Interfacial Thermal Contact Resistance Research Articles

Enhancement of thermal conductivity and insulation of silicone thermal interface material through surface modification and synergistic effects of nanofillers for thermal management of electronic devices

Thermal interface materials (TIMs) play an irreplaceable role in highly integrated microelectronic devices. In this work, the addition of acidified carbon nanotubes modified by 3-aminopropyl triethoxysilane (KH550) had an effective enhancement to the thermal conductivity, thermal stability, and electrical insulation performance of silicone grease. On this basis, multi-filled silicone grease composites with better thermal conductivity and electrical insulation were prepared by introducing zinc oxide (ZnO) and Graphene nanoflakes (GNFs). The thermal conductivity of silicone grease achieved 1.438 W m−1 K−1, while the volume resistivity still exceeded 1013 Ω·cm. Additionally, the study explored the impact of varying filler parameters, temperature, and contact pressure on the interface thermal contact resistance of silicone grease. The best performance silicone grease applied to the cooling of the high-power LED exhibited excellent heat dissipation. This work presented a reference for the design and development of low cost, high performance TIMs.

Fractional derivative modelling for consolidation of multilayered saturated soils with interfacial thermal contact resistance subjected to time-dependent heating and loading

In this paper, the one-dimensional rheological consolidation characteristics of multilayered saturated soil foundations under time-dependent loading and heating are investigated by considering the semi-permeability and the interface thermal resistance. By introducing the fractional derivative model and the thermos-elastic theory, a thermo-mechanical coupling model is established to describe the rheological properties of saturated soils. Semi-analytical solutions for strain, temperature increment, pore water pressure and settlement were derived through the Laplace transform and its inverse. The accuracy of the solutions proposed in this paper has been verified by comparing with existing solutions. The effects of different thermal contact models of the interface on the rheological properties of saturated soils under semi-permeable boundary are discussed, and the effects of fractional derivative order, constitutive material parameters, and thermal conductivity of soil on the thermal consolidation process are investigated. The results show that: neglecting the thermal resistance effect can result in an overestimates of the impact of rheological properties on the thermal consolidation process of saturated soils under semi-permeable boundaries; As the thermal resistance coefficient increases, the influence of soil thermal conductivity on settlement decreases.

Dependence of drying rate on interfacial thermal contact conductance in drum drying of thin materials

Drum dryers are widely employed in various industrial fields for their remarkable capability to efficiently dry thin porous materials such as textiles and paper. The heat transfer process in drum drying involves an interaction between the drum surface and the materials being dried. However, measuring interfacial thermal contact conductance during drum drying is very challenging, and little data has been reported in the literature. It is therefore unclear how changes in interfacial thermal contact conductance quantitatively affect drum drying in terms of drying time. We created an innovative laboratory-scale experimental setup designed to measure changes in moisture content of textiles at various contact pressures during drum drying. By combining our experiments with a simple yet effective heat transfer model, we were able to quantify the impact of interfacial thermal contact resistance on drying time. Specifically, in drying tests using thin cotton textiles, the experimental results revealed that when the contact pressure was increased from 120 Pa to 480 Pa, the thermal contact conductance increased by approximately 30% and the drying time decreased by approximately 20%. The outcomes of our study significantly advance the current understanding of drum drying processes and reveal vital insights into techniques for optimizing energy consumption.

Optimization design method of material stiffness of contact interface considering surface roughness for improving thermal contact performance

The contact interface of precision mechanical equipment, such as electronic equipment, is the crucial medium for transferring internal loads and physical properties and realizing the intended function of the equipment. The thermal contact performance of precision mechanical equipment determines its overall thermal performance. Previous studies have consistently ignored the activeness of differential distribution of contact interface material stiffness in improving thermal contact performance. Therefore, this paper creatively proposed a new idea to improve thermal contact performance by designing the material stiffness of the contact interface. Firstly, based on the precise analysis model of thermal contact performance considering surface roughness, a heuristic-based optimization design method of material stiffness of contact interface was developed, which took the contact interface temperature distribution non-uniformity (CITDN) and thermal contact resistance (TCR) as the optimization objectives. Then, based on this method, the optimization designs of electronic chip packaging and proton exchange membrane fuel cell (PEMFC) were carried out. The results showed that after optimization, the TCR and CITDN of the electronic chip package were reduced by 83.23% and 92%, respectively, and the TCR and CITDN of PEMFC were decreased by 99.78% and 88.71%, respectively. This method achieved a substantial improvement in thermal contact performance.

