Thermal Diffusivity Values Research Articles

HiPIMS obtained carbon nano-coatings on copper foil and their thermal conductivity

To prevent overheating of high-power electronic devices, effective cooling and thermal management is a key issue. Owing to the extraordinarily high thermal conductivity of graphene structure in nature, an approach for growth of carbon nano-coating with multiplex layer architecture on copper foil by using high power impulse magnetron sputtering (HiPIMS), as an alternative to the conventional chemical vapor deposition process, is reported for heat-spreading purposes. For successful deposition, a high peak current of 600 A with a short pulse of 30 μs at a relatively low substrate temperature of 600 °C was applied. Moreover, growth mechanisms without and with applying copper for Cu/carbon (Cu/C) nano-coating periodic deposition are revealed and discussed. Based on the measurement results using Angstrom's method, under optimum deposition time, the HiPIMS prepared carbon nano-coating with multiplex layer architecture, which contains in-plane-oriented multilayer graphene structure and the following out-of-plane-oriented turbostratic graphene structure, can enhance the heat spreading ability of the copper foil, reaching a thermal diffusivity value of 1.05 cm2/s. For Cu/C nano-coating periodic deposition, copper can act as catalyzing ingredient to inhibit amorphous carbon formation and promote the crystalline graphene-like structure growth, resulting in a further increase in the thermal diffusivity up to 1.21 cm2/s, twice that of the bare copper foil.

Effect of laser ablated gold nanoparticles on the nonlinear optical properties of π-extended BODIPY dyes

Dipyrromethene boron difluoride (BODIPY) and its derivatives have attracted considerable interest due to their remarkable photophysical properties beneficial for developing fluorescent sensors, biolabels, photodynamic therapy agents, photonic materials, and so on. Herein, we report gold nanoparticles (AuNPs) induced modulation of nonlinear optical properties of π-extended BODIPY derivatives BPA and BDIPA. The spherical gold nanoparticles with an average particle size of 11 ± 3.5 nm were synthesized by pulsed laser ablation technique and characterized by transmission electron microscopy and dynamic light scattering. The interaction of AuNPs with the dye molecules was confirmed by UV/vis absorption and steady-state emission spectroscopy studies. Further, the dual-beam thermal lens technique was used to validate dye-nanoparticle interaction. The thermal diffusivity values of the samples at an excitation wavelength of 532 nm were measured and found that the overall heat diffusion was slower in the AuNPs added samples than that of the dye alone sample, corroborating dye-nanoparticle interaction. The third-order nonlinear optical absorption properties of the samples were investigated by using the Z-scan technique in the infrared region (1064 nm). The open aperture configuration shows significant reverse saturable absorption characteristics for all the samples. Determination of nonlinear absorption coefficient for the dye samples at different input intensities identified two-photon absorption as the important mechanism that produces reverse saturable absorption. The AuNPs incorporated dye samples showed a substantial enhancement in the nonlinear optical behavior. The nonlinear absorption coefficient of the AuNPs incorporated dye samples (10 cm/GW) was enhanced almost two times than that of dye alone samples (5 cm/GW). The enhanced nonlinearity is attributed to the intense local field effect of AuNPs.

Thermal Properties of Illite-Zeolite Mixtures up to 1100 °C.

Illitic clays are the commonly used material in building ceramics. Zeolites are microporous, hydrated crystalline aluminosilicates, they are widely used due to their structure and absorption properties. In this study, illitic clay (Füzérradvány, Hungary) was mixed with natural zeolite (Nižný Hrabovec, Slovakia) with up to 50 wt.% of zeolite content. The samples were submitted to thermal analyses, such as differential thermal analysis, differential scanning calorimetry, thermogravimetry, and dilatometry. In addition, the evolution of thermal diffusivity, thermal conductivity, and specific heat capacity in the heating stage of firing were measured and discussed. The amount of the physically bound water in the samples increased along with the amount of zeolite. The temperature of the illite dehydroxylation (peak temperature) was slightly shifted to lower temperatures, from 609 °C to 575 °C (for sample IZ50). On the other hand, the mass loss and the shrinkage of the samples significantly increased with the zeolite content in the samples. Sample IZ50 reached 10.8% shrinkage, while the sample prepared only from the illitic clay contracted by 5.8%. Nevertheless, the temperature of the beginning of the sintering (taken from the dilatometric curves) decreased from 1021 °C (for illitic clay) to 1005 °C (for IZ50). The thermal diffusivity and thermal conductivity values decreased as the amount of zeolite increased in the samples, thus showing promising thermal insulating properties.

