Accurate Thermal Simulation Research Articles

An accurate thermal performance modeling and simulation method for motorized spindle of machine tool based on thermal contact resistance analysis

Motorized spindle is an inevitable choice of precision machine, but it has a prominent heat problem for its specific configuration of build-in motor. The paper proposed temperature distribution and thermal deformation modeling and a thermal-structural coupling simulation analysis method for a motorized spindle system from a vertical machining center. In order to establish an accurate finite element model, the boundary condition of joint thermal contact resistance (TCR) was taken into account. The paper detailed on how to obtain the TCR value which is related to the machine tool parameters by means of experimental and theoretical methods, and carried out a simulation experiment for the purpose of acquiring a quantitative analysis of the TCR influence on the temperature results. In order to verify the effectiveness of the TCR relevant methods, the experiment was carried out. The agreement between the experimental results and the simulation results showed that the proposed method can more accurately simulate the thermal characteristics of the motorized spindle.

Non-linear thermal simulation at system level: Compact modelling and experimental validation

In this work, a general methodology to extract compact, non-linear transient thermal models of complex thermal systems is presented and validated. The focus of the work is to show a robust method to develop compact and accurate non-linear thermal models in the general case of systems with multiple heat sources. A real example of such a system is manufactured and its thermal behaviour is analyzed by means of Infra-Red thermography measurements. A transient, non-linear Finite-Element-Method based model is therefore built and tuned on the measured thermal responses. From this model, the transient thermal responses of the system are calculated in the locations of interest. From these transient responses, non-linear compact transient thermal models are derived. These models are based on Foster network topology and they can capture the effect of thermal non-linearities present in any real thermal system, accounting for mutual interaction between different power sources. The followed methodology is described, verification of the model against measurements is performed and limitations of the approach are therefore discussed. The developed methodology shows that it is possible to capture strongly non-linear effects in multiple-heat source systems with very good accuracy, enabling fast and accurate thermal simulations in electrical solvers.

The Significance of Temperature Based Approach Over the Energy Based Approaches in the Buildings Thermal Assessment

Abstract The design of low energy buildings requires accurate thermal simulation software to assess the heating and cooling loads. Such designs should sustain thermal comfort for occupants and promote less energy usage over the life time of any building. One of the house energy rating used in Australia is AccuRate, star rating tool to assess and compare the thermal performance of various buildings where the heating and cooling loads are calculated based on fixed operational temperatures between 20 °C to 25 °C to sustain thermal comfort for the occupants. However, these fixed settings for the time and temperatures considerably increase the heating and cooling loads. On the other hand the adaptive thermal model applies a broader range of weather conditions, interacts with the occupants and promotes low energy solutions to maintain thermal comfort. This can be achieved by natural ventilation (opening window/doors), suitable clothes, shading and low energy heating/cooling solutions for the occupied spaces (rooms). These activities will save significant amount of operating energy what can to be taken into account to predict energy consumption for a building. Most of the buildings thermal assessment tools depend on energy-based approaches to predict the thermal performance of any building e.g. AccuRate in Australia. This approach encourages the use of energy to maintain thermal comfort. This paper describes the advantages of a temperature-based approach to assess the building’s thermal performance (using an adaptive thermal comfort model) over energy based approach (AccuRate Software used in Australia). The temperature-based approach was validated and compared with the energy-based approach using four full scale housing test modules located in Newcastle, Australia (Cavity Brick (CB), Insulated Cavity Brick (InsCB), Insulated Brick Veneer (InsBV) and Insulated Reverse Brick Veneer (InsRBV)) subjected to a range of seasonal conditions in a moderate climate. The time required for heating and/or cooling using the adaptive thermal comfort approach and AccuRate predictions were estimated. Significant savings (of about 50 %) in energy consumption in minimising the time required for heating and cooling were achieved by using the adaptive thermal comfort model.

