Thermophysical Behavior Research Articles

Experimental and comparative theoretical study of thermal conductivity of MWCNTs-kapok seed oil-based nanofluid

Despite the significant potential of nanofluids in energy storage applications, the experimental determination of thermophysical properties is relatively costly and time-consuming. Therefore, the modeling techniques can be used for the accurate estimation of thermo-physical behavior. The predictive models are useful for the understanding of thermo-physical behavior. Due to restrictions on classical models, there is a need to develop more reliable models to simulate the thermophysical behavior of nanofluids. This paper deals with the synthesis and experimental thermal conductivity measurement of the multi-walled carbon nanotubes (MWCNTs)-Kapok seed oil nanofluid. Additionally, two new correlations based on multiple non-linear regression analysis along well as dimensionless analysis are proposed to estimate thermal conductivity with high precision compared to the classical models. Based on the statistical analysis, the prediction accuracy of the proposed model was ranked. Finally, the sensitivity analysis has been carried out in combination with the residual analysis to assure the accuracy of the model parameters of both proposed models and adequacy of estimated values of model parameters, respectively. The results revealed the global minimum values for all parameters at 0% perturbations indicating that the model parameters were estimated with high accuracy and adequacy.

Temperature effect on thermal-diffusivity and heat-capacity and derived values of thermal-conductivity of reservoir rock materials

A laser flash method (micro-flash apparatus LFA 457) and differential scanning calorimeter (DSC 204 F1) were employed to study of the temperature effect on the thermophysical properties (thermal diffusivity $$a$$, heat capacity $$C_{\text{P}}$$ and thermal conductivity $$\lambda$$) of the natural reservoir rock sample. A relationship between the thermophysical properties behavior and the physical–chemical processes (thermal decomposition of pore heavy oil and volatilization of pore fluids) occurring in the rock’s pore fluids during heating in distinct temperature ranges was established. The measurements of the thermal-diffusivity have been made over the temperature range from 295 to 774 K. The isobaric heat capacities (CP) of the same sample were measured in the temperature range from 308 to 768 K. Uncertainties of the measurements are 3% and 1% for $$a$$ and $$C_{\text{P}}$$, respectively. The significant effect of thermal decomposition on the measured values of heat-capacity of reservoir rock sample at high temperatures (above 680 K) was experimentally found. We experimentally observed temperature anomaly of the heat capacity of rock sample in distinct temperature ranges, around 380 K (low-temperature range) and 680 K (high-temperature range).We attribute these anomalies to the dehydration (evolution of the volatile matter, VM, devolatilization) and aromatization of the carbon (thermal decomposition), which are known to occur under heat treatment. This leads to unusual increasing the heat capacity at high temperatures. Measured values of thermal diffusivity ($$a$$) and heat capacity ($$C_{\text{P}}$$) together with density data ($$\rho = { 2210}\;{\text{kg}}\;{\text{m}}^{ - 3}$$) were used to calculate the derived key properties, thermal conductivities ($$\lambda$$) of the rock sample, using very well-known relation, $$\lambda = a\rho C_{\text{P}}$$.

Heat-Absorbing Capacity of High-Heat-Flux Components in Nuclear Fusion Reactors

Nuclear fusion energy is a solution to the substitution of fossil fuels and the global energy deficit. However, among the several problems encountered for realizing a nuclear fusion reactor, the divertor presents difficulties due to the tremendous heat flux (~10 MW/m2) from high-temperature plasma. Also, neutrons produce additional heat (~17.5 MW/m3) from collisions with the materials’ atoms. This may lead to unexpected effects such as thermal failure. Thus, a comprehensive investigation on the divertor module is needed to determine the heat-absorbing capacity of the divertor module so to maintain the effect of incident heat flux. In this study, using an analytical approach and a simulation, the quantitative effect of heat generation on the thermophysical behavior, such as temperature and thermal stress, was analyzed while maintaining the incident heat flux. Then, a correlated equation was derived from the thermal design criteria, namely, the maximum thimble temperature and the safety factor at the vulnerable point. Finally, on the basis of the thermal design criteria, the heat-absorbing capacity of a nuclear fusion reactor in operating conditions was determined. This study contributes to the understanding of the divertor’s effects in nuclear fusion reactors for high-heat-flux and high-temperature applications.