Anisotropic thermal diffusivity and conductivity in SiC/SiC tubes studied by infrared imaging and X-ray computed tomography

Traditional flash diffusivity evaluation of thermal diffusivity/conductivity of composite tubes require machining of specimens. For a thin-wall tube, this method can only be used to obtain through-thickness transport property. A novel method to evaluate anisotropic thermal diffusivity in a composite tube has been developed. Braided SiC/SiC composite tubes were subjected to a xenon flash heating pulse. A high-speed, high-sensitivity infrared camera was used to measure surface temperature changes as a function of time and nondestructively detect subsurface defects/damages, such as macroscopic pores. Standard reference material (Pyroceram 9606) and curved SiC/SiC composite tube specimens were used to validate thermal diffusivity obtained from infrared imaging. Unlike the traditional method, there is no need prepare special specimens, and thermal diffusivity values in three orientations are obtained after a single flash. A finite element analysis model based on x-ray computed tomography scans was developed to simulate the heat transfer. This technique is significant in assessing thermal conductivity and inspecting the health of ceramic tubes during and after service.

Thermal diffusivity recovery and defect annealing kinetics of self-ion implanted tungsten probed by insitu transient grating spectroscopy

Tungsten is a promising candidate material for plasma-facing armour components in future fusion reactors. A key concern is irradiation-induced degradation of its normally excellent thermal transport properties. In this comprehensive study, thermal diffusivity degradation in ion-implanted tungsten and its evolution from room temperature (RT) to 1073 K is considered. Five samples were exposed to 20 MeV self-ions at RT to achieve damage levels ranging from 3.2 × 10−4 to 3.2 displacements per atom (dpa). Transient grating spectroscopy with insitu heating was then used to study thermal diffusivity evolution as a function of temperature. Using a kinetic theory model, an equivalent point defect density is estimated from the measured thermal diffusivity. The results showed a prominent recovery of thermal diffusivity between 450 K and 650 K, which coincides with the onset of mono-vacancy mobility. After 1073 K annealing samples with initial damage of 3.2 × 10−3 dpa or less recover close to the pristine value of thermal diffusivity. For doses of 3.2 × 10−2 dpa or higher, on the other hand, a residual reduction in thermal diffusivity remains even after 1073 K annealing. Transmission electron microscopy reveals that this is associated with extended, irradiation-induced dislocation structures that are retained after annealing. A sensitivity analysis shows that thermal diffusivity provides an efficient tool for assessing total defect content in tungsten up to 1000 K.

Prediction of divertor heat flux width for ITER pre-fusion power operation using BOUT++ transport code

Prediction of divertor heat flux width is performed for the first and the second pre-fusion power operation (PFPO) phases specified in the new ITER research plan using BOUT++ transport code (Li et al 2018 Comput. Phys. Commun. 228 69–82). The initial plasma profiles inside the separatrix are taken from CORSICA scenario studies. Transport coefficients in transport code are calculated by inverting the plasma profiles inside the separatrix and are assumed to be constants in the scrape-off-layer. An anomalous thermal diffusivity scan is performed with E × B and magnetic drifts. The results in two scenarios identifying two distinct regimes: a drift-dominant regime when diffusivity is smaller than the respective critical thermal diffusivity χ c and a turbulence-dominant regime when diffusivity is larger than it. The Goldston heuristic drift model and the ITPA multi-machine experimental scaling yield a lower limit of the width λ q . From transport simulations, we obtain the critical thermal diffusivity χ c = 0.5 m2 s−1 for the PFPO-1 scenario with toroidal magnetic field B = 1.77 T and plasma current I p = 5 MA, and χ c = 0.3 m2 s−1 for the PFPO-2 scenario with toroidal magnetic field B = 2.65 T and plasma current I p = 7.5 MA. Separatrix temperature and collisionality also have a significant impact on the heat flux width in the drift-dominant regime. The investigation clearly yields a scaling for critical thermal diffusivity using ITER scenarios with fixed safety factor q 95, major radius R, aspect ratio R/a, and the separatrix temperature T sep, and establishes the connection with CFETR and C-Mod discharges. This scaling implies that for a given tokamak device with q 95, R, R/a, and T sep fixed, a reduction of poloidal magnetic field by a factor of 3 leads to a 9 times higher critical value of thermal diffusivity χ c, possibly yielding a transition from turbulence- to drift-dominant regime.

