Development of a renewable technology for air heating and thermal cooling of sub-arctic mines using spray freezing

Mining industry is associated with high energy consumption and greenhouse gas (GHG) emissions due to intensive extraction processes and reliance on fossil fuel, specifically propane and diesel. In remote mines located in sub-arctic climates, heating and cooling operations can take up to half of this energy consumption, highlighting the importance of exploring innovative clean alternatives. The present study investigates one emerging solution to address this energy demand, known as spray freezing, in which the solidification of water droplets is used to provide the heating and cooling needs of mines. A multiscale thermo-hydraulic framework for spray freezing is developed, coupling the multi-stage droplet solidification process with a reduced-order spray-droplet dynamics model. Parametric studies are conducted using the Monte-Carlo method to quantify the effects of operating parameters on the system performance. It is found that the heat rate and cooling capacity of the spray freezing system are predominantly influenced by water flow rate and air temperature. Increasing the water flow rate from 7.5 kg/s to 30 kg/s can increase the heat rate to up to 400%. The ice generation of the system depends most on the air temperature, increasing significantly when the temperature drops below the water nucleation point, approximately -14 °C. Eventually, a multi-variate regression method is used to derive three user-friendly correlations that predict the heat rate, outlet air temperature, and ice generation of the spray freezing system, allowing a quick evaluation of the system performance in on-site applications.