Search Results (6)

Thermal oils have been utilized as heat transfer fluids for several decades in many applications, including industrial facilities, power plants and solar receiver systems. Despite their large employment, very few data are available about oils behavior under thermal stress and related degradation processes. For these reasons, the thermal stability of a silicone-based diathermic oil, Bluesil FLD 550 HT, was investigated in the present work. A laboratory-scale set-up was assessed to perform controlled heating tests, and fresh and thermally aged oils samples were analyzed to determine changes in chemical composition and thermo-physical features. Degradation products in the gaseous and vapor phase were also detected and analyzed by online and offline measurements. The obtained results are compared with the ones present for aromatic oils, largely employed as heat transfer media. Bluesil showed a higher thermal resistance compared to aromatic materials, and, thanks to its low volatility together with a high chemical stability, it was successfully tested up to 500 °C. According to its polymeric structure, thermal degradation processes occur mainly through Si-O bond scission, leading to both the segmentation of silicone chains and the formation of cross-linked species as byproducts. Full article

In the present work, a new kind of nanocomposite (NC)-based solid component was prepared for formulating nanofluids (NFs). The NC comprised metal oxide (titanium dioxide, TiO₂) dispersed in a conducting polymer with polyaniline (PANI) and chemically linked silyl–alkyl units in it (PSA) that were designated as T-PSA NC. The NFs with ethylene glycol (EG) as a base fluid were prepared with T-PSA NCs with various compositions of TiO₂ and PSA as well for various concentrations of T-PSA NCs. The scanning electron microscopic evaluation of the NC revealed that PSA deposition on TiO₂ nanoparticles (NPs) decreased particle agglomeration. The PSA coating on the TiO₂ NPs did not influence the crystalline structure of the TiO₂ NPs, according to the X-ray diffraction patterns. The thermophysical characterization and molecular interaction features of the NFs at 303 K including a novel inorganic–organic T-PSA NC, were detailed. Furthermore, the stability of the T-PSA NC-based NFs was investigated experimentally using the zeta potential, and the particle size distribution change was analyzed using the dynamic light scattering (DLS) method. The T-PSA NCs had particle sizes that were significantly bigger than pristine PSA and pure TiO₂. Most of the preparation conditions used to produce the T-PSA NCs resulted in moderately stable suspensions in EG. The results revealed that the ultrasonic velocity increased with the increase in the concentration of T-PSA NC mass % in the NFs, the refractive index and thermal conductivity increased with the increase in the concentration, and the surface tension exhibited a linear change when the ratio of mass % concentration of the T-PSA NCs increased. The combined presence of components that synergistically contribute to the electro, thermal, optical, and rheological properties is expected to attract advanced applications for NFs. Full article

Modern heat-conducting materials require special attention to analyze their thermophysical properties. Compared to classical methods, thermal lens spectrometry (TLS) has advantages due to its high sensitivity to physical and chemical composition. To avoid a systematic error in the analysis of complex systems, it is necessary to realize the limits of the applicability of the method. This study considers the features of thermal-diffusivity measurements by TLS in the stationary state for dispersed systems with absorbances up to 0.05. The limits of applicability of the method in analyzing heterogeneous systems are shown, and a mathematical apparatus is proposed for indicating a systematic error in finding thermal diffusivity that does not exceed 1%. Graphene oxide (GO), which has attractive physicochemical properties, was used as the object of analysis. GO belongs to 2D objects, the study of which requires highly sensitive methods and special attention when discussing the results. The thermophysical properties of aqueous dispersions of graphene oxide in a wide range of concentrations (up to 2 g/L) and lateral sizes (up to 4 µm) were studied by TLS. It has been found that with increasing nanophase concentration, the thermal diffusivity of graphene oxide dispersions passes through a minimum, which can be used in solving thermal insulation problems. It has been established that prolonged laser irradiation of the dispersion leads to a change in thermal diffusivity, which indicates the photochemical reduction of graphene oxide. Full article