Determination of thermal properties (and their uncertainties) during the cooling of apples (Malus communis)

AbstractThe present study goal was to determine the thermal properties of apples during their cooling. Fuji apple was cooled in a domestic refrigerator by natural convection. Thermal properties were determined assuming the geometry of an equivalent sphere. An optimizer software (LS Optimizer) was used for the inverse problem. A new heat conduction software was developed to solve the direct problem, using the spherical geometry of the diffusion equation with the boundary condition of the third kind. Thus, thermal properties of apples and their uncertainties were calculated during cooling. The developed software for the direct problem was used to simulate the cooling kinetics for any previously specified point within the sphere. The fitting of the simulated curve to the experimental points showed coefficient of determination (R2) greater than 0.99 and low values of the chi‐square function (). Therefore, it can be concluded that the spherical geometry and the boundary condition of the third kind were adequate to describe the process of heat removal for apple. Determined values of thermal diffusivity and convective heat transfer coefficient wereα = (1.38 ± 0.07) × 10−7 m2 s−1andh = (1.360 ± 0.018) × 10−6 m s−1, respectively, with confidence intervals of 95.4%. Another confirmation of the developed model was the fact that the thermal diffusivity was similar to the estimate by Riedel correlation (α = 1.38 × 10−7 m2 s−1). The position of the thermocouple in the equivalent sphere calculated by numerical solution wasr = 6.6 mm.Practical ApplicationsOne of the main contributions of this paper is the calculation of thermal parameters along cooling with their uncertainties. This will result in very accurate simulation of the pasteurization and freezing processes. Furthermore, the values obtained in the study can be used to predict new cooling curves for the same product, but with different dimensions.

PENENTUAN SIFAT TERMAL CABAI PUYANG (Piper retrofractum Vahl.) KERING PADA TIGA TAHAP KEMATANGAN

Dried cabya (Piper retrofractum Vahl.) is commonly used in making various types of herbs, spices, and cosmetic raw materials that require heating processes so that they require information on the value of thermal conductivity (k), thermal diffusivity (α), and specific heat (Cp). The thermal properties of dried cabya are affected by different phytochemical compositions at each maturity stage of the fruit. This study aims to determine and analyze the thermal properties and phytochemical content of dried cabya in three stages of green, orange and red maturity. Measurement of thermal diffusivity in this study uses the principle of onedimensional unsteady-state conduction heat flow using a vertical thermal diffusivity test. The value of thermal conductivity is determined indirectly by a calculation method based on the value of thermal diffusivity, specific heat, and density of the material. The thermal conductivity values of green, orange, and red paste cabya are 0.241 ± 0.016, 0.298 ± 0.005, and 0.344 ± 0.025 W/m°C. Reducing sugar levels in dried green, orange, and red cabya are 2.32 ± 0.16, 4.07 ± 0.13, and 6.44 ± 0.13 %, piperine levels are 2.42 ± 0.01, 1.97 ± 0.06, and 1.54 ± 0.05 %, and antioxidant levels are 87.15, 75.26, and 63.38 mg/mL. Based on the results of the study, red dried cabya have higher values of α, Cp, and k compared to orange and green because they contain higher levels of water and reducing sugars. However, red dried cabya have piperin and antioxidant levels which are getting lower

Hydrazine-nitrate combustion synthesis of BaCeO3 preceramic powders: structure, morphology and thermophysical properties

