scholarly journals Effect of In-Plane Aspect Ratio of Graphene Filler on Anisotropic Heat Conduction in Paraffin/Graphene Composite

2021 ◽  
Author(s):  
Hiroki Matsubara ◽  
Taku Ohara
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Aspect Ratio ◽  
Thermal Management ◽  
Graphene Composite ◽  
Molecular Scale ◽  
Anisotropic Heat Conduction

Enhancement of polymer thermal conductivity by nanographene fillers and clarification of its molecular-scale mechanisms are of great concern in the development of advanced thermal management materials. In the present study,...

Thermal Conductivity of Nanochanneled Alumina

2000 ◽  
Author(s):  
A. R. Kumar ◽  
D.-A. Achimov ◽  
T. Zeng ◽  
G. Chen
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Experimental Study ◽  
Heat Conduction ◽  
Room Temperature ◽  
Conduction Model ◽  
Heat Conduction Model ◽  
Anisotropic Heat Conduction ◽  
3Ω Technique

Abstract We present an experimental study on the thermal conductivity of anodized alumina with regular nanochannels. Thermal conductivity values in both directions parallel and perpendicular to the nanochannel axis are measured at room temperature using the 3ω technique. An anisotropic heat conduction model is developed to analyze the experimental data.

scholarly journals Effects of anisotropic composite skin on electrothermal anti-icing system

2019 ◽  
Vol 233 (14) ◽  
pp. 5403-5413 ◽  
Author(s):  
Xiaobin Shen ◽  
Xiaochuan Liu ◽  
Guiping Lin ◽  
Xueqin Bu ◽  
Dongsheng Wen
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Water Film ◽  
Transfer Model ◽  
Anisotropy Axis ◽  
Mass Model ◽  
Conduction Model ◽  
Anisotropic Thermal Conductivity ◽  
Anisotropic Heat Conduction ◽  
Heat And Mass Model

To study the effects of anisotropic thermal conductivity of composite aircraft skin on the heat transfer characteristics of electrothermal anti-icing system, the differential equation of anisotropic heat conduction was established using coordinate transformation of principal anisotropy axis. In addition, it was coupled with the heat and mass transfer model of the runback water film on the anti-icing surface to perform numerical simulation of the electrothermal anti-icing system. The temperature results of the vertical and cylindrical orthotropic thermal conduction in the rectangular and semi-cylindrical composite skin were consistent with those obtained by the traditional orthotropic model, which verified the anisotropic heat conduction model. The temperature distribution of anti-icing surface agreed well with the literature data, which validated the coupled heat and mass model of the runback water flow and the anisotropic skin. The anisotropic thermal conductivity of composite skin would make temperature change more gradual, and the effect was more significant where the curvature of the temperature curve was greater. However, the anti-icing surface of the electrothermal anti-icing system was slightly affected by the anisotropic heat conduction of the multilayered composite skin.

Heat Conduction Across Nanoscale Interfaces and Nanomaterials for Thermal Management and Thermoelectric Energy Conversion

2010 ◽  
Author(s):  
Theodorian Borca-Tasciuc
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Conduction ◽  
Thermal Management ◽  
Contact Area ◽  
Silicon Substrate ◽  
Mean Free Path ◽  
Contact Mode ◽  
Nanoscale Interfaces ◽  
Air Conduction

