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Measurement and prediction of thermal conductivity for hemp fiber reinforced composites
Abstract
The thermal conductivity of hemp fiber reinforced polymer composites were studied from the steady state temperature drop across samples exposed to a known heat flux. The transverse and in-plane thermal conductivities for oriented and randomly oriented composites for different volume fractions of fiber were investigated. Experimental results showed that the orientation of fibers has a significant effect on the thermal conductivity of composites. To validate the experimental results, the heating tests for the thermal conductivity measurements were simulated by a finite element model using the thermal conductivity values obtained from the experiments. Predicted temperatures show close agreement with measured temperatures. Moreover, the experimental results of thermal conductivities of composites at different directions were compared with two theoretical models and illustrated good agreement between the obtained results and models. POLYM. ENG. SCI. 47:977–983, 2007. © 2007 Society of Plastics Engineers
... In addition, natural fiber composites exhibit anisotropic thermal properties that enable efficient thermal dissipations along certain directionalities [7], and thus providing flexible alternative options for thermal insulators. In order to test the TCs in either direction, numerous experiments were conducted by focusing on microstructural details for various natural fibers, such as bamboos [8]; flax and hemp fibrous materials [9,10], banana-jute hybrid composites [11], kenaf fiber composites [12], Aleppo Pine wood and black agglomerated cork [13], and even biomimetic leaf composites [14], just to name a few. A brief review of the functional thermal properties of natural fiber composites is referred to Takagi [15]. ...
... Fig. 7 compares the present technique in simulating the manila hemp fiber composites against the FE results and experimental measurement. The constituent thermal conductivities of hollow fibers and polymer matrix are k hf = 0.185W/(mK) [20,21,43] and k m = 0.42W/(mK) [9,21], respectively. According to the literature, the thermal conductivity coefficient of hollow fibers is inversely determined through the experimental measurement of composite specimen and theoretical conductivity formulae between the composite and its constituents [43]; while the polymer matrix is an environmentally friendly thermoset water-based acrylic polymer that is an aqueous solution of a polycarboxylic acid and a polyhydric alcohol as a crosslinking agent in water (52% water) [9]. ...
... The constituent thermal conductivities of hollow fibers and polymer matrix are k hf = 0.185W/(mK) [20,21,43] and k m = 0.42W/(mK) [9,21], respectively. According to the literature, the thermal conductivity coefficient of hollow fibers is inversely determined through the experimental measurement of composite specimen and theoretical conductivity formulae between the composite and its constituents [43]; while the polymer matrix is an environmentally friendly thermoset water-based acrylic polymer that is an aqueous solution of a polycarboxylic acid and a polyhydric alcohol as a crosslinking agent in water (52% water) [9]. A portion of lumens are filled within the fiber bundles and α = 0.565. ...
The effective transverse thermal conductivity and localized thermal fields of unidirectional natural fiber composites is investigated through the proposed progressive micro-modeling technique. Different from the classical models, the present model starts from recovering the actual natural fibrous microstructures with fiber bundles filled with lumens and surrounded with matrix phase. Based on the concept of hierarchical microstructures, the fiber bundles with lumen and hollow fibers are treated as the lower-level composite unit cells while the composites with reinforced fiber bundles and matrix as the higher-level unit cells. The information transfer between two levels is guaranteed by a progressive homogenization technique-local exact homogenization theory that is presently extended with thermal conductivity for composites with nano-surface effects. The predicted effective transverse thermal conductivity coefficients of nano-/micro-composites are validated against the analytical and numerical simulations, as well as experimental data, where good agreement is generally obtained. An optimization procedure is also connected to the present micromechanics to search for the optimal microstructural parameter for the designed effective thermal coefficients at various fiber volume fractions. Finally, the local hierarchical thermal fields are also recovered to get insights into the microstructural concentrations. We have also encapsulated our progressive model into a black-box program with inputs/outputs, facilitating its application by other researchers.
... Since the presence of air cannot be neglected in the specimens, the true apparent thermal conductivity for a material devoid of air is determined through regression wherever necessary. This approach for predicting the true value, taken from Behzad and Sain, 29 is particularly helpful in predicting the true conductivity values of natural fibers such as hemp and flax. For instance, if the empirical measurements of a natural fiber specimen with entrapped air yields a conductivity value of k 1 for a volume fraction of V 1 , then for a volume fraction of 100% the true conductivity k 100 will be given by ...
... The authors were not able to find experimentally determined thermal conductivity of dry, aligned hemp fibers in the literature, and the measured value closely aligns with the predicted value from Behzad and Sain. 29 The thermal conductivities of hemp and flax are very similar, since both of them are bast fibers. Using the four mathematical models listed in The Experimental and Theoretical Plan and a V f = 50%, the mathematical predictions are calculated. ...
There is growing industrial and academic interest in manufacturing of biocomposite parts comprised of natural fibers in a thermoplastic matrix that begin as a commingled, unconsolidated preform. Unfortunately, little thermal property data exists in the literature for simulation/analysis of processes used to make parts (e.g., pultrusion, Automated Fiber Placement (AFP), and compression molding). In this paper, the authors explain how specific heat capacity and thermal conductivity values of both constituent materials and the biocomposite preform are measured in a direction transverse to the fiber length, and how the effect of entrained air is included. Thermal property values for hemp and flax fibers along with polypropylene and polyethylene filaments, measured both individually and combined into apparent values for the preforms, are compared with experimental values. Finally, determination of thermal properties for use in pultrusion simulation is explained as a case study.
... The thermal conductivity of hemp-reinforced polymer composite is studied and experimentally measured and compared with that of the poly matrix. It showed good relation between theoretical to actual [14,15]. The granite/basalt fiber/sandstone-reinforced polymer composite found better thermal stability at 25°C and 1000°C [16]. ...
... However, the thermal conductivity of epoxy composites was enriched by Kevlar fiber bonded with epoxy with a BF interlayer. The Kevlar fiber has good thermal conductivity [14,15,17]. ...
Polymer-based matrix hybrid composites meet their demand in various engineering applications and food industries due to their excellent mechanical, thermal, corrosion, and biodegradable performance. The polymer-based hybrid composites have been a better choice for high thermal insulation at low cost. This experiment attempted to find the thermal adsorption characteristics, heat deflection temperature, linear thermal expansion, and thermal conductivity of epoxy hybrid composites, which contained four different layers of Kevlar and basalt fiber fabricated via a low-cost conventional hand mold layup technique. This experiment revealed that the effect of basalt/Kevlar fiber on epoxy increased thermal performance. The results noted that the hybrid composite consists of less Kevlar fiber with the maximum basalt fiber of sample 4, showed excellent thermal adsorption effect on weight loss limited at 70.98%, and a better heat deflection temperature and 11.78 × 10 − 6 per °C linear thermal expansion were obtained. Sample 3 exhibited a maximum thermal conductivity of 0.251 W/mK. However, the thermal adsorption of hybrid composite has been limited by more basalt fiber, leading to a 1 wt%/°C decomposition rate.
... Thermal conductivity of hemp fiber reinforced polymer composite was compared between two theoretical models and an experimental results. There was good agreement between the results [2], [3]. Evaluation of thermos-physical properties of granite, sandstone and basalt in the temperature range of 25-1000 o C revealed that phase transition influenced the texture and stability of the materials [4]. ...
... where k is the thermal conductivity of the hybrid composite material (W/mK), q is the heat flux along the stacked layers of the hybrid composites, l is thickness of the hybrid composite and T is the difference in temperature between the top and bottom of the stack. In this case, q is found in using equation as in (2) q = (2) where Q is the heat transfer rate through the hybrid composite and A is the cross sectional area of the produced laminate. Fig. 2 shows the variation in thermal conductivity of the six hybrid composites produced for this research work. ...
Hybrid Composites comprising of two or more reinforcement materials are finding increase in demand in diverse field of applications such as building panels, automotive components and aero parts. There is a need to study the thermal properties to find the suitability of hybrid laminates as insulating materials. In this research article an attempt is made to find the thermal conductivity of laminate materials having varying stacking sequence of its reinforcement fibers. The said laminate is produced using hand layup method. It contain seven layers of reinforcement fibers stacked one over other in three different configurations. First the reinforcements kevlar (K49) and basalt fibers are stacked in alternating layers. Second configuration contain bilayers of kevlar or basalt sandwiching the inner three alternative layers. Third configuration contain tri layer of one of the reinforcement fibers sandwiched between bilayers of another reinforcement fibers. Epoxy resin is used as binding cum matrix element in all the hybrid laminates. The produced hybrid laminates are tested for its thermal conductivity and coefficient of thermal expansion. It is found that increasing the number of layers of basalt fibers increased the thermal conductivity of the hybrid laminate. On the other hand, kevlar fibers contributed in reducing the thermal conductivity of the hybrid laminates. Thermal expansion coefficient depended on the presence of basalt fibers as the outermost layers in the hybrid laminates. The hybrid laminates having kevlar fibers contributed in lowering thermal conductivity and also the coefficient of thermal expansion.
... Ex Chabaud) residues [8], and giant reed (Arundo donax L.) [9]. Likewise, other studies have been carried out using date palm fibers [10], hemp (Cannabis sativa L.) [11], sisal (Agave sisalana Perrine) [12], and canary palm residues [8] as thermal insulators. ...
