Solar chimney turbine performance
Date
2002-03
Authors
Gannon, Anthony John
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
This project investigates the performance of solar chimney power plant turbines. A solar chimney
power plant consists of a tall chimney surrounded by a transparent deck or solar collector. The sun
heats the air in the collector through the greenhouse effect. A turbine extracts energy from the hot
air rising up the chimney. An investigation of the requirements and operation of such turbines is
needed.
Correct matching of the turbine to the plant requires the determination of the turbine operational
range and other requirements. An air-standard cycle analysis is extended to include component and
system losses. Simple steady-state and transient collector models are added to take into account the
coupling effect of the collector air temperature rise and mass flow rate on the turbine operation. The
predicted turbine operational range for a representative day shows that the expected pressure drop
in a full-scale solar chimney turbine is significantly higher than has previously been predicted.
A turbine design method is developed and used to design a turbine for the representative day. The
methods can easily be extended to include more operating points for a full year of operation. A
turbine layout is suggested that uses the chimney support pillars as inlet guide vanes (IGVs). These
introduce pre-whirl to the turbine and reduce the amount of exit whirl thus decreasing the kinetic
energy at the turbine exit. Non-radial inlet guide vanes add to the torsional stiffness of the chimney
base. A matrix throughflow method is used to design the radial to axial duct between the IGVs and
rotor. The turbine blade profiles are simulated using a surface-vortex method. This is coupled to an
optimisation scheme that minimises both the chord length and maximum flow velocity of the
profile to reduce blade drag.
An experimental program investigates the performance of the turbine. Volume flow, pressure drop,
torque and speed are measured on a scale model turbine to map the turbine performance over a
wide range. The velocity and pressure profiles are measured at two design points to investigate the
flow through the turbine in more detail. These are compared to the design predictions and used to
improve the design method. The experiments show that the design of a solar chimney turbine with
a total-to-total efficiency of 85 % - 90 % and total-to-static efficiency of 75 % - 80 % is possible.
Analysis of the experimental results shows that the turbine efficiency can be improved.
Description
Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2002.
Keywords
Solar power plants, Solar collectors, Dissertations -- Mechanical engineering, Theses -- Mechanical engineering