Increase In Thermal Resistance Research Articles

Evaluation of Thermal and Mechanical Properties of Bi-In-Sn/WO3 Composites for Efficient Heat Dissipation

Phase change materials (PCMs) offer promising solutions for efficient thermal management in electronic devices, energy storage systems, and renewable energy applications due to their capacity to store and release significant thermal energy during phase transitions. This study investigates the thermal and physical properties of Bi-In-Sn/WO3 composites, specifically for their use as phase change thermal interface materials (PCM-TIMs). The Bi-In-Sn/WO3 composite was synthesized through mechanochemical grinding, which enabled the uniform dispersion of WO3 particles within the Bi-In-Sn alloy matrix. The addition of WO3 particles markedly improved the composite’s thermal conductivity and transformed its physical form into a putty-like consistency, addressing leakage issues typically associated with pure Bi-In-Sn alloys. Microstructural analyses demonstrated the existence of a continuous interface between the liquid metal and WO3 phases, with no gaps, ensuring structural stability. Thermal performance tests demonstrated that the Bi-In-Sn/WO3 composite achieved improved thermal conductivity, and reduced volumetric latent heat, and there was a slight increase in thermal contact resistance with higher WO3 content. These findings highlight the potential of Bi-In-Sn/WO3 composites for utilization as advanced PCM-TIMs, offering enhanced heat dissipation, stability, and physical integrity for high-performance electronic and energy systems.

Experimental study on the effect of CO2 desublimation on heat transfer

Revealing the influence mechanism of CO2 desublimation on heat transfer is crucial for developing new liquefied natural gas heat exchangers. In this paper, an experimental platform for CO2 desublimation was built to investigate and analyze the intrinsic connection between CO2 desublimation and heat transfer, and systematically elaborated the mechanism of the influence of CO2 desublimation on heat transfer under different operating conditions based on the values of the heat transfer coefficient and CO2 thermal resistance. The results of the study show that CO2 can rapidly start condensation on the cooling surface when the gas flow rate is too fast (60 kg/h), which leads to a weakening and then strengthening of the effect of CO2 condensation on the heat transfer as the gas flow rate increases. In addition, as the cooling temperature drops, the amount of heat exchange between CO2 and the refrigerant decreases, and the magnitude of the changes in the values of the heat exchange coefficient and CO2 thermal resistance increases, with the value of the heat exchange coefficient decreasing by up to 39.9 %. Compared with the gas flow rate, the cooling temperature was the main factor affecting CO2 desublimation, and it has a more significant effect on heat transfer. This experimental study provides a theoretical basis for the design of a new type of liquefied natural gas heat exchanger and provides valuable insights into the mechanism of CO2 desublimation.

Coupling effects of micro/nano-scale surface modification and electric current application on fouling resistance and heat transfer

The principle of saving energy and converting waste heat into valuable resources is a core concept. Heat exchange systems are significantly compromised by microbial fouling, which impedes heat transfer and increases energy consumption. This study investigated the coupling effects of micro/nano-scale surface modifications and the application of electric currents as a novel approach to inhibit microbial fouling. Smooth copper surface, electrochemical deposition (ECD) surface, and Nickel-Phosphorus-Polytetrafluoroethylene (Ni-P-PTFE) modified surface were tested and compared. Firstly, we analyzed the average heat transfer coefficient under clean conditions, taking into account different surface characteristics. Then, we employed a series of fouling experiments to evaluate the anti-biofouling performance of smooth copper surfaces, ECD surfaces, and Ni-P-PTFE surfaces. The assessment involved flow cytometry, Scanning Electron Microscopy (SEM) and measurements of thermal resistance. Finally, we investigated the effect of external electric current on microbial fouling mitigation. Results show that the ECD surface exhibited an enhanced heat transfer and a poor fouling resistance, while the Ni-P-PTFE surface demonstrated an excellent fouling resistance and a minimal increase in thermal resistance. The application of a low direct current density at 0.51 mA/cm² significantly reduced microbial viability on all surfaces. A higher electric current can further inhibit microbial adhesion and proliferation, enhancing the anti-fouling capability of the surfaces. Compared to surfaces without electric current, the smooth copper surface, ECD, and Ni-P-PTFE surfaces at 5.1 mA/cm² displayed a reduction in thermal resistance by 45.7%, 36.8%, and 38.1%, respectively. At 51 mA/cm², the reduction in thermal resistance for smooth copper surface, ECD, and Ni-P-PTFE surfaces was 75.7%, 78.2%, and 57.1%, respectively. This comprehensive study has validated the potential of combining micro/nano-scale surface modifications with electric current application as an effective strategy for enhancing heat transfer efficiency and anti-fouling properties of heat exchange systems.