... Mulberry wood prunnings 0.067 [24] Cork panel 0.065 [24] Commercial wood particleboard 0.180 [8] Canary palm 0.059 [25] Canary palm + cement 0.057 [25] Washingtonia palm + cement 0.059 [10] Date palm 0.083 [11] Hemp 0.111 [12] Sisal 0.070 Figure 2 shows the values obtained for the acoustic absorption coefficient (α) of the tests performed on the three specimens of each type of experimental particleboard. It could be observed that there were major differences between the boards based on the size of the particles. ...
The aim of this study was to determine the acoustic and thermal properties of particleboards made from mulberry wood pruning waste using urea formaldehyde resin (UF) as a binder. The investigation focused on the evaluation of the thermal conductivity and the acoustic absorption of the boards and the assessment of their feasibility for use in the construction sector. The mean thermal conductivity values of the particleboards (0.065–0.068 W/mK) were lower than those obtained in wood and similar to those in cork panels. The samples were tested with frequencies from 50 to 6300 Hz. In all cases, the results allowed us to conclude that they were better sound absorbers than commercial wood and plywood panels of the same average density for low frequencies, and with similar values for medium and high frequencies. The mechanical results reached the minimum requirement to be considered as boards for general use and, specifically with particles from 0.25 to 1.00 mm, for furniture according to European standards. The particle size of the particleboards was the variable that influenced all the acoustic properties, but did not affect the thermal conductivity. The experimental results indicated that the thermal and acoustic properties of these particleboards were promising for their application in commercial uses.
... 14 Improvement of the thermal insulation is happening due to the presence of thermal insulatingair in the lumen of the hollow structure of natural cellulosic fibre. [36][37][38][39][40][41] Apart from the above-mentioned reason, the void content also plays a vital role for enhancement in the thermal insulation values. Along with the addition of filler loading the void content proportionally increase. ...
... 38 Therefore, it can be inferred that a very low amount of moisture is present in the fabricated composites. 37 Several investigations show that the enthalpy change in this zone is significantly larger than what would be predicted if moisture were the only factor involved. As a result, the peak in this location may be regarded as comparable to the samples T g. 43 The FA dispersed composites show a small rise in T g as well. ...
The present investigation is carried out to study the swelling and thermal behaviours of alkali
treated cellulosic fibre (sisal and jute) with fly ash dispersed unsaturated polyester composites.
These composites are fabricated by compression moulding with a filler loading of 5, 15, 25, 35 and 45 wt. %. The electronic thermal insulation tester, differential scanning calorimeter, and thermogravimetric analyzer are used for thermal analyses of the synthesized composites. It was observed that the thermal stability and degradation temperature of the composites improved significantly with addition of the filler within the unsaturated polyester resin.The swelling behaviours are determined by immersing the synthesized samples in the different pH content of water. In case of swelling behaviours, the changes in water absorption are quite acceptable as compared to the treatment time
and the atmospheric condition. The fabricated composites displayed optimum results for filler content with 35 wt. % followed by saturation in properties with the dispersion above the same.
... Their correlations showed that coconut and sugarcane loose fibers have an optimum thermal conductivity at 24°C of 0.0488 W/m.K and 0.0483 W/m.K, respectively. The thermal conductivity of polymer composites using hemp as reinforced fiber has been studied by Behzad and Sain (2007). Their experiments showed that the orientation of the fibers plays a very important role on the composites' thermal conductivity. ...
... + 78.0%) −100.0 = 22.0%) which confirmed with Table 1, specimen number 3. It should be noted also that, each temperature profile has five points, which corresponding to specimen numbers 3, 4, 5, 6, and 7 starts from left to right in a row. Consequently, Figures 7-10 indicate that, using agave and wheat straw fibers either as loose, bound or hybrid will have thermal conductivity lower than or in the same range as that of sisal fiber (k = 0.07 W/m.K (Kalaprasad et al. 2000)), hemp (k = 0.115 W/m.K (Behzad and Sain 2007)), 0.044-0.094 and 0.040-0.082 ...
Agave (AF) and wheat straw (SF) fibers are good raw materials for thermal insulation. In this study, loose agave or wheat straw fibers and hybrid boards of agave/wheat straw with different compositions and densities are tested for their thermal insulation qualities. Three new novel hybrid specimens are considered. In all specimens, cornstarch (CS) was used as a binder for the fibers. Thermal conductivity coefficient is obtained for each specimen in the temperature range 10–60°C with the resulting average value in the range 0.04555–0.06835 W/m K. Without binding, loose fibers of agave and wheat straws have an average thermal conductivity of 0.043592 and 0.044678 W/m.K, respectively, at the same range of temperature. Micrographs of the wheat straw fibers (SF) are conducted using the scanning electron microscope (SEM) which showed an average outer diameter between 1.28 and 1.98 mm and an average diameter of the bound porous tubes (multicellular) within the straw in the range 34.5 to 75.6 μm. Fourier transformation infrared (FT-IR) analyses of the wheat straw fiber are carried out which indicated stretching wavenumbers which present different chemical functional groups. Thermogravimetric analysis of the wheat straw fiber (TGA and DTGA) showed that the straws lose less than 3% of its mass at temperatures as high as 184°. Finally, the differential scanning calorimetry (DSC) analysis test of the wheat straw fiber indicates that endothermic transition starts at 342°C with a peak value at 749°C. Three-point bending moment tests for bound specimens are made and show an increase in both flexural stress and flexural modulus of the hybrid specimens. Using these hybrid specimens, agro, renewable and environmentally friendly materials in buildings will share in energy saving when used as insulation materials for building walls.
... It should be mentioned that, the thermal conductivities ( Fig. 9(a)) at about 24°C are 0.0568, 0.0512, 0.0499, and 0.0493 W/mK corresponding to samples number 1, 2, 3, and 4 respectively. These values of thermal conductivities shown in Fig. 9 (a) for the four samples are lower than the corresponding insulating materials extracted from date palm leaf base (petiole) (0.083 W/mK) [10], sisal (0.070 W/mK) [30], hemp (0.115 W/mK) [31], and banana (0.117 W/mK) [32] which motivates the potential of using them as insulation materials. Fig. 9(b) shows the corresponding thermal resistance in terms of R-values for the same samples used in Fig. 9(a). ...
... It worth mentioning that the thermal conductivity at 24°C (typical temperature for building insulation material in the field) for the samples 5, 6, 7, and 8 are 0.0418, 0.0420, 0.0454, and 0.0515 W/m K respectively. These values of thermal conductivities shown in Fig. 10(a) for the four samples are lower than similar insulating materials extracted from other natural fibers as mentioned earlier compared to references [10,[30][31][32] which ensures the importance of using hybrid insulating materials. Fig. 10(b) presents the thermal resistance (R-value) for the samples 5, 6, 7, and 8. ...
Hybrid new insulating materials are proposed using different binders such as cornstarch, glue (wood adhesive) and white cement. Five hybrid samples were produced from date palm trees surface fibers (PTSF) and Apple of Sodom fibers (AOSF) for different ratio of mass and densities. One hybrid sample was produced from AOSF and agave fiber (AF) using glue (wood adhesive) as a binder. Thermal conductivity measurements were conducted for all samples at temperature ranging from 10 °C to 50 °C which resulted in average values of 0.04234–0.05291 W/m K. Microstructure analysis was conducted for AF using the scanning electron microscope (SEM) which resulted in an average diameter range of 170–259 μm. Infrared (FT- IR) Fourier transformation spectra of AF showed ranges of wavenumber functional groups. Thermogravimetric analysis (TGA and DTGA) was obtained for AF and showed that the fibers start to degrade and decompose at about 221 °C where the fiber loses 5% of its original mass. The Differential Scanning Calorimetry (DSC) analysis is also reported for AF and shows a broad endothermic transition range of 292–357 °C with a peak at 353 °C. Sound absorption coefficients were obtained for the hybrid samples and indicate the potential of using these samples for sound absorption. The current tests indicate the feasibility of using such hybrid samples as insulating materials for heat as well as sound absorption. The proposed tested hybrid samples are all natural, safe for human beings, utilize the wasted material and biodegradable therefore, it is good for saving our environment.
... Multiscale modeling of the electrical conductivity of composite materials is a complex topic, particularly if microstructural features lead to a size effect in electronic conduction and create an anisotropy (Heringhaus et al., 2003;Mallick, 2007;Behzad and Sain, 2007). ...
... In order to predict the anisotropic effective conductivity with considering the particular morphology of fiber-reinforced composites (such as Cu-Nb wires at different scales in Fig. 3.1), several homogenization models have been proposed. The homogenization models for composites can be separated into two types: mean-field analytical methods (Schulgasser, 1976a;Hasselman and Johnson, 1987;Tavman and Akinci, 2000;Hervé-Luanco and Joannès, 2016) and full-field ones (Islam and Pramila, 1999;Behzad and Sain, 2007). Among the analytical mean-field models, the Generalized Self-Consistent scheme (denoted GSC hereafter) has been found to be very efficient to estimate the electrical conductivity of Cu-Nb wires . ...
