Showing papers in "International Journal of Thermophysics in 2018"

Review on Variable Emissivity Materials and Devices Based on Smart Chromism

Abstract: Variable emissivity material (VEM) can dynamically vary its emissivity and infrared radiation under certain conditions, which may find potential applications in infrared stealth/camouflage, solar thermal collector, spacecraft thermal control, and smart energy-saving windows. In this paper, the variable emissivity materials and devices based on electrochromism and thermochromism are introduced. The basic principle and present status of the research in these fields are overviewed. Four kinds of representative VEMs are extensively summarized, which are tungsten trioxides ( $$\hbox {WO}_{3})$$ , conducting polymers (CPs), perovskite oxides ( $$\hbox {A}_{1-{x}}\hbox {B}_{{x}}\hbox {MO}_{3})$$ , and vanadium dioxide ( $$\hbox {VO}_{2})$$ . Finally, specific issues confronted with electrochromic and thermochromic materials and devices are prospected.

Canadian Field Soils IV: Modeling Thermal Conductivity at Dryness and Saturation

Abstract: The thermal conductivity data of 40 Canadian soils at dryness $$(\lambda _{\mathrm{dry}})$$ and at full saturation $$(\lambda _{\mathrm{sat}})$$ were used to verify 13 predictive models, i.e., four mechanistic, four semi-empirical and five empirical equations. The performance of each model, for $$\lambda _{\mathrm{dry}}$$ and $$\lambda _{\mathrm{sat}}$$ , was evaluated using a standard deviation (SD) formula. Among the mechanistic models applied to dry soils, the closest $$\lambda _{\mathrm{dry}}$$ estimates were obtained by MaxRTCM $$(\textit{SD} = \pm ~0.018\,\hbox { Wm}^{-1}\cdot \hbox {K}^{-1})$$ , followed by de Vries and a series-parallel model ( $$\hbox {S-}{\vert }{\vert }$$ ). Among the semi-empirical equations (deVries-ave, Advanced Geometric Mean Model (A-GMM), Chaudhary and Bhandari (C–B) and Chen’s equation), the closest $$\lambda _{\mathrm{dry}}$$ estimates were obtained by the C–B model $$(\pm ~0.022\,\hbox { Wm}^{-1}\cdot \hbox {K}^{-1})$$ . Among the empirical equations, the top $$\lambda _{\mathrm{dry}}$$ estimates were given by CDry-40 $$(\pm ~0.021\,\hbox { Wm}^{-1}\cdot \hbox {K}^{-1}$$ and $$\pm ~0.018\,\hbox { Wm}^{-1}\cdot \hbox {K}^{-1}$$ for18-coarse and 22-fine soils, respectively). In addition, $$\lambda _{\mathrm{dry}}$$ and $$\lambda _{\mathrm{sat}}$$ models were applied to the $$\lambda _{\mathrm{sat}}$$ database of 21 other soils. From all the models tested, only the maxRTCM and the CDry-40 models provided the closest $$\lambda _{\mathrm{dry}}$$ estimates for the 40 Canadian soils as well as the 21 soils. The best $$\lambda _{\mathrm{sat}}$$ estimates for the 40-Canadian soils and the 21 soils were given by the A-GMM and the $$\hbox {S-}{\vert }{\vert }$$ model.

Evaluation of Different Techniques of Active Thermography for Quantification of Artificial Defects in Fiber-Reinforced Composites Using Thermal and Phase Contrast Data Analysis

Abstract: For assuring the safety and reliability of components and constructions in energy applications made of fiber-reinforced polymers (e.g., blades of wind turbines and tidal power plants, engine chassis, flexible oil and gas pipelines) innovative non-destructive testing methods are required. Within the European project VITCEA complementary methods (shearography, microwave, ultrasonics and thermography) have been further developed and validated. Together with partners from the industry, test specimens have been constructed and selected on-site containing different artificial and natural defect artefacts. As base materials, carbon and glass fibers in different orientations and layering embedded in different matrix materials (epoxy, polyamide) have been considered. In this contribution, the validation of flash and lock-in thermography to these testing problems is presented. Data analysis is based on thermal contrasts and phase evaluation techniques. Experimental data are compared to analytical and numerical models. Among others, the influence of two different types of artificial defects (flat bottom holes and delaminations) with varying diameters and depths and of two different materials (CFRP and GFRP) with unidirectional and quasi-isotropic fiber alignment is discussed.