Fractional derivative modelling for rheological characteristics of multilayered saturated porous rock with interfacial thermal contact resistance

AbstractIn this paper, the one‐dimensional rheological characteristics of multilayered saturated porous rock subjected to a ramp‐type heating is investigated. By introducing the fractional order parameter and material parameters, a viscoelastic constitutive model is proposed to describe the rheological characteristics of multilayered saturated porous rock. The general incomplete thermal contact model is established to predict the interfacial thermal contact resistance of multilayered saturated porous rock. Based on the coupled thermo‐hydro‐mechanical theory, the semi‐analytical solutions of the excess pore water pressure, temperature increment and displacement are obtained by using the Laplace transform method. The accuracy of the present solutions is verified by comparing with the classic elastic and viscoelastic models, and existing solutions. In addition, the influence of fractional order parameter, material parameter ratio, thermal contact transfer coefficient and thermal partition coefficient on the excess pore water pressure, temperature increment and displacement of multilayered saturated porous rock are investigated.

Cu/oriented-carbon nanotubes composite with ultralow thermal contact resistance

In this paper, a simple material preparation method is proposed to meet the requirements of efficient heat exchange interface materials for spacecraft on-orbit modular assembly. First, carbon nanotubes (CNTs) were uniformly dispersed on the surface of spherical copper (Cu) powder, and then the bulk was obtained by hot-pressing sintering. Finally, the Cu on the surface was removed by electrolysis, so that the CNTs can protrude from the surface to a certain height. After contacting with the matching materials, the exposed CNTs can fill the inevitable pores at the interface, increase the heat transfer channel, and effectively reduce the interface thermal contact resistance (TCR). By adjusting the type of CNT, contact pressure, the height of CNT protruding from the surface of Cu powder, the minimum TCR of the interface between the obtained Cu/oriented carbon nanotube (Cu/OCNT) composite and pure Cu was 25.4 mm2 K W−1 under 2.26 MPa, which is superior to most existing commercial thermal interface materials. Moreover, the heat exchange interface designed based on the prepared materials can be repeatedly contacted and separated, which is expected to provide a solution for the heat exchange of on-orbit modular assembly spacecraft.

The effects of interfacial thermal contact resistance between yarns and matrixes on the thermophysical property of the plain woven C/SiC composite

The plain woven C/SiC composites with high thermal shock resistance are widely used in aerospace applications. For this composite, thermal contact resistance (TCR) has an unneglectable contribution to the thermophysical property. In this work, the influence of the TCR on the thermophysical property of a real 2D plain woven C/SiC composite is studied. X-ray CT scanning is used to obtain the microstructures of the C/SiC composite, and the complex structures are restructured and transformed into standard cube grids based on the theory of the intersection of rays and triangles. Combining with finite difference method (FDM) and multiple GPUs acceleration, an efficient approach for numerically predicting the thermophysical property of the real C/SiC composite is established. Based on the Laser Flash Method (LFM) and Differential Scanning Calorimeter (DSC) method, the effective thermal conductivities (ETCs) of the C/SiC composite at different temperatures are obtained experimentally. The results show that ETCs predicted by our numerical method are closer to the measured ones when TCR is considered. Through the numerical simulation and theoretical analysis, the correlation between the ETC and TCR is obtained, which is proved to be a typical Logistic function, and the physical meanings of various constants in the correlation are determined and discussed. Besides, the thermal response time increases with the TCR increasing, simultaneously, the distributions of isotherms and heat-flux trajectories more approach the distributions of fiber yarns in the material.

