Transient Thermal Behavior Research Articles

A Physics-Based Improved Cauer-Type Thermal Equivalent Circuit for IGBT Modules

A physics-based Cauer-type thermal equivalent circuit (TEC) can be constructed for an insulated-gate bipolar transistor (IGBT) module based on its geometry. In the conventional Cauer-type TEC, each layer of the IGBT module is modeled as a lump with the uniformly distributed temperature. However, this method oversimplified the transient thermal behavior of the IGBT module, leading to unsatisfactory transient junction temperature estimation. Based on a new concept of lumped-capacitance approximation error, this letter proposes a method to determine the number of sublayers that a layer in an IGBT module should be subdivided. For the bulky-baseplate layer, an analytical expression of its thermal impedance is derived and simplified to a first-order transfer function, which can be represented by a thermal resistance and capacitance pair in the TEC. The proposed Cauer-type TEC model is much more accurate than the conventional Cauer-type TEC model for the transient junction temperature estimation of IGBT modules with a slightly increased order only. The improvement of the proposed model over the conventional Cauer-type TEC model is validated by comparing with a finite element analysis model for a commercial IGBT module using simulation studies.

Numerical investigation of transient thermal behavior of a wall incorporating a phase change material via a hybrid scheme

This article deals with the numerical simulation of transient thermal behavior of a mortar wall containing a microencapsulated phase change material (PCM) using a hybrid finite volume/enthalpy method. Unlike explicit algorithms, the latent heat source term has been handled implicitly in the enthalpy equation. The current approach has been implemented considering a one-dimensional transient phase change problem with conduction. The numerical results agree well with available experimental results qualitatively. Subsequently, the model has been used to investigate the effect of the speed of heating or cooling on the performance of the thermal storage of PCM-Mortar during the phase-change process. The Micronal®DS5001X microcapsules containing a paraffin mixture with a melting point of 26°C has been used to improve the heat storage capacity of a cement-mortar. Simulation results indicated that the PCM is able to enhance the solid–liquid phase change heat transfer mainly because of thermal conduction, and that rate of heating/cooling has no influence on the profile of heat flux. They also showed that the model presented here is well-suited to the thermal behavior of an encapsulated PCM embedded in a mortar wall, and it is indicated to address similar problems.

Study of the effect of sun patch on the transient thermal behaviour of a heating floor in Algeria

Solar radiation is a renewable non polluting energy source which can be used in buildings through various systems technologies. Thermal radiation, absorbed or transmitted by the walls and windows, creates a solar gain which has a direct impact on the thermal behavior in the building. Most existing thermal models neglect the effect of the evolution of the sun patch position on the heating floor which can have a great impact on the indoor thermal comfort.In this paper, we present numerical model to calculate the transient sun patch position and its influence on the heating floor model in order to evaluate its impact on the heating floor operating conditions and on the indoor air temperature, which has a great influence on thermal comfort under the climatic conditions of Oran city in Algeria. The sun patch is calculated using Ray Tracing model as proposed in FLUENT whereas the room and the heating floor are modelled with TRNSYS software.Using literature data, the two proposed models (sun patch model and heating floor model) are validated and used to simulate the cases with different geographic locations and different window orientations, surfaces, and positions. Our results suggest that the displacement of the sun patch on the heating floor lead to a superheating of the irradiated zone and it affects the indoor air temperature and thermal comfort too.