Liquid Metal Corrosion Effects on Conventional Metallic Alloys Exposed to Eutectic Gallium-Indium Alloy Under Various Temperature States

Abstract: The effects of liquid metal corrosion on the thermophysical properties of three conventional metallic alloys, including T2 copper, 304 stainless steel and anodized 6061 aluminum alloy, in the range of 100–400 °C were comprehensively clarified in this paper. It was experimentally found that the corrosion products on the copper surface existed as the intermetallic compound of CuGa2, and that FeGa3 and Cr3Ga4 were formed on the surface of stainless steel. The heat conductivity of copper plate decreased with the increasing corrosion temperature. The heat conductivity of the corroded copper sample sharply decreased at the beginning stage. When the copper plate was exposed in liquid eutectic gallium–indium over 12 h, the trend of the tested heat conductivity changing curve showed a smooth tendency and reached a steady state finally. The heat conductivity of the corroded copper plate was decided by the corrosion speed with an exponential function of $$ v = a^{t} (0.4 < a < 0.6) $$ . Corrosion phenomena were not found on the surface of the anodized 6061 aluminum alloy according to the experimental results from ambient temperature to 400 °C, which disclosed their suitability as the structural material. The present findings would serve as an important reference for the use of liquid metal cooling in high-power electronic devices and high-temperature systems.

Measuring Sound Speed in Gas Mixtures Using a Photoacoustic Generator

Abstract: We present a new method which allows us to percentage distinction of gas composition with a fast response time. This system uses the speed of sound in a resonant cell along with temperature to determine the gas mixture composition. The gas mixtures contain two gases with an unknown combination. In our experiment, the acoustic waves were excited inside the acoustic longitudinal resonator with the use of a positive feedback. This feedback provides fast tracking of a resonance frequency of the cell and causes fast tracking changes in the speed of sound. The presented method corresponds to the theoretical description of this topic. Two gas mixtures—carbon dioxide and argon mixed with nitrogen—were tested.

Analytical and Numerical Investigations of Unsteady Graphene Oxide Nanofluid Flow Between Two Parallel Plates

Abstract: In this research, different analytical methods were applied to characterize thermal behavior of unsteady graphene oxide–water nanofluid flow between two parallel moving plates. First of all, partial differential equations (PDEs) were transformed to a system of nonlinear ordinary differential equations (ODEs) using similarity solution. Then, collocation method (CM), least square method (LSM) and Galerkin method (GM) were used to solve the system of ODEs and determine velocity and temperature distribution functions. In addition, effects of moving parameter, concentration, Eckert and Prandtl numbers on nanofluid velocity and temperature profiles were examined. Next, using numerical solution of the obtained system of differential equations, the results obtained from the analytical solutions were validated with that of the numerical solution. The validation results indicated high and appropriate accuracy of the analytical solutions compared to the numerical one.

Photoacoustic Spectroscopy Investigation of Zinc Oxide/Diatom Frustules Hybrid Powders

Abstract: Photoacoustic spectroscopy investigation was carried out on ZnO nanoparticles grown at 80 °C on porous surface of diatomite (DE) by sol–gel technique, using zinc acetate dihydrate as ceramic precursor and triethanolamine to mediate the surface growth of the nanoparticles. Absorption and scattering characteristics of hybrid ZnO/DE powder in the UV–Vis range were inferred by photoacoustic spectroscopy, and results were analyzed based on Helander’s theory. In particular, we discussed in detail the procedure to calculate the absorption and scattering spectra of the hybrid powder showing how from the scattering coefficient in the 300–450 nm range it is possible to obtain information on the size distribution of the ZnO nanospheres. By applying photoacoustic spectroscopy for different modulation frequencies, we showed that is also possible to perform a size distribution depth profile of the ZnO aggregates, opening the way to interesting developments in this research field.

Applicability of a 1D Analytical Model for Pulse Thermography of Laterally Heterogeneous Semitransparent Materials

Abstract: Pulse thermography (PT) has proven to be a valuable non-destructive testing method to identify and quantify defects in fiber-reinforced polymers To perform a quantitative defect characterization, the heat diffusion within the material as well as the material parameters must be known The heterogeneous material structure of glass fiber-reinforced polymers (GFRP) as well as the semitransparency of the material for optical excitation sources of PT is still challenging For homogeneous semitransparent materials, 1D analytical models describing the temperature distribution are available Here, we present an analytical approach to model PT for laterally inhomogeneous semitransparent materials We show the validity of the model by considering different configurations of the optical heating source, the IR camera, and the differently coated GFRP sample The model considers the lateral inhomogeneity of the semitransparency by an additional absorption coefficient It includes additional effects such as thermal losses at the samples surfaces, multilayer systems with thermal contact resistance, and a finite duration of the heating pulse By using a sufficient complexity of the analytical model, similar values of the material parameters were found for all six investigated configurations by numerical fitting