Experimental Evaluation of Thermoelectric Generator Performance under Different Heat Conduction Boundary Conditions

Heat conduction boundary conditions play a crucial role in the performance of thermoelectric generators (TEG). The TEG output voltage and power were measured under constant temperature boundary and heat flux conditions to evaluate the TEG performance under different heat conduction boundary conditions. External loading pressure and thermal interface material (TIM) were applied to reduce the interfacial thermal contact resistance. In our measurement setup, a fast-response electronic load was used for the rapid current-voltage scan, which can eliminate the thermal drift caused by the Peltier effect. A guard heater arrangement is used to minimize heat loss. In constant temperature boundary conditions, reducing the thermal contact resistance can increase the effective temperature drop across the TEG module and significantly improve the output voltage and power. But in the constant heat flux conditions, since the heat flux flow through the TEG is unchanged, the temperature drop across the TEG was unaffected by the thermal contact resistance. As a result, the TEG performance was lightly influenced by the thermal contact resistance.

Investigation of ambient temperature and thermal contact resistance induced self-heating effects in nanosheet FET

Self-heating effect (SHE) is a severe issue in advanced nano-scaled devices such as stacked nanosheet field-effect transistors (NS-FET), which raises the device temperature (T D), that ultimately affects the key electrical characteristics, i.e. threshold voltage (V T), DIBL, subthreshold slope (SS), I OFF, I ON, etc. SHE puts design constraints in the advanced CMOS logic devices and circuits. In this paper, we thoroughly investigated the impact of ambient temperature and interface thermal contact resistance induced-self heating effect in the NS-FET using extensive numerical simulations. The weak electron–phonon coupling, phonon scattering, and the ambient temperature-induced joule energy directly coupled with thermal contact resistance cause the SHE-induced thermal degradation, which increases the device temperature (T D) and affects the device reliability. The baseline NS-FET is well-calibrated with the experimental data and 3D quantum corrected drift-diffusion coupled hydrodynamic and thermodynamic transport models is used in our TCAD framework to estimate the impact of ambient temperature and interface thermal contact resistance on the device performance. Moreover, we also evaluate the SHE-induced performance comparison of NS-FET with conventional FinFET and found that thermal degradation in NS-FET potentially worsen the electrical characteristics. Thus, a detailed TCAD analysis shows that the ambient temperature and interface thermal contact resistances deteriorate the effective thermal resistance (R eff) and device performance metrics.

An imperfect thermal contact problem for consolidation of bilayered saturated soil subjected to ramp-type heating

This study proposes a generalized imperfect thermal contact model to simulate the thermal contact resistance existing at the interface between the two adjacent soil layers. Based on the generalized imperfect thermal contact model, a thermo-hydro-mechanical (THM) coupled consolidation model for bilayered saturated soil under ramp-type heating load is established. By means of the Laplace transform, the semi-analytical solutions of temperature increment, excess pore water pressure and displacement of the bilayered saturated soil are obtained. Based on the present solutions, the THM coupled consolidation behaviors are investigated through comparative and parametric analysis. The results show that the generalized imperfect thermal contact model can realistically describe the imperfect thermal contact problem and can be degenerated into other commonly-used thermal contact models. Due to the existence of interfacial thermal contact resistance, only a portion of heat flux passes through the interface, weakening the influence of the thermal load on the consolidation behaviors of non-heated layer. With the decrease of contact transfer coefficient and the increase of partition coefficient, the interfacial thermal contact resistance increases, and the influence of the thermal conductivity of soil grains reduces.

Thermal performance enhancement in open-pore metal foam and foam-fin heat sinks for electronics cooling

