Simultaneous Measurement Of Thermal Diffusivity Research Articles

Microscale heat-flux meter for low-dimensional thermal measurement and its application in heat-loss modified Angstrom method

A microscale heat-flux meter is designed based on micro-hotwire and infrared thermal microscopy. Its feasibility in low-dimensional thermal measurement is verified by its application in heat-loss modified Angstrom method for simultaneous measurement of thermal diffusivity, thermal conductivity and specific heat. The hotwire and the sample under test are placed in a vacuum chamber. Through an observation window, the infrared microscopy can capture the thermal image including the hotwire and the sample. When the hotwire is heated, the temperature distribution along the wire is acquired by the readings extracted from the thermal image, which enables the determination of nonlinear and local temperature gradient. This gradient, according to Fourier's Law, can be used to calculate the local heat flux. When a sample is attached to the middle of the hotwire, the attached point is appeared to be a singularity in the temperature distribution along the hotwire, which poses a rigorous challenge to calculate the heat flux flowing into the sample. Here we tried some approaching strategies and verified that the local heat flux at second derivative minima around the singularity is a good enough approximation. The mathematical and physical origins for this approximating strategy are also discussed. This microscale heat-flux meter is a general technique, which is promising for an extension to other thermal measurements.

Quadrupole modelling of dual lock-in method for the simultaneous measurements of thermal diffusivity and thermal effusivity

The simultaneous measurement of thermal diffusivity and thermal effusivity based on the temperature wave analysis (TWA) is proposed by introducing the dual lock-in temperature sensor with a photo-thermal ac heat source. The thermal effect from each component in the multilayered experimental system is simulated by the quadrupole modeling adopted to the pure periodic heating of the temperature wave. The frequency dependency of the thermal effect from the thermal contact resistance and capacitance in the sensor were analyzed and minimized by taking the optimal frequency range of the temperature wave. The proposed method is applied to examine the nematic-isotropic phase transition of the liquid crystal 4′-(pentyloxy)-4-biphenyl carbonitrile (5OCB). The results were compared with the previous results measured with a single sensor and the advantage of the dual lock-in temperature sensor was demonstrated.

Simultaneous Measurement of Thermal Diffusivity and Thermal Conductivity by Means of Inverse Solution for One-Dimensional Heat Conduction (Anisotropic Thermal Properties of CFRP for FCEV)

For safe and fast fueling of hydrogen in a fuel cell electric vehicle at hydrogen fueling stations, an understanding of the heat transferred from the gas into the tank wall (carbon fiber reinforced plastic (CFRP) material) during hydrogen fueling is necessary. Its thermal properties are needed in estimating heat loss accurately during hydrogen fueling. The CFRP has anisotropic thermal properties, because it consists of an adhesive agent and layers of the CFRP which is wound with a carbon fiber. In this paper, the thermal diffusivity and thermal conductivity of the tank wall material were measured by an inverse solution for one-dimensional unsteady heat conduction. As a result, the thermal diffusivity and thermal conductivity were $$2.09 \times 10^{-6}\hbox { m}^{2}{\cdot }\hbox {s}^{-1}$$ and $$3.06\hbox { W}{\cdot }\hbox {m}{\cdot }^{-1}\hbox {K}^{-1}$$ for the axial direction, while they were $$6.03 \times 10^{-7}\,\hbox {m}^{2}{\cdot }\hbox {s}^{-1}$$ and $$0.93\,\hbox {W}{\cdot }\hbox {m}^{-1}{\cdot }\hbox {K}^{-1}$$ for the radial direction. The thermal conductivity for the axial direction was about three times higher than that for the radial direction. The thermal diffusivity shows the same trend in both directions because the thermal capacity, $$\rho c$$ , is independent of direction, where $$\rho $$ is the density and c is the heat capacity.

