Effect of the chimney design on the thermal characteristics in solar chimney power plant
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Effect of the chimney design on the thermal characteristics in solar chimney power plant Haythem Nasraoui1 · Zied Driss1 · Hedi Kchaou1 Received: 19 March 2019 / Accepted: 7 November 2019 © Akadémiai Kiadó, Budapest, Hungary 2019
Abstract Solar chimney power plant (SCPP) is an interesting project to produce clean and sustainable energy. An efficient SCPP system requires a very high chimney, and thus the optimization of the chimney shape presents an important way to enhance the SCPP performance. The aim of this paper is to analyze the effect of the divergent chimney shape on the airflow behavior inside SCPP. A comparison between four chimney shapes is carried out using CFD method: two cylindrical chimneys with different diameters and two divergent chimneys with different shapes. Indeed, both parameters were studied: the ratio of the inlet and outlet diameter of the chimney and the shape of the chimney which both hyperboloid and conical. The SCPP prototype was tested numerically and experimentally to validate the present computational outcomes. The obtained results confirm that the divergence shape affects directly the efficiency of the SCPP system. Moreover, the hyperboloid chimney presents the efficient solution which produces an important power output with keeping the chimney height constant. Keywords Solar energy · Solar chimney power plant · CFD · Chimney shape · Hyperboloid List of symbols Ac Collector area (m2) Ai Area of the chimney entrance section Ao Area of the chimney exit section (m2) cp Specific heat capacity of the air (J kg−1) D1 Inlet chimney diameter (m) D2 Outlet chimney diameter (m) h Convection heat transfer (W m−2 K−1) Hch Chimney height (m) k Turbulent kinetic energy (m2 s−2) ṁ Masse flow rate (kg s−1) p Static pressure (Pa) Ppo Potential power output (W) Pr Prandtl number r Radial coordinate (m) T Temperature (K) T0 Ambient temperature (K) Ts Sky temperature (K) u Radial velocity (m s−1) V Air velocity (m s−1) * Haythem Nasraoui [email protected] 1
Laboratory of Electro‑Mechanic Systems (LASEM), National School of Engineers of Sfax (ENIS), B.P. 1173, km 3.5 Soukra, 3038 Sfax, Tunisia
vch Air velocity at the chimney entrance (m s−1) vout Air velocity at the chimney exit (m s−1) w Axial velocity (m s−1) z Axial coordinate (m) β Thermal expansion coefficient (K−1) ΔT Temperature rise in the collector (K) Δp Pressure drop in the chimney (Pa) ε Dissipation rate of turbulent kinetic energy (m2 s−3) λ Thermal conductivity of the air (W m−1 K−1) μ Dynamic viscosity (Pa s−1) μt Turbulent viscosity (Pa s−1) ρ Density of the air (kg m−3) ρ0 Reference density (kg m−3) ρch Density at the chimney entrance (kg m−3) ηc Collector efficiency ηch Chimney efficiency
Introduction Since the petrol crisis, the great needs of the free energy sources lead to promote renewable energy systems. Solar energy is an important renewable energy source. Around the world, there are several technologies for exploiting the solar energy, such as photovoltaic, concentration
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