物理化学的科学探究式教学研究——以标准生成热(焓)和标准燃烧热(焓)为例

对科学探究式教学方法在物理化学标准生成热(焓)和标准燃烧热(焓)的教学中的运用进行了一些尝试和实践,包括制定科学探究的教学目标;通过数据分析,探讨结论;模拟设计实验仪器等。     

Coherent structures in trailing-edge cooling and the challenge for turbulent heat transfer modelling

The present paper tests the capability of a standard Reynolds-Averaged Navier–Stokes (RANS) turbulence model for predicting the turbulent heat transfer in a generic trailing-edge situation with a cutback on the pressure side of the blade. The model investigated uses a gradient-diffusion assumption with a scalar turbulent-diffusivity and constant turbulent Prandtl number. High-fidelity Large-Eddy Simulations (LES) were performed for three blowing ratios to provide reliable target data and the mean velocity and eddy viscosity as input for the heat transfer model testing. Reasonably good agreement between the LES and recent experiments was achieved for mean flow and turbulence statistics. The LES yielded coherent structures which were analysed, in particular with respect to their effect on the turbulent heat transfer. For increasing blowing ratio, the LES replicated an also experimentally observed counter-intuitive decrease of the cooling effectiveness caused by the coherent structures becoming stronger. In contrast, the RANS turbulent heat transfer model failed in predicting this behaviour and yielded significantly too high cooling effectiveness. It is shown that the model cannot predict the strong upstream and wall-directed turbulent heat fluxes caused by large coherent structures, which were found to be responsible for the counter-intuitive decrease of the cooling effectiveness.     

Two numerical modelings of free convection heat transfer using nanofluids inside a square enclosure

This work describes the numerical simulation of natural convection heat transfer of Cu–water nanofluids in a square enclosure for Rayleigh numbers varying from 10³ up to 10⁵. Two different numerical approaches were used: the finite volume method and the finite element method. The nanofluids were assumed to be single-phase fluids with modified thermal properties obtained from experimental results and theoretical models. The results showed that the Nusselt number for nanofluids was basically the same as that obtained for the base fluid. Therefore, the enhancement observed in the heat transfer coefficient was significant due to the augmentation in the thermal conductivity.     

“Magnetic-ribs” in fully developed laminar liquid–metal channel flow

This paper documents the numerical investigation of the effects of non-uniform magnetic fields, i.e. magnetic-ribs, on a liquid–metal flowing through a two-dimensional channel. The magnetic ribs are physically represented by electric currents flowing underneath the channel walls. The Lorentz forces generated by the magnetic ribs alter the flow field and, as consequence, the convective heat transfer and wall shear stress. The dimensionless numbers characterizing a liquid–metal flow through a magnetic field are the Reynolds (Re) and the Stuart (N) numbers. The latter provides the ratio of the Lorentz forces and the inertial forces. A liquid–metal flow in a laminar regime has been simulated in the absence of a magnetic field (Re_H = 1000, N = 0), and in two different magnetic ribs configurations for increasing values of the Stuart number (Re_H = 1000, N equal to 0.5, 2 and 5). The analysis of the resulting velocity, temperature and force fields has revealed the heat transport phenomena governing these magneto-hydro-dynamic flows. Moreover, it has been noticed that, by increasing the strength of the magnetic field, the convective heat transfer increases with local Nusselt numbers that are as much 27.0% larger if compared to those evaluated in the absence of the magnetic field. Such a convective heat transfer enhancement has been obtained at expenses of the pressure drop, which increases more than twice with respect to the non-magnetic case.     

Flow of Oldroyd-B fluid with nanoparticles and thermal radiation

The two-dimensional boundary layer flow of an Oldroyd-B fluid in the presence of nanoparticles is investigated. Convective heat and mass conditions are considered in the presence of thermal radiation and heat generation. The Brownian motion and thermophoresis effects are retained. The nonlinear partial differential equations are reduced into the ordinary differential equation (ODE) systems. The resulting ODE systems are solved for the series solutions. The results are analyzed for various physical parameters of interest. Numerical values of the local Nusselt and Sherwood numbers are also computed and analyzed.     

Second-order slip MHD flow and heat transfer of nanofluids with thermal radiation and chemical reaction

The effects of the second-order velocity slip and temperature jump boundary conditions on the magnetohydrodynamic (MHD) flow and heat transfer in the presence of nanoparticle fractions are investigated. In the modeling of the water-based nanofluids containing Cu and Al₂O₃, the effects of the Brownian motion, thermophoresis, and thermal radiation are considered. The governing boundary layer equations are transformed into a system of nonlinear differential equations, and the analytical approximations of the solutions are derived by the homotopy analysis method (HAM). The reliability and efficiency of the HAM solutions are verified by the residual errors and the numerical results in the literature. Moreover, the effects of the physical factors on the flow and heat transfer are discussed graphically.     

