Values Of Thermal Effusivity Research Articles

Frequency-based electric fingerprint and thermal properties of the NWA 869 chondrite

The NWA 869 chondrite is among many common stony regolith breccia meteorites that have been collected from northwest Africa (NWA). It is composed of Fe sulphide and Fe-Ni metallic phase inclusions embedded in a silicate stony matrix (primarily pyroxene). Although the physical properties of meteorites are the implementation of their mineral and chemical compositions, their electric and dielectric properties (electric conductivity σ, dielectric constant ε′, and dielectric loss ε") are rarely studied, while no literature has been published on their thermal properties (thermal conductivity K, thermal diffusivity α, specific heat capacitance Cp, and thermal effusivity e). Consequently, the present study deals with studying the electric and dielectric properties of the NWA 869 chondrite at a frequency range (4.0 Hz-8.0 MHz), and their behavior against the applied frequency (fingerprint) was matched. Also, the thermal properties were measured at the ambient conditions. The porosity and density of the chondrite were also measured using helium injection technique. To explain the electric and thermal properties of the meteorite sample, its internal structure as well as its mineral and chemical compositions were revealed using the environmental Scanning electron microscopy (ESEM) supported by the EDAX technique. It is indicated that the chondrite is composed of iron sulphide and Fe-Ni inclusions scattered in a stony silicate matrix; it is characterized by moderate density (3.5069 g/cc) with a considerable porosity value (2.12 %). It is also characterized by moderate electric conductivity (σ), dielectric constant (ε′), and dielectric loss (ε") values (0.50 < σ < 2037.3 ohmm, 67.0 < ε' < 1713.7, and 0.22 < ε" < 12,432 at frequency range 4 Hz-8MHz, respectively). Also, it is characterized by thermal conductivity (K), thermal diffusivity (α), thermal capacitance (Cp), and thermal effusivity (e) values of average 1.5185 W/(K.m), 1.5425 mm2/s, 286 J/(K.kg), and 2628 W(s)0.5/m2K, respectively.

Measurement of thermal properties of ferro siliceous sacrificial radiation shielding concrete using semi-infinite transient heat conduction model

The accurate measurement of thermal properties of ferro siliceous sacrificial concrete (FSSC) is quite difficult but essential to study the radiation shielding behavior and molten core corium interaction (MCCI). The present study aims to propose a step-wise transient method based on a semi-infinite medium principle to measure the different thermal properties of FSSC using transient temperature measurement and a simple data processing approach. Various thermophysical properties such as specific heat, thermal conductivity, thermal diffusivity and thermal effusivity are determined, which can be helpful to understand the ablation behavior of the FSSC during molten core-corium interaction in nuclear power plants. The results of specific heat of the FSSC vary from 760 to 770 J/kg.K, while the value of thermal conductivity lies in the range of 7.0–7.4 W/m.K. The average value of thermal diffusivity and thermal effusivity is found to be 2.51 × 10−6 m2/s and 3900.5 Jm−2K−1s−1/2, respectively. The specific heat obtained using semi-infinite assumptions is predicted well by the rule of mixture. The results of thermal conductivity obtained from the present model are compared with the results of the Serial, Parallel and Lichtnecker models available in the literature. These models under predict the value of thermal conductivity obtained from the experimental results.

Thermal and optical characterization of rhodamine 6G doped silica-glasses

In heat-exchange applications, glasses with excellent heat transfer characteristics are essential. In this study, different concentrations of Rhodamine 6G (Rh6G) doped silica glasses were synthesized using the sol–gel method, and their thermal effusivities were measured and compared. The samples are structurally identified using the X-ray diffraction (XRD) technique. Using a UV–Vis spectrophotometer, the optical absorption spectra (in the range of 300–900 nm) of the intrinsic as well as Rh 1 × 10−4 M and Rh 1 × 10−3 M doped silica samples were recorded, which showed a peak centred at 500 nm for both the rhodamine doped silica samples and Fourier transform infrared (FTIR) spectroscopic techniques, that indicates modification of lattice due to presence of Rh6G. An increase in absorption with a concentration of Rh6G was observed from the optical absorption spectrum. Open cell photoacoustic technique was used for the Photoacoustic (PA) studies. The thermal effusivity values obtained increase with the doping concentration of Rhodamine 6G (maximum value of 2.298 × 103 Ws1/2 K−1 m−2 corresponding to 1 × 10−3 M).

