Thermal Management Devices Research Articles

Design and analysis of liquid cooling plates for different flow channel configurations

A number of thermal management devices are used to actuate concentrated electronic appliances in an efficient way. A liquid cooling plate acts as a heat sink enclosed by materialized walls. This work aims to carry out design of liquid cooling plates such that the heat diffused by the electronic equipment is removed while their temperatures levels remain within safe limits. The liquid cooling plates expose ?cold surfaces? to electronic appliances. The performance of a cooling plate is estimated depending upon heat carrying capacity, associated heat transfer rates and concentrated thermal regions on the plate surface. For this study, the design of liquid cooling plate was done with SOLIDWORKS. Pure water was used as a working fluid in test channels. A comparative analysis of flow distribution, temperature contours, pressure drop, and pumping power for different channel configurations was carried out with ANSYS. It was observed that a channel configuration is of key importance in liquid cooling plates. The findings from this study are beneficial for the optimum design of cooling systems for high heat flux applications, i.e., in electronic devices, computer processors and automotive engines.

Aln Coatings with High Thermal Conductivity and Excellent Electrical Insulation Properties for Thermal Management Devices

Aln Coatings with High Thermal Conductivity and Excellent Electrical Insulation Properties for Thermal Management Devices

A Novel Method to Prepare Transparent, Flexible and Thermally Conductive Polyethylene/Boron Nitride Films.

The high thermal conductivity and good insulating properties of boron nitride (BN) make it a promising filler for high-performance polymer-based thermal management materials. An easy way to prepare BN-polymer composites is to directly mix BN particles with polymer matrix. However, a high concentration of fillers usually leads to a huge reduction of mechanical strength and optical transmission. Here, we propose a novel method to prepare polyethylene/boron nitride nanoplates (PE/BNNPs) composites through the combination of electrostatic self-assembly and hot pressing. Through this method, the thermal conductivity of the PE/BNNPs composites reach 0.47 W/mK, which gets a 14.6% improvement compared to pure polyethylene film. Thanks to the tight bonding of polyethylene with BNNPs, the tensile strength of the composite film reaches 1.82 MPa, an increase of 173.58% compared to that of pure polyethylene film (0.66 MPa). The fracture stress was also highly enhanced, with an increase of 148.44% compared to pure polyethylene film. Moreover, the addition of BNNPs in PE does not highly reduce its good transmittance, which is preferred for thermal management in devices like light-emitting diodes. This work gives an insight into the preparation strategy of transparent and flexible thermal management materials with high thermal conductivity.

Designing thermoelectric self-cooling system for electronic devices: Experimental investigation and model validation

Thermal management of electronic devices is encountering a bottleneck due to the continuously increased heat flux generated from equipment. Fortunately, the development of thermoelectric self-cooling (TESC) technology provides new opportunities for cooling electronic devices passively. In this paper, a practical application of the TESC technology on an ultra-high performance (UHP) lamp used in commercial projectors is investigated both experimentally and numerically. Experimental results show that once the TESC system is carefully designed, it can perform better than conventional forced cooling systems with no power consumed. A numerical model is further established based on the thermal resistance-capacitance network. The comparison between experimental and simulation results proves the accuracy of the proposed model. The dynamic deviation of the numerical model is within 9%, and the steady-state deviation is within 2%. Furthermore, a parametric study is conducted to analyze the influence of different physical properties and structures of thermoelectric materials. Results indicate that choosing an appropriate configuration of physical properties is more important than purely improving the dimensionless figure of merit. Additionally, about 70% of the thermoelectric materials can be saved if a suitable fill factor and thickness of thermoelectric pairs were utilized.

High interfacial thermal conductance across heterogeneous GaN/graphene interface

Gallium nitride (GaN)-based high-electron-mobility transistors (HEMTs) have attracted significant research attention because of their high-power and high-frequency electronics applications such as 5G wireless networks and light-emitting diodes. Meanwhile, the output power density of these HEMTs is particularly high, and strong Joule self-heating hot spots formed at the near-junction seriously restricts device performance and reliability. Hence, heat removal is in urgent demand for GaN-based HEMTs. Multilayer graphene, featuring high thermal conductivity and being easily prepared, is of interest for integration with GaN to improve the device thermal management. In this work, we have investigated the interfacial thermal conductance (ITC) across GaN/graphene interface using nonequilibrium molecular dynamics simulations. The results show that a 0.6% point-defect concentration results in 2.4-fold enhancement in ITC. Moreover, the ITC value can be increased up to 520.7 MWm−2 K−1 by applying ∼ 1GPa cross-plane pressure, which is close to the measurement result for epitaxially grown GaN/ZnO interface. Detailed analyses of vibrational spectra and spectral phonon transmission are performed to help understand the significant enhancement of ITC. Furthermore, the ITC could be also regulated by the external temperature and h-BN intercalation. Our findings presented here provide important guidelines for solving the thermal management issue in GaN-based electronic devices.

