Thermal Management Devices Research Articles

Numerical Study on Heat Propagation in Laptop Cooling System

Thermal management of microelectronic devices has become increasingly important to maintain their performance and prolonging the lifespan of the devices. In this study, numerical simulation has been conducted to investigate the heat propagation for high performance microelectronic device of laptop. Two models are constructed and Ansys Fluent is used for the Computational Fluid Dynamics (CFD) simulation, source term is applied at the heat source, heat sink and two different material heat pipes are the main cooling components in the system. The results show that the improved design model is a better design for laptop cooling systems, and the increasing number of air vents, thermal conductivity, and length of heat pipes can effectively cool the high-powered microchip effectively. Transient simulation, considering the wick structure and working fluid in the simulation, is suggested for future work.

Experimental Investigation of a Battery Thermal Management Device Based on a Composite Phase Change Material Coupled with a Double Helix Liquid Cooling Plate

Experimental Investigation of a Battery Thermal Management Device Based on a Composite Phase Change Material Coupled with a Double Helix Liquid Cooling Plate

Molecular Dynamics Simulation on In-Plane Thermal Conductivity of Graphene/Hexagonal Boron Nitride van der Waals Heterostructures.

Graphene, hexagonal boron nitride (h-BN), and their heterostructures are promising thermal interface materials due to the outstanding thermal properties of graphene and h-BN. For the heterostructures, extensive work has mainly focused on the thermal transport of two-dimensional (2D) graphene/h-BN (GBN) in-plane heterostructures in which graphene and h-BN are bonded at the interface. In this study, we investigate the thermal conductivity of three-dimensional (3D) GBN van der Waals (vdW) heterostructures by means of nonequilibrium molecular dynamics (NEMD) simulations. Unlike the 2D GBN in-plane heterostructure, the 3D GBN vdW heterostructure consists of three layers where graphene is sandwiched by two h-BN sheets via vdW forces. Various techniques, including hydrogen-functionalization, vacancy defects, tensile strain, interlayer coupling strength, layer numbers of h-BN, size effect, and temperature, are extensively explored to find an effective route for the modulation of the thermal conductivity. It is found that the thermal conductivity of the triple-layer GBN vdW heterostructure is very sensitive to these extrinsic factors. Of these, hydrogen-functionalization is the most effective method. A low hydrogen coverage of 1% in the sandwiched graphene can lead to 55% reduction in the thermal conductivity of the vdW heterostructure. Vacancy defects on graphene exert a more significant effect on the thermal conductivity reduction for the vdW heterostructure than B or N vacancies in the outer h-BN layers. This work reveals the physical mechanism for manipulating the thermal transport along the GBN vdW heterostructures via structural modification and provides a useful guideline for designing novel thermal management devices based on the GBN vdW heterostructures.

Flexible and environmentally friendly graphene natural rubber composites with high thermal conductivity for thermal management

Composites with high thermal conductivity are urgently needed for thermal management devices. Although natural rubber (NR) with excellent elasticity are promising as flexible polymer for thermal management, their poor thermal conductivity limits their applications. In this work, a general water treatment route and an ice template process are used to prepare a 3D graphene aerogel. And environmentally friendly L-cysteine (Cys) are used to adjust the carbon-to-oxygen ratio of GO and thiol-functionalized GO. Benefiting from the 3D graphene network and strong interfacial interaction, the NR composites with graphene loading of 25 wt% showed thermal conductivity of 0.891 W/(m·K). At the same time, it also has good mechanical properties and antistatic properties. All the results indicate that Cys-GO@GNP/NR is expected to be a promising thermal management material.