Nanoscale heat conduction plays a critical role in applications ranging from thermal management of nanodevices to nanostructured thermoelectric materials for solid state refrigeration and power generation. This lecture presents recent investigations in our group. The first part of the lecture demonstrates heat conduction across nanoscale interfaces formed between individual nanoscale heaters and the silicon substrate [1]. A systematic experimental study was performed of thermal transport from individual nanoscale heaters with widths ranging between 77nm-250nm to bulk silicon substrates in the temperature range of 80–300K. The effective substrate thermal conductivity was measured by joule heating thermometry. We report up to two orders of magnitude reductions in the measured effective thermal conductivity of the silicon substrate when the heater widths are smaller than the mean free path of the heat carriers in the substrate, as summarized in Fig. 1. The effective mean free path of the silicon substrate was extracted from the measurements and was found to be comparable with recent molecular dynamics simulations. A proof of concept demonstration of a novel Thermal Interface Material (TIM) is presented next. The high thermal conductivity TIM is based on a highly connected high thermal conductivity nanostructured filler network embedded in a polymer matrix where the contribution of filler-matrix interfaces to thermal resistance is minimized. It was found [2] that the thermal conductivity could be varied from ∼0.2 to 20 W/mK when the volume fraction of metallic nanoparticles was varied from 0–20%. For similar volume fractions and filler composition, microparticle based composites have two orders of magnitude lower thermal conductivities. SEM characterization and thermal transport modeling are employed to support the conclusion that morphological changes in the nano-TIM are responsible for the thermal conductivity reduction. Thermoelectric transport investigations are discussed for a novel class of highly scalable nanostructured bulk chalcogenides developed at Rensselaer Polytechnic Institute [3]. Un-optimized, single-component bulk assemblies of Bi2Te3 and Sb2Te3 single crystal nanoplates show large enhancements (25–60%) in the room temperature thermoelectric figure of merit compared with individual bulk counterparts (Table 1). Nanostructuring was found to lead to strong thermal conductivity reduction without significantly affecting the mobility of the charge carriers, as shown in Table 2. A scanning thermal microprobe technique developed for simultaneous thermal conductivity (κ) and Seebeck coefficient (α) measurements in thermoelectric films is also presented [4]. In this technique, an AC alternative current joule-heated V-shaped microwire that serves as heater, thermometer and voltage electrode, locally heats the thin film when contacted with the surface (Fig. 2). The κ is extracted from the average DC temperature rise thermal resistance of the microprobe and α from the DC Seebeck voltage measured between the probe and unheated regions of the film by modeling the heat transfer in the probe, sample and their contact area, and by calibrations with standard reference samples. Application of the technique on sulfur-doped porous Bi2Te3 and Bi2Se3 films reveals α = −105.4 and 1.96 μV/K, respectively, which are within 2% of the values obtained by independent measurements carried out using microfabricated test structures. The respective κ values are 0.36 and 0.52 W/mK, which are significantly lower than the bulk values due to film porosity, and are consistent with effective media theory. The dominance of air conduction at the probe-sample contact area determines the microscale spatial resolution of the technique and allows probing samples with rough surfaces. Non-contact mode measurement of thermal conductivity was also demonstrated and confirmed by independent characterization [5]. In non-contact mode the technique utilizes ballistic air conduction as the dominant heat transfer mechanism between the thermal probe and the sample and thus eliminates uncertainties due to solid contact and liquid meniscus conduction.

The Effects of Processing Conditions on the Thermal Conductivity of Polycrystalline Silicon Films

2003 ◽  
Author(s):  
Samuel Graham ◽  
Brandon Olson ◽  
Channy Wong ◽  
Edward Piekos
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Thermal Management ◽  
Structural Properties ◽  
Polycrystalline Silicon ◽  
Thermal Dissipation ◽  
Processing Conditions ◽  
Mems Devices ◽  
Thermal Actuators ◽  
Polycrystalline Silicon Films

Polycrystalline silicon has been a primary material used in development of mocroelectrical mechanical systems due to its attractive structural properties and compatibility with CMOS processing. Among its many applications, polysilicon is currently being employed in MEMS devices that require thermal dissipation or thermal management to ensure functionality (thermal actuators, microengines, etc.). In these applications, heat conduction in polycrystalline silicon becomes a primary factor in the design, performance, and reliability of thermal MEMS.

CONSIDERATION OF CARBON NANOTUBE-BASED NANOFLUID IN THERMAL TRANSFER.

