A new solar simulator to study high temperature solid-state reactions with highly concentrated radiation

A solid simulator facility for the study of high temperature and flux effects has been established at Lawrence Berkeley Laboratory. The primary components consist of a high pressure arc lamp and power supply, a precision ellipsoidal concentrator, positioning device and ancillary equipment. A 20 or 30 kW xenon arc lamp is mounted at the focus of a coated aluminum ellipsoid with a maximum diameter of 80 cm. Various reactors and other equipment can be positioned at the second focus of the ellipsoid. The radiant flux distribution in the region of the second focal point was determined with calorimetric measurements. Peak fluxes up to 16,000 kW/m² were measured and the total flux in an area of 7 × 7cm was determined to be about 3 kW for the 20 kW lamp.

A concentric silica tubular flow through reactor was fabricated to study reactions in absorbing gas-particle mixtures initiated by direct irradiation. The thermal decomposition of Manganese(IV) dioxide was chosen as a test reaction. Small particles of MnO₂ were dispersed in nitrogen by an agitated filter/cyclone entrainment device. After entrainment, the suspension flowed through the reactor that was placed at the focus of the lamp. The gas-particle suspension was preheated by a small tube furnace. The particles leaving the reactor were collected on polymer filters and analyzed by x-ray diffraction and thermoanalytic methods. The results indicate that the direct absorption particle receivers offer a possible technique to carry out high-temperature solar chemistry processing. An important issue relating to the reactor design is the residence time in the reaction zone. The time must be sufficient to carry out the desired reaction. Therefore the reactor should be designed to maximize the residence time in the peak flux region. A second important consideration in this approach is the method used to suspend the particles in the flowing gas-stream.

Future experiments call for the use of alternative techniques to entrain particles to maximize their mass loading in the suspension and measurements with various types of manganese dioxide. The effect of size, morphology, and purity of the particles will be explored. Two additional improvements include the use of improved preheating of the particles as well as better methods to measure the temperature.