A solar thermal power project that makes use of a compact linear Fresnel reflector array to concentrate solar radiation onto a stationary absorber cavity suspended above the array has been proposed. The cavity is trapezoidal in cross-section. The upper surface of the cavity is a flat plate absorber with steam tubes running behind it. The lower surface is a glass window that allows solar radiation, focused by the mirror array, to enter the cavity. Heat loss from the absorber occurs via a complex interaction between radiation, convection and conduction within the cavity, and then from the cavity to the surroundings. This paper describes the experimental techniques used to investigate the heat losses from the absorber, and the flow visualization technique used to capture the flow patterns within the cavity. It then goes on to compare the experimental results with predictions obtained from a model developed using FLUENT, a commercially available computational fluid dynamics package. Excellent agreement is achieved between the flow patterns observed in the experiment and those predicted by the computational model. Reasonable agreement between the experimentally determined heat losses and those predicted by the computational model are also shown to exist.