Digital twins probe into food cooling and biochemical quality changes for reducing losses in refrigerated supply chains

Refrigerated transport and storage of mango fruit are essential to maintain quality, reduce food waste and the associated embodied energy losses. Refrigeration is also key to enable successful transcontinental export to distant markets. To minimize the environmental impact of the cold chain and to optimize logistics, a better knowledge of the fruit quality evolution within individual shipments would be extremely valueable. For this purpose, a digital fruit twin is developed, based on mechanistic modeling. This digital twin simulates the thermal behavior of mango fruit throughout the cold chain, based on the measured environmental temperature conditions, namely the air temperature in the vicinity of the fruit. At the same time, the evolution of associated quality attributes, due to enzymatically-driven, temperature-dependent biochemical degradation reactions, is quantified. Also, a biophysical counterpart of real mango fruit – an innovative fruit simulator sensing device – was developed and used for model validation of fruit pulp temperatures. We identified – in-silico – the impact of the unique delivery air temperature history and cold chain length on fruit quality evolution for actual maritime vs. airfreight transport pathways. Digital twins were found to provide complementary insights in the thermophysical behavior of fruit, particularly in supply chains of very perishable species, and for storage at low airflow rates. Such mechanistic modeling enabled to understand, record, and predict where temperature-dependent fruit quality loss occurs in each supply chain. In that way, digital twins can help to improve refrigeration processes and logistics to reduce food losses, thereby making the refrigerated supply chain greener.

The Unusual Thermophysical and Surface Properties of the Daedalia Planum Lava Flows

AbstractDaedalia Planum contains numerous young lava flows with diverse flow morphology. Previous thermal infrared studies avoided this region because of the moderately high visible albedo, assumed to be caused by optically thick dust, and overall low thermal inertia. The Daedalia Planum flows, however, have some of the roughest surfaces on Mars and display an unusual thermophysical behavior that most likely indicates different areal percentages of dust, sand, and lava outcrops. Recent studies suggest that these surfaces contain significant proportions of lava outcrops rising above low‐lying regions of sand with a spatially discontinuous dust layer. A multi‐instrument, multispectral approach combined with prior morphological mapping is applied here to discriminate between individual flows and determine the variation of thermophysical units on the surface. High‐resolution ConTeXt Camera and High‐Resolution Imaging Science Experiment data are used to investigate the flow surfaces and degree of mantling. Thermal Emission Imaging System and Thermal Emission Spectrometer thermal infrared data are analyzed to quantify the thermophysical variations between flows, identify surfaces with minimally mantled lava outcrops, and apply a thermophysical classification to differentiate the surface units. The results demonstrate that the observed thermal variations are due to different distributions of blocky lavas and sand infill. A majority of lava flows with rough surfaces display a diurnal and thermal inertia response indicative of a larger areal percentage of those outcrops versus that of sand and dust. This approach identifies surfaces with more exposed lava outcrops, promising targets for future composition analysis, in regions previously thought to be too dusty for such studies using thermal infrared data.

