Mass, momentum and energy transfer in aggregated particulate media.

摘要

Synthesis of nanoparticles in gas phase systems often results in the formation of non spherical particles which are commonly found as clusters of spherical particles, termed as aggregates. Prior studies have shown that these aggregates can be accurately modeled using statistical scaling law. While theories are available for determining the transport properties of spherical particles, the effect of the morphology of the particles has not been well studied. This dissertation focuses on studying how exactly the morphology of the aggregates arises in a given synthesis system and calculation of the transport properties of the formed aggregates. Given the particle morphology, this study also investigates the effect the aggregates have on altering the bulk properties of a system into which they are embedded. The study is computational, experimental and analytical in nature with specific emphasis on studying aggregate formation and transport properties of non spherical particles. An overview of the dissertation is given in Chapter 1. In Chapter 2, an expression is proposed for calculating the drag on non spherical particles (that determines their motion in gas phase systems) and is experimentally validated with a study on flame synthesized Titania aggregates. Chapter 3 looks at calculating collision rates between non spherical particles taking into account the morphology of both the colliding entities for all mass transfer regimes and in chapter 4; aerosol filtration process is studied as quintessentially a collision process. The proposed expressions are validated using a numerical study using Brownian Dynamics simulations. In chapter 5, aggregation process is studied in detail, with specific emphasis on aggregate formation and calculation of the transport properties of the formed aggregates, with the aggregation process occurring in different mass and momentum transfer regimes. Given the particle morphology, its effect in altering the bulk properties of the host medium into which they are embedded is dealt with in chapters 6 and 7, specifically looking into their effect on the thermal conductivity and convective heat transfer. The main conclusions from the study and suggestions for possible future studies based on this dissertation are explained in chapter 8.