Study of the Thermal Properties and Lattice Disorder Effects in CdTe–Based Crystals: CdBeTe, CdMnTe, and CdZnTe

Mixed semiconductor ternary crystals were grown using the Bridgman–Stockbarger method. This is a high–temperature and high–pressure crystal growth method. Cd1–xBexTe crystals were grown in the range of composition 0 &lt; x &lt; 0.1, such as 0.00, 0.01, 0.03, 0.05, and 0.1. The main goal of this paper was to compare the thermal properties of CdBeTe with previously grown CdMnTe and CdZnTe–mixed ternary crystals. The photopyroelectric technique was applied to examine the thermal properties. The thermal diffusivity and effusivity values were obtained after testing all the samples, and the thermal conductivity was calculated then. As such, a complete thermal characterization of the crystals was carried out. For further characterization, the thermal conductivity versus composition was checked by applying the Sadao Adachi model. Thanks to that, we were able to determine the total thermal resistivity of the crystals and the additional resistivity which arises from the lattice disorder. As such, the disorder effects arising from substituting the native atom with a foreign one were characterized for all crystals. We were looking for the best substitution of the Cd atom in the CdTe matrix based on the compounds’ thermal properties. It turned out that Zn and Mn introduce a similar disorder, with Be being the highest one.

Thermo-physical properties measurements of hygroscopic and reactive material (zeolite 13X) for open adsorptive heat storage operation

The determination of the thermo-physical properties (density, specific heat capacity, and thermal conductivity) of hygroscopic and reactive solid materials, as those applied in sorption thermochemical heat storage systems, is not trivial. Lack of precision in the measurement and contradictory results make it difficult to enter these thermal parameters in the programs used for simulating the functioning and operating scenarios of thermochemical heat storage devices. For this reason, different techniques have been applied and compared in order to improve the accuracy of the measurement. In particular, there was a difference in thermal conductivity (about 30%) between the hot disc experiments and the others, as well as a higher dispersion of the experimental data (MAD > 19%). The same was found for specific heat capacity (MAD ≈14%). Hence, the transient hot disk method is not suitable for estimating thermal conductivity and the specific heat capacity of this type of material. Nevertheless, this technique enables a good estimation of the thermal effusivity. The thermal conductivity and the specific heat capacity were investigated by the hot wire method and by TG-DSC, respectively. A slight increase in specific heat with temperature was observed, but in the range of 70–95 °C, this value is constant at 913 J kg−1 K−1. The applied methodology was validated by comparing the experimental and calculated thermal effusivity values.

Analysis of the Heat Transfer Coefficient, Thermal Effusivity and Mathematical Modelling of Drying Kinetics of a Partitioned Single Pass Low-Cost Solar Drying of Cocoyam Chips with Economic Assessments

This study examines the heat and mass transfer coefficient, thermal effusivity, and other thermal properties of solar-dried cocoyam chips, as well as the drying kinetics. The research also assessed the economics of the solar dryer. For these reasons, a solar dryer with a partitioned collector was developed that creates a double airflow travel distance to delay the airflow inside the collector. The partitioning of the collector delays the airflow and helps to create more turbulence for the airflow with increased energy. The solar dryer was locally developed at the Michael Okpara University of Agriculture and tested during the humid crop harvesting period of September for the worst-case scenario. The obtained drying curves and kinetics for cocoyam drying are subjected to the vagaries of weather conditions. The drying rate showed declining sinusoidal characteristics and took about 25 h to attain equilibrium. Analysis of the airflow velocity showed gravitation between laminar and turbulent flow, ranging from 171.69 to 5152.77. Specific heat capacity, thermal conductivity, and effusivity declined with moisture content while the thermal diffusivity increased. However, the values of thermal effusivity ranged from 12.2 to 47.94 W·s1/2·m−2·K−1, which is within the range of values for insulators. The heat and mass transfer coefficient varied as a function of the airflow velocity. Fitting the drying curve into semi-empirical models showed that the two-term model was the best-fitted model for the experimental data from drying cocoyam. Using the solar dryer in Nigeria can save $188.63–$1886.13 in running costs with a payback period of 0.059–0.59 years (21.54–215.35 days) at a rate of 10–100% of usage.

