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Nanofluids are potential new generation heat transfer fluids, which have been investigated meticulously, in recent years. Thermophysical properties of these fluids have significant influence on their heat transfer characteristics. Viscosity is one of the most important thermophysical properties that depends on various parameters. Size of the particles used in nanofluids is one of these effecting parameters. In this work, experimental studies considering the particle size effect on the viscosity of the nanofluid have been reviewed. Firstly, comparison of nanofluid and surfactant type, production and measurement methods were considered. Viscosity results of selected studies were evaluated in view of the parameters such as particle size, temperature and concentration. Furthermore, effective viscosity models of nanofluids, which include particle size as a parameter were discussed. The results indicate that there is a discrepancy about the effect of particle size on the viscosity of nanofluids. Moreover, it is observed from the evaluated data that the relative viscosity variation can be almost 40% either upwards or downwards by only altering the particle size.

This study aims to investigate experimentally the effects of aspect ratio (length/diameter ratio) and concentration of multiwalled carbon nanotubes (MWCNTs) on thermal properties of high density polyethylene (HDPE) based composites. The aspect ratios of two types of MWCNT fillers are in the range of 200-400 and 500-3000. Composite samples were prepared by melt mixing up to weight fraction of 19% filler content, followed by a compression molding. Measurements of density, specific heat and thermal diffusivity (by modulated photothermal radiometry, PTR) were performed and effective thermal conductivities k(e) of nanocomposites were calculated using these values. The results show that the composites containing MWCNTs with higher aspect ratio have higher thermal conductivities than the ones with lower aspect ratio. In terms of conductivity enhancement k(e)/k(m) - 1, the results indicate that MWCNTs with higher aspect ratio provide three to fourfold larger enhancement than the ones with lower aspect ratio, at low filler concentrations. (C) 2015 Elsevier Ltd. All rights reserved.

Recently polymer nanocomposites are used more and more frequently in industry due to the fact that the properties of the polymers can be altered to the specific requirements by the addition of particles and fibers of different properties, shapes. Polymers are poor thermal and electrical conductors, conductive fillers such as metallic powders, carbon black, graphite, are usually incorporated into polymer matrix to produce conducting composites. In this study composites were prepared using ethylenevinyl acetate (EVA) copolymer as matrix filled with two kinds of reinforcement graphite materials: untreated natural graphite (UG) and expanded graphite (EG). Composite samples up to 29.3 % graphite particle volumetric concentrations (50 % mass concentration) were prepared by the melt mixing process in a Brabender Plasticorder. Upon mixing, the EG particles originally 5μm to 6μm in size, exfoliates in the form of nanosheets having a few nanometer thickness; they have very big surface areas with high aspect ratio ranging between 20 and 250, as evidenced by TEM micrographs. From the experimental results it was deduced that the electrical conductivity was not only a function of filler concentration, but also strongly dependent on the graphite structure. The percolation concentration of the filler was found to be (15 to 17) vol% for micro-sized natural graphite, whereas the percolation concentration of the filler in nanocomposites filled with expanded graphite was much lower, about (5 to 6) vol%. The electrical conductivity of nanocomposites was also much higher than the electrical conductivity of composites filled with micro-sized filler at similar concentrations. Similarly, the values of the thermal diffusivity for the nanocomposites, EG-filled EVA, were significantly higher than the thermal diffusivity of the composites filled with micro-sized filler, UG-filled EVA, at similar concentrations. The effect of thermal cycling on the tensile behavior of EVA composites containing 4% and 15% of UG by mass and 6% and 15% of EG by mass were subjected to thermal cycling between-25 to +60 °C. Tension tests were conducted after thermal cycling for 50 and 100 cycles. Tensile strength remained practically unchanged after thermal cycling, while the Young modulus increased appreciably with the number of thermal cycle.

In this study, thermal properties of high-density polyethylene (HDPE) filled with nanosized Al particles (80 nm) were investigated. Samples were prepared using melt mixing method up to filler volume fraction of 29 %, followed by compression molding. By using modulated photothermal radiometry (PTR) technique, thermal diffusivity and thermal effusivity were obtained. The effective thermal conductivity of nanocomposites was calculated directly from PTR measurements and from the measurements of density, specific heat capacity (by differential scanning calorimetry) and thermal diffusivity (obtained from PTR signal amplitude and phase). It is concluded that the thermal conductivity of HDPE composites increases with increasing Al fraction and the highest effective thermal conductivity enhancement of 205 % is achieved at a filler volume fraction of 29 %. The obtained results were compared with the theoretical models and experimental data given in the literature. The results demonstrate that Agari and Uno, and Cheng and Vachon models can predict well the thermal conductivity of HDPE/Al nanocomposites in the whole range of Al fractions.

This study numerically investigates the influence of integration of a phase change material (PCM) slab inside a vertical beverage cooler (VBC) on the energy consumption, the thermal stability and flow characteristics of air inside the cooler. The PCM, water, slab is placed on the rear side of the flat plate roll bond evaporator with five different thicknesses, such as 2, 4, 6, 8, and 10 mm. In the current work, transient numerical analyses are performed with ANSYS-FLUENT software for an empty cooler. To simulate the on/off controller of the cooling system a dedicated user-defined-function (UDF) is implemented in the software. Unlike the counterparts in the recent literature, instead of reducing the problem into a 1D or 2D lumped models a three-dimensional cooler domain is simulated in a commercial CFD solver. The predictions are compared with the experimental measurement for the cooler without PCM regarding the transient variations of the mean temperatures of evaporator surface and the indoor air. Consequently, the parametric set of analyses deduced that the PCM integration into the cooler enhances the cooling performance of the VBC by prolonging compressor off duration. Moreover, during the compressor off time, PCM preserves the air temperature inside the refrigerated space in the desired range by limiting the sudden temperature increments. (C) 2017 Elsevier Ltd. All rights reserved.