Metal foam heat sinks can be employed for thermal management in high heat flux applications. They are generally produced by attaching metal foam to the metal substrate using heterogeneous epoxy-adhesives. This process is inefficient due to interfacial thermal contact resistance. Reducing the thermal contact resistance and minimizing the airflow resistance inside the foam enhance the thermal efficiency of the heat sink. We develop foam/foam-fin heat sinks to achieve this, wherein foam and substrate are thermally fused bonded. This paper presents an experimental study to investigate the influence of thermal contact resistance, geometrical configuration, and structural parameters such as pore density, foam height, and the number of fins on the thermal performance of novel integral foam/foam-fin heat sinks. The fused bonding method reduces the thermal contact resistance ∼ 19 times compared to the epoxy-gluing process. Consequently, the Nusselt number for the fused-bonded foam-fin heat sink increases by ∼ 30% than the epoxy-glued heat sink. Moreover, the heat transfer rate per unit mass of foam-fin heat sink is ∼ 2 times higher than the commercially available fin heat sink due to the higher specific surface area and reduced vortex formation adjacent to the foam-fins. Thus, fused-bonded foam-fin heat sinks are efficient, compact, lightweight, and easily recyclable heat exchangers. These results will be effective in designing efficient foam/foam-fin heat sinks for electronics cooling. • A novel integral foam/ foam-fin heat sink (HS) is produced via fused bonding method. • The effect of structural parameters on the thermal performance of the HS is studied. • Fused bonded HS shows ∼ 19 times lower thermal contact resistance and ∼ 30 % higher heat transfer than the epoxy-glued HS. • Foam-fin HS offers about twice the heat transfer rate per unit mass than commercially available heat sinks.

Enhanced thermal insulation properties of PI nanofiber membranes achieved by doping with SiO2 nanoparticles

At present, energy consumption is a worldwide topic and it is an urgent requirement for the development of energy-saving materials. Thermal insulation materials with a low thermal conductivity show a significant potential to reduce energy waste. In this study, polyimide (PI) and silica/polyimide (SiO2/PI) nanofiber membranes (NFMs) with low thermal conductivity were prepared by electrospinning. The effect of different content of SiO2 nanoparticles (SiO2 NPs) on the thermal insulation properties of PI NFMs and the thermal insulation mechanism were studied. SiO2/PI NFMs has the lowest thermal conductivity of 0.033 W/(m·K) when the content of SiO2 NPs was 2 wt%. The experimental results reveal that when the addition of SiO2 NPs was low, the dominant factor of the increasing thermal insulation is the interfacial thermal contact resistance between the SiO2 NPs and PI nanofibers. Moreover, the SiO2 NPs can improve the thermal stability and hydrophobic of SiO2/PI NFMs. This study indicates the SiO2/PI NFMs has the potential applications in thermal insulation.

Facial fabrication of aramid composite insulating paper with high strength and good thermal conductivity

High strength and good thermal dissipation become the inevitable requirements for the next generation of insulation materials. Here, we report a facile method to prepare composite insulating papers by incorporating two-dimensional layered boron nitride nanosheets (BNNSs) into aramid nanofibers and aramid pulp. Their layer-by-layer structure fabricated by a vacuum-assisted filtration of their mixture suspension is similar to “brick – mortar” arrangement, contributing to the enhanced mechanical properties due to their strong interaction. Meanwhile, BNNSs act as heat-conducting “bridges”, which provide the phonon conduction channels and reduce the interface thermal contact resistance. The thermal conductivity of the composite paper with 20% loading of BNNS reaches 4.34 W m-1 K-1 and the dielectric strength is up to 59.6 kV mm-1; whereas, the values of the parallel sample without BNNS are only 0.98 W m-1 K-1 and 25.1 kV mm-1, respectively. The composite papers possess highly thermal conductivities, outstanding electrical insulation and thermal stabilities, and excellent mechanical strength and flexibility, showing great potential applications in the field of flexible electronics.

Thermal rectification enhancement of bi-segment thermal rectifier based on stress induced interface thermal contact resistance

Thermal rectification is the phenomenon that heat flows much easier from forward direction than reverse direction across the structure. Materials with temperature-dependent thermal conductivity and/or variable cross section area segments are always adopted to utilize obvious thermal rectification effect. Previous studies often ignored the effect of thermal contact resistance between the two segments of traditional bi-segment thermal rectifier. Since interface thermal contact resistance also contributes significantly to the total effective thermal conductivity of the rectifier, the present paper proposed a finite element scheme to simulate the thermomechanical coupling problem caused by the stress-dependent thermal contact resistance. The proposed method is verified and validated with analytical and experimental examples respectively, and numerical results show the effect of thermal contact resistance on the optimization of thermal rectification ratio. Several key parameters such as the initial gap between the two segments and the thermal contact resistance model parameters are investigated numerically, and the present paper provide a novel approach and design guidance to manipulate heat flux through stress-dependent thermal contact resistance.