Thermal Characterization of an Eco Conce Based on Lateritic Gravel, Millet Pods and Cement

To simultaneously meet the need of thermal confort and living environment protection, vegetable biomass valorisation in building sector is of particular importance. In this context, the main objective of this study is to produce a lightweight composite concrete based on millet pods and lateritic gravel with a cement matrix for use in buildings to help improve thermal comfort and protect environment. To achieve this, the composite formulation with 250 kg.m-3 cement dosage and an 0.8 water to cement ratio was used to manufacture two type test specimens of (4 × 4 × 16) cm3 dimensions for porosity tests and (4 × 4 × 5) cm3 for thermal tests with a millet pod rate varying from 0 to 6% with a step of 2%. Average thermophysical characteristics of 5 tests carriesd out over 5 days, namely: Thermal conductivity, thermal diffusivity, thermal effusivity, thermal phase and damping, were experimentally measured using fluxmetric method similar to that of mini hot plate method with two Peltier elements as fluxmeters. Results obtained showed that for 0, 2, 4 and 6% millet pods dosage, thermal conductivity values obtained are respectively 1.18 W.m-1.K-1, 0.74 W.m-1.K-1, 0.63 W.m-1.K-1 and 0.61 W.m-1.K-1, i.e., a reduction of 93.44%. For same millet pod dosage, thermal effusivity values are 2157.33 J.m-2.K-1.s-0.5, 1236.34 J.m-2.K-1.s-0.5, 946.03 J.m-2.K-1.s-0.5 and 775.04 J.m-2.K-1.s-0.5, i.e., a reduction of 64.07%. On the other hand, it was observed 3.00.10-7 m2.s-1, 3.56.10-7 m2.s-1, 4.47.10-7 m2.s-1 and 6.25.10-7 m2.s-1, i.e., an increase of 108.33% for thermal diffusivity. With regard to dynamiquc thermal characteristics, it was obtained an increase from 5.43 to 13.18% for thermal damping and, from 61.00 to 84.20 min for thermal phase. Through on the one hand, thermal conductivity and effusivity decrease and on the other hand, thermal damping and phase shift increase, it is retained that characterized eco-concrete should contribute to thermal losses limitation, energiy saving and improved thermal comfort.

Optimum mass percentage of microencapsulated PCM mixed with gypsum for improved latent heat storage

The present investigation aims at invalidating the idea that increasing the mass percentage of microencapsulated phase change material (mPCM) in gypsum always leads to an increase in heat absorption. This assertion is based solely on the thermophysical properties used to determinate four essential parameters that are the volumetric heat capacity, the thermal diffusivity, the thermal effusivity and the temperature range where the use of mPCM is better compared to the use of standard gypsum board. The findings show that an increase in the mPCM mass percentage in gypsum results in an improvement in heat storage when considering only volumetric heat capacity (steady-state). However, it is observed that 30% of mPCM in the composite can store more heat than 40% and 50% of mPCM when considering the thermal effusivity (dynamic state). Furthermore, it can be recommended to consider only 20% of mPCM's mass percentage, since it results in an optimal value of thermal effusivity and it yields an output very close to that of 30% of mPCM's mass percentage. In addition, increasing the mass percentage of mPCM allows a reduction of the suitable temperature range for high storage of thermal energy.

Comparative Analysis of Thermal Properties of Two Varieties of Periwinkle Relevant to Its Processing Equipment Design

