Papers by Keyword: Temperature Gradient

Abstract: In high voltage direct current (HVDC) cable accessories, there is a large difference of conductivity between crosses linked polyethylene (XLPE) and liquid silicone rubber (LSR), especially considering the presence of temperature gradient and the changing of operating temperature. In this paper, nano silicon carbide (SiC) was adopted to prepare five kinds of nanocomposites with filler fractions of 1%, 2%, 3%, 4% and 5%, respectively. The conductivity and DC breakdown strength of SiC/LSR nanocomposites were measured under different temperatures. The results show that the nano SiC doping does not has the great influence on LSR DC breakdown strength, and the nano SiC doping can improve the conductivity of LSR effectively, which can realize the conductivity matching between the LSR and XLPE to homogenize the electric field distribution in cable accessory.

Abstract: We consider the problem of a density-graded cellular rod in a temperature gradient field axially subjected to a mass impact. Two-dimensional cell-based finite element models and one-dimensional shock models are employed to explore the mechanisms of deformation and wave propagation. The yield stress distribution in a cellular specimen depends on both the density gradient field and the temperature gradient field. The stress distribution and the yield stress distribution are analyzed. For the increasing yield stress along the impact direction, one shock front propagates from the proximal end to the distal end of the specimen. For the decreasing yield stress along the impact direction, two shock fronts propagate in opposite directions and the one close to the proximal end ceases at a particular time. The predicted stresses of the extended shock models are compared well with the numerical results.

Abstract: The coating of the fluorescent-lamp material inside the fluorescent tube is prone to defect such as dark line formation. A one-dimensional mathematical model based on Navier-Stokes equation, which describes the flow of drying coating on horizontal planar substrates, was developed to investigate the defect formation. The effect of temperature distribution on surface tension gradient was incorporated into the model, to quantify defect formation in drying coating. The results showed that, temperature-induced surface tension gradient plays a major role in defect formation while the effect of pressure gradient is insignificant. The evaporation rate and viscosity affect the defect thickness and spread, and also the defect formation time. The temperature gradient seems to have the largest influence on surface tension gradient, thus defect formation. The model developed can be used as a process analysis tool in industrial applications of fluorescent tube coating.

Abstract: A model for simulating mushy zone resolidification in a temperature gradient is presented. For describing macroscopic mass transport in the liquid phase in the mushy zone, an extended diffusion equation is solved numerically using the Finite Difference Method. Temperature dependent local equilibria at each position in the mushy zone are calculated using the thermodynamic software package ChemApp. The resolidification model treats multicomponent alloying systems and accounts for multiphase equilibria. Simulation results for peritectic Cu-40wt%Al and eutectic Al-5wt%Si-1wt%Mg alloys are compared with microstructures from temperature gradient annealing experiments. It is shown that the model is well suited to predict mushy zone resolidification in multicomponent and multiphase alloys. The predicted evolution of the liquid fraction is qualitatively in full agreement with the observed microstructures, including local remelting at the peritectic temperature prior to resolidification, an effect that was first predicted by the model and confirmed by the experiments.

Abstract: An experimental approach employing temperature and concentration gradients is presented that is suitable for determining impurity diffusion coefficients in a single experimental cycle. The Al-Cu system is used to illustrate the feasibility of the method. In a single phase α-Al solid solution, concentration gradients are generated by exposing a cylindrical sample to steep temperature gradients and by annealing until the initially formed mushy zone is re-solidified. The annealing is performed such that a symmetric, ramp shaped profile in the form of a roof is generated. The sample is then again exposed to a temperature gradient at somewhat lower temperatures for an extended time period. The symmetric profile then becomes asymmetric due to the varying diffusion coefficient along the sample. Information on the pre-exponential factor D₀ and the activation energy for diffusion Q_D is retrieved from the asymmetry of the resulting concentration profile. The asymmetry becomes increasingly pronounced with longer diffusion times, yielding an increasing accuracy of the diffusion coefficients. The experimental approach is generally applicable to alloy systems with finite solubility.

Abstract: This thesis makes a feasibility analysis of the method and effect of collecting geothermal energy from the waste oil wells, based on which it foresees the economic, environmental and social benefits brought by geothermal energy collection from the waste oil wells. With the advances of technology, geothermal energy collection methods will continue to improve, and bring even greater benefits.

Abstract: This paper built the three dimension mechanics model of CRTSII slab ballastless track structure on subgrade with ANSYS software. Analysis the influence of deformation and stress characteristics caused by different temperature gradients and the coupling action of temperature gradients and train loads under different work conditions, including no-separated, separated, and multiple-slabs separated with the cement asphalt mortar layer. The results show that, temperature gradients on track slab is one of the main reasons which caused the gap appearing between the bottom of slab track and cement asphalt mortar elastic cushion. And the joint main cause the deterioration of vibration of track slab, accelerating the deterioration of the cement asphalt mortar layer.

Abstract: This study examined the effect of fluid convection on microstructures of directionally solidified high-chromium white cast iron (ASTM A532-87 Class III) with carbon equivalents of 4.5. The iron was first melted in a high-frequency induction furnace, and then poured into a sandwiched cylindrical Furan resin sand mold. The middle part is a chilled copper mold kept cold by circulating water, enabling simultaneous directional solidification in the upper and lower zones. The microstructure thus solidified is affected by directionally chilled between these parts. Distribution of temperature in the mold during cast solidification was measured by K-type thermocouples. The measured results show that the lower zone has stronger thermal convection and faster cooling rate than the upper zone. The lower zone has smaller liquidus and solidus gradients than the upper zone.

Abstract: Based on evolutionary structural optimization (Abbr. ESO) theory, the mathematical model using for topology optimal design of heat conductive structure is constructed by deleting the elements which temperature gradient is lower .Based on the selecting logic method, the numerical calculating program is developed by using APDL command in ANSYS. The feasibility and universality of this method have been well verified in the numerical calculating examples.

Abstract: In this article the computational algorithm and solution technique of the problem of identifying temperature field as well as strain and stress components throughout the rod length exposed to heat flows supplied to cross section areas of both ends and heat exchange in its lateral surface on the basis of heat quantity variation law are developed. Herewith the tested rod physical and mechanical properties are taken into account. The solutions so acquired are presented in a graphical form. Certain dependencies between temperature pivotal values and capacities of the set heat flows are found.