Fabrication of Dodecanol/Diatomite Shape-Stabilized PCM and Its Utilization in Interior Plaster

Abstract: A novel shape-stabilized phase change material (PCM) is prepared as an energy-efficient solution aimed at the improvement of thermal stability of building materials. Dodecanol having a suitable temperature interval of phase transition and high latent heat is selected as the PCM medium. Diatomite powder used as the PCM core material is impregnated by dodecanol using the vacuum impregnation method. The particle size distribution of the prepared PCM is analyzed at first to find the possible agglomeration of particles. A detailed characterization of mutual material compatibility is performed by scanning electron microscopy and Fourier transform infrared spectroscopy. The melting and solidification temperatures of the developed PCM are found at 23.3 °C and 21.2 °C, respectively; the measurement of corresponding latent heats shows 71.4 J·g−1 and 72.6 J·g−1. The incorporation of the novel PCM into cement–lime plaster does not significantly affect its phase change behavior and confirms its good potential for applications in building practice.

A Study on Variation of Thermal Characteristics of Insulation Materials for Buildings According to Actual Long-Term Annual Aging Variation

Abstract: Insulation materials used for buildings are broadly classified as organic insulation materials or inorganic insulation materials. Foam gas is used for producing organic insulation materials. The thermal conductivity of foam gas is generally lower than that of air. As a result, foam gas is discharged over time and replaced by outside air that has relatively less thermal resistance. The gas composition ratio in air bubbles inside the insulation materials changes rapidly, causing the performance degradation of insulation materials. Such performance degradation can be classified into different stages. Stage 1 appears to have a duration of 5 years, and Stage 2 takes a period of over 10 years. In this study, two insulation materials that are most frequently used in South Korea were analyzed, focusing on the changes thermal resistance for the period of over 5000 days. The measurement result indicated that the thermal resistance of expanded polystyrene fell below the KS performance standards after about 80–150 days from its production date. After about 5000 days, its thermal resistance decreased by 25.7 % to 42.7 % in comparison with the initial thermal resistance. In the case of rigid polyurethane, a pattern of rapid performance degradation appeared about 100 days post-production, and the thermal resistance fell below the KS performance standards after about 1000 days. The thermal resistance decreased by 22.5 % to 27.4 % in comparison with the initial thermal resistance after about 5000 days.

Research of Ultra-Black Coating Emissivity Based on a Controlling the Surrounding Radiation Method

Abstract: A method of controlling the surrounding radiation, proposed to measure the emissivity of the sample with high accuracy, is introduced. Two disks at different temperatures are moved alternately in front of the sample for controlling the surrounding radiation of the sample. The emissivity of the sample is obtained from the relationship between the measured value of the radiation thermometer and the radiation from the sample. There are three samples, including the Japansensor JSC-3, Tempil Pyromark 1200, and NEXTEL Velvet Coating 811-21 ultra-black coating, measured by this method. The uncertainty contributions of this method are analyzed, and the uncertainty of the emissivity measurement method is 0.54 % (k = 1). The surface microstructure of the coatings is measured by scanning electron microscopy, and the relationship between emissivity and the surface properties is discussed.

Solid–Liquid Phase Equilibria, Molecular Interaction and Microstructural Studies on ( N -(2-ethanol)- p -nitroaniline + N -(2-acetoxyethyl)- p -nitroaniline) Binary Mixtures

Abstract: Differential scanning calorimetry (DSC) is used to investigate the thermal properties of N-(2-ethanol)-p-nitroaniline + N-(2-acetoxyethyl)-p-nitroaniline, and their binary systems. The experimental results demonstrate that the studied binary system presents a simple eutectic behavior and the corresponding mole fraction (xeu) of N-(2-ethanol)-p-nitroaniline at the eutectic point is 0.5486, whereas the temperature (Teu) is found to be equal to 363.6 K. The quality of the solid–liquid equilibria (SLE) data has been checked by thermodynamic consistency tests, presenting good quality factor. The SLE data have been correlated by means of Wilson, NRTL, and UNIQUAC equations. The three models describe satisfactorily the phase diagram as the root-mean-square deviations for the equilibrium temperatures vary from 1.25 K to 2.07 K. Nevertheless, the Wilson model provides the best correlation results. The three equations have also been used to compute excess thermodynamic functions viz. excess Gibbs energy, enthalpy and entropy. The obtained results revealed a sensitive positive deviation to ideality thus demonstrating the nature of the interactions between the compounds forming the mixture. Microstructural studies have been carried out by FTIR, XRD and optical microscopy showing weak molecular interactions for the eutectic mixture.