Graphite particles filled high density polyethylene (HDPE) conductive polymer nanocomposites were prepared by melt mixing process. The conductive filler which consists of graphite particles (average particle size of 400 nm) were mixed with the HDPE matrix at different weight percentage (wt%) up to 30 wt% in a Brabender Plasticorder PLE 331 internal mixer at 180 degrees C for 15 min Various thermophysical properties of HDPE/graphite nanocomposites, such as thermal conductivity, specific heat capacity, electrical conductivity, mechanical properties were investigated. Thermal conductivities were measured using transient plane source technique and the results obtained were compared with already existing models. Thermal conductivity increased from 0.53 W/m.K for pure HDPE to 2.64 W/m.K for 30 wt% of graphite particles. Heat capacities were measured using a differential scanning calorimeter (DSC). The percolation threshold for electrical conductivity is 16w% of graphite particle filler; the electrical conductivity increased from 8.07x10(-14) S.cm(-1) for neat HDPE to 2.02x10(-4) S.cm(-1) for composites with 30 wt% of graphite particles.

In this study, flax fibers were treated by argon and air atmospheric pressure plasma systems under various plasma powers to improve interfacial adhesion between the flax fiber and high density polyethylene (HDPE) and unsaturated polyester. The interfacial adhesion of argon treated flax fiber for HDPE matrix is superior than those of air treated and untreated flax fiber. However for the adhesion between flax fiber and polyester matrix, air treatment is more efficient than argon treatment. Besides, greater plasma power causes greater interfacial adhesion, which was proved by pull out tests. The surface characteristics of flax fibers were examined using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Scanning electron microscopy (SEM), and roughness tests. X-ray photoelectron spectroscopy analysis (XPS) indicated that the air plasma-treated fiber had higher oxygen concentration and higher oxygen/carbon ratio than the untreated fiber and argon plasma treated fiber. Changes in the surface chemical composition and functional groups, and increases in surface roughness were obtained. After both plasma treatments, it was clearly seen that a new functional group (O-C=O) generates on the flax fiber surface. (c) 2012 Elsevier Ltd. All rights reserved.

Photothermal (PT) methods are able to characterize effective thermooptical properties of particulate two-phase polymer nanocomposites. Modulated laser light is used to generate a thermal response of the sample which contains information on its thermophysical and optical properties. Thus frequency- or time-domain PT spectra can be acquired by various PT methods. The sample structure, which is beyond the reach of pure optical methods, becomes accessible to a depth known as the thermal diffusion length. This frequency-dependent parameter is the basis of PT tomography. After the presentation of a literature survey on PT studies on composite materials, the authors’ results on polymer-based (high- and low-density polyethylene, EVA, PLA, PBS) composites with carbon (expanded and unexpanded graphite, carbon nanotubes), montmorillonite clay, and Al particles are presented. Thermooptical parameters of nanocomposites are then extracted and correlations are made with the different aspect ratios of the fillers in the frame of mean field theory models, allowing for the estimation of interfacial thermal resistance.

This work aimed at thermal transport characterization of high density polyethylene (HDPE) filled with 5 and 50 mu m expanded graphite (EG) particles and with 0.4 mu m unexpanded graphite (UG) particles. Sample platelets were produced by melt mixing followed by compression molding. Thermal conductivity k was determined by combining measurements of density, specific heat capacity and thermal diffusivity, the latter by modulated photothermal radiometry (PTR). Starting from an effective medium approximation model, we derived a linearized expression for the effective k of composites with low particle charge. It explains the unusually high experimental k values (up to four-fold increase) as the effect of strongly non-spherical EG particles (aspect ratio 1/p = 110-290). Larger particle sizes produce higher k enhancement, while the interfacial thermal resistance (R-bd = 21.10(-7) m(2).K/W) has an opposite effect. The same model is consistent with experimental k for low particle charge HDPE/UG composites. At higher particle charge the model fails due to particle interaction leading to validity break of the effective medium approximation. (C) 2012 Elsevier Masson SAS. All rights reserved.

Submitted by Jairo Amaro (jairo.amaro@sibi.ufrj.br) on 2019-06-28T13:23:42Z No. of bitstreams: 1 2012_COTTA_IJT_v33_p1-10-min.pdf: 268917 bytes, checksum: 99cd157df3011793fb3240e9444f53f9 (MD5) Made available in DSpace on 2019-06-28T13:23:42Z (GMT). No. of bitstreams: 1 2012_COTTA_IJT_v33_p1-10-min.pdf: 268917 bytes, checksum: 99cd157df3011793fb3240e9444f53f9 (MD5) Previous issue date: 2012-06-24 Indisponível. In this research, the thermal diffusivity of composites based on ethylene- vinyl acetate (EVA) copolymer filled with two kinds of reinforcement graphite materials was investigated. The reinforcement graphite fillers were untreated natural graphite (UG) and expanded graphite (EG). Composite samples up to 29.3 % graphite particle volumetric concentrations (50 % mass concentration) were prepared by the melt- mixing process in a Brabender Plasticorder. Upon mixing, the EG exfoliates in these films having nanosized thicknesses as evidenced by TEM micrographs. Thus, the thermal diffusivity and electrical conductivity of composites based on the ethylene-vinyl acetate matrix filled with nanostructuralized expanded graphite and standard, micro-sized graphite were investigated. From the experimental results it was deduced that the electrical conductivity was not only a function of filler concentration, but also strongly dependent on the graphite structure. The percolation concentration of the filler was found to be (15 to 17) vol% for micro-sized natural graphite, whereas the percolation concentration of the filler in nanocomposites filled with expanded graphite was much lower, about (5 to 6) vol%. The electrical conductivity of nanocomposites was also much higher than the electrical conductivity of composites filled with micro-sized filler at similar concentrations. Similarly, the values of the thermal diffusivity for the nanocomposites, EG-filled EVA, were significantly higher than the thermal diffusivity of the composites filled with micro-sized filler, UG-filled EVA, at similar concentrations. For 29.3 % graphite particle volumetric concentrations, the thermal diffusivity was 8.23 × 10−7 m2 · s−1 for EG-filled EVA and 6.14 × 10−7 m2 · s−1 for UG-filled EVA. The thermal diffusivity was measured by the flash method.