Study of ferromagnetism, spin-polarization, thermoelectrics and thermodynamics of layered perovskite Ba2FeMnO6 under pressure and temperature

A systematic evaluation of experimentally studied prototypical magnetic, Fm-3m (225) structured double perovskite Ba2FeMnO6 has been explored first time theoritically to investigate the electronic structure, magnetic, thermoelectric and thermodynamic properties. The optimized lattice constant by structural optimization is found to be consistent and in rational accord with the experimental lattice constant. The magnetic interactions were taken into consideration, among which ferromagnetic configuration was found stable. Band structure is predicted using the more sophisticated GGA + Hubbard model, where we find density of states feature half-metallic nature with a direct energy band gap of 3 eV. In addition, semi-classical Boltzmann theory for heat transport is used to check the applicability of the material for thermoelectric applications. Remarkably, thermoelectric Seebeck coefficient as well as spin resolved band structures, reflects the majority of p-type conduction of charge carriers as heat transporters. The conductivity due to phonon lattice vibrations show a decresing trend along the selected range of temperature. Also, complete and precise description of thermo-physical behavior of the vital quantities like Debye temperature, thermal expansion, Grüneisen parameter and specific heat were examined to check its thermodynamical stability against temperature and pressure variation.

Design and Development of Shielded Metal Arc Welding (SMAW) Electrode Coatings Using a CaO-CaF2-SiO2 and CaO-SiO2-Al2O3 Flux System

This study aims to investigate the physicochemical and thermophysical behavior of the electrode coatings produced using CaO-CaF2-SiO2 and CaO-SiO2-Al2O3 ternary phase systems. Electrode coating compositions for welding power plant materials are either patented or not available in the public domain so researchers need to explore the flux coatings to improve the properties of welds produced. An extreme vertices design methodology was used to obtain the different flux combinations to study the effect of electrode coating constituents on weight loss, density, specific heat, change in enthalpy, thermal diffusivity and thermal conductivity. These properties play an important role in achieving better weld quality. X-ray diffraction and Fourier-transform infrared spectroscopy techniques were used to analyze the different phases present and their structural behavior. Multi-response optimization was carried out to obtain the optimum flux composition and study the effect of individual constituents and their interaction effects on the thermophysical and physicochemical properties.

A detailed investigation on the thermo-physical and rheological behavior of MgO/TiO2 aqueous dual hybrid nanofluid

Experimental study of thermo-physical properties and rheological behavior of MgO-TiO2/DW (distilled water) nanofluids with the weight percent of 50:50, 80:20, 20:80, 60:40 and 40:60 are presented in this paper. Dual Hybrid Nanofluids (DHNFs) were prepared by suspending MgO and TiO2 nanoparticles in distilled water in the presence of Sodium Dodecyl Sulfate (SDS) as a surfactant. The temperature dependence of the properties in the range from 15 to 60 °C was measured. All experiments were fulfilled at different solid volume concentrations (0.1–0.5 vol%). The stability time of nanofluids was more than 3 days. The experimental results showed that the thermal conductivity of DHNFs strongly depended on solid volume concentration and rarely enhanced with enhancing temperature. The highest enhancement of thermal conductivity of DHNFs related to solid volume concentration was found to be 21.8% for 80 wt% MgO-20 wt% TiO2 equivalent to 0.3 solid vol% at 60 °C. The dynamic viscosity of DHNFs increased with enhancing solid volume concentration and reduced with enhancing temperature. The rheological behavior of MgO-TiO2/DW DHNFs was Newtonian in all laboratory conditions. The specific heat capacity of DHNFs (80 wt% MgO-20 wt% TiO2) decreased by 1.08% with a solid volume concentration of 0.5%. The temperature had not much impact on density enhancement. Additionally, 3 empirical correlations were presented to predict the aforementioned properties of DHNFs and the calculated results of which are in good agreement with the experimental data.

Zirconium-Doped Hybrid Composite Systems for Ultrahigh-Temperature Oxidation Applications: A Review

The re-entry phase of a space vehicle demands thermal shielding against the heat elicited by an aerodynamic heating process. The quantity of heat spawned in such process is close to 11.35 × 105 kJ m–2 and temperature reaching 8000 °C at the stagnation point on the surface of the re-entry vehicle. Ablative materials are effectual for heat shielding re-entry vehicles, and their performance is improved by various physicochemical techniques. Utilization of ultrahigh-temperature ceramics to enhance the performance of ablative materials has set a new milestone in heat shielding applications. The article briefly introduces the conditions that prevail during a re-entry phase, discusses thermophysical properties that are to be adorned by ablative materials other mere thermal insulation. This review article uniquely discusses the effect of the selection of ceramic filler system on the formation of an oxidation layer, the emissivity of the oxidation layer and thermophysical behavior of the oxidation layer.