The current analysis aims to exhibit the nanoparticles of Al₂O₃ + Cu-water hybrid nanofluid flow for Darcy–Forchheimer with heterogeneous–homogeneous chemical reactions and magnetic field aspects past a stretching or shrinking cylinder with Joule heating. This paper performed not only with the hybrid nanofluid but also the shape of Al₂O₃ and Cu nanoparticles. The model of single-phase hybrid nanofluid due to thermophysical features is utilized for the mathematical formulation. In the present exploration equal diffusions factors for reactants and auto catalyst are instituted. The system of governing equations has been simplified by invoking the similarity transformation. The numerical computations are invoked due to the function bvp4c of Matlab, with high non-linearity. Numerical outcomes illustrated that; sphere shape nanoparticles presented dramatic performance on heat transfer of hybrid nanofluid movement; an opposite behavior is noticed with lamina shape. The local Nusselt number strengthens as the transverse curvature factor becomes larger. In addition, the homogeneous–heterogeneous reactions factors lead to weaken concentration fluctuation. Full article

The effect of the soft and hard polyurethane (PU) segments caused by the hydrogen link in phase-separation kinetics was studied to investigate the morphological annealing of PU and thermoplastic polyurethane (TPU). The significance of the segmented PUs is to achieve enough stability for further applications in biomedical and environmental fields. In addition, other research focuses on widening the plastic features and adjusting the PU–polyimide ratio to create elastomer of the poly(urethane-imide). Regarding TPU- and PU-nanocomposite, numerous studies investigated the incorporation of inorganic nanofillers such as carbon or clay to incorporating TPU-nanocomposite in several applications. Additionally, the complete exfoliation was observed up to 5% and 3% of TPU–clay modified with 12 amino lauric acid and benzidine, respectively. PU-nanocomposite of 5 wt.% Cloisite^®30B showed an increase in modulus and tensile strength by 110% and 160%, respectively. However, the nanocomposite PU-0.5 wt.% Carbone Nanotubes (CNTs) show an increase in the tensile modulus by 30% to 90% for blown and flat films, respectively. Coating PU influences stress-strain behavior because of the interaction between the soft segment and physical crosslinkers. The thermophysical properties of the TPU matrix have shown two glass transition temperatures (T_g’s) corresponding to the soft and the hard segment. Adding a small amount of tethered clay shifts T_g for both segments by 44 °C and 13 °C, respectively, while adding clay from 1 to 5 wt.% results in increasing the thermal stability of TPU composite from 12 to 34 °C, respectively. The differential scanning calorimetry (DSC) was used to investigate the phase structure of PU dispersion, showing an increase in thermal stability, solubility, and flexibility. Regarding the electrical properties, the maximum piezoresistivity (10 S/m) of 7.4 wt.% MWCNT was enhanced by 92.92%. The chemical structure of the PU–CNT composite has shown a degree of agglomeration under disruption of the sp2 carbon structure. However, with extended graphene loading to 5.7 wt.%, piezoresistivity could hit 10⁻¹ S/m, less than 100 times that of PU. In addition to electrical properties, the acoustic behavior of MWCNT (0.35 wt.%)/SiO₂ (0.2 wt.%)/PU has shown sound absorption of 80 dB compared to the PU foam sample. Other nanofillers, such as SiO₂, TiO₂, ZnO, Al₂O₃, were studied showing an improvement in the thermal stability of the polymer and enhancing scratch and abrasion resistance. Full article

Agriculture can provide biomass for bioproducts, biofuels and as energy feedstock with a low environmental impact, derived from carbohydrate, protein and oil annual crops, as well from lignocellulosic crops. This paper presents the thermophysical and chemical features of camelina and crambe straw depending on nitrogen fertilisation rate with a view to their further use in a circular bioeconomy. A two-factorial field experiment was set up in 2016, with camelina and crambe as the first factor and the N fertilizer rate (0, 60 and 120 kg·ha⁻¹·N) as the second factor. Ash content in crambe straw (6.97% d.m.) was significantly higher than in camelina straw (4.79% d.m.). The higher heating value was higher for the camelina (18.50 MJ·kg⁻¹·d.m.) than for the crambe straw (17.94 MJ·kg⁻¹·d.m.). Sulphur content was also significantly higher in camelina than in crambe straw. An increase in nitrogen content with increasing fertilisation rate was visible in the straw of both species (from 1.19 to 1.33% d.m., for no fertilisation and for a rate of 120 kg·ha⁻¹·N, respectively). Crambe straw contained more than five times more chlorine than camelina straw. In conclusion, despite certain adverse properties, camelina and crambe straw can be an alternative to other types of biomass, both for direct combustion, gasification and in the production of second-generation biofuels. Full article