Temperature Wave Method Research Articles

Design of wood-like metallic material using metal sheet architecture

Abstract This study proposed a new metal-based material design with a modulus of elasticity and thermal conductivity comparable to that of wood by architecturing of metal sheets. The proposed new material is designed in a form in which metal sheets of the same shape with beads are repeatedly stacked. In order to find a design with the target modulus of elasticity and thermal conductivity values, designs were derived using the Design of Experiment (DOE) and the material properties were predicted accordingly. For the prediction of material properties designed in the shape of a metal sheet architecture, finite element analysis combined with the homogenization method was used in consideration of the repeatability of the material microstructure. The reliability of the prediction of material properties based on the finite element analysis using a unit cell was verified by comparison with the results obtained from the compression test and the temperature wave method for the specimen. By analysing the modulus of elasticity and thermal conductivity data corresponding to the designs derived by DOE, we evaluated the effect of the design variables of the metal sheet architecture on the material properties. In addition, we investigated whether the material properties comparable to wood or leather were included within the derived design domain, and presented detailed design data of a metal sheet architecture that provides targeted material properties. It can be inferred from this study that the use of architecturing of metal sheets enables the development of new metal-based materials that can simulate the properties of other materials while utilizing the advantages of fire resistance and recyclability inherent in metals.

Nano-rescaling of gold films on polystyrene: thermal management for SERS.

Nano-textured Au surfaces were prepared on pre-stretched 2D polystyrene (PS) sheets sputtered with different thicknesses of Au. The Au-coated PS was subjected to thermal annealing above the glass transition temperature at ∼150 °C, thus undergoing surface area rescaling via a volume phase transition. The yellow color of the Au changed from the typical mirror-like appearance to a diffusive dark yellow, progressing to dark brown at the smallest feature size, hence, electromagnetic energy was coupled into the substrate. While the surface area footprint is the same after shrinking the PS, the roughness can be modified from the nano- to the micro-scale for different initial thicknesses of sputtered Au. The nanometer-sized features of surface wrinkles on the Au films make them suitable for surface-enhanced Raman scattering (SERS) sensors that can reach ∼104 counts per s per mW. The thermal diffusivity of the contracted surfaces was determined by a non-contact temperature wave method and was larger than that of PS (α ≃ 1.1 × 10-7 m2 s-1) with a linear scaling on the Au thickness: each 10 nm addition of Au increased the diffusivity by 4%. This allows improved heat dissipation from the laser irradiated spot during SERS measurements.

Thermal diffusivity of side-chain-polymer smectic liquid crystals

The thermal diffusivity in the smectic liquid crystals (LCs) of side-chain PmBEn polymers was measured using the temperature wave method. PmBEn polymers form two types of smectic LCs that differ in their degree of side-chain overlap, which affects the thermal diffusivity. Smectic A1 (SmA1) LCs with fully interdigitated side chains have 20% greater thermal diffusivity than smectic Ad LCs with side chains overlapping at the alkyl tail. The results for magnetically oriented SmA1 LCs show that the thermal diffusivity component along the LC director direction (α//) is larger than that perpendicular to the director direction (α⊥). Upon increasing the number m of methylene units in the spacer from 5 to 12, α// increases from 2.50 × 10−7 to 3.11 × 10−7 m2 s−1 and is larger for odd-m homologues, although α⊥ is almost constant around 1.25 × 10−7 m2 s−1. These variations in thermal diffusivity in PmBEn polymers are correlated with the smectic LC structures characteristic of side-chain LC polymers.

Natural heat accumulation in large enclosures of premises with an insulation passive solar heating system

This article provides the results of design studies intended to determine the specific amount of heat accumulated in the inner layers of vast enclosures used in premises with an insulation passive solar heating system (Qacc) by the temperature-wave method. As shown by the calculation data, the value of Qacc depends significantly on the ratio of the Fte surface area of the translucent enclosure of the considered premise to the Ffl surface area of its floor slabs and the amplitude of air motion in the heated premise. According to the calculated data, Qacc, at the end of the second decade of March, is 169.0 kJ/m2 at Fte/Ffl = 0.30–0.40 whereas the coefficient of natural heat accumulation in the inner layers of the given vast enclosure is ≈0.12.