A Study of Variable Cell Spacings to the Heat Transfer Efficiency of Air-Cooling Battery Thermal Management System

The air-cooling battery thermal management system has been widely adopted as the thermal management device for power accumulators on electric vehicles nowadays. To improve the system heat transfer coefficient with the minimum rise in cost, this study modified conventional rectangular cell arrangements for 21,700 cylindrical cell battery packs with two approaches: 1. increase the vertical spacings; 2. convert constant vertical spacings to gradient vertical spacings. The results show that smaller vertical spacings are beneficial to the overall cooling performances of the constant vertical spacings designs at almost all flow rates. The gradient vertical spacing design with larger spacing could deliver better temperature uniformity, while the one with smaller spacings could suppress the maximum temperature more efficiently at higher flow rates. However, the total battery pack volume of Design 7 (the largest gradient vertical spacing design) is 7.5% larger than the conventional design.

Lattice Thermal Transport in the Homogeneous Cage‐Like Compounds Cu3VSe4 and Cu3NbSe4: Interplay between Phonon‐Phase Space, Anharmonicity, and Atomic Mass

AbstractUnderstanding the correlation between crystal structure and thermal conductivity in semiconductors is very important for designing heat‐transport‐related devices, such as high‐performance thermoelectric materials and heat dissipation in micro‐nano‐scale devices. In this work, the lattice thermal conductivity ( ) of the cage‐like compounds Cu3VSe4 and Cu3NbSe4 was investigated by experimental measurements and first‐principles calculations. The experimental of Cu3NbSe4 is approximately 25 % lower than that of Cu3VSe4 at 300 K. The relevant important physical parameters, including the sound velocity, heat capacity, weighted phonon phase space (W), and third‐order force constants along with atomic mass were theoretically analyzed. It is found that W is the dominant parameter in determining the , and the other factors only play a minor role. The physical origin is the relatively “soft” lattice of Cu3NbSe4 with heavier atomic mass. This research provides deep insight into the correlation between the thermal conductivity and crystal structure and paves the way for discovering high‐performance thermal management device and thermoelectric materials with intrinsically low .

Functionalized Graphene Origami Metamaterials with Tunable Thermal Conductivity

Graphene with tunable thermo-mechanical property is of great importance for next-generation thermal management devices. Distinct from previously reported porous graphene materials that tune the thermal conductivity at the cost of degrading their mechanical properties, non-porous hydrogenated graphene origami metamaterial exhibits a unique combination of tunable thermal conductivity, high strength, and enhanced stretchability. Through molecular dynamics simulation, an extremely broad range of thermal conductivity can be obtained by tuning the geometrical parameters of the Miura-ori nanoarchitecture of graphene origami, altering the adatom types and density, designing new origami patterns, and applying mechanical strains. By analyzing and comparing the results from atomistic and continuum-based simulations, the effect of length scale on the thermal property of graphene origami metamaterials is explored. The temperature distribution and the phonon density of states of the proposed graphene origami are examined to illustrate the heat conduction mechanism. Finally, 3D graphene origami metamaterials are constructed based on the coupling and assembling of graphene origami strips, and their thermo-mechanical performance is elucidated. Negative coefficients of thermal expansion are obtained in graphene origami nanotubes. The introduced strategy for controlling the thermo-mechanical properties of graphene metamaterials can open up new avenues for developing thermoelectric devices, heat management systems, and flexible nanoelectronics.

Photonic Janus Carbon Fibers with Structural Color Gradient for Multicolored, Wirelessly Wearable Thermal Management Devices

AbstractJanus structure offers materials unique functionalities which are difficult to achieve otherwise with isotropic counterpart, opening up new avenues in diverse application fields. Here, a series of novel photonic Janus carbon fibers (PJCFs) with structural color gradient and excellent mechanical stability are reported by introducing 1D photonic layers with a gradient of periodicity. By virtue of the unique photonic architecture, the PJCFs exhibit a multiple and continuous variation of structural color (i.e., structural color gradient) in a full spectrum. By controlling the thickness of periodic layer, a series of PJCFs with vivid and tunable structural colors ranging from blue, green, orange, to violet‐red can be obtained. Furthermore, their gradient structural colors remain constant after reciprocating rubbing and laundering, showing outstanding mechanical robustness. Notably, benefiting from the inherent electrothermal property and flexibility of CFs, the PJCFs display stable Joule heating performance even under deformation. As proof‐of‐concept, the PJCFs are further integrated with wireless transmission system to construct a multicolored, wirelessly controlled thermal management device, realizing remote and precise temperature manipulation via Bluetooth. This work provides not only a new platform for achieving distinct structural color gradient of CFs, but also a promising strategy toward next‐generation multicolored personal healthcare devices.