This study was conducted to investigate and compare the thermal properties of two varieties: Tympanotonus fuscatus and Pachymelania aurita of Periwinkle in Nigeria. The thermal properties, namely; specific heat capacity,Cp, thermal conductivity, k, thermal diffusity,, thermal absorptivity, and thermal effusivity, of Periwinkle samples were determined. The mean thermal conductivity of T. fuscatus was found to be 0.085±0.00015 W/m.K at temperatures of 308 – 373 K, while that of P. aurita was 0.0952±0.00056 W/m.K at the same temperature range.The average specific heat capacity value of T. fuscatus was found to be 2403.663±3.4379 J/kg.K at temperature of 308 – 373 K lower than that of P. aurita having a mean value of 2832.314±1.7385 J/kg.K at the same temperature. The mean thermal diffisivity of T. fuscatus was found to be 2.6553×10-8 m2/s while that of P. aurita was found to be 5.6790×10-8 m2/s. The average values for thermal absorptivity and effusivity of T. fuscatus and P. aurita were obtained as 81.085m-1; 525.084 W.s1/2/m2K and 55.441 m-1; 396.952 W.s1/2/m2K, respectively. The results shown that average thermal absorptivity and effusivity values were higher in T. fuscatus than P. aurita. A Tukey pairwise comparison analysis carried out on the mean values of these thermal properties of T. fuscatus and P. aurita revealed that there is statistically significant difference at <5% between the thermal properties of the two varieties of periwinkle samples. These data would help us in predicting and controlling the heat flux during the design of periwinkle processing equipment.

Photothermal Techniques for Thermal Characterization of Linear Alcohols

Photothermal techniques were used for the thermal characterization of linear alcohols. This was carried out by measuring the thermal diffusivity (by means of a photopyroelectric technique) and thermal effusivity (by means of a photoacoustic technique) of ten linear alcohols, from methanol to 1-decanol. The thermal conductivity and specific heat for these substances were obtained by means of their relations with the two previous thermal properties, by using the values reported for the densities of the alcohols. The values of thermal effusivity showed a decreasing behavior with the increase in length of the linear molecule, and the values of thermal diffusivity, on the other hand, showed a similar behavior but only up to 1-pentanol, from which these values began to increase; this latter behavior was also observed, although to a lesser extent, for thermal conductivities. This peculiar behavior for thermal diffusivity and thermal conductivities is attributed to the influence of the hydroxyl group, which is strong for low molecular weight alcohols, but it diminishes as the size of alcohol’s molecule increases.

In search of thermal effusivity reference materials

Quality initiatives such as ISO 9001 require reference values for laboratory measurements. There are no certified reference materials for the secondary material property of thermal effusivity. Reference values are derived from measurements of thermal conductivity, specific heat capacity, and density. A search of the literature is conducted to find materials with the “best’ values for thermal conductivity, specific heat capacity, and density so that a table of reference values for thermal effusivity may be obtained. Tabulated thermal effusivity values range from 0.04 kW s1/2 m−2 K−1 for expanded polystyrene board to 40 kW s1/2 m−2 K−1 for copper metal.

Thermal microscope measurement of thermal effusivity distribution in compositionally graded PbTe–Sb2Te3–Ag2Te alloy system

A compositionally graded alloy in the PbTe–Sb2Te3–Ag2Te system was fabricated by the Bridgeman method. In the sample obtained for analysis, the length of the graded area was of the order of several tens of nanometers. Its thermal effusivity was measured with a thermal microscope, which required sputtering of a Mo film on the surface of the sample. The measured values of thermal effusivity depended on the thickness of the Mo film. However, it was difficult to sputter the Mo film uniformly in the wide area. Even though a relatively large target was used in the sputtering apparatus on the laboratory scale, the thickness of the Mo film just under the center of the target was larger than that in other areas. In this study, the measured thickness of the Mo film was calibrated with a high degree of accuracy against the reference glass slide. The thermal effusivity of the PbTe–Sb2Te3–Ag2Te alloy was in the range of 400–800 Ws0.5m−2K−1.

Thermal effusivity measurement of conventional and organic coffee oils via photopyroelectric technique

In this work, oil samples extracted from organic and conventional coffee beans were studied. A fatty acids profile analysis was done using gas chromatography and physicochemical analysis of density and acidity index to verify the oil purity. Additionally, Mid-Infrared Fourier Transform Photoacoustic Spectroscopy (FTIR-PAS) aided by Principal Component Analysis (PCA) was used to identify differences between the intensities of the absorption bands related to functional groups. Thermal effusivity values between 592±3 and 610±4Ws1/2m−2K−1 were measured using the photopyroelectric technique in a front detection configuration. The acidity index was between 1.11 and 1.27% and the density changed between 0.921 and 0.94g/mL. These variables, as well as the extraction yield between 12,6 and 14,4%, showed a similar behavior than that observed for the thermal effusivity, demonstrating that this parameter can be used as a criterion for discrimination between oil samples extracted from organic and conventional coffee beans.