Experimental investigation of the effects of using nano/phase change materials (NPCM) as coolant of electronic chipsets, under free and forced convection

In this paper, an experimental investigation is performed to study the effects of using nano/phase-change-materials (NPCM) as coolant for an electronic chipset in various scenarios that include both free and forced convection. Development of efficient cooling methods in electronic technology is significant mainly for enhancement of functionality and lifetime of electronic devices. Six different scenarios of cooling systems are conducted for an electronic chipset under various values of heat flux. The cooling scenarios include simple heat-sink (referred to HS in this paper), heat-sink that contains a phase change material (HS/PCM), and heat-sink that contains NPCM (HS/NPCM) in both free and forced convection. The PCM used in this study, Mn(NO3)2, is an inorganic salt-hydrate type; and the selected nanoparticles are Fe3O4 dispersed in the PCM by an ultrasound mechanism by a weight fraction of 1%. The steady and transient thermal behavior of the electronic chipset are investigated under different operating conditions by applying various heat fluxes from 1000 to 4000W/m2. Results show that presence of the PCM and NPCM can decrease the steady temperature of the chipset up to 14°C and 10.5°C compared to that of the HS for both free and forced convection, respectively. Furthermore, it is observed that the HS/PCM has better cooling and time efficiency for longer period usage whereas the HS/NPCM is preferable in temporary and intermittent use.

Transient Thermal Simulation of Liquid-Cooled 3-D Circuits

The 3-D integrated circuits (3-D ICs) are emerging as a viable solution to enhance the performance of many-core platforms. These architectures generate a high and rapidly changing thermal flux that makes conventional air-cooled devices more susceptible to overheating. Liquid cooling is an alternative that can improve dissipation and reduce thermal issues. Fast and accurate thermal models are needed to appropriately dimension the cooling system at design time. Several models have been proposed to study different designs, but generally with low simulation performance. In this paper, we present an efficient model of the transient thermal behavior of liquid-cooled 3-D ICs. This paper presents an approach with extremely low memory usage and advanced numerical methods to efficiently compute the transient temperature of 3-D ICs. Our experiments show the $100\times $ speedup versus the state-of-the-art models, while maintaining the same level of accuracy, and demonstrate the efficiency of liquid cooling to remove the heat from 3-D many-core platforms.

Large‐scale transient electrical‐thermal co‐simulation of interconnects under electromagnetic pulses

ABSTRACTThe electrical‐thermal co‐simulation is employed to analyze the transient electrical and thermal behaviors of large‐scale on‐chip and 3‐D interconnects. The analyses are performed when the interconnects are exposed to electromagnetic pulses in order to simulate both self‐heating effects under normal working conditions and thermal breakdowns under electrostatic discharge stresses. The impact of power maps on the transient thermal responses under the electrostatic discharge stress is also studied. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2559–2563, 2016

A new method for calculating the thermal effects of irregular internal mass in buildings under demand response

Accurately modeling thermal storage and discharge play a pivotal role in predicting the peak savings of demand response buildings. Considerable studies have been conducted on the transient thermal behavior of building envelopes, much of which has focused on the thermal mass effects of building envelopes and floors. However, it is unclear how to precisely describe the cooling storage effects of irregular internal mass such as furniture. EnergyPlus and other simulation tools have internal mass models, but these models require ambiguous inputs such as internal mass surface area, thickness, volume and thermal properties. These inputs are impossible to obtain due to the irregular shapes and random spatial distributions of internal mass. In this paper, the novel “Effective Area” method is proposed that improves the theory of the conventional “Equivalent Slab” method. The new method establishes a relationship between the actual furniture and the equivalent furniture through a converted coefficient in the dynamic heat transfer equations. Experiments are conducted to test and verify the accuracy of the new method and to calculate common parameters, such as the converted coefficient and the distribution density of the irregular internal mass in some typical office setups.

