Improved Heat Conduction Research Articles

Research on surface integrity of titanium alloy in V-groove micro-textured ball-end milling cutter

In order to realize chip guiding control in titanium alloy machining, reduce the negative influence of unstable chip flow direction on the milling environment, and improve the performance and reliability of parts, this article adopts the V-groove micro-texture carbide tool as the research object and takes the laser preparation of the V-groove micro-texture as a breakthrough point, analyzes the influence of laser parameters on the aspect ratio of V-groove micro-texture, and optimizes the laser parameters. The titanium alloy milling test platform was built to analyze the influence of the micro-texture parameters of the V-groove on the surface integrity of the workpiece, reveal the action mechanism, and optimize the relevant parameters based on the artificial bee colony algorithm. The results show that laser power has the largest influence on the aspect ratio of the groove. The power determines the melt content in the groove and influences the width and depth of the micro-texture. The optimized laser combination parameters are: laser power 42.5 W, scanning speed 10 mm/s scanning times nine times, scanning frequency 30 kHz, and spot diameter 30 μm. The V-groove micro-texture on the tool surface can change the chip flow direction, reduce the contact area of the chip, accommodate the cutting particles, and improve heat conduction, reducing cutting resistance and friction, thereby optimizing cutting control distance, thereby improving the surface integrity of the workpiece becomes. The optimized V-groove micro-texture parameters are as follows: V-groove angle X = 46.2°, V-groove height H = 175 μm, radial spacing L = 259.4 μm, circumferential angle J = 2.1°, and distance from the edge K = 120 μm.

Highly efficient multi-layer flexible heatsink for wearable thermoelectric cooling

Flexible thermoelectric cooler (fTEC), which interfaces well with curved human body surface and provides cooling functions, is an emerging candidate for personal thermal management and non-hospitalized medical treatment. Achieving efficient and long-term cooling performance of TEC requires high thermal conductivity and heat diffusion of the hot side, which has yet to achieve. In this study, we design and fabricate a highly thermally conductive and flexible heatsink with a multi-layered structure especially for wearable TEC wristband, which obtains a large temperature drop (8.8 °C) for imitated on-body test and the maxim 13.1 °C temperature decrease in air. Here, we demonstrate that a well-designed functional composite layer, including phase change material, thermally conductive fillers and metal foam, can establish an effective equilibration among cooling performance, thermal management capacity and mechanical property. Particularly, the heatsink with highly thermal conductive skeleton (k ∼ 2.7 W/mK) and effective heat dissipating fins can significantly improve heat conduction and dissipation, which improve the cooling performance by more than 55 %. With the help of theoretical simulation, we propose a promising strategy for heat management on thermoelectric device through a flexible multi-layered structure, paving the way for achieving practical applications of wearable thermoelectric coolers for personal thermal regulation or cooling therapy.

Characteristics of low-temperature plasma for activation of plastic-degrading microorganisms

Plastic pollution is a problem that threatens the future of humanity, and various methods are being researched to solve it. Plastic biodegradation using microorganisms is one of these methods, and a recent study reported that plastic-degrading microorganisms activated by plasma increase the plastic decomposition rate. In contrast to microbial sterilization using low-temperature plasma, microbial activation requires a stable plasma discharge with a low electrode temperature suitable for biological samples and precise control over a narrow operating range. In this study, various plasma characteristics were evaluated using SDBD (Surface Dielectric Barrier Discharge) to establish the optimal conditions of plasma that can activate plastic-degrading microorganisms. The SDBD electrode was manufactured using low-temperature co-fired ceramic (LTCC) technology to ensure chemical resistance, minimize impurities, improve heat conduction, and consider freedom in designing the electrode metal part. Plasma stability, which is important for microbial activation, was investigated by changing the frequency and pulse width of the voltage applied to the electrode, and the degree of activation of plastic-degrading microorganisms was evaluated under each condition. The results of this study are expected to be used as basic data for research on the activation of useful microorganisms using low-temperature plasma.

