Thermal Resistance Research Articles

High throughput screening of thermal interface materials by machine learning

Till now, it remains a challenge for effective prediction and screening of novel materials with high thermal conductivity, as well as further optimization of the interface thermal resistance. Normally, people have to spend long time on tedious calculations when predicting and screening these materials. In this paper, I combined machine learning with molecular dynamics simulations to investigate the thermal conductive properties of materials with the aim of significantly reducing computational consumption. I first applied molecular dynamics simulations to obtain the relevant properties of materials, then generated models for predicting physical properties by machine learning, and finally made predictions of thermophysical properties of materials. The use of machine learning significantly reduces the prediction time compared to direct molecular dynamics simulations. Especially when the XGBoost and the neural network models are employed, the prediction efficiency is significantly improved. This work guides a new way for the future screening of high-performance thermal interface materials.

New design concept and thermal performance of a composite wall applied in solar greenhouse

Traditional solar greenhouse wall combines the functions of heat preservation and heating. It cannot accommodate both heat storage and insulation that the heat stored in the wall is uncontrollably lost as the temperature difference between the interior and exterior increases. This study proposed a novel composite wall (NCW) with an independent modular wall made of expanded polystyrene board and reinforced concrete (EPCW), and a solar water heating system (SWHS). The thermal properties of traditional brick walls and novel composite walls were assessed through field tests. Numerical simulations were utilized to analyze the heat transfer processes occurring within the wall, enabling determination of the magnitude of heat transfer towards both the interior and exterior. The thermal resistance of the ECPW with the same thickness is 1.5 times higher than that of clay bricks. Meanwhile, the heat loss from the exterior wall is reduced by 44 % through the EPCW. The SWHS installed on the greenhouse north wall increases heat storage by 89 % and heat release by 256 %. The greenhouse annual input cost for using NCW is 2.5 USD m−2 year−1 in 20-year life. It is 32.4 % lower than that of a conventional clay brick greenhouse, and has some promotional and application value.

Boosting thermal energy transport across the interface between phase change materials and metals via self-assembled monolayers.

Thermal energy storage using phase change materials has great potential to reduce the weather dependency of sustainable energy sources. However, the low thermal conductivity of most phase change materials is a long-standing bottleneck for large-scale practical applications. In modifications to increase the thermal conductivity of phase change materials, the interfacial thermal resistance between phase change materials and discrete additives or porous networks reduces the effective thermal energy transport. In this work, we investigated the interfacial thermal resistance between a metal (gold) and a polyol solid-liquid phase change material (erythritol) at various temperatures including temperatures below the melting point (300 and 350 K), near the melting point (390, 400, 410 K, etc.) and above the melting point (450 and 500 K) adopting non-equilibrium molecular dynamics. Since the gold-erythritol interfacial thermal conductance is low regardless of whether erythritol is melted or not (<40 MW m-2 K-1), self-assembled monolayers were used to boost the interfacial thermal energy transport. The self-assembled monolayer with carboxyl groups was found to increase the interfacial thermal conductance most (by a factor of 7-9). As the temperature increases, the interfacial thermal conductance significantly increases (by ~50 MW m-2 K-1) below the melting point but decreases little above the melting point. Further analysis revealed that the most obvious influencing factor is the interfacial binding energy. This work could build on existing composite phase change material solutions to further improve heat transfer efficiency of energy storage applications in both liquid and solid states.

Enhanced thermo‐mechanical properties of carbon fiber reinforced thermoresistant polymer, a blend of di‐functional epoxy bisphenol A and a tri‐functional epoxy Tactix 742

