field are discussed for pure fluid, nanofluid, and hybrid nanofluid. The Hamilton-Crosser model of thermal conductivity is applied for the nanofluid as well as hybrid nanofluid. The existing nonlinear partial differential equations are solved by Runge-Kutta-Fehlberg technique. The present code is validated numerically with previous works and found in good agreement with them. The results affirm that all fluids velocities declined with increase in Casson factor values. Moreover, increasing magnetization, the entropy profiles are depreciated significantly for the case of pure fluid, nanofluid, and hybrid nanofluid. This comparative study reveals that hybrid nanofluid dominates on both nanofluid and pure fluid.

MHD Convection with Joule Heating and Internal Heat Generation in a Two‐Layer Discretely Heated Chamber Partly Filled with Porous Medium

The present research presents an innovative approach by integrating magnetohydrodynamic (MHD) flow with resistive heating, integrating a partly permeable layer and interior heat production to scrutinize natural convective flow within a square domain. It also examines both straight and wavy interfaces between the porous and fluid domains. Engaging the Galerkin finite element‐based weighted residual approach, numerical solutions are obtained by unraveling the two‐dimensional Navier–Stokes and thermal energy equations for pure fluid and fluid‐saturated porous domains. The parametric variations include Rayleigh numbers (Ra), porous layer thickness (H), corrugation frequency (f), corrugation amplitude (A), Hartmann number (Ha), and the heat production coefficient (∆). This study assesses the thermal effectiveness of a discrete thermal source, considering variations in porous layer thickness, corrugation frequency and amplitude, magnetic force intensity, and heat production impacts. The discoveries are demonstrated resolvably through the Nusselt number along the warmed edge, thermal performance criterion, and a qualitative portrayal of flow and thermal fields. After extensive analysis, it becomes apparent that reduced thickness of the porous layer, corrugation frequency, and amplitude enhance thermal performance. However, diminished porous layer thickness and corrugation frequency contribute to higher thermal performance criterion (TPC), whereas decreased corrugation amplitude results in a lower TPC. Specifically, the lowest values of H, A, and f result in 11.5%, 0.6%, and 0.1% higher thermal performance, respectively, compared to their highest values. Furthermore, a straight fluid‐saturated porous to the pure fluid domain interface, as opposed to a wavy interface at the highest H, A, and f values, offers a 0.7% improvement in thermal performance.

Techno-economic-environmental analysis and fluid selection of transcritical organic Rankine cycle with zeotropic mixtures

Waste heat recovery is regarded as highly efficacious in ameliorating energy and environmental problems brought on by rapid economic and societal growth. The organic Rankine cycle (ORC), specifically transcritical ORC (tORC) garners significant attention for its potential in waste heat power generation. Researchers still seek to further improve performance for tORC, such as using zeotropic mixtures. Aimed at selecting the working fluid pairs that can bring better performance for tORC, this study provides a more comprehensive performance evaluation of tORC systems by developing a novel multi-attribute integrated assessment model that encompasses techno-economic-environmental aspects. To establish this model, the detailed mathematical models of the tORC are established first and used to obtain system performance indicators. Then, a refined analytic hierarchy process to assign weights to various performance indicators to complete the multi-attribute integrated assessment model. With the utilization of the proposed model, a thorough comparative analysis of the tORC system with ten groups of zeotropic mixtures is performed. Thus, the results of the working fluid selection can be obtained. Results show that R245fa/R600 and R600/R600a are more recommended than other working fluid pairs, with R600/R600a being the preferable choice when prioritizing environmental impact. While R245fa/R1234yf has the worst thermodynamic and environmental performance and R245fa/R227ea owns the worst economic performance. In conclusion, the findings show that employing a zeotropic mixture combines the benefits of the pure working fluids that comprise it. Compared to previous studies, this study provides a more comprehensive look at the selection of working fluids for tORC systems. It can offer valuable insights for selecting the appropriate working fluid more effectively for future applications.