Nanostructured Antireflective and Thermoisolative Cicada Wings.

Inter-related mechanical, thermal, and optical macroscopic properties of biomaterials are defined at the nanoscale by their constituent structures and patterns, which underpin complex functions of an entire bio-object. Here, the temperature diffusivity of a cicada (Cyclochila australasiae) wing with nanotextured surfaces was measured using two complementary techniques: a direct contact method and IR imaging. The 4-6-μm-thick wing section was shown to have a thermal diffusivity of α⊥ = (0.71 ± 0.15) × 10(-7) m(2)/s, as measured by the contact temperature wave method along the thickness of the wing; it corresponds to the inherent thermal property of the cuticle. The in-plane thermal diffusivity value of the wing was determined by IR imaging and was considerably larger at α∥ = (3.6 ± 0.2) × 10(-7) m(2)/s as a result of heat transport via air. Optical properties of wings covered with nanospikes were numerically simulated using an accurate 3D model of the wing pattern and showed that light is concentrated between spikes where intensity is enhanced by up to 3- to 4-fold. The closely packed pattern of nanospikes reduces the reflectivity of the wing throughout the visible light spectrum and over a wide range of incident angles, hence acting as an antireflection coating.

Photo-controllable thermal diffusivity and thermal conductivity driven by the orientation change of nematic liquid crystal with azo-dendrimers

We measured the temperature dependences of anisotropic thermal properties, i.e., thermal diffusivity, thermal effusivity, thermal conductivity, and heat capacity per unit volume, of a nematogen 4′-n-pentyloxybiphenyl-4-carbonitrile (5OCB) containing a small amount (0.02 wt. %) of dendritic azobenzene derivatives (azo-dendrimer), using a temperature wave method. The azo-dendrimers spontaneously adsorb on cell surfaces and act as a command surface, i.e., photo-induced planar/homeotropic alignment by ultraviolet/visible light illumination. By using this effect, we demonstrated thermal property changes except for the heat capacity by almost two times within a few tens of seconds. The phenomenon can be applied to a sheet with photo-controllable thermal diffusivity or thermal conductivity.

Condensed Materials Thermal Diffusivity Measurements Using Temperature Waves Method in Adiabatic Regime

Temperature wave method is a quasi-stationary method for measuring thermal diffusivity of a substance. Method of plane temperature waves is a derivative of temperature wave method based on the notion of applying heat flux to first side of a sample and measuring temperature fluctuation on the second side of a sample. Changing temperature wave frequent allows us to enter adiabatic regime. Considering that phase of heat flux is known, the only parameter to be measured is phase of temperature changes on the second side of a sample relative to the phase of heat flux, which (in adiabatic regime) gives us thermal diffusivity.

Thermal diffusivity anisotropy measured by a temperature wave method in the homologous series of (p-alkoxybenzylidene)-p'-octylaniline (nO.8).

The anisotropy of thermal diffusivity in four homologues of (p-alkoxybenzylidene)-p'-octylaniline (nO.8, n = 4 - 7) was measured using a temperature wave method. The results show that the thermal diffusivity component along the director (α(∥)) is considerably larger than that perpendicular to the director (α(⊥)) in all mesophases, i.e., nematic (N), smectic A (SmA), smectic B (SmB), and smectic G (SmG) phases. Both components of the thermal diffusivity show a dip at the second- or weakly first-order N-SmA phase transition due to the heat capacity anomaly. In contrast, at the first-order SmA-SmB phase transition, thermal diffusivity exhibits a stepwise increase. The x-ray and calorimetric measurements enable a calculation of the thermal conductivity and the study of the effect of the molecular length on the thermal conductivity and diffusivity in the SmA and SmB phases. For the homologues n = 4, 5, and 6, which exhibit the same phase sequence upon cooling, the parallel component of the thermal conductivity k(∥) in the SmA and SmB phases systematically increases with increasing length of the molecular tails, while no such increase is observed in the thermal diffusivity α(∥). We thus conclude that the molecular model [Urbach et al., J. Chem. Phys. 78, 5113 (1983)] is valid for the qualitative prediction of the effect of the molecular length on the magnitude of the thermal conductivity.

