Three Dimensional CFD Analysis of Solar Chimney Power Plant /

Abstract

Solar chimney power plant (SCPP) or solar updraft tower is a renewable type power generation technology, having a promising potential for large scale usage of solar energy. It operates on the basis of three technologies: a transparent collector, chimney and wind turbine. Greenhouse effect due to collector and stack effect of chimney induces an air flow, driving wind turbine coupled with generator, thereby generating electricity. In this study a comprehensive three dimensional CFD analysis of SCPP, utilizing the dimensions of first working Spanish prototype has been explicated in ANSYS FLUENT to examine heat transfer and fluid flow patterns. Numerical models were incorporated with solar load, DO (discrete ordinates) and RNG k-ɛ turbulence models. Firstly, CFD simulations results were validated by comparing them with the reported experimental results of Manzanares prototype and then, on the basis of robustness of numerical methods adopted, several numerical simulations were performed on varying collector‘s slope and chimney diverging angles to improve the performance of solar chimney. The chimney diverging angle was varied from 10-30. Moreover, numerical simulations were also conducted at collector slope = 40, 60, 80 and 100 sequentially, while keeping all other parameters constant. Based on computed results, it was discovered that both velocity and temperature increases with increasing collector‘s slope due to enhanced heat transfer and mass flow rate, but simultaneously higher collector slopes also deteriorate the smooth air flow by developing vortices and recirculation of air, which obstruct the air flow and may reduce the overall performance. In addition, chimney diverging angle = 10 raises the velocity from 9.1 m/s to a remarkable value of 11.6 m/s; therefore, this approach is believed to be a beneficial tool in improving performance of solar chimney power plant. Furthermore, a MATLAB program based on a simple mathematical model was also developed to evaluate the annual performance of SCPP in Pakistan. Four suitable regions from Southern Punjab, Sindh and Baluchistan were selected to assess the potential of developing SCPP. Obtained theoretical model results were compared with the experimental results and were found to be in good agreement with each other. Results depicted that SCPP having dimensions equal to the Spanish prototype can produce 10-20 MWh/month of electricity in selected regions of Pakistan, which is sufficient to fulfill basic needs of these abandoned regions.