Experimental and theoretical investigation of the dry ice sublimation temperature for varying far-field pressure and CO2 concentration

Abstract

Solid carbon dioxide, also known as dry ice, is extensively used in various applications, such as cleaning large telescopes, refrigeration, spray cooling, and biological processes like cryopreservation. In standard atmospheric conditions, dry ice sublimates continuously because the triple point pressure of carbon dioxide is higher than the atmospheric pressure. While the sublimation temperature of dry ice at atmospheric pressure is widely reported in the literature to be approximately −78.5∘C, this value is only conditionally true as it refers to dry ice exposed to an ambient saturated with its vapor. In reality, dry ice is mainly utilized in an unsaturated atmosphere. This study investigates the effect of the atmosphere on the sublimation temperature of a dry ice sphere, both experimentally and theoretically. Specifically, the far-field pressure is varied from 0.6 bar to 1.3 bar in steps of 0.1 bar, and the far-field CO2 concentration is varied from 100%vol to 0%vol in steps of 20%vol. The results show that the sublimation temperature reduces and reaches a lower thermodynamic wet-bulb temperature when the far-field CO2 concentration is lowered from the previously set value at a given ambient pressure. The lowest value of the sublimation temperature, for the ambient pressure of 1 atm and 0%vol CO2 concentration, is measured to be −97.3∘C, which deviates from the commonly quoted value in the literature by approximately 19∘C. Finally, the results are presented in the form of an extended phase diagram showing the solid-vapor coexistence line for various far-field CO2 concentrations in comparison to the standard coexistence line present on the phase diagram. A mathematical model that considers heat and mass transport phenomena in the surroundings of a dry ice sphere is developed, and its predictions are found to be in encouraging agreement with the experimental results. This study provides important insights into the behavior of dry ice under different atmospheric conditions and can be useful in various industrial and scientific applications.