Thermal Management Of Electronic Devices Research Articles

Thermophysical characteristics and application of metallic-oxide based mono and hybrid nanocomposite phase change materials for thermal management systems

This experimental study covers the chemical, physical, thermal characterization and application of novel nanocomposite phase change materials (NCPCMs) dispersed by TiO2, Al2O3, and CuO nanoparticles for thermal management systems. A commercial-grade of paraffin, namely RT-35HC, was considered as a phase change material (PCM). The mono and hybrid NCPCMs were synthesized at a constant weight concentration of 1.0 wt.%. In the first phase, various characterization techniques were used to explore the thermophysical properties and chemical interaction of mono and hybrid NCPCMs. In the second phase, the thermal cooling performance was investigated by filling the prepared NCPCMs in a heat sink at various input power levels. The results showed the uniform dispersion of TiO2, Al2O3, and CuO nanoparticles onto the surface of both mono and hybrid NCPCMs without altering the chemical structure of RT-35HC. The optimum latent-heat of fusion and highest thermal conductivity of 228.46 J/g and 0.328 W/m K were obtained, respectively, of Al2O3+CuO dispersed hybrid NCPCM compared to pure RT-35HC. In comparison of RT-35HC, the increasing trend in specific heat capacity was observed of NCPCMs and 36.47% enhancement was obtained for hybrid NCPCM in solid-phase. The reduction in heat sink base temperature was achieved of 3.67%, 6.13%, 13.95% and 8.23% for NCPCMTiO2, NCPCMAl2O3, NCPCMCuO and NCPCMAl2O3+CuO, respectively, compared to RT-35HC. Further, no phase segregation, less subcooling, smaller phase transition temperature, higher chemical and thermal stability were observed with hybrid NCPCMs which can be used potentially for thermal management of electronic devices, Li-ion batteries and photovoltaic (PV) modules systems.

Artificial Nacre Epoxy Nanomaterials Based on Janus Graphene Oxide for Thermal Management Applications.

Owing to the development of microelectronics, demands for excellent thermal dissipation materials have substantially increased. Learning from natural nacre, thermally conductive epoxy nanocomposites were prepared based on asymmetrically polydopamine-functionalized Janus graphene oxide (JPGO) scaffolds. The required highly oriented JPGO scaffolds were prepared via the bidirectional freeze-casting method. With the addition of epoxy resin, the resulting nanocomposite reveals anisotropic thermal properties. With the total content of the JPGO scaffold being 0.93 wt %, almost 35 times enhancement of in-plane thermal conductivity (perpendicular to the lamellar structure) (∼5.6 W m-1 K-1) has been obtained. The single-side-functionalized JPGO scaffolds play an important role in forming thermal conductive networks for the epoxy nanocomposites. Importantly, the nanocomposites present electrically insulating properties (>1014 Ω cm). Such high-performance nanocomposites have promising applications for thermal management in electronic devices.

Two-phase flow boiling in a microfluidic channel at high mass flux

We report the experimental investigations of two-phase flow boiling heat transfer characteristics of a refrigerant in a microfluidic channel at a high mass flux (more than 1000 kg/m2 s). We investigate the heat transfer coefficients at a heat flux range of 7.63 kW/m2–49.46 kW/m2, mass flux range of 600 kg/m2 s–1400 kg/m2 s (high mass flux), and saturation temperature range of 23 °C–31 °C. We propose the new two-phase flow boiling heat transfer correlation of a refrigerant, which is used as the working fluid for the present experiments, at the microfluidic scale. We experimentally establish the functional relationship of two-phase flow boiling heat transfer correlation of the refrigerant during flow boiling in a rectangular microchannel with the Reynolds number, the boiling number, and the Weber number. We believe that the inferences of this study may provide a design basis for the micro-heat exchanger, typically used for thermal management in electronic devices, micro-electro-mechanical systems, and electric vehicle battery cooling system.