Electrothermally controlled origami fabricated by 4D printing of continuous fiber-reinforced composites

Active origami capable of precise deployment control, enabling on-demand modulation of its properties, is highly desirable in multi-scenario and multi-task applications. While 4D printing with shape memory composites holds great promise to realize such active origami, it still faces challenges such as low load-bearing capacity and limited transformable states. Here, we report a fabrication-design-actuation method of precisely controlled electrothermal origami with excellent mechanical performance and spatiotemporal controllability, utilizing 4D printing of continuous fiber-reinforced composites. The incorporation of continuous carbon fibers empowers electrothermal origami with a controllable actuation process via Joule heating, increased actuation force through improved heat conduction, and enhanced mechanical properties as a result of reinforcement. By modeling the multi-physical and highly nonlinear deploying process, we attain precise control over the active origami, allowing it to be reconfigured and locked into any desired configuration by manipulating activation parameters. Furthermore, we showcase the versatility of electrothermal origami by constructing reconfigurable robots, customizable architected materials, and programmable wings, which broadens the practical engineering applications of origami.

Thermal performance of phase change materials with anisotropic carbon fiber inserts

In thermal energy storage systems, phase change materials (PCMs) are widely used for thermal energy management. Most PCMs have low thermal conductivities, which limits the heat transfer rate within PCM and thus makes the phase-changing process very slow. However, thermal conductivities of PCMs can be altered by inserting targeted additives. We hypothesize that the size and shape of these additive inserts play a key role in thermal management efficiency. To this end, the impacts of carbon fiber (CF) inserts on the phase change behavior and consequent heat transfer efficiencies of inorganic and organic PCMs were investigated using experiments and simulations. Long, anisotropic CFs with high thermal conductivities formed continuous fast heat flux tunnels inside PCMs to enhance the heat transfer. Such CFs could extend the phase change fronts from the limited container-shaped interface to the larger surface of numerous CF inserts inside the PCM. These special CF inserts work with a new heat transfer mechanism, different from conventional small additives or long isotropic CF inserts. The thermal energy release rate increased by 2.5 times with 1 wt.% anisotropic CF inserts in inorganic PCM. However, CF inserts in liquid organic PCM hindered the natural convection and compromised the improved heat conduction. The lab-scale multiphysics simulations support these experimental observations and indicate that CF inserts have potential to enhance heat transfer in inorganic PCMs, but they are less effective in organic PCMs.

Eco-friendly green roof solutions: Investigating volcanic ash as a viable alternative to traditional substrates

This research investigates the potential of volcanic ash as a green roof material, focusing on its thermal conductivity, physical characteristics, and permeability. Laboratory tests were conducted to determine thermal conductivity under different moisture conditions using two measurement devices, TLS 100 and HFM 436/3/1 Lambda. The results revealed that thermal conductivity increases with higher moisture content, indicating improved heat conduction as the material becomes more saturated with water. Particle size distribution analysis demonstrated that the majority of volcanic ash particles fall within the range of sand and gravel, providing a porous and well-draining material. Sand-sized particles create interconnected voids, facilitating efficient water movement, while gravel-sized particles enhance structural stability and load-bearing capacity. The limited presence of silt-sized particles further validated the material's suitability for green roof applications. Permeability tests on loosely compacted volcanic ash revealed higher permeability at 0% compaction, aligning with intended green roof configurations. This high permeability ensures effective drainage, preventing water accumulation and promoting healthy vegetation growth. At 20% compaction, the material still effectively managed water under potential compaction forces, striking a balance between drainage and water retention. Visual examination of green roof samples demonstrated that volcanic ash substrates resisted weed growth due to the absence of fertilization. While the commercial substrate exhibited better vegetation development due to added nutrients, volcanic ash substrates supported vegetation survival throughout the summer period with an irrigation system, reducing maintenance and lifecycle costs. In conclusion, the research findings indicate that volcanic ash possesses desirable thermal properties, a suitable particle size distribution, and favorable permeability characteristics for green roof applications. Its potential as a sustainable and cost-effective alternative to commercial substrates is evident, offering resilient urban landscapes with reduced environmental impact. Further exploration and optimization could solidify volcanic ash as a valuable component in advancing green roof technologies, promoting sustainable urban development.