Long-Term Estimation of Depositions on Heating Surface During Boiling of Long-Life Coolant

Abstract Long-term boiling experiments with long-life coolant have been made with the aim to apply a boiling cooling technology to the next generation high exothermic electronic devices. The long-life coolant commonly used for cooling electronic devices is a mixture of ethylene glycol and water with multiple antirust inhibitors as additives, which may result in some depositions on the heat transfer surface during the boiling. In this study, the heat transfer surface made of copper was set vertically, and long-term experiments have been performed under the pool boiling. The deposition process was monitored for constant heating conditions. From experimental results, a distinct surface temperature change was observed under constant heat flux conditions. Just after keeping constant heat flux, the surface temperature increases with time, a certain time later decreases, and finally takes a stable value. During the temperature rise, the deposition adheres to the heat transfer surface in dots, which may cause an increase in thermal resistance between the wall surface and the working fluid. However, during the temperature drop, large growth of dot-like depositions on the heat transfer surface could alter wettability and surface roughness, enhancing boiling heat transfer. In addition, to investigate the characteristics of the depositions adhered to the heat transfer surface, a component analysis has been performed, which shows that the main substance was strontium hydroxyapatite, which might be formed by chemical reaction between components in the additives under the boiling.

Inhibiting Leidenfrost phenomenon with granulated polymer film

Inhibiting Leidenfrost phenomenon has been conventionally mediated by texturing materials to facilitate the solid-liquid contact or by arranging vapor channels to promote vapor evacuation. However, it remains challenging to break the trade-off between the high Leidenfrost point and the high heat transfer efficiency because elevating Leidenfrost point is often accompanied by the increase of thermal resistance. We propose a method using Rayleigh-Bénard-Marangoni convection and non-solvent induced phase separation to create granulated matrices that prevent the Leidenfrost effect at temperatures up to 400 °C. These matrices offer strong capillary adhesion, ensuring water droplets remain pinned and provide effective cooling. Additionally, the unique bubble dynamics prevent film boiling and Leidenfrost levitation. The matrices are mechanically robust and thermally stable, making them suitable for cooling high-power electronic devices at high temperatures. These results highlight the potential of using polymer matrices for cooling devices at elevated temperatures, potentially advancing cooling technologies.

Experiments on a Mine System Subjected to Ascensional Airflow Fire and Countermeasures for Mine Fire Control

The disorder and disaster evolution characteristics of ascensional airflow fires in mine ventilation systems has been the focus of mine fire research. In this work, through repeated experiments, the variation characteristics of the temperature and air volume in the main and side branches of an ascensional airflow fire were obtained under different ventilation capacities. Using the TF1M(3D) software to solve the problems of mine physical ventilation and combined with the analysis of an example, the variation in the ascensional airflow fire and the process of disordered airflow in the ventilation system in an entire area mine were described in detail. Fire combustion served as the power source for uncontrolled energy release, and its fire pressure interacted with the thermal resistance of the mine ventilation, directly causing airflow disorder. As the fire intensified, the ascensional airflow fire caused the airflow in the side branch to decrease, stagnate, or reverse. Improving the fan supply capacity can not only help reduce the increase in the ventilation thermal resistance of the side branch but also help avoid the airflow reversal of the side branch. From the regular variation characteristics, the theoretical results were found to be in good agreement with the experimental results.

