Showing papers on "Thermal contact conductance published in 2022"

Oriented BN/Silicone rubber composite thermal interface materials with high out-of-plane thermal conductivity and flexibility

Abstract: Polymer composites with high out-of-plane thermal conductivity, flexibility, and low modulus have always been one of the ideal thermal interface materials. Using softer polymer composites can reduce thermal contact resistance and stress caused by the mismatch of the coefficient of thermal expansion, as well as heat can be quickly transferred due to its high out-of-plane thermal conductivity. Herein, we report a silicone rubber-based composites with high out-of-plane thermal conductivity and softness prepared by combining shear orientation and layer-by-layer stacking methods. The composites exhibit an out-of-plane thermal conductivity of 7.62 Wm-1K−1, while maintain the flexibility and high elastic recovery of silicone rubber. According to finite element simulation analysis, the increase in thermal conductivity comes from the orientation of the BN flakes and the formation of the thermal network. This work provides a simple method for the preparation of flexible thermal interface materials with high out-of-plane thermal conductivity for many potential applications.

Performance of Thermal Interface Materials.

Abstract: The thermal interface materials (TIMs) used for improving thermal contacts are considered in terms of the performance, performance consideration criteria, performance evaluation methods, and material development approaches. The performance is described mainly by the thermal contact conductance, which refers to the conductance across the thermal contact surfaces that sandwiches the TIM. This conductance depends on the conformability, thermal conductivity, and small-thickness feasibility. However, the vast majority of published work does not consider this conductance, but only the thermal conductivity within the TIM. The highest TIM performance is exhibited by the thermal pastes and low-melting alloys.

Promoting the thermal transport via understanding the intrinsic relation between thermal conductivity and interfacial contact probability in the polymeric composites with hybrid fillers

Abstract: Polymeric composites with thermally conductive hybrid fillers are significant in the electronics and thermal dissipation , where thermal transport along with multifunctionality is required to meet the application needs. Introduction of hybrid fillers would induce multiple interface scattering and rational design on the filler contact should be the critical criteria, while there is insufficient principle. To promote the thermal transport capability, in this paper, a contact probability model has been established to quantitatively analyze the thermal conductivity and contact probability in the silicone rubber composites with hybrid fillers (including various aluminium oxides and silicon carbide whisker). The results from experiment and simulation suggest that three critical parameters, i.e. volume fraction, filler shape and filler size, are the essential factors of hybrid fillers on impacting the thermal conductivity of composites. With understanding the contact types of hybrid filler, the optimized thermal conductivity has been obtained in the composites with aluminium oxides and silicon carbide whisker fillers. The model and analysis here have provided new contact mechanism for understanding the thermal transport in composites, which could be extended to rationally design and fabricate other types of polymeric composites with hybrid fillers.

Phase change mediated graphene hydrogel-based thermal interface material with low thermal contact resistance for thermal management

Abstract: Thermal interface materials (TIMs) are the key to solving heat dissipation problems in high-power electrical equipment. TIMs with high thermal conductivity and low thermal contact resistance (TCR) will enhance interfacial heat transfer. In this work, a phase-change mediated graphene composite hydrogel with low TCR and high thermal conductivity is designed. In addition, by introducing the hydrogel cross-linked network into the phase change material, the phase change material leakage problem is effectively solved. The thermal conductivity of the phase change hydrogel is enhanced by 324% from 0.3 W m − 1 K − 1 to 1.23 W m − 1 K − 1 at a filling rate of 7 wt% of graphene. The effects of temperature and pressure on phase change composite hydrogels are investigated. When the temperature is increased from 50 °C to 80 °C, TCR decreases rapidly from 90 K ∙ c m 2 / W to 0.2–0.5 K ∙ c m 2 / W , which is attributed to the improved interfacial wettability mediated by the phase change. When the pressure is increased from 10 Psi to 50 Psi with 80 °C, TCR decrease from 20 K ∙ c m 2 / W to 0.5 K ∙ c m 2 / W , improving interfacial contact and enhancing interfacial heat transfer. Combining a hydrogel with a cross-linked structure with the phase change material resulted in an excellent encapsulation of the phase change material. The thermal management performance of the phase change hydrogel is evaluated using infrared thermography and shows good thermal response behavior as the temperature rose to 68.7 °C after 120 s of heating. The strategy of combining phase change materials with hydrogels will provide new ideas for the design of TIMs.

