Transverse Thermal Conductivity Research Articles

Cryogenic thermal conductivity of carbon fiber reinforced polymer composite laminates

Carbon fiber reinforced polymer (CFRP) composites with excellent mechanical properties and low thermal conductivity are promising materials for cryogenic facility support structures. However, the temperature dependence and stacking sequence dependence of the laminates’ thermal conductivities challenge their thermo-mechanical design. Previous work dealing with the cryogenic thermal conductivity of laminates was relatively inadequate, and the effect of stacking sequence has not been sufficiently clarified. Herein, the cryogenic thermal conductivity of CFRP composite was investigated, and a theoretical model for the out-of-plane thermal conductivity of laminate was developed. To this end, the thermal conductivities of epoxy resin and laminates were measured at temperatures from 20 K to 293 K. The cryogenic thermal conductivity of carbon fiber was then extrapolated. Subsequently, a theoretical model was developed based on the thermal-electrical analogy method to evaluate the effect of stacking sequence. The obtained model was then validated by numerical analysis and experimental work. Lastly, the effects of lay-up angles and component properties on out-of-plane conductivity were examined. The test results suggested longitudinal thermal conductivity of composites exhibiting significant temperature dependence, with a decreasing trend recorded from 6.317 Wm−1K−1 to 0.355 Wm−1K−1 and transverse thermal conductivity decline from 0.626 Wm−1K−1 to 0.156 Wm−1K−1. The theoretical analysis indicated that the stacking sequence could reduce the out-of-face thermal conductivity by up to approximately 6.5 %, while the lay-up angle did not show any influence. In sum, novel insights into the cryogenic thermal conductivity of CFRP composites were provided, with guidance for the design and analysis of CFRP composites in cryogenic applications.

A novel numerical method to evaluate the heat transfer characteristics of complicated CICC structures

In this article, we propose a numerical model for calculating the external heat transfer coefficient between the bundle region and its wall for cables in conduit conductor (CICC). With the assumption of local thermal equilibrium, one macro equation describing the steady heat transfer on the cross section of the CICC can be obtained. A key parameter, the effective transverse thermal conductivity keff, which takes the contribution of both strands and flowing fluid into consideration, is introduced. To calculate the effective transverse thermal conductivity keff, we first obtain the true distribution of different phases (fluid, copper and superconducting material) on a cross section of CICC with the help of the image recognition technique. Based on this, the value of the effective transverse thermal conductivity keff can be calculated numerically. Due to the large difference among the component thermal conductivities (at 4.5 K, typical values of the thermal conductivity of liquid helium, superconducting material and copper are kHe=0.024Wm−1K−1, kNb3Sn=0.04Wm−1K−1 and kCu=708Wm−1K−1; and the maximal ratio of thermal conductivity can be as high as about 30,000), the high-performance finite analytical method (FAM) is recommended to calculate keff. After obtaining the effective transverse thermal conductivity keff of the bundle region, the heat transfer coefficient can be calculated directly by solving a simple Poisson equation under proper boundary conditions. Two case studies are performed, including the JT-60 Super Advanced (JT-60SA) CICC and the dual channel International Thermonuclear Experimental Reactor, Toroidal Field Performance Sample (ITER-TFPS). The calculated values of heat transfer coefficient are consistent with the experimental results, which verifies our proposed model.

Thermal and Morphological Assessment of the Penta-Layered, Hybrid U-Polyester Composite Reinforced with Glass Fibers and Polypropylene

