Research On Thermo-kinetic Problems Of The Solar Chimney Power Plant Systems

On the basis of thermodynamic theory for flow and heat transfer in the solar chimney power plant system, systematic investigations to the Helio-Aero-Gravity Effect (HAG Effect), effects of geometric size on the flow and heat transfer characteristics, effects of energy storage medium and turbine on the system performance are made in this dissertation, with some useful results obtained as follows:(1) An analysis of the thermodynamic processes in different regions of the solar chimney is carried out, in which the thermodynamic cycle of the system is rebuilt, the concept of energy utilization degree is put forward, and the mathematical models of practical and ideal efficiencies of the cycle and exergy efficiencies of different parts of the system are established. It is a Brayton cycle in the solar chimney power plant systems. High chimney is used to increase the efficiency of the system, but a great deal of heat energy will be lost when the working fluid passes through the chimney, which results in a much lower thermal efficiency of the system compared with that of the ideal Brayton cycle of the same pressure ratio. In addition, the kW-graded solar chimneys have a comparatively higher exergy efficiency of the collector and a lower one of the chimney, while the exergy efficiency of the collector decreases and that of the chimney increases significantly for the large scale systems with the output power about 200MW.(2) A further investigation to the Helio-Aero-Gravity Effect of the solar chimney power plant is producted. A more comprehensive model is advanced to evaluate the performance of the solar chimney power plant system, in which the effects of various parameters on the relative static pressure, driving force, power output and efficiency have been further investigated. Using the solar chimney prototype in Manzanares, Spain, as a practical example, the numerical studies are performed to explore the geometric modifications on the system performance, which show reasonable agreement with the analytical model.(3) Numerical simulation of the solar chimney power plant system with no load conditions is carried out. From the simulation results of the temperature, velocity and pressure distributions, we can find that the geometry parameters such as collector radius, chimney height and shape have significant effect on the flow and heat transfer characteristic of the solar chimney power plant systems. Furthermore, a new helix-collector solar chimney power plant system is designed, and the simulation results of this new model show that helix-collector solar chimney power plant system has economical and commercial advantages over the traditional solar chimney systems.(4) A set of more comprehensive mathematical models for the solar chimney power plant system including energy storage layer is established, and conjugate numerical simulations of the solar chimney power plant system with energy storage layer under no load conditions are carried out. The numerical results show that energy storage medium has thermal inertia and also has remarkable effects on the heat transfer and flow characteristic of the system, and that the adoption of energy storage medium with comparatively higher heat conductivity and heat capacity will be helpful to improve the continuity of power output, to modulate the difference of output power during the day and night, and to increase the energy utilization degree of the system.(5) A set of mathematical models to explore the performance of the solar chimney power plant systems coupled with turbine is also founded and conjugate numerical simulation on different sizes of the systems is carried out. Numerical simulation results show that, with the increase the turbine rotation speed, both output power and efficiency of the turbine have their maximum values, and that the mass flow rate of the system and temperature of the chimney outlet vary remarkably. The numerical simulation method put forward in this dissertation could give a useful reference to a further investigation of the solar chimney power plant systems coupled with turbines.(6) A minitype solar chimney power plant prototype has been built up, temperature distribution of the system with the time and space and the variation of chimney velocity with time have been measured. The experimental data show that temperature distribution inside the collector and the effects of season on the performance of the system are in great agreement with the theoretical analysis.