The Effect of the Surface Roughness Characteristics of the Contact Interface on the Thermal Contact Resistance of the PP-IGBT Module

Abstract: In this article, the correlation between the thermal contact resistance and the surface roughness characteristics of the contact interface in the press-pack insulated-gate bipolar transistor (PP-IGBT) modules during power cycling was studied by experimental measurements and finite-element (FE) simulation-based factorial design analysis. Thermal transient test technology was applied to examine the change in the thermal characteristic parameters of the PP-IGBT module. This shows that the increase in the thermal contact resistance of the Al metallization/emitter Mo contact interface occurs more dramatically during power cycling. A 3-D surface profilometer was used to evaluate the surface morphology parameters of the Al metallization/emitter Mo contact interface. The equivalent root-mean-square (RMS) roughness increases during power cycling, and the equivalent asperity slope and the equivalent spacing between asperities increase slightly. Additionally, the surface roughening in the corner area of the chip is more obvious than in other regions. A fractional factorial design analysis based on FE simulations was performed. The results indicate that the thermal contact resistance strongly depends on the main effects of the real contact area and the spacing between the asperities, and the RMS roughness and the asperity slope interaction.

Ultralow Interfacial Thermal Resistance of Graphene Thermal Interface Materials with Surface Metal Liquefaction

Abstract: Developing advanced thermal interface materials (TIMs) to bridge heat-generating chip and heat sink for constructing an efficient heat transfer interface is the key technology to solve the thermal management issue of high-power semiconductor devices. Based on the ultra-high basal-plane thermal conductivity, graphene is an ideal candidate for preparing high-performance TIMs, preferably to form a vertically aligned structure so that the basal-plane of graphene is consistent with the heat transfer direction of TIM. However, the actual interfacial heat transfer efficiency of currently reported vertically aligned graphene TIMs is far from satisfactory. In addition to the fact that the thermal conductivity of the vertically aligned TIMs can be further improved, another critical factor is the limited actual contact area leading to relatively high contact thermal resistance (20-30 K mm2 W-1) of the "solid-solid" mating interface formed by the vertical graphene and the rough chip/heat sink. To solve this common problem faced by vertically aligned graphene, in this work, we combined mechanical orientation and surface modification strategy to construct a three-tiered TIM composed of mainly vertically aligned graphene in the middle and micrometer-thick liquid metal as a cap layer on upper and lower surfaces. Based on rational graphene orientation regulation in the middle tier, the resultant graphene-based TIM exhibited an ultra-high thermal conductivity of 176 W m-1 K-1. Additionally, we demonstrated that the liquid metal cap layer in contact with the chip/heat sink forms a "liquid-solid" mating interface, significantly increasing the effective heat transfer area and giving a low contact thermal conductivity of 4-6 K mm2 W-1 under packaging conditions. This finding provides valuable guidance for the design of high-performance TIMs based on two-dimensional materials and improves the possibility of their practical application in electronic thermal management.

A general interfacial thermal contact model for consolidation of bilayered saturated soils considering thermo‐osmosis effect

Abstract: In this paper, a general interfacial thermal contact model is proposed to investigate the heat conduction characteristics at the interface of bilayered saturated soils. The semianalytical solutions of thermal consolidation of the bilayered saturated soils considering thermo‐osmosis effect under ramp‐type heating are derived by using the Laplace transform. Then, the expressions of the temperature increment, excess pore water pressure, and displacement are obtained in time domain by using the Crump's method. Comparisons are performed to verify the rationality of the obtained solutions, and the influences of contact transfer coefficient, partition coefficient, and the thermo‐osmosis coefficient on the thermal consolidation of the bilayered saturated soil are illustrated and discussed. Neglecting the thermal contact resistance would overestimate the thermal consolidation behavior of the bilayered saturated soils. The calculated excess pore water pressure and displacement considering thermo‐osmosis effect are much larger than those without thermo‐osmosis effect.

Tuning the interfacial friction force and thermal conductance by altering phonon properties at contact interface

Abstract: Controlling friction force and thermal conductance at solid/solid interface is of great importance but remains a significant challenge. In this work, we propose a method to control the matching degree of phonon spectra at the interface through modifying the atomic mass of contact materials, thereby regulating the interfacial friction force and thermal conductance. Results of Debye theory and molecular dynamics simulations show that the cutoff frequency of phonon spectrum decreases with increasing atomic mass. Thus, two contact surfaces with equal atomic mass have same vibrational characteristics, so that more phonons could pass through the interface. In these regards, the coupling strength of phonon modes on contact surfaces makes it possible to gain insight into the nonmonotonic variation of interfacial friction force and thermal conductance. Our investigations suggest that the overlap of phonon modes increases energy scattering channels and therefore phonon transmission at the interface, and finally, an enhanced energy dissipation in friction and heat transfer ability at interface.