The interaction between the fibers and matrix in a fiber-reinforced polymer composite material is important in figuring out its properties. The incorporation of fibers with polymers can result in composites with enhanced strength and stiffness. This study aims to investigate the thermal and morphological characteristics of hybrid u-polyester composites reinforced with glass fibers and polypropylene. The fabrication of composite specimens was conducted through a straightforward cold press method. The compositions of the composites were held constant, except for the orientation of the glass fibers and polypropylene. In this study, the TG/DTG technique was used to analyze the thermal characteristics of the composites. In addition, transverse thermal conductivity was measured using the ASTM E1530 method. The test results showed that the composite reinforced with glass fibers exhibited the lowest weight loss and minimal thermal conductivity among all the samples, followed by the hybrid composite. Based on the TGA curves of the samples, the matrix experienced a weight loss of 9.7% at a temperature of 300°C, which reduced to 2.6% and 2.1% for hybrid composites and glass fiber-reinforced composites, respectively. DTG curves for composites demonstrate that the hybrid and fiber-reinforced composites degraded at rates of 0.64 mg/min and 0.36 mg/min, respectively, at 392.3°C and 395.7°C. Moreover, transverse thermal conductivity of the composite which consists of five-glass-fibered layers shows a minimal thermal conductivity of 0.05 W/m·K. The morphological properties were also investigated using scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The findings from SEM and FTIR showed that a higher proportion of glass fibers led to a more oriented composite structure, demonstrating enhanced crosslinking between fibers and polyester. Therefore, the insights of this study can be used to improve the performance of glass fibers and polypropylene hybrid-laminated composites intended for high-temperature applications.

Analysis of transverse thermal conductivity for mesophase pitch-based carbon fibers and the through-thickness heat conduction of their composites

A quantitative analysis method for the transverse thermal conductivity (TC) of carbon fiber is developed, which consists of three steps including TC and morphology characterization of unidirectional composite laminate, fiber contour extraction, and finite element inverse analysis. Two different pitch-based carbon fibers with folded-radial and onion-skin microstructure are characterized, and the influences of fiber volume fraction and microstructure on the heat conduction of their composites are investigated. The equivalent transverse TCs of TC–HC–800 and PCF-1 carbon fibers are measured to be 9.27 and 2.87 W m−1 K−1, respectively. The through-thickness TC of unidirectional composite exhibits rapid growth with the increase in fiber volume fraction. The finite element analysis reveals that more continuous heat conduction paths are formed with the increase in fiber volume fraction. Benefited from the bigger graphitization degree, larger cross-sectional area, and bigger aspect ratio, TC–HC–800 unidirectional composite shows higher through-thickness TC than PCF-1 composite at the same fiber volume fraction.

Advancing the precision of thermal Hall measurements for novel materials research

Precision thermal Hall measurements unlock potential for unraveling fundamental thermal transport principles in novel materials. This work addresses the challenge of resolving sub-mK temperature differences in magnetic fields by employing high-precision capacitance thermometry with thermalized electronics, achieving a background noise of approximately ▪ at ▪. The novelty lies in the improvement and combination of innovative approaches, including the application of attenuators for thermal anchoring, a modular multi-stage approach to reduce thermal gradients, direct thermometer-sample assembly, and the use of individual capacitance bridges for faster measurements. The setup performance is demonstrated for the pyrochlore oxide terbium titanate and the longitudinal and transverse thermal conductivities agree with the literature. We show that the transverse temperature difference is proportional to the product of magnetic field times heating power for fields up to ▪, enabling improved statistics compared to individual sweeps analysis. We conduct an analysis of uncertainties in the transverse thermal conductivity, considering various thermometer calibrations for extracting temperature differences. This analysis reveals a significant influence of the longitudinal conductivity on the transverse thermal conductivity. These advancements allow for unprecedented temperature resolution and stability, while identified resolution limitations pave the way for next-generation setups.

Analysis of heat transfer in an aquifer thermal energy storage system: On the role of two-dimensional thermal conduction

Aquifer thermal energy storage (ATES) system plays an important role in application of renewable energy, efficient energy utilization, and reduction of CO2 emission. To realize the successful operation of ATES systems, it is essential to understand the thermal behaviors thoroughly during heat injection. Serving as a powerful tool, analytical model is widely adopted while the existing analytical models usually simplify ATES systems by ignoring aquifer transverse thermal conduction and rock longitudinal thermal conduction. This study develops a novel analytical model for an ATES system, which accounts for thermal convection, dispersion, longitudinal and transverse thermal conduction in the aquifer, and longitudinal and transverse thermal conduction in the surrounding rocks. The Green's function method is applied to derive the semi-analytical solutions of temperature. A global sensitivity analysis is conducted to analyze the relative importance of each parameter. The results indicate that ignoring the aquifer transverse thermal conductivity will overestimate the temperature in the aquifer and ignoring the caprock longitudinal thermal conductivity may underestimate the heat loss in ATES systems. Similar conclusion can be made about the bedrock longitudinal thermal conductivity. The global sensitivity analysis indicates that temperature is sensitive to the changes in the flow velocity, thermal dispersivity and aquifer thickness.