On the origin of Sanchez-Lacombe equation of state theory in hydrostatic strain energy model for rubber-like materials

To capture the volume deformation of rubber-like materials, the strain energy density (SED) function of a compressible hyperelastic model is formulated as the hydrostatic/liquid-like term from interchain interaction changes plus the compressible elastic term owing to elastic deformation of crosslinking network. Notably, the former term dominates volume responses. Although the physics of the hydrostatic term is relatively clear, to our knowledge, few physically-based models are available. However, in our previous work (Liu and Lu, 2023), we constructed a physically-based hydrostatic SED function inspired by the Flory-Orwoll-Vrij equation of state (EOS) theory for pure polymer fluids, and proposed the general strategy for developing hydrostatic functions according to the EOS theories. Sanchez-Lacombe EOS theory (note: a type of lattice-fluid EOS theory) inspired this work. We assume: (i) a rubber-like material consists of polymer segments occupying lattice sites and unoccupied/vacant lattice sites, and the compressibility of the material corresponds to changes in vacant sites fraction; (ii) the hydrostatic strain energy is associated with the interchain interaction energy change and the mixing entropy change between network and vacant sites. According to the Helmholtz free energy in Sanchez-Lacombe EOS theory and limiting our attention to the isothermal condition, another physically-based hydrostatic SED function is constructed; a specific compressible hyperelastic model is provided by further combining compressible 8-chain elastic SED function. The basic framework of this compressible model is inherently consistent with the Flory-Rehner framework for swollen elastomers. Our model provides good predictions for volume deformation data of ten different rubber-like materials in hydrostatic compression (HC), uniaxial tension (UT), and constrained uniaxial compression (CUC). The proposed model reveals that HC, CUC, or uniaxial compression correspond to the entropy-decreasing process and they all are controlled by entropy changes; while for UT, equibiaxial tension, or pure shear, the entropy first increases and then decreases, and the interchain interaction energy and entropy changes control the responses for initial small stretches and remaining large stretches, respectively. This study aims to provide a new physical insight and a valid physically-based hydrostatic SED function for the compressibility of rubber-like materials.

Secondary nucleation in symmetric binary SALR mixtures.

Monte Carlo simulation is used to study secondary nucleation, fissioning, or 'reproduction', of giant clusters in a symmetric binary model fluid with competing short-range (SA) and long-range (LR) interactions. Previous work [M. B. Sweatman, Mol. Phys., 116(15-16), 1945-1952] suggests that a pure SALR fluid can exhibit secondary nucleation if the solute concentration is slowly increased. We show this is also true for a binary symmetric SALR mixture where the cross-interactions can be tuned to generate clusters with three different kinds of structure; (i) independent clusters of each component, (ii) contact clusters of different components, and (iii) mixed clusters. In each case, the overall concentration of each component is identical. This binary model is an initial step towards using SALR fluids to model the intra-cellular space of biological cells that contain a wide range of membraneless organelles and the chemical 'soup' at the origin of life.

Studies of interfacial wave properties during displacement with pure viscoelastic fluids in microchannels

In this study, new experimental data for the displacement of a Newtonian liquid by three pure viscoelastic (Boger) fluids with different relaxation times were obtained with imaging in a 500 μm microchannel. Results were compared against those from displacement using a Newtonian liquid. Small irregular waves were observed at the interface for the Newtonian displacement, while periodic instabilities were seen for all Boger fluid cases. The elastic Mach number (Ma), describing the ratio of the flow velocity with the elastic wave propagation velocity, was found to be the key parameter for correlating the wave properties in the case of Boger fluids. The amplitude of the wavy interface initially increased up to Ma = 0.5, before decreasing again. The frequency and the wave velocity increased monotonically with increasing Ma. For all configurations, a phase shift of π was found between the top and the bottom interfaces. Correlations from experimental data were developed for all wave properties. Based on these correlations, an empirical wave model was developed to describe the observed planar images and to reconstruct the three-dimensional waves, which resemble a helical structure.