Investigation of thermal performance of modified vertical rectangular fin array in free convection using experimental and numerical method

Heat transfer by free convection from fin array is influenced by modification in size and shape of the fins as well as interruption in fluid flow. The objective of heat sink is the thermal management of electronic devices by removing excessive heat and improve the lifespan of the device. The paper investigates the thermal performance of free convection heat transfer with vertical heat sink by providing slits along the vertical surface of the fins. For the evaluation purpose two different arrangements viz. plain fin and slitted fin are selected. Fins are made from high thermal conductivity aluminium material and five dissimilar heat inputs are selected for study. The experimental and numerical findings are confirmed using the theoretical correlations available from the literature.The effect of number of slits and width of slits is investigated on convective heat transfer coefficient. Numerical study is used to understand the flow patterns around the vertical fin surface. It has been observed that the presence of slits on the surface appreciably improves the thermal performance of vertical fin array.

Thermal Management of Electronic Devices Using Gold and Carbon Nanofluids in a Lid-Driven Square Cavity Under the Effect of Variety of Magnetic Fields

Heat is an inevitable by-product of every electronic device and thermal management is very much essential for them to improve reliability and to prevent premature failure. Liquid coolants are one of the best switching options to achieve higher cooling rates. However, by adopting them in cooling systems such as microchannel heat sinks in which flow enters in to and out of the system may cause leakage of the coolant, which results in the complete firing of the electronic device. Hence, in the present study, this problem is avoided by adopting lid-driven square cavity as a cooling system. A 2-D numerical study has been carried out to obtain the convective heat transfer efficiency (CHTE) of gold and carbon nanofluid (NF) in a lid-driven square cavity over silicon solid block under the influence of a variety of magnetic fields. The geometrical domain consists of a square cavity containing NF that is driven by means of lid moving in one direction. This circulating NF will extract an enormous amount of heat from the solid block underneath the cavity resulting in conjugate heat transfer. A finite volume method-based conjugate homogeneous heat transfer model has been developed, validated, and used in the present study. The heat efficient Gold (Au) and single-walled carbon nanotube (SWCNT) NF pairs obtained by Nimmagadda and Venkatasubbaiah are used in the present study. Moreover, efficiently varied magnetic fields identified by Nimmagadda et al. are also implemented and compared with the uniform magnetic field. Furthermore, the magnetic field is applied over the geometrical domain along the two axial directions separately and the effective CHTE is obtained. The significant impact of broad parameters, such as magnetic field type, location and strength, nanoparticle concentration and type, and Reynolds number on the CHTE, is systematically analyzed and presented.

Development and characterization of form‐stable porous TiO 2 /tetradecanoic acid based composite PCM with long‐term stability as solar thermal energy storage material

The present study focused on the preparation of form-stable composites of 1-tetradecanoic acid (TDA)/titanium dioxide (TiO2) powder via a facile impregnation method. The use of powdered TiO2 as porous material and thermal conductivity enhancer for TDA is a novel attempt. The morphological, chemical, and crystalline properties of form-stable composite PCMs (Fs-CPCMs), containing different amounts of TiO2, were characterized using field emission scanning electron microscope, Fourier transform infrared spectroscopy, and X-ray diffraction techniques. The finding supports that the produced composites were chemically and structurally stable. The latent heat storage (LHS) properties of composites were obtained from differential scanning calorimeter instrument, and the findings revealed that the Fs-CPCM with 50 mass% TDA has a melting temperature of 52.04°C and a considerably good LHS capacity of 97.75 J/g. The thermal conductivity of TDA was increased remarkably by the addition of TiO2 micro particles. The results obtained from thermogravimetric analysis and thermal cycling test exhibited that the Fs-CPCM, containing 50 mass% TiO2, possesses great thermal degradation durability, cycling chemical stability, and thermal reliability. This composite PCM can be very well used for passive thermal management of electronic devices, automotive components, photovoltaic thermal hybrid designs, solar air/water heating systems, etc.