Wide-range measurement of thermal effusivity using molybdenum thin film with low thermal conductivity for thermal microscopes

Thermal microscopes are a useful technology to investigate the spatial distribution of the thermal transport properties of various materials. However, for high thermal effusivity materials, the estimated values of thermophysical parameters based on the conventional 1D heat flow model are known to be higher than the values of materials in the literature. Here, we present a new procedure to solve the problem which calculates the theoretical temperature response with the 3D heat flow and measures reference materials which involve known values of thermal effusivity and heat capacity. In general, a complicated numerical iterative method and many thermophysical parameters are required for the calculation in the 3D heat flow model. Here, we devised a simple procedure by using a molybdenum (Mo) thin film with low thermal conductivity on the sample surface, enabling us to measure over a wide thermal effusivity range for various materials.

Role of decoration method of gold nanoparticles on the thermal and optical properties of mesoporous silica-Rhodamine 6G hybrids

Nanotechnology offers the potential for creating new optical imaging agents with novel properties which has been used in molecular imaging and photothermal therapy. Mesoporous silica materials have attained great attention in industry due to its high thermal and chemical stability and non toxic behavior. The performance of mesoporous silica materials depends on composition, morphology and structure of made-up materials. The synthesis of mesoporous silica nanoparticles is highly sensitive because the size, morphology and pore structure changes with small change in procedure. Surface modification of mesoporous enables to incorporate metal nanoparticles in to its pores by co-condensation and post-synthesis method and hence an enhancement in optical and thermal properties of mesoporous silica nanoparticles. In the present work, we have synthesized gold nanoparticles incorporated mesoporous silica by three methods such as non functionalized, co-condensation and post-synthesis modification which is denoted as sample I, sample II and sample III. Thermal parameters such as thermal diffusivity and effusivity of the synthesized samples are measured by thermal lens and photoacoustic techniques respectively. From the values of thermal diffusivity and effusivity, thermal conductivity is estimated and a high value of thermal conductivity is obtained for sample II because of the proper encapsulation of gold nanoparticles in mesoporous silica. The influence of Rhodamine 6G concentrations on the thermal parameters of mesoporous silica is also studied which shows that thermal conductivity decreases with the addition of higher concentration of Rhodamine 6G due to the interface thermal resistance effects. In addition, we have investigated the influence of gold nanoparticle incorporated mesoporous silica on the emission properties of Rhodamine 6G and fluorescein dyes. Irrespective of dye concentration, due to plasmonic field effect and non aggregation of dye molecules, the fluorescence signal is enhanced for both dyes with the addition of gold incorporated mesoporous silica.

Thermal Effusivity Determination of Metallic Films of Nanometric Thickness by the Electrical Micropulse Method

The thermal effusivity of gold, aluminum, and copper thin films of nanometric thickness (20 nm to 200 nm) was investigated in terms of the films’ thickness. The metallic thin films were deposited onto glass substrates by thermal evaporation, and the thermal effusivity was estimated by using experimental parameters such as the specific heat, thermal conductivity, and thermal diffusivity values obtained at room conditions. The specific heat, thermal conductivity, and thermal diffusivity values of the metallic thin films are determined with a methodology based on the behavior of the thermal profiles of the films when electrical pulses of few microseconds are applied at room conditions. For all the investigated materials, the thermal effusivity decreases with decreased thickness. The thermal effusivity values estimated by the presented methodology are consistent with other reported values obtained under vacuum conditions and more elaborated methodologies.

Rapid, non-destructive determination of butter adulteration by means of photopyroelectric (PPE) calorimetry

The study focuses on the application of the photopyroelectric (PPE) technique combined with gas chromatography to detect adulteration of cow milk-obtained butter. The thermal diffusivity and effusivity have been directly measured using back and front PPE detection, respectively, and the results have been correlated with the composition of adulterated butter samples. The back detection configuration has been used in the case of butter adulterated with palm oil, and a possible correlation of the thermal diffusivity with total amount of monounsaturated fatty acids composition has been proposed. For butter adulterated with soy milk, we used the front PPE configuration in order to measure the samples’ thermal effusivity. A strong dependence of the value of thermal effusivity as a function of soy milk content was found.