Measurements of the Thermal Characteristics of Materials by Regular Mode Methods of the Third Kind

Methods of measuring the thermal characteristics of materials using periodic heating are considered. A classification of the regular-mode methods of the third kind as a function of the method of producing the temperature oscillations, forms of temperature waves and a mathematical model, used in the method, is proposed. A review of measuring equipment which employs the temperature-wave method is presented.

Discontinuous Thermal Diffusivity Change due to the Anchoring Transition of a Liquid Crystal on a Perfluoropolymer Surface

Thermal diffusivity of a liquid crystal, 4'-butyl-4-heptyl-bicyclohexyl-4-carbonitrile, was measured using a temperature wave method. The liquid crystal was sandwiched by two glass substrates, which were treated with three different surface agents for providing distinct molecular orientations. Here, we demonstrate that: 1) a large thermal diffusivity anisotropy arising from different orientations, that is, planar and homeotropic states, was found in the nematic and smectic A phases; 2) when substrates were coated with a perfluoropolymer, abrupt changes of the thermal diffusivity were observed in the nematic phase both on cooling and heating due to the discontinuous anchoring transition between planar and homeotropic states. The temperature dependence of the thermal diffusivity anisotropy was well described by a power law, with an exponent of 0.27 according to the mean-field theory.

Thermal diffusivity of submicro- and nanocrystalline niobium, titanium, and zirconium at high temperatures

The results of thermal diffusivity measurements of pure niobium, titanium, and zirconium with the standard, submicro-, and nanocrystalline structures at high temperatures are presented; the results were obtained in the automated regime by the dynamic method of plane temperature waves.

Critical anomalies in thermal diffusivity of liquid-crystalline terephthal-bis-(4-n-butylaniline)

A temperature wave method has been applied to observe the thermal diffusivity through the isotropic (Iso)-nematic (N)-smectic Sm-A-Sm-C-Sm-B-crystals VI-VII-VIII phase transitions of terephthal-bis-(4-n-butylaniline) (TBBA). Critical anomalies have been found in the N-Sm-A and Sm-C-Sm-B phase transitions as diplike shaped, consistent with the predictions based on the dissipative couplings between the order parameter and the conserved free-energy density. Singular points with a gap have been observed at the Sm-B-crystal VI, crystals VI-VII, and crystals VII-VIII phase transitions, which show polymorphic behaviors on heating and cooling. The second-order Sm-A-Sm-C phase transition emerged as a singular temperature dependence. In all the phases thermal diffusivity decreases with increasing temperature except for Sm-C, where thermal diffusivity increases with increasing temperature. The origin of the anomaly in the thermal diffusivity in Sm-C is discussed based on the parametric analysis of dynamic critical behavior in the Sm-A-Sm-C phase transitions together with the tilt angle change obtained by use of simultaneous measurements of x-ray diffraction and differential scanning calorimetry.

Thermal diffusivity of iron at high temperatures

The results of the thermal diffusivity measurements for pure iron within the temperature range from 830 K up to 1820 K obtained in automated mode by the dynamic plane temperature wave method have been presented.