This study intends to produce plasma polymer thin films of γ-glycidoxypropyltrimethoxysilane (γ-GPS) on glass fibers in order to improve interfacial adhesion of glass fiber-reinforced epoxy composites. A low frequency (LF) plasma generator was used for the plasma polymerization of γ-GPS on the surface of glass fibers at different plasma powers and exposure times. X-ray photoelectron spectroscopy (XPS) and SEM analyses of plasma polymerized glass fibers were conducted to obtain some information about surface properties of glass fibers. Interlaminar shear strength (ILSS) values and interfacial shear strength (IFSS) of composites reinforced with plasma polymerized glass fiber were evaluated. The ILSS and IFSS values of non-plasma polymerized glass fiber-reinforced epoxy composite were increased 110 and 53%, respectively, after plasma polymerization of γ-GPS at a plasma power of 60 W for 30 min. The improvement of interfacial adhesion was also confirmed by SEM observations of fractured surface of the composites.

In this study, glass fibers. were modified using gamma-glycidoxypropyltrimethoxysilane of different concentrations to improve the interfacial adhesion at interfaces between fibers and matrix. Effects of gamma-glycidoxypropyltrimethoxysilane on mechanical properties and fracture behavior of glass fiber/epoxy composites were investigated experimentally. Mechanical properties of the composites have been investigated by tensile tests, short beam tests, and flexural tests. The short-beam method was used to measure the interlaminar shear strength (ILSS) of laminates. The tensile and flexural properties of composites were characterized by tensile and three-point bending tests, respectively. The fracture surfaces of the composites were observed with a scanning electron microscope. On comparing the results obtained for the different concentrations of silane solution, it was found that the 0.5% GPS silane treatment provided the best mechanical properties. The ILSS value of heat-cleaned glass fiber reinforced composite is enhanced by similar to 59% as a result of the glass fiber treatment with 0.5% gamma-GPS. Also, an improvement of about 37% in tensile strength, about 78% in flexural strength of the composite with the 0.5% gamma-GPS treatment of glass fibers was observed. POLYM. COMPOS., 30:1251-1257, 2009. (C) 2008 Society of Plastics Engineers

The primary purpose of the study is to evaluate and compare the mechanical properties of epoxy-based composites having different fiber reinforcements. Glass and carbon fiber composite laminates were manufactured by vacuum infusion of epoxy resin into two commonly used noncrimp stitched fabric (NCF) types: unidirectional and biaxial fabrics. The effects of geometric variables on composite structural integrity and strength were illustrated. Hence, tensile and three-point bending flexural tests were conducted up to failure on specimens strengthened with different layouts of fibrous plies in NCF. In this article, an important practical problem in fibrous composites, interlaminar shear strength as measured in short beam shear test, is discussed. The fabric composites were tested in three directions: at 0°, 45°, and 90°. In addition to the extensive efforts in elucidating the variation in the mechanical properties of noncrimp glass and carbon fabric reinforced laminates, the work presented here focuses, also, on the type of interactions that are established between fiber and epoxy matrix. The experiments, in conjunction with scanning electron photomicrographs of fractured surfaces of composites, were interpreted in an attempt to explain the failure mechanisms in the composite laminates broken in tension. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

In this study, effects of fiber surface treatments on mechanical behavior and fracture mechanism of glass fiber/epoxy composites were investigated experimentally. To change the composition of the glass and regenerate to the hydroxyl groups, activation pretreatment of heat cleaned woven glass fabric was performed using (v/v) HCl aqueous solution at different concentrations before silane treatment. The treatment of silanization of heat cleaned and acid activated glass fibers with gamma-glycidoxypropyltrimethoxysilane were performed. In this work, short beam shear test has been conducted to determine the performance of the acid treatment and the silane treatment in terms of the interlaminar shear strength. The silane coating on the heat cleaned glass fibers increased the interlaminar shear strength of the composite. However, the silane coating on the acid activated glass fibers did not improve the interlaminar shear strength of the composite. In addition, the strengths of the glass fabric specimens in tension and flexure were investigated. When the glass fibers are first treated with HCl solution and then with silane coupling agent, the tensile strengths of the composites decreased significantly. Scanning electron photomicrographs of fractured surfaces of composites were performed to explain the failure mechanisms in the composite laminates broken in tension.

We present a new application of a hot wire sensor for simultaneous and independent measurement of thermal conductivity k and diffusivity a of (nano)fluids, based on a hot wire thermal probe with ac excitation and 3 omega lock-in detection. The theoretical modeling of imaginary part of the signal yields the k value while the phase yields the alpha value. Due to modulated heat. flow in cylindrical geometry with a radius comparable to the thermal diffusion length, the necessary sample quantity is kept very low, typically 25 mu l. In the case of relative measurements, the resolution is 0.1% in k and 0.3% in alpha. Measurements of water-based Aerosil 200V nanofluids indicate that ultrasound treatment is more efficient than high pressure dispersion method in enhancing their thermal parameters.