AbstractFiber reinforced polymer composite structures are particularly vulnerable to high temperatures as their strength drastically reduces under elevated temperature conditions. Therefore, it is important to improve the thermal stability of such composite structures to expand their potential range of applications. In this study, the effect of mixing two epoxy monomers, DGEBA and Tactix 742, which are di‐ and tri‐functional, respectively, on the thermal stability of their composites is investigated. The thermo‐mechanical analysis of these composites revealed that the glass transition temperature rose from 123 to 229°C when Tactix 742 is increased from 25% to 75%. The thermal resistance property is attributed to a three‐dimensional crosslink network which is initiated by tri‐functional Tactix 742. However, the higher percentage of Tactix led to a reduction in strength, possibly due to decreased crystallinity and formed amorphous phase material. Subsequently, a tensile strength model was employed to assess the performance at elevated temperatures. It was shown that a matrix with a mix of di‐ and tri‐functional monomers is highly promising for manufacturing thermoresistant polymeric composites with robust mechanical properties, thereby expanding their potential applications across various engineering fields such as civil and construction industries.Highlights A thermoresistant matrix by blending di‐ and tri‐functional epoxy monomers. Improved thermo‐mechanical properties and increased glass transition temperature of fiber reinforced composites. Mechanical performance of carbon fiber reinforced composites at elevated temperatures. Validated a model to estimate the tensile strengths of the composites at elevated temperatures.

Development and characterization of fly ash enriched epoxy coatings for corrosion protection in deep sea water

Fly ash (FA) has recently received increasing attention as inexpensive and readily abundant filler for development of epoxy-based anticorrosive coatings. In the present investigation a series of FA enriched epoxy coatings (FECs) has been developed and investigated for their anticorrosive behaviour under immersion in DSW (pH 8.2) over 48 h. The development of FECs was conducted through enrichment of FA ranging 0 to 80 phr (parts of FA per 100 g of epoxy) into epoxy matrix. The formation of FECs was ascertained through spectral, thermal, electrical and microscopic methods. Electrochemical impedance spectra in coherence with DC polarization measurements reveal enhanced corrosion protection efficiency (83 %) of FECs derived at 40 phr enrichment of FA. Enrichment of FA (phr) ranging 40 to 60 has rendered fair (0.01) to moderate (0.05) resistance (mm/year) to FECs against pitting corrosion in DSW. Whereas, FECs derived at 60 phr of FA has shown promising electrical behaviour, moderate heat resistance (TG onset 200 °C with 94.70 % weight residue) with enhanced limiting oxygen index (38.50 %). FECs developed in the present investigation may find their possible applications as anticorrosive coatings sustainable in DSW over 48 h.

Single-phase thermosyphon heat transport device, a future prospect for heat removal applications: An experimental comparison with heat pipe and two-phase closed thermosyphon

Over the years, the passive mode of heat transportation has gained immense popularity, which includes two-phase devices viz. Heat pipe (HP) and Two-phase closed thermosyphon (TPCT). But recently, the thermosyphon heat transport device (THTD) entered the pool, wherein the heat transfer fluid (HTF) in liquid phase transports heat by natural circulation (thermosyphon). Hence, to gauge their efficacy, in the present experimental investigation, the three devices (with the same geometry and HTF) are compared by imposing isothermal (40°C–90 °C) and isoflux (50–900 W) heating conditions.In isothermal mode, HP transports heat with a minimal temperature gradient compared to TPCT and THTD. The thermal resistance (TR) of TPCT and THTD is 5.4 to 10.1 times and 6.6 to 10.1 times respectively greater than HP. For isothermal temperatures below 80 °C, the TR of THTD is less than TPCT (viscous limit). Later the trend reverses as the TPCT outperforms, while THTD experiences HTF boiling. Further, the heat extracted by HP is 2.1 to 3.9 times and 3 to 3.5 times greater than TPCT and THTD respectively. Hence, its application is justified if cost is not a concern, while THTD (with high-temperature HTF) is suggested over TPCT on an economic basis. Even the isoflux mode showed a similar trend of TR. The system response (based on time constant) depicted both HP and TPCT have similar and nearly constant values over the heat load range, while in THTD, it decreases with an increase in heat load and approaches the other two. Hence, a high-temperature HTF would lead to competitive results. Further, concerning the heat transport distance, as the TR of THTD remained the same compared to the increment in TPCT, the application of the former is justified in long-distance heat transportation. Ultimately, HP is the front-runner, while TPCT and THTD perform on par depending on operating conditions and geometry.