Comprehensive study and optimization of concentrated photovoltaic-thermoelectric considering all contact resistances

A consequence of the integration of photovoltaic module and thermoelectric generator is the presence of thermal contact, which affects the heat transfer in the hybrid system. Thermal and electrical contact are inevitable in a thermoelectric generator and their effects on the performance of the thermoelectric generator can be significant if not properly managed. Therefore, this study presents a comprehensive three-dimensional numerical investigation on the effect of contact resistances on the performance of concentrated photovoltaic-thermoelectric using COMSOL 5.4 Multiphysics software. Four contact resistances are studied including thermoelectric thermal contact resistance, thermoelectric electrical contact resistance, photovoltaic-thermoelectric interface thermal contact resistance and thermoelectric generator-heat sink interface thermal contact resistance. Twelve contact resistance cases are considered, and a comparison study is presented to investigate the most important contact resistance. In addition, a parametric optimization study is performed to investigate the optimum values for thermoelectric leg height, load resistance, concentration ratio and convective heat transfer coefficient. Results show that ignoring all contact resistances in the hybrid system causes an overestimation of overall power output and efficiency by 7.6% and 7.4% respectively using the base values considered in this study. In addition, the thermal contact resistance between the thermoelectric generator and heat sink, and that between the photovoltaic-thermoelectric interface are found to be the most important contact resistances, which should be reduced. Furthermore, results show that the optimum thermoelectric external load resistance in a hybrid system is lower than that of the thermoelectric generator only system. This study will provide valuable guidance on photovoltaic-thermoelectric accurate modelling.

Thermal rectification mechanism of one-dimensional composite structure with interface thermal contact resistance

Thermal rectification refers to the phenomenon that heat fluxes or equivalent thermal conductivities are different under the same temperature difference when temperature gradient directions are different. The nature of the thermal rectification is that the structure has different effective thermal conductivities in different directions. Most of previous studies focused on thermal rectification of temperature-dependent thermal conductivity materials or variable cross section area structure, and the effect of thermal contact resistance at the interface was investigated very rarely. In the present paper we present the analytical and finite element numerical solution of temperature field and thermal rectification ratios of a composite structure with variable cross section area and thermal conductivity under different interface thermal contact resistances. The prescribed temperature boundary condition is introduced by penalty method, and the temperature jump condition at the interface is implemented by the definition of thermal contact resistance directly. The nonlinear heat conduction problem caused by temperature-dependent thermal conductivity and interface thermal contact resistance is then solved with a direct iteration scheme. Comparisons between experimental results and the present theoretical and numerical results show the feasibility of the proposed model. Then parameter investigations are also conducted to reveal the effect of some key geometric and material parameters. Numerical results show that thermal contact resistance plays an important role in the temperature field and thermal rectification ratio of the two-segment thermal rectifier. With the increase of the length ratio, thermal ratification ratio increases first and decreases then, and the optimal length ratio varies with both thermal contact resistance and cross-section radius change rate of the two segments. In general, the existence of thermal contact resistance can increase the total thermal resistance of the rectifier and magnify the distinction of the heat flux in forward and reverse cases. However, if the thermal contact resistance is too large, this distinction will decrease and correspondingly the thermal rectification ratio becomes low. With the increase of the boundary temperature difference, thermal rectification ratio increases due to the effect of temperature-dependent thermal conductivity. In the present study, we propose a theoretical and numerical approach to designing and optimizing the length ratio, cross-section radius change rate, thermal conductivity, boundary temperature difference and interface thermal contact resistance to obtain the maximal thermal rectification ratio of a bi-segment thermal rectifier, as well as the manipulation of thermal flux in engineering applications.