Constraining the thermal properties of planetary surfaces using machine learning: Application to airless bodies

We present a new method for the determination of the surface properties of airless bodies from measurements of the emitted infrared flux. Our approach uses machine learning techniques to train, validate, and test a neural network representation of the thermophysical behavior of the atmosphereless body given shape model, illumination and observational geometry of the remote sensors. The networks are trained on a dataset of thermal simulations of the emitted infrared flux for different values of surface rock abundance, roughness, and values of the thermal inertia of the regolith and of the rock components. These surrogate models are then employed to retrieve the surface thermal properties by Markov Chain Monte Carlo Bayesian inversion of observed infrared fluxes. We apply the method to the inversion of simulated infrared fluxes of asteroid (101195) Bennu – according to a geometry of observations similar to those planned for NASA's OSIRIS-REx mission – and infrared observations of asteroid (25143) Itokawa. In both cases, the surface properties of the asteroid – such as surface roughness, thermal inertia of the regolith and rock component, and relative rock abundance – are retrieved; the contribution from the regolith and rock components are well separated. For the case of Itokawa, we retrieve a rock abundance of about 85% for pebbles larger than the diurnal skin depth, which is about 2 cm. The thermal inertia of the rock is found to be lower than the expected value for LL chondrites, indicating that the rocks on Itokawa could be fractured. The average thermal inertia of the surface is around 750 J s−1/2 K−1 m−2 and the measurement of thermal inertia of the regolith corresponds to an average regolith particle diameter of about 10 mm, consistently with in situ measurements as well as results from previous studies.

Study of excess thermodynamic properties of binary systems containing cinnamaldehyde with alcohols supported by ATR-FTIR spectral studies

Abstract The thermophysical behavior of the binary mixtures trans-cinnamaldehyde (CA) with alcohols namely, methanol (MO), ethanol (EO), propanol (PO), isopropanol (IPO) has been studied through the measurement of density (ρ), speed of sound (u), over the entire mole fraction range at T = (298.15, 303.15, 308.15, 313.15) K under atmospheric pressure. Excess volume (VE) and excess isentropic compressibilities ( κ S E ) were also calculated and correlated with Redlich–Kister equation. Except for CA with MO and EO, the remaining investigated systems exhibit positive values of VE and all the four systems exhibit negative κ S E values over the entire composition range. Moreover, all the systems behave differently when the temperature is raised. Besides, ATR-FTIR spectroscopy is used for finding molecular interactions in component molecules.

Design and Development of Submerged Arc Welding Slags Using CaO-SiO2-CaF2 and CaO-SiO2-Al2O3 System

The aim of present study is to investigate the physicochemical and thermophysical behaviour of submerged arc welding slags designed by CaO-SiO2-CaF2 and CaO-SiO2-Al2O3 system. Slag was produced during submerged arc welding using laboratory prepared agglomerated fluxes. By using mixture design and extreme vertices approach twenty one submerged arc welding slags were formulated. X-ray fluorescence technique was used to find the elemental weight percentage of each flux ingredient. The thermophysical behavior such as specific heat, thermal conductivity and thermal diffusivity of each slag was evaluated by hot disc technique. Density of submerged arc welding slags was evaluated at room temperature. FTIR technique was used to study the structural behaviour of submerged arc welding slags. Multi objective optimization technique was performed to derive the optimized slag formulations. Individual, binary and ternary slag constituents have been developed using various regression models for thermophysical and physicochemical properties. Significance level (upto 95%) has been checked for regression models by using F-test.

