Research on ventilation-spray coupled flow characteristics and phase-change cooling mechanisms in deep thermal hazard tunnels

High-temperature thermal hazards in deep engineering environments seriously jeopardize the health and safety of underground workers, as well as production safety. Spray phase-change cooling technology has attracted increasing attention in the field of deep engineering cooling. However, complex mechanisms of polydisperse droplet diffusion and phase-change heat transfer under ventilation still restrict the application of spray cooling in deep environments. In this work, considering the two-way coupling between polydisperse droplet non-uniform diffusive heat transfer and the temperature-humidity field in deep underground space, the spray cooling characteristics under typical metal mine thermal hazard conditions were numerically investigated. The movement of droplet particles driven by airflow is coupled by comprehensive interphase forces based on the Euler-Lagrange method. The droplet size and velocity after breakup and coalescence are calculated from the Taylor Analogy Breakup (TAB) model and critical collision offset, respectively. Within the airflow-droplet dynamic multiphase flow field, the convective heat transfer and latent heat exchange associated with mass transfer are calculated. Numerical results indicate that axial and radial vortex zones are formed on both sides of the nozzle within the tunnel, with noticeable fluctuations in airflow velocity downstream of the spray device. Driven by the ventilation flow field, the polydisperse droplets exhibit heterogeneous distribution characteristics, while their velocity displays a stratified profile along the vertical direction. Under the influence of spray phase-change and local ventilation, the high-humidity and low-temperature core zone is formed at the nozzle and its downwind side within the tunnel. Furthermore, the influence mechanisms of inlet air humidity, velocity, nozzle pressure, flow rate, aperture size, single nozzle location and multi-nozzle configuration on spray cooling inside the tunnel were revealed.