Effect of layering outerwear on innerwear and air gap between the two layers on thermal comfort properties of knitted fabrics

PurposeIn everyday life, people generally wear two layers of clothes (a knitted vest and a knitted t-shirt) during the summer. It is essential to understand which types of innerwear and outerwear maximize comfort. The primary objective of this research is to investigate the influence of layering outerwear on innerwear, as well as the air gap between two layers, on thermal comfort properties.Design/methodology/approachIn this study, a total of 12 combinations were created from four vest fabrics and three T-shirt fabrics. The thermal properties (thermal conductivity, thermal resistance, thermal absorptivity, thermal diffusion and peak heat flow) were evaluated for the individual inner and outer layers. Each inner layer was layered with an outer layer to observe the effect of layering on the thermal properties. An air gap of 2 mm was introduced between the inner and outer layers to study the effect of air gap on thermal properties.FindingsTencel fibre exhibits higher thermal conductivity and absorptivity than cotton and polyester. Upon layering an outer layer on an inner layer, the thermal conductivity and thermal absorptivity increase to a slight extent, thermal resistance and diffusion increase drastically and the peak heat flow reduces. With an air gap between the two layers, the thermal conductivity did not improve, the difference in thermal resistance among all the combinations reduced, the thermal absorptivity of the combination textiles was lower than that of the innerwear alone, the thermal diffusion increased and the peak heat flow diminished for all the combinations.Practical implicationsIn practice, this comprehensive thermal comfort analysis provides specific combinations of inner and outer articles of clothing that are most appropriate for enhancing comfort during the summer season.Originality/valueThough there are many studies on the effect of multilayer fabrics on thermal properties, no extensive research analyses the influence of innerwear and outerwear combinations on thermal comfort properties.

Energy demand and carbon emission analyses of a solar-driven domestic regional environment mobile robot as household auxiliary heating and cooling method

Under the trend of energy saving and carbon reduction, reducing household energy consumption, which is an important part of social energy consumption, has become a hot topic. In order to solve the problem of mismatch between supply and demand of household environment control systems as well as to better meet the individual needs of users, we innovatively designed a solar-driven domestic regional environment mobile robot as auxiliary heating and cooling method. In this paper, a simplified thermal network analysis of the thermal conditions of a dwelling is utilized to calculate the energy saving and carbon reduction potential on summer and winter reference days in Beijing and Guangzhou, China. The simulation results show that the system has good energy saving potential and carbon reduction effect. In particular, the single-day energy saving potential of the system on winter days in Beijing reaches to 583.6 kWh compared to the traditional method. Under the power supply mode, the single-day carbon reduction can reach 462 kg CO2 on winter days in Guangzhou, and it can reach 333.2 kg CO2 on summer days in Beijing. We also discuss the effect of regional space size and clothing thermal resistance. As the local space size and the clothing thermal resistance increases, the energy saving potential and carbon reduction benefits of the system decrease, but the overall impact is small. The proposed mobile robot following in the vicinity of home inhabitants to help maintain their thermal comfort, can improve the efficiency of dwellings heating and cooling systems and utilize the limited solar energy resources in family area.

Micro-structured lateral thermal lens for increased output power and narrowed beam divergence in kilowatt-class 9xx nm diode laser bars

Local temperature non-uniformity is a critical limit to power in large-area semiconductor lasers, playing a larger role than the conversion efficiency and temperature sensitivity in the most efficient modern devices. For the specific case of kilowatt-level edge-emitting diode laser bars, we demonstrate that laterally re-distributing current locally within each emitter using a customized micro-structuring of the electrical contact can flatten the thermal profile, based on the thermal design using COMSOL. The concept is demonstrated experimentally in adapted bars that contain eight broad-area emitters, each having wide (∼1100 μm) stripes and a 4 mm long resonator. Each emitter in the laser bar has an electrical contact layer that is electrically structured into parallel sub-contacts using implantation, essential to prevent lateral lasing, implemented here with a period of 29 μm. The width of the individual sub-contacts is narrowed in the device center and then monotonically increased toward the emitter edges to collect a higher proportion of heat at the edges, for a fivefold reduction in the thermal lens, despite a significant (20%) overall increase in electrical and thermal resistance. Two performance benefits are observed. First, the slope varies more slowly with average temperature, recovering (here) around half of the efficiency penalty from in-stripe temperature non-uniformity, and hence increasing the power conversion efficiency at 800 W optical output power by around 5%. Second, the lateral far field (95% power content) is narrowed by around 2° at 800 W optical output power, corresponding to a reduction of around half of the thermal contribution.