Membrane role in heat and mass transfer resistance distribution and performance of hollow fiber membrane contactor for SGMD desalination

Hollow fiber membrane contactor (HFMC) is the core device of heat mass exchange between seawater solution and sweeping air in sweeping gas membrane distillation (SGMD) desalination. In order to reveal the distribution of heat and mass transfer resistance on feed solution side, porous membrane side and sweeping air side, a mathematical model considering the simultaneous heat mass transfer and water vapor diffusion mechanism in the membrane pores was established for the cross-flow HFMC. The simulation results of the model were compared with experimental results and literature results. Comparison shows that the deviation of simulation results of the model is less than 13.4 %, which verifies the accuracy and reliability of the simulation results. Influences of the main structural characteristics of porous membrane on the resistance distribution of heat and mass transfer, efficiency and membrane flux were explored. Air side dominates the heat transfer process, while the membrane side accounts for less than 39 % of the total heat transfer resistance for the main range of membrane microstructure parameters investigated. The mass transfer is controlled by the porous membrane except for thin membrane with a thickness of less than 100 μm. Membranes with porosity above 0.8 and as thin as possible can achieve better mass transfer efficiency and freshwater flux. Increasing mean pore diameter has a strong promotion effect on the increase of membrane flux before it reaches 150 nm, and beyond this critical value, the water vapor diffusion mechanism changes from Knudsen collision to molecular collision. Effects of different operating parameters and membrane microstructure parameters on air temperature distribution and humidity distribution were also analyzed.

Evaluating perovskite solar panels for thermal stability and inclination performance through finite element modelling

This paper presents a foresight simulation of perovskite solar modules, focusing on their behavior under different wind velocities and the thermal effects of varying solar irradiance conditions. Despite the burgeoning interest in Perovskite solar panels (PSPs) due to their lower material costs and promising efficiencies, there exist significant research gaps, particularly in the interaction between wind flow and thermal variations, as well as the performance dynamics under distinct wind velocities. To address these gaps, Finite Element Modelling (FEM) simulations were conducted to analyze the thermal stability and wind stress resistance of PSPs, employing a structural design analogous to commercial silicon PV panels. The simulations revealed that the implementation of a cooling system effectively lowered the average temperature of the perovskite layer by a factor of 2.46, significantly reducing the risk of thermal degradation. Additionally, wind stress simulations demonstrated a direct proportionality between the vertical pressure on the panels and their inclination angles, suggesting that lower angles could minimize wind-induced damage while considering daily solar azimuth. The study’s outcomes contribute to the understanding of PSPs’ mechanical and thermal resilience, proposing an optimized design approach for enhanced durability and efficiency in real-world applications. However, the segregation of thermal and wind flow simulations suggests an area for further integrated studies to fully comprehend the simultaneous effects of environmental factors on PSP performance.

Preparation and performance research of ecological concrete using waste wood

To mitigate environmental damage from mineral aggregate extraction, bio-based materials have garnered research interest as potential replacements for natural mineral aggregates. This work utilized waste wood as filler to prepare lightweight foam concrete with thermal insulation, low-temperature and corrosion resistance properties. The feasibility of using wood aggregate-based foam concrete (WFC) was explored in terms of dry density, softening coefficient, compressive strength, thermal conductivity, chloride ion permeability, freezing resistance, and sulfate attack resistance. Results showed that simultaneous addition of waste wood aggregate (WA) and foam effectively reduced WFC bulk weight and thermal conductivity while enhancing water resistance. However, the porous morphology of WA and foam caused the reduction of mechanical properties. In terms of durability, the addition of WA can increase the energy absorption capacity when WFC is subjected to expansion stress, reduce the damage to the structure, and have an inhibiting effect on the cracking of WFC caused by sulfate attack and freeze-thaw cycles. Nevertheless, WA's high water absorption loosened the matrix in WFC's interfacial transition zone (ITZ), increasing harmful pores and negatively affecting durability. In addition, in order to predict the mechanical properties of WFC and the resistance to sulfate attack, this study established a function model for the relationship between the compressive strength (Maintenance specimens of the same age and Specimen of sulfate attack) and the WA dosage. In conclusion, The use of waste wood for the preparation of WFC is more advantageous and sustainable than conventional foam concrete for the insulation of precast walls and coastal structures.

