The "porcupine": A novel high-flux absorber for volumetric solar receivers

A new volumetric (directly irradiated) solar absorber, nicknamed Porcupine, is presented. It was tested over several hundreds of hours at the Weizmann Institute's Solar Furnace, using several flow and geometric configurations, at various irradiation conditions. The experiments, which were conducted at a power level of about 10 kW, showed that the new absorber can accommodate different working conditions and provide a convective cooling pattern to match various irradiation flux distributions. The capability of the Porcupine to endure a concentrated solar flux of up to about 4 MW/m(2), while producing working gas exit temperatures of up to 940 degrees C, was demonstrated. In comparative tests, the Porcupine sustained an irradiation solar flux level about four times higher than that sustained by other volumetric absorbers (foam and honeycomb matrices). Due to its ability to sustain and transport a much higher energy fluxes, the Porcupine yielded twice the power output of the other absorbers while its exit gas temperature was 300-350 degrees C higher. The Porcupine design is highly resistant to thermal stresses development; none of the Porcupine absorbers tested showed any sign of deterioration after hundreds of operating hours, although temperature gradients of several hundreds degrees C/cm developed in some experiments. The basic Porcupine structure provides convective and radiative energy transport between the matrix elements, therefore alleviating the development of flow instabilities; this phenomenon causes local overheating and restricts the operation of other volumetric matrices. A Porcupine absorber was subsequently incorporated into the directly irradiated annular pressurized receiver (DIAPR), where it has been operating flawlessly at an incident flux of several MW/m(2) and temperatures of up to 1,700 degrees C.