Measurement Of Effective Thermal Conductivity Research Articles

Measurement of through-plane effective thermal conductivity and contact resistance in PEM fuel cell diffusion media

An experimental study was performed to determine the through-plane thermal conductivity of various gas diffusion layer materials and thermal contact resistance between the gas diffusion layer (GDL) materials and an electrolytic iron surface as a function of compression load and PTFE content at 70 ° C. The effective thermal conductivity of commercially available SpectraCarb untreated GDL was found to vary from 0.26 to 0.7 W/(m ° C) as the compression load was increased from 0.7 to 13.8 bar. The contact resistance was reduced from 2.4 × 1 0 − 4 m 2°C/W at 0.7 bar to 0.6 × 1 0 − 4 m 2°C/W at 13.8 bar. The PTFE coating seemed to enhance the effective thermal conductivity at low compression loads and degrade effective thermal conductivity at higher compression loads. The presence of microporous layer and PTFE on SolviCore diffusion material reduced the effective thermal conductivity and increased thermal contact resistance as compared with the pure carbon fibers. The effective thermal conductivity was measured to be 0.25 W/(m ° C) and 0.52 W/(m ° C) at 70 ° C, respectively at 0.7 and 13.8 bar for 30%-coated SolviCore GDL with microporous layer. The corresponding thermal contact resistance reduced from 3.6 × 1 0 − 4 m 2°C/W at 0.7 bar to 0.9 × 1 0 − 4 m 2°C/W at 13.8 bar. All GDL materials studied showed non-linear deformation under compression loads. The thermal properties characterized should be useful to help modelers accurately predict the temperature distribution in a fuel cell.

Structural and thermal transport properties of Zn xTe 100− x ( x = 5, 10, 30 and 50) alloys

Measurements of effective thermal conductivity ( λ e) and effective thermal diffusivity ( χ e) of twin pellets of Zn x Te 100− x ( x = 5, 10, 30 and 50) chalcogenide materials, prepared under load of 5 tons (equivalent pressure ≈433 MPa) have been made simultaneously at room temperature using transient plane source (TPS) technique. Specific heat per unit volume ( C p ) has also been determined from the so obtained data of λ e and χ e. The material has been prepared by melt quenching method. The results indicate that both the values of λ e and χ e increase logarithmically with increasing Zn concentration. This behaviour of λ e and χ e with zinc concentration can be explained by change of bond formation from covalent to ionic in this system. An effort has also been made to predict these values by an empirical relation. X-ray diffraction (XRD) studies for structural investigation of ZnTe have also been carried out and found to be polycrystalline in nature.

Comparative analysis of some thermo-physical properties of Se 90Zn 10 and Te 90Zn 10 alloys

The present paper reports a comparative study of some thermo-physical properties (thermal conductivity, diffusivity and specific heat per unit volume) of Se 90Zn 10 and Te 90Zn 10 alloys. Simultaneous measurements of effective thermal conductivity ( λ e) and effective thermal diffusivity ( χ e) of twin pellets of Se 90Zn 10 and Te 90Zn 10 alloys using transient plane source (TPS) technique have been made at room temperature. From the measured values of λ e and χ e, the specific heat per unit volume ( C v) has been calculated. The results indicate that the measured values of these parameters are higher for Te 90Zn 10 alloy as compared to Se 90Zn 10 alloy. This is explained in terms of thermal conductivity of chalcogen elements Se and Te.

Application of a co-continuous composite model of effective thermal conductivity to ice–air systems

Effective thermal conductivity measurements were performed for two ice–air systems (ice chips produced by a commercial ice-maker and synthetic snow) using a transient comparative technique. These systems were chosen because the ice fraction could be controlled, thereby de-coupling the problems of ice fraction and thermal conductivity prediction. None of the commonly used simple effective thermal conductivity models (specifically the Series, Parallel, two forms of the Maxwell–Eucken and Effective Medium Theory models) provided adequate prediction accuracy over the full range of ice fractions in the experimental data. The best predictions were provided by a composite model that combined the Effective Medium Theory structure and the recently developed co-continuous structure.