In the present work, preceramic nanocrystallite barium cerate (BaCeO3) was successfully synthesized using the hydrazine-nitrate combustion method. Using carbon-free hydrazine (N2H4) as fuel significantly reduced the formation of carbonate by-products. Subsequent annealing of combustion products in the air atmosphere at temperatures in the range of 500–1000 °С yielded preceramic powders based on chemically and phase-pure BaCeO3. Characterization of the as-received powders was performed by X-ray diffraction, energy-dispersive X-ray spectroscopy (EDXS), scanning electron microscopy (SEM), simultaneous thermal analysis (DTA-TGA) and adsorption-structural analysis (N2, 77 K). Thermophysical properties of the sample annealed at 1000 °С were investigated using laser flash analysis (LFA) in the temperature interval of 1000 °С. As a result of a comprehensive study, the sequence of chemical and phase transformations that lead to the formation of barium cerate with a rhombic structure (Pnma, a = 6.2145 Å, b = 8.7776 Å, c = 6.2337 Å) during the thermal processing of combustion products was investigated. It was established that the average size of the obtained nanocrystals is 38 ± 3 nm and that they form micron-sized agglomerates with a specific surface area of the powder of 4.8 m2/g. It was shown that the sintered sample of barium cerate is characterized by thermal diffusivity values of 0.28 to 0.20 mm2/s and thermal conductivity values of 0.41–0.35 W/mK, depending on temperature. These results, given the impact of porosity on the sample (~40%), show very good agreement with the thermophysical characteristics of densely sintered ceramics based on BaCeO3—a solid oxide electrolyte SOFC. Consequently, the proposed method of hydrazine-nitrate synthesis of barium cerate presents itself as a promising approach to obtaining preceramic powders and ceramics in the area of solid oxide fuel cells.

Comparative Study of Thermophysical Parameters of Different Types of Upholstery Wood and the Influence of Density on Combustion Parameters at Microscale

The fire behaviour of five types of wood was studied on a microscale. Some thermophysical parameters such as thermal conductivity, effusivity and diffusivity were also evaluated. The microscale analysis is based on the analysis of several parameters such as the assessment of heat released rates (HRR), peak heat released rates (pHRR), total heat released (THR), enthalpy variation (Δh) and residue rates with the combustion microcalorimeter (PCFC). The PF2C device was used to measure the conductivity, effusivity and diffusivity of wood, while the PCFC for the microscale study of wood behaviour in combustive situations. In terms of thermal conductivity, wood conducts heat with difficulty, while the other types, namely frake, bete, tek and red wood, more easily conduct heat and therefore cannot be considered as thermal insulators. For results, in terms of measuring effusivity, white wood has the smallest value, which means that it exchanges less thermal energy with its environment. Red and tek woods exchange much more energy with the environment compared to other types of wood. We observe that tek wood has the highest diffusivity, which means that it is the wood that reacts as quickly as possible to the change in temperature. White and frake woods have the same value of thermal diffusivity as red and bete wood which have the lowest thermal diffusivities. The fire behaviour of these materials is a very little variable on the microscale and we can conclude that at this level there is no major difference for our different types of wood. Hence, there is no influence of density on the microscale. We can say that for the white and tek wood the complete combustion begins at 700°C. By this same method of analysis, we come to the conclusion that the frake, bete and red woods tend towards a complete combustion at 675°C. At 675°C the bete and frake woods have the best combustive yields, to a lesser extent than the red and tek woods. The bete wood has the highest activation energy and the white wood the lowest.

Determination of thermal properties of ternary Al-La-Ni cast alloy

In current work, thermal conductivity, enthalpy of fusion, specific heat, and thermal diffusivity of the Al-8.8La-1.2Ni cast alloy has been investigated. Chemical element analysis of the studied alloy was determined with X-Ray Fluorescence Spectrometer (XRF) and SEM microscopy with Energy Dispersive X-Ray Spectroscopy (EDS). Thermal conductivity of ascast Al-8.8La-1.2Ni alloy was measured using comparison cut bar method in the temperature range of 308–773 K. Thermal conductivity values decreased gradually in the studied alloy with the increase of temperature. The thermal temperature coefficient was calculated from the thermal conductivity-temperature graph. The heat flow-temperature curve was obtained by performing Differential Scanning Calorimetry (DSC) analysis. Enthalpy of fusion and specific heat values were also determined. Thermal diffusivity values were calculated as a function of temperature using the relevant equation. It was determined that the thermal diffusivity values increased with increasing temperature.

