Search results for " Conduction"
showing 10 items of 373 documents
A Meshless Approach for Electromagnetic Simulation of Metallic Carbon Nanotubes
2009
In this paper, a study on the electromagnetic behaviour of a single wall carbon nanotube model is described. The electrons available for conduction are treated as a thin cylindrical layer fluid and their motion is described by means of classical hydrodynamics equations in linearized form. These equations are solved in time domain using the Smoothed Particle Hydrodynamics method. The method suitably handled runs on GRID environment.
Nonstationary heat conduction in a stator
1996
In this chapter we describe a method for computing the 3d nonstationary temperature field in the lamination pack of a stator of a synchronous or asynchronous (induction) motor with a centrifugal, meander or chamber ventilation (see [Křižek, Preiningerova]). The stator of a motor has quite a complicated geometrical form. Moreover, it consists of anisotropic materials which have very different heat conductivities, e.g., 332.8 [W/mK] for copper wires and 0.2 [W/mK] for their insulations. This causes big jumps in coefficients of the appropriate heat conduction equation, and is the main source of numerical difficulties in practical calculations.
Enhanced Conductivity of Composite Membranes Based on Sulfonated Poly(Ether Ether Ketone) (SPEEK) with Zeolitic Imidazolate Frameworks (ZIFs)
2018
The zeolitic imidazolate frameworks (ZIFs) ZIF-8, ZIF-67, and a Zn/Co bimetallic mixture (ZMix) were synthesized and used as fillers in the preparation of composite sulfonated poly(ether ether ketone) (SPEEK) membranes. The presence of the ZIFs in the polymeric matrix enhanced proton transport relative to that observed for SPEEK or ZIFs alone. The real and imaginary parts of the complex conductivity were obtained by electrochemical impedance spectroscopy (EIS), and the temperature and frequency dependence of the real part of the conductivity were analyzed. The results at different temperatures show that the direct current (dc) conductivity was three orders of magnitude higher for composite …
The effect of a liquid CTBN rubber modifier on the thermo-kinetic parameters of an epoxy resin during a pultrusion process
2003
Abstract Rheo-kinetic behaviour of an epoxy resin, coupled with an anhydride hardener, with different CTBN liquid rubber concentration (0–15 phr), used in fibre reinforced plastics, was analysed comparing experimental data with theoretical models. The modelling of technological pultrusion process for thermoset matrix composites, developed through a numerical code realised with MATLAB, is reported, too. The model includes conduction and cure heat, degree of cure and viscosity evolution during the curing within the die. Considerable differences in process condition, using different rubber amount, are obtained. The numerical modelling of process conditions shows that the CTBN rubber presence i…
Ion conduction in the KcsA potassium channel analyzed with a minimal kinetic model.
2004
We use a model by Nelson to study the current-voltage and conductance-concentration curves of bacterial potassium channel KcsA without assuming rapid ion translocation. Ion association to the channel filter is rate controlling at low concentrations, but dissociation and transport in the filter can limit conduction at high concentration for ions other than ${\mathrm{K}}^{+}$. The absolute values of the effective rate constants are tentative but the relative changes in these constants needed to qualitatively explain the experiments should be of significance.
Measurement of the surface resistivity and electrical conductivity of carbon nanotube sheets using the resonant post-method
2016
Abstract The dielectric post-resonant measurement method is extended to characterize the conduction properties of carbon nanotube sheets in the GHz frequency range ( 3 GHz f 20 GHz ) without the need for external contacts or the necessity of carbon coating. Three low-loss reference dielectrics ( TiO 2 , BaTi 4 O 9 , Teflon) with known dielectric properties are used. Conductivity values of various metals (steel, lead, brass, aluminium, copper) of the order 106–107 S/m were measured to show the suitability of the method. The electrical conductivity of the carbon nanotube sheets could be determined to approximately 1.7·105 S/m.
Heat under the microscope
2014
[Introduction] Recent advances in computational and spectroscopic tools offer new insights into the nature of thermal conduction at ever-finer length scales and ways to control it. Heat conduction is familiar to us all and yet requires a wide range of physics—statistical mechanics, crystallography, and quantum mechanics among them—to fully explain. At the macroscale, heat conduction can be described as a diffusion process in which energy moves along a temperature gradient. The heat flux dissipated by the gradient depends on a material property, the thermal conductivity, as described by the constitutive relation, Fourier’s law. The heat equation, which is derived from Fourier’s law and the c…
Nanowires: A route to efficient thermoelectric devices
2019
Miniaturization of electronic devices aims at manufacturing ever smaller products, from mesoscopic to nanoscopic sizes. This trend is challenging because the increased levels of dissipated power demands a better understanding of heat transport in small volumes. A significant amount of the consumed energy in electronics is transformed into heat and dissipated to the environment. Thermoelectric materials offer the possibility to harness dissipated energy and make devices less energy-demanding. Heat-to-electricity conversion requires materials with a strongly suppressed thermal conductivity but still high electronic conduction. Nanowires can meet nicely these two requirements because enhanced …
Space charge limited current mechanism in Bi2S3 nanowires
2016
We report on the charge transport properties of individual Bi2S3 nanowires grown within the pores of anodized aluminum oxide templates. The mean pore diameter was 80 nm. Space charge limited current is the dominating conduction mechanism at temperatures below 160 K. Characteristic parameters of nanowires, such as trap concentration and trap characteristic energy, were estimated from current-voltage characteristics at several temperatures.
Low-Temperature Coherent Thermal Conduction in Thin Phononic Crystal Membranes
2016
In recent years, the idea of controlling phonon thermal transport coherently using phononic crystals has been introduced. Here, we extend our previous numerical studies of ballistic low-temperature heat transport in two-dimensional hole-array phononic crystals, and concentrate on the effect of the lattice periodicity. We find that thermal conductance can be either enhanced or reduced by large factors, depending on the the lattice period. Analysis shows that both the density of states and the average group velocity are strongly affected by the periodic structuring. The largest effect for the reduction seen for larger period structures comes from the strong reduction of the group velocities, …