Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.
A heat source can be considered as the Brayton cycle’s life
support. This heat source can be extracted from solar energy.
The small-scale open and direct solar thermal Brayton cycle
with recuperator has several advantages, including lower cost,
low operation and maintenance costs and it is highly
recommended. The main disadvantages of this cycle are the
pressure losses in the recuperator and receiver, turbo-machine
efficiencies and recuperator effectiveness, which limit the net
power output of such a system. The irreversibilities of the solar
thermal Brayton cycle are mainly due to heat transfer across a
finite temperature difference and fluid friction. Thermodynamic
optimization can be applied to address these disadvantages to
optimize the receiver and recuperator and to maximize the net
power output of the system at any steady-state condition. The
dynamic trajectory optimization method is applied to maximize
the net power output of the system by optimizing the
geometries of the receiver and recuperator limited to various
constraints. Standard micro-turbines and parabolic dish
concentrator diameters of 6 to 18 meters are considered. An
optimum system geometry and maximum net power output is
generated for each operating condition of each micro-turbine
and concentrator combination. Results show the optimum
operating conditions as a function of system mass flow rate.
The optimum operating point of a specific micro-turbine is at a
point where the internal irreversibilities are approximately three
times the external irreversibilities. For a specific environment
and parameters there exists an optimum receiver and
recuperator geometry so that the system produces maximum net
power output.