Thermal conductivity of Aluminum/Graphene metal-matrix composites: From the thermal boundary conductance to thermal regulation

Abstract: Aluminum is a commonly used heat dissipation material, and further improvement of its cooling performance is usually by adding an appropriate reinforcement phase into its composites. Graphene holds great promise for thermal enhancement in composites due to its outstanding thermal properties. However, the systematic study of the thermal conductance of the Aluminum/Graphene (Al/Gr) interface and thermal conductivity of Al/Gr metal-matrix composites (MMCs) are still lacking. The thermal properties of Al/Gr MMCs are explored using molecular dynamics simulation methods. Thermal boundary conductance of the Al/Gr interface plays a crucial role in the whole thermal properties of the Al/Gr composite. The parameters of model size, layer number, temperature, and strain are considered. The results show that the thermal boundary conductance (TBC) decreases with increasing layer number, and reaches a plateau at n = 5. TBC falls under tensile strain and, in turn, it grows with compressive strain. The variation of TBC is explained qualitatively by the phonon coupling factor and surface potential energy barrier. The thermal conductivity of Al/Gr MMCs is computed taking into account TBC effects at Al/Gr interfaces, and its thermal conductivity increases with graphene volume content. Our findings also provide insights into ways to optimize future thermal management based on MMCs materials.

Fractal model of thermal contact conductance of two spherical joint surfaces considering friction coefficient

Abstract: Purpose The purpose of this study is to propose a fractal model of thermal contact conductance (TCC) of two spherical joint surfaces, considering friction coefficient based on the three-dimensional fractal theory. Design/methodology/approach The effects of friction coefficient, fractal parameters, radius of curvature and contact type on TCC were analyzed using numerical simulation. Findings The results indicate that the TCC decreases with the increase of friction coefficient and fractal roughness and increases with the increase of fractal dimension and radius of curvature; the contact type of two spherical joint surfaces has an important influence on the TCC, and the TCC of external contact is smaller than that of internal contact under the same contact load. Originality/value A fractal model of TCC of two spherical joint surfaces considering friction coefficient is proposed in this paper. Achievements of this work provide some theoretical basis for the research of TCC of bearings and other curved surfaces.

Near-field radiation analysis and thermal contact radius determination in the thermal conductivity measurement based on SThM open-loop system

Abstract: With the rapid development of materials science, plenty of materials with micro-nano structures are emerging in various fields due to their outstanding physical properties. In order to fulfill the needs of micro-nano-scale thermal measurement, a series of thermophysical characterization methods have been evolving. In this article, a measurement method based on the Scanning Thermal Microscopy open-loop system is proposed to realize nano-scale thermal conductivity characterization. Both forward and backward thermal contact radius are measured. The heat transfer tunnel raised by the near-field radiation is calculated to be 1.73 × 10−14 W/K as the upper limit, which can be neglected compared to the total value. The total thermal conductance between tip and sample was calibrated as 1.8 × 10−6 W/K by several standard bulk samples, and thermal conductivity varies from 0.28 to 237 Wm−1 K−1.

Effect Mechanism and Performance Evaluation of Flange Contact Thermal Resistance in an Aero-Engine

Abstract: According to the discontinuous structural characteristics of a gas turbine, by considering the contact thermal resistance of the rough surface, a contact thermal resistance measurement experiment was conducted in this study. The main objectives of this work were to investigate the influence mechanism and change law of the contact thermal resistance characteristics on flange installation. Furthermore, this study conducted a theoretical analysis of contact thermal resistance and the calculation of a typical flange mounting edge based on actual operating conditions. The research results show that the contact thermal resistance of a typical flange mounting edge increases with an increase in flange clearance under different tightening torques, which is essentially proportional to the flange clearance. As the flange clearance increases, the unit contact thermal conductivity firstly decreases rapidly. Then, as the flange clearance reaches 0.4 mm, the decreasing rate of unit contact thermal conductivity tends to flatten. In addition, the contact thermal resistance of the typical flange mounting edge decreases with the increase in the tightening torque under different flange clearances. Furthermore, the contact area ratio is not related to the material, and the contact thermal resistance under actual working conditions can be calculated using the unit contact area.