Comparison of the generation characteristics and application performance of nanomaterials-enhanced ionic wind

Ionic wind technology is a right candidate for the thermal management of electronic devices. However, some highly-oxidizing substances are produced during corona discharge, which can destroy the electrode and shorten its service life. In the present work, nanomaterials were coated on the surfaces of needles, which act as emitting electrodes. The generation characteristics of ionic wind and the working durability of an ionic wind generator (IWG) were compared experimentally. The generator modified by nanomaterials was subsequently used to cool high-power LED chips, and the changes in the optical properties of the chips were studied. The results indicate that the electric field intensity and corona current increased after the application of the nanomaterials. The nanomaterials-decorated IWG performed better in operating durability than the original prototype. When the nanomaterials-decorated IWG was applied to cool LEDs, the case temperature at a discharge power of 3 W was reduced by 5.8 °C compared with the original generator. The luminous flux output increased by 28 lm and took less time to reach a stable working state. The ionic wind velocity and the energy conversion efficiency of the system were also greatly improved. This study provides a potential solution for the efficient thermal management of electronic devices.

Experimental study on the heat transfer performance of a gallium heat sink

Phase change thermal storage technology has received considerable attention in the thermal management of electronic devices. Unfortunately, the efficiency using paraffin is too low to meet the heat dissipation requirements of high power devices. In this work, gallium is selected as the phase change material, and the melting mechanism of gallium heat sink in spatial distributions is examined by experiment. Results show that the heat transfer efficiency of regions in the Y-cross section near the heating surface and in the X-cross section near the upper surface of the gallium heat sink are better than other regions. The average effective thermal conductivity of the gallium heat sink reaches 71.97 W/(m·K). The natural convection promotes the overall melting rate, but it results in the inefficient heat transfer in the middle melting stage and worse heat transfer in the later melting stage. Compared with the copper foam/paraffin composite heat sink in the same size, the overall and most of melting time of the gallium heat sink is reduced by 55.5% and 56.0%, respectively. At the same thermal storage capacity, the volume and weight of the gallium heat sink are reduced by 67% and 18%, respectively, compared with the copper foam/paraffin composite heat sink.

Study of phononic thermal transport across nanostructured interfaces using phonon Monte Carlo method

Reducing the phonon-dominated thermal interfacial resistance (TIR) is an effective way to reduce the junction temperature of electronic devices. Several researches have demonstrated that fabricating nanostructures at interface, i.e., constructing nanostructured interface, could significantly enhance the interfacial thermal transport. Here, we conducted a parametrical study on the phononic thermal transport across nanostructured interfaces using phonon Monte Carlo (MC) technique, and analyzed the dependence of effective thermal resistance ratio between the nanostructured and planar interfaces on the various parameters and the heat flux distributions. Our simulations and analyses indicate that the interfacial thermal transport improvement should be attributed to two mechanisms: the change of heat conduction pathways resulted from the interfacial nanostructures and the phonon transmission enhancement induced by the multiple reflection at the interface. The former is predominant when the diffusive transport dominates, while the latter becomes dominant with the enhancement of ballistic transport effect. Additionally, the diffuse scattering of phonons at the interface, which is enhanced with the increasing interface roughness, has a strong negative effect on the improvement of interfacial thermal transport. Due to the combination of those three mechanisms above, the effective thermal resistance ratio decreases to a minimum value and then increases with the increasing contacting area. The present work provides a more in-depth understanding on the interfacial thermal transport in nanostructured interfaces, and can be helpful for the thermal management of electronic devices.

Network Structural CNTs Penetrate Porous Carbon Support for Phase‐Change Materials with Enhanced Electro‐Thermal Performance

AbstractElectro‐thermal phase‐change materials (PCMs) enable continuous operation of heating‐related processes, which is urgently required for modern thermal‐management devices. Driven by the unmet needs to develop promising electro‐thermal PCMs with low operation voltage and high electro‐thermal storage efficiency simultaneously, unique ZIF@MOF‐derived carbon‐nanotube (CNT)‐penetrated porous carbon supports for electro‐thermal PCMs are introduced. The network structure of the support decreases the resistivity of the composite and ensures a low operation voltage. Furthermore, abundant CNT cores in porous carbon shells facilitate interfacial interaction between the PCMs and the support and realize a rapid heat transformation. It is noted that low thermal conductive porous carbon shells prevent convective heat dissipation at the CNT‐air interface to a great degree which leads to enhanced electro‐thermal storage efficiency. Consequently, the obtained electro‐thermal PCMs exhibit a low operation voltage of 1.1 V and a record‐high electro‐thermal storage efficiency of 94.5%, which shows great potential in thermal management of electronic devices.