Extending the Linearity of AlScN Contour-Mode Resonators Through Acoustic Metamaterials-Based Reflectors.

This work describes the implementation of acoustic metamaterials (AMs) made of a forest of rods at the sides of a suspended aluminum scandium nitride (AlScN) contour-mode resonator (CMR) to increase its power handling without causing degradations of its electromechanical performance. The increase in usable anchoring perimeter with respect to conventional CMR designs, enabled by the adoption of two AM-based lateral anchors, permits to achieve improved heat conduction from the resonator's active region to the substrate. Furthermore, thanks to such AM-based lateral anchors' unique acoustic dispersion features, the attained increase of anchored perimeter does not cause any degradations of the CMR's electromechanical performance, even leading to a ~15% improvement in the measured quality factor. Finally, we experimentally show that using our AM-based lateral anchors leads to a more linear CMR's electrical response, which is enabled by a 32% reduction of its Duffing nonlinear coefficient with respect to the corresponding value attained by a conventional CMR design that uses fully etched lateral sides.

Coloration of cotton fibers with inorganic pigments using a transient high-temperature technology

Inorganic pigments have received considerable attention due to their color brilliance and thermal stability, which results in beautiful visual effects and desirable specific functions. Herein, we demonstrated a strategy for the coloration of cotton fabrics coloring with inorganic pigments using a transient high-temperature coloration method. The uniform color, excellent brilliance, and satisfactory fastness were given to the cotton fabrics after the coloration process. The cotton fabrics could be also colored by a mixture of various inorganic pigments. Meanwhile, the colored cotton fabrics exhibited improved heat conduction compared with the control sample, showing an increase in surface temperature by 2 °C. The heating conduction rate of cotton colored using inorganic pigments was also superior to the raw cotton fabric. Therefore, the proposed transient high-temperature coloration technology using inorganic pigments may be a potential industrialization method to improve coloration and functional properties in cotton applications.

Significance of improved heat conduction on unsteady axisymmetric flow of Maxwell fluid with cubic autocatalysis chemical reaction

This paper investigates the effect of chemical reactions on the flow of magnetized Maxwell fluid generated by an unsteady stretching surface. The thermal transport phenomenon is analyzed by using the Cattaneo-Christov theory. By applying the appropriate similarity transformations, the governing equations of motion turn into a set of nonlinear differential equations. For the velocity, temperature, and concentration fields, the resultant equations are then solved as series solutions using the homotopy analysis approach. Using graphical representations, the physical behavior of significant factors is examined in depth. The analysis reveals that higher Maxwell parameter values reduce the flow field while increasing energy transportation in the fluid flow. Further, it is noted that thermal distribution declines for the higher values of the thermal relaxation parameter. Additionally, the solutal distribution bootup for the increasing values of Schmidt number while it shows a decreasing trend for homogeneous and heterogeneous reactions strength. In order to verify our findings, a comparison to earlier research is also included.

Pool boiling on micro-structured surface with lattice Boltzmann method

In this paper, pool boiling on micro-pillar structured surfaces is studied by using a three-dimensional pseudo potential phase-change lattice Boltzmann method (LBM). The joint enhancing effects on bubble nucleation and boiling performance are discussed in detail regarding various surface wettability and pillar geometrical parameters. Results show that on neutral and hydrophobic surfaces, enlarging the spacing of micro pillars delays the nucleation but can reduce the temperature inside vapor film and improve heat conduction. Despite that increasing the pillar height can improve heat flux, it is adverse to nucleation due to the increased cooling effect on the roots of micro pillars. In contrast, on hydrophilic surfaces, the impact of pillar spacing on nucleation is not monotonous and relatively much complicated. The heat flux is enhanced with increasing pillar spacing because of the extended three-phase contact line. And, the nucleation positions differ significantly by varying pillar geometrical parameters on hydrophilic surfaces.