Uncertainty in the prediction of the thermophysical behavior of new halogenated working fluids

Halogenated olefins can be an attractive alternative to working fluids that are under consideration for phase-out. In order to evaluate the potential of halogenated olefins as working fluids for organic Rankine cycle units with a realistic perspective it is necessary to predict both their primary thermophysical properties and their associated uncertainties. In this work we evaluated the uncertainty of two predictive models, based on the classical group contribution approach and on neural networks, for the critical temperature, critical pressure, acentric factor, and ideal gas heat capacity of halogenated substances. Based on this, guidelines for the most convenient model depending on the property and the fluid molecular structure were provided. The non-linear propagation of the uncertainty through the Peng-Robinson equation of state for the simulation of an organic Rankine cycle unit were also studied. The results suggest that the uncertainty of the predicted properties is highly dependent on the molecular structure for the classical model. The propagation of uncertainties in the simulation of an organic Rankine cycle unit also depends on the saturation properties of the fluid.

Water Clathrates in Nanostructural Organization of Hydrated Ionic Liquids Manifest a Peculiar Density Trend.

Ionic liquid-water binary solutions have significantly expanded the applications of ionic liquids (ILs) in chemical and biological research. Therefore, considerable research has focused on measuring the thermophysical properties of these binary mixtures. From low-to-moderate concentrations of water, several IL/water mixtures exhibit deviations from expected trends in thermophysical behavior. One such example is a unique density trend observed for certain IL classes, which exhibit a characteristic increase in density with the addition of small amounts of water. Since water primarily interacts with the IL anion, such deviations have always been explained in the context of anion-water associations. Surprisingly, however, IL/water mixtures containing different cations but a common lactate anion exhibit similar peculiarities in density trends. Using atomistic level molecular dynamics simulations, we show that diverse density trends are caused by cation-mediated modulations in the IL nanostructure. Depending on its nature, the IL cation can play a dual role in modulating the IL nanostructure: (i) resist water-mediated breakdown of the nanostructure by interacting with the anion very strongly, (ii) further strengthen the nanostructure by incorporating water in the IL framework. The [emim] cation fails to play both roles resulting in the density decrease, while the [tmg] cation fulfills both roles leading to a density rise. The choline cation resists the density fall by inducing the formation of "water-clathrates" in the solution. Such occurrence of clathrates in IL/water binary mixtures, reported for the first time in this study, further emphasizes that the properties of ILs and its mixtures are not merely determined by the chemical nature of the component ions, but also by their unique nanostructural organizations. These unique nanostructural organizations also manifest in their unusual dynamics.

Utilization of shale cuttings in production of lightweight aggregates

The development of technologies for unconventional hydrocarbon exploration requires designing procedures to manage drilling waste that are consistent with the waste management hierarchy. In view of this, the possibility to apply shale drill cuttings as a prospective additive (replacing bentonite) to fly ash used for the production of lightweight aggregates (LWAs) was investigated. Moreover, a facile, waste-free method of LWAs production with using shales was proposed. Cuttings were characterized in terms of their mineralogical and elemental composition (XRD and XRF) as well as thermophysical behavior (TG–DTA and fusibility test). The sintered product, in turn, was assessed taking into account its structure, physicochemical and mechanical properties.It was found that the composition of the shale drill cuttings meets the conditions required for the bloating (as expressed by the SiO2/ΣFlux and Al2O3/SiO2 ratios) and binding processes (Al2O3 content), essential for the aggregates production. In comparison to bentonite, shales provided an additional source of kaolinite, which thermal transformation to mullite is crucial for the formation of mechanically durable structure of the aggregate. Moreover, the bulk density of the sintered product was found to be less than 1200 kg/m3, and the dry particle density below 2000 kg/m3, confirming that the obtained porous material belong to lightweight aggregates with accordance to European standard (UNE-EN-13055-1). The porosity of LWA was found to be higher (even up to 50%), thus the apparent density lower, compared with the reference product containing bentonite. These properties were accompanied by the relatively high crushing resistance which was up to 4.4 N/mm2. Hereby, usefulness of shale drill cuttings for LWAs production was confirmed.