Evaluation of Building Energy Saving Through the Development of Venetian Blinds’ Optimal Control Algorithm According to the Orientation and Window-to-Wall Ratio

Abstract: As various studies focusing on building energy saving have been continuously conducted, studies utilizing renewable energy sources, instead of fossil fuel, are needed. In particular, studies regarding solar energy are being carried out in the field of building science; in order to utilize such solar energy effectively, solar radiation being brought into the indoors should be acquired and blocked properly. Blinds are a typical solar radiation control device that is capable of controlling indoor thermal and light environments. However, slat-type blinds are manually controlled, giving a negative effect on building energy saving. In this regard, studies regarding the automatic control of slat-type blinds have been carried out for the last couple of decades. Therefore, this study aims to provide preliminary data for optimal control research through the controlling of slat angle in slat-type blinds by comprehensively considering various input variables. The window area ratio and orientation were selected as input variables. It was found that an optimal control algorithm was different among each window-to-wall ratio and window orientation. In addition, through comparing and analyzing the building energy saving performance for each condition by applying the developed algorithms to simulations, up to 20.7 % energy saving was shown in the cooling period and up to 12.3 % energy saving was shown in the heating period. In addition, building energy saving effect was greater as the window area ratio increased given the same orientation, and the effects of window-to-wall ratio in the cooling period were higher than those of window-to-wall ratio in the heating period.

Photo-Acoustic Spectroscopy Reveals Extrinsic Optical Chirality in GaAs-Based Nanowires Partially Covered with Gold

Abstract: We report on the extrinsic chirality behavior of GaAs-based NWs asymmetrically hybridized with Au. The samples are fabricated by a recently developed, lithography-free self-organized GaAs growth, with the addition of AlGaAs shell and GaAs supershell. The angled Au flux is then used to cover three-out-of-six sidewalls with a thin layer of Au. Oblique incidence and proper sample orientation can lead to circular dichroism. We characterize this chiral behavior at $$ 532\,{\text{nm}} $$ and $$ 980\,{\text{nm}} $$ by means of photo-acoustic spectroscopy, which directly measures the difference in absorption for the circularly polarized light of the opposite headedness. For the first time to our knowledge, circular dichroism is observed in both the amplitude and the phase of the photo-acoustic signal. We strongly believe that such samples can be used for chiral applications, spanning from circularly polarized light emission, to the enantioselectivity applications.

Density of Liquid Tantalum and Estimation of Critical Point Data

Abstract: In order to determine the density of tantalum over the entire liquid phase (at the pressure applied) and several hundred K into the super-heated region, the method of ohmic pulse-heating was applied For this purpose, images of the thermal radial expansion of the resistively heated sample wires were taken with an adapted CCD system A newly integrated high-power photoflash and improved triggering of the experiment allowed the acquisition of high-contrast shadow images of the expanding wires To reduce the uncertainty arising from simultaneous pyrometric temperature measurement, the change in normal spectral emissivity as a function of temperature was additionally taken into account In this work, the density versus temperature relationship of tantalum is reported and compared to existing literature data From the newly obtained liquid-phase density, critical point data of tantalum, such as critical temperature and critical density, were estimated via an extrapolation procedure Furthermore, an estimate of the phase diagram in the density versus temperature plane is given The work is concluded by a rigorous density uncertainty estimation according to the guide to the expression of uncertainty in measurement (GUM)

Investigation on Thermal Conductivity of Steel Fiber Reinforced Concrete Using Mesoscale Modeling

Abstract: A mesoscale model was developed to investigate the effect of steel fiber on the thermal conductivity of steel fiber-reinforced concrete (SFRC). Delaunay triangulation was employed to generate the unstructured mesh for SFRC materials. The model was validated using the existing experimental data. Then, it was used to study how model thickness affected simulation outcomes of thermal conductivity of models with different fiber lengths, by which an appropriate thickness was determined for the later analyses. The validated and optimized model was applied to the study of relationships between thermal conductivity and factors such as fiber content, fiber aspect ratio and different parts of an SFRC block by conducting steady-state heat analyses with the finite element analysis software ANSYS. The simulation results reveal that adding steel fiber increases thermal conductivity considerably, while fiber aspect ratio only has an insignificant effect. Besides, the presence of steel fibers has an obvious impact on the distribution of temperature and heat flux vector of the SFRC blocks.

