Vapor density gradients near the sublimating interface of a carbon dioxide sphere

Investigating the sublimation characteristics of dry ice particles exposed to convective heating in an unsaturated gaseous medium holds significance for applications employing cooling through dry ice sprays. While the transport phenomena between dry ice and its surrounding gas medium are central to various applications, a comprehensive understanding of these processes during dry ice sublimation remains incomplete. As a model problem, this study experimentally and numerically examines the sublimation of an isolated dry ice sphere within a controlled gas flow environment. Schlieren imaging is utilized in experiments to visualize density gradients at the dry ice-vapor interface for different CO2 concentrations in the surrounding gas. An additional set of experiments involving backlight imaging is conducted to observe dry ice morphology and track its boundary over time. Numerical simulations using COMSOL Multiphysics software are performed to simulate the shrinkage of the sublimating dry ice sphere, accounting for heat, mass, and momentum transport in the gas mixture surrounding the dry ice. The numerical predictions of the density gradient near the sublimating dry ice interface exhibit qualitative agreement with the variations in light intensity observed in Schlieren images, thus confirming the predictive capabilities of the numerical model in this context. Furthermore, the numerical prediction of the temporal variation in dry ice mass closely aligns with experimental observations up to a certain duration, until the onset of frost formation on the dry ice surface, causing distortion in its morphology as evident in the images obtained during the experiments.