Thermal performance and cost analysis of a multi-layered solid-PCM thermocline thermal energy storage for CSP tower plants

Thermocline storage in packed-bed is taken into consideration for cost reduction of thermal energy storage (TES) system in concentrating solar power (CSP). With a novel packed-bed configuration proposed recently, multi-layered solid-PCM (MLSPCM) thermocline TES is regarded as a more cost-effective alternative for current TES due to its lower thermocline degradation, which results in a higher energy utilization during the cyclic operation of the system comparing to other thermocline TES patterns. Thermal performance of several MLSPCM thermocline TES system with specific packed-bed configurations have been numerically evaluated both on pilot and practical scale. In this work, transient thermal behaviors of charging and discharging process in a cyclic operating state of a practical scale MLSPCM thermocline TES is investigated using a modified one-dimensional dispersion-concentric (D-C) model, while a comprehensive cost model is adopted to estimate capital cost of TES system. The influence of packed-bed configuration on several evaluation indexes of system performance such as cyclic operating time duration, total capacity factor and capital cost per kWht are explored based on parametric studies. Optimum design configurations are identified to minimize capital cost per kWht on the specific operating requirements. A cost comparison among different thermocline TES patterns as well as the two-tank TES are presented. The results show that the MLSPCM thermocline TES with an optimum packed-bed configuration is more cost-competitive than the two tank TES and any other thermocline TES systems. Overall, this study illustrates a methodology for packed-bed configuration optimization of a practical-scale MLSPCM thermocline TES and provide a design reference on cost-effective TES system for current CSP tower plants.

Three-Dimensional Finite-Element Analysis of the Short-Time and Peak Withstand Current Tests in Substation Connectors

Power devices intended for high-voltage systems must be tested according to international standards, which includes the short-time withstand current test and peak withstand current test. However, these tests require very special facilities which consume huge amounts of electrical power. Therefore, mathematical tools to simulate such tests are highly appealing since they allow reproducing the electromagnetic and thermal behavior of the test object in a fast and economical manner. In this paper, a three-dimensional finite element method (3D-FEM) approach to simulate the transient thermal behavior of substation connectors is presented and validated against experimental data. To this end, a multiphysics 3D-FEM method is proposed, which considers both the connector and the reference power conductors. The transient and steady-state temperature profiles of both the conductors and connector provided by the 3D-FEM method prove its suitability and accuracy as compared to experimental data provided by short-circuit tests conducted in two high-current laboratories. The proposed simulation tool, which was proven to be accurate and realistic, may be particularly useful during the design and optimization phases of substation connectors since it allows anticipating the results of mandatory laboratory tests.

Thermal Response of Multi-Microchannel Evaporators During Flow Boiling of Refrigerants Under Transient Heat Loads With Flow Visualization

Multi-microchannel evaporators with flow boiling, used for cooling high heat flux devices, usually experience transient heat loads in practical applications. These transient processes may cause failure of devices due to a thermal excursion or poor local cooling or dryout. However, experimental studies on such transient thermal behavior of multi-microchannel evaporators during flow boiling are few. Thus, an extensive experimental study was conducted to investigate the base temperature response of multi-microchannel evaporators under transient heat loads, including cold startups and periodic step variations in heat flux using two different test sections and two coolants (R236fa and R245fa) for a wide variety of flow conditions. The effects on the base temperature behavior of the test section, heat flux magnitude, mass flux, inlet subcooling, outlet saturation temperature, and fluid were investigated. The transient base temperature response, monitored by an infrared (IR) camera, was recorded simultaneously with the flow regime acquired by a high-speed video camera. For cold startups, it was found that reducing the inlet orifice width, heat flux magnitude, inlet subcooling, and outlet saturation temperature but increasing the mass flux decreased the maximum base temperature. Meanwhile, the time required to initiate boiling increased with the inlet orifice width, mass flux, inlet subcooling, and outlet saturation temperature but decreased with the heat flux magnitude. For periodic variations in heat flux, the resulting base temperature was found to oscillate and then damp out along the flow direction. Furthermore, the effects of mass flux and heat flux pulsation period were insignificant.