Facile fabrication of green and sustainable functionalized Bombax ceiba L. wood based aerogel for multifunctional applications

Design and development of biobased porous, strong, and anisotropic aerogels through easy and ecofriendly process for multifunctional applications has been research priority for the globe. Wood is considered as a preferable renewable precursor to prepare aerogels with inherent heirarchical structure and high porosity. In this work, Bombax ceiba L. wood has been delignified through a top to bottom process to develop wood aerogel (WA) which retain the heirarchical nature of wood. Wood aerogel (WA) was functionalized with 3-Aminopropyl triethoxy silane (APTES) to graft silane functionality for achieving multifunctional applications like oil/water separation, thermal insulation, acoustic panel making etc. Prepared delignified and silanised wood aerogels (DWS10 or DWS) showed good surface morphology, impressive super hydrophobicity (167.6° ± 5.4°) and high compression modulus of 82.6 ± 5.0 MPa which is 3.75 times greater than that for the wood aerogel (WA). The longitudinal (along the fibres) and transverse (across the fibres) thermal conductivity of DWS (0.122 ± 0.006 and 0.081 ± 0.002) showed 15.3 % and 27.7 % decrease respectively with respect to native wood. TGA analysis revealed the improvement in thermal stability after the silanisation of the aerogel. Acoustic properties showed ∼80 % sound absorption over a frequency range of 1500–3000 Hz for DWS with a maximum sound absorption coefficient of 0.8 at high frequency range. Thus, the current work paves the way to replace the petroleum-based aerogels currently used for such multifunctional applications being ecofriendly and biodegradable in nature.

Influence of fibre cross-section profile on the multi-physical properties of uni-directional composites

The present work comprehensively examines the influence of fibre-matrix interface perimeter on the multi-physical properties of uni-directional composite materials. Three-dimensional microstructures (containing fibres of triangular, elliptical, rectangular, C-shape and two-lobe cross-section shape) are analysed to evaluate effective thermal conduction, thermo-elastic and piezo-electric properties. Each of these properties is normalised with the respective property of RVE with circular fibre cross-section; These normalised properties are, objectively, compared with the normalised fibre cross-section perimeter (shape factor). For all the considered properties and fibre cross-sectional shapes, a novel observation is that the property experiences a drop (or rise) in the initial range of the shape factor but rises (or drops) monotonically afterwards. This is in contrast with the existing literature observations, where properties are understood to have only a monotonic increase/decrease with the shape factor. Further, it is observed that the magnitude of the initial drop (or rise) is sensitive to the fibre volume fraction and the fibre-matrix property contrast. In accordance with the literature, a strong correlation is observed among the variation of in-plane shear moduli, transverse thermal conduction and transverse dielectric constants.

Statistical upscaling workflow for warm solvent injection processes – Longitudinal and transverse dispersivity and thermal conductivity

Accurately simulating, upscaling, and optimizing the warm solvent injection process (WSI) is challenging due to its complex heat and mass transfer mechanisms. This manuscript presents a comprehensive two-step flow-based upscaling workflow designed explicitly for WSI simulation in heterogeneous reservoirs. The technique builds upon previous research on particle transport in single-phase flow and extends the upscaling method to incorporate multiple correlated properties relevant to the process physics. Specifically, the upscaling methodology considers the correlation between longitudinal and transverse dispersivities. The influence of scale variation on thermal conductivity is examined. The proposed statistical upscaling technique does not rely on explicit assumptions about the distribution of heterogeneity. The results highlight the directionality in dispersivity. Due to the limited temperature variation observed in the case study, upscaling thermal conductivity has little impact. The method's efficiency can be verified by coarser model simulations that capture similar fine-scale model responses with less computational run time.

