Heat Transfer and Dynamics of Impinging Droplets on Hot Horizontal Surfaces

Abstract

In fluidised bed olefin polymerisation reactors, a liquid monomer is added for enhancing heat removal (super-condensed mode). This broadens the operating window and can substantially increase the capacity of a given reactor hardware. Design and location of liquid injection nozzles play a key role in dictating the performance of condensed mode operations. An understanding of the fundamental characteristics of droplet impingement onto solid particles is critical for proper design. In this paper, we study the interactions between liquid droplets and hot solid surfaces across various boiling regimes. High-speed digital imaging is used to capture the droplet vaporisation process. Water droplets impacting on a solid wall with different Weber numbers are investigated. The effect of various parameters such as surface and initial droplet diameter, liquid velocity and surface tension is studied. Experimental data of dynamic drop impact on a flat hot surface are reported. A phenomenological model is developed to describe the droplet vaporisation phenomena in single phase and nucleate boiling regimes. The results from the phenomenological model are compared with the experimental data presented here and the experimental results reported in the literature. The study provides useful clues for understanding the real case when solid particles are much larger than the injected liquid droplets.