Acclimatization through thermal diffusivity tuning of coconut oil – A mode mismatched dual-beam thermal lens study

BackgroundAyurvedic medicinal oils traditionally prepared by blending herbal extracts in different compositions are commonly used for treatment and improving health. The estimation of the thermal properties of medicinal oils is essential for practical applications. ObjectiveThe present work aims to expound the ability of medicinal oils for the acclimatization of body temperature by determining its thermal diffusivity and thereby providing a validation to the traditional knowledge. Materials and methodsThe medicinal oils are prepared by incorporating black pepper (Piper nigrum), aloe vera (Aloe barbadensis), hibiscus bud (Hibiscus rosa-sinensis) and Ocimum sanctum in coconut oil base. The samples are subjected to thermal diffusivity study using the mode-mismatched dual-beam thermal lens technique. ResultsThe study reveals that the incorporation of black pepper (Piper nigrum), having hot potency (Ushna veerya), to the base fluid lowers the thermal diffusivity value, suggesting its potential in heat-trapping. The addition of aloe vera (Aloe barbadensis), hibiscus bud (Hibiscus rosa-sinensis), and O. sanctum dissipates heat energy quickly, thus increases the thermal diffusivity of coconut oil revealing a cold potency (Sheeta veerya). The study provides a validation for traditional knowledge and delineates the possiblity of thermal diffusivity tuning of the base fluids. ConclusionThe thermal diffusivity tuning through incorporation of herbal extracts can effectively be used to acclimatize the human body temperature with the surroundings. A higher thermal diffusivity value induces a cooling effect and the lower value causes heating effect. This, opens up the possibility of using thermally tuned oils depending on climate and geographical location.

Determination of thermal conductivity, thermal diffusivity and specific heat capacity of porous silicon thin films using the 3ω method

Here the thermal transport properties of low thermal conductivity porous silicon thin films attached to high thermal conductivity silicon substrates are studied using the 3ω method implemented over the 100 Hz to 33 kHz frequency range. The thermal conductivity and thermal diffusivity of the films are extracted using temperature impedance monitoring of electrical contacts deposited on films, combined with an extended-frequency, multi-layer thermal model. From the extracted thermal conductivity and diffusivity of the films, the heat capacity could be determined. Validation of the approach is performed using the known properties of thick substrate glass and SU-8 layers spun on silicon substrates, the latter ranging in thickness from 1.35 to 12.5 µm. The technique was then applied to porous silicon films with porosities ranging from 45% to 77%. The extracted thermal properties for as-fabricated films show a reduction of thermal conductivity and diffusivity from 1.7 to 0.15 W/mK and 1.9 to 0.2 mm2/s, respectively as the porosity increases. After passivation by annealing in nitrogen and at 600 °C, the same films exhibited higher values of thermal conductivity and diffusivity ranging from 2.7 to 0.7 W/mK and 2.5 to 0.65 mm2/s. The ability to extract both thermal conductivity and thermal diffusivity for these films removes the need to make assumptions around specific heat capacity, commonly made during analysis of porous media. These results show for the first time a monotonic increase in specific heat capacity of porous silicon films as a function of porosity.

Prospective theoretical investigations of optical, dielectric, mechanical and third-order NLO property in potassium tri-hydrogen di-succinate single crystal

A propitious third-order nonlinear optical crystal potassium tri-hydrogen di-succinate (PTHS) (C8H11O8K) is grown by conventional slow evaporation technique maintained at 303 K. Single crystal XRD analysis (SXRD) evidences the grown crystal pertain to centrosymmetric space group P21/c with monoclinic crystal system and powder X-ray diffraction (PXRD) confirms the purity of the grown crystal. The existence of various functional groups was assessed by Fourier transform infrared (FTIR) spectral analysis and the optical absorption study authenticates to the transparency in the visible region. ICP-OES study substantiates the prevalence of alkali metal potassium. Interestingly, the Urbach energy of the grown crystal is explored to be minimum proving the good crystalline nature of the yielded crystal. The various optical constants were calculated in detail. The optical band gap was used to determine the position of the valence band (Ev) and conduction band (Ec) and the Wemple-Di-Domenico single oscillator method was used to find the different dispersive parameters. In dielectric, the various solid state parameters including electronic polarizability were calculated with different formulas and the value was proved to be higher than that of KDP. To determine the mechanical stability, Vickers microhardness test was carried out and their indentation size effect was elucidated by using different models. The crystal exhibits negative photoconductivity. By using photo acoustic study, the thermal diffusivity value is 1.25 times greater than standard KDP, signifying that the harvested crystal is remarkable material for nonlinear optical applications. In brief, the real and imaginary parts are reviewed by Z-scan technique and the susceptibility was compared with other single crystals.