Vapor–Liquid Transition‐Based Broadband Light Modulation for Self‐Adaptive Thermal Management

AbstractConsiderable research efforts have aimed to control indoor temperatures to improve daily life and industrial production. However, current strategies, which involve active regulation of energy input or passive regulation of sunlight transmission, cannot control indoor temperatures under all weather conditions. Herein, a self‐adaptive thermal management device (STMD) that uses solar energy (heating) and radiative cooling (cooling) by exploiting the temperature differences across the device is reported. The adaptive heating and cooling functions are achieved by modulating sunlight transmittance and reflectance using a porous SiO2 coating separated/merged with a refractive index‐matched liquid which serves as a shutter. As a result, the STMD in the opaque mode exhibits low transmittance and in the transparent mode exhibits sufficiently high solar transmittance. Taking advantage of this self‐regulated shuttering mechanism, the developed STMD enables i) an increase of ≈10 °C relative to the ambient temperature under a solar intensity of 400 W m−2 in cold weather and ii) a temperature reduction of ≈5 °C under a solar intensity exceeding 900 W m−2 in hot weather. The described design strategy offers an approach for constructing smart light‐controlling devices and thermal‐controlling building materials.

Bioinspired zero-energy thermal-management device based on visible and infrared thermochromism for all-season energy saving

Radiative thermal management provides a zero-energy strategy to reduce the demands of fossil energy for active thermal management. However, whether solar heating or radiative cooling, one-way temperature control will exacerbate all-season energy consumption during hot summers or cold winters. Inspired by the Himalayan rabbit's hair and Mimosa pudica's leaves, we proposed a dual-mode thermal-management device with two differently selective electromagnetic spectrums. The combination of visible and infrared "thermochromism" enables this device to freely switch between solar heating and radiative cooling modes by spontaneously perceiving the temperature without any external energy consumption. Numerical prediction shows that a dual-mode device exhibits an outstanding potential for all-season energy saving in terms of thermal management beyond most static or single-wavelength, range-regulable, temperature-responsive designs. Such a scalable and cost-efficient device represents a more efficient radiative thermal-management strategy toward applying in a practical scenario with dynamic daily and seasonal variations.

Conformally Adhesive, Large-Area, Solidlike, yet Transient Liquid Metal Thin Films and Patterns via Gelatin-Regulated Droplet Deposition and Sintering.

Adhesion and spreading of liquid metals (LMs) on substrates are essential steps for the generation of flexible electronics and thermal management devices. However, the controlled deposition is limited by the high surface tension and peculiar wetting and adhesion behavior of LMs. Herein, we introduce gelatin-regulated LM droplet deposition and sintering (GLMDDS), for the upscalable production of conformally adhesive, solidlike, yet transient LM thin films and patterns on diverse substrates. This method involves four steps: homogeneous deposition of LM microdroplets, gelation of the LM-gelatin solution, toughening of the gelatin hydrogel by solvent displacement, and peeling-induced sintering of LM microdroplets. The LM thin film exhibits a three-layer structure, comprising an LM microdroplet-embedded tough organohydrogel adhesion layer, a continuous LM layer, and an oxide skin. The composite exhibits high stretchability and mechanical robustness, conformal adhesion to various substrates, high conductivity (4.35 × 105 S·m-1), and transience (86% LM recycled). Large-scale deposition (i.e., 5.6 dm2) and the potential for patterns on diverse substrates demonstrate its upscalability and broad suitability. Finally, the LM thin films and patterns are applied for flexible and wearable devices, i.e., pressure sensors, heaters, human motion tracking devices, and thermal management devices, illustrating the broad applicability of this strategy.

Thin-Film Evaporation in a Mesh Screen Wick

Abstract Porous capillary wick structures are being employed in two-phase thermal management devices owing to their pumping capabilities and thermal performance enhancement during evaporation of the working fluid. Thin-film evaporation in a porous wick depends primarily on the shape of the liquid–vapor meniscus, especially near the wall. The primary objective of this paper is to study and investigate the thin-film evaporation of the liquid in a unit cell representation (UCR) of a single layer of a metallic wire mesh screen. The volume-of-fluid (VOF) method, which is an interface-capturing technique in multiphase flow modeling, is employed to obtain the steady-state meniscus shape under equilibrium conditions. This paper demonstrates the impact of the equilibrium contact angle (θ) and the initial meniscus height (H) on the steady-state interfacial pressure difference. It outlines a detailed process for estimating 3D interfacial surfaces, obtained from the VOF solution, to generate the final geometry for the thin-film evaporation analysis. A static meniscus heat-transfer model is subsequently solved using the commercial finite volume code, ansysfluent, to obtain the temperature and flow characteristics during evaporation. The relationship of parameters such as the average evaporation mass fluxes and heat transfer coefficients are estimated and presented in this paper. Finally, the relationship between the pressure drop across the liquid–vapor meniscus and the thin-film evaporation rate for screen mesh wicks is discussed.