Les fils composites nanostructurés et architecturés cuivre-niobium sont de candidats excellents pour la génération de champs magnétiques intenses (>90T); en effet, ces fils allient une limite élastique élevée et une excellente conductivité électrique. Les fils Cu-Nb multi-échelles sont fabriqués par étirage et empaquetage cumulatif (une technique de déformation plastique sévère), conduisant à une microstructure multi-échelle, architecturée et nanostructurée présentant une texture cristallographique de fibres forte et des formes de grains allongées le long de l'axe du fil. Cette thèse présente une étude compréhensive du comportement électrique et élasto-plastique de ce matériau composite, elle est divisée en trois parties: modélisation multi-échelle électrique, élastique et élasto-plastique. Afin d'étudier le lien entre le comportement effective et la microstructure du fil, plusieurs méthodes d'homogénéisation sont appliquées, qui peuvent être séparées en deux types principaux: la méthode en champs moyens et en champs complets. Comme les spécimens présentent plusieurs échelles caractéristiques, plusieurs étapes de transition d'échelle sont effectuées itérativement de l'échelle de grain à la macro-échelle. L'accord général parmi les réponses de modèle permet de suggérer la meilleure stratégie pour estimer de manière fiable le comportement électrique et élasto-plastique des fils Cu-Nb et économiser le temps de calcul. Enfin, les modèles électriques prouvent bien prédire les données expérimentales anisotopique. De plus, les modèles mécaniques sont aussi validés par les données expérimentales ex-situ et in-situ de diffraction des rayons X/neutrons avec un bon accord.
... Researchers synthesized the hemp fibre-bonded polymer matrix composite via the conventional technique. Hemp fibre in the polymer matrix resulted in good thermal properties compared to the polymer matrix composite without hemp fibre [26]. ...
A thermal gravimetric analyzer analyzed the thermal adsorption properties of developed composites with the temperature range of 28°C–650°C at a 20°C/min constant heat flow rate. The epoxy hybrid composites were synthesized using natural jute/sisal fibre hybridized with the addition of synthetic E-glass fibres at 0-degree, 0/90-degree, and intralaminar orientations through the wet filament-winding process. The effects of orientations on tensile, flexural, and impact strengths of epoxy hybrid composites were studied using ASTM D3039, D790, and D6110. The evaluated results were compared, and the epoxy hybrid composite containing intralaminar orientations found better thermal stability with reduced weight loss at 650°C. Similarly, the test result for mechanical studies of the hybrid composite showed superior tensile, flexural, and impact strengths. The epoxy hybrid composite with intralaminar orientation was found to have a maximum tensile, impact, and flexural strength of 61.91 MPa, 770.61 J/m, and 83.90 MPa, respectively.
... Because thermal conductivity of pure flax fibres along their axis is 1.232 W/(k.m) while transversely to their main axis is 0.17 W/(k.m). These results are consistence with the thermal conductivity measurements for hemp (Behzad and Sain, 2007), flax (Li et al., 2008), bamboo (Takagi et al., 2007), and banana (Annie Paul et al., 2008) embedded into thermoplastic polymers. Therefore, since thermal resistance along the axis of Flax/PP fibre is less than the thermal resistance across the axis, the most portion of heat is transferred along the Flax/PP axis. ...
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.
... In that context, Sain et al. measured and analytically compared the thermal conductivity of hemp fiberreinforced composite [95] . Experimental results show that the fibers' orientation significantly affects the composites' thermal conductivity and that coating hemp fiber with a polymer can also improve these properties while mitigating the disadvantages mentioned above. ...
... Based on the rule of mixtures, the thermal conductivity of unidirectional fiberreinforced composites in the direction parallel to the fibers is well-understood. Behzad and Sain [36] demonstrated the excellent predictability of the rule of mixtures for the equivalent thermal conductivity of fiber-reinforced composites by comparing them with experimental data. Devireddy and Biswas [34] reported the effects of the geometry and volume fraction of the fibers on the equivalent thermal conductivity. ...
The miniaturization of power conversion systems requires high-power density operation of power modules, causing the heat-density increase. Therefore, it is essential to develop bonding technology to realize highly thermally conductive and reliable high-temperature joints. In this study, we propose a novel anisotropic microcomposite (AMC) joint that integrates a lotus-type porous Cu (LPC) sheet and Sn-based solder for high-temperature electronic applications. The AMC joint was successfully fabricated by infiltrating the molten solder into the unidirectional pores of the LPC sheet during a simple reflow process. Steady-state thermal conductivity measurements for a uniquely designed specimen revealed its equivalent thermal conductivity (142.4 W/m·K), 2.5 times higher than the solder. Finite element simulations supported its excellent thermal performance by investigating the heat flux distribution and thermal conductivity prediction that utilize a three-dimensional image-based constructed model. In addition, the aging test at 200 °C for 1008 h clarified a stable shear strength of over 46 MPa. This indicates a reliable mechanical performance at 200 °C, which is only 20 °C below the melting point of the solder. These experimental and numerical studies proved the potential of the novel joint as a high-temperature electronics joint and offered possible mechanisms for its thermal and mechanical property enhancement.
... The theoretical prediction using ROM is not restricted to mechanical properties, but it can also be applied to predict the physical and thermal properties of composite materials. Behzad and Sain (2007) employed ROM to predict the thermal properties of unidirectional hemp fiber-reinforced composites. The predicted thermal properties obtained from ROM model showed a strong correlation with the experimental findings. ...
The contemporary trend has attested that fiber-reinforced composites have been utilized to replace steel and other metal alloys in a broad range of engineering applications, particularly in the transportation sectors to improve energy efficiency without compromising safety performance. The intensive research works toward the excellent mechanical performance of composite materials without compromising the environmental friendliness have stimulated the growth of hybrid composites. The hybrid composites refer to the materials which are composed of multiple types of synthetic or natural fibers within a single polymer matrix. Over the years, it has been proven that hybrid composites have shown innumerable benefits over non-hybrid composite materials in terms of mechanical performance and ecological concerns. Nevertheless, the challenging issues which affect the miscellaneous properties of hybrid composite materials still exist and have not been fully resolved. This chapter aims at providing brief overview of the factors influencing the miscellaneous properties of composite materials. Furthermore, the miscellaneous properties of various types of hybrid composites are briefly discussed and demonstrated.
... Unlike porous materials, plant fillers also provide strong mechanical resistance to the biocomposite. Several studies have shown good thermal insulating properties as well as strong mechanical properties, especially at higher filler percentages (Behzad and Sain 2007;Agoua et al. 2013;Li et al. 2008;Qi et al. 2013). Furthermore, filler treatment, additives and coupling agents also affect the thermal properties of biocomposites (Gardner et al. 2018;Kairytė et al. 2019;Ahmad et al. 2019). ...
Plant fiber biocomposites have the potential of being thermal insulating materials with strong mechanical resistance. However, they are vulnerable to defects due to the incompatibility of the materials. In that prospect, this study focuses on the determination of thermal properties of wood particles reinforced HDPE composites (WPC) using experimental, theoretical, and computational modeling approaches. From the laser flash analysis in the experimental setup, the results show that the addition of 30 and 60 wt\% of wood particles leads to a reduction of 20 and 44% in thermal conductivity, respectively, as compared to the neat HDPE. This demonstrates the thermal insulation capabilities of the wood particles. The use of several theoretical models to determine the WPC’s effective thermal conductivity shows good consistency with the experimental results, with a maximum discrepancy error of 4%. However, a noticeable divergence is observed as the wood content increases. Further study on the effective properties is carried out using the pixel-based computational homogenization analysis. This computational method carries out finite element calculations on representative 2D images of the WPC. The computational results are also consistent with the experimental results, but similar divergence like the theoretical models is still observed. The divergence is suspected to originate from the presence of porosity in the experimental specimens. The percentage of porosity is estimated using theoretical models and is integrated into the computational homogenization technique by introducing another phase in a different color code. This leads to the convergence of computational and experimental results. The pixel-based homogenization method has shown great flexibility and is able to integrate defects like porosity to yield precise results of the effective thermal conductivity of WPC which can then be used in structural engineering analysis.
... Thermal conductance of composite material containing hemp as the reinforcement and polymer matrix was studied by Behzad and Sain (2007) and Sayyidmousavi et al (2019). They compared the thermal conductance of the composite material measured experimentally. ...
Use of lightweight composite materials in automobile applications such as doors, bonnets, and bumpers and also the utilization of composite materials in building insulations require superior mechanical and thermal properties. This study attempts to determine the thermal conductivity, linear thermal expansion coefficient, heat deflection temperature and thermo gravimetric analysis of hybrid composite containing reinforcement fibers stacked in seven different combinations in an epoxy matrix as per ASTM standards. Each composite contained two different fibre materials, i.e., Kevlar and basalt. The study revealed that the stacked layers of basalt fibers had more influence on the thermal properties. It was observed that the hybrid composite made of least quantity layers of Kevlar and most of basalt exhibited the maximum thermal conductance of 0.219W/mK, while with vice versa laminate developed 0.191W/mK which was least thermal conductance. The composition prepared by made Kevlar as core layer and basalt as its outer layers exhibited coefficient of linear thermal expansion above 11.5x10-6/oC. Maximum decomposition weight loss of 76.92% occurred in the composition prepared by keeping basalt as core and Kevlar as outer layer. The differential thermal graph showed that the said hybrid composite exhibited the peak decomposition rate of 1wt.%/oC. The thermal properties of the laminate prepared by keeping two layers of Kevlar sandwiched between the basalt were excellent when compared to other six hybrid composites investigated in this study.
... However, a precise information about material properties is required for obtaining desired materials that are to be implemented for developing hybrid composite. Thermal conductivity is the material property which describes capability to transfer heat and also helps to encourage the temperature deviation inside the composite materials during specific operations [8]. Enhancing the thermal property of this epoxy-based polymer at present is considered to be challenging. ...
