Transient Modelling of Cavity Receiver Heat Transfer for the Compact Linear Fresnel Reflector



An investigation into unsteady flow patterns in the cavity receiver of the Compact Linear Fresnel Reflector was performed using computational methods. Results indicate that periodic or even chaotic flow patterns may occur for some conditions and cavity designs. However, the results indicate that unsteadiness in the flow structure does not result in significant variation in the over heat loss rate from the cavity.

The Compact Linear Fresnel Reflector (CLFR) is a design concept for low-cost collection of solar thermal energy for high-temperature steam generation applications. A series of line-focus parabolic mirrors reflect light upwards into a series of shared linear cavity absorbers, from which heat is removed by the direct boiling of water in tubes at the top of the absorber cavity. Compact linear Fresnel reflector field. Inset: reflected light is focussed upward into alternate cavity absorbers (left then right, then left, then right); this allows mirrors to be more closely packed while avoiding mirror-shading losses when light is incident at lower angles. A prototype CLFR system is currently under construction in the Hunter Valley in New South Wales, thanks to the Mandatory Renewable Energy Targets of the State government. These Targets require power generators to produce 2% of their energy from renewable sources. Macquarie Generation has chosen to fund the installation of a large solar collection array to replace bled steam for feedwater preheating at the Liddell power station. The concept for the CLFR system was originally presented in 1996 (Mills & Morrison) and in Solar Energy in 2000 (Mills & Morrison). It is a promising design for large-scale solar thermal energy collection because of its use of low-cost, off-the-shelf materials, simple structural design, and efficient use of available land. Initial cost estimates and designs for the CLFR assumed that an inclined system would be used, with light focussed on an array of evacuated tubes, and end losses eliminated by using a mirror across one end of the absorber and reflectors. Newer designs opt for lower efficiency but lower cost by using a North-South oriented horizontal array without end-mirrors, and direct steam generation in steel pipes.

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