Sublimation Kinetics of Carbon Dioxide

The objective of the research outlined in this thesis is to comprehend the fundamental phenomenon of dry ice sublimation, with a particular focus on its behavior in a gaseous environment, on a hot solid surface, and in an insulated container.

In Part I (Chapters 2-3), we study the sublimation of a dry ice sphere in a gaseous environment under varying far-field conditions. Chapter 2 demonstrates that for a given far-field pressure, the dry ice sublimation temperature decreases significantly from the commonly quoted value of 194.6 K as the far-field CO2 concentration reduces due to sublimative cooling. Furthermore, a decrease in far-field pressure for a given CO2 concentration further lowers the sublimation temperature due to increased diffusion of CO2 vapor away from the dry ice surface. Chapter 3 qualitatively compares the nature of density gradients of the CO2 vapor near the phase-changing interface with the light intensity variations observed via Schlieren imaging. Both parameters progressively increase in a similar manner along the curvature of the dry ice sphere, peaking at the horizontal plane before decreasing towards the bottom. Additionally, these parameters decrease exponentially along the radial direction at the sphere's horizontal plane.

In Part II (Chapters 4-5), we investigate the Leidenfrost phenomenon for a disc-shaped dry ice pellet. Chapter 5 employs the Optical Coherence Tomography (OCT) technique to reveal the spatial and temporal evolution profiles of the vapor layer beneath the dry ice pellet. Unlike Leidenfrost puddles, the vapor layer beneath the pellet is found to be approximately flat, increasing over time until the near end of its lifetime. As a simpler alternative to existing optical techniques, Chapter 6 demonstrates the use of a non-invasive capacitive method to investigate the Leidenfrost phenomenon. This method's results for vapor layer thickness and pellet lifetime were validated by comparing them to those obtained from OCT for different substrate temperatures.

In Part III (Chapter 6), we experimentally and numerically evaluate the sublimation rate of dry ice pellets placed inside an insulated container—a scenario directly relevant to cold-chain logistics applications. It is shown that the contact area between the inner walls of the container and the pellets significantly contributes to the total heat transfer rate for the majority of the dry ice’s lifetime. Additionally, the dry ice sublimation rate can be considerably reduced by lowering the surface emissivity of the inner walls of the insulated container.