Thermal Conductivity of Graphene on Nanostructure Size from Nonequilibrium Molecular Dynamics Simulations

Thermal transport of graphene occupies a unique place in thermal management of electronic devices, especially for nanosize devices with high-density integration and high dissipated power. The structure of graphene on nanometer scale changes its thermal conductance. Here, the thermal characters of graphene have been researched by nonequilibrium molecular dynamics simulation (NEMDS) at room temperature. Special attention is focused on the edge type (zigzag or armchair) and nanostructure size dependence of conductivity for heat. The consequences suggest that the thermal conductivity of zigzag edge has been higher than that of armchair, which is because of the higher phonon group velocities. Furthermore, thermal conductivity shows a rising tendency, when the model is calculated from length of 21.84 nm to 43.78 nm. The result indicates that the thermal property performs a strong dependence on nanostructure size which is less than phonon mean free path (775 nm). Our research highlights the significance of structure attribute relationships together with providing useful guideline in calculations for nanosize devices thermal management.

Experimental study on melting performance of phase change material-based finned heat sinks by a comprehensive evaluation

Efficient thermal management has become an important challenge for the integration and miniaturization of electronic devices with high power density. Phase change material (PCM)-based finned heat sink is an efficient passive cooling technology for an intermittent-use electronic device with high power density. The present work reports an experimental study on the transient thermal performance of PCM-based finned heat sinks for thermal management of electronic devices, with particular emphasis on the roles of heat load and PCM volumetric fraction. The temperature response and melting front evolution in heat sinks are analyzed and compared with the corresponding cavity. Moreover, the effects of heat load, fin geometry and PCM volumetric fraction on the melting performance of heat sinks are discussed. The results indicate the presence of fins effectively improves the thermal performance of PCM-based heat sinks, and a more fin number leads to a lower operating temperature and hence the duration of electronic devices is longer in an accepted temperature. Moreover, a higher input heat flux results in a higher operating temperature and a shorter duration of low operating temperature. The increase in PCM volumetric fraction enhances the thermal storage capacity of finned heat sinks and reduces the operating temperature. Therefore, the finned heat sinks filled with PCM ensure sufficiently low operating temperature for perfect reliability and duration of high-power-density electronic devices.

Intercalation of copper microparticles in an expanded graphite film with improved through-plane thermal conductivity

As a type of heat dissipation material, graphite has attracted great attention due to its outstanding thermal conduction. However, the relatively poor through-plane thermal conductivity restricts its applications in certain areas. In this work, a novel thermally conductive film was developed via in situ growth of Cu microparticles between interlayers of expanded graphite (EG). The intercalation of Cu microparticles in EG improved the through-plane thermal conductivity of the film from 8.5 to 11.1 W/(m K), owing to the three-dimensional stacking architecture of Cu/EG hybrid framework, which leads to more thermal paths along the vertical direction. This Cu/EG hybrid film showed better heat spreading ability than the pristine EG film, reducing the working temperature of the LED device by 1.9 °C. Furthermore, the through-plane thermal conductivities of Cu/EG hybrid films can be controlled by the amount of Cu precursors, and the highest through-plane thermal conductivity of 11.1 W/(m K) was achieved with intercalation of 0.8–4.5 μm Cu microparticles by adding 50% Cu precursors. This thermally conductive Cu/EG hybrid film has great potential in the thermal management of electronic devices.

Nanocelluloses and Related Materials Applicable in Thermal Management of Electronic Devices: A Review.