In this study thermal conductivity of tarhana, a traditional Turkish fermented food product, was measured over the temperature range -25 degrees C and +50 degrees C using the needle probe method. Empirical equations for thermal conductivity calculations were obtained by application of statistical analysis to the results. Thermal conductivity of the samples was found to increase with temperature in the unfrozen state; in the frozen state it decreased with temperature. The probe method of conductivity measurement was found to give accurate and consistent results. (c) 2006 Elsevier Ltd. All rights reserved.

The aim of the experimental study is to determine thermal conductivity of composites as a function of volume fraction and size of aluminum (Al) particles. High density polyethylene (HDPE) were filled with Al particles that have different particle sizes, 80 nm and 40-80 μm. Nanocomposites were prepared by the melt-mixing technique at various volume fractions (up to 33%). Thermal conductivity of polymer composites has been measured by C-Therm thermal analyzer depending on the modified transient plane source technique. Thermal conductivity of HDPE/Al composites increases by increasing volume fraction of Al in HDPE matrix. It is found that size of Al particles hasn’t significant effect on thermal conductivity, thermal conductivity of HDPE/Al (80 nm) is close to thermal conductivity of HDPE/Al (40-80 μm).

Conductive polymer composites were prepared by mixing high density polyethylene (HDPE) with aluminum powder at various volumetric concentrations, then the mixed sample is placed in a die and melted at 185 degrees C under 4 MPa pressure. The filler content varies from the pure HDPE to 50% by volume of aluminum particles. After cooling and solidification under pressure the samples are taken out of the die, for thermal diffusivity measurements, samples are rectangular in form with 20mm length, 10mm width, and 1mm thickness. The matrix material is commercial high density polyethylene in powder form, density 0.968 g/cm(3) melt index 5.8 g/10min. The metallic filler is aluminum in the form of fine powder with particle size in the range of 10-20 microns, the solid density of Al is 2.7 g/cm(3) and its solid thermal conductivity 204 W/mK. A microscopic study shows that aluminum particles are uniformly distributed in HDPE matrix, with no voids in the composite structure. Thermal diffusivity measurements were performed using photothermal method with step heating. Thermal diffusivity varied from 2.45x10(-7) m(2)/s for pure HDPE to 11.30x10(-7) m(2)/s for 50% by volume of aluminum particles. Heat capacities were also measured using a differential scanning calorimeter (DSC).

The effective thermal conductivity of two varieties of Triticum durum wheat and a wheat product, bulgur, is determined at different moisture contents and at ambient temperature by the transient line heat source method. The moisture contents of the samples ranged from 9.17 to 38.65 percent wet basis and the bulk densities ranged from 675 to 827 kg/m(3). Under those conditions, the measured effective thermal conductivities ranged from 0.159 to 0.201 W/m.K. The effective thermal conductivity is found to be linearly increasing with moisture content. The results are also in good agreement with literature values. (C) 1998 Elsevier Science Ltd.

In this study thermal diffusivity of two varieties of Triticum durum wheat and a wheat product, bulgur, is determined at different moisture contents and the results are compared with predictive models as well as with literature values. Thermal diffusivity is measured with transient heat conduction method which consists of placing a cylindrical sample in a constant temperature environment and recording the temperature at the center of the sample with respect to time. If the surface convective resistance is negligible, thermal diffusivity is determined from the time-temperature history and the dimensions of the sample. The measured thermal diffusivity values ranges between 8.92x10(-8) and 11.43x10(-8) m(2)/s for Eregli, 8.76x10(-8) and 10.78x10(-8) m(2)/s for Saruhan and 8.28x10(-8) m(2)/s for Bulgur. The results are in good agreement with literature values and close to Riedel and Martens models. (C) 1997 Elsevier Science Ltd.

The thermal conductivity and mechanical properties such as tensile strength, elongation at break, modulus of elasticity, and toughness of composites formed by copper powder filler embedded in a high density poly(ethylene) matrix are investigated experimentally and the results compared with existing theories. Thermal conductivity measurements are performed up to a filler concentration of 10 vol.%. A modified hotwire technique is used to measure the thermal conductivity. The conductivity is best predicted by the Lewis and Nielsen model which takes into account the shape of the particles as well as the type of packing. The mechanical properties of high density poly(ethylene) filled with up to 18 vol.% Cu particles are investigated. The tensile strength, elongation at break and toughness decreased with increasing copper content. attributed to the introduction of discontinuities in the structure. The modulus of elasticity increased with increasing copper content.

High density polyethylene (HDPE) were filled with expanded graphite particles that have different particle sizes, 5-7 mu m (EG5) and 40-55 mu m (EG50) in diameter. Nanocomposites were prepared by the melt-mixing technique using EG5 and EG50 at different weight ratios. Transmission Electron Microscopy (TEM) was used to observe the morphology of the nanocomposites. X-ray diffraction patterns of EG5-HDPE and EG50-HDPE nanocomposites were investigated. Tensile tests were carried out to determine tensile strength, Young's modulus and elongation at break values. The storage modulus and loss modulus were evaluated by Dynamic Mechanical Analysis (DMA). The effect of EG5 and EG50 on electrical conductivity of HDPE was also determined. The tensile strength of HDPE increased 18.7% and 8.5% when 40 wt% EG5 and EG50 was added into HDPE, respectively. The storage modulus of EG5-HDPE and EG50-HDPE is higher compared to that of HDPE. Incorporation of EG5 and EG10 into HDPE also increased the relaxation transition peak of HDPE. The values of electrical conductivity for EG50-HDPE nanocomposites under the same filler content obtained higher in comparison with those for EG5-HDPE nanocomposites. (C) 2013 Elsevier Ltd. All rights reserved.

