The paper presents results from three large scale experiments on seven reinforced concrete panels obtained during an extensive experiemental program. This was aimed at possible application of cement reduced (fly ash replaced)) concretee in the production of precast segmental linings for tunnels created by a tunnel boring machine (TBM). In particular, this paper is focused on the comparison of fire resistance of enhanced mixtures loaded by the Rijkswaterstaat (RWS) fire curve, which assumes 50 m3 fuel tanker fire lasting for 120 minutes. The presented results include spalling, overall damage of the surface and temperature distribution of the tested panels The paper also presents description of the proposed method for the evaluation of the extent of spalling during the experiments since, due to the extreme temperatures, the direct observation of the exposed surface is not possible. and Obsahuje seznam literatury
We describe behavior of the air-coal mixture using the Navier-Stokes equations for gas and particle phases, accompanied by a turbulence model. The undergoing chemical reactions are described by the Arrhenian kinetics (reaction rate proportional to exp(−ERT), where T is temperature). We also consider the heat transfer via conduction and radiation. Moreover we use improved turbulence-chemistry interactions for reaction terms. The system of PDEs is discretized using the finite volume method (FVM) and an advection upstream splitting method as the Riemann solver. The resulting ODEs are solved using the 4th-order Runge-Kutta method. Sample simulation results for typical power production levels are presented.
The unsteady Hartmann flow of a conducting incompressible non-Newtonian viscoelastic fluid between two parallel horizontal insulating porous plates is studied with heat transfer. A uniform pressure gradient which decays exponentially is imposed in the axial direction. An external uniform magnetic field and uniform suction and injection through the surface of the plates are applied in the vertical direction. The two plates are kept at different but constant temperatures while the Joule and viscous dissipations are considered in the energy equation. Numerical solutions for the governing momentum and energy equations are obtained using finite differences. The effect of the magnetic field, the parameter describing the non-Newtonian behavior, and the velocity of suction and injection on both the velocity and temperature distributions is investigated. and Obsahuje seznam literatury
Energy consumption in buildings in EU is app. 40 % of the total consumption. Due to an effort to decrease energy consumption, the attention is paid to the energy consumption on building sector and related energy saving measures, as well. The obvious measure is to increase thermal insulation properties of buildings envelopes, however nowadays buildings are reaching the economically proved limit. The one of possible ways to further decrease energy consumption for heating/cooling of buildings is to optimise the energy supply strictly per time schedule. This concept requires the necessity to consider of thermal accumulative properties of buildings as well. There are presented several computed methods and tools for heat transfer calculation as well as building simulation. and Téměř 40 % spotřeby elektrické energie v zemích Evropské unie je spotřebováno v budovách a z tohoto důvodu je trendem posledních let snižovat jejich energetickou náročnost. Toho je momentálně dosahováno převážně tepelnou izolací, která ale začíná dosahovat ekonomické meze návratnosti. Dalším krokem by proto měla být snaha optimalizovat stávající vytápěcí a chladicí systémy s ohledem na jejich využití v průběhu dne. Článek se zabývá popisem několika metod, kterými lze k tomuto problému přistupovat. V příspěvku jsou představeny jak nástroje založené na numerickém výpočtu rovnic přenosu tepla, tak i řešení využívající zjednodušených metod nebo předdefinovaných modelů jednotlivých tepelných zařízení.