Temperature-dependent dual-mode thermal management device with net zero energy for year-round energy saving

Reducing needs for heating and cooling from fossil energy is one of the biggest challenges, which demand accounts for almost half of global energy consumption, consequently resulting in complicated climatic and environmental issues. Herein, we demonstrate a high-performance, intelligently auto-switched and zero-energy dual-mode radiative thermal management device. By perceiving temperature to spontaneously modulate electromagnetic characteristics itself, the device achieves ~859.8 W m−2 of average heating power (∼91% of solar-thermal conversion efficiency) in cold and ~126.0 W m−2 of average cooling power in hot, without any external energy consumption during the whole process. Such a scalable, cost-effective device could realize two-way temperature control around comfortable temperature zone of human living. A practical demonstration shows that the temperature fluctuation is reduced by ~21 K, compared with copper plate. Numerical prediction indicates that this real zero-energy dual-mode thermal management device has a huge potential for year-round energy saving around the world and provides a feasible solution to realize the goal of Net Zero Carbon 2050.

Mechanically strong, flexible, and multi-responsive phase change films with a nacre-mimetic structure for wearable thermal management

Phase change materials (PCMs) are a highly promising candidate for thermal energy storage owing to their large latent heat and chemical stability. However, their intrinsic brittle induces poor flexibility and low mechanical strength, which limits them use for wearable thermal management. And, the electrical insulation and weak solar absorption make them lack multi-responsive capability. Herein, we report a facile strategy to synthesize mechanically strong and flexible multi-responsive phase change films by stirring an aqueous dispersion of cellulose nanofibrils (CNFs), MXene (Ti2C3) nanosheets, and polyethylene glycol (PEG), followed by air-drying self-assembly and coating with hydrophobic fluorocarbon. The hydrogen bonds and nacre-mimetic synergistic toughening networks formed by ternary CNFs, Ti2C3 nanosheets, and PEG endow films with high mechanical strength (16.7 MPa) and strain (10.4%), which are 18.6 and 8.7 times higher than those of pure PEG film, respectively. The films exhibit outstanding flexibility and do not crack or fracture even when bent, twisted, and folded into a complex small boat. Meanwhile, the laminar structure formed by the self-assembly Ti3C2 nanosheets enhances electrical conductivity (3.95 S/m) and solar absorption, affording excellent electro-thermal (68.3%–81.0%) and solar-thermal (85.6%–90.6%) conversion efficiency, thus achieving multi-response to external stimuli (electron/solar radiation). In addition, the as-prepared films also deliver large latent heat (136.1 J/g), outstanding cyclic and shape stability, leak-free encapsulation even under compressed at above 5000 times its weight, excellent hydrophobicity (131.4°), and self-cleaning function. This work paves the way for developing flexible, mechanically strong, and self-cleaning phase change film with multi-responsive function for wearable thermal management devices under high humidity condition.

Face-on orientation of spin ladders in La5Ca9Cu24O41 films deposited by radio-frequency magnetron sputtering on heated SiO2 and Si substrates

Spin-ladder cuprates such as La5Ca9Cu24O41 are promising materials for advanced thermal management applications owing to their highly anisotropic and dynamically controllable thermal conductivity originating from spin ladders. Therefore, the orientation control of spin ladders is required in film fabrication methods that are extensively used in device engineering, such as sputtering. We found that La5Ca9Cu24O41 films with a columnar structure and the face-on orientation of spin ladders are formed on heated SiO2 (glass) and Si substrates via radio-frequency magnetron sputtering. The structural properties of the films were investigated, and the film formation mechanism was discussed. Our film fabrication method can pave the way for the development of new thermal management devices, such as active heat spreaders.

