Browsing by Author "Lohrengel, Joachim"
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- ItemAngular emissivity at room temperature and spectral reflectance at near normal incidence of float glass, borosilicate glass and glass-ceramics(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Lohrengel, Joachim; Rasper, Manfred; Geotti-Bianchini, Franco; De Rio, LucaAn accurate investigation of the emissivity of uncoated flat glass (necessary to calculate the solar factor and the U value of glazing according to standardized procedures) was performed in agreement with Groupement Europeen des Producteurs de Verre Fiat, in support of CEN and ISO standardization activities. The total angular emissivity of a range of uncoated float glass samples was determined between 10 and 80 °C with an uncertainty of 0.5%. Both the normal and the hemispherical emissivity were nearly identical for all the samples investigated. No significant differences between the top and the bottom side were observed. Measurements were also extended to borosilicate glass and glass-ceramic plates used for fire-resistant glazing, determining their thermal conductivity and angular emissivity behaviour. In order to obtain addidonal information, also the spectral reflectance curves at near normal incidence between 2000 and 200 c m ⁻¹ were obtained using a spectroradiometer. The fact that almost identical curves were obtained for a wide range of float glasses (both sides) as well as for the fire-resistant materials confirms the correctness of the close emissivity values found. On the basis of the resuhs obtained, a Standard value of εn = 0.900 and a εh/εn ratio = 0.936 is suggested for both float glass and for the two other materials.
- ItemThermal conductivity of float glass at room temperature(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1993) Geotti-Bianchini, Franco; Lohrengel, JoachimWhen the heat transfer coefficient of multiple glazings is to be determined, it is important to know the exact thermal conductivity value of the glasses used for building purposes. The values given for flat glass lie between 0.8 and 1.15 W/(m K ) . The thermal conductivity of 11 float glass samples of 4 different colours, manufactured in 5 European countries, has been determined in the temperature range between 10 and 90 °C with an uncertainty of less than 1.5 %. At 10 °C, the mean value of all glasses investigated amounts to 1.022 W/ (m K); the individual values vary between 1.033 and 1.017 W/(m K) . On the basis of the composition, the basicity and the density, the measurement results could be well interpreted by known theoretical considerations. The slight variation of the thermal conductivity values obtained by measurement is in agreement with the values calculated from the composition and the density and can be explained by the fact that all float glasses are of nearly the same composition. By interpolation of the measurement data, coefficients could be determined to calculate the thermal conductivity from the oxide composition. The investigation has shown that - at 10 °C - a value of 1.02 W/(m K) can be applied for the thermal conductivity of flat glasses used for building purposes, independent of their colour or manufacturer.