Polymer composites with high thermal conductivity are used more frequently in thermal management of electronic packaging systems. In this study, conductive polymer composites were prepared by melt mixing of ethylene-vinyl acetate (EVA) copolymer with graphite at different volumetric concentrations up to 29.3%. Two kinds of graphite were used as reinforcement to prepare composites: untreated natural graphite (UG) having particle sizes ranging from 20 mu m to 25 mu m and expanded graphite (EG) having originally particle sizes ranging from 5 to 6 mu m in length. Upon mixing at high shear forces EG exfoliates in thin sheets of a few nanometers in thickness. Due to this high aspect ratio of graphite sheets, nanocomposites filled with expanded graphite have a lower percolation threshold for electrical conductivity, about (5 to 6) vol.% compared to the composites filled with untreated graphite (UG) which have a percolation threshold of (15 to 17) vol.%. Thermal diffusivity of the samples was measured by photothermal radiometry. At similar concentrations, thermal diffusivity values for the nanocomposites, EG-filled EVA, were significantly higher than those composites filled with UG.

In this research thermal and fluid fields of a 32-inch commercial thin film transistor liquid crystal display (TFT-LCD) TV panel were investigated numerically and experimentally. The new trend in the production of TFT-LCD, TV panel is to have slimmer screen displays. The original design with 180 LEDs (light emitting diodes) placed at the top and bottom edges of the panels was modified. In the new design, the panels were illuminated using only 72 LEDs placed underside and inside the panels. By this modification an important cost reduction has been achieved alongside having slimmer screen displays. Heat dissipated by these 72 LEDs must be removed in order to assure good image quality and long service life. Hence an appropriate thermal management is indispensable. To analyze temperature distribution at steady state condition a CFD (computational fluid dynamics) computer code 'FloEFD' was used. The results obtained from the computational analysis have been validated by using experimental techniques. For this purpose thermocouples were attached on the panel and after the steady state has been reached, temperatures have been recorded in order to compare them to the distribution obtained by 'FloEFD'. Furthermore, a thermal camera image of the panel by FLIR Thermacam SC2000 test device was obtained as another validation for temperature distribution. © 2012 IEEE.

The effective thermophysical and optical properties of high density polyethylene (HDPE) filled with 50 mu m and 5 mu m particle sizes of expanded graphite (EG50, EG5) are characterized. The methods used were front- and back-detection modulated photothermal radiometry (FD-, BD-PTR) and BD-flash IR thermography. Results were interpreted according to one-dimensional heat diffusion models. The absolute thermal diffusivity was determined at low frequency from FD- and BD-PTR spectra, while the volumetric heat capacity, the thermal effusivity, and the optical absorption coefficient were determined from broad-band FD-PTR spectra. The directly obtained diffusivity values compare well with those calculated from the heat capacity and thermal effusivity, and with BD-flash results. The errors caused by the finite absorption coefficient of diluted samples are also evaluated and corrected for. A particle-size effect with the opposite influence on thermal and optical properties has been observed. Heat transport parameters of HDPE/EG composites are significantly enhanced (factor of 3 to 4 in thermal diffusivity) at low particle charge before reaching saturation above a 0.10 particle volume fraction. These features are explained in the framework of effective medium models by strongly non-spherical EG particles.

In this study, we investigate the Dikili geothermal district heating system (GDHS) in Izmir, Turkey. The system mainly consists of three cycles, namely (i) the transportation network, (ii) the Danistay region, and (iii) the Bariskent region. While the Bar Construction & Building Technology; Green & Sustainable Science & Technology Construction & Building Technology; Science & Technology - Other Topics

High-density polyethylene (HDPE)/graphite nanocomposites containing up to 30 vol% of graphite powder filler were prepared by melt mixing in a Brabender Plasticorder at 180 degrees C for 15 min. The nanocomposites were characterized for their rheological, dynamic mechanical, crystallographic, and electrical properties as a function of graphite loading. The results indicated that graphite loading affects storage modulus, loss modulus, complex viscosity, and conductivity of HDPE matrix. The storage modulus increases while the graphite loading increases in the studied concentration range (up to 30%). When the graphite loading was increased to 30%, storage modulus at room temperature was about 300% higher than that of pure HDPE. Also, the composites containing 20 and 30% graphite shows more conductivity than the others. POLYM. COMPOS., 2012. (C) 2012 Society of Plastics Engineers

This research explored the thermal analysis and modeling of a 32'' thin film transistor liquid crystal display (TFT-LCD) panel, in the purpose of making possible improvements in cooling efficiencies. The illumination of the panel was insured by 180 light emitting diodes (LEDs) located at the top and bottom edges of the panels. These LEDs dissipate high heat flux at low thermal resistance. Hence, in order to insure good image quality in panels and long service life, an adequate thermal management is necessary. For this purpose, a commercially available computational fluid dynamics (CFD) simulation software "FloEFD" was used to predict the temperature distribution. This thermal prediction by computational method was validated by an experimental thermal analysis by attaching 10 thermocouples on the back cover of the panel and measuring the temperatures. Also, thermal camera images of the panel by FLIR Thermacam SC 2000 test device were also analyzed. © 2011 IEEE.

In recent years, LCD (Liquid Crystal Display) TVs are taking the place of CRT (Cathode Ray Tube) TVs very fast by bringing new display technologies into use. LCD module technology is divided into two main groups; the first one is CCFL (Cold Cathode Fluorescent Lamp) display which was the first type used in LCD TV, the other one is the LED (Light Emitting Diode) module which is the newest display technology comes to make slim TV design. There is a thermal challenge making slim TV design. The purpose of this paper is to investigate the thermal analysis and modeling of a 32'' TFT-LCD LED module, The performance of LCD TV is strongly dependant on thermal effects such as temperature and its distribution on LCD displays The illumination of the display was insured by 180 light emitting diodes (LEDs) located at the top and bottom edges of the modules. Hence, in order to insure good image quality in display and long service life, an adequate thermal management is necessary. For this purpose, a commercially available computational fluid dynamics (CFD) simulation software "FloEFD" was used to predict the temperature distribution. This thermal prediction by computational method was validated by an experimental thermal analysis by attaching 10 thermocouples on the back cover of the modules and measuring the temperatures. Also, thermal camera images of the display by FLIR Thermacam SC 2000 test device were also analyzed. © 2011 IEEE.