SI-Traceable Water Content Measurements in Solids, Bulks, and Powders

Abstract: Methods such as Karl Fischer titration and Loss-on-Drying, commonly used for estimating moisture content in samples, have been in existence for many years, but have difficulties obtaining a direct calibration chain toward water content. In recognition of this challenge, the joint research project, METefnet, was funded by the European Metrology Research Programme in 2012. The goal of METefnet is to establish a European metrology infrastructure for water content measurement and to develop primary standards for unambiguous determination of water mass fraction in materials. Here, we describe the primary standard developed by Danish Technological Institute in METefnet. This standard establishes traceability of the water content of a sample to dewpoint temperature. The standard only measures water, and the measurement result is not affected by other components.

Viscosity Prediction for Petroleum Fluids Using Free Volume Theory and PC-SAFT

Abstract: In this study, free volume theory (FVT) in combination with perturbed-chain statistical associating fluid theory is implemented for viscosity prediction of petroleum reservoir fluids containing ill-defined components such as cuts and plus fractions. FVT has three adjustable parameters for each component to calculate viscosity. These three parameters for petroleum cuts (especially plus fractions) are not available. In this work, these parameters are determined for different petroleum fractions. A model as a function of molecular weight and specific gravity is developed using 22 real reservoir fluid samples with API grades in the range of 22 to 45. Afterward, the proposed model accuracy in comparison with the accuracy of De la Porte et al. with reference to experimental data is presented. The presented model is used for six real samples in an evaluation step, and the results are compared with available experimental data and the method of De la Porte et al. Finally, the method of Lohrenz et al. and the method of Pedersen et al. as two common industrial methods for viscosity calculation are compared with the proposed approach. The absolute average deviation was 9.7 % for free volume theory method, 15.4 % for Lohrenz et al., and 22.16 for Pedersen et al.

Heat and Moisture Transport and Storage Parameters of Bricks Affected by the Environment

Abstract: The effect of external environment on heat and moisture transport and storage properties of the traditional fired clay brick, sand–lime brick and highly perforated ceramic block commonly used in the Czech Republic and on their hygrothermal performance in building envelopes is analyzed by a combination of experimental and computational techniques. The experimental measurements of thermal, hygric and basic physical parameters are carried out in the reference state and after a 3-year exposure of the bricks to real climatic conditions of the city of Prague. The obtained results showed that after 3 years of weathering the porosity of the analyzed bricks increased up to five percentage points which led to an increase in liquid and gaseous moisture transport parameters and a decrease in thermal conductivity. Computational modeling of hygrothermal performance of building envelopes made of the studied bricks was done using both reference and weather-affected data. The simulated results indicated an improvement in the annual energy balances and a decrease in the time-of-wetness functions as a result of the use of data obtained after the 3-year exposure to the environment. The effects of weathering on both heat and moisture transport and storage parameters of the analyzed bricks and on their hygrothermal performance were found significant despite the occurrence of warm winters in the time period of 2012–2015 when the brick specimens were exposed to the environment.

Semi-empirical Density Estimations for Binary, Ternary and Multicomponent Alkali Nitrate–Nitrite Molten Salt Mixtures

Abstract: For sensible thermal energy storage in Concentrating Solar Power (CSP) plants, a molten salt mixture of 60 wt% sodium nitrate (NaNO3) and 40 wt% potassium nitrate (KNO3), known as Solar Salt, is commonly utilized. The paper presents semi-empirical estimation results of the density of Solar Salt and alternative molten salt mixtures with low melting temperatures in a range from 70 °C to 140 °C. These mixtures are Hitec, HitecXL, LiNO3–KNO3–NaNO3 and a multicomponent mixture. The paper shows that density values of mixtures can be closely predicted from single salt densities. The paper examines different estimation rules for mixtures. The quasilinear volumetric additivity rule (QVAR) is known for ternary reciprocal systems. For the first time, the presented work extends the QVAR to multicomponent mixtures. Temperature-dependent densities of selected salt mixtures of the system Ca,Li,K,Na//NO2,NO3 were estimated. Estimations are motivated by a fast and reliable method compared to time-consuming and error-prone measurements of several mixtures.

