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This paper presents a numerical investigation of lubricating slider bearings with conducting couple stress fluids using externally applied magnetics fields. The modified two-dimensional magnetohydrodynamic couple stress Reynolds-type equation is obtained. This governing equation is resolved numerically by using finite difference scheme, which involves the Gauss–Seidel method to compute the bearing characteristics. Numerical results using different considered values of the couple stress and Hartman number are presented. These results demonstrate that the transverse magnetic field and couple stress effects are significant.

A three-dimensional thermohydrodynamic model is developed to predict non-Newtonian lubricant behavior in slider bearings ,and channel flow. The generalized Reynolds equation is established using the concept of generalized Newtonian fluids (GNF) and the temperature field is determined with the energy equation. The chosen rheological models are the power-law, Bingham, and Hershel-Bulkley models. The last two models hold uniformly in yielded and unyielded regions using the approach proposed by Papanastasiou. The results present the evolution of the velocity, pressure, and thermal fields. The power loss, load capacity, and friction coefficient are analyzed. Comparisons are made with Newtonian lubricants and other recent non-Newtonian computational analyses. [DOI: 10.1115/1.2736732] Keywords: non-Newtonian lubricants, thermohydrodynamic lubrication, slider bearing flow, channel flow

The La0.8Na0.1MnO3 oxide was prepared by the solid-state reaction and annealed in air. The X-ray diffraction data reveal that the sample is crystallized in a rhombohedral structure with R3c space group. Magnetic study shows a second-order magnetic phase transition from ferromagnetic to paramagnetic state at the Curie temperature TC = 295 K. In addition, the magnetizations as a function of temperature and the magnetic field is used to evaluate the magnetic entropy change ΔSM. Then, we have deduced that the La0.8Na0.1MnO3 oxide has a large magnetocaloric effect at room temperature. Such effect is given by the maximum of the magnetic entropy change ΔSMmax=5.56, and by the Relative cooling power (RCP) factor which is equal to 235 under a magnetic field of 5 T. Moreover, the magnetic field dependence of the magnetic entropy change is used to determine the critical exponents β, γ, and δ which are found to be β=0.495, γ=1.083, and δ=3.18. These values are consistent with the prediction of the mean field theory (β=0.5, γ=1, and δ=3). Above all, the temperature dependence of electrical resistivity shows a metal-insulator transition at Tρ. The electrical resistivity decrease when we apply a magnetic field giving a magnetoresistance effect in the order of 60% at room temperature. [ABSTRACT FROM AUTHOR]

The La0.8Na0.1MnO3 oxide was prepared by the solid-state reaction and annealed in air. The X-ray diffraction data reveal that the sample is crystallized in a rhombohedral structure with R3c space group. Magnetic study shows a second-order magnetic phase transition from ferromagnetic to paramagnetic state at the Curie temperature TC = 295 K. In addition, the magnetizations as a function of temperature and the magnetic field is used to evaluate the magnetic entropy change ΔSM. Then, we have deduced that the La0.8Na0.1MnO3 oxide has a large magnetocaloric effect at room temperature. Such effect is given by the maximum of the magnetic entropy change ΔSMmax=5.56, and by the Relative cooling power (RCP) factor which is equal to 235 under a magnetic field of 5 T. Moreover, the magnetic field dependence of the magnetic entropy change is used to determine the critical exponents β, γ, and δ which are found to be β=0.495, γ=1.083, and δ=3.18. These values are consistent with the prediction of the mean field theory (β=0.5, γ=1, and δ=3). Above all, the temperature dependence of electrical resistivity shows a metal-insulator transition at Tρ. The electrical resistivity decrease when we apply a magnetic field giving a magnetoresistance effect in the order of 60% at room temperature. [ABSTRACT FROM AUTHOR]

A systematic investigation of the effect of Strontium (Sr) doping on the structure, magnetic behavior, and magnetocaloric properties of the manganite perovskites La 0.67 Ca 0.33 - x Sr x Mn 0.98 Ni 0.02 O 3 (LCSMNO) has been performed. The Sr content x takes three values, namely 0.15, 0.2, and 0.3. The sol–gel technique has been employed in the preparation of our compounds. The structural analysis has revealed that our samples exhibit a rhombohedral structure with R 3 ¯ c space group symmetry, close to ambient temperature. A second-order paramagnetic (PM) to ferromagnetic (FM) transition has been validated over the Curie temperature range TC between 319 K (x = 0.15) to 353 K (x = 0.3), based on Arrott's analysis with the behavior of the master curve. According to the calculations made, the maximal values of the magnetic entropy change (- Δ S M max ) resulting through Landau's theory and the ones obtained by the classic Maxwell relationship are very close. We find the value of (- Δ S M max ) is equal to 4.386, 4.469, and 4.250 J Kg−1 K−1, respectively, for x = 0.15, 0.2, and 0.3, when an external magnetic field μ0H = 5 T is applied. Based on the results of the study in this work, we find that controlled Sr doping adapts perfectly to the magnetic as well as the magnetocaloric properties of the LCMNO, which plays an important role in the implementation of many potential applications of the material in the field of near-ambient temperature magnetic refrigeration technology. [ABSTRACT FROM AUTHOR]