Fast Thermal Simulation of FinFET Circuits Based on a Multiblock Reduced-Order Model

A methodology for fast and accurate thermal simulation of integrated circuits (ICs) is presented based on a multiblock reduced order modeling approach. The model projects the heat equation from a physical domain onto a functional space to represent the thermal solution using a small number of degrees of freedom (DOFs). The approach requires no assumptions about the physical geometry, dimensions, boundary conditions or heat flow pathways, as is usually needed for compact or lumped thermal models. The developed multiblock thermal model is applied to FinFET device/circuit structures including a three-block circuit structure consisting of several NAND gates. The model is verified on multiblock structures against a detailed numerical simulation (DNS). It is shown that the developed multiblock model gives accurate thermal solutions for a multiblock IC structure subjected to power pulse excitations whose pulse frequency, width, shape, and shift in time substantially deviate from those used in model construction. In general, the approach offers accurate thermal solutions as detailed as a DNS with a reduction in the numerical DOF by 5 to 6 orders of magnitude.

Simple and accurate thermal simulation model of supercapacitor suitable for development of module solutions

In this article, first the design procedure of the thermal model of a EDLC type wound capacitor (Electrochemical double layer capacitor) is described, whereby the main objective of modeling is achievement of a very close accordance of simulation results compared to measurements in various operating conditions. Development process is supported by the mathematical analysis of the internal structure of EDLC. Based on the requirements on high degree of model's accuracy, three alternatives of model's complexity are shown. Instead of accuracy the proper model has to fulfill also requirement on the computation time. Next, to meet further demands of complex modeling of supercapacitor modules, mentioned abilities (accuracy of simulation results and fast computation time of solution) must be as lowest as possible.The second important aim of this paper is the description of the development procedure of thermal simulation model of EDLC module (multi-cell supercapacitor system). Consequently simplifications targeting lowest simulation time with achievement of high model's accuracy are provided. At the end of the paper, reader is able to find simulation experiments which are confirming the proposed design procedure.

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.

Compact model of power MOSFET with temperature dependent Cauer RC network for more accurate thermal simulations

A new, more accurate SPICE-like model of a power MOSFET containing a temperature dependent thermal network is described. The designed electro-thermal MOSFET model consists of several parts which represent different transistor behavior under different conditions such as reverse bias, avalanche breakdown and others. The designed model is able to simulate destruction of the device as thermal runaway and/or overcurrent destruction during the switching process of a wide variety of inductive loads. Modified thermal equivalent circuit diagrams were designed taking into account temperature dependence of thermal resistivity. The potential and limitations of the new models are presented and analyzed. The new model is compared with the standard and empirical models and brings a higher accuracy for rapid heating pulses. An unclamped inductive switching (UIS) test as a stressful condition was used to verify the proper behavior of the designed MOSFET model.

Thermal Analysis of Engine Cylinder Fin by Varying Its Geometry and Material

The Engine cylinder is one of the major automobile components, which is subjected to high temperature variations and thermal stresses. In order to cool the cylinder, fins are provided on the surface of the cylinder to increase the rate of heat transfer. By doing thermal analysis on the engine cylinder fins, it is helpful to know the heat dissipation inside the cylinder. We know that, by increasing the surface area we can increase the heat dissipation rate, so designing such a large complex engine is very difficult. The main aim of the present paper is to analyze the thermal properties by varying geometry, material and thickness of cylinder fins using ansys work bench. Transient thermal analysis determines temperatures and other thermal quantities that vary over time. The variation of temperature distribution over time is of interest in many applications such as in cooling. The accurate thermal simulation could permit critical design parameters to be identified for improved life. Presently Material used for manufacturing cylinder fin body is Aluminum Alloy A204 which has thermal conductivity of 110-150W/mk. Presently analysis is carried out for cylinder fins using this material and also

Fast 3-D Thermal Simulation for Integrated Circuits With Domain Decomposition Method

For accurate thermal simulation of integrated circuits (ICs), heat sink components in chip package must be considered. In this letter, techniques based on the domain decomposition method (DDM) are presented for the 3-D thermal simulation of nonrectangular IC thermal model including heat sink and heat spreader. A relaxed nonoverlapping DDM algorithm is employed to convert the problem to subproblems on rectangular subdomains. Then, a nonconformal discretization strategy is proposed to reduce the problem complexity with negligible error. Numerical experiments on several 2-D and 3-D IC test cases demonstrate that the relaxed nonoverlapping DDM is faster than the other preconditioned conjugate gradient algorithms with same mesh grid. The nonconformal discretization achieves further 10× reduction of runtime and memory usage.