Analytical fin efficiency model for open-cell porous metal fins based on Kelvin cell assumption

Open-cell porous metals are widely used to enhance convective heat transfer of thermal management devices. In this paper, the open-cell porous metal structure was represented by a polyhedron model known as the Kelvin cell, and an analytical model for the efficiency of the porous metal fin attached to an isothermal surface was derived. The forced convective heat transfer coupled with heat conduction through the ligaments of porous metal was analyzed to derive the fin efficiency model. The effects of pore diameter, ligament diameter, and porous metal fin height on the fin efficiency and heat transfer rate of porous metal fins were also investigated. The new analytical fin efficiency model based on the Kelvin cell was compared with the fin efficiency evaluated using computational fluid dynamics analysis results; good agreement was found. The proposed analytical fin efficiency model avoids the numerical calculations required for heat transfer analysis of porous metals used as extended surfaces in many engineering applications such as heat sinks and heat exchangers, and can produce simple but effective results.

Tunable Thermal Switch via Order-Order Transition in Liquid Crystalline Block Copolymer.

Organic material-based thermal switch is drawing much attention as one of the key thermal management devices in organic electronic devices. This study aims at tuning the switching temperature (TS) of thermal conductivity by using liquid crystalline block copolymers (BCs) with different order-order transition temperature (Ttr) related to the types of mesogens in the side chain. The BC films with low Ttr of 363 K and high Ttr of 395 K exhibit reversible thermal conductivity switching behaviors at TS of ∼360 K and ∼390 K, respectively. The BC films also exhibit thermal conductivity variation originating from the anisotropy of the internal structures: poly(ethylene oxide) domains and liquid crystals. These results demonstrate that the switching behavior is attributed to an order-order transition between BC films with vertically arranged cylinder domains and the ones with ordered sphere domains. This highlights that BCs become a promising thermal conductivity switching material with tailored TS.

Deep learning based design of thermal metadevices

Thermal metadevices obtained from transformation optics have recently attracted wide attention due to their vast potential for thermal management. However, these devices require extreme material parameters that are difficult to achieve in large-scale applications. Here, we design a thermal concentrator using a machine learning method and demonstrate the thermal concentration performance of the designed device. We first define an architecture with a single isotropic material. Deep learning models based on artificial neural networks are implemented to retrieve design geometry parameters ensuring that the required spatially varying anisotropy is achieved. We implement the optimized architecture into a thermal concentrator, fabricate samples and experimentally demonstrate that the designed metamaterial can simultaneously concentrate the heat flux in its core and minimize perturbations to the external thermal field. Our approach paves new avenues for the design of thermal management devices and, more generally, enables feasible solutions for inverse heat manipulation problems.

Bead-like PCM composite network with reinforced heat storage performance for highly efficient battery cooling

High-performance heat storage phase change materials (PCMs) is urgently required for modern thermal-management device, like Li-ion battery in electrical vehicle. Driven by the unmet needs to develop promising PCM composite with high stability, thermal conductivity and loading capacity simultaneously, unique bead-like three-dimensional network support as biMOF (ZIF67@ZIF8) particles encapsulated in carbon fibers was introduced for loading lauric acid. Carbon fibers from electric-spinning strung dispersed biMOF-C particles and constructed 3D network to facilitate heat transfer. Furthermore, biMOF structure and carbon fiber encapsulation worked synergistically to improve PCM loading capacity. Consequently, the obtained PCM composite exhibited high latent heat (132.5 J/g) and thermal conductivity (2.5 W/mk), which worked efficiently to decrease single battery temperature by 3.2 °C and improve charge-discharge performance by 15.7 %.

Lattice thermal conduction in cadmium arsenide

Lattice thermal conductivity (LTC) of cadmium arsenide (Cd3As2) is studied over a wide temperature range (1–400 K) by employing the Callaway model. The acoustic phonons are considered to be the major carriers of heat and to be scattered by the sample boundaries, disorder, impurities, and other phonons via both Umklapp and normal phonon processes. Numerical calculations of LTC of Cd3As2 bring out the relative importance of the scattering mechanisms. Our systematic analysis of recent experimental data on thermal conductivity (TC) of Cd3As2 samples of different groups, presented in terms of LTC, κ L, using a nonlinear regression method, reveals good fits to the TC data of the samples considered for T < ∼ 50 K, and suggests a value of 0.2 for the Gruneisen parameter. It is, however, found that for T > 100 K the inclusion of the electronic component of TC, κ e, incorporating contributions from relevant electron scattering mechanisms, is needed to obtain good agreement with the TC data over the wide temperature range. More detailed investigations of TC of Cd3As2 are required to better understand its suitability in thermoelectric and thermal management devices.

