NUMERICAL STUDY ON TRANISENT NATURAL CONVECTION IN COAL SHED ENCLOSED OF SINGLE COAL PILE

In recent years, the environmentally friendly closed coal shed has been widely used in actual production and life. The heat released from the coal pile will cause local overheating of the environment, which will affect the comfort and health of workers. So the problem of convective heat transfer in coal shed has attracted extensive attention. In order to reduce the harm of coal heap heat release, it is necessary to understand the mechanism of heat transfer and flow in the process of coal heap heat release. CFD numerical simulation method is used to study the natural convection phenomenon in the closed large span coal shed with a single coal pile. Under unsteady conditions, the heat transfer characteristics and flow transition around coal pile with fixed Rayleigh number are studied. The emergence time of symmetric and asymmetric flow structures in coal shed under different Rayleigh numbers are studied. The unsteady characteristics of flow in full development stage are given. The results show that the transient flow in the coal shed will go through three different stages: initial stage, transitional stage and quasi-steady stage. During the transitional stage, the separation and shedding of the plume will promote the formation of asymmetric structure in coal shed, and the emergence time of asymmetric phenomenon will advance with the increase of Rayleigh number. In the quasi-steady stage, the flow in the coal shed presents the characteristics of irregular unsteady turbulent flow, and the time to reach full-development state is delayed with the increase of Rayleigh number.