Fast thermal simulations and temperature optimization for hyperthermia treatment planning, including realistic 3D vessel networks

Accurate thermal simulations in hyperthermia treatment planning require discrete modeling of large blood vessels. The very long computation time of the finite difference based DIscrete VAsculature model (DIVA) developed for this purpose is impractical for clinical applications. In this work, a fast steady-state thermal solver was developed for simulations with realistic 3D vessel networks. Additionally, an efficient temperature-based optimization method including the thermal effect of discrete vasculature was developed. The steady-state energy balance for vasculature and tissue was described by a linear system, which was solved with an iterative method on the graphical processing unit. Temperature calculations during optimization were performed by superposition of several precomputed temperature distributions, calculated with the developed thermal solver. The thermal solver and optimization were applied to a human anatomy, with the prostate being the target region, heated with the eight waveguide 70 MHz AMC-8 system. Realistic 3D pelvic vasculature was obtained from angiography. Both the arterial and venous vessel networks consisted of 174 segments and 93 endpoints with a diameter of 1.2 mm. Calculation of the steady-state temperature distribution lasted about 3.3 h with the original DIVA model, while the newly developed method took only ≈ 1-1.5 min. Temperature-based optimization with and without taking the vasculature into account showed differences in optimized waveguide power of more than a factor 2 and optimized tumor T90 differed up to ≈ 0.5°C. This shows the necessity to take discrete vasculature into account during optimization. A very fast method was developed for thermal simulations with realistic 3D vessel networks. The short simulation time allows online calculations and makes temperature optimization with realistic vasculature feasible, which is an important step forward in hyperthermia treatment planning.

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 %.

Fast and accurate thermal modeling and simulation of manycore processors and workloads

Today's microprocessors require careful analysis of their thermal behavior both at design time as well as at runtime. However, accurate prediction of thermal behavior is possible only through simulations due to the complexity and the high dynamicity of their operation. Unfortunately, accurate simulations of such complex systems are computationally intensive, therefore time consuming, while on the other hand, simplified models often cause mispredictions leading to overdesign and lowered performance. In our work, we propose a new discrete-time method of assessment of the run-time temperature of a processor based on an approximation of its instructions-per-cycle (IPC) by a finite Fourier series expansion. Our method is AC-based, and shows significant increase of accuracy in comparison to well-known DC (average)-based models. Furthermore, we provide a new Dynamic Voltage and Frequency Scaling (DVFS) model based on our estimations.

A Fast Loss and Temperature Simulation Method for Power Converters, Part II: 3-D Thermal Model of Power Module

This paper describes the development and implementation of an analytical 3-D thermal model for fast and accurate thermal simulation of power device modules in electrothermal converter simulation. A Fourier-based solution is used to solve the 3-D heat equation. The solution can describe the variation of temperature through the whole inverter power module structure as a function of time. The model can simulate thermal interactions resulting from multiple heat sources. The thermal model is extremely fast to simulate compared to finite-element (FEM) approaches. The new model has been implemented in MATLAB/Simulink in order to cosimulate with the converter model which is in the same form. The model has been validated against the computational fluid dynamics (CFD) software package FLOTHERM and shows good agreement. The required aspects of 3-D heat diffusion are captured successfully by the Fourier-based model.

Power and Thermal Constrained Test Scheduling Under Deep Submicron Technologies

Conventional power constrained test scheduling methods do not guarantee a thermal-safe solution. In this paper, we propose a test scheduling algorithm that satisfies the resource, power, and thermal constraints. First, in contrast to existing schemes, the proposed algorithm exploits superposition principle to perform fast and accurate thermal simulation, which, in turn, allows the algorithm to search for solutions which introduce cooling periods between tests to reduce the overall test length. Second, we propose a test partition-based method to further improve the performance of the test scheduling. We apply our test scheduling algorithm to ITC'02 SoC benchmarks and the results show considerable improvement in the total test length over existing methods.