Simultaneous measurement of thermal diffusivity and effusivity of solids using the flash technique in the front-face configuration

Both thermal diffusivity and effusivity (or conductivity) are necessary to characterize the thermal transport properties of a material. The flash method is the most recognized procedure to measure the thermal diffusivity of free-standing opaque plates. However, it fails to simultaneously obtain the thermal effusivity (or conductivity). This is due to the difficulty of knowing the total energy absorbed by the sample surface after the light pulse. In this work, we propose using the flash method in the front-face configuration on a two-layer system made of the unknown plate and a fluid of known thermal properties. We demonstrate that the surface temperature is sensitive to the thermal mismatch between the plate and the fluid, which is governed by their thermal effusivity ratio. In order to verify the validity of the method and to establish its application limits we have performed flash measurements, using a pulsed laser and an infrared camera, on a set of calibrated materials (metals, alloys, ceramics and polymers) covering a wide range of thermal transport properties. These results confirm the ability of the flash method to simultaneously retrieve thermal diffusivity and effusivity in a fast manner in samples whose effusivities are lower than three times the effusivity of the liquid used as backing fluid.

Simultaneous measurement of thermal diffusivity and effective infrared absorption coefficient in IR semitransparent and semiconducting n-CdMgSe crystals using photothermal radiometry

In this paper we propose a new procedure of simultaneous estimation of the effective infrared optical absorption coefficient and the thermal diffusivity of solid state samples using the photothermal infrared radiometry method in the transmission configuration. The proposed procedure relies on the analysis of the frequency dependent signal obtained from the samples covered with thin aluminum foil. This method can be applied for both optically opaque and transparent samples. The proposed method is illustrated with the results of the thermal diffusivity and the effective IR absorption coefficient obtained for several Cd1−xMgxSe crystals.

Simultaneous Measurement of Thermal Diffusivity and Optical Absorption Coefficient of Solids Using PTR and PPE: A Comparison

Modulated photothermal radiometry (PTR) and a modulated photopyroelectric (PPE) technique have been widely used to measure the thermal diffusivity of bulk materials. The method is based on illuminating the sample with a plane light beam and measuring the infrared emission with an infrared detector (PTR) or the electric voltage produced by a pyroelectric sensor in contact with the sample (PPE). The amplitude and phase of both photothermal signals are recorded as a function of the modulation frequency and then fitted to the theoretical model. In this work, we compare the ability of modulated PTR and PPE to retrieve simultaneously the thermal diffusivity and the optical absorption coefficient of homogeneous slabs. In order to eliminate the instrumental factor, self-normalization is used, i.e., the ratio of the photothermal signal recorded at the rear and front surfaces. The influence of the multiple reflections of the light beam and the transparency to infrared wavelengths are analyzed. Measurements performed on a wide variety of homogeneous materials, transparent and opaque, good and bad thermal conductors, confirm the validity of the method. The advantages and disadvantages of both techniques are discussed.

Simultaneous measurement of thermal diffusivity and optical absorption coefficient using photothermal radiometry. II Multilayered solids

The aim of this work is to analyze the ability of modulated photothermal radiometry to retrieve the thermal diffusivity and the optical absorption coefficient of layered materials simultaneously. First, we extend the thermal quadrupole method to calculate the surface temperature of semitransparent multilayered materials. Then, this matrix method is used to evaluate the influence of heat losses by convection and radiation, the influence of the use of thin paint layers on the accuracy of thermal diffusivity measurements, and the effect of lateral heat diffusion due to the use of Gaussian laser beams. Finally, we apply the quadrupole method to retrieve (a) the thermal contact resistance in glass stacks and (b) the thermal diffusivity and optical absorption coefficient depth profiles in heterogeneous materials with continuously varying physical properties, as is the case of functionally graded materials and partially cured dental resins.

Simultaneous measurement of thermal diffusivity and optical absorption coefficient using photothermal radiometry. I. Homogeneous solids

Modulated photothermal radiometry (PTR) has been widely used to measure the thermal diffusivity of bulk materials. The method is based on illuminating the sample with a plane light beam and measuring the infrared emission with an infrared detector. The amplitude and phase of the PTR voltage is recorded as a function of the modulation frequency and then fitted to the theoretical model. In this work, we test the ability of modulated PTR to retrieve simultaneously the thermal diffusivity and the optical absorption coefficient of homogeneous slabs. In order to eliminate the instrumental factor, self-normalization is used, i.e., the ratio of the PTR signal recorded at the rear and front surfaces. The influence of the multiple reflections of the light beam, the heat losses, and the transparency to infrared wavelengths are analyzed. Measurements performed on a wide variety of homogeneous materials, covering the whole range from transparent to opaque, confirm the validity of the method. In Part II of this work, the method is extended to multilayered materials.