Structural and Synthetic Modification of Graphitic Foams and Dendritic Graphitic Foams for Thermal Management

The performances of porous graphitic foams in flexible electronic, electrochemical, and thermal management devices can be enhanced by increasing the interfacial charge or heat transport between the 3D graphitic network and the functional materials filled into the pore space. Herein, an investigation of the effects of chemical vapor deposition (CVD) conditions on the structure and thermal conductivities of both graphitic foams grown from reticular Ni foams and dendritic graphitic foams (DGFs) synthesized from electrodeposited dendritic Ni foams is reported. A room‐temperature solid thermal conductivity () up to 800 W m−1 K−1 is obtained from the graphitic foams (GF) with less than 1% volume fraction. In comparison, the DGFs, which provide a large increase of the specific surface area for enhanced interfacial heat transfer, achieve an effective thermal conductivity of 2.5 ± 0.2 W m−1 K−1 because of an enhanced volume fraction to about 5% despite a compromised around 200 W m−1 K−1 due to the increased defect density. Through systematical variations of the catalyst template morphology and CVD conditions, this work reveals the distinct roles of catalyst surface curvature and graphitic strut thickness in controlling the properties of GFs and DGFs for thermal management.

Controlling the thermal conductivity of multilayer graphene by strain

Straintronics is a new concept to enhance electronic device performances by strain for next-generation information sensors and energy-saving technologies. The lattice deformation in graphene can modulate the thermal conductivity because phonons are the main heat carriers. However, the device fabrication process affects graphene’s heat transport properties due to its high stretchability. This study experimentally investigates the change in the thermal conductivity when biaxial tensile strain is applied to graphene. To eliminate non-strain factors, two mechanisms are considered: pressure-induced and electrostatic attraction–induced strain. Raman spectroscopy and atomic force microscopy precisely estimate the strain. The thermal conductivity of graphene decreases by approximately 70% with a strain of only 0.1%. Such thermal conductivity controllability paves the way for applying graphene as high-efficiency thermal switches and diodes in future thermal management devices.

Super tough and stable solid–solid phase change material based on π-π stacking

The solid–solid phase change materials (SSPCMs) have become the preferred materials in thermal energy storage via absorbing latent heat from ambient environment. However, the trade-off between the mechanical properties, stability and recyclability is still the obstacle and barrier for development of SSPCMs. Herein, we proposed a facile and novel strategy to prepare SSPCMs for address above issues by introducing π-π stacking to form physical crosslinking points in linear polyethylene glycol (PEG). The strong intermolecular forces formed by π-π stacking not only prevented leakage of the PEG even at 130 °C but imparted high temperature stability and excellent toughness (172.44 MJ/m3) to fabricated SSPCMs. It is worth mentioning that the prepared PCMs can be added with CNT in a simple process way to improve the photo-thermal conversion ability and thermal conductivity of SSPCMs. Besides, the as-prepared SSPCMs exhibited excellent flexibility, and were expected to be excellent thermal/photo energy storage materials for human thermal management and wearable devices.

Fanless, porous graphene-copper composite heat sink for micro devices

Thermal management in devices directly affects their performance, but it is difficult to apply conventional cooling methods such as the use of cooling liquids or fans to micro devices owing to the small size of micro devices. In this study, we attempted to solve this problem by employing a heat sink fabricated using copper with porous structures consisting of single-layer graphene on the surface and graphene oxide inside the pores. The porous copper/single-layer graphene/graphene oxide composite (p-Cu/G/rGO) had a porosity of approximately 35%, and the measured pore size was approximately 10 to 100 µm. The internal GO was reduced at a temperature of 1000 °C. On observing the heat distribution in the structure using a thermal imaging camera, we could observe that the p-Cu/G/rGO was conducting heat faster than the p-Cu, which was consistent with the simulation. Furthermore, the thermal resistance of p-Cu/G/rGO was lower than those of the p-Cu and pure Cu. When the p-Cu/G/rGO was fabricated into a heat sink to mount the light emitting diode (LED) chip, the measured temperature of the LED was 31.04 °C, which was less than the temperature of the pure Cu of 40.8 °C. After a week of being subjected to high power (1000 mA), the light intensity of p-Cu/G/rGO decreased to 95.24%. However, the pure Cu decreased significantly to 66.04%. The results of this study are expected to be applied to micro devices for their effective thermal management.

