Width Of Heat Source Research Articles

Accurate estimation of thermal properties for AlGaN/GaN HEMTs on diamond

For accurate estimation of the thermal characteristics of AlGaN/GaN high electron mobility transistors on diamond, the anisotropic thermal conductivities of polycrystalline diamond (PCD) and GaN with their thickness dependences are included in the finite element simulation model, of which the PCD thermal conductivity kPCD is calculated through detailed analyses of the grain sizes in the directions parallel and vertical to the interface and relative phonon-grain boundary scatterings. In addition, the GaN thermal conductivity kGaN is the result of an approximate solution of the phonon Boltzmann transport equation. To investigate the effects of anisotropic GaN and PCD thermal conductivity, four cases of thermal conductivity models are compared: anisotropic kGaN and kPCD, anisotropic kGaN with constant kPCD, constant kGaN with anisotropic kPCD, and constant kGaN and kPCD. Then the maximum channel temperature simulated from the four above-mentioned models and the errors relative to the case of anisotropic kGaN and kPCD are investigated with respect to thermal boundary resistance, GaN layer thickness, gate pitch, heat source width, and power dissipation. The results show that the combination of anisotropic kPCD and constant kGaN overestimates the maximum channel temperature rise, and using constant kPCD and anisotropic kGaN underestimates the maximum channel temperature rise for almost all the simulations in the text. However, the channel temperature stemming from constant kPCD and kGaN is generally closer to the case with anisotropic PCD and GaN thermal conductivity.

Multi-objective optimization of mixed convection air cooling in an inclined channel with discrete heat sources

In this paper, a multi-objective optimization of mixed convection air-cooling of two identical discrete heat sources mounted in an inclined channel is conducted to obtain the optimal design parameters, using Response Surface Methodology (RSM) and desirability function approach. Reynolds number (Re), inclination of the channel (r) and the width of the discrete heat source (b) are selected as the input parameters. The computational simulations are done for different Reynolds numbers (25-Re-250), inclination angles of the channel (0o-r-360o) and the width of the heat source (5-b-10 mm). A central composite design (CCD), which comes under the RSM approach, with design parameters was used for analysis of variance (ANOVA). A second-order regression models were developed to correlate the design parameters (Re, r and b) with mean Nusselt number (Nu) and maximum temperature (TMax). The optimum values of design parameters produce the lowest value of maximum temperature (TMax) with a higher mean Nusselt number (Nu) are Reynolds number (Re)=209.94, inclination angle of the channel (r)=330o and heat source width (b)=5.13 mm.

CONJUGATE NATURAL CONVECTION IN A POROUS ENCLOSURE SANDWICHED BY FINITE WALLS AND SUBJECTED TO CONVECTION COOLING CONDITION

Steady conjugate natural convection heat transfers in a two-dimensional enclosure filled with fluid saturated porous medium is studied numerically. The two vertical boundaries of the enclosure are kept isothermally at same temperature, the horizontal upper wall is adiabatic, and the horizontal lower wall is partially heated. The Darcy extended Brinkman Forcheimer model is used as the momentum equation and Ansys Fluent software is utilized to solve the governing equations. Rayleigh number (1.38 ≤ Ra ≤ 2.32), Darcy number (3.9 * 10-8), the ratio of conjugate wall thickness to its height (0.025 ≤ W ≤ 0.1), heater length to the bottom wall ratio (1/4 ≤  ≤ 3/4) and inclination angle (0°, 30° and 60°) are the main considered parameters. The presented results show the effect of these parameters on the heat transfer and fluid flow characteristics. These results include streamlines, isotherm patterns, and local and average Nusselt number for different values of the governing parameters. It is found that either increasing the Rayleigh number and the ratio of conjugate wall thickness to its height (d/H) or decreasing the ratio of heat source width to bottom wall (l/L), the average Nusselt number is increased. Also, it was observed that the average Nusselt number does not change substantially with inclination angle.

Effects of heat source geometric parameters and arc efficiency on welding temperature field, residual stress, and distortion in thin-plate full-penetration welds

The Goldak’s double-ellipsoid volumetric heat source model is commonly used for arc welding in numerical simulation. Usually, heat source geometric parameters and arc efficiency need to be calibrated in thermal analysis until a good agreement with experiments is achieved. However, the influence of individual heat source geometric parameters and arc efficiency on welding temperature field, residual stress, and distortion is still unclear. In this study, this influence has been systematically investigated in a thin-plate full-penetration weld by methods of both numerical simulation and experimental method. The predicted and measured results indicate that the location of HAZ boundary and the Δt8/5 time can only be influenced by arc efficiency (significantly) and heat source width (slightly) in thin-plate full-penetration welds. Furthermore, the variation of arc efficiency can significantly affect welding residual stress and distortion, while the reasonable change of heat source geometric parameters has a slight effect. In this study, a calibration procedure of heat input model in FE simulation of thin-plate full-penetration welds is provided.

Effects of Model Reduction on Simulated Temperature Fields in Milling

Temperature fields generated in machining processes affect, among other internal material loads, the material modifications in the workpiece surface layer and therefore influence the functional performance of the final component. In particular this might become critical for multipass machining where the amount of heat in the workpiece is accumulated with every path and layer being cut. In the present work a finite element modelling approach for the milling of a complete steel plate is proposed that minimizes computation time while providing a reasonable accuracy of predicted temperature fields. The milling process is modelled as a moving heat source taking into account material removal. Computation time can be reduced up to 98% by systematically increasing the width of the material removal and the heat source width. The effects of the model reduction regarding the temperature fields are investigated in comparison to a reference simulation and furthermore to experiments.