The scarcity of nonrenewable resource motivated inclination towards the environmental-friendly novel materials and development of waste natural filler-based hybrid composite is encouraged to fulfill the material demand. Epoxy resins-based composites are high-performing thermosetting polymers and have outstanding blending properties, good machinability, and low cost. Due to these advantages, thermoset plastic is largely used in a broad range of engineering applications; however, thermomechanical properties of neat epoxy are low. Thus, to enhance the thermomechanical properties of epoxy, it is interfaced materials such as graphite, graphene nanoplatelet, boron, carbon fiber, aluminium, silver, etc. Among various substances, graphene has been deliberated as an acceptable novel filler because of its exceptional properties. In addition to inorganic filler inclusion, natural filler/fiber like hemp, sisal, flax, bamboo, jute, etc. can be utilized in a higher percentage as biodegradable material. The present article assisted to improve thermomechanical properties of neat epoxy. This work identifies and addresses (i) processes used for graphene modification; (ii) treatment utilized for enhancing the binding properties of natural filler; (iii) various natural filler extraction process employed; (iv) neat epoxy modification; and (v) influence of different dimensions of fillers.
... De ce fait, le diamètre de ce dernier est réduit [70] [74], et la surface de contact efficace des fibres avec la matrice est augmentée ; ce qui améliore davantage l'adhérence avec la matrice [31], [75], [74]. Cette amélioration affecte les propriétés thermo-physiques des composites et contribue à une conductivité thermique plus élevée [76]. ...
Dans l’optique de répondre à la demande du marché des matériaux biosourcés en France pour le secteur du bâtiment, les travaux présentés dans cette thèse avaient pour objectif de formuler un nouveau matériau biosourcé en exploitant des nouvelles ressources végétales, telle que la plante de Diss. Ce matériau sera destiné pour la production des panneaux de bardage pour la réhabilitation énergétique des bâtiments. Dans un premier lieu, une étude sur l’extraction, le traitement et la caractérisation des fibres de Diss a été menée. Elle a été suivie dans un deuxième temps par une application de ces fibres comme renfort à une matrice thermoplastique, le polypropylène. La caractérisation mécanique et hydrothermique, l’étude de durabilité et l’évaluation environnementale de la phase de production de ces biocomposites ont été abordées. Les résultats montrés sont prometteurs, notamment pour une telle application où les fibres de Diss ont présenté des propriétés mécaniques et hydro/hygrothermiques intéressantes. De plus, l’incorporation de ces fibres a amené à une amélioration des propriétés mécaniques de la matrice. D’autre part, l’étude de durabilité a mis en évidence l’effet du vieillissement hydrothermique sur leurs propriétés mécaniques. Il a été conclu également que l’utilisation des fibres de Diss avait un effet nettement positif sur la réduction des impacts relatifs au réchauffement climatique, grâce à la séquestration biogénique du CO2. Ces résultats aident à mieux anticiper une future industrialisation de ces fibres et mettre en amont leur effet bénéfique sur l’environnement.
... W/m.K, showing increasing values, depending on the density of the straw bale [39]. Regarding hemp, the thermal conductivity values that were found in the experimental analyses varied from 0.039 to 0.123 W/m.K [28,40], depending on fibres direction, with lower λ values for fibres positioned in perpendicular direction with respect to the heat flux, and higher ones for fibres in the parallel direction [41]. A further consideration concerns the fire resistance of these two materials, which is very low (category E) due to their organic origin [34]; however, it should be emphasized that the presence of natural origin binders, which are necessary for the realization of the panels, generates an increase in the fire resistance approximately around +30% [42]. ...
Nowadays, energy retrofit interventions on the existing building stock are of paramount importance towards energy consumption and emissions reductions in the construction sector. Such interventions are also crucial in the view of increasing cities resilience with respect to the intensification of frequent extreme weather events, such as cold spells and heatwaves. Indeed, a wide portion of our cities is dated and lacking with respect to performances. These are the motivations behind the proposed sustainable approach, which deals with the environmental perspective, but also with social and economic ones, by proposing the retrofit of the Public Residential Building stock (Edilizia Residenziale Pubblica, ERP). The objective is to improve the energy performance of ERP stock by means of construction materials coming from local km0 agricultural waste and by-products. The research was conducted by means of in field and numerical analyses of the energy performances of a relevant case study building. Different layers of bio-based, recycled construction materials for the envelope were tested with respect to their efficacy in improving the energy performance of a case study building. The results demonstrate that the most performing envelope solutions and their combination are able to reduce up to 36% of the yearly energy consumption for heating.
... conform to a general relationship between material density and thermal conductivity. Application of hydrophobic agents could reduce the rate of degradation of the thermal insulation properties. Zach et al. (J. Zach, 2013) found that the hydrophobic treatments considerably affected the absorbability of thermal-insulating mats based on hemp fibres. Behzad et al. (T. Behzad, 2007)studied the thermal conductivity of hemp fiber reinforced polymer composites. Hemp fibers were formed on a perforated screen and the acrylic resin solution was circulated to impregnate the fibers with the solution. Experimental results showed that the orientation of fibers has a significant effect on the thermal conductivity of composite ...
The aim of this study was to investigate the thermal conductivity of natural fiber reinforced polymer composites (NFRP) as potential structural materials. As a natural fiber, Bermuda grass seeds, conifer cones and pinecones are selected. The matrix comprised Vinyl ester resin. The mechanical properties (tensile strength and Young’s modulus) and fractography analysis were investigated in our previous study (Dikici B. M. S.-H., 2019).
In the current study, the thermal conductivity was probed using transient plane source technique implemented in the TPS 2500S Thermal Constants Analyzer. The addition of 9% Bermuda fibers yielded a decrease of approximately 19.3% in thermal conductivity compared to that of the neat epoxy. With the addition of 9% nano cellulose fibers, a decrease of approximately 40.7% in thermal conductivity was observed in the nanocellulose/vinyl ester resin composite compared to the neat vinyl ester samples.
... The greatest challenge when working with plant fibers is the considerable variation in their thermal properties and characteristics, which depend on their complex structural geometric architectures [2]. Numerous studies have been carried out on the insulating properties of plant waste: Coconut fiber [3], paper manufacturing waste and corn peel [4], kenaf fibers [5], cotton stalk fibers [6,7], coconut husk and bagasse [8], hemp fibers [9,10], date palm fibers and gypsum [11], flax [12], flax and hemp [13], rice straw [14], sisal [15], sugarcane bagasse [16], giant reed [17][18][19], Canary Islands palms [20], and Washingtonia palms [21]. ...
: In Europe, vine (Vitis vinifera L.) prunings are one of the most abundant types of agricultural waste. It is, therefore, essential to organize the removal of vine waste from the fields in order to prevent the spread of fires, pests, or diseases. Using plant biomass in buildings will help achieve greater energy efficiency and cause less environmental pollution. The objectives of this work were to minimize burning of agricultural waste, reduce the use of natural wood, and obtain a product by using vine pruning waste to manufacture particleboards, assessing their use as an insulating material and their fire-resistance qualities. Eight types of boards were manufactured with vine prunings (two particle sizes, two times, and two pressures), using 9% by weight of urea-formaldehyde as a bonding resin. Experimental tests were conducted to determine the physical, mechanical, thermal, and fire-resistance properties. In general, the panels manufactured performed well as a thermal insulating material with a conductivity between 0.0642 and 0.0676 W/m·K and a classification of Bd0 according to the European standards on fire resistance; some of them may be used to manufacture furniture, interior décor, and load-bearing panels in dry conditions.
... It is a bast fibre and due to the porous structure of bast fibers, hemp fibers are also suitable for thermal insulations [9]. Existing literature mainly focused on investigating thermal insulation of hemp composites [10][11][12]. ...
In the present research, the thermal properties of the traditional fabric of the Rize city (Turkey) were investigated. A Feretiko, which is a fabric produced from hemp fibers at handlooms, were chosen and the thermal properties were evaluated via thermal manikin as well as the Alambeta tester and Air permeability tester. The thermal manikin tests were performed at 23 °C ± 1 constant ambient temperature and 75 ± 5% relative humidity regarding to the past annual average temperature and relative humidity data of Rize city were considered. The thermal resistance of Feretiko was measured 0.011 m²K/W by Alambeta tester and the total clothing insulation of the shirt manufactured from Feretiko was measured as 0.032 m²K/W by thermal manikin. Moreover, in ASHRAE Standard 55-2013, the clothing insulation of a long-sleeve shirt ensemble stated as 0.25 clo. The clothing insulation of the shirt manufactured from Feretiko was 0.20 clo, which is close to the value stated in the standard.
... Existen trabajos sobre las propiedades aislantes de residuos vegetales: cáscara de coco [1], residuos de fabricación de papel y médula de maíz [2], fibras de kenaf [3], fibras de tallo de algodón [4,5], cáscara de coco y bagazo [6], fibras de cáñamo [7,8], fibras de palmera datilera y yeso [9], lino [10], lino y cáñamo [11], tallo de arroz [12], sisal [13], bagazo de caña de azúcar [14], caña común [15,16], palmera canaria [17] y palmera washingtonia [18]. ...
... They also completely explained about different types natural fibers. Behzad et al. [2], completely discussed about measuring methods of thermal conductivity with the help of volume fraction of natural fiber composite. They clearly showed SEM micrographs of oriented and randomly oriented composite. ...
Banana, Pineapple and Jute fiber were mixed with different combination of volume percentage by hand layup technique. For this investigation six types of combinations used. Banana fiber has 60% in all the combination and remaining 40% of fiber only shared with Pineapple fiber and Jute fiber for six different combinations and also each combination with three different (5 mm, 10 mm and 15 mm) thicknesses. The corresponding thermal analysis such as thermal conductivity and thermal resistance of six combination fiber composites were compared for the good thermal insulator for insulation applications.
