Browsing by Author "Endrýs, Jiří"

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    Experimental determination of the effective thermal conductivity of glass by steady-state method
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1993) Endrýs, Jiří; Blažek, Antonin; Ederová, Jana
    An experimental furnace for the determination of the effective thermal conductivity of molten glass was constructed. As the values of thermal conductivities previously measured by direct experimental methods depend strongly on the thickness of the glass layer it was necessary to make the measurements on thicker layers of glass. The thermal conductivity values have been calculated from temperature distributions measured on the molten glass layer and from the temperature drops on the ceramic bottom of the furnace the thermal conductivity of which was known. From the physical point of view this is a steady-state comparative method with linear heat flow. The values of the effective thermal conductivity of four commercial glasses experimentally determined by this measuring procedure are compared to the radiative thermal conductivities computed from the measured absorption coefficients by means of Rosseland's diffusion approximation. The great differences between effective and radiative thermal conductivities, which have been found especially with weakly absorptive colorless glasses, are critically discussed.
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    Strahlungswärmeleitfähigkeit von Glas Einfluß der Glaszusammensetzung auf seine Wärmedurchlässigkeit
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1976) Blažek, Antonín; Endrýs, Jiří; Kada, Josef; Staněk, Jaroslav
    Es wird eine Methode zur Bestimmung der Wärmeleitfähigkeit von Glasschmelzen beschrieben, die auf der Bestimmung der Absorptionseigenschaften des Glases im nahen infraroten Gebiet und auf Berechnung der Wärmeleitfähigkeit (kr) auf Grund von theoretisch abgeleiteten Gleichungen beruht. Die Strahlungsdurchlässigkeit des Glases wurde dabei im Temperaturbereich von 20 bis 1400° C und im Wellenlängengebiet von 0,5 bis 4,75 µm gemessen. Der Einfluß der chemischen Zusammensetzung auf die Wärmeleitfähigkeit wurde bei elf Weißgläsern untersucht und mathematisch formuliert. Der wesentliche Einfluß von Fe₂O₃ auf die Wärmedurchlässigkeit der Glasschmelze konnte nachgewiesen werden. Thermal radiation conductivity of glass — influence of glass composition on its heat transmission — A method of determining the thermal conductivity of glass melts has been described. This is based on the determination of absorption properties in the near infrared and calculations based on theoretically derived equations. The transmissivity of glass has been measured from 0,5 to 4,75µm between 20 and 1400° C. The influence of glass composition on thermal conductivity has been investigated and formulated mathematically using results for 11 colourless glasses. The important influence of the Fe₂O₃ content on the heat transmission can be established. Conductibilité thermique par rayonnement du verre Influence de la composition du verre sur sa conductibilité thermique — On décrit une methode de détermination de la conduc-tibilité thermique d'une fonte de verre basée sur la déter-mination des propriétés d'absorption du verre dans l'infra-rouge proche et sur le calcul de la conductibilité thermique (kr) au moyen des equations dérivées théoriquement. La transmission de rayonnement du verre est alors mesurée dans le domaine de températures de 20 à 1400 °C et dans le domaine de longueurs d'ondes de 0,5 à 4,75µm. L'influence de la composition chimique sur la conductibilité thermique est étudiée dans 11 verres blancs et est formulée mathématique-ment. L'influence prépondérante de Fe₂O₃ sur la conduc-tibilité thermique de la fonte de verre a pu être mise en évidence.
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    Study of the high-temperature spectral behavior of container glass
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Endrýs, Jiří; Geotti-Bianchini, Franco; De Riu, Luca
    The spectral absorption coefficients of container glasses in the wavelength region from 0.4 to 4.5 µm and in the temperature range from room temperature to 1400 °C were measured by a single-beam spectrophotometer by means of the transmission method. From the measured absorption coefficients radiative thermal conductivities in the temperature ränge from 600 to 1400 °C were calculated by means of Rosseland's diffusion approximation. The intensity of the band at 2.8 µm due to dissolved hydroxyl groups in glass was also calculated. While most previous measurements were performed on model glasses with a very simple basic composition, molten in laboratory furnaces from pure raw materials, the glasses investigated in this paper are the most frequently used types of container glasses with a complex composition and different chromophores. The influence of different coloring agents and dissolved water on the spectral behavior and radiative thermal conductivity of glass were studied, checking how the spectra change from room temperature to high temperature.