This work aimed at thermal transport characterization of high density polyethylene (HDPE) filled with two sizes (5 and 50 mu m) of expanded graphite (EG) particles. Sample platelets were produced by melt mixing followed by compression molding. Thermal conductivity k was determined by combining measurements of density, specific heat capacity and thermal diffusivity. For the latter, we used the self-checking, non-contact method of photothermal radiometry (PTR) in back detection configuration. Starting from an effective medium approximation model, we derived a simple linearized expression for the effective k of composites with low particle charge. It explains the unusually high experimental k values (up to four-fold increase) as the effect the strongly non-spherical EG particles (aspect ratio 1/p = 110 - 290). Larger particle sizes produce higher k enhancement, while the interfacial thermal resistance (R-bd = 2.1.10(-7) m(2).K/W) has an opposite effect on k. The eventual deviation of experimental k from the model at high particle charge is possibly due to limitation of interparticle free space preventing random orientation of high aspect ratio particles.

This paper reports an experimental work on the measurements of thermal conductivity and viscosity of Al2O3-water and Al2O3-ethylene glycol nanofluids. Results show that thermal conductivity values are within the limits of Maxwell model while viscosity increases dramatically with increasing particle concentration and decreases with increasing temperature. However, the relative viscosity is independent of temperature. Also pH, particle size and zeta potential of nanofluid samples are characterized.

Recently we reported on simultaneous thermal conductivity k and thermal diffusivity a measurement of liquids and in particular of nanofluids in a configuration using an ac excited hot wire combined with lock-in detection of the third harmonic (3 omega method) [1]. The conductive wire is used as both heater and sensor. The requirements for the asymptotic validity of the line heat source model are fulfilled at low modulation frequencies below a few Hz. The study of the relative sensitivity of signal amplitude and phase to changes in k and a indicates that there is an optimum frequency range for accurate and stable results. We extend by up to two decades the feasible frequency range for 3 omega measurements by considering various more elaborate models for the heat transfer between the wire and the fluid. Finally we show that the same ac hot wire method can be applied to soft solid, composite materials. We measured the k enhancement of a poly(ethylene vinyl acetate) EVA polymer matrix charged with various fractions of graphite.

In this study we report a literature review on the research and development work concerning thermal conductivity of nanofluids as well as their viscosity. Different techniques used for the measurement of thermal conductivity of nanofluids are explained, especially the 3 omega method which was used in our measurements. The models used to predict the thermal conductivity of nanofluids are presented. Our experimental results on the effective thermal conductivity by using 3 omega method and effective viscosity by vibro-viscometer for SiO2-water, TiO2-water and Al2O3-water nanofluids at different particle concentrations and temperatures are presented. Measured results showed that the effective thermal conductivity of nanofluids increase as the concentration of the particles increase but not anomalously as indicated in the some publications and this enhancement is very close to Hamilton-Crosser model, also this increase is independent of the temperature. The effective viscosities of these nanofluids increased by the increasing particle concentration and decrease by the increase in temperature, and cannot be predicted by Einstein model.

Thermal conductivity and viscosity of deionized water-based TiO(2), SiO(2), and Al(2)O(3) nanofluids were investigated for various volume fractions of nanoparticles content and at different temperatures. A 3 omega technique was developed for measuring thermal conductivity of nanofluids. The theory and the experimental setup of the 3 omega measuring system is explained; a conductive wire is used as both heater and sensor in this system. At first, the system is calibrated using water with known thermophysical properties. Measured results showed that the effective thermal conductivity of nanofluids increases as the concentration of the particles increases but not anomalously as indicated in the majority of the literature and this enhancement is very close to the Hamilton-Crosser model; also this increase is independent of the temperature. The effective viscosities of these nanofluids increase by the increasing particle concentration and decrease with an increase in temperature, and cannot be predicted by the Einstein model.

The primary purpose of the study is to investigate the temperature dependence of heat capacity and thermal conductivity of composites having different fiber/matrix combinations by means of heat-flux differential scanning calorimetry (DSC). The materials used as samples in this study were epoxy- and polyester-based composites. Noncrimp stitched glass, carbon, and aramid fabric were used as reinforcements for making unidirectional composites. For the heat capacity measurements the composite sample and a standard material are separately subjected to same linear temperature program. By recording the heat flow rate into the composite sample as a function of temperature, and comparing it with the heat flow rate into a standard material under the same conditions, the temperature dependence of heat capacity of the composite sample is determined. Measurements were carried out over a wide range of temperatures from about 20 to 250 degrees C. The differential scanning calorimeter was adapted to perform the thermal conductivity measurements in the direction perpendicular to the fiber axis over the temperature range of 45-235 degrees C. The method used in this study utilizes the measurement of rate of heat flow into a sensor material during its first-order phase transition to obtain the thermal resistance of a composite material placed between the sensor material and the heater in the DSC. POLYM. COMPOS., 30:1299-1311, 2009. (C) 2008 Society of Plastics Engineers

This study aims to form a functional film on the glass substrates by plasma polymerization of glycidoxypropyltrimethoxysilane (gamma-GPS). Low frequency plasma generator was used to prepare plasma polymer thin films of gamma-GPS (PlzP-gamma-GPS) on glass substrates at different plasma powers (30, 60 and 90W) and exposure times (5, 15 and 30 min). XPS analyses were utilized to reveal the presence of functional groups in plasma polymer films. When higher plasma powers are applied, relative amount of Si-C bonds decreases and the amount of Si-O bonds increases. Contact angle measurements were performed to evaluate surface characteristics. Atomic force microscopy (AFM) studies were carried out to elucidate morphological changes. From AFM observations, it was obtained that the surface roughness slightly increased with the increase of plasma power from 30 to 90 W. (C) 2009 Elsevier B.V. All rights reserved.