Transient Behaviors of No-Insulation REBCO Pancake Coil During Local Normal-State Transition

Recently, no-insulation (NI) winding techniques have been proposed for achieving high current density and high thermal stability. To verify the excellent characteristics achieved using these techniques, we investigated the transient behaviors of NI REBCO pancake coils. In this paper, we evaluate transient electromagnetic and thermal behaviors during a local normal-state transition, based on a partial element equivalent circuit and thermal coupled numerical analysis. Moreover, we investigate temporal and spatial current distributions in the NI coil winding after a local normal transition occurs. We also clarify the reason for the suppression of temperature increase caused by the local normal-state transition in the NI winding. Subsequently, we evaluate the influence of the thickness of a Cu stabilizer on the thermal stability of the NI and conventional insulation windings. Finally, we discuss the mechanism of high thermal stability attained in the NI coil winding technique.

Thermal and mechanical transient behaviour of steel doors installed in non‐load‐bearing partition wall assemblies during exposure to the standard fire test

SUMMARYIn this paper, the authors present experimental results and observations of four full‐scale standard fire tests on single‐leaf steel doors and steel frames installed in 3 × 3 m non‐load‐bearing partition walls. Three full‐scale fire tests were performed on steel doors installed in lightweight partition walls constructed by using steel C‐section studs with gypsum boards fixed on both sides. Two lightweight walls incorporated Rockwool cavity insulation, while the third lightweight wall was constructed without cavity insulation. The fourth fire test involved a steel door installed in a masonry partition wall. While the steel door leaf and door frames were identical in all four full‐scale tests, only the steel door installed in the masonry wall achieved the desired fire resistance rating of 30 min. The integrity criterion for fire resistance was determined for the scenario when the door opened away from the furnace. The duration of fire resistance according to the integrity criterion was found to be 38, 25 and 19 min for the same door when installed in masonry wall, uninsulated lightweight wall and insulated lightweight wall respectively. For the thermal insulation criterion of fire resistance, the scenario of the door opening into the fire was found to be the most onerous. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Thermofluid effect on energy storage in fluidized bed reactor

The development of innovative systems of heat storage is imperative to improve the efficiency of the existing systems used in the thermal solar energy applications. Several techniques were developed and realized in this context. The technology of the sand fluidized bed (sandTES) offers a promising alternative to the current state-of-the-art of the heat storage systems, such as fixed bed using a storage materials, as sand, ceramic, and stones, etc. Indeed, the use of the fluidization technique allows an effective heat transfer to the solid particles. With the sand, an important capacity of storage is obtained by an economic and ecological material [N. Mahfoudi, A. Moummi, M. El Ganaoui, Appl. Mech. Mater. 621 , 214 (2014); N. Mahfoudi, A. Khachkouch, A. Moummi B. Benhaoua, M. El Ganaoui, Mech. Ind. 16 , 411 (2015); N. Mahfoudi, A. Moummi, M. El Ganaoui, F. Mnasri, K.M. Aboudou, 3 e Colloque internationale Francophone d”energetique et mecanique, Comores, 2014 , p. 91]. This paper presents a CFD simulation of the hydrodynamics and the thermal transient behavior of a fluidized bed reactor of sand, to determine the characteristics of storage. The simulation shows a symmetry breaking that occurs and gave way to chaotic transient generation of bubble formation after 3 s. Furthermore, the predicted average temperature of the solid phase (sand) increases gradually versus the time with a gain of 1 °C in an interval of 10 s.

TameTire: Introduction to the Model

ABSTRACT Tire modeling is an ever-growing area of interest for vehicles as more efficient development processes are desired in terms of time and resources. Vehicle simulations offer an opportunity for development teams to predict tire and vehicle performance before the construction of a physical prototype. Michelin has identified the need for more robust and accurate tire models that can be used for such simulations to give an accurate description of the transient mechanical and thermal behavior of a tire. Rubber's viscous and elastic properties are heavily dependent on their thermal state; when this effect is not modeled, it results in mathematical tire models that insufficiently predict tire performance. TameTire aims to fill this void for a broad range of maneuvers, track characteristics, and operating conditions based on the ability to predict tire forces and moments with physically based parameters. Some physical characteristics contained within a TameTire model include contact patch dimensions, tread, sidewall and belt stiffnesses, and rubber compound properties. Empirical tire models for handling have limited representation of tire physical properties due to the dependence on the measurement protocol and lack of identification of the thermal state of the tire. TameTire's advance modeling techniques include capturing a tire's thermal effects, thereby allowing for a more accurate and thorough analysis of tires behavior while being physically based (e.g., parameters for stiffness, rubber properties) and allowing the model to be grounded in the actual physics of a tire operating.