Vibration Analysis of Laminated Composite Plate under Thermo- Mechanical Loading

The present study focused mainly on the vibration analysis of composite laminated plates subjected tothermal and mechanical loads or without any load (free vibration). Natural frequency and dynamicresponse are analyzed by analytical, numerical and experimental analysis (by using impact hammer) fordifferent cases. The experimental investigation is to manufacture the laminates and to find mechanicaland thermal properties of glass-polyester such as longitudinal, transverse young modulus, shear modulus,longitudinal and transverse thermal expansion and thermal conductivity. The vibration test carried tofind the three natural frequencies of plate. The design parameters of the laminates such as aspect ratio,thickness ratio, boundary conditions and lamination angle were investigated using classical laminatedplate theory (CLPT) and Finite element coded by ANSYS, in addition to the design parameters ofdynamic response such as load type with respect to time, x and y dimension and temperature value forsimply supported symmetric cross ply. The main conclusion was the natural frequency could increaseand decrease depending on the boundary conditions, thickness ratio, and lamination angle, the aspectratio of the plate. Present of temperature could increase dynamic response of plate also depending onlamination angle, type of mechanical load and the value of temperature.

Assessment of transverse thermal conductivity of coir fibre using experimental, analytical, and numerical methods

The Journal of the National Science Foundation of Sri Lanka publishes the results of research in all aspects of Science and Technology. The journal also has a website at http://www.nsf.gov.lk/. 2021 Impact Factor: 0.682The JNSF provides immediate open access to its content on the principle that making research freely available to the public supports a greater global exchange of knowledge.Cover :Leatherback (a), green (b - adult & f - hatchling), hawksbill (c) and olive ridley (d) turtles who nest in Sri Lankan beaches, green turtle crawl marks (e) and by-catch of sea turtles in fisheries (c & d)Photo credits: SJ Perera (a & c), WPN Perera (b & e), K Ekaratne (d & f)

A novel approach for prediction of transverse thermal conductivity of unidirectional random fiber composites

In fiber-reinforced composites, fibers are randomly positioned during the manufacturing process. Most of the theoretical studies assume regular arrangement of fibers in matrix that permits the use of representative volume element (RVE) for prediction of mechanical properties. Theoretical methods established in the literature for random fiber composites are complex and approximate. A simple approach is established in this work to accurately predict the transverse thermal conductivity of unidirectional random fiber-reinforced composites using the principle of electrical analogy (EA). In this study, circular fiber is transformed into an equivalent square fiber that facilitates the application of EA, and predicted the transverse thermal conductivity of random fiber composites. The conductivity of equivalent square fiber is evaluated by back-track approach using an equivalent thermal system. Python code is developed to generate the random location of fibers in the composite. The results obtained in this way are verified and found to be in good agreement with benchmark results over a wide range of fiber composites with varying conductivity ratios, fiber volume fraction, and randomness.

On the relationship of morphology evolution and thermal conductivity of flax reinforced polypropylene laminates

This paper focuses on the morphology evolution in the forming process of unidirectional flax reinforced polypropylene composite laminates. The link between the morphology evolution and thermal conductivity during consolidation stages is investigated. Hot press forming allows to manufacture several composite laminates at different consolidation stages as a function of the compaction thickness. Microscopic evolution of the laminates in terms of morphology and porosity fractions are evaluated by scanning electron microscopy and X-ray microtomography (µ-CT). Hot disk technique is applied to measure the thermal conductivity of the laminates in in-plane and transverse directions. It is found that the in-plane thermal conductivity almost linearly increases with the reduction of porosity fraction. However, the transverse thermal conductivity remained constant. Beside the proposed relations, a theoretical model, based on a two-level Mori-Tanaka homogenization method is proposed. Considering the three-phases material (i.e., porosity, fiber, and polymer matrix), there is a good agreement between the experiment data and model predictions, but limited predictivity for porosity level above 15% certainly due to simplifying assumptions used in the predictive model.