nanofluids were investigated for various volumefractions of nanoparticles content and at different temperatures. A 3ωtechnique was developed for measuring thermal conductivity of nano-fluids. The theory and the experimental setup of the 3ω measuringsystem is explained; a conductive wire is used as both heater and sen-sor in this system. At first, the system is calibrated using water withknown thermophysical properties. Measured results showed that theeffective thermal conductivity of nanofluids increases as the concen-tration of the particles increases but not anomalously as indicated inthe majority of the literature and this enhancement is very close tothe Hamilton–Crosser model; also this increase is independent of thetemperature. The effective viscosities of these nanofluids increase by

Thermal conductivities of three different edible oils, namely sunflower oil, corn oil and olive oil, were measured at temperatures 25, 40, 60, and 80 degrees C. The measurements were carried out using a hot wire probe method. The calibration of the probe was performed using 0.3% agar gel with water and glycerin. In general, thermal conductivities of oils used in this study are found to be decreasing with temperature. The values of thermal conductivity measured are quite near to each other, the highest and the lowest being respectively 0.168 W/m K for sunflower oil at 25 degrees C and 0.152 W/m K for corn oil at 80 degrees C.

In this study, the thermal conductivity and viscosity of TiO2 nanoparticles in deionized water were investigated up to a volume fraction of 3% of particles. The nanofluid was prepared by dispersing TiO2 nanoparticles in deionized water by using ultrasonic equipment. The mean diameter of TiO2 nanoparticles was 21 nm. While the thermal conductivity of nanofluids has been measured in general using conventional techniques such as the transient hot-wire method, this work presents the application of the 3 omega method for measuring the thermal conductivity. The 3 omega method was validated by measuring the thermal conductivity of pure fluids (water, methanol, ethanol, and ethylene glycol), yielding accurate values within 2%. Following this validation, the effective thermal conductivity of TiO2 nanoparticles in deionized water was measured at temperatures of 13 A degrees C, 23 A degrees C, 40 A degrees C, and 55 A degrees C. The experimental results showed that the thermal conductivity increases with an increase of particle volume fraction, and the enhancement was observed to be 7.4% over the base fluid for a nanofluid with 3% volume fraction of TiO2 nanoparticles at 13 A degrees C. The increase in viscosity with the increase of particle volume fraction was much more than predicted by the Einstein model. From this research, it seems that the increase in the nanofluid viscosity is larger than the enhancement in the thermal conductivity.

Received 18 August 2006; accepted 26 November 2007DOI 10.1002/app.27857Published online 5 February 2008 in Wiley InterScience (www.interscience.wiley.com).ABSTRACT: Polyester- and epoxy-based composites con-taining glass and carbon fibers were manufactured using avacuum-assisted resin transfer molding (VARTM) process.Fourier transform infrared (FTIR) spectroscopy analyseswere conducted to determine the interaction betweenfibers and matrix material. The results indicate that stronginteraction was observed between carbon fiber and epoxyresin. However, weak interactions between remaining fiber-matrix occur. Scanning electron microscopy (SEM) analysiswas also performed to take some information about strengthof interaction between fibers and matrix material. From SEMmicrographs, it is concluded that the findings in SEM analy-sis support to that obtained in FTIR analysis. Another aim ofthe present work was to investigate the influence of matrixon composite properties. Hence, the strengths of compositeshaving same reinforcement but different matrix systems inaxial tension and transverse tension were compared. Shortbeam shear test has been conducted to characterize the inter-facial strength in the composites.

The primary purpose of the study was to investigate the anisotropic behavior of different noncrimp stitched fabric reinforced polyester composites. The effects of geometric variables on composite structural integrity and strength are illustrated. Hence, tensile, three-point bending flexural and short beam shear tests were conducted up to failure on specimens strengthened with different layouts of fibrous plies in noncrimp stitched fabric. The remark, based on the observations while tensile testing, is that the stress–strain curves of polyester based composites were linear in the direction of fibers. However, in the matrix dominated orientations nonlinear relation between the stress and the strain was observed. Another aim of the present work was to investigate the interaction between glass fiber and polyester matrix. The experiments, in conjunction with scanning electron photomicrographs of fractured surfaces of composites, were interpreted in an attempt to explain the interaction between glass fiber and polyester and were interpreted in an attempt to explain the instability of polyester resin–glass fiber interfaces. It was concluded that the polymer was either deposited between adjacent fibers or as widely separated islands on the fiber surface. Infrared spectra of the cured polyester and its glass fiber composite were obtained by Fourier transform infrared spectroscopy. POLYM. COMPOS., 2008. © 2007 Society of Plastics Engineers

This study deals with determination of optimum pipe diameters based on economic analysis and the performance analysis of geothermal district heating systems along with pipelines using energy and exergy analysis methods. In this regard, the Dikili geothermal district heating system (DGDHS) in Izmir, Turkey is taken as an application place, to which the methods presented here are applied with some assumptions. The system mainly consists of three cycles, namely (i) the transportation network, (ii) the Danistay region, and (iii) the Bariskent region. The thermal capacities of these regions are 21,025 and 7975 kW, respectively, while the supply (flow) and return temperature values of those are 80 and 50 °C, respectively. Based upon the assessment of the transportation network using the optimum diameter analysis method, minimum cost is calculated to be US$ 561856.906 year −1 for a nominal diameter of DN 300. The exergy destructions in the overall DGDHS are quantified and illustrated using exergy flow diagram. Furthermore, both energy and exergy flow diagrams are exhibited for comparison purposes. It is observed through analysis that the exergy destructions in the system particularly take place due to the exergy of the thermal water (geothermal fluid) reinjected, the heat exchanger losses, and all pumps losses, accounting for 38.77%, 10.34%, 0.76% of the total exergy input to the DGDHS. Exergy losses are also found to be 201.12817 kW and 1.94% of the total exergy input to the DGDHS for the distribution network. For the system performance analysis and improvement, both energy and exergy efficiencies of the overall DGDHS are investigated, while they are determined to be 40.21% and 50.12%, respectively.

