Design and Performance Simulation of a Novel Liquid CO2 Cycle Refrigeration System for Heat Hazard Control in Coal Mines

LCO2 (liquid CO2) can absorb heat and release latent heat via phase transition, which can provide considerable cooling energy and effectively solve the problem of thermal damage in deep coal mining processes. A LCO2 cycle refrigeration system is designed to continuously cool down the working face in a mine, and CO2 is cyclically utilized. Additionally, LCO2 is used not only as a cold source but also to prevent spontaneous combustion of coal in the gob. COMSOL Multiphysics simulation software is used to characterize the thermal performance of the heat exchange system, where the heat transfers between the CO2 and the airflow. For a LCO2 consumption of 13.54 m3/h, the temperature of the airflow in the tunnel decreases by 7.72 degrees C, and the cooling volume of the system reaches 142.99 kW/h; the cooling volume provides a latent heat release of 46.68 kW/h. The main influencing factors of the refrigeration system, such as ventilation flux, LCO2 flow, LCO2 temperature and initial tunnel temperature, are also analyzed quantitatively through the software. The temperature of the steady airflow in the tunnel is proportional to the square of the local fan ventilation flux, and it decreases linearly with an increase in the LCO2 flow but increases with both the temperature of the LCO2 and the initial temperature in the tunnel. When the temperature difference between the LCO2 and wind increases, the heat exchange between the CO2 and wind intensifies, and the cooling volume increases.