Hexakis[p-(hydroxymethyl)phenoxy]cyclotriphosphazene as an Environmentally Friendly Modifier for Polyurethane Powder Coatings with Increased Thermal Stability and Corrosion Resistance.

Protection against fire and the corrosion of metals is necessary to ensure human safety. Most of the fire and corrosion inhibitors do not meet the ecological requirements. Therefore, effective and ecological methods of protecting metals are currently a challenge for researchers. In this work, the influence of hexakis(4-(hydroxymethyl)phenoxy)cyclotriphosphazene (HHPCP) on the characteristics of powder coatings was examined. The coatings' properties were investigated by measuring the roughness, hardness, adhesion to the steel surface, cupping, gloss, scratch resistance, and water contact angle. The thermal stability was studied by furnace test and TGA analysis. The corrosion resistance test was carried out in a 3.5% NaCl solution. The distribution of phosphazene-derived segments in the coating was examined by GD-EOS analysis. Modified coatings show better corrosion and thermal resistance and can be used for the protection of the steel surface. Their better corrosion resistance is due to the electroactive properties of the phosphazene ring and its higher concentration at the coating surface, confirmed by GD-EOS analysis. The increase in thermal resistance is due to the effect of the formation of phosphoric metaphosphoric and polyphosphoric acids during the decomposition of HHCPC, which remain in the condensed char phase and play a crucial role in surface protection.

Numerical study on the forced convective flow and heat transfer mechanism with macro-patterned hydrophilic-hydrophobic hybrid surfaces

Hydrophilic-hydrophobic hybrid surfaces can be used to harmonize the drag and heat transfer. However, the hybrid surfaces are almost microscopic scale and hardly used for forced convection at present. In this study, six macro-patterned hydrophilic-hydrophobic hybrid surfaces (square, diamond, circle, ellipse, triangle, and sector) and a no-slip surface are built. The performances are studied with the k-ε turbulent model by COMSOL, and the mechanism of performance change is analyzed with large eddy simulation (LES). The results show that macro-patterned hybrid surfaces can all reduce the flow drag but have different influences on heat transfer. With the increasing Reynolds number, the drag reduction rate (DR) declines. The largest DRs are 14.57% with the ellipse-patterned at lower Reynolds numbers, and 13.18% with the triangle-patterned at higher Reynolds numbers. For heat transfer capability, although adding hydrophobic parts, the square-patterned and diamond-patterned hybrid surfaces can raise Nusselt numbers. Combined above, the largest goodness factor (φ) enlarged rates are 16.43% (square-patterned) and 16.35% (diamond-patterned). Meanwhile, the influencing mechanism with the macro-patterned hybrid surface concludes four factors: the velocity slip, thermal resistance increases of air cavities, eddies of hydrophilic-hydrophobic interfaces, and the guiding effect of hydrophobic patterns' edges.