Owing to formidable advances in the electronics industry, efficient heat removal in electronic devices has been an urgent issue. For thermal management, electrically insulating materials that have higher thermal conductivities are desired. Recently, nanocelluloses (NCs) and related materials have been intensely studied because they possess outstanding properties and can be produced from renewable resources. This article gives an overview of NCs and related materials potentially applicable in thermal management. Thermal conduction in dielectric materials arises from phonons propagation. We discuss the behavior of phonons in NCs as well.

Elastic inhomogeneity and anomalous thermal transport in ultrafine Si phononic crystals

Controlling nanoscale thermal transport via phonon engineering is a promising path for novel thermal management in electronic devices and high performance thermoelectrics. Here we report that ultrafine nanofabrication allows us to change the lattice vibrational properties such that reduces the material thermal conductivity in an unusual manner. This is demonstrated in ultrafine silicon (Si) phononic crystals with two-dimensional arrays of through-holes. We reveal that thermal conductivity of Si can be reduced far below the theoretical limit predicted from a phonon particle model when the through-holes are arranged at sub-100 nm periods. Significant elastic softening is identified in these fine phononic crystals, which indicates change in the lattice vibrational properties. Interestingly, we find that the change in elasticity occurs locally and non-uniformly, suggesting that additional phonon scattering mechanism or a change in sound velocity needs to be considered in phononic crystals. The present result provides new thinking for understanding thermal transport of solids and opens a new avenue to tailor phonon transport in thermal-energy-related materials and devices.

Subcooled flow boiling in an expanding microgap with a hybrid microstructured surface

Flow boiling in microgap is attracting increasingly wide attention in heat transfer community due to its promising application potential for thermal management of electronic devices. In this study, an expanding microgap with a hybrid microstructured surface is proposed. It consists of a roughened inlet region followed by an array of staggered micro triangular pin-fins machined downstream. Subcooled flow boiling tests were conducted using distilled water as the working fluid with the inlet subcooling between 20 °C and 40 °C at different flow rates ranging from 80 to 480 mL/min over a heat flux range of 100.0–651.7 W/cm2. High-speed visualization was performed to explore the flow pattern transitions and the effects of operating conditions on heat transfer and pressure drop characteristics. A new flow pattern was observed in which the bubbles blanket the surface over both roughened upstream surface and the micro pin-fins downstream surface at higher flow rates and higher heat flux conditions. Combination of the increased bubble nucleation site density on the roughened surface and suppression of local dryout from the micro pin-fins due to their capillary effect jointly led to the high heat transfer performance in the bubble blanket pattern. In addition, the expanding configuration provides additional space downstream to facilitate bubble growth and two-phase flow in the direction of expansion with reduced resistance, resulting in a relatively low pressure drop in the present system.

Hierarchically Porous PVA Aerogel for Leakage-Proof Phase Change Materials with Superior Energy Storage Capacity

Organic phase change materials (PCMs) have been widely used in the thermal energy storage field, but melt leakage above the phase change temperature has greatly hindered their practical applications. Herein, poly(vinyl alcohol) (PVA) aerogels with hierarchically porous structure are fabricated and introduced into phase change matrices to obtain novel leakage-proof composite PCMs (CPCMs). The thermal storage efficiency of the working substance in the CPCMs reaches as high as 95.6%, maintaining a tremendously high energy storage density. More importantly, the CPCMs exhibit prominent shape stability when heated at 80 °C, higher than the phase change temperature, for 60 h. Finally, the leakage-proof CPCMs exhibit great application potential in the thermal management of electronic devices.