Application of hot isostatic pressing (HIP) technology to diffusion bond refractory metals for proton beam targets and absorbers at CERN

A target assembly, composed of several collinear molybdenum (Mo)-based and tungsten (W)-based cylindrical blocks, will reside in the core of the new beam dump facility (BDF) being designed at the European Laboratory for Particle Physics (CERN). The target blocks will be protected from the cooling water erosion-corrosion by a tantalum (Ta)-based cladding. In order to obtain intimate and reliable bonding between the several cylinders composing each target block and with the cladding, hot isostatic pressing (HIP) assisted diffusion bonding technique was explored. Several down-scaled target block prototypes were conceived to investigate the bondings. Starting from the previously gained experience in Ta cladding on W from neutron spallation targets, here, we present results on Ta cladding on TZM (Mo alloy), Ta2.5W (Ta alloy) cladding on TZM and W, and on TZM to TZM and W to W self-bondings. The resulting interfaces were systematically characterized with electron microscopy, tensile testing, and thermal conductivity measurements. Successful diffusion bonding was achieved for all the studied material combinations, resulting in homogeneous and defect-free interfaces, strong interfacial bondings, and limited interfacial thermal contact resistance. The HIP parameters and diffusion interfacial aids were of great importance to optimize the interface and bulk material properties.

Thermal Conductivity of Molten Carbonates with Dispersed Solid Oxide from Differential Scanning Calorimetry.

Recently, there has been a noticeable increase in the applications of composite mixtures containing molten salt and solid oxide for thermal energy conversion and storage systems. This highlights that thermal conductivity of the composites are central for the purpose of designing and devising processes. Measuring the thermal conductivity of molten samples at elevated temperatures remains challenging. In this study, the possibility to use heat flux differential scanning calorimetry (DSC) to measure the thermal conductivity of molten samples at elevated temperatures is reported for the first time. The thermal conductivity of composite mixtures containing eutectic (Li,Na)2CO3 with and without selected solid oxides at ~675 °C was determined by using the proposed DSC approach. This mixture is a candidate for high temperature waste heat conversion to electric energy. In the DSC measurement program, steps with repeated thermal cycles between 410 and 515 °C were included to limit the effect of the interface thermal contact resistance. The determined values 0.826 ± 0.001, and 0.077 ± 0.004 W m−1K−1 for the carbonate mixtures with and without solid MgO were found to match the reliable analysis at similar conditions.

Modelling the spreading behaviour of plasma-sprayed nickel droplets under different impact conditions

Droplet spreading behaviour is critical in influencing the spreading diameters, material splashing and interfacial bonding conditions with the substrate during plasma spraying. Numerical simulations were performed to understand the effects of droplet impact temperatures, velocities and contact angle on spreading dynamics during the deposition of plasma-sprayed nickel splats. It was found that increasing droplet superheat (droplet temperature of 3000 K) was beneficial for increasing the degree of substrate melting and the droplet spreading diameters due to constrained solidification. However, solidification occurring at the droplet expanding front pinned the liquid–solid contact line and induced finger splashing for the case of 2800 K droplet temperature. The solidified layer disturbed droplet spreading and induced material jetting at the early spreading stage under the circumstance of high droplet impact velocities. A new simplified equation relating the maximum spreading ratios and Reynolds number was proposed. The effect of contact angle influenced droplet spreading under the condition of a large interfacial thermal contact resistance.

The design of high-temperature thermal conductivity measurements apparatus for thin sample size

This study presents the designing, constructing and validating processes of thermal conductivity apparatus using steady-state heat-transfer techniques with the capability of testing a material at high temperatures. This design is an improvement from ASTM D5470 standard where meter-bars with the equal cross-sectional area were used to extrapolate surface temperature and measure heat transfer across a sample. There were two meter-bars in apparatus where each was placed three thermocouples. This Apparatus using a heater with a power of 1,000 watts, and cooling water to stable condition. The pressure applied was 3.4 MPa at the cross-sectional area of 113.09 mm 2 meter-bar and thermal grease to minimized interfacial thermal contact resistance. To determine the performance, the validating process proceeded by comparing the results with thermal conductivity obtained by THB 500 made by LINSEIS. The tests showed the thermal conductivity of the stainless steel and bronze are 15.28 Wm-1K-1 and 38.01 Wm-1K-1 with a difference of test apparatus THB 500 are −2.55% and 2.49%. Furthermore, this apparatus has the capability to measure the thermal conductivity of the material to a temperature of 400°C where the results for the thermal conductivity of stainless steel is 19.21 Wm-1K-1 and the difference was 7.93%.