Evaluation of Thermodynamic Models for Predicting Phase Equilibria of $$\hbox {CO}_{2}$$ CO 2 + Impurity Binary Mixture

Abstract: For the design and operation of $$\hbox {CO}_{2}$$ capture and storage (CCS) processes, equation of state (EoS) models are used for phase equilibrium calculations. Reliability of an EoS model plays a crucial role, and many variations of EoS models have been reported and continue to be published. The prediction of phase equilibria for $$\hbox {CO}_{2}$$ mixtures containing $$\hbox {SO}_{2}$$ , $$\hbox {N}_{2}$$ , NO, $$\hbox {H}_{2}$$ , $$\hbox {O}_{2}$$ , $$\hbox {CH}_{4}$$ , $$\hbox {H}_{2}\mathrm{S}$$ , Ar, and $$\hbox {H}_{2}\mathrm{O}$$ is important for $$\hbox {CO}_{2}$$ transportation because the captured gas normally contains small amounts of impurities even though it is purified in advance. For the design of pipelines in deep sea or arctic conditions, flow assurance and safety are considered priority issues, and highly reliable calculations are required. In this work, predictive Soave–Redlich–Kwong, cubic plus association, Groupe Europeen de Recherches Gazieres (GERG-2008), perturbed-chain statistical associating fluid theory, and non-random lattice fluids hydrogen bond EoS models were compared regarding performance in calculating phase equilibria of $$\hbox {CO}_{2}$$ -impurity binary mixtures and with the collected literature data. No single EoS could cover the entire range of systems considered in this study. Weaknesses and strong points of each EoS model were analyzed, and recommendations are given as guidelines for safe design and operation of CCS processes.

Qualitative Assessments via Infrared Vision of Sub-surface Defects Present Beneath Decorative Surface Coatings

Abstract: In this work, the potentialities of the infrared vision to explore sub-superficial defects in polychromatic statues were investigated. In particular, it was possible to understand how the reflector effect of the exterior golden layers could be minimized, applying advanced statistical algorithms to thermal images. Since this noble metal is present as external coating in both artworks, an in-depth discussion concerning its physicochemical properties is also added. In this context, the principal component thermography technique and, the more recent, partial least squares thermography technique were used on three different datasets recorded, providing long thermal stimuli. The main images were compared both to phasegrams and to the thermographic signal reconstruction results in order to have a clear outline of the situation to be debated. The effects of view factors on the radiation transfer linked to the specular reflections from the surface did not falsely highlight certain features inadvertently. Indeed, the raw thermograms were analyzed one by one. Reflectograms were used to pinpoint emissivity variations due to, e.g., possible repainting. The paper concludes that, as it is possible to understand from a physical point of view, the near-infrared reflectography technique is able to examine the state of conservation of the upper layers in cultural heritage objects, while the infrared thermography technique explores them more in-depth. The thesis statement is based on the thermal and nonthermal parts of the infrared region, therefore, indicating what can be detected by heating the surface and what can be visualized by illuminating the surface, bearing in mind the nature of the external coating.

Resonant Absorption in GaAs-Based Nanowires by Means of Photo-Acoustic Spectroscopy

Abstract: Semiconductor nanowires made of high refractive index materials can couple the incoming light to specific waveguide modes that offer resonant absorption enhancement under the bandgap wavelength, essential for light harvesting, lasing and detection applications. Moreover, the non-trivial ellipticity of such modes can offer near field interactions with chiral molecules, governed by near chiral field. These modes are therefore very important to detect. Here, we present the photo-acoustic spectroscopy as a low-cost, reliable, sensitive and scattering-free tool to measure the spectral position and absorption efficiency of these modes. The investigated samples are hexagonal nanowires with GaAs core; the fabrication by means of lithography-free molecular beam epitaxy provides controllable and uniform dimensions that allow for the excitation of the fundamental resonant mode around 800 nm. We show that the modulation frequency increase leads to the discrimination of the resonant mode absorption from the overall absorption of the substrate. As the experimental data are in great agreement with numerical simulations, the design can be optimized and followed by photo-acoustic characterization for a specific application.

