Experimental and numerical study on heat emission characteristics of ventilated air annular in tunneling roadway

With the increase in mining depth, thermal hazard becomes a prominent problem. Reducing heat dissipation of the surrounding rocks on the basis of artificial refrigeration can be an important thermal hazard-control technique. There are several researches on spray and surrounding rock-filling insulations, but only a few researches were conducted on air jacket heat insulation performance. To enrich the research content of air jacket heat insulation, a similar experiment platform was designed. Based on the analysis of the test data, the friction factor for the turbulent flow in the interlayer of air annular is obtained and a modified equation for calculating the friction factor is proposed based on the Blasius equation model. The average Nusselt number of the inner and outer wall surfaces in the annular air of roadway is calculated under turbulent state, and the Gnielinski equation is modified based on the experimental results. Based on the finite volume method, the unsteady mathematical model of the heat dissipation structure of ventilated air annular with surrounding rock was established. A computer program was developed, and the accuracy of the mathematical model was verified using experimental results. The numerical calculation results were used to analyze the variations of heat absorption of airflow in the main roadway and heat exhaust of the ventilated air annular at different wind speeds and annular diameters. The results show that the heat insulation effect of interlayer of ventilated air is the best when the air flow in the annular is at the turning point of laminar flow turbulence. The heat insulation effect of ventilated air interlayer is the best in the early ventilation stage, and the heat insulation rate will decrease with the increase of ventilation time, but the heat insulation rate can reach more than 69.7% in 10 years