Thermal Analysis and Design Optimization of Photovoltaic Module for Improved Heat Dissipation From Photovoltaic Module

The performance of a photovoltaic (PV) module is largely dependent on the temperature of the PV cell. Hence, heat management in a PV module is crucial to improving the performance and predicting the generated energy. The thermal conductivity of the backsheet affects the direction of the heat dissipation inside the module, with the heat generated by the cell and transferred through the backsheet increasing with increasing thermal conductivity of the backsheet, resulting in improved heat conduction in the in-plane direction. In this article, the temperature of the PV cell in two modules with different types of backsheet was predicted through numerical simulation and the results were compared with experimental results. The factors that affect the heat dissipation in the PV module and the heat dissipation mechanism were investigated, and a thermally efficient structure for improving the PV module performance was developed.

Paving 3D interconnected Cring-C3N4@rGO skeleton for polymer composites with efficient thermal management performance yet high electrical insulation

Polymer-based thermal interface materials (TIMs) with good electrical insulation property is essential in the thermal management of microelectronic devices. A common approach to increasing the polymer's low intrinsic thermal conductivity is to introduce thermally conductive fillers. In most cases, those fillers are also electrically conductive, which destroys the origin electrical insulation property. In this work, we develop a novel heterogeneous two-dimensional hybrid filler by assembling circular carbon nitride (Cring-C3N4) and graphene oxide (GO), aiming to bring the insulation property via Cring-C3N4. With an ordered 3D interconnected structure, the assembled filler shows enlarged sheet size and compact sheet stacking, which facilitates heat conduction. Additionally, the adopted ice-templated method further arranges the filler with the largest thermal conductivity reaching 4.12 W/mK. Meanwhile, it also shows a lower electrical conductivity of 3.6 × 10−7 S/m, meeting most electrical insulation required occasions. Practical heat dissipation performance tests reveal that both larger temperature change rate and maximum attainable temperature are observed for ice-templated treated composite, indicating the reduced thermal contact resistance (TCR) is responsible for the overall improved heat conduction process. This viewpoint is also supported by the practical application of the material functioning as TIMs from both experimental and simulative aspects.

Research Needs for the Solid Oxide Electrolyzer (SOEC) with a Proton-Conducting SOEC (H-SOEC) Electrochemical Hydrogen Compressor (EHC) Energy Conversion Network (ECN)

A high temperature solid oxide electrolysis cell (SOEC) for electrolysis of water is paired with a H-SOEC for hydrogen compression. SOEC and EHC have been integrated into an ECN in a series configuration and then simulated and analyzed. Adding heat and minimizing area specific resistance (ASR) would be highly desirable for further developing highly-efficient SOEC H-SOEC EHC ECN’s. It is important to note there is a maximum possible heat generation rate with a given ASR when operated below the thermoneutral point. There is a maximal heat addition rate for optimal efficiency of the SOEC, and it is not at thermoneutral. Many developers have expressed interest in the thermal management of electrolyzer cells and in the possible existence such an optimum. It is important to understand in general that heat removal can allow increase hydrogen production rate over the thermoneutral path at constant temperature. For this reason, the SOEC H-SOEC EHC ECN was simulated over a range of currents and ASR’s to determine the heat addition or removal required. If the internal resistance of an SOEC could be lowered sufficiently via the development of new, high-performing materials, the efficiency of hydrogen production could be very high, especially when supplementary heat is provided from solar or other waste heat sources such as nuclear or coal power plants. It is remarkable that a quarter to a third of the energy for the combined high-temperature electrolysis and hydrogen compression system could be provided by solar, nuclear or geothermal energy. The goal of HT electrolysis research and development should be to lower ASR and improve heat conduction or heat transfer into and out of the SOEC. The promise of the H-SOEC electrochemical hydrogen compressors depends on its stability, durability and improved transference numbers. The goal of future research should be to improve the potential of this new SOEC H-SOEC EHC ECN.