Thermal conductivity of copper powder filled polyamide composites are investigated experimentally in the range of filler content 0-30% by volume for particle shape of short fibers and 0-60% by volume for particle shapes of plates and spheres. The thermal conductivity of polymer composites is measured by the Hot-Disk method. It is seen that the experimental values for all the copper particle shapes are close to each other at low particle content, φ

In this study, thermal conductivity of particle filled polymer composites is investigated numerically and experimentally. In the numerical study, the finite-element program ANSYS is used to calculate the thermal conductivity of the composite by using the results of the thermal analysis. Three-dimensional models are used to simulate the microstructure of composite materials for various filler concentrations at various ratios of thermal conductivities of filler to matrix material. The models used to simulate particle filled composite materials are cubes in a cube lattice array and spheres in a cube lattice array. A modified hot wire method is used to measure the thermal conductivity of the composites consisting of a high-density polyethylene (HDPE) matrix filled with tin particles up to 16% by volume. The experimentally measured thermal conductivities are compared with numerically calculated ones by using the spheres in cube model and also with the already existing theoretical and empirical models. At low particle content, up to 10% of volume content of tin filler, numerical estimation and all other models except for the Cheng and Vachon model, predict well the thermal conductivity of the composite. For more heavily filled composites there is an exponential increase in thermal conductivity and most of the models fail to predict thermal conductivity in this region.

In this study, the effective thermal conductivity of aluminum filled high-density polyethylene composites is investigated numerically as a function of filler concentration. The obtained values are compared with experimental results and the existing theoretical and empirical models. The thermal conductivity is measured by a modified hot-wire technique. For numerical study, the effective thermal conductivity of particle-filled composite was calculated numerically using the micro structural images of them. By identifying each pixel with a finite difference equation and accompanying appropriate image processing, the effective thermal conductivity of composite material is determined numerically. As a result of this study, numerical results, experimental values and all the models are close to each other at low particle content, For particle content greater than 10%, the effective thermal conductivity is exponentially formed. All the models fail to predict thermal conductivity in this region. But, numerical results give satisfactory values in the whole range of aluminum particle content. (C) 2002 Elsevier Science Ltd. All rights reserved.

In designing food freezing equipment and processes, knowledge of physical and thermal properties of foods is essential. The computation of refrigeration requirements and freezing times can be done only when quantitative information on food properties is available. Considerable research has been done to measure and model properties of foods undergoing various processing treatments. The key properties of interest in food freezing include density, thermal conductivity, specific heat and thermal diffusivity.

Thermal conductivity of eleven kinds of cheese, four kinds of yogurt and a butter sample has been measured at about 15 degrees C and 30 degrees C. A modified hot wire method was used for thermal conductivity measurements. The effect of the water, fat and protein content on the thermal conductivity has been investigated, the measured thermal conductivity values were linearly dependent on water content, and inversely dependent on fat and protein contents of the various dairy products. A slight increase in the thermal conductivity with temperature has been noticed for four cheese samples studied over a wider range of temperature, between 4 degrees C and 44 degrees C. (C) 1999 Elsevier Science Ltd. All rights reserved.

Thermal conductivity and mechanical properties such as tensile strength, elongation at break, and modulus of elasticity of aluminum powder-filled high-density polyethylene composites are investigated experimentally in the range of filler content 0-33% by volume for thermal conductivity and 0-50% by volume for mechanical properties. Experimental results from thermal conductivity measurements show a region of low particle content, 0-12% by volume, where the particles are distributed homogeneously in the polymer matrix and are not interacting with each other; in this region most of the thermal conductivity models for two-phase systems are applicable. At higher particle content, the filler tends to form agglomerates and conductive chains resulting in a rapid increase in thermal conductivity. The model developed by Agari and Uno estimates the thermal conductivity in this region. Tensile strength and elongation at break decreased with increasing aluminum particles content, which is attributed to the introduction of discontinuities in the structure. Modulus of elasticity increased up to around 12% volume content of aluminum particles. Einstein's equation, which assumes perfect adhesion between the filler particles and the matrix, explains the experimental results in this region quite well. For particle content higher than 30%, a decrease in the modulus of elasticity is observed which may be attributed to the formation of cavities around filler particles during stretching in tensile tests. (C) 1996 John Wiley & Sons, Inc.

In this study, various conduction models for two-phase materials are considered and the range of applicability of these models is discussed. Experimental work is carried out on construction sand of various grain size and different porosity in air at atmospheric pressure, and the results are compared with theoretical models. A modified hot-wire method is used in the measurement of effective thermal conductivities.

In this paper the flash method of measuring the thermal diffusivity, heat capacity, and thermal conductivity is described. A high intensity short duration heat pulse is absorbed in the front surface of a thermally insulated disc shaped specimen. The thermal diffusivity is determined by the shape of the temperature versus time curve at the rear surface. The thermal diffusivity is then given by: a = 1, 38 e2/(π2.t1/2), where (t1/2) is the time required for the temperature of the rear face to reach half of the value of the maximum temperature rise and (e) is the thickness of the sample. Various methods to correct for the finite pulse time effect and for the heat losses are cited.