Anisotropically conductive phase change composites enabled by aligned continuous carbon fibers for full-spectrum solar thermal energy harvesting

Solar thermal energy harvesting with phase change materials (PCMs) can overcome the intermittent nature of solar energy through thermal energy storage to provide uninterruptible heat supply. However, the PCMs' intrinsically low thermal conductivities and weak solar absorptances pose considerable challenges to achieving high photothermal efficiency, and most PCMs also suffer from leakage and poor stability. Herein, we propose a simple and scalable approach to develop anisotropically conductive phase change composites (PCCs) by fabricating and embedding aligned continuous carbon fibers (CFs) in paraffin wax (PW)/olefin block copolymer (OBC) blends. The aligned CFs provide continuous and directional thermal conduction paths within the PCCs, enabling a high lengthwise thermal conductivity of 5.63 W·K−1·m−1 and a low transverse thermal conductivity of 0.77 W·K−1·m−1 with a rather high anisotropic degree of 7.31. The excellent anisotropic thermal conductivity can enhance the lengthwise heat transfer from the PCC surface to the deep inside and reduce the transverse heat loss from PCC to the surroundings. Furthermore, to enhance the solar absorption, carbon black is coated on the PCC surface to boost the full-spectrum solar absorptance up to 0.988. Because of the synergetic effects of the excellent anisotropic thermal conductivity and high full-spectrum solar absorptance, the PCC can achieve high photothermal efficiencies of 79.17 %-98.31 % under 1 sun-3 suns. Moreover, the PCC also demonstrates excellent thermal, cyclic and shape stability. This work offers a promising strategy for fabricating anisotropically conductive PCCs for efficient solar thermal energy harvesting.

Thermal and arc erosion behavior of CuCr contact material based on large plastic deformation treatment

CuCr alloys are the main contact materials used in medium-voltage and high-current vacuum interrupters. In this paper, the effect of large plastic deformation on microstructure and the transverse/longitudinal thermal conductivity of CuCr30 contact material were studied. The results show that the morphology of Cr particles in CuCr30 changes from dendritic to oriented fibrous after large plastic deformation, and the longitudinal thermal conductivity of CuCr30 contact material is about 1.5 times higher than its transverse thermal conductivity. During the electrical contacting process, the mass loss of the extruded CuCr30 contact material is lower than that of as-cast CuCr30 contact material, which is directly related to the significantly higher longitudinal thermal conductivity of the extruded CuCr30 contact material. The enhancement of longitudinal thermal conductivity is beneficial to reduce the mass loss of the contact material and improve the arc erosion resistance of the contact material. The mass loss of the cathode with higher longitudinal thermal conductivity is significantly lower than that of the anode contact in extruded CuCr30 contact material.

Вплив поздовжньої і поперечної теплопровідності міжфазних щілин на ефективні параметри біматеріалу

The effective parameters of the bi-material with a periodic system of interfacial cracks are studied, taking into account their longitudinal and transverse thermal conductivity. The bi-material is subjected to tensile forces and uniform heat flow. The transverse and longitudinal thermal conductivity of the cracks is taken into account by the thermal resistance of the filler and the thermal conductivity of the surface films, respectively. The thermal resistance of the filler is directly proportional to the opening of the cracks and inversely proportional to the thermal conductivity of the filler. Thermal conductivity of surface films does not change under the influence of load. The thermo-elastic problem is reduced to nonlinear systems of singular integro-differential equations for an opening cracks and a temperature jump between the cracks faces. An analytical-numerical iterative procedure for solving this system is proposed. Based on the obtained solution, the effective temperature jump and the effective thermal resistance of the bi-material are determined. The dependences of the effective parameters of the bi-material on the applied load and thermal conductivity coefficients of the filler and the surface films of the cracks are analyzed.

The effect of nanoparticle fillers on glass fiber/poly‐ether‐ether‐ketone prepreg laser absorbance, thermal conductivity and interlayer performance