... The mean value of the thermal conductivity of pure date palm samples studied by Agoudjil et al. [32] was 0.083 W/ m K at atmospheric pressure. The thermal conductivity of the prepared DPPpolystyrene composite materials is very promising when it is compared with the other proposed composites containing date palm fibers (0.075-0.6 W/ m K ) [18], hemp fibers (0.115 W/ m K ) [33], and banana fibers (0.117 W/ m K ) [34]. On the other hand, the thermal conductivity of composites reported here is much less than the thermal conductivity of hemp, jute, and glass fiber-reinforced polyester composites studied by Subba Raju et al. [35], as the thermal conductivity of their composites varied between 0.207 and 0.190 W/ m K at 30°C for filler contents ranging between 18 and 36 vol.%. ...
This study is aimed at developing a thermoplastic composite based on date pit powder waste for use as a thermal insulator in building industries. Date pits are the by-product of date stoning, either for the production of pitted dates or for the manufacture of date paste. The date pit powder (DPP) used in this study was obtained from the UAE University farm in Al Foah, UAE. DPP waste contents ranging from 0 wt.% to 50 wt.% were used to prepare the DPP-polystyrene composite. Date pit powder was mixed with polystyrene using a melt extruder, and then the mixture was transferred to the hot press to produce the final sample. The thermal and physical characteristics of the produced composites were measured experimentally and analyzed theoretically in terms of date pit and polystyrene properties. The characterized properties of the DPP-polystyrene composites, namely, density, thermal conductivity, water retention, thermal stability, and microstructure, showed that a stable composite material with insulation and construction capacity can be formed by the addition of date pit powder to the polystyrene matrix. The theoretical modeling of the measured thermal conductivity and the scanning electron microscope (SEM) monographs supported the hypothesis of date pit agglomeration in the composite matrix. The prepared composites showed low thermal conductivity (0.0515-0.0562 W/m K at 25°C) and very low density (457-630 kg/m3 ), thus demonstrating their potential for use as a thermal insulator for building materials. In addition, replacing one-third of the classical construction wall content with DPP-polystyrene composite showed promise for constructive applications as a thermal insulator with 85% reduction in the overall thermal conductivity. Indeed, these properties are similar to those of other conventional insulating materials. This will lead to produce an inexpensive insulation material that exploits a common waste product in date fruit-producing countries.
... However, as a fiber reinforced composite, the thermal conductivity of the CMC material is anisotropic [7,8] due to the significant differences between the thermal conductivities in the fiber's axial direction and the radial direction and the differences between the thermal conductivities of the fibers and the matrix. Lebel et al. [9] investigated the thermal and mechanical performances of the CMC materials under the cyclic thermal stresses of a gas turbine combustion chamber. ...
The thickness of the hot component in a turbine engine is usually small. Therefore, the traditional prediction model of anisotropic thermal conductivity (ATC) based on the periodic hypothesis may be improper for use in the thermal analysis of ceramic matrix composite (CMC) components with a thin-wall structure. Thus, the prediction model for the ATC of a 2.5-D braided CMC was investigated, taking into account the actual thickness of the CMC thin-wall structure. An RVE (Representative Volume Element) model with a periodic boundary and a full-size model with the actual thickness were built to study the temperature field, the heat flux field, and the effective thermal conductivity of the CMC. A validation experiment was carried out to verify the accuracy of the two prediction models. The effect of the composite’s thickness on the ATC and the critical thickness suitable for the RVE model were also studied. The results showed that in the thermal analysis of the thin-wall structure, the RVE model had a large deviation in the estimation of the effective thermal conductivity in the thickness direction. The relative error between the numerical data based on the RVE model and the experimental data reached 10.93%, while the relative error was only 3.53% for the full-size model. Additionally, with increasing thickness, the effective thermal conductivities, based on the RVE model and the full-size model, were close to each other. For the critical thickness for the RVE model, which would be suitable for the prediction of the ATC, if the material’s thermal properties such as the absolute value ratio and the level of anisotropy changed, the corresponding critical thickness was also different. For the ATC of the SiC/SiC composites used in this study, the critical thickness was found to be 18.4 mm, nearly 31 times larger than the RVE model’s thickness.
... Despite the number of reprocessing cycles, the mechanical properties of recycled hemp fiber/PP biocomposites remain well preserved. Thermal conductivity for hemp fiber reinforced PP [89], mechanical performance of hemp fiber reinforced PP biocomposites at different operating temperatures [90], and rheological properties of hemp fiber/PP composites [91] were also evaluated. ...
Natural fiber reinforced polypropylene (PP) biocomposites and nanobiocomposites are gaining more attraction in research and industrial applications because of their advantages, including low cost, low density, high specific mechanical properties, and less abrasion for processing machineries. These biocomposites can be processed by various conventional plastic processing methods like extrusion, thermoform- ing, and injection molding. Because of incompatibility between polypropylene and natural fibers, various physical and chemical methods are applied on natural fibers for improving interfacial adhesion between polymer and fiber, and, consequently, mechanical properties of final product. At present, natural fiber reinforced PP bio- composites are used in automobile, packaging, and construction sectors. © 2018 by World Scientific Publishing Europe Ltd. All rights reserved.
... The heat change with environment in x-y plane for horizontal composite is less effective than that with heat sink. Since graphene consists of polycrystalline lattices that are parallel arranged in its plane, graphene is highly anisotropic, which gives less thermal resistance along its plane compared with across its plane [45]. For vertical composite, both graphene film and interface planes are along the heat transfer plane, so the heat engendered by LED can easily transfer from composite plate to heat sink. ...
Efficient removal of heat has become one of the most critical challenges in the development of modern microelectronic devices. However, it is hard to dramatically improve thermal conductivity of composite materials even with highly loaded thermally conductive fillers due to the lack of efficient heat transfer paths. In this article, both horizontal and vertical graphene film/epoxy (GF/E) composites were designed and fabricated and their thermal and mechanical properties were studied. Vertically aligned structure constructed of continuous graphene films forms channels for heat removal. The thermal conductivity of vertical GF/E composites reaches 384.9 W m À1 K À1 at 44 vol% graphene, i.e. a dramatic enhancement of 3570% per vol% compared to the pure epoxy, and representing the highest value of all epoxy based composites. The cooling performance of light-emitting diode (LED) package with the application of GF/ E composites is enhanced by reducing the temperature of LED lamp about 20.7 °C compared with the application of pure epoxy. The vertical GF/E composite proved to be a potential material for heat management of LED or other electronic devices.
Ceramic matrix composite (CMC), with higher thermal limit and lower density relative to the superalloy, is regarded as the most important structural material for modern gas turbine engines. However, the anisotropic thermal conductivities caused by the weave patterns totally change the thermal conduction performance inside the solid domain. Therefore, the present study aims to use the infrared thermographic to measure the SiC/SiC composite platform with staggered effusion holes along with the superalloy platform. CMC platform is prepared by 2-D plain weave braid structure with chemical vapor infiltration (CVI) process. The temperature of mainstream is 900 K to match the real mainstream to coolant temperature ratio (Tg/Tc=1.5, 2.1). The experimental was conducted with seven mass flow ratios (MFR=1.5%–4.5%). The results indicate that the thermal conductivity along the thickness direction is of great importance for the CMC platform. The superalloy platform obtains higher level of overall cooling effectiveness than CMC at Tg/Tc=1.5. However, the CMC platform achieves greater overall cooling effectiveness relative to superalloy at Tg/Tc=2.1. In addition, CMC platform presents enhanced uniformity of overall cooling effectiveness due to the larger in-plane thermal conductivity.
Bio-based products are paving a promising path towards a greener future and helping win the fight against climate change and global warming mainly caused by fossil fuel consumption. This paper aims at highlighting the acoustic, thermal, and mechanical properties of hemp-based biocomposite materials. Change in sound absorption as a result of hemp fibers and hemp particle reinforcement are discussed in this paper. The thermal properties characterized by the thermal conductivity of the composites are also presented, followed by the mechanical properties and the current issues in biocomposite materials mainly containing hemp as a constituent element. Lastly, the effects of biofillers and biofibers on the various properties of the hemp-composite materials are discussed. This paper highlights the development of and issues in the field of hemp-based composite materials.
The use of by-products from agricultural and forestry activity, apart from many other environmental benefits, constitutes an alternative source of income, cost reduction, and support for the principles of the circular economy. The bobal grape is a variety of red grape that is cultivated on 65 thousand hectares only in Spain. Periodic maintenance of the crop must be carried out through winter pruning from December to March. The pruning biomass is burned or crushed and incorporated into the soil, producing environmental contamination and disease transmission. The objective of this work was to use the biomass from vineyard residues in the production of binderless particleboards without using any adhesives, thereby obtaining an ecological product that would benefit the environment. In the manufacturing process, the press temperature (130 °C) and pressure (2.6 MPa) were fixed, varying the particle size (<0.25, 0.25 to 1.00, and 1.00 to 2.00), and the pressing time (15, 30, and 45 min). The results showed that by using particles smaller than 0.25 mm and applying 45 min in the hot press, panels were manufactured that are suitable for general use in a dry environment and for the manufacture of furniture according to European standards.
Plant Fiber Reinforced Composites (PFRCs) not only possess excellent mechanical properties, but also have unique chemical composition and lumen and hierarchical structure. Compared with man-made fiber reinforced composites, PFRCs show excellent physical properties such as sound absorption, heat insulation, electromagnetic wave absorption, damping and noise reduction, which makes it possible to realize the development of composite structure with integrated structure and function.
