Thermal Simulation Method Research Articles

An Analytical Convergence Study of the Forced Air Cooling in Electronic Packaging

A forced air thermal cooling model has been developed by using Ansys software, to study at each step of the input power, what will be the corresponding junction temperature Few approaches were used to ensure the accuracy of the thermal simulation method, ranging from the minimum number of simulation iterations required in the finite element analysis, to the residuals target in terms of the momentum, continuity and energy equations, the objective is to ensure the simulations are converged and provide the reasonable results, which is also an indication of how the partial equations have successfully been solved with analytic method. The thermal resistance network in the model has also been established, mainly to understand the next level details in this thermal model by analyzing the correlation between the air flow and the thermal resistance at each junction, and also to understand the effect of the air flow with respect to the total thermal resistance. The thermal analytic model that built has proven to be healthy and it requires 200 iterations to achieve steady state with the reasonable temperature output, and there is no convergence issue in which the continuity, momentum and energy graphs showed the healthy trend, it achieved 10-7 for continuity, energy and momentum equations. it shows that when the air flow reduces the overall thermal resistance increases, in other word, reducing the air flow will increase the thermal resistance

A Review of Structural and Thermal Analysis of Traction Motors

Traction motors for hybrid electric powertrains have stringent operational requirements including delivering high torque at low speeds and high power at cruising speeds. They require a wide speed range and high efficiency along with high power density and mechanical robustness. Traction motors and their drives are also expected to deliver superior performance throughout the lifetime of the vehicle. Considering the extreme loading conditions, the motors should be designed for very strict thermal requirements. Therefore, all electromagnetic, mechanical, and thermal variables must be thoroughly addressed in motor design. In this review paper, a summary of current structural and thermal simulation methods applicable for traction motors is presented. Prominent design issues along with appropriate analysis methodologies are explained. In addition, brief case studies of electromagnetic, structural, and thermal analysis performed at Fiat Chrysler Automobiles (FCA) US LLC are highlighted. A detailed list of references and an analysis road map are also provided to aid practicing engineers and researchers involved in electric machine design.

Effect of nitrogen on the microstructures and mechanical properties in simulated CGHAZ of vanadium microalloyed steel varied with different heat inputs

The microstructures and mechanical properties of simulated weld coarse heat affected zone (CGHAZ) of two kinds of vanadium microalloyed steel, i.e. V–Ti and V–N–Ti steel, had been studied using the welding thermal simulation method on a Gleeble-3800 thermal simulator, under different welding heat input. The yield strength of simulated CGHAZ decreases with heat input increasing. The 50% fraction appearance transition temperature (50% FATT) of simulated CGHAZ in V–N–Ti steel decreased at first, and then increased. While for the V–Ti steel, 50% FATT increased with t8/5 increasing. The V–N–Ti steel had a better combination of strength and toughness of simulated CGHAZ compared with V–Ti steel. Increasing nitrogen cannot only refine the austenite grain size, but also simulate V-rich cap part forming on the TiN core part which can be as intragranular ferrite nucleation positions, resulting in refining the effective grain size and raising cleavage fracture stress of simulated CGHAZ. The detrimental effect of the free N on toughness can be remedied by austenite grain and effective grain size refinement.

Hybrid thermal link-wise artificial compressibility method

Thermal flow prediction is a subject of interest from a scientific and engineering points of view. Our motivation is to develop an accurate, easy to implement and highly scalable method for convective flows simulation. To this end, we present an extension to the link-wise artificial compressibility method (LW-ACM) for thermal simulation of weakly compressible flows. The novel hybrid formulation uses second-order finite difference operators of the energy equation based on the same stencils as the LW-ACM. For validation purposes, the differentially heated cubic cavity was simulated. The simulations remained stable for Rayleigh numbers up to Ra=108. The Nusselt numbers at isothermal walls and dynamics quantities are in good agreement with reference values from the literature. Our results show that the hybrid thermal LW-ACM is an effective and easy-to-use solution to solve convective flows.