Investigation of the Parameter-Dependence of Topology-Optimized Heat Sinks in Natural Convection

The thermal design of natural convection heat sinks is critical to the heat management of electronic devices. In this paper, topology optimization (TO) with a new parameter advancing scheme is employed to study the effect of the heating power, heat source size, allowed volume and material thermal conductivity on the optimized design of natural convection heat sinks. Except for the heating power, the other three factors also play an important role on the optimization results. For the small heating power, TO predicts the tree-like heat sink with many secondary-branches to improve heat conduction, but the specific structure is highly dependent on the heat source size, allowed volume and material thermal conductivity. For the large heating power, TO prefers to produce the taper-like heat sink where the tiny branches fade away to adapt to the strong flow, and the influences of the other three factors are reduced. However, two primary branches that connect the heat source and top corners of the design domain always exist, indicating that they are the most effective ways to improve heat transfer. This work has highlighted the impact of different parameters in TO of natural convection heat sinks and provides a more in-depth understanding of the design guidelines.

Heat Flow in Fractured Rocks: Stress and Moisture-Dependent Thermal Contact Resistance

The thermal conductivity of fractured rock masses is an important parameter for the analysis of energy geosystems, yet, its measurement is challenged by specimen size requirements. Fluids within fractures have lower thermal conductivities than rock minerals and heat flow lines constrict through contacting asperities. Together, heat flow constriction and phonon boundary scattering cause an apparent temperature discontinuity across the fracture, typically represented as a thermal contact resistance. We investigate the thermal contact resistance in fractured limestone and its evolution during loading and unloading (σ’=10 kPa to σ’=3000 kPa) for clean and gouge-filled fractures, under both air-dry and water-saturated conditions. The fracture thermal contact resistance decreases during loading because of the increase in the true contact area, gouge and asperity crushing, and fracture filling by produced fines that contribute new conduction pathways. These processes convey high stress sensitivity and loading hysteresis to the fracture thermal contact resistance. Water fills the fracture interstices and forms menisci at mineral contacts that significantly improve heat conduction even in partially saturated rock masses. The rock mass effective thermal conductivity can be estimated by combining the intact rock thermal conductivity with measurements of the thermal contact resistance of a single fracture under field boundary conditions.

Liquid metal-based thermal interface materials with a high thermal conductivity for electronic cooling and bioheat-transfer applications

• Liquid metal-based thermal interface materials (LM TIMs) containing metal nanoparticles exhibit enhanced thermal conductivity. • Soft thermal composites with liquid–metal particles enable tunable thermal or electrical conductivity. • Application of LM TIMs in soft electronics improves their working performance by efficient heat dissipation. • Via bioheat transfer, LM-based e-skin TIMs can enhance the efficiency of targeted tumor therapy. Effective heat transfer is imperative in devices with high power densities, for which thermal interface materials (TIMs) may be used to improve heat conduction across interfaces. Compared to conventional TIMs such as thermal grease and solder, liquid metal (LM) TIMs offer several advantages owing to their intrinsically high thermal and electrical conductivities, flexibility, and low melting points. Moreover, their unique properties, such as a low vapor pressure, subcooling, and biocompatibility, enable their application in thermal management and biomedical therapy. This review provides a basic understanding of LM-based TIMs by discussing their fundamental characteristics and correlative theories. Several representative applications of LM TIMs in electrical devices, soft electronics, and bio-heat transfer are presented. Furthermore, the challenges facing these materials are highlighted and their future application prospects are delineated to present the readers with a comprehensive overview of this class of materials.

Increasing the transmission performance of a conventional 110 kV cable line by combining a hydronic concrete pavement system with photovoltaic floor tiles

By combining the photovoltaic (PV) effect, heat exchanger principle, heat storage capability and phenomena of heat generation in PV cells and power cables, it is possible to increase significantly the transmission performance (i.e. the ampacity) of any 110 kV underground cable line. This can be achieved by installing power cables in a trench which is completely filled with high thermal conductivity bedding and which is covered with a hydronic concrete pavement (HCP) and a layer of PV floor tiles. This HCP, a heat storage system and a circulating pump are the three main parts of a HCP system, which should be used as a cooler for the PV tiles and cables. In particular, the PV cells would generate waste heat and direct current electricity from sunlight (using the PV effect), the cable bedding would conduct waste heat well from the cables to the heat collecting pipes of the HCP system (by improved heat conduction), while the HCP system would collect and store waste heat from the PV cells and cables as well as some heat from the Sun (using the heat exchanger principle and heat storage capability). The main aims of this paper are to show that the proposed method is highly energy-efficient, cost-effective and applicable in practice. The proposed method is regarded as a novelty, while the electricity generation in the PV floor tiles and the storage of heat within the HCP system represent additional advantages of this method. An adequate experimental background, one reference FEM-based model and one necessary base case are provided. For specified environmental conditions, the proposed method is verified numerically by means of COMSOL Multiphysics. Finally, the results of a techno-economic analysis are presented and discussed.