La0.8Ca0.2 - x[larger_open_square]xMnO3 (x = 0.00, 0.10, and 0.20) perovskite was prepared by the conventional solid-state reaction and annealed at 1473 K. X-ray diffraction and scanning electron microscopy shown the existence of a secondary phase attributed to the unreacted Mn3O4 oxide. The magneto transport properties have been investigated based on the temperature dependence of the resistivity ρ(T) measurements under several applied magnetic fields. We note that the La0.8Ca0.2MnO3 (x = 0.00) sample has a classical metal-insulator transition at Tρ. But we have observed that the lacunars samples (x = 0.10 and 0.20) include a metallic and insulator behavior simultaneously below Tρ and the resistivity is dominated by tunneling through the barriers associated with the insulating phase. In other words, the calcium deficiency favors the enhancement of the insulator behavior. The electrical resistivity is fitted with the phenomenological percolation model, which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. Furthermore, we found that the estimated results are in good agreement with experimental data. Above all, the resistivity dependence on the temperature and magnetic field data is used to deduce the magnetic entropy change. We have found that these magnetic entropy change values are similar to those calculated in our previous work from the magnetic measurements. Finally, we have found an excellent estimation of the magnetic entropy change based on the Landau theory. [ABSTRACT FROM AUTHOR]

CaCu2.8Ni0.2Ti4O12 ceramics were elaborated using the solid-state reaction technic. The pellets were annealed at 1000 °C for 24 h. The X-ray diffraction (XRD) analysis proves the main phase formation of our sample crystallize in the cubic structure with Im 3 ¯ space group. The diffuse reflectance analysis allow us to calculate the optical band gap energy which is equal to 3.172 eV. The dielectric properties of our compound were studied using complex impedance spectroscopy showing a lowering in dielectric loss (tan δ = 0.07) at 1 kHz and at room temperature. The impedance studies reveal the presence of temperature dependent dielectric relaxation. Thus, the electrical modulus studies show that the relaxation is associated with grain boundaries effects. The activation energy calculated from the electric modulus spectra, related to the electrical relaxation, is found to be 0.60 eV. This result suggests the hopping mechanism of oxygen vacancies produced at grain boundaries in relaxation processes. [ABSTRACT FROM AUTHOR]

The structural, magnetic and magnetocaloric properties of La 0.67 Ca 0.23 Sr 0.1 Mn 0.98 Ni 0.02 O 3 nano-crystalline manganite are investigated systematically. The compound is elaborated based on Pechini sol–gel method and then annealed at 1000 °C for 24 h. X-ray powder diffraction shows that, the sample crystallizes in a rhombohedral structure with R 3 ¯ C space group. A magnetization versus temperature study shows that the compound exhibits a second-order magnetic transition from a ferromagnetic to a paramagnetic state at a Curie temperature T C = 296 K. To evaluate the magnetic entropy change Δ S M , we measure the magnetization as a function of temperature and magnetic field. At ambient temperature, we find that La 0.67 Ca 0.23 Sr 0.1 Mn 0.98 Ni 0.02 O 3 sample has a very important magnetocaloric effect (MCE). In a magnetic field variation of 5 T, this MCE is explained by a maximum of magnetic entropy change Δ S M max and a big RCP values at 4.92 J. Kg - 1 K - 1 and 145 J/kg, respectively, around room temperature (296 K), which give the possibility of technologic application in magnetic refrigeration area. In addition, we find an admirable estimate of the magnetic entropy change, which is based on the Landau theory. Finally, we use the magnetic field dependence of Δ S M to determine the critical exponents of the system and we find that β = 0.39, γ = 1.35, and δ = 4.43, are very close to those predicted to the 3D-Heisenberg model. These results indicate that the present compound is one of candidate materials for magnetic refrigerators near room temperature. [ABSTRACT FROM AUTHOR]

La0.8Ca0.2MnO3 manganese oxides have been prepared by the conventional solid-state reaction. The samples crystallize in the orthorhombic structure with Pnma space group. A first-order magnetic phase transition from ferromagnetic to paramagnetic state is observed at the Curie temperature that is found to be around 241 K. The magnetic and magnetocaloric properties have been simulated using a phenomenological model. The maximum of magnetic entropy change is of order 8.2 J/kg K for an applied magnetic field of 5 T, and the adiabatic temperature change is found to be of 4 K under a same magnetic field; this high value gives the sample the possibility of technologic application in the magnetic refrigeration area. The simulated results of magnetization and magnetic entropy change are compared with the experimental measurements. Finely, we found a good agreement between experimental and theoretical results. [ABSTRACT FROM AUTHOR]

La0.8Ca0.2MnO3 manganese oxides have been prepared by the conventional solid-state reaction. The samples crystallize in the orthorhombic structure with Pnma space group. A first-order magnetic phase transition from ferromagnetic to paramagnetic state is observed at the Curie temperature that is found to be around 241 K. The magnetic and magnetocaloric properties have been simulated using a phenomenological model. The maximum of magnetic entropy change is of order 8.2 J/kg K for an applied magnetic field of 5 T, and the adiabatic temperature change is found to be of 4 K under a same magnetic field; this high value gives the sample the possibility of technologic application in the magnetic refrigeration area. The simulated results of magnetization and magnetic entropy change are compared with the experimental measurements. Finely, we found a good agreement between experimental and theoretical results. [ABSTRACT FROM AUTHOR]

The critical behavior associated with the magnetic phase transition has been investigated by in La 0.8 Na 0.2− x □ x MnO 3 (0.00 ≤ x ≤ 0.15) (□ is the sodium deficiency). The critical exponents are estimated by various techniques such as the modified Arrott plot, Kouvel–Fisher plot and critical isotherm technique. Compared to standard models, the critical exponent values determined in our work are close to those expected by the tricritical model (β = 0.25, γ = 1, and δ = 5) for x = 0.00 and 0.05 samples and by mean field theory (β = 0.5, γ = 1, and δ = 3) for x = 0.10 and 0.15 samples. We conclude that the Na deficiency rate affect the critical exponents. [ABSTRACT FROM AUTHOR]