Browsing by Author "Krumov K."
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Item IMPROVEMENT OF FIRING CURVE OF CERAMIC WARE VIA MODELLING AND NUMERICAL SIMULATION OF THE COUPLED THERMO-MECHANICAL PROCESSES IN THE MATERIAL(2021-01-01) Penkova N.; Krumov K.; Zlateva P.A mathematical model of coupled heat transfer and mechanical processes in ceramic ware at firing is developed. It is based on information about the thermo-mechanical behaviour of the material at sintering, obtained experimentally. The model is solved numerically for massive bodies of technical ceramics to estimate and prevent the reasons for cracks appearance at their firing in chamber kilns. The transient thermo-mechanical processes in the fired mass are simulated varying with the heating rate of the firing curves. The investigated thermal regimes are analysed on the base of the results about the temperature and stresses fields in the articles. Approaches for improvements of the fired curve are discussed in order to prevent defects of the products.Item 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.Item Modelling and numerical simulation of fire in a coffee storage hall(2021-11-22) Krumov K.; Penkova N.; Mladenov B.; Stoyanov Y.An approach for modelling of fire in halls at solid materials burning, based on gas phase combustion models in ANSYS/CFX, is proposed. The models are suitable for quick prediction of the flue gases distribution and thermal loads on the building envelopes at a design stage. They was applied for numerical simulation of such processes in a coffee storage hall at different fire positions and forced anti-smoke ventilation. The thermal, fluid flow and concentration field were obtained at the modelled scenarios. Maximal thermal loads on the building envelopes are established at the case of fire near their non-streamlined parts.Item Modelling and numerical simulation of the heat transfer and natural ventilation in storage halls(2020-11-18) Penkova N.; Krumov K.; Mladenov B.; Stoyanov Y.An algorithm for modelling of the heat transfer in storage halls at different combinations of open doors and smoke vents is developed. The models allow numerical simulations of velocity, pressure and temperature fields in the halls in cases of transient and steady state conditions, taking into account the indoor buoyancy, heat sources, heat transfer through the building envelopes and outdoor wind pressures. The models are solved numerically via finite volume method in order to estimate the necessity of additional heating at a design stage of a courier logistic storage hall, situated in the temperate climate zone, at the hardest winter conditions of the region. Recommendations about the organization of the heating and the cargo input are done based on the analyses of the fluid flow and thermal fields at the modelled scenarios.Item Numerical analysis of the transient heat transfer in high temperature chamber furnaces(2019-09-20) Krumov K.; Penkova N.An algorithm for numerical analysis of the transient thermal processes in high temperature gas chamber furnaces for ceramic firing is developed. It is based on mathematical models of the conjugate heat transfer, including combustion, turbulent flows of the torch and gas mixtures, heat transfer through radiation, conduction and convection. The algorithm is used for analysis and improvement of the efficiency of a furnace for firing of technical ceramics.Item Performance of diffusion absorption refrigerators at variable power input(2024-01-01) Stoyanov Y.; Penkova N.; Krumov K.Absorption refrigerators have been used in recent decades for utilization of waste or solar energy to produce heat or cold for industrial purposes or to condition the microclimate in buildings. Although these units are designed at nominal power input in the generator, they can also operate at variable parameters of the heat source, which is possible in the real situations. An experimental determination of the operating range and the performance of a diffusion absorption refrigerator at heat pump and refrigeration mode were carried out in the present study. The results are useful for predicting the efficiency and the effectiveness of such systems at variable heat source capacities.Item Stress analysis of insulating glass units under transient thermal loadings(2018-01-01) Ivanov I.; Velchev D.; Penkova N.; Krumov K.; Iliev V.Finite element stress analysis of glass panels in insulating glass units (IGU) is carried out based on the temperature field determined by serial numerical simulations of the conjugate heat transfer varying with the ambient temperature and solar radiation during a year. The hermetically sealed gas cavity between glass panels is modelled by finite elements and the stress is analyzed when the gauge pressure is maximum positive or negative due to gas temperature change at different seasons. The influence of the primary and secondary sealant of IGU is discussed. The combination of loadings due to thermal expansion and to cavity pressure is analyzed. Important conclusions about IGU structure and its durability are drawn.