Phase-state identification bypass method for three-phase thermal compositional simulation

In this paper, we propose a strategy to bypass the phase identification of fluid mixtures that can form three, or more, phases. The strategy is used for reservoir simulation of multicomponent, three-phase, thermal compositional displacement processes. Since the solution path in compositional space is determined by a limited number of “key” tie-simplexes, the proposed “bypass” method uses information from the parameterized tie-simplexes and their extensions. The tie-simplex parameterization is performed in the discrete phase-fraction space. Once the phase-fraction space is discretized, a conventional three-phase flash is used adaptively to compute the phase states at the discretization nodes. If all discretization vertices of a given discrete cell, in phase-fraction space, have the same phase state, then this state is assigned to the entire cell and expensive flash calculations are bypassed. We demonstrate the robustness and efficiency of our phase identification bypassing strategy for several cases with three-phase flow, including a six-component ES-SAGD (enhanced solvent SAGD) model.

Simulating heat transfer from moving rigid bodies using high-order ghost-cell based immersed-boundary method

In this paper we develop a new high-order ghost-cell based Immersed Boundary Method (IBM) for flow and thermal simulation of multiphase flow system with moving bodies, based on our previous edition with only stationary boundary treatment. The newly developed approach is validated by comparing with earlier reported simulation and experimental results of both the pressure drag coefficient of a prescribed harmonic in-line oscillating sphere and the trajectory, velocity history of a free falling sphere under gravity and the rising of a spherical catalyst particle in an enclosure, using relatively coarse mesh resolution. Excellent agreement is obtained, demonstrating the accuracy and efficiency of our newly developed method. Finally, we employ the new method to investigate the cooling process of a freely settling spherical particle under gravity, aiming at revealing the impact of natural convection on particle cooling. It turns out that the heat transfer and hydrodynamics interaction is the most obvious when the Richardson number is the largest in our simulations. When the Reynolds number equals, the Nusselt number is always higher for the no buoyancy case than the case with buoyancy force.

Fast alternating direction implicit method for efficient transient thermal simulation of integrated circuits

SummaryThis paper presents fast alternating direction implicit (FADI) method for efficient transient thermal simulation of integrated circuits. The FADI method is formulated from Peaceman–Rachford's ADI and Douglas–Gunn's ADI methods. The update procedure of the proposed method has basic implicit form that features derivative‐free right‐hand side and hence, better efficiency and conciseness. Subsequently, through the basic implicit form of FADI method, the relationship between classical Peaceman–Rachford's and Douglas–Gunn's ADI methods can be clarified and elucidated in detail. A unified boundary condition that can cater to common kinds of boundary conditions in thermal simulation is also introduced. To further accelerate FADI method, the graphics processing unit is also utilized through Compute Unified Device Architecture implementation. It is shown that high efficiency gain can be achieved using the proposed FADI method through large time step size and data parallelism, while maintaining stability and good accuracy. As numerical illustration, an integrated circuit structure with microchannel cooling is demonstrated. Numerical results further ascertain the cooling effect of the microchannels. Copyright © 2015 John Wiley & Sons, Ltd.

P‐67: Research on Thermal Mura in Edge‐Type LCD Module and Improvement by Heat Sink Design

AbstractThis paper provides a way to quantify thermal mura by heat stress on panel using thermal and structure coupling simulation method. Meanwhile, we use this method to investigate the influence of heat sink width and propose its critical value under different power density, which is meaningful to module design.

Numerical Simulation of Subcooled Boiling Inside High-Heat-Flux Component with Swirl Tube in Neutral Beam Injection System

In order to realize steady-state operation of the neutral beam injection (NBI) system with high beam energy, an accurate thermal analysis and a prediction about working conditions of heat-removal structures inside high-heat-flux (HHF) components in the system are key issues. In this paper, taking the HHF ion dump with swirl tubes in NBI system as an example, an accurate thermal dynamic simulation method based on computational fluid dynamics (CFD) and the finite volume method is presented to predict performance of the HHF component. In this simulation method, the Eulerian multiphase method together with some empirical corrections about the inter-phase transfer model and the wall heat flux partitioning model are considered to describe the subcooled boiling. The reliability of the proposed method is validated by an experimental example with subcooled boiling inside swirl tube. The proposed method provides an important tool for the refined thermal and flow dynamic analysis of HHF components, and can be extended to study the thermal design of other complex HHF engineering structures in a straightforward way. The simulation results also verify that the swirl tube is a promising heat removing structure for the HHF components of the NBI system.

