Characteristics of natural convection heat transfer in composite cavity

Abstract

In order to study the influence of the nature of the mining airspace on the natural convection heat transfer in the unventilated working face, we establish a numerical model of natural convection in a composite cavity containing porous media by CFD method. The effects of different Rayleigh numbers (Ra), porous media thicknesses, and porosities ε on the natural convection temperature and velocity fields and heat dissipation from the heat source were comparatively analyzed. The results show that the larger Ra is, the stronger the natural convection flow and heat transfer in the composite cavity; when the thickness of porous media increases from 0.2 to 0.75, the average Nussel number (Nuave) of the high-temperature wall surface decreases by 40.38%, the Nuave of the interfaces decreases by 6.15%, the maximum dimensionless velocity of the boundary layer in the porous region decreases from 10,771 to 3775, and the dimensionless horizontal line in the center of cavity decreases by 0.05, indicating that the natural convection temperature and velocity fields and heat dissipation from the heat source are affected by different Ra. Temperature decreased by 0.05, demonstrating that the increase in the thickness of porous media will weaken the strength of the fluid side of the flow and heat transfer; porosity increased from 0.2 to 0.8, and the interfacial Nuave increased by 5.61%, demonstrating that the larger porosity makes the porous media area flow and heat transfer enhancement, but has a certain weakening effect on the flow and heat transfer in the fluid domain. The results of the study can be used for the natural convection flow and heat transfer in the unventilated coal mining face, and provide some reference value for avoiding the thermal damage of mechanical equipment.

Keywords

• Natural convection
• Numerical simulation
• Composite cavity
• Rayleigh number
• Porosity