THE PORCUPINE - A NOVEL HIGH-FLUX ABSORBER FOR VOLUMETRIC SOLAR RECEIVERS

A new volumetric (directly irradiated) solar absorber, nicknamed Porcu pine, is presented. It was tested over several hundreds of hours at th e Weizmann Institute's Solar Furnace, using several flow and geometric configurations, at various irradiation conditions. The experiments, w hich were conducted at a power level of about 10 kW, showed that the n ew absorber can accommodate different working conditions and provide a convective cooling pattern to match various irradiation flux distribu tions. The capability of the Porcupine to endure a concentrated solar flux of up to about 4 MW/m(2), while producing working gas exit temper atures of up to 940 degrees C, was demonstrated. In comparative tests, the Porcupine sustained an irradiation solar flux level about four ti mes higher than that sustained by other volumetric absorbers (foam and honeycomb matrices). Due to its ability to sustain and transport a mu ch higher energy fluxes, the Porcupine yielded twice the power output of the other absorbers while its exit gas temperature was 300-350 degr ees C higher. The Porcupine design is highly resistant to thermal stre sses development; none of the Porcupine absorbers tested showed any si gn of deterioration after hundreds of operating hours, although temper ature gradients of several hundreds degrees C/cm developed in some exp eriments. The basic Porcupine structure provides convective and radiat ive energy transport between the matrix elements, therefore alleviatin g 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 i rradiated annular pressurized receiver (DIAPR), where it has been oper ating flawlessly at an incident flux of several MW/m(2) and temperatur es of up to 1,700 degrees C.