AbstractAiming at the use of glass fiber reinforced poly‐ether‐ether‐ketone (GF/PEEK) with low laser absorbance in laser assisted tape winding/placement (LATW/LATP), a method for dyeing GF/PEEK prepreg with nanoparticle fillers (NFs) is presented. First, the effects of carbon black (CB) and graphite (G) NFs on composites laser absorbance and reflection pattern were quantified, and the complex refractive index model was derived. Next, the effects of NFs on composites transverse thermal conductivity were tested, and the accuracy of four thermal conductivity prediction models were compared. Finally, the effects of NFs on composites interlayer performance were studied. The optical test results showed that NFs could improve laser absorbance while not changing reflection pattern, and the increase rate of absorbance for CB was higher than for G. As calculated by complex refractive index model, GF/PEEK with 1‐layer thickness could achieve complete laser absorption by addition of either 2.74%CB or 3.78%G. The thermal conductivity test results showed that NFs could improve composites transverse thermal conductivity. The increase rate of thermal conductivity for G was higher than for CB. Among the four prediction model, the Lewis‐Nielsen model had correct prediction regularity and was within 10% predict deviation. Based on this model, the transverse thermal conductivity of GF/PEEK/2.74%CB was 0.557 W/m K, and of GF/PEEK/3.78%G was 0.592 W/m K. The mechanical test results showed that the CB loading ≤4% had little effect on interlayer performance, while the G decreased interlayer performance. Consequently, adding CB at a low loading is a better way to realize GF/PEEK application in LATW/LATP.

Colossal Nernst power factor in topological semimetal NbSb2

Today solid-state cooling technologies below liquid nitrogen boiling temperature (77 K), crucial to quantum information technology and probing quantum state of matter, are greatly limited due to the lack of good thermoelectric and/or thermomagnetic materials. Here, we report the discovery of colossal Nernst power factor of 3800 × 10-4 W m-1 K-2 under 5 T at 25 K and high Nernst figure-of-merit of 71 × 10-4 K-1 under 5 T at 20 K in topological semimetal NbSb2 single crystals. The observed high thermomagnetic performance is attributed to large Nernst thermopower and longitudinal electrical conductivity, and relatively low transverse thermal conductivity. The large and unsaturated Nernst thermopower is the result of the combination of highly desirable electronic structures of NbSb2 having compensated high mobility electrons and holes near Fermi level and strong phonon-drag effect. This discovery opens an avenue for exploring material option for the solid-state heat pumping below liquid nitrogen temperature.

Significantly improving thermal conductivity of carbon fiber polymer composite by weaving highly conductive films

This paper significantly improved the transverse thermal conductivity (TC) of unidirectional carbon fiber reinforced polymer (CFRP) laminates by a simple and effective method of weaving highly conductive films (HCFs), including Copper (Cu) film and highly oriented graphite film (HOGF). The TC and interlaminar shear strength (ILSS) of HCF enhanced CFRP (HCF-CFRP) composite laminates were measured. The results show that the HCF-CFRP composite with a larger geometric undulation of HCF has a higher through-thickness TC. And the through-thickness and in-plane transverse TCs can be regulated by the undulation of HCF. The maximum through-thickness TCs of HCF-CFRPs are up to 49.19 W m−1 K−1 for HOGF-CFRP with 1.97 vol% HOGF, and up to 21.45 W m−1 K−1 for Cu-CFRP with 1.74 vol% Cu film, which are 11029% and 4753% higher than that of CFRP, respectively. Numerical simulation and infrared thermography demonstrate that the geometric undulation and ultrahigh in-plane TC of HOGF lead to the formation of a rapid through-thickness heat transfer path. In addition, the ILSSs of HOGF-CFRP and Cu-CFRP are 44.01 and 40.91 MPa, respectively, which are 13.76% and 19.77% lower than that of CFRP.

Phonon thermal Hall effect in a metallic spin ice

It has become common knowledge that phonons can generate thermal Hall effect in a wide variety of materials, although the underlying mechanism is still controversial. We study longitudinal κxx and transverse κxy thermal conductivity in Pr2Ir2O7, which is a metallic analog of spin ice. Despite the presence of mobile charge carriers, we find that both κxx and κxy are dominated by phonons. A T/H scaling of κxx unambiguously reveals that longitudinal heat current is substantially impeded by resonant scattering of phonons on paramagnetic spins. Upon cooling, the resonant scattering is strongly affected by a development of spin ice correlation and κxx deviates from the scaling in an anisotropic way with respect to field directions. Strikingly, a set of the κxx and κxy data clearly shows that κxy correlates with κxx in its response to magnetic field including a success of the T/H scaling and its failure at low temperature. This remarkable correlation provides solid evidence that an indispensable role is played by spin-phonon scattering not only for hindering the longitudinal heat conduction, but also for generating the transverse response.