The Role of Unsteady Heat and Mass Transfer Processes in Shaping Air Conditions in Large-Section Blind-End Chambers

This study investigates the influence of unsteady heat and mass transfer processes on the formation of gas composition and thermal conditions in a large cross-section (132 m2) blind-end chamber of a gypsum mine during the operation of diesel-powered mining equipment, including a front-end loader representing the LHD class and a dump truck. The modeled system considers a chamber where the LHD operates continuously, while the dump truck enters periodically to perform haulage cycles. Ventilation is provided from an adjacent panel haulage drift using a booster fan. Numerical simulations were carried out using ANSYS Fluent within the RANS framework, employing the realizable k-ε turbulence model, with consideration of thermal and gas convection. A dynamic mesh approach was applied to explicitly represent the motion of the dump truck. Both steady-state scenarios, corresponding to extreme equipment positions, and a fully transient case involving dump truck entry into the chamber followed by idling were analyzed. The results demonstrate that the movement of the dump truck generates a pronounced piston effect, which alters the jet flow structure and temporarily increases the supply of fresh air to the working face. It is shown that steady-state assumptions based on prolonged equipment presence near the face overestimate the total NOx concentration within the large chamber and may not adequately reflect actual gas conditions over typical loading cycle durations. The analysis of unsteady processes using the dynamic mesh approach reveals significant inertia in contaminant accumulation within the chamber. This finding enables a more accurate estimation of the required airflow rate, reducing excessive safety margins compared to calculations based on the assumption of continuous equipment operation near the face.