Steady-state Conduction Analysis Research Articles

Analysis of thermal conductivity in HI-LEDs lighting materials

The present study devised a measurement system to estimate the thermal conductivity of electronic product materials, especially in HILEDs lighting materials, exhibiting distinct thermal characteristics by conducting thermal performance experiments and theoretical analyses. First, steady-state conduction analysis with thermal resistance method was investigated on three composite material substrates of unknown heat conduction coefficients through a substrate material named Bakelite of low thermal conductivity revealing stable quality. Second, one-dimension semi-infinite transient conduction analysis was utilized to investigate metal materials with high thermal conductivities. Results showed that the Bakelite experimental module was verified for 62.5 % of the original wattages, which closest to the thermal conductivity 0.233 W/m-K of the Bakelite. And these composite materials M1, M2 and M3 composed of polymer and epoxy were 1.311, 0.844 and 2.403 W/m-K, respectively. The thermal performance experiments were investigated and the results have proved the correctness of the theoretical model. According to the experimental results, calculating the temperature value of the metal materials comprising cotton insulation and the transient analysis, this study determined the temperature error to be less 20 %. Consequently, a transient measurement system and method for metal materials with high heat conduction coefficients was established. Finally, the results of this work are the useful thermal conductivity method to facilitate rapid analysis in the future.

The role of interparticle contact in conductive properties of random particulate materials

The effective conductivity of material systems consisting of contacting particles is studied computationally using a model of monodisperse circular disks. The electrical or thermal conductivity is computed by modeling the relevant mechanical contact problem followed by a steady-state conduction analysis. The interparticle contact resistance is incorporated via the introduction of gap conductance in the contact pairs. Monte Carlo simulations show that the overall effective conductivity is much lower than that predicted by the model using an overlap assumption, even when the contact resistance is zero. The results also display a nonlinear relationship between the contact resistance and the effective conductivity. Therefore, in practical applications involving particulate inclusions of high density, the interfacial contact must be considered to reliably predict the relevant transport properties. Although the methodology is developed in the context of circular disks, it can be extended to deal with more general situations.

THEORETICAL DETERMINATION OF ANISOTROPIC EFFECTIVE THERMAL CONDUCTIVITY IN TRANSFORMER WINDINGS

A two-dimensional region representing a typical transformer winding cross-section is studied analytically and numerically. The winding region is characterized by layers of round or flattened conductors separated in one direction by insulating paper. The voids within the windings are filled with transformer oil. The theoretical limits of the effective thermal conductivity in two directions are determined using both the parallel isotherms and the parallel adiabats approaches. A steady state conduction analysis in the composite region is performed using standard commercial finite element analysis software. The conductor curvature radius and contact widths were varied relative to the paper thickness for a typical value of oil thermal conductivity and for aluminum and copper conductors. It was found that the effective thermal conductivity was strongly affected by the paper and that there was negligible difference between results for aluminum and copper conductors. It was observed that the ratio of the effective thermal conductivities in the two directions could be 300 in some cases.