Low dielectric constant silica-containing cross-linked organic-inorganic materials based on fluorinated poly(arylene ether)s

In this work, for the first time, we describe the design and synthesis of novel fluorinated poly(arylene ether)/silica cross-linked materials (FPAE/SiO1.5) through a sol-gel process by using the triethoxysilyl-containing fluorinated polyethers as precursors for both organic and inorganic networks formation. The polyether-based precursors with the sol-gel active species were synthesized via hydrosilylation reaction between triethoxysilane and the corresponding allyl-functionalized FPAE under Pt catalysis. Herein, we present two approaches of hydrolysis triethoxysilane groups to silanol ones within sol-gel chemistry: (1) hydrolysis with air moisture and (2) hydrolysis of the ethoxysilyl groups at the interface between two liquids. The mechanical and thermal properties of the FPAE/SiO1.5 materials were studied depending on the structure of macromolecular chains and synthetic route. Scanning electron and atomic force microscopies were employed to investigate the morphology of the resulting silica-containing cross-linked materials. The resulting FPAE/SiO1.5 films were flexible and tough with tensile strength above 25 МPа, and exhibited high thermal stability, having the initial decomposition temperature about 300°С. For more detailed explanation of the thermophysical behavior of the FPAE/SiO1.5 materials, the synthesis method of new silica-containing organic-inorganic system was developed by the direct hydrosilylation reaction between allyl-functionalized polyethers and 1,1,3,3-tetramethyldisiloxane. All films exhibited high hydrophobic properties (water contact angles above 102°), low dielectric constants and losses at room temperature. In particular, the FPAE/SiO1.5 film prepared from tetrafluorobenzene-based polyether showed the ultra-low dielectric constant of 1.86 at 10 kHz. This makes the obtained polymer FPAE/SiO1.5 materials attractive for microelectronics and many other emerging applications.

Investigating the physicochemical and thermophysical properties of submerged arc welding fluxes designed using TiO2-SiO2-MgO and SiO2-MgO-Al2O3 flux systems for linepipe steels

Submerged arc welding is widely used for manufacturing of pipelines. In the present study physicochemical and thermophysical properties of TiO2-SiO2-MgO and SiO2-MgO-Al2O3 based rutile acidic SAW fluxes were studied. Twenty one flux formulations were designed based on the extreme vertices design methodology. Fluxes were analyzed using x-ray fluorescence (XRF), TGA, DSC, Hot-disc and XRD techniques. Bond length behavior of different fluxes were analyzed using Fourier transform infrared spectroscopy. For finding the thermal stability and enthalpy change of fluxes TGA and DSC was performed in the range 25–900 °C. Hot disc technique was used to estimate the thermophysical behavior such as specific heat, thermal diffusivity and thermal conductivity of each flux. Density and grain fineness number of flux was investigated at room temperature. Multi response optimization was carried out to derive the optimized flux combinations.

Low-temperature specific heat capacity measurements and application to Mars thermal modeling

