Part-I: Dilute gas-solid flow in riser reveals complex gas-particle interactions that lead to formation of particle clusters. In this project, an impact of gas-particle interactions and various interparticle forces on the formation of the clusters will be investigated. Part-II: Efforts will be made to enhance our understanding on the onset of the churn turbulence regime from the bubbly flow regime. The effects of bubble size and liquid/gas properties on the drag forces experienced by the bubbles will be identified, along with the effects of turbulence on the hydrodynamics of the bubbles. Furthermore, we will analyse the interaction, breakup and coalescence of the bubbles, especially in the churn-turbulence regime. Part-III: The dynamics of a droplet upon collision with a heated particle will be analysed, with the aim of characterizing the convective heat transfer between the two phases.