Investigation of the effects of tool micro-geometry and coating on tool temperature during orthogonal turning of quenched and tempered steel

Reliable information about tool temperature distribution is of central importance in metal cutting. Application of dedicated charge-coupled device (CCD) sensor based near infrared (0.85–1.1 μm) imaging technique to the orthogonal turning of quenched and tempered steel is presented. Special attention was paid to the role of calibration on the interpretation of isotherms. Experimental results from systematic studies devoted to the role of heat source width, cutting parameters, edge micro-geometry and coating indicate the flexibility and reliability of this approach. Results compare favourably with those from other techniques capable of indicating tool isotherms as well as with numerical models based on FEM.

磁気記憶装置ヘッド・媒体インタフェースにおける熱点温度推定法 第１報 表面温度推定式の導出

The feasibility is investigated of estimating the flash temperature of intermittent magnetic head/media contacts using the output of a magnetoresistive (MR) micro-sensor embedded in the head. On the assumption that a uniform square heat source moves on the head surface at a high speed, an apporoximate relationship between the surface temperature rise and the sensor output change is presented by applying the profile method in heat conduction theory. In order to calculate the surface temperature using this relationship, it is necessary to know the heat source width. In this paper, the width is assumed to be equal to its length that can be observed from the sensor output increasing duration. A finite difference numerical simulation is performed to verify the estimation accuracy of this method for different sensor heights in the range from 2.5 to 20 L' m. The influences of the thermal properties of the sensor surrounding material are also made clear. As a result, in the case of MR sensor NiFe and its surrounding material A12O3-TiC, the surface temperature can be estimated with an accuracy of about 10% for sensors of less than 10 u- m high and a heat source duration more than 0.5μs.

Thermal Analysis for Thermoplastic Composite Tow/Tape Preheating and Pultrusion

The on-line consolidation of thermoplastic composites is a relatively new technology that can be used to manufacture composite parts with complex geometries. The localized melting/solidification technique employed in this process can reduce the residual stresses and allow for improved dimensional stability and performance. An additional advantage of this technique is elimination of the curing steps that are necessary in the processing of thermoset-matrix composites. This paper discusses analytical and numerical anisotropic thermal analysis for preheating and/or pultrusion of impregnated composite tows or tapes. Heat of melting/solidification is included in the form of a heat generation term. A separation of variable method is employed to solve the governing equations analytically. In the numerical analysis, the governing equations are discretized using a nonuniform mesh and solved employing a finite difference approach. The processing parameters, such as processing speed, heat intensity, heat source width, etc., as well as material properties are incorporated in the analysis. The maximum error between the analytical solution and the numerical result is found to be 1%.

Numerical Study of Forced Convection in a Partially Porous Channel With Discrete Heat Sources

A numerical study was performed to analyze steady laminar forced convection in a channel partially filled with a fluid-saturated porous medium and containing discrete heat sources on the bottom wall. Hydrodynamic and heat transfer results are reported for the configuration in which the porous layers are located above the heat sources while the rest of the channel is nonporous. The flow in the porous medium was modeled using the Brinkman-Forchheimer extended Darcy model. Parametric studies were conducted to evaluate the effects of variable heat source spacing and heat source width on heat transfer enhancement and pressure drop in the channel. The results indicate that when the heat source spacing was increased within the range considered, there was a negligible change in heat transfer enhancement while the pressure drop decreased significantly. When the heat source width was decreased, there was a moderate increase in heat transfer enhancement and a significant decrease in pressure drop.

Thermal Analysis of in-situ Thermoplastic Composite Tape Laying

This paper presents analytical and numerical thermal analysis for melting and consolidating impregnated composite tapes in the presence of a localized heat source. This analysis also leads to the prediction of the processing window for a given tape-laying configuration. Heat of melting/solidification is included in the form of a heat generation term. A separation of variables method is employed to solve the governing equations ana lytically. In the numerical analysis, the governing equations are discretized using a non uniform mesh and are solved using a finite difference approach. The processing parame ters, such as consolidation speed, heat intensity, heat source width, etc., as well as material properties are incorporated within the analysis. The results show large thermal gradients in the vicinity of the consolidation point. The error between the analytical solu tion and the numerical result is found to be 3 % for the maximum temperature, and the maximum error for the temperature over the entire domain is observed to be 7%. The effects of processing speed, heat intensity, and the width of the local heat source are inves tigated, and the overall optimization of the process is discussed.

A simplified analysis of the residual longitudinal stresses and strains due to the gas-cutting and welding of thin steel plate

The paper describes a simplified analysis of the residual longitudinal stresses induced in a steel plate by a moving heat source of finite width. The effects of a point source are treated as a limiting case. A linear temperature distribution, identical at every cross section and subject to the condition of zero heat loss, is shown to be an adequate model for the purpose of the analysis. The relationship of the residual stresses to the linear heat input, to the width of heat source and to the stiffness of the plate is established. The particular results for a point source agree closely with more complex published work.