Flow Analysis and Heat Transfer of Nanofluid Flow in Different Geometries: A Review with Focus on Recent Development

In a thermo-dynamical system loss of energy takes the centre of attention. Laws of thermodynamics stated that energies of the system cannot be lost, but this energy could be engaged to perform useful work, or wastefully lost in form of rises in temperature of the system. It is eminent to control the factors which act in rising values of loss in energy. Nanofluids uses nanosized particles with very high thermal conductivity uniformly distributed in base fluids which increases the conductivity of the base fluid ridiculously. Nanofluid play a vital role in reducing the loss of energy and improve heat conduction. An effort has been made in this paper is to carry out an extensive review of the literature regarding Nanofluid in recent years. Some basic components and properties of nanofluids are deeply elaborated in this article. Preparation of nanofluids perform a very significant role in recent decades. The new advanced results in nanofluids helps the reader to clarify their concepts are argued using two major dynamical models.

Simulation of heat transfer processes in a diesel engine equipped with pistons coated by using Galvanic-plasma Method

The methodology for analyzing the thermodynamics and heat transfer of the combustion chambers of a diesel engine is presented. The work is devoted to the modified quasi-steady method (MQM) for the analysis of a diesel engine piston coated with an aluminum alloy. The oxide-coated piston using a galvanic-plasma modification (GPM) depending on the thickness of the coating, including comparison with the results for uncoated piston temperature, to achieve higher characteristics of the Cummins KTA-50 diesel engine. In thermodynamic modeling of a diesel engine, instantaneous gas temperatures and convective heat exchanges are first predicted. The time-dependent boundary conditions are then applied to the gas-blown surfaces of two-dimensional, transitional finite element models of the components of the combustion chamber. Further, the predictions on the finite elements of the instantaneous heat flux passing through each surface of the component are used to determine when the engine goes into quasi-stationary operation. The results show that our path in methodology can identify the complex transition paths of the heat process in the engine combustion chamber and significantly improve heat conduction and convection heat models when modeling a diesel engine.

Processing and characterization of TiO2 filled polymer composites

This paper reports on the research dealing with the processing and characterization of TiO 2 filled polymer composites. It also presents the test results in regard to the physical, mechanical and micro-structural characteristics of the epoxy and polypropylene composites filled with micro-sized TiO 2 particles. The effective thermal conductivity of polymer composites with uniformly distributed micro-sized particulates are estimated using a theoretical heat conduction model proposed previously by the authors and the correlation is validated for TiO 2 filled polymers through numerical analysis and experimentation. Some other important thermal characteristics, such as glass transition temperature (T g ) and coefficient of thermal expansion (CTE) of epoxy and polypropylene composites are also estimated. The effects of TiO 2 content on these properties of epoxy and polypropylene have been studied experimentally. The estimation of effective thermal conductivity of the composites using finite element method (FEM) and the proposed theoretical model is done and the results are validated by corresponding experimental results. The findings of this research suggest that incorporation of TiO 2 into epoxy and polypropylene leads to substantial improvement in thermal conductivity and glass transition temperature of the resins. At the same time, TiO 2 helps in lowering the coefficient of thermal expansion of such composites. This work further shows that the FEM serves as a good predictive tool for assessment of thermal conductivity of these composites. The theoretical correlation proposed in this work can serve as a very good empirical model for spherical inclusions to estimate the effective thermal conductivity of the composites within the percolation limit. With light weight and improved heat conduction capability, the TiO 2 filled polymer composites can be used for applications such as electronic packaging, encapsulations, communication devices, thermal interface material, printed circuit board substrates etc.