Entropy scaling framework for transport properties using molecular-based equations of state

Modeling transport properties is important for many applications. In this work, an entropy scaling framework for modeling transport properties using molecular-based equations of state (EOS) is presented. It can be applied for modeling the viscosity, thermal conductivity, and self-diffusion coefficients. The framework is formulated in a general way such that it can be coupled with various EOS. It is demonstrated that the model, when coupled to molecular-based EOS, provides not only good descriptions of existing data but also reasonable predictions in a wide range of states covering liquid, gaseous, supercritical, and meta-stable regions. Moreover, the model can be used for reliably predicting transport properties of mixtures. The universal parameters of the model were fitted to computer experiment data of the Lennard-Jones fluid. This procedure provides inherently a robust form of the basic scaling function. Thereby, only few data points are required for the determination of the component-specific model parameters. The applicability of the developed framework is demonstrated for model fluids as well as for a wide variety of real substances including non-polar, polar, and associating pure fluids and mixtures.

Investigation of the Thermophysical Properties of Nanofluids Based on Metal Oxides: Application in Concentrated Solar Power Plants

Solar energy is a renewable source of energy that does not emit greenhouse gases. The sun is free, inexhaustible and available all over the world. The sun's rays can be used to produce energy in two ways. The first technique converts the sun's rays into electricity using photovoltaic panels, while the second converts the sun's rays into heat using concentrated solar power plants (CSP). Several studies have been carried out with the aim of improving the performance of these solar power plants in order to achieve high efficiency, which is the case in our study. In this work a numerical study was carried out on the effect of nanoparticles on the thermophysical properties of nanofluids with the aim of determining the most optimal nanofluid for use as a heat transfer fluid in concentrated solar power plants. The nanoparticles examined were metal oxides (SIO2, MgO and Fe3O4), which were dispersed in Therminol VP-1 and Syltherm 800. The thermophysical properties examined were density, thermal conductivity and heat capacity. To carry out this study, we set the temperature from 200 to 400°C at the same operating temperature as the concentrating solar power plant.After evaluating the effect of nanoparticles on the thermophysical properties, we studied the behaviour of the CSP plant based on nanofluids using SAM (System Advisor Model) software. The results obtained are very encouraging and show that the addition of nanoparticles to a base fluid improves its thermophysical properties compared with the pure base fluid, and the rate of improvement in thermal conductivity exceeds 9%. We also found that the nanofluid (Fe3O4 /Therminol Vp1) is the best selected for use as a heat transfer fluid in concentrated solar power plants with an efficiency and thermal energy produced equal to 40.87% and 588164 MWht, respectively.

Modeling Sorption of Hydrocarbons in Polyethylene with the SAFT-γ Mie Approach Combined with a Statistical-Mechanical Model to Describe Semicrystalline Polymers.

A recently developed statistical-mechanical model is applied systematically to estimate the fraction of tie-molecules (polymer chains linking different crystals directly or via entanglements) in semicrystalline polyethylene (PE) samples. The amorphous domains of the polymer are divided into constrained interlamellar domains and "free" outer-lamellar domains. A set of model parameters is assigned to each sample by correlating previous experimental measurements and minimizing the difference between the predicted solubility of pure hydrocarbons in the sample and the experimental values. We show that the sorption isotherms of multiple pure fluids in each sample can be described by a single parameter set, proving that the polymer-solute interactions (described accurately by the SAFT-γ Mie EoS) are decoupled from the sample-specific properties of the polymer. We find that ∼30% of the crystalline stems in the lamellae of PE are connected to tie-molecules, within the bounds suggested by previous theoretical and computational work. The transferability of the sample-specific parameters is assessed by predicting cosolubility effects and solubility at different temperatures, leading to good agreement with experimental data.