E134 円筒座標系非定常熱伝導逆問題解を用いた熱物性値測定法(熱物性III)

A simultaneous measurement of thermal diffusivity and heat conductivity using inverse solution is significantly improved by introducing a new idea. In the idea, a data window for series of sampled temperature is opened for a time interval, where number of measured temperature in a solid are enough to estimate the temperature at any time and any position. The size of window is determined by Fourier number including thermal diffusivity.

Relaxation behavior of ultradrawn poly(ethylene) film by temperature wave analysis

A new sensitive thermal analysis for the observation of re-orientation behavior in the melting region of the ultradrawn poly(ethylene) film was proposed by the simultaneous measurement of thermal diffusivity and birefringence under optical microscope in a constant heating rate. Thermal diffusivity was obtained by the phase delay of temperature wave passed through the thickness direction of the specimen. The results correspond with each other over wide temperature range including melting temperature. It was concluded that the thermal diffusivity measurement was more sensitive not only to detect the molecular relaxation in a continuous heating run, but also to find out the delicate variation of chain direction.

A new apparatus for thermal diffusivity and specific heat measurements of films and liquids by means of Fourier transform thermal analysis

A new apparatus based on the technique of Fourier transform thermal analysis for the measurement of thermal diffusivity, specific heat per unit volume, thermal effusivity, and thermal conductivity of thin solid and liquids films (of the order of micrometres) has been developed. The apparatus consists of the following components: specimen assembly; function synthesiser; DC potentiometer circuit; lock-in amplifier; DC microvoltmeter; temperature controller; computer; and special attachments. An electrically insulating specimen, 5 x 10 mm 2 and 1 ∼ 100 μm in thickness, is sandwiched between two gold layer resistors sputtered on two Pyrex glass plates, one being the heat generator and the other the sensor. For an electrically conductive specimen, a three-layered specimen stack, insulating film/conductive specimen/insulating film, can be used. By means of the Fourier transform technique, the thermal diffusivity across the specimen thickness can be obtained under heating or cooling at a constant rate of 0.2 ∼ 10 K min - 1 from -50 °C to 300 °C. By prior calibration measurements with a reference material of known properties, the specific heat per unit volume of the specimen film can be obtained simultaneously, so that the thermal conductivity and thermal effusivity can be derived. In addition, simultaneous measurement of thermal diffusivity, specific heat per unit volume, and thermal conductivity can be obtained during the melting process. Experiments illustrating various applications and measurements are described and discussed.

Simultaneous measurement of thermal diffusivity, heat capacity, and thermal conductivity by Fourier transform thermal analysis

The Fourier analysis of higher-order harmonics of a temperature wave provides a new technique for simultaneous measurement of thermal properties of thin films as a function of frequency under temperature scanning. The mathematical formula for the propagation of a square wave is examined first in comparison with that of a sine wave and the principle of Fourier transform thermal analysis is validated experimentally. Results on thermoplastics are shown and the glass transition and crystallisation are discussed. The features are summarised as follows: it employs a thin high-sensitivity sensor with negligible heat capacity; the actual temperature wave that is propagating in the specimen can be directly observed; the thermal properties of thin film specimens (thickness of the order of micrometres) can be determined nondestructively at a single time measurement. The principle applied to the technique, called Fourier transform thermal analysis', makes it possible to determine simultaneously thermal diffusivity, heat capacity per unit volume, and thermal conductivity as a function of frequency and temperature.

Simultaneous measurement of heat capacity and thermal diffusivity in solid–solid and solid–liquid phase transitions of n-alkane

A new technique analyzing Fourier spectrum of higher harmonics of temperature wave is proposed, which is called as Fourier Transform Temperature Wave Analysis (FT-TWA). It enables a simultaneous measurement of thermal diffusivity, heat capacity per unit volume, and thermal conductivity at a time by temperature scanning under multiple frequencies. This method was applied to solid–solid and solid–liquid phase transitions of n-alkane, which is usually used as a model of molecular crystal. The frequency dependence of heat capacity and thermal diffusivity in the phase transitions was observed.