Multiscale analysis of heat treatments in steels: Theory and practice

Multiphase steels offer impressive mechanical properties. However, their characterisation still represents a challenge. In a quenching process, phenomena such as undesirable strains or residual stresses are inevitable and can be the cause for non-admissible final parts. Microstructural phase transformations generally magnify the problem. The non-existence of efficient non-destructive experimental procedures capable of measuring them leads to the need of numerical tools capable of quantifying these undesirable effects.In this work, a numerical multiscale transient model, that uses the Asymptotic Expansion Homogenisation (AEH) methodology combined with Finite Element Method (FEM), is proposed for the analysis of heat treatments in steels. The implementation of the AEH method is carried out using the commercial program Abaqus, considering an uncoupled and transient problem with implicit time integration. Within the homogenisation method, the existence of two distinct scales is assumed, defining a micro- and a macroscale. In the smaller scale, the evolution of a steel periodic microstructure is analysed in detail and an equivalent homogeneous material model is established for macroscopic use. Moreover, it is presented in this work that AEH is a rigorous and effective homogenisation method that allows the modelling of the thermomechanical and transient thermal behaviour in periodic materials, particularly in heat treatments.

Minimization of lumen depreciation in LED lamps using thermal transient behavior analysis and design optimizations.

We expansively investigate thermal behaviors of various general-purpose light-emitting diode (LED) lamps and apply our measured results, validated by simulation, to establish lamp design rules for optimizing their optical and thermal properties. These design rules provide the means to minimize lumen depreciation over time by minimizing the periods for lamps to reach thermal steady-state while maintaining their high luminous efficacy and omnidirectional light distribution capability. While it is well known that minimizing the junction temperature of an LED leads to a longer lifetime and an increased lumen output, our study demonstrates, for the first time, to the best of our knowledge, that it is also important to minimize the time it takes to reach thermal equilibrium because doing so minimizes lumen depreciation and enhances light output and color stability during operation. Specifically, we have found that, in addition to inadequate heat-sink fin areas for a lamp configuration, LEDs mounted on multiple boards, as opposed to a single board, lead to longer periods for reaching thermal equilibrium contributing to larger lumen depreciation.

A new thermal model for power MOSFET devices accounting for the behavior in unclamped inductive switching

The main aim of this work was the analysis of the transient thermal behavior of several typologies of power MOSFET devices. The commonly used thermal model has been applied to different device families with different breakdown voltages. The large difference between the experimental results and the simulation runs, performed with the classic approach for some kinds of devices, leads to correct the traditional mathematical thermal model and to build up a new one in which the real size of the epitaxial layer is taken into account. A new model will be shown performing a better fitting with the experimental evidence and confirming its suitability for all the proofed families of devices. The mathematical process developed to build up the model is shown, and a comparison is carried out between the measured temperatures on the device and estimation by the model. The results discussed in the paper show how the developed model allows a better fitting of the achieved model with the experimental measurements and demonstrate the suitability of the proposed approach.