Mineral Transformation in Char and Its Effect on Coal Char Gasification Reactivity at High Temperatures Part 3: Carbon Thermal Reaction

The reaction between mullite and carbon in char between 1200 and 1500 °C during coal gasification was investigated by XRD, FactSage, and molecular simulation. The mechanism of thermal reaction is discussed by both thermal dynamic and molecular simulation methods. The effect of carbon thermal reaction on the char gasification was also discussed. The results show that the carbon thermal reaction between mullite and carbon in char only occurs in argon above 1300 °C and the mullite could react with carbon completely to form moissanite (SiC) and corundum (Al2O3) at 1500 °C in argon. This reaction is restrained by the existence of CO, and it occurs between 1300 and 1500 °C when the partial pressure of CO in the atmosphere is less than 0.4 according to results of the thermodynamic calculation. In hence, carbon thermal reaction only happens in two following situations during gasification. One is the melted ash or slag over the surface of the char and the other is that the char particle is wholly covered by melted...

Investigation on solidification conditions in functionally Si-gradient Al alloys using simulation and cooling curve analysis methods

During recent years, functionally graded alloys have been widely produced by melt processing routes to achieve advanced material properties. In this paper, the new cast-decant-cast (CDC) method has been used to produce the gradient in concentration of Si particles in cross section of final Al–Si castings. For this purpose, the hypereutectic LM28 and hypoeutectic LM25 alloys were selected for each step casting into the steel mold. Cooling curve thermal analysis and simulation methods were applied to investigate the cooling behavior of first poured LM28 alloy and improve the accuracy of CDC process by determining the curves of solid fraction and temperature profiles. The final products were studied through optical microscopy, image analysis, and Brinell hardness measurement. The results showed that the silicon concentration decreased along transition zone between two alloys by increasing the decanting time in the order of 25, 40, and 50 s. This can be due to the lower temperature of exterior LM28 alloy in semi-solid state and shorter solidification time of interior LM25 alloy. This can lead a to reduction of the diffusion rate of elemental silicon along the transition zone. The microscopic scale of transition zone between two alloys developed the maximum thickness of 438 μm and hardness value of 83 HB comparing with the hardness of 88 and 62 HB for external and internal alloys, respectively. The microscopic observations and hardness evaluations confirmed the creation of functionally Si-gradient products.

Hot Ductility of DSS and Its Microstructure Observation During Hot Deformation

By selecting several typical duplex stainless steels (DSS), i. e., 00Cr22Ni5Mo3N, 00Cr21Ni2Mn5N and 00Cr25Ni7Mo4N, as research materials, hot ductility characteristic of DSS was studied by thermal simulation method and microstructure evolution during hot compression was observed through TEM. The results show that the optimum hot ductility temperature range of DSS is 1050–1200°C. 00Cr25Ni7Mo4N exhibits the worst hot ductility and 00Cr21Ni2Mn5N has similar hot ductility to 00Cr22Ni5Mo3N. During hot compression, the dynamic recovery of austenite occurs in DSS while the dynamic recovery and reerystallization of ferrite take place in 00Cr22NioMo3N and 00Cr21Ni2Mn5N, but only the dynamic recovery of ferrite can be observed in 00Cr25Ni7Mo4N.