Enhanced Quality Control in Pharmaceutical Applications by Combining Raman Spectroscopy and Machine Learning Techniques

Abstract: In this work, we applied machine learning techniques to Raman spectra for the characterization and classification of manufactured pharmaceutical products. Our measurements were taken with commercial equipment, for accurate assessment of variations with respect to one calibrated control sample. Unlike the typical use of Raman spectroscopy in pharmaceutical applications, in our approach the principal components of the Raman spectrum are used concurrently as attributes in machine learning algorithms. This permits an efficient comparison and classification of the spectra measured from the samples under study. This also allows for accurate quality control as all relevant spectral components are considered simultaneously. We demonstrate our approach with respect to the specific case of acetaminophen, which is one of the most widely used analgesics in the market. In the experiments, commercial samples from thirteen different laboratories were analyzed and compared against a control sample. The raw data were analyzed based on an arithmetic difference between the nominal active substance and the measured values in each commercial sample. The principal component analysis was applied to the data for quantitative verification (i.e., without considering the actual concentration of the active substance) of the difference in the calibrated sample. Our results show that by following this approach adulterations in pharmaceutical compositions can be clearly identified and accurately quantified.

Simultaneous Measurement of Thermal Conductivity and Specific Heat in a Single TDTR Experiment

Abstract: Time-domain thermoreflectance (TDTR) technique is a powerful thermal property measurement method, especially for nano-structures and material interfaces. Thermal properties can be obtained by fitting TDTR experimental data with a proper thermal transport model. In a single TDTR experiment, thermal properties with different sensitivity trends can be extracted simultaneously. However, thermal conductivity and volumetric heat capacity usually have similar trends in sensitivity for most materials; it is difficult to measure them simultaneously. In this work, we present a two-step data fitting method to measure the thermal conductivity and volumetric heat capacity simultaneously from a set of TDTR experimental data at single modulation frequency. This method takes full advantage of the information carried by both amplitude and phase signals; it is a more convenient and effective solution compared with the frequency-domain thermoreflectance method. The relative error is lower than 5 % for most cases. A silicon wafer sample was measured by TDTR method to verify the two-step fitting method.

Study on the Detection of CFRP Material with Subsurface Defects Using Barker-Coded Thermal Wave Imaging (BC-TWI) as a Nondestructive Inspection (NDI) Tool

Abstract: In this paper, a Barker-coded thermal wave imaging approach is reported on the detection of carbon fiber reinforced polymer (CFRP) laminate with subsurface defects, using an integrated Barker code sequence and sinusoidal carrier-modulated laser as the excitation source. Artificial flat bottom holes as subsurface defects are prepared for the experimental investigation. Cross-correlation (CC) algorithm is applied for extracting characteristics of thermal wave signal and forming the corresponding peak delay time and phase images. The effects of Barker code sequence length and carrier-modulated frequency are investigated, which are both most important factors on the detectability of BC-TWI method. The results of the experiments show 5-bit Barker code and 0.1 Hz carrier frequency are the most suitable selection for enhancing inspection capability and obtaining the highest image SNR for a given CFRP laminate material. Furthermore, a comparative experiment is carried out between BC-TWI and lock-in thermography (LIT) method by taking the defect contrast and SNR into account. The results indicate that the BC-TWI CC phase image has higher contrast and SNR than the LIT phase image.

Simulation and Experimental Study on Thermal Conductivity of [EMIM][DEP] + $$\mathbf{H}_\mathbf{2}{} \mathbf{O}$$ H 2 O + SWCNTs Nanofluids as a New Working Pairs

Abstract: In this paper, the single-wall carbon nanotubes (SWCNTs) were dispersed into ionic liquid, 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]), and its aqueous solution [EMIM][DEP](1) + $$\hbox {H}_{2}\hbox {O}(2)$$ to enhance the thermal conductivity of base liquids, which will be the promising working pairs for absorption heat pumps and refrigerators. The enhancement effects on thermal conductivity were studied by experiment and molecular dynamic simulation (MD) methods. The thermal conductivities of [EMIM][DEP] + SWCNTs (INF) and [EMIM][DEP](1) + $$\hbox {H}_{2}\hbox {O}(2)$$ + SWCNT(SNF) both with SWCNT mass fraction of 0.5, 1, and 2 (wt%) were measured by transient hot-wire method. The results indicate that the enhancement ratio of thermal conductivity of INF, and SNF can approach 1.30 when SWCNT is 2 (wt%). Moreover, SWCNTs has a higher enhancement ratio than multi-wall carbon nanotubes (MWCNTs). Density and thermal conductivity of [EMIM][DEP], [EMIM][DEP](1) + $$\hbox {H}_{2}\hbox {O}(2)$$ , INF and SNF systems, together with self-diffusion coefficients of $$\hbox {[EMIM]}^{+}$$ , $$\hbox {[DEP]}^{-}$$ , [EMIM][DEP] and water in solution [EMIM][DEP](1) + $$\hbox {H}_{2}\hbox {O}(2)$$ , were investigated by MD simulations. The results indicate that the maximum relative error between the simulated and experimental densities is about 2 %, and the simulated self-diffusion coefficient of [EMIM][DEP] is in the order of magnitude of $$10^{-11}\,\hbox {m}^{2}\cdot \hbox {s}^{-1}$$ . The average relative deviation for the simulated thermal conductivity of [EMIM][DEP](1) + $$\hbox {H}_{2}\hbox {O}(2)$$ , INF and SNF from experimental ones are 23.57 %, 5 %, and 5 %, respectively. In addition, the contributions of kinetic energy, potential energy, and virial and partial enthalpy terms to thermal conductivity were also calculated. The results indicate that virial term’s contribution to thermal conductivity is the maximum, which accounts for 75 % to 80 % of total thermal conductivity.