In this study, the thermal conductivity (k-values) of pure and composite samples obtained from raw materials which these samples came from different parts (stalk, fiber) and different regions (bottom, middle and top) of nettle plants and collected from low and high altitudes (350 and 2100) in the Black Sea regions were investigated depending on orientation and temperature. According to the ASTM C518 standard, the k-value is only given for the temperature value of 10 °C. However, it is also important to determine the thermal conductivity depend on climatic conditions, ambient temperature, and humidity. It is known that the thermal conductivity coefficient changes depend on the density, pore structure and size, humidity, and temperature. However, for materials with a fibrous structure (rock wool, glass wool, VIP), the orientation of the fiber structure depends on the heat transfer direction also significantly affects the thermal conductivity. In the first stage of the study, the pure thermal conductivity of cellulosic materials was determined. The fiber parts of the nettle plant, which have low thermal conductivity (k < 0.040 W/mK), were used in the formation of the composites. In this context, the thermal conductivity of composites formed with fibers obtained from two different altitudes was characterized depend on temperature (0 ºC, 10 ºC, 20 ºC, 30 ºC, 40 ºC) and orientation (0º, 45º, 90º). Ratios such as 2.5 %, 5 %, 7.5 %, and 10 % by volume were used to form the composite, and the effect of orientation and temperature was measured in composites with a 10 % reinforcement ratio. The manual laying method was used in the production of test samples. The physical and chemical properties of the reinforcement material affecting the thermal conductivity of the composites were determined and its effect on the thermal conductivity coefficient was discussed. In the conducted study, it was determined that the altitude difference affects the characteristic features of the plant (such as fiber diameter, crystal structure, and density), and accordingly, the thermal conductivity behaviors show differences. On the other hand, it was determined that orientation significantly affects the thermal conductivity coefficients, but the effect of temperature increase on the thermal conductivity coefficient change in the same composites is low. As a result, it has been concluded that the fibers obtained from the bottom parts of the plants obtained from high altitudes may be a more suitable insulation material than the fibers obtained from the other part.
Alkali-treated discontinuous cellulosic fibers (jute and sisal)-based heat-treated silanized fly ash-dispersed hybrid polyester composites were fabricated using a compression molding technique. The morphological features were observed using a scanning electron microscope and a high-resolution transmission electron microscope. The bulk mechanical testing namely, microhardness, tensile, flexural as well as Izod impact was successfully executed. The significant effect of the filler (cellulosic fibers as well as modified fly ash) dispersion within the polymeric matrix with respect to mechanical properties was thoroughly examined in this present investigation.
The effective thermal conductivity (ETC) of roughened porous media (RPM) is of interest in a number of applications of heat transfer. In this work, a fractal analytical model for the ETC of RPM with microscale effect is proposed. The proposed fractal model is expressed in terms of relative roughness, the molecular mean free path, porosity, fractal dimensions (pore area fractal dimension and tortuosity fractal dimension), maximum pore diameter, capillary straight length, and the thermal conductivity of the solid matrix and gas. It is observed that the dimensionless ETC of RPM decreases with increasing relative roughness, pore area fractal dimension and tortuosity fractal dimension. Besides, it is found that the dimensionless ETC of RPM increases with thermal conductivity ratio of gas phase over solid phase. In addition, it is found that the dimensionless ETC of RPM is slightly dependent on the relative roughness and tortuosity fractal dimension when [Formula: see text]. The determined dimensionless ETC of RPM is in good agreement with experimental data and existing models reported in the literature. With the proposed fractal model, the physical mechanisms of heat transport through RPM with microscale effect are better elucidated. Every parameter in the fractal analytical model has clear physical meaning, with no empirical constant.
The anisotropic micro-structure of fiber will lead to the macroscopic anisotropic properties of fiber reinforced composites in both heat transfer and mechanical strength. However, few experimental studies have be made on the anisotropic heat transfer properties of fiber reinforced composites. In this study, the anisotropic thermal conductivities of two-dimensional (2D) plain woven and twill woven carbon-fiber/epoxy composites are measured at different temperature with the one-dimensional (1D) steady-state method, transient plane source (TPS) method and transient hot wire method, respectively. The out-of-plane thermal conductivity and in-plane thermal conductivity at the temperature ranging from -45 ℃ to 160 ℃ are obtained and comparisons are made among the three methods. The results show that all the three methods can be used to measure the anisotropic thermal conductivity of fiber/epoxy woven composites. Both the out-of-plane thermal conductivity and in-plane thermal conductivity of carbon-fiber/epoxy woven composites increase with temperature, and the in-plane thermal conductivity is approximately four times as high as the out-of-plane thermal conductivity for the plain woven composites. Compared with the results of 1D steady-state method, the max deviations of TPS method and hot wire method are 18.1% and 17.1%, respectively. The sources of error that leading to the deviations are also discussed.
The raw materials used to manufacture thermal insulation in buildings consume a large amount of energy and are not generally biodegradable, which means it is necessary to increase the use of renewable, eco-friendly resources such as plant fibers in order to reduce the environmental problems this generates. The wood adhesives developed by the petrochemical industry offer excellent performance and are affordable. However, their use has an expiry date and in the future they will be rejected due to the environmental and health problems they can cause. The objective of this work was to develop a new eco-friendly biocomposite that could be used for thermal insulation in buildings. Boards were manufactured from giant reed particles with a particle size of 2 to 4 mm, using 5 and 10% by weight of citric acid as a natural binder. Experiments were then carried out to investigate the effect of board density on mechanical, physical, and thermal properties. A new type of composite was obtained with a thermal conductivity of 0.081–0.093 W/m K, which makes it suitable as an insulating material. The boards with a density of 850 kg/m3 had a modulus of rupture (MOR) of 12.5 N/mm2, a modulus of elasticity (MOE) of 2440 N/mm2, and an internal bonding strength (IB) of 0.61 N/mm2, and they could be used as insulation panels for divisions and enclosures in buildings.
A recent interest in the mechanical properties of spider silk has also brought about investigations into the thermal properties of thin fibers, often with contradictory results. Because of the high length-to-diameter ratio of fibers, two key obstacles arise during their thermal characterization: the need to develop non-standard techniques to measure properties and the lack of reliable methods to confirm the validity of those measurements. This is especially important since standard reference materials are difficult or impossible to produce at these small scales. This paper presents a review on the thermal conductivity and diffusivity of spider dragline silk and how the use of a suite of measurement techniques that complement each other can bound the uncertainty of the measured property. The properties of silkworm silks are then presented as evidence of a field where complementary techniques could be applied to resolve property discrepancies. This complementary approach to validating novel techniques will increase the confidence in measured properties and will open new avenues of thermal science applications.
The effective thermal conductivity of unsaturated porous media is of interest in a number of applications of heat transfer. In this paper, a novel fractal solution for effective thermal conductivity is derived based on the fractal distribution of surface roughness and pore size in unsaturated porous media with roughened surfaces. The proposed fractal model explicitly relates the effective thermal conductivity to the microstructural parameters (relative roughness, porosity and fractal dimensions). The proposed fractal model is verified by a satisfying agreement of the effective thermal conductivity predicted by our model and that reported as existing experimental data in the literature. A parametric study is also elaborated to investigate the influences of the microstructural parameters on the effective thermal conductivity. The results demonstrate that our proposed fractal model improves our understanding of the physical mechanisms of heat transport through unsaturated porous media with roughened surfaces. One advantage of our fractal analytical model is that it contains no empirical constant, while it is usually required in previous models.
Using natural fibers as reinforcement in polymer matrix composites necessitates evaluating the latter under different modes of solicitation. This allows extracting its material properties for engineering design and research purposes. The main objective of the study is preparing a consistent set of material properties for unidirectional flax fiber-reinforced epoxy composite with defined composition and basic configuration. These data are prerequisites for growing researches on flax fiber-reinforced epoxy composites, especially for numerical analysis purposes using the finite element method. In this work, partially green unidirectional-flax fiber-reinforced epoxy composites are tested for physical and mechanical properties and studied for their failure modes. Tension, compression, flexion, and shear properties, as well as physical properties like density, specific heat capacity and thermal diffusivity, are evaluated according to ASTM standard test methods. Flax fibers, which are composites by themselves, come in bundles in the composites and demonstrate a complex behavior. Therefore, a fractographic analysis has been conducted to understand the macro and microscale failure mechanisms to correlate them with the material properties. The results are in good agreement with those of the literature, when available, but they mainly show the specific behavior of unidirectional-flax composites subject to different solicitation modes, especially compression and direct shear modes evaluated this way for the first time for unidirectional-flax fiber-reinforced epoxy composite. They cover most of the data required for engineering design and numerical analysis by methods like finite element method, particularly for simulating the machining process of flax fiber-reinforced epoxy composite in the ongoing works.
Problems related to the production of composite materials based on synthetic polymer matrices reinforced with natural fibers of different classes are considered. The main natural fibers of plant and animal origin used to create polymer composites are characterized, and the properties of the composites are described. The advantages and disadvantages of using natural fibers for the production of polymeric composite materials for various purposes are discussed.
Unsaturated Polyester (UP) based composites with 5, 15, 25, 35 and 45 wt% filler content have been fabricated by compression moulding technique. The NaOH treated discontinuous jute fibre has been used along with vinyl silane treated zirconia (ZrO2) particle as the dispersing phases. The structures were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The thermal stability of the UP and UP based composites were observed using electronic thermal insulation tester, thermo-gravimetric analyser, differential scanning calorimetry and limiting oxygen index analyser. The swelling behaviour has been investigated in different solutions having a range of pH values. The optimum results were obtained with 35 wt% filler content for UP/Jute/ZrO2 composites.