Effects of Mo, Cr and Nb on microstructure and mechanical properties of heat affected zone for Nb-bearing X80 pipeline steels

The microstructure and mechanical properties of welding heat affected zone (HAZ) of three typical X80 pipeline steels, i.e. Mn–Cr–Nb, Mn–Mo–Nb and/or Mn–Cr–Mo–Nb steels, have been studied using the welding thermal simulation method on a Gleeble-3500 thermal simulator. The results show that the chemical compositions and welding process parameters have significant effects on the microstructure and properties of HAZ. With increase of the cooling rate, the amount of microstructure transformed at lower temperature increases, and the microstructure becomes finer, furthermore, the strength and toughness of HAZ show a rising trend. Within the range of the peak temperature from 600 to 1350°C, there are two brittle zones and one major strength weakening zone in HAZ, especially for high-Nb added Cr steel, weaken of HAZ is very serious. Effects of the key chemical elements such as Mo, Cr and Nb on microstructure transformation of HAZ have been discussed. Although these three alloy system steels in this work display good weldability, the Mn–Mo–Nb and/or Mn–Cr–Mo–Nb steels show better combination of strength and toughness of HAZ compared with the Mn–Cr–Nb steels. Therefore, for high-Nb steels, it is necessary to add suitably Mo to improve the toughness and strength of HAZ, especially, increase the strength.

Deformation behavior and microstructure evolution of wrought magnesium alloys

There are many researches on the deformation behavior of wrought magnesium alloys, such as AZ31, AZ80, AZ91, and ZK60 magnesium alloys at different temperatures and strain rates, but few of them focuses on the deformation behavior of AZ41M and ZK60M alloys, especially under the twin-roll casting (TRC) state. Meanwhile, the existing researches only focus on the grain refinement law of the magnesium alloys under deformation conditions, the deformation mechanism has not been revealed yet. The hot compression behavior of AZ41M and ZK60M magnesium alloys under the temperature and strain rate ranges of 250–400 °C and 0.001–1 s−1 are studied by thermal simulation methods using Gleeble 1500 machine and virtual simulation using finite element analysis software. Simulation results show that sine hyperbolic law is the most suitable flow stress model for wider deformation conditions. The most reasonable selected deformation conditions of ZK60M alloy is 350 °C/0.1 s−1 for TRC and 350 °C/1 s−1 for conventional casting (CC), while AZ41M alloy is 300 °C/0.01 s−1 for TRC and 350 °C/0.1 s−1 for CC. Deformation behavior and dynamic recrystallization (DRX) mechanism of them are analyzed at the same deformation conditions. The microstructures of AZ41M and ZK60M alloys are observed at different deformed conditions by optical microscopy (OM) and electron back scatter diffraction (EBSD) and it reveals the flow behavior and deformation mechanism of them. Working harden and work soften contribute to the activation of basal, non-basal slip systems which promote DRX. The proposed research reveals the deformation behavior and mechanism of the AZ41M and ZK 60M magnesium alloys and concludes their optimized deformation parameters and processes and provides a theory basis for their manufacturing and application.

A method for thermal performance modeling and simulation of machine tools

The development of precision machine tools requires an accurate understanding of the thermal be- haviour of the tools. Therefore, by developing highly accurate machine tool thermal behaviour simulations, it can accurately forecast the functional performance of a machine tool at the prototype design stage and provide guidance on its design and performance optimization. To improve the accuracy of the thermal simulation of machine tools, it proposed whole-machine temperature field and thermal deformation modeling and a simula- tion method for vertical machining centers. Based on the studies of thermal-structure coupling finite-element data flow and its critical conditions, it also proposed design and computational methods for obtaining the heat-source power, when various rotational speeds, the forced convection heat transfer coefficient between a rotating surface and the air, the combined heat transfer coef- ficient between a stationary surface and the air/environment, and key contact surface thermal resistances were considered. Furthermore, this paper performed finite-element simulation analysis based on the constructed whole-machine thermal model, and the temperature characteristics and heat deforma- tion mechanism/state were obtained. After comparing the simulation and experimental results, it verified the effective- ness of the finite-element simulation model and the relevant methods and confirmed that the simulation accuracy for both the temperature characteristics and the thermal defor- mation had been improved significantly, with a simulation error less than 10 %.