Ångström methods applied to simultaneous measurements of thermal diffusivity and heat transfer coefficients: Part 1, theory

We present a method for simultaneous measurement of thermal diffusivity and local heat transfer coefficient based on a theory originally stated by Ångström. We apply a sinusoidally varying thermal flux incident on one face of a one-dimensional specimen and convectively cool its opposite face. This results in a sinusoidally varying temperature on the cooled face with a measurable phase lag between the incident and transmitted waves that depends upon the material properties and the heat transfer coefficient.

ハロゲンフラッシュ法による熱拡散率,比熱,熱伝導度の同時測定におけるMarquardt法の適用

ハロゲンフラッシュ法による熱拡散率,比熱,熱伝導度の同時測定におけるMarquardt法の適用

Temperature oscillation techniques for simultaneous measurement of thermal diffusivity and conductivity

Simple temperature ocillation techniques are described for the last measurement of thermal dill'usivity and conductivity of liquids. The liquid specimen is a slab bounded above and below by a reference material. Two Peltier elements mounted on the outer Surfaces of the reference layers generate temperature ocillationS of these surfaces. Temperature waves propagate tluough the reference layers into the specimen. The thermal dilhusivity of the specimen is deduced by measuring all evaluating the amplitude attenuation and or the phase shift between the fundamental temperature oscillations at the surface of the liquid specimen and at a well-defined position inside the specimen. If the thermal diffusivity of the specimen is known. the thermal conductivity is determined by the measured amplitude attenuation and or the phase shill between the fundamental temperature oscillations at the surface of the reference layer and at the surface of the specimen. Slab and semi-infinite body geometries are considered. Measurement cells are designed and experiments are carried out with water, ethanol. heptane. monane. and glycerine. The results of the measurements of thermal dilhusivity asree very well, and those of thermal conductivity reasonably well, with the data obtained from the literature.

Simultaneous Measurement of Thermal Diffusivity and Conductivity Applied to Bi-2223 Ceramic Superconductors

A method to measure the thermal diffusivity α and the conductivity κ under an identical experimental setup has been developed and α and κ of Bi-2223 oxide superconductor have been measured quasi-simultaneously. The results are analyzed on the basis of the BRT and Tewordt-Wolkhausen theory. The simultaneous measurement makes it possible to estimate the specific heat C and the Debye temperature Θ D , as well as to separate the electron and phonon contributions to the diffusivity. The simultaneous measurement also provides a useful check on the reliability and the consistency of the analyses.

Simultaneous measurement of thermal diffusivity, thermal conductivity and specific heat by impulse-response photopyroelectric spectrometry

A novel photothermal technique is developed, which enables the simultaneous measurement of the thermal diffusivity α, thermal conductivity κ, and the specific heat C of a sample. The technique is based on frequency-modulated time-delay photopyroelectric spectrometry (FM-TDPS), which consists of chirped laser excitation of the sample and detection of the thermal impulse response by a thin-film pyroelectric detector. No calibration is required for the measurements; absolute values for α, κ, and C may be obtained without having to employ a reference sample. Results on superconducting YBa2Cu3O7−x are reported for the temperature range 50–300 K; the values obtained compare favorably with reported measurements of α, κ, and C for YBa2Cu3O7−x , which previously required separate experiments for their determination.

The harmonics of the nonlinear pyroelectric current and the simultaneous measurement of thermal diffusivity, pyroelectric coefficient and spontaneous polarization

Theoretical principles of simultaneous measurements of the pyroelectric coefficient λ, spontaneous polarization Ps and thermal diffusivity α, based on analysis of high order harmonics of the nonlinear pyroelectric current, are given.

Simultaneous measurement of thermal diffusivity and specific heat at high temperatures by a single rectangular pulse heating method

A method for the simultaneous measurement of thermal diffusivity and specific heat by a single rectangular heating pulse on a finite cylindrical specimen is described. The method takes into account radiation losses from all the surfaces of the specimen. The theoretical principle of the technique was studied by solving the transient heat conduction equation for a finite disk heated on the front surface by a single rectangular radiant energy pulse. An apparatus was constructed to comply with the theoretical conditions and was connected to a personal computer. Thermal diffusivity and specific heat were determined from the data obtained on the temperature response of the back surface of the specimen and from the theoretical results. This method can be applied to materials having a wide range of thermal conductivity values and has a good accuracy at high temperatures. Examples of the measurements are presented.