New temperature dependent thermal conductivity data for water-based nanofluids

This paper presents effective thermal conductivity measurements of alumina/water and copper oxide/water nanofluids. The effects of particle volume fraction, temperature and particle size were investigated. Readings at ambient temperature as well as over a relatively large temperature range were made for various particle volume fractions up to 9%. Results clearly show the predicted overall effect of an increase in the effective thermal conductivity with an increase in particle volume fraction and with a decrease in particle size. Furthermore, the relative increase in thermal conductivity was found to be more important at higher temperatures. Obtained results compare favorably with certain data sets and theoretical models found in current literature.

A New Panel Test Facility for Effective Thermal Conductivity Measurements up to 1,650°C

A new steady-state panel test facility is presented which has been designed and constructed for effective thermal-conductivity measurements of insulations in the temperature range between 300 and 1,650°C following ASTM C201-93 and DIN V ENV-1094. Square-shaped samples (length of 400 mm) are used, heated from above and settled on a water-cooled calorimeter system to obtain a one-dimensional steady-state temperature field. The heat is supplied by electrical heating elements freely hanging inside a furnace which is completely constructed from ceramic components to withstand temperatures up to about 1,800°C. The calorimeter system consists of a square central measuring zone (length of 100 mm) surrounded by guard loops to avoid heat losses in all directions. The samples, e.g., a number of fiber mats, one on top of the other up to a maximum height of 110 mm, are open to ambient pressure and atmosphere (air). Measurements include the heat flow rate (taken in the central calorimeter), temperature differences across individual layers of the sample (measured by a series of thermocouples which regularly have to be calibrated), and the thickness of the respective layers (before and after the experiment). The thermal conductivities range from 0.025 to 2 W · m−1 · K−1, and both isotropic and non-isotropic materials can be investigated due to the one-dimensional characteristic of the temperature field. Measurements for alumina fiber mats are presented, and good agreement is found with respective results from other methods and test facilities.

Intercomparison of Insulation Thermal Conductivities Measured by Various Methods

In the present contribution, systematic effective thermal-conductivity measurements with different methods are reported for various materials. One of the materials studied, calcium silicate, is isotropic; the other two, alumino-silicate and alumina fiber mats, are non-isotropic. The measurements were carried out with two different steady-state panel test apparatus (according to ASTM C201, designed and constructed by authors), two guarded hot-plate apparatus (ISO 8302, with either one or two samples), one steady-state radial heat flow apparatus (designed by authors), and one transient hot-wire instrument (DIN EN 993-14). These apparatus are operated at ambient pressure and atmosphere (air) between 20 and 1,650°C, and are briefly described in the article. The results show the well-known increase of effective conductivity with temperature, mainly due to radiation heat transfer. For the case of the isotropic calcium silicate material (bulk density of 220 kg m−3), no significant differences between the various methods have been found and the results can easily be correlated within ± 10%. The fiber-mat results, however, show additional effects of the density (between 103 and 170 kg m−3) and the fiber orientation. Large differences exceeding 30% are found between plate and hot-wire results.

Measurement of dough effective thermal conductivity using an integrated thermocouple during the bread baking process

AbstractThe present study produced an integrated thermocouple in order to gain an understanding of the heat transfer mechanism during baking. The thin film thermocouple was made by depositing copper‐nickel on a polyimide sheet base, and five hot junctions were arranged at regular intervals. Thermal electromotive force was proportional to the temperature difference between the reference and hot junctions. The study also used the integrated thermocouple to investigate heat transfer properties during baking that are equivalent to effective thermal conductivity, which include latent heat transport, water vapor diffusion, and heat conduction. The effective thermal conductivity crumbs increased according to the latent heat transportation effect caused by water vapor diffusion, and the thermal conductivity of crust was in agreement with its effective thermal conductivity value measured by the steady state parallel plate method. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(6): 373–385, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20165

Temperature dependence of effective thermal conductivity and effective thermal diffusivity of Se90In10 bulk chalcogenide glass

Abstract Measurement of effective thermal conductivity (λe) and effective thermal diffusivity (χe) of twin pellets of Se90In10 bulk chalcogenide glass has been carried out in the temperature range from 303 to 323 K and cooling from 323 to 303 K using transient plane source (TPS) technique. In the heating process variation of effective thermal conductivity (λe) and effective thermal diffusivity (χe) is observed. Both quantities are found to be maximum at 313 K, which lies in the vicinity of glass transition temperature (Tg). During the cooling process λe and χe remain same at all temperatures. Such type of behavior shows thermal hysteresis in this sample, which can be explained on the basis of structural change of the Se90In10 bulk chalcogenide glass.