A waste hemp‐based biomass carbon aerogel with high fire‐resistance

AbstractTo enhance the efficient utilization of waste hemp rods, a kind of three‐dimensional (3D), mesh‐like lamellar structured hemp‐based biomass carbon aerogel (CA) was developed by freeze‐drying and subsequent high‐temperature carbonization method. The microstructure, flame resistance, thermal stability, and thermal conductivity of CA were investigated using several analytical techniques, including scanning electron microscopy (SEM), Fourier‐transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), simulated combustion tests, and thermogravimetric analysis (TG). Optimum formulation yielded at an alkali treatment concentration of 20% and a carbonization temperature of 700°C, CA with a 3D network of reticulated lamellae was obtained. CA exhibited minimal values for thermal conductivity (0.06 W/m K) and thermal diffusion coefficient (0.41 mm2/s), which are indicative of superior insulative properties. Moreover, the material demonstrated remarkable thermal endurance and flame resistance, achieving a char yield of 70.03% when subjected to a temperature of 700°C in an oxidative environment.

Carbon nanotubes grafting aminated epoxy resin with improved elasticity and surface adhesion for enhanced thermal management performance

It is a great challenge to develop thermal interface materials that enable fast heat transfer between the surface of microelectronic materials and heat sinks. In this paper, multi-walled carbon nanotube/epoxy composites (EP-NH2-x) were synthesized by amidation reaction using aminated epoxy resin as matrix and carboxylated multi-walled carbon nanotubes. EP-NH2-x can reduce the interfacial thermal resistance and the promotion of phonon conduction through the chemical bonding connection between the resin and the carbon nanotubes, which will in turn improve the thermal conductivity of the composites. The thermal conductivity of EP-NH2-10 reaches 0.531 W·m−1·K−1 at a and has good variable temperature cycling stability, internal elasticity and surface adhesion. This work highlights the potential application of carbon materials to improve the thermal conductivity of epoxy resins.

The importance of using active thermal protection following restoration work on old buildings

The paper deals with the issue of humidity and the unhealthy environment of old buildings. Humidity is a very widespread problem not only in historical buildings, but also in newer buildings. This problem can be observed in various parts of the world and thus it can be said that it is a global problem. Humidity in these buildings causes an unhealthy environment, which has a negative effect on individual building constructions, but also on people’s health. Humidity is also associated with the form of disruption of the individual layers of the construction and the disruption of the thermal resistance of these constructions. Buildings such as these subsequently have an unhealthy environment. After a part of the description of the known issue, the contribution follows on from this part by indicating possible remedial interventions and analyses the systems of additional thermal insulation (ETICS, ATP), ensuring the improvement of the internal environment. Finally, the article presents possible connections and extensions of this research and its application directly in practice. The results of the proposed research will significantly contribute to the approach to rehabilitated older buildings and their long-term sustainability from an economic point of view, as well as the possible use of them.

Visualized study and performance evaluation on a micro-grooved vapor chamber

The evaporation resistance and capillary flow both dominates the heat transfer performance of aluminum vapor chamber (VC) with micro-grooved wicks (MGW). This study presents the visualization experiments for three MGW VC samples with different cross-sectional shapes, including semicircular (MGW-S), V-shaped (MGW-V) and trapezoidal (MGW-T). The characterization of capillary rise dynamics is evaluated and compared by depicting the transient liquid front in vertical installation while the thermal spreading capability is examined horizontally at the quasi-steady state. Results show that the MGW-T exhibits the highest capillary pressure, and higher capillary rise rate can be obtained when applying acetone as working medium. As the groove shape impacting on the rate of bubble generation and detachment during evaporation process, the MGW-S obtains the lowest average thermal resistance. However, compared to the uniformly generated bubbles of acetone, it is revealed that ethanol might result in the slug or puddle at the evaporation area, which shortens the flow length of vapor and increases the average thermal resistance. When conducting under incremental heat loads, the boiling phenomenon of the working liquid becomes increasingly turbulent, and the average thermal resistance can be minimized from 2.6 K/W to the level lower than 1 K/W. As the result, when using acetone with filling ratio of 30%, the average thermal resistance of the MGW-T reaches 0.92 K/W under heat load of 60 W.

