Browsing by Author "Chervenliev P."

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    Amorphous silicate and zeolite effect on the thermal conductivity and porosity of ceramic building bricks
    (2015-01-01) Djambazov S.; Yoleva A.; Chervenliev P.; Georgiev A.
    The effect of amorphous silicate and zeolite on the thermal conductivity and porosity of ceramic building bricks is studied. The aim of the present work is to produce porous bricks of reduced thermal conductivity and acceptable compressive strength by using a combination of natural raw materials (amorphous silicate and zeolite) as well as sawdust and coal dust as pore forming agents. Clay from Lucovite deposits is used as the main component of the ceramic bodies (over 60 %). The content of amorphous silicate is increased from 7 mass % to 20 mass %, while that of zeolite - from 7 mass % to 30 mass %. The green samples are prepared by plastic extrusion. After moulding and drying at 100oC, the samples are fired at 800oC and 850oC for one hour. Then their water absorption, apparent density and apparent porosity, mechanical compressive strength and thermal conductivity are analyzed. It is found that the amorphous silicate has a small effect on the properties of the bricks obtained. The bricks containing zeolite have low?r thermal conductivity and higher porosity when compared to those of other compositions. A tendency of thermal conductivity decrease and porosity increase with zeolite quantity increase is found at both firing temperatures. Bricks of improved properties are prepared at the lower firing temperature. The highest porosity (36,00 %) and the lowest thermal conductivity (0,67 W/mK) is obtained in case of bricks containing 30 % zeolite and firing temperature of 800oC. The results of this work show that building bricks of lower thermal conductivity and higher porosity can be produced at a lower firing temperature by introducing zeolite to their composition. They are a potential heat insulating material.
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    Mathematical modeling and numerical simulation of coupled mass transfer and mechanical processes in ceramic ware at industrial drying
    (2019-07-01) Penkova N.; Chervenliev P.; Mladenov B.; Krumov K.
    An algorithm for numerical simulation of transient moisture content fields and mechanical processes in ceramic ware at drying in industrial aggregates is developed. It is based on mathematical models of the mass transfer and mechanical behavior in the ceramic bodies, data for the drying regime and physical properties of the material as function of water content. The models allow variations of the drying conditions in order to choice the most efficient regime at existing or design dryers. The algorithm is applied for a direct coupled finite element analysis of wet bricks behavior in continuous working drying installation. The shrinkage mode, modulus of elasticity, Poisson ratio, modulus of rupture, effective mass transfer coefficient and critical moisture content are determined by experimental tests of the material. They are used to simulate numerically three-dimensional moisture, stress and strain fields in ceramic bodies at the existing drying regime. Ways for improvement of the models and their application for estimation of the potential for energy savings in industrial dryers are discussed.