Thermal analysis of anti-icing systems in aeronautical velocity sensors and structures

This work reviews theoretical–experimental studies undertaken at COPPE/UFRJ on conjugated heat transfer problems associated with the transient thermal behavior of heated aeronautical Pitot tubes and wing sections with anti-icing systems. One of the main objectives is to demonstrate the importance of accounting for the conduction–convection conjugation in more complex models that attempt to predict the thermal behavior of the anti-icing system under adverse atmospheric conditions. The experimental analysis includes flight tests validation of a Pitot tube thermal behavior with the military aircraft A4 Skyhawk (Brazilian Navy) and wind tunnel runs (INMETRO and NIDF/COPPE/UFRJ, both in Brazil), including the measurement of spatial and temporal variations of surface temperatures along the probe through infrared thermography. The theoretical analysis first involves the proposition of an improved lumped-differential model for heat conduction along a Pitot probe, approximating the radial temperature gradients within the metallic and ceramic (electrical insulator) walls. The convective heat transfer problem in the external fluid is solved using the boundary layer equations for compressible flow, applying the Illingsworth variables transformation considering a locally similar flow. The nonlinear partial differential equations are solved using the Generalized Integral Transform Technique in the Mathematica platform. In addition, a fully local differential conjugated problem model was proposed, including both the dynamic and thermal boundary layer equations for laminar, transitional, and turbulent flow, coupled to the heat conduction equation at the sensor or wing section walls. With the aid of a single-domain reformulation of the problem, which is rewritten as one set of equations for the whole spatial domain, through space variable physical properties and coefficients, the GITT is again invoked to provide hybrid numerical–analytical solutions to the velocity and temperature fields within both the fluid and solid regions. Then, a modified Messinger model is adopted to predict ice formation on either wing sections or Pitot tubes, which allows for critical comparisons between the simulation and the actual thermal response of the sensor or structure. Finally, an inverse heat transfer problem is formulated aimed at estimating the heat transfer coefficient at the leading edge of Pitot tubes, in order to detect ice accretion, and estimating the relative air speed in the lack of a reliable dynamic pressure reading. Due to the intrinsic dynamical behavior of the present inverse problem, it is solved within the Bayesian framework by using particle filter.

Modeling of transient thermal dissipation of nanoscale phase-change memory cells in the pulse domain

As size downscaling and operation speed increasing, understanding thermal dissipation of phase-change random access memory (PCRAM) during pulse interval is of great importance to gain an insight into its internal transient thermal dissipation behavior. A simplified transient thermal dissipation model and a method of extracting time constants, thermal resistances and capacities in the pulse domain based on the resistance-to-pulse-number (R-PN) curve are proposed. The results show that the R-PN curve calculated by the compact HSPICE model agrees with the one by an experiment. Though this simplified transient thermal dissipation model is obtained under the condition of short pulse interval, it can be available for the transient temperature simulation of a cell under any conditions, especially for understanding thermal behavior of cycle times and programmable synapse based on phase-change materials.

Analysis of the transient thermal behaviour of a solar honeycomb (SHC) façade element with and without integrated PV cells

The transient thermal behaviour of a ventilated solar honeycomb (SHC) façade element was investigated with the help of numerical simulations. Therefore two three-dimensional CFD models were used to consider a SHC façade element with and without attached PV cells at the exterior glass pane. Beside a natural convective flow model also a radiation model with two wavebands was implemented to enable the differentiation between short-wave solar radiation and long-wave thermal radiation.In a laboratory experiment temperatures in the ventilation cavity and the heat flux at the rear wall of the SHC façade were monitored and compared to simulation results.The experiment using a solar simulation device was carried out for one façade element with PV cells at the exterior glass pane and for one façade element without PV cells.The time-step size for the transient simulations was dramatically reduced after the determination of the maximum time-step size, which finally enabled the analysis of the thermal behaviour over a prolonged period (one day or longer) within reasonable simulation durations.Moreover, the impact of the SHC’s material properties on the dynamic thermal behaviour was analysed with the three-dimensional CFD-model. Differences in heating rate, heat flux and temperatures were determined and compared by using five different materials instead of the cellulose honeycomb.Finally this study obtained the impact of hourly changing external climate conditions on the thermal behaviour of a single 1×1m SHC façade element using climate data from a cold winter’s day and a hot summer’s day which were measured in Graz, Austria.