Advanced functional Kevlar composite with excellent mechanical properties for thermal management and intelligent safeguarding

Fabric-based personal thermal management devices propel the development of flexible heaters which play important roles in medicinal therapy and protecting humans from cold environments. However, due to the poor mechanical properties, most heaters are easy to be damaged under dynamic loading forces, and also difficult to provide necessary anti-impact protection for human beings. Therefore, it is significant to develop multifunctional fabric heaters with high mechanical properties. Herein, a novel MXene/SSG/Kevlar-based multifunctional textile composite (MS-Kevlar) with sensitive monitoring, thermal management and impact protection is developed by assembling Kevlar fiber, shear stiffening gel (SSG) and two-dimensional MXene. This MS-Kevlar has high sensitive monitoring properties to various stimuli from slight physiological activities to high-speed bullet impact. MS-Kevlar with excellent conductivity shows high thermal management properties which can reach 80.9 °C at 6 V working voltage. Besides thermal protection property, the multifunctional MS-Kevlar can absorb 55.4% force under low-speed impact and still retain the electro-thermal performance after impacted. More importantly, the ballistic limit velocity of MS-Kevlar increases more than 142.1% compared with that of neat Kevlar which could provide safeguarding for humans. Finally, a smart curtain with thermal and anti-impact performance was designed and the based wireless impact alarm system is beneficial for people to assess and avoid dangers.

Mechanically Tunable Superhydrophobic Surfaces Enabled by the Rational Manipulation of Microcrack Networks in Nanoporous Films

AbstractAdaptive materials with tunable superhydrophobic surfaces promise to impact a range of fluid handling technologies; however, adaptive superhydrophobic materials remain difficult to fabricate, control, and switch rapidly. Here, a versatile method for generating hierarchically structured and adaptive superhydrophobic silicone films for the rational control of surface wettability and droplet adhesion is reported. Specifically, mechanical tension is utilized to manipulate networks of microcracks in nanoporous layers supported on elastomeric silicone films, enabling dynamic modulation of superhydrophobicity and droplet adhesion. The reported mechano‐responsive superhydrophobic surfaces are applied to directional droplet shedding and “no‐loss” droplet transport and are used to generate artificial “skins” with droplet tweezing capabilities. This approach provides materials with enhanced functionality useful to a range of emergent technologies, including adaptive textiles, biocompatible (wearable) sensors, soft robotics, anti‐icing systems, “no‐loss” droplet manipulators, and thermal management devices.

Personal Thermal Management by Single-Walled Carbon Nanotubes Functionalized Polyester Fabrics.

In this work, a personal thermal management (PTM) device based on single walled carbon nanotubes (SWCNTs) functionalized polyester fabrics had been studied. Polyester fabrics were functionalized with SWCNTs through coating method with poly (butyl acrylate) emulsion as the adhesive. The SEM images exhibited that SWCNTs formed high-efficiently conductive networks due to the large aspect ratio and uniform dispersion. A steady-state temperature of 40 °C was achieved at the input voltage of 2.5 V within 7 s, which exhibited excellent electro-thermal performance. Even under periodic heating-cooling conditions, heating system still displayed relatively stable temperature and relative resistance, which could have potential application for wearable clothes.

An experimental investigation of a PCM-based heat sink enhanced with a topology-optimized tree-like structure