An experimental evaluation of the performance of a remote 2U loop thermosyphon

In recent years, the increasing application and diversity of electronic systems have resulted in a significant demand for research and development in electronic cooling. Designing and evaluating thermal modules is crucial, especially for systems generating high heat flux levels. This study proposes a novel remote loop thermosyphons (RLTS) for high heat flux applications and cooling 2U servers, which has been assessed experimentally. Additionally, several critical factors are examined, including the filling ratio (FR), air flow rate, and heat load. The experimental study evaluated air flow rates range from 130 to 170 cubic feet per minute (CFM), and the filling ratios span from 40 % to 70 %. The heat load varied from 100 W to 700 W. Compared to the conventional loop thermosyphon, the remote loop thermosyphon exhibited superior performance and sustained higher heat flux. Specifically, this thermal module can effectively manage 640 W at an inlet air temperature of 28 °C with an airflow rate of 170 CFM. Moreover, compared to other available loop thermosyphons, the proposed thermal module demonstrated enhanced heat flux up to 94 W/cm2. These results suggest that the new remote loop thermosyphon is a promising solution for cooling high heat flux applications, such as 2U servers. Furthermore, among all the investigated FR effects the 50 % FR performed better than the other filling ratios. At this filling ratio, the thermal resistance reached a minimum value of 0.078 K/W. The findings indicated that increasing the heat load decreased thermal resistance to a certain threshold, beyond which thermal resistance started to increase. This increase in thermal resistance was caused by restricted space above the evaporator. The confined space effect in a loop thermosyphon system significantly influences the performance and should be considered as a crucial factor in future design endeavors.

Summer thermal performance analysis of an Opaque ventilated Façade operating under the dynamic insulation principle

Opaque Ventilated Facades (OVFs) have gained significant scientific interest over the last decades, as the requirement for buildings to adapt to their environment is increasingly becoming more important. However, the continuous increase of the envelope thermal resistance, despite the undoubtable contribution in the building’s energy efficiency during the heating season, may raise a penalty during the warm period of the year, which in term gains a continuously increasing importance due to climate change. Dynamic insulation concept on the other hand is based on the idea of on-demand modifying the thermal resistance of the envelope significantly, allowing the building to take advantage of the environmental conditions on an annual, if not on a diurnal basis. In this study, the OVF technology is combined with the dynamic insulation concept in a naturally ventilated OVF configuration where the ambient air can surpass the insulation layer to decrease its effect and to enhance heat loss whenever this could relieve the building envelope from daytime’s thermal stress. A detailed thermal analysis was conducted for the summer climatic conditions of the Mediterranean area and the efficiency of the system in passively extracting stored heat was assessed for four different wall assemblies. The results revealed an efficiency 2.1–2.6 times higher than a conventional OVF’ s in removing heat, with the maximum one observed when the thermal mass was equally split in the two cavity sides. A qualitative comparison of the system’s performance with conventional OVF solutions and other adaptive façade systems was also conducted revealing the current system’s advantages.

Surface decoration of flexible Si3N4 nanowire membrane by hydroxyapatite micron-flake with excellent thermal insulation at 1300 °C

Flexible and excellent thermal insulation membranes are required as the thermal protection system materials of aerospace vehicles for next-generation space missions. Using ceramic membranes with ultralow thermal conductivity has been proved to be an effective way to protect the electronic components inside the fuselage. Herein, we decorate hydroxyapatite (HA) micron-flake onto Si3N4 nanowire membrane (SR), and investigate the thermal stability, fire-resistance and thermal insulating properties of the obtained SR decorated by HA micron-flake (SRHM). Surface decoration of HA micron-flake onto the SR results in the formation of well-interconnected junctions and the increase of interfacial thermal resistance. Due to the increased interfacial thermal resistance, the as-prepared SRHM exhibits good thermal insulation and outstanding fire-retardant performance. SRHM shows robust mechanical property with tensile strength value of 4.10 MPa, increased by 247.5% compared to the SR without the surface decoration by HA micron-flake. The thermal conductivity of SRHM is as low as 0.037 W m−1 K−1, reduced by 33.9% compared to the SR without the surface decoration by HA micron-flake. After SRHM is heated by a butane blow torch at 1300 °C for 30 min, no obvious change is observed in the macroscopic morphology. And the temperature of the backside for SRHM maintains at a stable temperature of ∼260 °C for 300 s, which is 1040 °C lower than that of the front side. Additionally, SRHM can protect the electronic components form being burnt under the heating of an alcohol lamp for 30 min. The successful preparation of such thermal insulating and fire-retardant SRHM will open up a new world for the widespread applications of ceramic membranes in the fields of aerospace vehicles.