Thermal characterization of a liquid resin for 3D printing using photothermal techniques

Thermal properties of a liquid resin were studied by thermal lens spectrometry (TLS) and open photoacoustic cell (OPC), respectively. In the case of the TLS technique, the two mismatched mode experimental configuration was used with a He–Ne laser, as a probe beam and an Argon laser was used as the excitation source. The characteristic time constant of the transient thermal lens was obtained by fitting the theoretical expression to the experimental data in order to obtain the thermal diffusivity (α) of the resin. On the other hand, the sample thermal effusivity (e) was obtained by using the OPC technique. In this technique, an Argon laser was used as the excitation source and was operated at 514 nm with an output power of 30 mW. From the obtained thermal diffusivity (α) and thermal effusivity (e) values, the thermal conductivity (k) and specific heat capacity per unit volume (ρc) of resin were calculated through the relationships k = e(α)1/2 and ρc = e/(α)1/2. The obtained thermal parameters were compared with the thermal parameters of the literature. To our knowledge, the thermal characterization of resin has not been reported until now. The present study has applications in laser stereo-lithography to manufacture 3D printing pieces.

To Evaluate the Effect of Solvents and Different Relative Humidity Conditions on Thermal and Rheological Properties of Microcrystalline Cellulose 101 Using METHOCEL™ E15LV as a Binder.

The solvent used for preparing the binder solution in wet granulation can affect the granulation end point and also impact the thermal, rheological, and flow properties of the granules. The present study investigates the effect of solvents and percentage relative humidity (RH) on the granules of microcrystalline cellulose (MCC) with hydroxypropyl methyl cellulose (HPMC) as the binder. MCC was granulated using 2.5% w/w binder solution in water and ethanol/water mixture (80:20 v/v). Prepared granules were dried until constant percentage loss on drying, sieved, and further analyzed. Dried granules were exposed to different percentage RH for 48h at room temperature. Powder rheometer was used for the rheological and flow characterization, while thermal effusivity and differential scanning calorimeter were used for thermal analysis. The thermal effusivity values for the wet granules showed a sharp increase beginning 50% w/w binder solution in both cases, which reflected the over-wetting of granules. Ethanol/water solvent batches showed greater resistance to flow as compared to the water solvent batches in the wet granule stage, while the reverse was true for the dried granule stage, as evident from the basic flowability energy values. Although the solvents used affected the equilibration kinetics of moisture content, the RH-exposed granules remained unaffected in their flow properties in both cases. This study indicates that the solvents play a vital role on the rheology and flow properties of MCC granules, while the different RH conditions have little or no effect on them for the above combination of solvent and binder.

Contact Photothermal Techniques for Thermal Characterization of Liquids

Two contact photothermal (PT) techniques, the well-known photopyroelectric (PPE) calorimetry, and a recently introduced photothermoelectric (PTE) one, are proposed for thermal inspection of some liquid samples. The paper contains a summary of the recent results and a comparison of the investigations performed with the previously mentioned techniques for the measurement of the dynamic thermal parameters (thermal diffusivity and effusivity) of some liquids of interest: magnetic nanofluids with transformer oil as carrier liquid and various concentrations of magnetite (Fe3O4) nanoparticles. For both techniques, the same detection configurations have been used: (i) the front detection configuration, together with the thermal-wave resonator cavity (TWRC) method as scanning procedure, was used to measure the value of thermal effusivity; (ii) the back configuration, together with the same TWRC technique, leads to the direct measurement of thermal diffusivity. The main theoretical aspects of the particular detection cases for both techniques are described and the performances (advantages and limitations) of the methods are analyzed. Concerning the nanofluid under investigation, small increases of thermal diffusivity (9.33 m2s-1 – 10.33 m2s-1) and effusivity (450 Ws1/2 m-2K-1 – 530 Ws1/2 m-2K-1) with increasing nanoparticles' concentration (0.156 mg(Fe3O4)/ml fluid - 0.623 mg(Fe3O4)/ml fluid) are observed.