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Polymer composites are widely used in different areas such as the aircraft industry, automotive industry, electronic industry and packaging industry etc. Polymer composites should have various physical, mechanical and thermal properties, within various thermal properties thermal conductivity is an important parameter to simulate heat transfer process and mechanisms in composite materials.
This paper deals with various analytical methods and models for determining the effective thermal conductivity of different polymer composite materials for various applications. There are basic models, modified models and semi-empirical models to determine thermal conductivity analytically, which are discussed in brief. After that, the comparison between different models is investigated. Finally different conductive fillers, the effect of their shape, size and volume fraction on the effective thermal conductivity of composite materials are discussed.
Sisal fiber along with ZrO2 particles dispersed unsaturated polyester (UP) composites were fabricated by compression molding technique. The filler contents were varied from 5 to 45 wt% with a gradual increase of 10%. The structural investigation was done using Scanning electron microscopy, X‐ray diffraction, and Fourier transform infrared spectroscopy. Mechanical testing was performed through microhardness tester, tensile, flexural, and Izod impact test. The optimum mechanical properties were obtained at 35 wt% of filler incorporation within UP matrix followed by a slight deterioration at 45 wt%. Fractographic images of the composites display the phenomena of fiber pull‐out, debonding and breakage. The water absorption test was performed both at room temperature and boiling water temperature conditions. The thermal insulation measurement was performed by Kawabata method. POLYM. COMPOS., 2018.
In this experimental investigations deals with the natural fiber composites such as Abaca and kenaf with carbon for thermal insulation performance enhancement. The square matrix used for this analysis. Volume fractions, ratio of thermal conductivity lumen were the most important considerations for this investigation with respect to the thermal conductivity of the corresponding composites. The experimental and theoretical results were compared for the performance identifications.
A parametric finite element analysis was carried out to investigate the sensitivity of the effective thermal conductivity of fibers to orientation clustering. Randomly-positioned fibers with von Mises orientation distributions were used in different considerations and volume fractions to generate the dispersion in a partitioned representative volume element. It was found that increasing the fiber volume fraction increases the thermal conductivity; this improvement is significant specially when a preferred orientation is detected with a cluster-free state. Further reinforcement of the composite is made possible by increasing the maximum principal value of the orientation tensor provided that the principal direction is set accordingly. Furthermore, clustering index does not seems to be affected by volume fraction when an equal distribution is present in partitions.
Chemical treatment of natural fibers is a well-defined means of mechanical property improvement in natural fiberreinforced composites. An understanding of mechanical and thermal properties in these media is essential for evaluating heat transfer, thermal degradation, and overall performance of these composites over their product lifetime. However, very little information is available illustrating the effect of such treatment on the thermal properties of kenaf composites. Also, no study to date has reported the thermal conductivity of individual kenaf fibers. This study reports the effects of fiber treatment (in 6 % NaOH) on thermal transport in unidirectionally oriented kenaf-epoxy composites and individual kenaf fibers. The effective thermal conductivities and thermal diffusivities of chemically treated fiber composites show a general increase over untreated fiber composites (0.210 to 0.232 W/m/K at 28 °C, 0.206 to 0.234 W/m/K at 200 °C). This improvement may be attributed to improved interfacial contact between the fibers and epoxy matrix shown in microstructural images after chemical treatment. The thermal conductivity of individual fibers was evaluated at room temperature using two techniques. Results from both techniques showed slight increases after chemical treatment (0.58±0.53 to 1.0±0.13 W/m/K and 1.2±0.54 to 1.6±0.28 W/m/K) but lacked statistical significance. Any improvement in surface crystallinity after chemical treatment does not appear to affect overall fiber thermal conductivity. A better understanding of thermal transport in kenaf fibers and composites enables better estimation of the performance of these composites in different applications. Moreover, the thermal conductivities of individual fibers are useful in understanding the fiber’s contribution to conduction in different fiber reinforcement configurations.
Natural fibers (such as kenaf) have garnered interest recently for use in composites because of their relatively high specific properties, low cost, and low environmental impact. Their thermal property information is limited, lacking experimental data on key properties such as thermal conductivity, specific heat, and CTE of the component fiber. This paper presents, for the first time, the thermal property data on kenaf fiber reinforced composites, and an approach to obtain the composite thermal properties based on constituent properties. Individual, plant-based fibers were measured independently and were then used to inform successful predictions of the effective thermal conductivity of the fiber reinforced composites. A unit cell model has been developed to predict the thermal properties of a planar, randomly oriented kenaf fiber-reinforced composite (near 22% volume fraction loading), which includes the effect of void content on the predicted thermal conductivity. A lower-level model is also developed for individual fiber thermal properties based on its constituents (lignin, cellulose, and hemicellulose). To validate this multi-level model, experimental measurements of the thermal diffusivity, coefficient of thermal expansion, and specific heat for the composite, the matrix, and the fibers were performed in the range from 30 °C to 160 °C, based on TMA, DSC, LFA, and transient electro-thermal (TET) techniques. Model results compare favorably with the experimental data, and are consistent with FEM modelling results based on fiber properties and fiber constituent materials (lignin, cellulose, and hemicellulose). This approach provides the basis for understanding component contribution to the fiber properties, as well as a technique to obtain fiber composite thermal property based on component properties. The composite thermal property data also fills an information gap and can be directly used in component design.
The Second International Conference on Green Communications, Computing and Technologies (GREEN 2017), held between September 10-14, 2017 in Rome, continued the inaugural event focusing on current solutions, stringent requirements for further development, and evaluations of potential directions. The event targeted to bring together academia, research institutes, and industries working towards green solutions.
Expected economic, environmental and society wellbeing impact of green computing and communications technologies led to important research and solutions achievements in recent years. Environmental sustainability, high-energy efficiency, diversity of energy sources, renewable energy resources contributed to new paradigms and technologies for green computing and communication.
Economic metrics and social acceptability are still under scrutiny, despite the fact that many solutions, technologies and products are available. Deployment at large scale and a long term evaluation of benefits are under way in different areas where dedicated solutions are applied.
The conference had the following tracks:
Improving Green-ness
Smart Energy and Smart Grid
We take here the opportunity to warmly thank all the members of the GREEN 2017 technical program committee, as well as all the reviewers. The creation of such a high quality conference program would not have been possible without their involvement. We also kindly thank all the authors that dedicated much of their time and effort to contribute to GREEN 2017. We truly believe that, thanks to all these efforts, the final conference program consisted of top quality contributions.
We also gratefully thank the members of the GREEN 2017 organizing committee for their help in handling the logistics and for their work that made this professional meeting a success.
We hope that GREEN 2017 was a successful international forum for the exchange of ideas and results between academia and industry and to promote further progress in the field of green communications, computing and technology. We also hope that Rome, Italy provided a pleasant environment during the conference and everyone found some time to enjoy the historic charm of the city.
Two models. E-S anti R-S unit cell models, are presented based on the thermal-electrical analogy technique. The analytical expressions for transverse thermal conductivities of unidirectional composites are derived. The dimensionless effective transverse thermal conductivities k(e) are expressed as a junction of the ratio (beta) of thermal conductivities of filler to matrix. filler volume fraction (v(f)) and the geometry ratio (rho = a/b) of the filler The optimization of transverse thermal conductivities of unidirectional composites is then analyzed under different filler volume fractions v(f), thermal conductivity ratios beta and different geometric architectures. The present analysis allows for a fairly precise evaluation of configuration performance and comparisons of different arrangements. The results show that if a composite is designed,for insulation material, we should choose rho< 1, and if a composite is designed for heat dissipating purpose, we should choose ρ > 1.
In the present study, a new environmentally friendly thermoset resin was used to manufacture hemp fiber acrylic composites by sheet molding process for automotive applications. A finite difference method was applied to predict the cure behavior and temperature variation of hemp fiber acrylic based composites during the process. Dynamic Differential Scanning Calorimetry (DSC) was employed to determine the kinetic parameters for the curing reaction at different heating rates. It was found the experimental and predicted values are in good agreement at the lower heating rate. The thermophysical properties of the resin, fiber and composite were obtained to use in the model. The temperature profile and the degree of cure of the composite with 40% resin and 60% fiber were simulated and a comparison of numerical results with known experimental data confirms the approximate validity of the model.
In the past few years, natural fibers are finding an increased interest in polymer matrices. The natural fibers serve as reinforcement by enhancing the strength and stiffness to the resulting composite structure. In this study, a novel processing technique has been developed for water based thermoset polymers to prepare resin-impregnated mats, which can be used for sheet molding process to manufacture complex automotive semi-structural and structural parts. In order to optimize the curing conditions the mechanical properties of composites at different curing temperature and the crosslink density of the composites cured at different times were evaluated. The optimum curing cycle was obtained at 180 ºC for 10 min. Composites with one and two layers of impregnated mat with 40 % resin and 60 % fiber were manufactured and their performance were evaluated. The mechanical properties of the cured pure resin and hemp fiber acrylic based composites with two different fiber lengths were measured and the effect of fiber content and fiber length were investigated. The flexural strength was found to be around 94 MPa and the flexural modulus was 14 GPa for the composite.
