Carbon particle cloud generation for a solar particle receiver

The development and performance of a full-scale carbon particle cloud generator together with the evaluation of nine commercial carbon blacks is reported. Large variations were found in the dispersability and settling properties of the investigated powders. Scanning electron microscope analysis of cloud samples from different powders showed unequal state of agglomeration and particle size. The particle population distribution of the most suitable powder was determined, showing that the particle cloud consisted of 99.8% spheroid primary particles (25-570 nm dia) and 0.2% large irregularly shaped agglomerates. Although the numerical fraction of the agglomerates was only 0.2%, they contributed 40% to the cloud's geometrical cross section. Significant variations in the population distribution were found from different batches of the same particle powder The developed full-scale particle generator was capable of sustained operation, creating a particle cloud with an extinction coefficient exceeding 40 m(-1) at a nominal flow rate of 25 SLPM. The dispersal efficiency of the system with the optimal ejection nozzle was 25%, compared to less than 1% for free ejection. The particle dispersal rate was 30 g/hr at 25 SLPM at an evacuation efficiency of 87%. Specific extinction cross-sections of 5.8 m(2)/g were measured for particle mass loading higher than 2 g/m(3).