Effective Thermal Conductivity Measurement and Heat Transfer Enhancement of Metal Hydride Bed for Heat Driven Type Refrigerator

Effective Thermal Conductivity Measurement and Heat Transfer Enhancement of Metal Hydride Bed for Heat Driven Type Refrigerator

Temperature dependence of effective thermal conductivity and effective thermal diffusivity of CdZnSe composite

Samples of selenium rich Se85Cd15−xZnx (x = 0, 3, 7, 11 and 15) system in bulk form have been prepared using a technique of slow cooling of the melt. Measurements of effective thermal conductivity (λe) and effective thermal diffusivity (χe) of Se85Cd15−xZnx pellets, prepared at constant load of 10 tons, have been carried out from room temperature to 200 °C using the transient plane source technique. The variation in λe and χe of Se85Cd15−xZnx with the concentration of zinc and temperature is explained on the basis of structure modifications of the samples and the mean free path of the phonons due to scattering from defects and voids.

Thermal transport and its structure dependence in ZnxSe100−x (x=10, 20, 40 and 50) alloys

Abstract Simultaneous measurements of effective thermal conductivity (λe) and effective thermal diffusivity (χe) of twin pellets of ZnxSe100−x (x = 10, 20, 40 and 50) chalcogenide materials, prepared under a load of 5 tons (equivalent pressure ≈ 433 MPa), have been made at room temperature using transient plane source (TPS) technique. From the measured values of λe and χe specific heat per unit volume (Cp) has been calculated. The results indicate that both the values of λe and χe increase linearly with increasing Zn concentration. Similar to λe and χe, the Cp also shows a linear increase with the increase in Zn concentration. This behaviour of λe and χe with increasing Zn concentration can be explained using structural information obtained from X-ray diffraction (XRD) of these materials and also using the change in the nature of bond from covalent to iono-covalent in this system. Comparative XRD studies for structural investigation of ZnxSe100−x (x = 10 and 40) have also been discussed. An effort has also been made to predict these values by an empirical relation. The values obtained through empirical relations are in good agreement with the experimental values of λe, χe and calculated values of Cp.

食パンの高温域における有効熱伝導率の測定

食パンの高温域における有効熱伝導率の測定

Fundamental Study on Injection Molding of Magnesium Alloy (2nd Report, Effective Thermal Conductivity of Packed Bed of Magnesium Alloy Particles)

The present study investigated experimentally the effects of temperature and pressure upon effective thermal conductivity of packed bed of magnesium alloy particles. The test particles made of AM50A or AZ91D were poured into a cylindrical vessel and were applied a given superficial pressure for six hours under a constant temperature condition. The superficial pressure was changed between 2.5 MPa and 10 MPa, and the temperature was varied from 95.5°C to 457°C. After removing the packed bed of magnesium alloy particles from the cylindrical vessel, the measurement of effective thermal conductivity was carried out under the steady state comparison method. The effective thermal conductivity increased with an increasing in the pressure, temperature and the thermal conductivity of the particle. At a given material of particle, the effective thermal conductivity was mainly dominated by the relative density and was increased with an increasing in the relative density. The dependency of the effective thermal conductivity upon the relative dencity was remarkable in the low relative dencity region and the high relative dencity region.