Design and optimization of three segmented thermoelectric generator for nuclear reactor application

With the scientific exploration in deep space and deep sea, traditional fossil energy and solar energy cannot supply energy for deep space aircrafts and deep sea vehicles continuously, new energy power systems with the features of long endurance, high reliability and high energy density are imperative. Small nuclear reactor has become one of the best solutions for deep space energy demand in the future due to its strong environmental adaptability and long-life time. To improve the reliability of the static heat pipe reactor, the thermoelectric generators (TEGs) are utilized to convert fission heat into electrical energy. Focusing on the demands of improving the conversion efficiency, a new three segmented TEG is proposed based on the Bi2Te3, CoSb3 and Half-Heusler thermoelectric materials in this paper. Combined with the application requirements of heat pipe reactor, the geometric configuration such as different heights and the cross-sectional area of the three different materials in the PN legs is designed and optimized under different heat flux boundary conditions. The influences of contact electrical resistance and contact thermal resistance on the conversion efficiency have been investigated. When the contact electrical resistivity increases from 0.01 μΩ cm2 to 1000 μΩ cm2, the conversion efficiency loss increases from 2.6% to 80.1%. As the surface roughness rises from 0.1 μm to 100 μm, the conversion efficiency loss increases from 0.9% to 42.7%. Based on the heat flux boundary conditions provided by the heat pipes, the thermoelectric conversion performances of three segmented TEG under different external loads are investigated. Through the geometric optimization of the three segmented TEG with total height 20 mm, the thermoelectric conversion efficiency improves from 6.9% to 15.34%. For the simulation heat flux density conditions of 70 kW m−2, 75 kW m−2, 80 kW m−2, 85 kW m−2 and 90 kW m−2, the maximum output power of a thermoelectric generator can reach 8.56W, 9.71W, 10.85W, 12.00W, and 13.11W, respectively. The output characteristics of the three segmented TEGs meet the design demands of the static conversion system.

Enzymatic modification lowers syneresis in corn starch gels during freeze–thaw cycles through 1,4-α-glucan branching enzyme

The current research in the food industry regarding enzymatic modification to enhance the freeze–thaw (FT) stability of starch is limited. The present study aimed to investigate the FT stability of normal corn starch (NCS) modified using 1,4-α-glucan branching enzyme (GBE) derived from Geobacillus thermoglucosidans STB02. Comprehensive analyses, including syneresis, scanning electron microscopy, and low-field nuclear magnetic resonance, collectively demonstrated the enhanced FT stability of GBE-modified corn starch (GT-NCS-30) in comparison to its native form. Its syneresis was 66.4 % lower than that of NCS after three FT cycles. Notably, GBE treatment induced changes in the pasting properties and thermal resistance of corn starch, while simultaneously enhancing the mechanical strength of the starch gel. Moreover, X-ray diffractograms and microstructural assessments of freeze–thawed gels indicated that GBE treatment effectively hindered the association of corn starch molecules, particularly amylose retrogradation. The enhanced FT stability of GBE-modified starch can be attributed to alterations in the starch structure induced by GBE. This investigation establishes a foundation for further exploration into the influence of GBE treatment on the FT stability of starch and provides a theoretical basis for further research in this area.

Bioinspired Wearable Thermoelectric Device Constructed with Soft‐Rigid Assembly for Personal Thermal Management

AbstractThe development of high‐performance thermoelectric devices (TEDs) with personal thermoregulation is crucial for the advancement of next‐generation wearable technologies. Most efforts focus on optimizing mechanical flexibility in fully encapsulated devices, but parasitic heat loss induced by the layer‐packed polymer matrices with high thermal impedance typically leads to degradation in sensing and bidirectional conversion capabilities. Here, a bioinspired architectural strategy is proposed for this problem that demonstrates the feasibility of single‐sided assembly based on a soft‐rigid “skin‐spine” configuration to improve heat utilization efficiency. With active TE units connected via serpentine electrodes, skin‐spine‐structured wearable thermoelectric devices (SSSW‐TEDs) are successfully fabricated enabling temperature sensing and bidirectional heat‐to‐electricity conversion under mild forced convection. This contributes to significant enhancements in power delivery (by 300%) and cost‐benefit analysis (by 100%) through efficient air convection heat dissipation. Moreover, SSSW‐TED enables personal thermal regulation by harnessing body heat, cooling the skin, and perceiving behaviors such as touching and blowing. This study not only provides novel insights for high‐performance TEDs but also lays the foundation for the widespread implementation of skin thermoregulation.