Data returned from Martian missions have revealed a wide diversity of surface mineralogies, including in geological structures interpreted to be sedimentary or altered by liquid water. These terrains are of great interest because of their potential to document the environment at a time when life may have appeared. Intriguingly, Martian sedimentary rocks show distinctly low thermal inertia values (i.e. 300 - 700 Jm−2K−1s−1/2, indicative of a combination of low thermal conductivity, specific heat capacity, and density). These low values are difficult to reconcile with their competent bedrock morphologies, whereas hundreds of bedrock occurrences, interpreted as volcanic in origin, have been mapped globally and display thermal inertia values > 1200 Jm−2K−1s−1/2. Bedrock thermal inertia values are generally assumed to be driven by their bulk thermal conductivity, which in turn is controlled by their micro- and macro-physical properties (i.e., degree and style of cementation in the case of detritic rocks, horizontal fractures and layering, etc.), and not by their density (well-known from terrestrial analog measurements, and with modest variability) or specific heat capacity (generally uncharacterized for non-basaltic materials below room temperature). In this paper, we demonstrate that specific heat capacity cannot be a potential cause for the differential thermophysical behavior between magmatic and sedimentary rocks through a series of experimental Cp(T) measurements at 100–350 K using differential scanning calorimetry. The results on 20 Martian-relevant minerals investigated in this work indicate that these materials exhibit very similar specific heats, ranging from 0.3–0.7 Jg−1K−1 at 100 K to 0.6–1.7 Jg−1K−1 at 350 K. When used in a Martian thermal model, this range of Cp values translate to very small surface temperature differences, indicating that uncertainty in composition (and its effect on the specific heat) is not a noticeable source of thermal inertia variability for indurated units on Mars. We therefore conclude that the low thermal inertia value of sedimentary rocks compared to magmatic/volcanic rocks is likely due to their low apparent bulk conductivity, which bears information on their internal physical structure. Future work combining the analysis of thermal observations acquired at various local times and seasons will help further characterize this heterogeneity.

Thermophysical and tribological properties of dispersions based on graphene and a trimethylolpropane trioleate oil

The objective of this work is to study the tribological and thermophysical properties of nanolubricants composed by a trimethylolpropane trioleate (TMPTO) oil, and graphene nanoplatelets (GnP). For this aim, nanolubricants based on TMPTO with 0.05, 0.10, 0.25 and 0.50 wt% of graphene nanoplatelets were prepared. The dependence on temperature and concentration of the viscosity, density and speed of sound was determined by means of a rotational viscometer and two mechanical oscillation densimeters. Likewise, the antifriction and antiwear properties of these nanolubricants were analyzed. For this purpose, tribological tests were carried out at room temperature in a tribometer operating in ball on plate configuration and in reciprocating mode under a working load of 2.5 N. A 3D optical profilometer was used to analyze the wear track through the width of the scar. As regards thermophysical behavior of density and viscosity, both increase as the concentration of nanoparticles increases, whereas the speed of sound slightly diminishes when the GnP concentration increases. The best antifriction-antiwear performance was obtained for the nanolubricant containing 0.25 wt% in GnP.

Thermophysical behavior of three algal biodiesels over wide ranges of pressure and temperature

The knowledge of density and viscosity is important both for the optimization of diesel engines operation and the fuel quality specification. To this end, the present work focuses on the study of these thermophysical properties for three algal biodiesels. The samples were produced by transesterification of dry biomass supplied from different microorganisms, the marine strain Nannochloropsis gaditana, the freshwater strain Scenedesmus almeriensis and the freshwater cyanobacteria Spirulina platensis. The protocol of production is detailed. The purity of biodiesels is low, ranging from 63,7% to 68,1% because the produced biodiesel was not purified in order to evaluate the characteristics of the crude biodiesel produced from microalgae. The relative new technique based on a simple process is attractive for an industrial point of view. The (FAMEs) profile of the biodiesels were characterized using a GC–MS technique. The density measurements were performed over expanded ranges of pressure [0,1–140 (MPa)] and temperatures [293,15 (K)–353,15 (K)] compatibles with their engines applications. The isothermal compressibility and the isobaric thermal expansion were estimated within the same experimental range by density differentiation. The cinematic viscosity was also measured for the three biodiesels at atmospheric pressure for temperatures ranging from 293.15 (K) to 353.15 (K). The storage stability of the biodiesels was assessed in terms of reproducibility of the measured properties. Spirulina biodiesel was not affected by oxidation process. Additionally, its density and viscosity values meet the standards specifications that support the use of this production process.