Experimental investigation on boiling heat transfer characteristics of R1234yf/R1336mzz(Z) in horizontal flow

Due to the inclusion of 18 HFCs, including R134a and R245fa, in the Kigali Amendment as controlled working fluids, the search for excellent alternatives to R134a and R245fa is urgent. R1234yf and R1336mzz(Z) are potential alternative working fluids to R134a and R245fa, but most studies have focused on the comparison of thermodynamic performance and boiling heat transfer capability of these pure working fluids. There is limited research on the boiling heat transfer performance of their mixed working fluids. Therefore, this study focuses on the flow boiling heat transfer characteristics of the mixed working fluid R134a/R245fa under non-azeotropic conditions. Experimental methods were employed to investigate the boiling heat transfer performance of the alternative working fluids R1234yf/R1336mzz(Z) (including R245fa/R1234yf and R1234yf/R1336mzz(Z) mixed working fluids) and evaluate the feasibility of R1234yf and R1336mzz(Z) as substitutes for R134a and R245fa. The results indicate that among the three mixed refrigerants, R134a/R245fa exhibits the highest heat transfer coefficient, while R1234yf/R1336mzz(Z) shows the lowest heat transfer coefficient. However, the differences in heat transfer coefficients among these three are relatively small, and their overall trends under different operating conditions are similar. It is evident that R134a/R245fa, with its good thermodynamic performance and stability, still holds potential as a transitional working fluid. R1234yf/R1336mzz(Z), with similar physical and thermodynamic properties, is an excellent alternative to R134a/R245fa.

Micro FT-IR spectroscopic measurements of CH4: Experimental calibration with high-pressure and high temperature optical cell (HPOC)

Fourier transform infrared spectroscopy (FTIR) is a prevalent nondestructive in situ analytical technique widely employed for the qualitative characterization of natural fluid inclusions. Presently, the quantitative determination of the temperature, pressure, and composition of natural inclusions stands as a pivotal challenge in the geological application of laser spectroscopy. Through the integration of the capillary high-pressure optical cell (HPOC) technique and Fourier transform infrared spectroscopy, infrared quantitative models for the C–H symmetric stretching band (v3) in the vapor phase of CH4 under varying temperature (40–200 °C) and pressure (20–500 bar) conditions are established for the first time. This accomplishment is achieved through fitting and calculation of infrared spectra. A linear quantitative relationship and the dynamic evolution of infrared spectral parameters (peak area, full width at half maximum, peak height ratio, and peak shifts) concerning temperature, pressure, and density are meticulously investigated. The findings reveal that the peak area and full width at half maximum exhibit an upward trend with increasing pressure and density, and are inversely proportional to temperature. The height ratio (P band/Q band, R band/Q band) experiences an increase as density escalates. Moreover, the CH4v3 band position shows a higher wavenumber shift with increasing temperature, while its position correlates negatively with pressure and density. Thus, this method demonstrates its applicability in deducing the PVT-x properties of CH4-bearing systems, including CH4-rich fluid inclusions, CH4 content within hydrocarbon inclusions, and experimental fluid investigations. In contrast to the Raman quantitative approach, the infrared quantitative formula can be universally adopted in any infrared laboratory owing to the quantitative theory (Beer–Lambert law) governing infrared absorption spectra. By collecting Raman spectra and infrared spectra of pure methane fluid inclusions from the central region of the Alps and subsequently calculating the results using two distinct quantitative methods for fluid inclusions, we have demonstrated the feasibility of applying infrared spectroscopy in natural fluid inclusion studies.

Role of R717 blends in ocean thermal energy conversion organic Rankine cycle

Ammonia (R717) is widely deemed to be the potential working fluid of the ocean thermal energy conversion (OTEC) system. To further improve the performance of OTEC Rankine cycle, R717-based binary non-azeotropic blends are employed as the working fluids, where R134a and R125 are selected as the additives. The thermodynamic model as well as the cost estimation model of OTEC system is developed to demonstrate the potential of power generation. The energy, net efficiency, and Levelized cost of electricity are evaluated and examined for OTEC system employing different blends, encompassing R717/R134a and R717/R125. The results indicate that the thermodynamic and economic indexes of R717-based blends are superior to pure fluids (i.e., R134a, R125, and R717). To maximize the net power, the mass fractions of R717 are 0.1 and 0.5 for the R717/R134a and R717/R125 blends, respectively, in a 30 kW-scale OTEC system, where the net power are higher than that of the pure R717 by 134% and 87%. In addition, R717-based blends perform better in energy cost than pure fluids, with 0–67% lower Levelized cost of electricity. Especially, a large-scale OTEC power plant is more economically profitable than a small one.