Through-Plane and In-Plane Thermal Diffusivity Determination of Graphene Nanoplatelets by Photothermal Beam Deflection Spectrometry.

In this work, in-plane and through-plane thermal diffusivities and conductivities of a freestanding sheet of graphene nanoplatelets are determined using photothermal beam deflection spectrometry. Two experimental methods were employed in order to observe the effect of load pressures on the thermal diffusivity and conductivity of the materials. The in-plane thermal diffusivity was determined by the use of a slope method supported by a new theoretical model, whereas the through-plane thermal diffusivity was determined by a frequency scan method in which the obtained data were processed with a specifically developed least-squares data processing algorithm. On the basis of the determined values, the in-plane and through-plane thermal conductivities and their dependences on the values of thermal diffusivity were found. The results show a significant difference in the character of thermal parameter dependence between the two methods. In the case of the in-plane configuration of the experimental setup, the thermal conductivity decreases with the increase in thermal diffusivity, whereas with the through-plane variant, the thermal conductivity increases with an increase in thermal diffusivity for the whole range of the loading pressure used. This behavior is due to the dependence of heat propagation on changes introduced in the graphene nano-platelets structure by compression.

Computational prediction of electrical and thermal properties of graphene and BaTiO3 reinforced epoxy nanocomposites

Graphene based materials e.g., graphene oxide (GO), reduced graphene oxide (RGO) and graphene nano platelets (GNP) as well as Barium titanate (BaTiO3) are emerging reinforcing agents which upon mixing with epoxy provides composite materials with superior mechanical, electrical and thermal properties as well as shielding against electromagnetic (EM) radiations. Inclusion of the aforementioned reinforcing agents has shown to improve the performance, however, the extent of improvement has remained uncertain. In this study, a computational modelling approach was adopted using COMSOL Multiphysics software in conjunction with Bayesian statistical analysis to investigate the effects of including various filler materials e.g. GO, RGO, GNP and BaTiO3 in influencing the direct current (DC) conductivity (σ), dielectric constant (ε) and thermal properties on the resulting epoxy polymer matrix composites. The simulation of epoxy composites were performed for different volume percentage of the filler materials by varying the geometry of the filler material. It was observed that the content of GO, RGO, GNPs and the thickness of graphene nanoplatelets can alter the DC conductivity, dielectric constant, and thermal properties of the epoxy matrix. The lower thickness of GNPs was found to offer the larger value of DC conductivity, thermal conductivity and thermal diffusivity than rest of the graphene nanocomposites, while, the RGO showed better dielectric constant value than neat epoxy, and GO, GNP nanocomposites. Similarly, BaTiO3 nanoparticles content and diameter were observed to alter the dielectric constant, DC conductivity and thermal properties of modified epoxy in several order magnitude than neat epoxy. In this way, the higher diameter particles of BaTiO3 showed better DC conductivity properties, dielectric constant value, thermal conductivity and thermal diffusivity. Moreover, this research provides guidance for further computational examination on the selection of GNP and BaTiO3 materials for the enhancement of the electrical and thermal properties of the epoxy matrix.

Determination of Some Selected Thermal Properties of Pumpkin Seeds (Cucurbita pepo)

In this study, some selected thermal properties (specific heat, thermal conductivity and thermal diffusivity) in the moisture content range of 5.0-5.6% or green and 4.80 – 5.20% for white varieties of pumpkin seeds were determined. The specific heat was measured using mixture method while the thermal conductivity was measured by transient technique using the heat line source. The green pumpkin seed has average moisture content of 5.2% higher than moisture content of white pumpkin seed of average 4.8%. The average specific heat values of green pumpkin seed are 6.171kJ/kgK and white pumpkin seed 4.327kJ/kgK. The thermal conductivity values for white pumpkin seed ranged from 0.074 to 0.288 W/m°C while that for green pumpkin seed ranged from 0.079 to 0.433 W/m°C. The thermal diffusivity values for green pumpkin ranged from 0.0011 to 0.06 m2/s while that for white pumpkin seed ranged from 0.01 to 0.06 m2/s. It was concluded that the higher the moisture content (5.2%) the higher the value of specific heat of seed (6.171kJ/kgK). It can also be concluded that the thermal conductivity (0.079 to 0.433 W/m°C) value is higher with high moisture content (5.2%).