Infrared thermography measurement of the thermal parameters (effusivity, diffusivity and conductivity) of materials

Accurate thermal simulations require the knowledge of both the thermal conductivity and the thermal effusivity of samples materials. Most of the time, the thermal conductivity and the specific heat have to be measured with two different setups. In this paper, we will show that a combination of two experiments done with the same setup - stimulated infrared thermography - allows to measure the absolute value of the thermal diffusivity and to get the relative value of the effusivity or the specific heat, and so to determine independently all the thermal parameters: thermal conductivity, thermal effusivity and thermal diffusivity.

Investigation of some large building energy conservation opportunities using the doe-2 model

Owing to their complexity, the design and efficient operation of HVAC systems in commercial buildings can be greatly enhanced by using accurate thermal simulation models. The DOE-2 model was validated using monitored data for a large (28,000 m 2) commercial building. The model provided a means to evaluate some conservation measures which included window glazings, occupancy sensors, cold deck temperature set point and reduced ventilation air. Reductions in cold deck temperature and ventilation air were attractive as no-cost options which could be easily returned to original settings if problems arose. The potential energy savings for occupancy sensors was substantial and could prove economical.

Compact Modeling Approach using GA for Accurate Thermal Simulation.

In this paper, we propose a technique that uses thermal measurement results for improved accuracy in thermal simulation of electronic apparatuses. Because the modeling of the electronic components in such apparatuses has hitherto been very poor, the thermal simulation results cannot satisfy the required accuracy. To solve this problem, we first represent a component as a set of cubic blocks with equivalent thermal conductivities and contact thermal resistances, and then identify these by using the thermal measurement results for the component. We regard the identification of parameters as an optimization problem that involves minimizing the difference between the calculated and measured results.n To solve the problem, we combine genetic algorithms and a thermal simulation tool. Our technique was successfully applied to the construction of an accurate thermal model, which we validated by using thermal measurement results.

Temperature-Dependent Thermal Conductivity of Single-Crystal Silicon Layers in SOI Substrates

Self heating diminishes the reliability of silicon-on-insulator (SOI) transistors, particularly those that must withstand electrostatic discharge (ESD) pulses. This problem is alleviated by lateral thermal conduction in the silicon device layer, whose thermal conductivity is not known. The present work develops a technique for measuring this property and provides data for layers in wafers fabricated using bond-and-etch-back (BESOI) technology. The room-temperature thermal conductivity data decrease with decreasing layer thickness, ds, to a value nearly 40 percent less than that of bulk silicon for ds = 0.42 μm. The agreement of the data with the predictions of phonon transport analysis between 20 and 300 K strongly indicates that phonon scattering on layer boundaries is responsible for a large part of the reduction. The reduction is also due in part to concentrations of imperfections larger than those in bulk samples. The data show that the buried oxide in BESOI wafers has a thermal conductivity that is nearly equal to that of bulk fused quartz. The present work will lead to more accurate thermal simulations of SOI transistors and cantilever MEMS structures.

On the rate of heat transfer between a lake and an ice sheet

The flux of heat between water and ice is either ignored or set to a constant value in present sea ice models. More accurate treatment of this flux may be desirable in the vicinity of polynyas and ice margins, and for more accurate thermal simulation of lakes and reservoirs. Observations of currents and temperatures under the ice in three large lakes of the headwater region of the Yukon River Basin permit the determination of the coefficient of sensible heat transfer between water and ice by various indirect methods. At a depth of 1 m and an estimated surface roughness of about 0.01 m, the coefficient of sensible heat transfer between water and ice was found to be (0.8±0.3)×10 −3. This value is within the limits of smooth and rough ice conditions found in laboratory investigations and appears to be somewhat less than that found in recent sea ice studies.