A Novel Semiaromatic Polyamide Thermoplastic Elastomer with Excellent Heat Resistance and Mechanical Properties

A Novel Semiaromatic Polyamide Thermoplastic Elastomer with Excellent Heat Resistance and Mechanical Properties

SC crystals of porous PLA via thermally–induced phase separation: Effects of process conditions, solvent composition and nucleating agent

The formation of stereo-complex crystals (SC) in porous poly (lactic acid) (PLA) material is intricately linked with improving its comprehensive properties. In this work, the effects of process conditions, solvent composition and additional nucleating agent on SC crystals during the fabrication of porous PLA through thermally-induced phase separation method were studied. Crystallization behavior of SC crystals during the pore-forming process is systematically investigated, revealing that higher quenching temperature and longer quenching period facilitate the formation of SC crystals. Additionally, the addition of deionized water to the solvent effectively enhances SC crystals formation by reducing solution viscosity and prolonging the phase separation time. The highest crystallinity of SC crystals (XSC) can be achieved, reaching 30.6%, when the water content is controlled at 1.6%. Furthermore, the introduction of carbon nanotubes (CNTs) as a nucleating agent exhibits a pronounced effect on the formation of SC crystals. When incorporating a 3 wt% content of CNTs, XSC reaches its peak value at 37.7%. This work is helpful to provide reference for improving mechanical properties and heat resistance of porous PLA, thereby expanding its potential outdoor applications.

Advanced cooling channel structures for enhanced heat dissipation in aerospace

Thermal protection is crucial for active cooling runner structures. It’s highly effective for achieving thermal insulation in aerospace applications. This study focuses on evaluating the thermal insulation performance of the heat dissipation runner structure under varying flow rates. The results demonstrate the exceptional thermal insulation capabilities of the heat dissipation runner structure, with a noticeable positive impact on thermal protection through appropriate flow rate increments. A simulation and analysis model for thermal insulation performance is developed and validated against experimental findings. By delving into robust heat transfer theory and turbulence mechanisms, it is observed that the local turning radius and length of the runner exhibit an inverse relationship with the heat dissipation performance of the structure. Through localized optimization of the runner design and implementation of a series–parallel connection mechanism, eight distinct heat dissipation runner structures are meticulously crafted. Analysis of temperature uniformity and flow consistency within the runner structure is conducted using thermal resistance, inlet pressure loss, and comprehensive evaluation criteria. Results underscore the strong thermal insulation performance of the eight runner structures, highlighting a direct correlation between the number of parallel runners and enhanced heat dissipation efficiency, while revealing an inverse correlation with the number of local turns. Notably, at a flow rate of 0.0005 m3/s, the thermal insulation performance of the eight flow channel structures peaks. Furthermore, it is observed that increasing the series connection of the runners only serves to complicate the structural design without significant benefits to heat dissipation. Thus, it is recommended to minimize the series connection direction in the runner design to optimize thermal management effectiveness.

MODELLING AND 3D PRINTING OF GAS ENGINE TURBINE BLADE

A turbine blade is the individual component which makes the turbine section of a gas turbine. The blades are used for extracting energy from the high temperature, high pressure gas produced by the combustor. This research focuses on the modeling, Analysis and 3D printing of gas engine turbine blades, aiming to enhance efficiency and performance in power generation. Utilizing advanced modelling softwares such as CATIA software, a detailed digital representation of the turbine blade was created, considering the aerodynamic feature. Further, the model is analysed in ANSYS for Subsequently, additive manufacturing techniques were employed to produce physical prototypes using high-strength, heat-resistant materials. The study evaluates the structural integrity, thermal resistance, and overall performance of the 3D-printed turbine blades, comparing them with traditional manufacturing methods. The findings contribute to the advancement of turbine technology, demonstrating the feasibility and benefits of 3D printing in optimizing gas engine turbine blade design for increased efficiency and reliability.