Papers by Frank Hemberger
Thermochimica Acta, Jun 10, 2011
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ABSTRACT Poster Temporary entry (new)
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Even though Differential Scanning Calorimetry (DSC) is a well established method for the determin... more Even though Differential Scanning Calorimetry (DSC) is a well established method for the determination of specific heat capacity of various materials, there is also need for methods suitable for larger specimen sizes in the range of several cubic centimeters instead of micro liters. For phase change materials, i.e. a class of materials used for technical heat storage applications, or compounds which show size dependent thermophysical caloric properties below a critical specimen volume, e.g. subcooling effects, the larger specimen volumes are absolutely essential. The Longitudinal Guarded Heat Flow Method is a well-known steady state method to measure the thermal conductivity of medium sized solid samples. With a modification of the measurement procedure to a transient temperature step at the top and bottom end of the sample it is possible to determine the heat capacity of a specimen in a defined temperature interval. An apparent heat flux is determined during the transient heating p...
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High Temperatures-High Pressures
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Amorphous carbon samples with a total porosity of about 85% were synthesized via pyrolysis of sol... more Amorphous carbon samples with a total porosity of about 85% were synthesized via pyrolysis of sol-gel derived resin precursors. Since the pores in the samples investigated have dimensions of a few tens of nanometers only, the gaseous contribution to the thermal conductivity is largely suppressed at ambient pressure. Values for the total thermal conductivity as low as 0.054 W(mK) -1 at 300°C are detected. However, the pyrolysis temperature has a great impact on the contribution of the solid backbone to the total thermal conductivity. From the same precursor a series of samples was prepared via pyrolysis at temperatures ranging from 800 to 2500°C. The thermal conductivity of this series of carbons at 300°C under vacuum increases by a factor of about 8 if the pyrolysis temperature is shifted from 800 to 2500°C. To elucidate the reason for this strong increase the infrared radiative properties, the electrical conductivity, the macroscopic density, the microcristallite size, the sound ve...
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High Temperatures-High Pressures, 2002
Because of the semitransparency of pBN in the infrared spectral region, the heat flux within this... more Because of the semitransparency of pBN in the infrared spectral region, the heat flux within this material does not only depend on its solid thermal conductivity, but also on its radiative properties. In order to characterise the heat transfer in pBN samples, the thermal and infrared optical properties were determined. From the measured spectral reflectance and transmittance of the samples, the radiative heat-transfer coefficient was derived. In addition, the thermal conductivity was determined via laser-flash and differential scanning calorimetry measurements. It was found that for temperatures above 600 K the radiative transport influenced the total heat-transfer coefficient significantly.
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High Temperatures-High Pressures, 1998
ABSTRACT The thermal conductivities of several carbon blacks are determined as a function of temp... more ABSTRACT The thermal conductivities of several carbon blacks are determined as a function of temperature and gaseous pressure. The measurement of the thermal conductivity, lambda, is performed with a transient hot-wire method. For the data evaluation an extended theoretical solution is used that considers both axial heat losses and a thermal contact resistance at the wire-medium interface. A platinum-rhodium wire (13% rhodium) with a diameter of 200 mu m is used as a probe. The thermal conductivity is measured as a function of gas pressure, p(g), at ambient temperature. The temperature-dependent measurements are performed under 1 bar of nitrogen atmosphere up to 1500 K in order to prevent oxidation for temperatures (T) above 600 K. Additionally, the thermal conductivity under vacuum (p(g)/Pa < 1) is measured up to 1300 K. For the evacuated samples the thermal conductivity is 0.001-0.002 W m(-1) K-1 at room temperature, increases proportional to T-3, and reaches 0.040-0.060 W m(-1) K-1 at T/K = 1300. A direct correlation is found between particle size and thermal conductivity. In nitrogen atmosphere the most efficient carbon-black insulation has thermal conductivities 0.030 W m(-1) K-1 at 300 K and 0.100 at 1500 K.
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High Temperatures-High Pressures, 2002
ABSTRACT To simulate and predict the behaviour of a lava flow, it is essential to have a thorough... more ABSTRACT To simulate and predict the behaviour of a lava flow, it is essential to have a thorough knowledge of its thermophysical properties. Therefore, thermal conductivity, specific heat, and viscosity of volcanic rock material were determined in a wide temperature range. Especially, the properties of the molten material were investigated in detail. The material was taken from the Pietre-Cotte lava flow located on the isle of Vulcano, north of Sicily. The thermal conductivity of the material was determined in the temperature range 293 - 1623 K by the hot-wire method. Melting occurs above HOOK The specific heat was measured by differential scanning calorimetry between 347 and 1671 K. The viscosity of the lava melt was determined with a rotational viscometer HAAKE M5. The viscometer was enclosed in a high-temperature furnace optimised for the temperature range 1373 - 1598 K.
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High Temperatures-High Pressures, 2000
Abstract. An important parameter for the insulation capability of rigid polyurethane foam is the ... more Abstract. An important parameter for the insulation capability of rigid polyurethane foam is the thermal conductivity of the nonporous polyurethane. This work focuses on ways to produce non-porous polyurethane materials and to determine their thermal conductivity. ...
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International Journal of Thermophysics, 2014
ABSTRACT A round-robin test between three institutes was performed on a paraffin phase-change mat... more ABSTRACT A round-robin test between three institutes was performed on a paraffin phase-change material (PCM) in the context of the German quality association for phase-change materials. The aim of the quality association is to define quality and test specifications for PCMs and to award certificates for successfully tested materials. To ensure the reproducibility and comparability of the measurements performed at different institutes using different measuring methods, a round-robin test was performed. The sample was unknown. The four methods used by the three participating institutes in the round-robin test were differential scanning calorimetry, Calvet calorimetry and three-layer calorimetry. Additionally, T-history measurements were made. The aim of the measurements was the determination of the enthalpy as a function of temperature. The results achieved following defined test specifications are in excellent agreement.
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Thermochimica Acta, 2011
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International Journal of Thermophysics, 2012
ABSTRACT A new method for evaluation of the specific heat capacity in the temperature regime betw... more ABSTRACT A new method for evaluation of the specific heat capacity in the temperature regime between 77K and 330K using laser-flash calorimetry is presented. Usually, laser-flash calorimetry is accomplished by performing an additional laser-flash measurement on a reference specimen with a known specific heat capacity and by comparing the maximum rear-side temperatures rises. In this study, the calibration is achieved by comparison of the rear-side temperature rise to specific-heat-capacity data determined by other methods in an adjacent temperature regime. Subsequently, the thus yielded proportional factor is used for the evaluation of the specific heat capacity from laser-flash measurements at temperatures where no specific-heat-capacity data are available. The reliability of this method is shown by performing measurements on a material with known specific heat capacity, aluminum oxide. Furthermore, the specific heat capacity and thermal conductivity of borosilicate crown glass (BK7) was determined experimentally.
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International Journal of Thermophysics, 2010
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International Journal of Thermophysics, 2006
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International Journal of Thermophysics, 2009
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International Journal of Thermophysics, 2007
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International Journal of Thermophysics, 2005
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Papers by Frank Hemberger