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[en] In this study, in a floor heated room, natural convection heat transfer over the floor is analysed numerically for different thermal conditions. An equation relevant to Nusselt number over the floor has been obtained by using the numerical data. Different equations are given in the literature. They consider the effect of floor Rayleigh number while neglecting the effect of wall and ceiling thermal conditions. Numerical data obtained in this study show that the Nusselt number over the floor depends on not only the floor Rayleigh number but also the wall Rayleigh number (for insulated ceiling conditions). The equations given in the literature are different from each other due to their not considering the effect of wall and ceiling Rayleigh numbers. This difference between the equations may be eliminated by obtaining an equation containing the effect of floor, wall and ceiling Rayleigh numbers. In this new approach, an equation relevant to the floor Nusselt number that depends on the floor and wall Rayleigh numbers has been obtained in the floor heating system for insulated ceiling conditions. The equation obtained in this study has been compared with the equations given in the literature. It has been seen that the equation obtained in this study matches the numerical values under more extensive thermal conditions than the equations given in the literature. The maximum deviation for the equations given in the literature is 35%, but in the current study, the maximum deviation has been found to be 10%. As a result, it is more convenient to use the equation found in the new approach as a function of Rayleigh number over the floor and wall for insulated ceiling conditions
[en] In this study, the Nusselt number over the floor is analysed numerically for different thermal conditions in a floor heated room. A new equation related to floor Nusselt number is developed. In the literature, there have been a number of equations, different from each other and appropriate only for the conditions at which the studies were performed, have been presented. While the mentioned equations were dependent only on the floor Rayleigh number, numerical data obtained in the current study show that the floor Nusselt number depends not only on the floor Rayleigh number but also the wall and ceiling Rayleigh numbers. Therefore, the new equation developed in the current study is a function of the Rayleigh numbers over the floor, wall and ceiling surfaces. This equation is compared with those found in the literature. It is seen that while the maximum deviation from the numerical data is 35% for the equations given in the literature, it is only 10% for the new equation. Therefore, the given equation is verified to be more reliable and appropriate for the calculation of Nusselt number
[en] In a conventional coal-fired power plant, which is only designed for electricity generation, 2/3 of fuel energy is wasted through stack gases and cooling water of condensers. This waste energy could be recovered by trigeneration; modifying the plants in order to meet district heating/cooling demand of their locations. In this paper, thermodynamical analysis of trigeneration conversion of a public coal-fired power plant, which is designed only for electricity generation, has been carried out. Waste heat potentials and other heat extraction capabilities have been evaluated. Best effective steam extraction point for district heating/cooling system; have been identified by conducting energetic and exergetic performance analyses. Analyses results revealed that the low-pressure turbine inlet stage is the most convenient point for steam extraction for the plant analyzed.
[en] This paper presents performance assessments of thermal power plant-based co/tri-generation systems for district heating/cooling system. The power plants were originally designed exclusively for the generation of electricity. With respect to the renovation of power plants to co/tri-generation systems, the analysis of performance variations in the systems has been undertaken. For the purpose of simulation analysis, thermodynamic models of the eight thermal power plants have been developed. The performance variations have been evaluated with different performance criteria, including electrical power output, classical thermal efficiency, coefficient of performance and comprehensive thermal efficiency. The comprehensive thermal efficiency takes into account all products (electricity, heating and cooling energy) generated from the power plant-based tri-generation system. The results of analysis show that the comprehensive thermal efficiencies of the eight considered systems range from 49% to 61% in the heating mode, although their generated electrical power amounts decrease slightly. As a result, this type of modification for an existing power plant can greatly benefit the cause of energy efficiency and sustainable development. - Highlights: • Two new performance parameters are defined for renovated power plants. • The first parameter is named “The comprehensive thermal efficiency”. • The second parameter is named “coefficient of performance for heating/cooling”. • According to analysis all examined power plants can be converted to co-tri generation plant