2016 ◽  
Vol 78 (8-4) ◽  
Author(s):  
Thierry Mare ◽  
Patrice Estelle ◽  
Salma Halelfadl ◽  
Normah Mohd Ghazali
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Carbon Nanotube ◽  
Aspect Ratio ◽  
Thermal Management ◽  
Thermophysical Properties ◽  
Current Trend ◽  
Heat Removal ◽  
Thermal Transfer ◽  
Low Viscosity

In the current trend towards demand for effective heat removal of high density heat flux, research into nanofluids have escalated due to the rise in thermal conductivity associated with the coolants. Are nanofluids a solution for a better thermal management? Does the application of nanofluids as coolants have limitations? This article presents a review of the thermophysical properties of carbon nanotube-water nanofluids, in particular the desired properties of low viscosity and high thermal conductivity. The effects of the concentration, temperature, aspect ratio, and surfactant on the thermal conductivity and viscosity of carbon nanotube nanofluid have been studied experimentally. These effects are thendiscussed for evaluation of the applicability of carbon nanotube-based nanofluidas a coolant for heat removal purposes.

scholarly journals APPROXIMATE ANALYTICAL SOLUTION OF THE PROBLEM OF CONJUGATE HEAT TRANSFER BETWEEN THE BOUNDARY LAYER AND THE ANISOTROPIC STRIP

2019 ◽  
Vol 16 (32) ◽  
pp. 572-582
Author(s):  
Vladimir F. FORMALEV ◽  
Sergey A. KOLESNIK ◽  
Ekaterina L. KUZNETSOVA
Keyword(s):  
Thermal Conductivity ◽  
Boundary Layer ◽  
Heat Conduction ◽  
Analytical Solution ◽  
Integral Transform ◽  
External Boundary ◽  
Interface Boundary ◽  
Heat Flows ◽  
Anisotropic Heat Conduction ◽  
Longitudinal Variable

Optimization of technological processes in metallurgy related to transfer and use of heat energy makes more complicated demands for calculation of heat exchange. Therefore, the work, the approximate analytical method for solving the conjugate problems of viscous gas-dynamic boundary layer and thermal conductivity in the anisotropic strip, has been developed. The paper uses modern numerical methods for solving differential equations in partial derivative and analytic methods on the basis of an integral transform of Fourier and Laplace. Boundary equations have been solved analytically with certain simplifications, and the problem of anisotropic heat conduction has been solved analytically. The heat flows are determined analytically by the longitudinal variable at the interface boundary. It has been established that temperature increase of the external surface contributes to that all factors directly impacting on the magnitude of heat flows act towards their reduction. The analytical solution for the problem of thermal conductivity in the anisotropic strip with a general type of anisotropy when the heat flows from the boundary layer are determined at the boundaries is obtained. The conducted research for the temperature of external boundary and heat flow from gas to it demonstrates that with increasing the degree of longitudinal anisotropy the surface temperature of the strip downstream increases from increasing longitudinal heat conduction An original conjugation method using the continuous heat flows, and temperatures at the interface boundary is found. The numerical results for the heat flows and temperatures at the interface boundary have been obtained and analyzed.

scholarly journals Wide range continuously tunable and fast thermal switching based on compressible graphene composite foams

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Tingting Du ◽  
Zixin Xiong ◽  
Luis Delgado ◽  
Weizhi Liao ◽  
Joseph Peoples ◽  
...  
Keyword(s):  
Thermal Management ◽  
Dynamic Control ◽  
Operating Conditions ◽  
Dynamic Thermal Management ◽  
Graphene Composite ◽  
Continuous Tuning ◽  
Composite Foams ◽  
Wide Range ◽  
Thermal Switches ◽  
Thermal Switching

AbstractThermal switches have gained intense interest recently for enabling dynamic thermal management of electronic devices and batteries that need to function at dramatically varied ambient or operating conditions. However, current approaches have limitations such as the lack of continuous tunability, low switching ratio, low speed, and not being scalable. Here, a continuously tunable, wide-range, and fast thermal switching approach is proposed and demonstrated using compressible graphene composite foams. Large (~8x) continuous tuning of the thermal resistance is achieved from the uncompressed to the fully compressed state. Environmental chamber experiments show that our variable thermal resistor can precisely stabilize the operating temperature of a heat generating device while the ambient temperature varies continuously by ~10 °C or the heat generation rate varies by a factor of 2.7. This thermal device is promising for dynamic control of operating temperatures in battery thermal management, space conditioning, vehicle thermal comfort, and thermal energy storage.

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