Assessing thermal resistance as a degradation metric for solder bump arrays in discrete SiC MOSFET packages

The development of innovative power electronics solutions for automotive applications introduces new reliability requirements for electronic assemblies and interconnection technologies. Many of the reliability methods used in power electronics require extensive experimental data, resulting in long product design cycles. This work focuses on developing a simulation-driven approach to assess the solder joint reliability of a discrete silicon carbide MOSFET by monitoring its degradation under power cycling in the thermal and thermo-mechanical domains using the thermal resistance of the stack as a failure metric. Active power cycling tests are performed to determine the loading condition at which end-of-life is reached due to a 20% increase in thermal resistance. Numerical analysis using finite element simulations is conducted to gain a physical understanding of the failure criterion, allowing to monitor solder degradation based on the thermal resistance and to pinpoint failure at individual interconnects within a solder bump array. The proposed methodology aims to accelerate the quality assurance and product qualification processes of discrete power electronic devices.

Development of a genetic algorithm based interatomic potential and application in thermal conductivity study of ThO2 grain boundaries

ThO2 is a promising fuel for next-generation reactors due to its superior thermo-physical properties. In this study, we present a Coulomb-Buckingham-Morse interatomic potential for ThO2, developed using a homemade genetic algorithm (GA) method. The potential accurately captures fundamental properties, such as lattice constants, elastic constants, point defect energies, phonon spectra, and thermal conductivity. We apply this potential to perform a systematic study of thermal transport of twenty-one tilt grain boundaries (GBs) in ThO2, which have a significant effect on the macroscopic properties of polycrystalline materials. We demonstrate that the microscopic structure, GB excess energy, and GB disorder index are well correlated with the Kapitza conductance for a wide variety of GBs. Additionally, we discuss the effect of high temperature on the Kapitza conductance, where the GB structure undergoes disordering when approaching the melting temperature, resulting in an increase of thermal resistance. Finally, a detailed analysis of the phonon density of states is presented to reveal the mechanisms of thermal conductance in ThO2.

Thermal analysis and structure optimization of wavy microchannel with combining ribs of porous layer and solid wall in multi objective genetic algorithm

The combining rib of porous layer and solid wall is set in wavy microchannel heat sink to enlarge heat transfer area and convection with smaller increase in flow resistance, in which the consumption of pump power relates to the ratios of wave amplitude to length or to width and the thickness of porous layer due to vortices generation while coolant passing through channel. The local thermal equilibrium occurs in porous layer, and the Forchheimer-Brinkman-Darcy relations were used to describe the flow inside porous ribs. The effects of channel-to-pitch width ratio, width ratio of porous layer to pitch and microchannel height on its cooling performance are investigated, and the parameter of figure of merit (FOM) is defined to evaluate thermo-hydraulic performance in wavy microchannel. Besides, the multi objective genetic algorithm method is employed to optimize structure parameters in wavy microchannel to obtain better performances, in which the increase in thermal resistance from 0.062 K/W to 0.166 K/W together with consumption of pump power decreasing from 0.00416 W to 0.00185 W can be obtained in the Pareto front set, and it relates to the heat dissipation in convection between coolant and bottom surface or vertical side ribs. Compared to wavy microchannel with solid rib, the 37.61% and 16.67% decreases respectively in thermal resistance and consumption of pump power occur in the case with optimal combining rib of porous layer and solid wall.

Unphysical grain size dependence of lattice thermal conductivity in Mg3(Sb, Bi)2: An atomistic view of concentration dependent segregation effects

Grain boundary (GB) engineering is one of the most common strategies to reduce the lattice thermal conductivity and improve thermoelectric materials. However, in the case of the promising thermoelectric material Mg3(Sb1−xBix)2, an abnormal dependence of lattice thermal conductivity on grain size was observed at the concentration of x = 0.25, where smaller grain polycrystalline materials exhibited higher lattice thermal conductivity compared to larger grain materials. The proposed theory about the overestimation of lattice thermal conductivity in inhomogeneous materials with GBs cannot clarify the concentration dependence of this anomaly. Here we elucidate the interplay between segregation, concentration, and lattice thermal conductivity in Mg3(Sb1−xBix)2 alloys through atomistic simulations with a highly accurate machine learning interatomic potential. We find the largest segregation of Bi atoms to GBs in Mg3(Sb1−xBix)2 at the concentration of x = 0.25 for both twist and tilt GB structures due to the combination effects of site spectrality and solute interactions. Our molecular dynamic simulations demonstrate that the pronounced segregation of heavier Bi atoms, particularly at x = 0.25, leads to a substantial increase in the lattice thermal resistance at GBs, thus contributing to the degree of inhomogeneity. The concentration dependent segregation reveals the atomic origin of the observed unphysical inverse relationship between grain size and lattice thermal conductivity at the specific concentration of x = 0.25. These results highlight the need to design the alloy concentration to tune the atomic segregation and tailor the thermal properties of thermoelectric materials with GBs.