Coherent and incoherent phonon thermal transport in group-III nitride monolayer superlattices with Tersoff type interatomic potential

The existence of a crossover from coherent to incoherent phonon transport for different monolayer superlattices such as h-BN/h-AlN, h-BN/h-GaN, h-AlN/h-GaN, and h-BN/h-AlN/h-GaN using large-scale non-equilibrium molecular dynamics simulations is unveiled. In this context, the lattice thermal conductivities of considered superlattice structures are obtained for varying period lengths, sample lengths, and temperatures. It is predicted that the thermal conductivities of superlattice structures can be lowered even up to 99% than that of their pristine counterparts. Also, it is revealed that a minimum thermal conductivity resulting from the competition between coherent, wave-like, and incoherent, particle-like, phonon transport can be achieved by altering the period length for all the superlattice structures. Moreover, it is observed that the thermal conductivity minimum at higher temperatures compared to low temperatures occurs at shorter period lengths for binary superlattices, and the minimum depths decrease with increasing temperature. Results point out that group-III nitride superlattices can be considered as an alternative option in controlling the heat flow for thermal management and thermoelectric device applications.

Thermal transport properties of hexagonal monolayer group-III nitride nanoribbons

In this study, the thermal transport properties of hexagonal monolayer BN, AlN, and GaN nanoribbons are systematically investigated using non-equilibrium molecular dynamics simulations. Firstly, the effect of length, width, and temperature on the lattice thermal conductivities of these ribbons are explored. It is observed that increases in sample geometry lengths of simulations and decreases in temperature lead to an increase in the thermal conductivity of all three materials. Secondly, thermal rectification coefficients of ribbons are calculated by creating asymmetric thermal contacts through non-equilibrium molecular dynamics simulations. Thus, it is shown that thermal rectification factors of up to 20% can be achieved by manipulating the thermal asymmetry ratio in pristine structures without asymmetry of group-III nitride nanoribbons. These results imply that group-III nitride nanoribbons may be considered as an alternative option to control the heat flow in thermal management and thermoelectric device applications.

Experimental evaluation of thermal rectification in a ballistic nanobeam with asymmetric mass gradient

Practical applications of heat transport control with artificial metamaterials will heavily depend on the realization of thermal diodes/rectifiers, in which thermal conductivity depends on the heat flux direction. Whereas various macroscale implementations have been made experimentally, nanoscales realizations remain challenging and efficient rectification still requires a better fundamental understanding of heat carriers’ transport and nonlinear mechanisms. Here, we propose an experimental realization of a thermal rectifier based on two leads with asymmetric mass gradients separated by a ballistic spacer, as proposed in a recent numerical investigation, and measure its thermal properties electrically with the microbridge technique. We use a Si_{3}N_{4} nanobeam on which an asymmetric mass gradient has been engineered and demonstrate that in its current form, this structure does not allow for thermal rectification. We explain this by a combination of too weak asymmetry and non-linearities. Our experimental observations provide important information towards fabricating rigorous thermal rectifiers in the ballistic phonon transport regime, which are expected to open new possibilities for applications in thermal management and quantum thermal devices.

Effect of Dimple Arrangement on The Thermal Performance of Dimpled Stepped Plate Heat Sink

Thermal management of electronic devices is the biggest problem in the electronic industry today. Heat sinks are one such devices that are used to cater this need and addition of dimples to these devices are proved to improve the thermal performance further. In the present study, computational analysis is carried out for comparing the stepped fin heat sinks with inline and staggered dimple arrangements having same number of dimples on each fin plate at velocities in the range of 0.5m/s to 4.5 m/s for 9 cases. The results of the computational study are validated by comparing it with the experimental results of previous literature. The outcomes reveal that there is negligible difference in thermal performance of the two heat sinks at lower velocities and this gap widens with increase in velocity. Out of the two-heat sink model, heat sink with inline arranged dimples proved to have better thermal performance at all the velocities considered.