A heat sink filled with phase change material (PCM) is an efficient thermal management device which utilizes the high latent heat of fusion of PCM in the cooling process. To improve the thermal performance of the PCM-based heat sink, a topology optimization (TO) strategy is devised to develop a new class of enhanced structures. This is achieved by carrying out a comprehensive numerical study to identify the effects of various thermal transport mechanisms on the TO design by considering two different heat transfer problems, i.e., steady-state heat conduction and transient heat conduction with phase change. To enable easy fabrication and performance evaluation of the new heat sink design predicted by the TO process, the resulting heat sink with tree-like structure was fabricated by selective laser melting (SLM), a metal additive manufacturing (AM) technique. Experimental characterization of the TO heat sink was carried out using three different types of PCMs, i.e., RT35, RT35HC and RT44HC and heat fluxes ranging from 4.00 kW/m2 to 7.24 kW/m2. Our experimental results show that the TO tree-like structure heat sink has better performance, exhibiting up to 4 °C lower wall temperatures, than the conventional fin-structure heat sink. At low heat fluxes, the best thermal performance can be obtained with RT35HC whereas at high heat fluxes, lower wall temperatures were achieved with RT44HC. In addition, the tree-like structure increases operational time by up to 13% as compared to the fin-structure heat sink. The better thermal performance of the tree-like structure heat sink is due to its optimized heat conduction paths that allow heat from the concentrated heat source to be efficiently dissipated to the PCM. This work not only demonstrates the potential of enhancing electronics cooling with TO PCM-based heat sinks, but it also outlines key guidelines for the design and implementation of TO structures for other cooling applications.

Construction of 3D MXene/Silver nanowires aerogels reinforced polymer composites for extraordinary electromagnetic interference shielding and thermal conductivity

The novel multifunctional materials with anti-electromagnetic interference (EMI) and effective thermal management are ideal for modern electronic industry. Generally, the EMI shielding effectiveness (SE) and thermal conductivity (TC) of materials can be effectively enhanced by compounding with high electrically and thermally conductive fillers. However, it seems that the high-performance cannot be compensated without sacrificing the high fillers loading. Herein, from one-dimensional silver nanowires (AgNWs) and two-dimensional MXene, three-dimensional MXene/AgNWs aerogels were designed as electric and heat transferring skeletons for epoxy nanocomposites by directional-freezing and freeze-drying methods. The resultant MXene/AgNWs/Epoxy nanocomposites with a low MXene/AgNWs content of 8.2 wt% combine a high electrical conductivity of 1532 S/m, and an exceptional EMI SE value of 94.1 dB with 3 mm thickness at the X-band frequency, as well as an improved TC of 2.34 W/m·K. The fabricated MXene/AgNWs/Epoxy nanocomposites possess excellent comprehensive properties enable valuable applications in electronic devices for EMI shielding and thermal management.

Design and preparation of Ag modified expanded graphite based composite phase change materials with enhanced thermal conductivity and light-to-thermal properties

Phase change materials (PCMs) is an excellent performance candidate for thermal energy storage and utilization. However, low thermal conductivity and low light-to-thermal conversion efficiency of PCMs are the serious limitation factors for highly efficient energy storage and photothermal conversion. In this paper, we reported a novel composite PCM based on lauric acid (LA) as the PCM supported by Ag nanoparticles modified expanded graphite (Ag-EG). The composite PCM of Ag-EG/LA possessed good energy thermal storage properties, which melted at 47.2 °C with the latent heat of 129.5 J/g at the LA maximum loading of 70.2%. Meanwhile, based on the high thermal conductivity and local surface plasma resonance effect of Ag, the composite (Ag-EG/LA) exhibits improved thermal conductivities (2.85 W/(m•K)) and high light-to-thermal energy conversion efficiency (η=81.2%). Moreover, the TGA and thermal cycles test results shown that Ag-EG/LA have good thermal stability and reliability. Hence, this novel composite of Ag-EG/LA could be potentially applicated in solar energy harvesting system and electric devices for thermal energy management.

Flame‐Retardant Host–Guest Films for Efficient Thermal Management of Cryogenic Devices

AbstractPhase change materials hold tremendous potential for thermal energy storage and temperature management due to their high latent heat and chemical stability. However, the manufacture of flame‐retardant, form‐stable phase change films working under a cryogenic environment remains difficult. Herein, an organic polydopamine‐aramid nanofiber (PANF) aerogel film with a limiting oxygen index (LOI) of 32 is applied as a host to confine a unique phase change guest material (i.e., deep eutectic solvent, DES) to fabricate PANF‐DES host–guest flame‐retardant cryogenic phase change films. The PANF aerogel film is prepared through the in situ polymerization of dopamine within the aramid nanofiber hydrogel film, exhibiting a high specific surface area of 289 m2 g−1. The cryogenic phase change material is a ternary DES composed of ammonium chloride (NH4Cl), ethylene glycol (Eg), and deionized water (H2O). The as‐prepared PANF‐DES host–guest films with the phase transition temperature of −21 °C and melting enthalpy of 225 J g−1 can withstand fire for 60 s without naked flame, and the peak of heat release rate (pkHRR) is only 26.0 MJ kg−1. This study opens the way for developing ultra‐low flammable phase change composite films, as well as shows great potential applications for thermal management in cryogenic devices.