Inverse Identification of Temperature-Dependent Thermal Properties Using Improved Krill Herd Algorithm

Abstract: A novel intelligent algorithm, krill herd (KH), is firstly introduced to solve the inverse identification of temperature-dependent thermal properties of materials. To promote the searching ability and accelerate the convergence velocity, three improved KH (IKH) algorithms are proposed and developed for solving the optimization tasks. The temperature-dependent thermal conductivity and specific heat of a building material are estimated by using the KH algorithms, and the IKHs achieve better performance than the original KHs. Moreover, the functional forms of thermal conductivity of insulating and refractory materials are also reconstructed. The IKH algorithm is proved to be more accurate than other algorithms. Finally, a two-dimensional nonhomogeneous heat conduction model is investigated and the thermal conductivities of materials at specified temperatures are reconstructed, in which no prior information is needed for the expressions of the thermal conductivity to be identified. All the retrieval results show that IKH algorithm is robust and effective for solving the inverse heat conduction problems.

Effect of Al $$_2$$ 2 O $$_3$$ 3 Nanoparticles Additives on the Density, Saturated Vapor Pressure, Surface Tension and Viscosity of Isopropyl Alcohol

Abstract: This paper presents results of an experimental study of the density, saturated vapor pressure, surface tension and viscosity of Al $$_2$$ O $$_3$$ nanoparticle colloidal solutions in isopropyl alcohol. Studies of the thermophysical properties of nanofluids were performed at various temperatures and concentrations of Al $$_2$$ O $$_3$$ nanoparticles. The paper gives considerable attention to a turbidimetric analysis of the stability of nanofluid samples. Samples of nanofluids remained stable over the range of parameters of the experiments, ensuring the reliability of the thermophysical property data for the Al $$_2$$ O $$_3$$ nanoparticle colloidal solutions in isopropyl alcohol. The studies show that the addition of Al $$_2$$ O $$_3$$ nanoparticles leads to an increase of the density, saturated vapor pressure and viscosity, as well as a decrease for the surface tension of isopropyl alcohol. The information reported in this paper on the various thermophysical properties for the isopropyl alcohol/Al $$_2$$ O $$_3$$ nanoparticle model system is useful for the development of thermodynamically consistent models for predicting properties of nanofluids and correct modeling of the heat exchange processes.

Thermal Diffusivity of High-Density Polyethylene Samples of Different Crystallinity Evaluated by Indirect Transmission Photoacoustics

Abstract: In this work, thermal diffusivity of crystalline high-density polyethylene samples of various thickness, and prepared using different procedures, was evaluated by transmission gas-microphone frequency photoacoustics. The samples’ composition analysis and their degree of crystallinity were determined from the wide-angle X-ray diffraction, which confirmed that high-density polyethylene samples, obtained by slow and fast cooling, were equivalent in composition but with different degrees of crystallinity. Structural analysis, performed by differential scanning calorimetry, demonstrated that all of the used samples had different levels of crystallinity, depending not only on the preparing procedure, but also on sample thickness. Therefore, in order to evaluate the samples’ thermal diffusivity, it was necessary to modify standard photoacoustic fitting procedures (based on the normalization of photoacoustic amplitude and phase characteristics on two thickness levels) for the interpretation of photoacoustic measurements. The calculated values of thermal diffusivity were in the range of the expected literature values. Besides that, the obtained results indicate the unexpected correlation between the values of thermal diffusivity and thermal conductivity with the degree of crystallinity of the investigated geometrically thin samples. The results indicate the necessity of additional investigation of energy transport in macromolecular systems, as well as the possible employment of the photoacoustic techniques in order to clarify its mechanism.