Thermal management of electronic devices using pin-fin based cascade microencapsulated PCM/expanded graphite composite

Microencapsulated phase change material (MEPCM) could be used for effective thermal management of electronic devices due to its large latent heat, phase change at nearly constant temperature, low volume expansion, and anti-leakage characteristics. Unfortunately, the low thermal conductivity of MEPCM hinders the heat dissipation rate from electronic devices especially at high heat flux conditions. Although the heat transfer capability of MEPCM could be accelerated by adding expanded graphite (EG) or inserting high thermal conductivity pin-fins, the latent heat energy storage capacity of MEPCM composite becomes less which reduces the corresponding operating time of limiting the electronic device temperature rise through solid–liquid phase change. In purpose of clarifying and optimizing this tradeoff effect on electronic device thermal management using MEPCM–EG composite with pin-fins, a numerical study is carried out through 3D lattice Boltzmann method with respect to different pin-fin configurations, EG content, PCM melting temperature, and heat flux conditions. The results indicate that the pin-fin array with medium fin number and fin thickness is beneficial for balancing the increased heat transfer capability and the decreased latent heat of MEPCM so that its optimum thermal performance is achieved. At the early working stage of electronic device, the pin-fin based MEPCM is demonstrated to be more effective than MEPCM–EG composite for controlling the electronic device temperature rise because of the direct contact between pin-fins and electronic heat sink base. However, as the electronic device working time evolves, the MEPCM–EG composite with network heat transfer channel is found to be more efficient for dissipating heat out of electronic device due to the relatively high average thermal conductivity throughout the whole heat sink system. Furthermore, the thermal performance of electronic device is found to be improved by inserting MEPCM–EG composite with cascade melting temperature decreasing from the heat sink base to heat sink cover.

On the transient thermal response of thin vapor chamber heat spreaders: Optimized design and fluid selection

Vapor chambers provide highly effective heat spreading to assist in the thermal management of electronic devices. Although there is a significant body of literature on vapor chambers, most prior research has focused on their steady-state response. In many applications, electronic devices generate inherently transient heat loads and, hence, it is critical to understand the transient thermal response of vapor chambers. We recently developed a semi-analytical transport model that was used to identify the key mechanisms that govern the thermal response of vapor chambers to transient heat inputs (Int. J. Heat Mass Trans. 136 (2019) 995–1005). The current study utilizes this understanding of the governing mechanisms to develop design guidelines for improving the performance of vapor chambers under transient operating conditions. Two key aspects of vapor chamber design are addressed in this study: first, a parametric optimization of the wall, wick, and vapor-core thicknesses; and second, the selection of the working fluid. A protocol is demonstrated for selecting these parameters given the external vapor chamber envelope dimensions and boundary conditions. The study helps provide a framework for designing vapor chambers subject to transient heat loads, and to differentiate such design from the practices followed traditionally for steady-state operation.

Thermal and electrical anisotropy of polymer matrix composite materials reinforced with graphene nanoplatelets and aluminum-based particles

Graphene nanoplatelet-reinforced polymers are one of the most potential thermal interface materials used for thermal management of electronic devices and systems. These uncured polymer matrix composite materials are typically anisotropic, leading to both advantageous and disadvantageous effects. Graphene nanoplatelet-based thermal interface materials benefit from thermal anisotropy. What is not entirely clear, however, is how to avoid the adverse effects caused by thermal and electrical anisotropy. Accordingly, the primary focus of this study was on how to effectively reduce thermal resistance and electrical conductivity for graphene nanoplatelet-based thermal interface materials. The relative performance of thermal interface materials reinforced with various thermally conductive fillers was evaluated. Design rules were developed for the optimization of anisotropic composite materials. The results indicated that additional reinforcement material such as aluminum-based particles should be further incorporated into a graphene nanoplatelet-based thermal interface material so that the overall performance is not adversely affected by thermal and electrical anisotropy after improvements in physical properties. With such a hybrid filler, a two-fold increase in thermal conductivity can be achieved due to the synergistic effect existing within the resultant composite material, and the degree of electrical anisotropy can be reduced by at least one order of magnitude. Furthermore, there exists an optimum hybrid-filler weight fraction, at which both thermal resistance and electrical conductivity are minimum and a low degree of anisotropy can be achieved. Finally, the results will provide a theoretical basis for the development of effective graphene nanoplatelet-based thermal interface materials.