Study of the effect of temperature on thermophysical properties of ethyl myristate by dual-beam thermal lens technique

One of the components of biodiesels is ethyl myristate and the study and measurement of its thermal parameters are of great importance. The dual-beam laser thermal lens spectroscopy is used for accurate measurement of thermophysical parameters of ethyl myristate. First, to check the accuracy of our optical setup, thermal lens characteristic time, thermal diffusivity and thermal conductivity of carbon disulfide and benzene were measured at 298 K. There was a reasonable agreement between the measured values and the reference values. Then, the effect of temperature changes on thermal diffusivity and thermal conductivity values of ethyl myristate was studied. The results showed that with increasing temperature from 285 to 358 K, thermal diffusivity decreases from 8.75 to 7.45 × 10−8 m2/s, and thermal conductivity from 0.155 to 0.1432 W/mK. It was also shown that by changing in pump laser energy in the range of 0.06–0.12 joules, both thermal diffusivity and thermal conductivity of ethyl myristate are almost constant.

Experimental Study on the Thermal Performance of Rice Straw-Mortar Composite Materials

Thermal properties of mortar block can be improved through adding straw, which is related to the type, size, amount of the straw, and so on. In order to test the thermal insulation performance of rice straw-mortar composite materials, this paper adopted response surface methodology (RSM), which employed a four-factor, three-level Box-Behnken design regarding gypsum content (% mass fraction of gypsum), straw size (mm), straw content (% mass fraction of straw) and water content (g) of rice straw-mortar composite materials as independent variables. Thermal conductivity, thermal diffusivity and thermal resistance of composite materials were response variables. The straw content and water content extremely significantly affected all the responses; the straw size had extremely significant effect on the thermal resistance as well as significant effect on the thermal conductivity. According to the optimum solution of regression equations, the optimum values of thermal conductivity, thermal diffusivity and thermal resistance were 0.048 W (m K)−1, 0.163 mm2 s−1, and 12.743 K W−1, respectively. The optimization options of gypsum content, straw size, straw content and water content were 5.01%, 20 mm, 22.7% and 0.06 g, respectively. Due to the state change of pore water, thermal conductivity of rice straw-mortar composite materials containing free water decreased seriously after complete freezing and increased slightly after 15 times freeze-thaw. During first freezing process, the thermal conductivity increased obviously with the increasing of freezing time, then increased slowly. A theoretical basis was provided by the experimental results, which was essential for the study on the thermal performance of rice straw-mortar composite materials as well as the application of similar materials.

Characterization and thermal performance assessment of earthen adobes and walls additive with different date palm fibers

This study deals on the one hand, with experimental characterization of the thermophysical properties of adobes made from raw earth reinforced with five different plant waste fibers from palm trees in the Drâa-Tafilalet region in southeastern Morocco (Pinnate leaves, Palm fiber mesh, Palm trunk, Petiole and Palm cluster) and on the other hand, with numerical simulation based on the one-dimensional numerical model to evaluate the effect of the wall constructed in studied adobe on the heat flux and the thermal comfort of the building. The results of the experimental study show that the thermal properties of the samples improve and are different depending on the type of fibers incorporated. Indeed, the thermal insulation property improves at least by about 30% for a mass fraction of 6% of the petiole and palm fiber mesh and at most 48% for 6% of the pinnate leaf fibers. Moreover, the adobes containing the Pinnate leaf fibers offer the best insulation property compared to those containing the other four fibers with thermal conductivities of about 0.312 W/(m.K) and 0.265 W/(m.K) respectively for the two mass fractions of 3% and 6%, as well as its rate thermal damping of diffusion is maximum due to its low value of thermal diffusivity. Numerical simulation results show a maximum decrease of about 46% of the flux through the walls contained the fibers of pinnate leaves. In addition, the heat flux time lag and the heat flux decrement factor improve, ensuring good energy efficiency.