Simplified thermal modeling of indirect evaporative heat exchangers

A simplified model using a modified effectiveness–Number of Transfer Units (NTU) method for thermal performance simulation of indirect evaporative heat exchangers is presented and then validated utilizing experimental data from the literature. The objective of this model is to facilitate efficient computer simulation of indirect evaporative cooling or hybrid indirect evaporative cooling/direct expansion vapor compression systems, both of which include an indirect evaporative heat exchanger as a core component. Through some approximations, the governing differential equations that describe indirect evaporative heat exchanger heat/mass transfer behavior are modified to produce a methodology that is analogous to the effectiveness–NTU method for sensible-only heat exchangers. The simplified set of equations can then be solved within short computation times and with numerical stability. An examination of the Lewis factor impact on evaporation processes using this model indicates that the approximation of unity for the Lewis factor may not be valid when the inlet air to the wet side is cold and dry.

ТеплообміН пучкіВ труБ З рівнорозвиненоЮ поверхнеЮ

Наведено результати експериментальних досліджень конвективного теплообміну шахових пучків труб з рівнорозвиненою поверхнею в діапазоні зміни чисел Рейнольдса від 5000 до 70000. Запропоновано узагальнену залежність для розрахунку конвективних коефіцієнтів тепловіддачі таких пучків. Показано, що коефіцієнт Сq при числі Рейнольдса в рівнянні подібності залежить від геометричних характеристик пучків та труб.

温熱シミュレーションによる熱負荷の分析

The thermal simulation method for the air-conditioning system using floor-chambers in a residence was developed and verified the validity as shown on the Part 2. In this paper, heating load was analyzed using the thermal simulation, a methodology of which was shown on the Part2. The simulation was performed for the experimental residence shown on the Part 1 and for a model residence. As one of several results, difference is found in heating load between the air-conditioning system using floor-chamber and the conventional one. Some useful knowledge in designing the air-conditioning system using floor-chamber was shown by that thermal simulation.

Multifractal properties of denaturation process based on Peyrard–Bishop model

DNA has attracted the interest of physicists for a long time. One interesting theoretical question is its melting behavior. The Rényi dimension spectrum of the melting transition of DNA, reveals the multifractal nature of the dynamics of the Peyrard–Bishop model. In this Letter, the effects of different parameters involved in the Peyrard–Bishop model on the multifractal nature of the melting dynamics of a DNA chain are investigated in details. As a result, it can be concluded that not only the best multifractality nature of the model arises from the Morse potential term which is taken in the model but also the multifractal nature of the model is independent of the homogeneity, the length of chain, stacking terms, the thermal bath simulation methods and even the potentials which describe the interaction between the two bases in a pair. Furthermore, our results confirm that, the best potential to describe the interactions between the bases in pairs in the PB and PBD models is the Morse potential.

Radiofrequency heating induced by 7T head MRI: Thermal assessment using discrete vasculature or pennes' bioheat equation

To evaluate and compare the maximum temperature (T(max) ) in the head after exposure to a 300 MHz radiofrequency (RF) field induced by a magnetic resonance imaging (MRI) coil using two thermal simulation methods: Pennes' bioheat equation (PBHE) and discrete vasculature (DIVA). The electromagnetic field induced in the head by a 7T birdcage coil was simulated using finite-difference time-domain (FDTD) and validated by MRI. The specific absorption rate (SAR) distributions normalized to the 10-gram maximum or the whole-head average were used for PBHE and DIVA simulations. For all cases, the T(max) in PBHE was slightly higher than in DIVA. The T(max) was 37.9-38.4°C, depending on the simulation method or perfusion rate. In some situations, RF exposure limited to SAR(max,10g) led to a T(max) higher than allowed by International Electrotechnical Commission (IEC) regulations. Therefore, it is advisable to use thermal simulations to evaluate RF safety of MRI. The simulation method used only slightly influenced the observed maximum temperature; the observed temperature with PBHE was higher in all situations. So PBHE is an appropriate method for RF safety assessment of MRI in the head. Using DIVA simulations, it was found unlikely that the body temperature increases significantly due to energy deposited by a head coil under normal circumstances.