Captured CO2 is in a subcritical state, whereas CO2 deep underground is in a supercritical state because of the high geothermal heat and pressure. The properties of CO2 can change rapidly at the critical point and in the near-critical region during the transportation and injection process. This study aims to identify the instabilities in the CO2 flow in these regions, along with the causes and effects, during the transportation and injection process, and propose relevant design specifications. Thus, the critical points and near-critical region of CO2 flow were numerically analyzed. The unstable region is presented in terms of temperature and pressure ranges, and the changes in the CO2 properties in this region were analyzed. In the unstable region, the sudden change in density was similar to the density wave oscillation of a two-phase flow. The CO2 stability map we obtained and the stability map of supercritical water show similar trends. Flow instability was also found to occur in standard CO2 transportation pipelines. We demonstrate that flow instability in CO2 transportation and injection systems can be avoided by maintaining the proposed conditions.
Turnout equipment plays a vital role in the safe operation of railroad systems. It is of great importance in ensuring safety and punctuality, and in the smooth operation of point switching mechanisms. Failure of switching gear due to climatic conditions at their site of installation is a frequent occurrence, in particular, breakdown resulting from the effects of snow and ice or of piled-up snow. To prevent this happening, heating equipment can be installed to get rid of the ice and snow. Generally speaking, a point heater comprises a heating system, an electricity supply unit, and various kinds of sensor. However, overheating sometimes occurs owing to failures caused by inadequate sensor installation, resulting in the heater becoming unusable. Therefore, a converter is proposed to prevent this overheating by controlling the electricity supply to the heater while detecting the ambient temperature without the use of such sensors.
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