Thermal and optical properties of femtosecond-laser-structured PMMA

Thermal diffusivity of laser micro- and nano-structured regions in polymethylmethacrylate (PMMA) was measured by the temperature wave method with a lateral resolution reduced to ∼10 μm using an array of micro-sensors. The volume fraction of laser modified phase was maximized by implementing tightly focused femtosecond laser pulses inside PMMA and maintaining distance of few micrometers between the irradiation spots. The absolute value of thermal diffusivity of PMMA 1.066±0.08×10−7 m2/s was reliably determined with the miniaturized sensors. Regions laser structured by single pulses had no trace of carbonization, almost the same thermal diffusivity as the host PMMA, and a stress-induced birefringence Δn∼10−4 modulated with period ∼2 μm.

Thermal and optical properties of the femtosecond-laser-structured and stress-induced birefringent regions in sapphire

Temperature diffusivity of laser micro-structured regions in sapphire is determined by a temperature wave method with a lateral resolution reduced to ~10 microm using a directly sputtered micro-sensor and heater. A record high reduction of the temperature diffusivity of sapphire by 12% from its (1.26+/-0.02) x 10(-5)m(2)/s in-bulk value inside the femtosecond laser-structured volumes is determined; in a BK7 glass (~4.8x10(-7) m(2)/s), a 2% decrease of the thermal diffusivity has been observed. Origin of the reduction is consistent with disorder and scattering of phonons around the laser photo-modified micro-volumes. The stress-induced birefringence is directly measured by polariscopy together with its radial distribution, and azimuthal orientation of the polarization ellipsis near the laser structured regions in sapphire. The maximum birefringence of Deltan approximately 1x10(-3) is achieved without crack formation and corresponds to a local stress of ~1.3 GPa. The stress (and birefringence) decay radially with a single-exponential constant of tau(R) = 24 microm while the azimuthal orientation of the polarization ellipsis is spiraling around the laser structured volume. Such structures are promising in waveguiding and lasing applications of optical vortices where spatial control of birefringence and optical activity are required.

Thermal diffusivity in femtosecond-laser-structured micro-volumes of polymers

Thermal diffusivity of laser micro-structured regions in plastics was determined using a temperature wave method with a lateral resolution reduced to ∼10 μm using an array of micro-sensors. A high volume fraction (>25%) of laser modified phase was recorded by tightly focused femtosecond-laser pulses inside films of poly-methylmethacrylate, non-oriented polyethylene, polystyrene, and polyimide-Kapton. Changes in thermal diffusivity inside the laser-structured volumes of the order of a few percent were reliably determined with the miniaturized sensors. The origin of the change of thermal properties in plastics is discussed.

Method of temperature waves in thermophysical investigations (Analysis of Soviet and Russian Experiences)

The procedure of employing temperature waves for the investigation of the thermophysical properties of condensed materials is considered. Some experimental facilities utilizing this method are described.

Thermal diffusivity of mantle (Pyrolite) minerals at temperatures between room temperature and melting point (300–1700 K)

An original experimental apparatus developed at the Geothermometry Laboratory of the Faculty of Physics of the MSU was used to measure the thermal diffusivity of several mantle minerals over a wide temperature range, extending up to the melting point. Application of the temperature wave method made it possible to account for the radiative heat transfer from the sample surface into ambient space and, thus, to achieve high accuracy in measuring this important thermal characteristic for each substance.

Thermal diffusivity measurement of polyethylene melt by a new temperature wave method

Thermal diffusivity of high density polyethylene (PE) has been measured by a new a. c. Joule-heating method. The diffusivity was determined at various temperatures between room temperature and above melting point in heating and cooling processes. This method is based on the phase shift of temperature waves across film sample, so that it offers several advantages, e.g., easy measuring in polymer melts.

Temperature wave method for heat-insulating materials

The article presents a new method of solving the inverse boundary-coefficient heat conduction problem with the pulse-period action of the heat flux on one of the surfaces of a flat body. The method is bases on the use of a numerical Fourier analysis for processing temperature fluctuations recorded on the opposite surface of the body.