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Start date: 1990 × End date: 1999 × Author: Kawase, Yoshinori ×

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Now showing 1 - 5 of 5
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    Evaluation of reaction rate of refining agents
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Kawachi, Shinji; Kato, Mitsuo; Kawase, Yoshinori
    To elucidate the thermal decomposition behavior of antimony oxide which is added to promote (re)fming of bubbles in TV glass, an evolved gas analysis (EGA) was conducted using a newly designed device for detecting the gases from the glass batch at increasing temperatures. Furthermore, a mathematical formulation was made to describe the above behavior. From the results of the EGA measurements, three parameters, which govern the reaction rate constant, viz. reaction order, activation energy and frequency factor, were decided. By coupling this mathematical model and the thermal fluid model of glass melts in tank furnaces, it is possible to simulate the conditions of generating refming oxygen in the furnace.
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    Significance of redox reactions in glass refining processes
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Yoshikawa, Hidemi; Kawase, Yoshinori
    The role of the redox reactions due to refining agents in the glass refining processes was examined. Α new approximate model for shrinkage (or growth) of gas bubbles in glassmelts in which redox reactions caused by refining agents were taken into account was developed. The proposed model is a modification of the quasi-stationary model by which the redox reactions due to refining agents can not be considered. It was found that the shrinkage (or growth) of gas bubbles in melts with refining agents is quite faster than that in those without refining agents. Numerical results for single-component and multicomponent gas bubbles indicate that the mechanism of the bubble shrinkage (or growth) in the refining process is significantly controlled by the oxidation of refining agents, which decreases (or increases) the oxygen concentration in the glassmelt and as a result causes the rapid oxygen transfer across the bubble/glassmelt Interface and hence the fast shrinkage (or growth) of the gas bubble. The applicability of the proposed model was examined using the computational results and experimental measurements in the literature. It was also found that the proposed model provides better predictions compared with the quasi-stationary model.
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    Evaluation of bubble removing Performance in a TV glass furnace : Part 2. Verification using real furnace data
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Kawachi, Shinji; Kawase, Yoshinori
    In part 2, a furnace for melting TV panel glass is studied to examine the effectiveness of the Simulator developed by the authors. Because panel glass is used as a part of a cathodic ray tube where the TV image is projected and its defect is easily recognizable, bubble-free glass quality is defmitely required. If the bubble quality becomes worse, a heap of rejected products is piled up, which leads to tremendous economical loss. In order to avoid such trouble designing and operating a TV glass furnace and inspecting glass quality are conducted with great care, and therefore, lots of field data have been accumulated so far. Accordingly, it is meaningful to utilize a TV glass furnace to verify the effectiveness of such simulating technology. The values and phenomena predicted by the Simulator and the data having been observed in real furnaces were found to be in reasonable agreement. Therefore, it may be concluded that the proposed Simulator is useful as a method of scale-up and trouble-shooting for glass furnaces.
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    Evaluation of bubble removing Performance in a TV glass furnace : Part 1. Mathematical formulation
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Kawachi, Shinji; Kawase, Yoshinori
    The bubble evolution and dissolution process in a glass furnace is an extremely complicated physico-chemical phenomenon. Most of the huge number of bubbles, generated in molten glass during the decomposition of the glass batch, are removed during the trajectory from the charging end to the forming section, but some remain in fmal products. On the basis of the two mechanisms, flotation and absorption, in the bubble removing process, a numerical Simulator was developed to evaluate the influence of first, glass and batch composition, including refining agents, second, geometrical tank design and third, furnace operating conditions upon the bubble quality in products. In particular, the Simulator enabled the estimation of the effect of refining gases which are caused by decomposition of the refining agents. Furthermore, an index was devised to synthetically assess the numbers of bubbles in final products. In part 1, the principles of the model which composes the Simulator are described in mathematical formulation. The basic equations with boundary conditions and calculation procedures for thermal flow of molten glass, gas concentration in glass melt and gas evolvement from the refining agents are presented. The calculation strategy of the bubble removing process is also described.
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    Modeling of bubble removal from glassmelts at fining temperatures
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Itoh, Eiji; Yoshikawa, Hidemi; Kawase, Yoshinori
    Α new model based on the quasi-stationary approximation is developed for removal of gas bubbles from glassmelts due to buoyant rise of bubbles. The growth and rising of multicomponent gas bubbles in glassmelts are examined from the view point of interfacial mass transfer. It is shown that the models for rising bubbles in glassmelts available in the literature are based on the quasi-steady approximation which is not very reasonable. The growth of a gas bubble initially consisting of nitrogen only is studied in a glassmelt whose diffusing gases are oxygen, water, carbon dioxide, sulfide and nitrogen. The proposed model based on the unsteady-state mass transfer (the quasi-stationary approximation) is compared with the model based on the steady-state mass transfer (the quasisteady approximation). The former, which provides more rational and better descriptions of bubble behavior in refming processes compared with the latter, predicts rather shorter refming times than the latter.