Power-cycling degradation monitoring of an IGBT module with VCE(sat) measurement in continuous operation of a chopper circuit

This paper presents a power-cycling degradation monitoring method of an IGBT module with a VCE(sat) sensing circuit and junction temperature prediction by a three-dimensional structure model. A chopper circuit was introduced to provide a continuous-current-conducting operation of the IGBT module. The VCE(sat) sensing circuit with a low-cost IoT platform “Leafony” was utilized to monitor the junction temperature of an IGBT chip, which transferred the measured signal as digital data, and thus obtained a higher noise immunity than an analog-based circuit. The junction temperature of IGBT chip in the power module was analyzed from the dissipated power of IGBT and the transient thermal impedance between the chips and the ambient. This analysis is effective not only to observe the degradation but also to estimate the thermal resistance. Comparing the temperature profile between experiment and prediction provides health condition of the IGBT model.Predicted thermal profiles agreed with measured ones with 10 % increase of thermal resistance, which was degraded by a power cycle tester. From these results, the proposed monitoring method is effective to detect the progress of power cycle degradation.

The effect of the viscoelastic support and GRPL-reinforced foam material on the thermomechanical vibration response of piezomagnetic sandwich nanosensor plates

This paper investigates the vibration characteristics of a sandwich nanosensor plate composed of piezoelectric materials, specifically barium and cobalt, in the upper and lower layers, and a core material consisting of either ceramic (silicon nitride) or metal (stainless steel) foams reinforced with graphene (GPRL). The study utilized the novel sinosoidal higher-order deformation theory and nonlocal strain gradient elasticity theory. The equations of motion for nanosensor sandwich graphene were derived using Hamilton's principle, considering the thermal, electroelastic, and magnetostrictive characteristics of the piezomagnetic surface plates. These equations were then solved using the Navier method. The core element of the sandwich nanosensor plate can be represented using three distinct foam variants: a uniform foam model, as well as two symmetric foam models. The investigation focused on analyzing the dimensionless fundamental natural frequencies of the sandwich nanosensor plate. This analysis considered the influence of three distinct foam types, the volumetric graphene ratio, temperature variation, nonlocal parameters, porosity ratio, electric and magnetic potential, as well as spring and shear viscoelastic support. Furthermore, an analysis was conducted on the impact of the metal and ceramic composition of the central section of the sandwich nanosensor plate on its dimensionless fundamental natural frequencies. In this context, the use of ceramic as the central material results in a mean enhancement of 33% in the fundamental natural frequencies. In contrast, the incorporation of graphene into the core material results in an average enhancement of 27%. The thermomechanical vibration behavior of the nanosensor plate reveals that the presence of graphene-supported foam and a viscoelastic support structure in the core layer leads to an increase in thermal resistance. This increase is dependent on factors such as the ratio of graphene, porosity ratio of the foam, and parameters of the viscoelastic support. Metal foam or ceramic foam has been found to enhance thermal resistance when compared to solid metal or ceramic core materials. The analysis results showed that it is important to take into account the temperature-dependent thermal properties of barium and cobalt, which are piezo-electromagnetic materials, and the core layer materials ceramics and metal, as well as the graphene used to strengthen the core. The research is anticipated to generate valuable findings regarding the advancement and utilization of nanosensors, transducers, and nano-electromechanical systems engineered for operation in high-temperature environments.