食パン焼成過程における集積型熱電対を利用したパン生地有効熱伝導度の測定

食パン焼成過程におけるパン生地内の伝熱機構の解明を目的として集積型の薄膜熱電対，細線熱電対を作製した．薄膜熱電対はバルクと比較して熱起電力が低下したが，均質であり，温度と熱起電力の関係は線形であった．そこで，実際の食パン焼成過程において集積型熱電対を用いて温度測定を行った結果，その高い位置精度により，両者ともクラスト近傍の温度場を良好に再現した．さらに，食パン焼成中の熱流束を測定し，焼成中の水分移動の寄与を含めた有効熱伝導度に相当する量を計算した．焼成中のクラムの有効熱伝導度は，定常時の熱伝導度と比較して非常に大きなものとなった．一方，クラストの有効熱伝導度は小さく，平板比較法で測定を行った有効熱伝導度に概ね一致した．

Effective thermal conductivity of a compressed Li 2TiO 3 pebble bed

In order to study combined phenomena of thermal and mechanical properties of Li 2TiO 3 pebble bed, simultaneous measurement of effective thermal conductivity and stress–strain property was conducted. Effective thermal conductivity of the bed was measured under compressive load up to 10 MPa at temperatures ranging from 673 to 973 K. At all temperatures, increases of effective thermal conductivity due to the compressive deformation were confirmed. When successive loads, heating–cooling or compression, worked on the bed, effective thermal conductivity increased according to promotion of the compressive deformation.

Composition dependence of effective thermal conductivity and effective thermal diffusivity of Se100−xInx (x=0, 5, 10, 15 and 20) chalcogenide glasses

Simultaneous measurement of effective thermal conductivity (λe) and effective thermal diffusivity (χe) of twin pallets of Se100−xInx (x=0,5, 10, 15, and 20) glasses, prepared under a load of 5 tons, have been made at room temperature using the Transient Plane Source (TPS) technique. The values of λe and χe were found to increase initially with the increase of concentration of In in Se–In alloy and had their maximum at 10at.wt% of indium. For indium concentration beyond 10at.wt% of the values of effective thermal conductivity and effective thermal diffusivity decrease linearly. This is suggestive of fact that 10at.wt% of indium can be considered as a critical composition at which the alloy becomes, chemically ordered and maximum thermally stable than other composition. Further addition of indium in selenium decreases the values of λe and χe. The behaviour is explained on the basis of decrease of localized states and increase in disorderness for higher composition indium.

Relaxation processes in phonon–impuriton system and effective thermal conductivity of superfluid 3He– 4He solutions

By the method of stationary thermal flow, the measurements of effective thermal conductivity in the superfluid solution 3He– 4He with initial molar concentration 9.8% 3He in the temperature range 0.1–0.5 K have been carried out. At temperatures below 0.23 K, where the phase separation of the mixture occurs, the measurements were carried out in the lower superfluid phase with changing concentration following the phase diagram with decreasing the temperature. Experimental data were compared with the prediction of the kinetic theory of the phonon–impuriton system of a solution. The analysis allows us to establish the relaxation time hierarchy in such a system and to provide the quantitative estimation of the times of impuriton–impuriton and phonon–impuriton relaxation. It is shown that a rather good agreement between experimental data and theory can be obtained by the use of one fit parameter.

An effective thermal conductivity measurement system

In the technical literature, there is a lack of reliable thermal parameters and, often, it is necessary to do in situ measurements for every particular material. An effective thermal conductivity measurement system has been designed and implemented to provide reliable and accurate values for that thermal parameter. The thermal conductivity of a given material is deduced from thermal resistance differential measurements of two samples. All parts of the implemented system as well as practical and theoretical solutions are described, including a power controller circuit exclusively conceived for this application. Experimental considerations to reduce the measurement error are exposed, as well as some results obtained for three different materials.

Measurement and analysis of effective thermal conductivities of lotus-type porous copper

Lotus-type porous copper is a porous medium made of copper that contains many straight pores. To effectively employ lotus-type porous copper as a heat sink, it is necessary to clarify the pore effect on the thermal conductivity of lotus copper. This article describes an experimental and analytical investigation on the effective thermal conductivities of lotus copper parallel and perpendicular to the pores. The lotus copper displayed anisotropy of the effective thermal conductivity. The effective thermal conductivity keff⊥ perpendicular to the pores was lower than that of the parallel ones keff∥ and was 40% that of lotus copper material ks with porosity ε of 0.4. Experimental data for keff∥ showed good agreement with analytical results derived from the assumption that heat flow through the cross-sectional area parallel to the pore axis is proportional to (1−ε). Experimental data for keff⊥ showed good agreement with the analytical results derived from the assumption of orthorhombic symmetry and with the numerical results under a uniform staggered array with a nonuniform pore diameter.