The study of the parameters of the heat transfer process at carbon dioxide sublimation

When calculating the carbon cycle, it is important to take into account the influence of temperature gradients on the mechanisms of absorption and desorption of carbon dioxide. To determine the dependence of the duration of sublimation of dry ice on temperature, density of pressed CO2, as well as environmental humidity and concentration, a series of experiments was conducted in the laboratory of the Thermal Cooling Engineering Department of Kemerovo State University. The experiments were carried out under atmospheric pressure in the temperature range from minus 80 to minus 20 °C. The temperatures were provided by a two-stage automated cascade refrigeration unit, stable humidity in the chamber was maintained by an air humidifier. Thermally insulated box measuring 0.2×0.15×0.2 m in which the test samples were located was placed into the chamber. To obtain cylinder-shaped attachments, special copper thin-walled hollow cylindrical molds were used, which were filled with snowy carbon dioxide obtained in the apparatus. To form a block of dry ice, the press was used to create the pressures of 90, 75, 50, and 25 kN/m2. The effect of moisture condensation on the rate of sublimation was lower than it was expected. The appearance of hoarfrost and the increasing of the surface due to it resulted in the intensification of heat exchange. However, a significant part of the moisture was frozen out before reaching the surface of the dry ice, and the resulting layer of loose hoarfrost was like thermal insulation and sublimation under it was less intense. Direct effect on the sublimation process was exerted by the pressure. An equally important factor was the storage temperature of carbon dioxide, due to high energy consumption for the operation of the low-temperature chamber. According to the obtained experimental data, the dependence of the intensity of the sublimation process on the ambient temperature, under the above conditions, is linear.