Analysis of the absorptance and emittance in particle curtains by means of a discrete MCRT method

Abstract

Apparent optical properties, absorptance and emittance, in particle curtains are analyzed by means of a discrete Monte Carlo Ray-Tracing model. The effect of solid volume fraction, particle diameter and curtain thickness on these properties is investigated for two types of particles with different absorptivity and emissivity: sand and CARBO HSP. Absorptance and emittance achieved by curtains made of these particles are greater than the values of absorptivity and emissivity of material. The increase in curtain absorptance/emittance compared to the particle absorptivity/emissivity is higher as the particle property is poorer, such as in sand. Both absorptance and emittance are maximum for opaque curtains, which entails high thicknesses. Assuming opaque curtains, the absorptance and emittance increase as the solid volume fraction decreases. The results obtained with the Monte Carlo Ray-Tracing model are used to estimate particle curtain radiative losses including emission and reflection losses. If material properties absorptivity and emissivity are used instead of the obtained curtain properties absorptance and emittance, sand curtain losses are up to 35 pp and only 9 pp in the case of CARBO HSP. Absorptivity is more important than emissivity, that is, it is preferable having high absorptivity than low emissivity to achieve low radiative losses. Emission losses are less important than reflected losses being very similar in both types of curtains. Sand curtains lose 33% of the incoming power while CARBO curtains lose only 7%. Radiative losses are significantly higher than advection losses in sand curtains. However, in CARBO curtains, advection losses are higher.