Periodic orbits, damped transitions and targeted energy transfers in oscillators with vibro-impact attachments

We study complex damped and undamped dynamics and targeted energy transfers (TETs) in systems of coupled oscillators, consisting of single-degree-of-freedom primary linear oscillators (LOs) with vibro-impact attachments, acting, in essence, as vibro-impact nonlinear energy sinks (VI NESs). First, the complicated dynamics of such VI systems is demonstrated by computing the VI periodic orbits of underlying Hamiltonian systems and depicting them in appropriate frequency–energy plots (FEPs). Then, VI damped transitions and distinct ways of passive TETs from the linear oscillators to the VI attachments for various parameter ranges and initial conditions are investigated. As in the case of smooth stiffness nonlinearity [Y. Lee, G. Kerschen, A. Vakakis, P. Panagopoulos, L. Bergman, D.M. McFarland, Complicated dynamics of a linear oscillator with a light, essentially nonlinear attachment, Physica D 204 (1–2) (2005) 41–69], both fundamental and subharmonic TET can be realized in the VI systems under consideration. It is found that the most efficient mechanism for VI TET is through the excitation of highly energetic VI impulsive orbits (IOs), i.e., of periodic or quasiperiodic orbits corresponding to zero initial conditions except for the initial velocities of the linear oscillators. In contrast to NESs with smooth essential nonlinearities considered in previous works, VI NESs are capable of passively absorbing and locally dissipating significant portions of the energies of the primary systems to which they are attached, at fast time scale. This renders such devices suitable for applications, like seismic mitigation, where dissipation of vibration energy in the early, highly energetic regime of the motion is a critical requirement.     

Characteristic and microstructure of the microarc oxidized TiO2-based film containing P before and after chemical- and heat treatment

Chemical- and heat treatment was performed to modify the surface of the microarc oxidized TiO₂-based (TOB) film containing P to produce nano-scale compounds containing Na, Ti and O elements. In the TOB film, anatase and rutile nanocrystals were randomly distributed in P-doped matrix. On the surface of the chemically treated TOB (C-TOB) film, amorphous titanium oxide containing Na shows nano-scale ribbonlike morphology. Na, Ti and O show uniform distribution in the outer layer of the C-TOB film along surface depth. Chemical treatment did not alter the surface roughness of the TOB film obviously; however, it improved its hydrophilic property. Heat treatment has no influence on the chemical states of Ti, Na and O, as well as wetting ability, elemental composition and atomic concentration in the outer layer of the C-TOB film. However, the phase compositions and surface morphology of the C-TOB film after heat treatment are dependent on the heat treatment temperature.     

The role of Pb ions doping in the mechanism of chromate adsorption by goethite

Pure and 0.384% Pb²⁺ ions doped goethite samples were prepared in the laboratory by the coprecipitation method. The laboratory-prepared goethite samples were characterized for pH of point of zero charge (pH_pzc), surface area, XRD, TG-DTA, TEM, SEM and FTIR analysis, which suggest that the Pb²⁺ ions are incorporated into the crystals of goethite and are also present on the surface in the hydroxylated form. Chromate adsorption studies were carried out in the concentration range 0.25-2.01 mmol L⁻¹ at pH 3, 5 and 7, which show that maximum chromate is adsorbed at the lowest pH of 3 by both the samples of goethite. Effect of temperature on the adsorption of chromate, in the range 303-323 K, shows that the process of adsorption is endothermic in case of pure goethite and exothermic in case of Pb-doped goethite. The values of isosteric heat of adsorption were positive for pure goethite and negative for Pb-doped goethite, which are consistent with the effect of temperature on the process of adsorption. Langmuir isotherm was found applicable to the experimental data. FTIR analysis and equilibrium pH changes reveal that at pH 3 outersphere while at pH 5 and 7 innersphere complexation is the dominant mechanism for chromate adsorption by both the samples of goethite.     

Exergy analysis of ramjet

An exergy analysis of possible regimes of energy supply to the air flow in the ramjet duct is carried out. A condition for the supply of a given heat amount to supersonic flow and a condition of the passage across the sound velocity are obtained for a duct with variable cross-sectional area. An analysis of the flow in a model ramjet duct at a pulsed-periodic energy supply is carried out. For a clear demonstration of possible schemes of heat supply in such a duct, a diagram in the temperature-exergy coordinates is proposed. A duct configuration in which the heat supply to supersonic flow is realized with regard for the limitation of the gas static temperature is proposed.