Recently the critical discussion about the preservation of natural resources and recycling has led to the renewed interest concerning biomaterials with the focus on renewable raw materials. Because of increasing environmental consciousness and demands of legislative authorities, use and removal of traditional composite structures, usually made of glass, carbon or aramid fibers being reinforced with epoxy, unsaturated polyester, or phenolics, are considered critically. Recent advances in natural fiber development, genetic engineering and composite science offer significant opportunities for improved materials from renewable resources with enhanced support for global sustainability. The important feature of composite materials is that they can be designed and tailored to meet different requirements. Since natural fibers are cheap and biodegradable, the biodegradable composites from biofibers and biodegradable polymers will render a contribution in the 21st century due to serious environmental problem. Biodegradable polymers have offered scientists a possible solution to waste‐disposal problems associated with traditional petroleum‐derived plastics. For scientists the real challenge lies in finding applications which would consume sufficiently large quantities of these materials to lead price reduction, allowing biodegradable polymers to compete economically in the market. Today's much better performance of traditional plastics are the outcome of continued R&D efforts of last several years; however the existing biodegradable polymers came to public only few years back. Prices of biodegradable polymers can be reduced on mass scale production; and such mass scale production will be feasible through constant R&D efforts of scientists to improve the performance of biodegradable plastics. Manufacture of biodegradable composites from such biodegradable plastics will enhance the demand of such materials. The structural aspects and properties of several biofibers and biodegradable polymers, recent developments of different biodegradable polymers and biocomposites are discussed in this review article. Collaborative R&D efforts among material scientists and engineers as well as intensive co‐operation and co‐ordination among industries, research institutions and government are essential to find various commercial applications of biocomposites even beyond to our imagination.
The contents of this book are: Theory of Heat Conduction and Heat-conduction Equations; Thermal Conductivity; Steady Heat Conduction; Unsteady Heat Conduction; Forced Convection in Laminar Flow; Forced Convection in Turbulent Flow; Dimensional Analysis; Forced Convection in Separated Flow; Natural Convection; Radiation of Strongly Absorbing Media; and Radiation of Weakly Absorbing Media.
In the present study a new environmentally friendly acrylic resin was characterized to develop a high-performance biocomposite for future work. Differential scanning calorimetry measurements were used to determine onset of curing reaction as well as the degree of cure at a certain temperatures. Swelling equilibrium data for an acrylic resin were generally analyzed using the Flory–Rehner equation for a perfect network, to obtain a measurement of the molar mass between two crosslinks and the crosslink density of polymer, and to establish the effect of temperature and time on these parameters. The crosslink density of cured resin at 180°C and 10 min indicates the completion of a major part of the reaction under those conditions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 757–762, 2004
The thermal conductivity and thermal diffusivity of oil-palm-fiber-reinforced untreated (Sample 1) and differently treated composites were measured with the transient plane source technique at room temperature and under normal pressure. All the composites were 40% oil-palm fiber by weight. The fibers were treated with alkali (Composite 2), silane (Composite 3), and acetic acid (Composite 4) and reinforced in a phenolformaldehyde matrix. The thermal conductivity and thermal diffusivity of the composites increased after treatment to different extents. The thermal conductivity of the treated fibers as well as of the untreated fibers was calculated theoretically. The model results show that the thermal conductivity of the untreated fiber was smaller than the thermal conductivity of the treated fibers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 916–921, 2000
Recently the critical discussion about the preservation of natural resources and recycling has led to the renewed interest concerning biomaterials with the focus on renewable raw materials. Because of increasing environmental consciousness and demands of legislative authorities, use and removal of traditional composite structures, usually made of glass, carbon or aramid fibers being reinforced with epoxy, unsaturated polyester, or phenolics, are considered critically. Recent advances in natural fiber development, genetic engineering and composite science offer significant opportunities for improved materials from renewable resources with enhanced support for global sustainability. The important feature of composite materials is that they can be designed and tailored to meet different requirements. Since natural fibers are cheap and biodegradable, the biodegradable composites from biofibers and biodegradable polymers will render a contribution in the 21st century due to serious environmental problem. Biodegradable polymers have offered scientists a possible solution to waste-disposal problems associated with traditional petroleum-derived plastics. For scientists the real challenge lies in finding applications which would consume sufficiently large quantities of these materials to lead price reduction, allowing biodegradable polymers to compete economically in the market. Today's much better performance of traditional plastics are the outcome of continued R&D efforts of last several years; however the existing biodegradable polymers came to public only few years back. Prices of biodegradable polymers can be reduced on mass scale production; and such mass scale production will be feasible through constant R&D efforts of scientists to improve the performance of biodegradable plastics. Manufacture of biodegradable composites from such biodegradable plastics will enhance the demand of such materials. The structural aspects and properties of several biofibers and biodegradable polymers, recent developments of different biodegradable polymers and biocomposites are discussed in this review article. Collaborative R&D efforts among material scientists and engineers as well as intensive co-operation and co-ordination among industries, research institutions and government are essential to find various commercial applications of biocomposites even beyond to our imagination.
Simultaneous measurment of effective thermal conductivity (λ) and effective thermal diffusivity (κ) of pineapple leaf fiber reinforced phenolformaldehyde (PF) composites have been studied by transient plane source (TPS) technique. The samples of different weight percentage typically (15, 20, 30, 40 and 50%) have been taken. It is found that of effective thermal conductivity and effective thermal diffusivity of the composites decrease, as compared with pure PF as the fraction of fiber loading increases. Using Y. Agari, model thermal conductivity of pure fiber is evaluated and compared with the thermal conductivity of fiber determined by extrapolated experimental value of composite. Also, we have compared the results of thermal conductivity of composites with two models (Rayleigh–Maxwell and Meredith–Tobias model). Good agreement between theoretical and experimental result has been found.
Natural fiber reinforced composites is an emerging area in polymer science. These natural fibers are low cost fibers with low density and high specific properties. These are biodegradable and non-abrasive. The natural fiber composites offer specific properties comparable to those of conventional fiber composites. However, in development of these composites, the incompatibility of the fibers and poor resistance to moisture often reduce the potential of natural fibers and these draw backs become critical issue. This review presents the reported work on natural fiber reinforced composites with special reference to the type of fibers, matrix polymers, treatment of fibers and fiber-matrix interface. © 1999 John Wiley & Sons, Inc. Adv in Polymer Techn 18: 351–363, 1999
Precise conductivity measurements on models sectioned out from a cubic lattice of spheres in a continuous medium indicate that the effective conductance of such a system deviates from the values predicted by Lord Rayleigh's analytic solution of this potential distribution problem. Deviations become particularly significant when the spheres approach close packing, and when the conductance of spheres is much greater than that of the continuum. By use of a different function for potential, and by consideration of higher terms in the series expression for the potential in the continuous phase, Rayleigh's results are modified, yielding an analytical expression that represents effective conductance satisfactorily in the concentration region approaching close packing.
The thermal conductivity and thermal diffusivity of sisal-reinforced polyethylene (SRP), glass-reinforced polyethylene (GRP) and sisal/glass hybrid fibre-reinforced polyethylene (GSRP) has been evaluated at cryogenic to high temperature (120–350 K). It has been observed that the variation of thermal conductivity with temperature is almost the same for LDPE and SRP containing perpendicularly oriented sisal fibres. The difference between the values of thermal conductivity shown by LDPE and GRP is greater than that of SRP and LDPE. The enhanced thermal conductivity of glass fibre is due to the presence of Fe2+ ions in the glass fibres. The linear variation in thermal conductivity with fibre loading is explained with the help of a model suggested by Agari. The difference between the thermal conductivity properties in directions parallel and perpendicular to the applied flux is a maximum for SRP owing to the anisotropic nature of sisal fibre. The difference is marginal for GRP on account of its isotropic nature. The position of GSRP is found to be intermediate. It can been observed that the variation of thermal diffusivity with temperature is just opposite to that of thermal conductivity. This may be due to a reduction in the mean free path of phonons. An empirical equation is derived to explain the variation in thermal conductivity and thermal diffusivity with temperature.
Existing micromechanical approximation formulae for predicting the transverse thermal conductivity of unidirectional CFRP laminates from the properties of the constituents provide rather different results. The analytical accuracy of such formulae is examined by comparing with finite-element calculations and yields a pre-selection of two equations. Measurements by two different methods reveal that the self-consistent formula is the most realistic one.
A new method has been developed to determine the in-plane and through-thickness thermal conductivities of polymer matrix composites. In the method, the thermal gradient produced by an imposed one-dimensional heat flow in a given direction is measured experimentally. The recorded temperature gradient is used to calculate the thermal conductivity using an inverse numerical approach. Benchmarking was conducted using an aluminium alloy with known thermal properties, yielding excellent correlation. Testing was then performed on F593 carbon-epoxy laminates and the thermal conductivity curves for a service temperature range were determined.
The purpose of this work was to measure the thermal conductivity of polyacrylamide (PAG) and compare it with previously reported values. Polyacrylamide phantoms play an important role in the development of hyperthermia and high-temperature thermal therapies based on electromagnetic (EM) radiation by providing a material that mimics the electrical and thermal properties of human tissue. The thermal properties of PAG have, up until now, not been thoroughly investigated and at least two significantly different values have been published. In this study, the thermal conductivity of polyacrylamide was measured from the steady state temperature drop across samples exposed to a known heat flux. The measured conductivity was 0.56 +/- 0.047 W m(-1) degrees C(-1). To validate the correct set of thermal properties for polyacrylamide, simple heating experiments were performed in a PAG phantom and then simulated using a finite element numerical model that incorporated the measured thermal conductivity along with literature values for specific heat and density. Temperature predictions from the model agreed with average temperatures measured in the phantom to within 1 SD of the measured temperatures.
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