Numerical investigation on thermal-hydraulic performance of helical-coiled tube air cooler used for underground mine

Abstract

The helical-coiled tube air cooler has widely used as one of the most important terminal equipment in underground coalmine cooling systems. The mechanism of flow and heat transfer considering the structural feature of the mine-used helical-coiled tube air cooler are necessary to be investigated for optimal design guidance of the equipment, yet have not been investigated and well understood. In this work, a three-dimensional numerical model is established to investigate the thermal-hydraulic performance of the helical-coiled tube air cooler, with emphasis on quantifying the effects of the main geometrical parameters such as the number of tubes arranged under constant number of coil layer, the outer diameter of tube, the helix angle, the number of coil layers and the spacing between external tube walls at adjacent layers on the flow and heat transfer performance of the helical-coiled tube air cooler. Then the sensitivity analysis of the main geometric factors via Taguchi method is discussed under the dense tube layout condition. The results show that the Nusselt (Nu) number and pressure drop per unit tube length (Δp/L) increase with the increase of the number of tubes arranged under constant number of coil layer and the outer diameter of tube, while the Nu decreases and Δp/L increases when helix angle increase. The Nu and Δp/L keep stable with the increase of number of coil layers under constant inlet velocity. The increase of spacing between external tube walls results in the decrease of Nu and Δp/L. The sensitivity analysis indicates that the outer diameter of tube affects the Nu, f factor and the comprehensive performance factor (CPF=Nu/f13) most. Taking CPF as index, the effect of four main factors ranks as Dt>α>Nc>δ, and the optimal design is determined with CPF of 143.46 to 485.99 at inlet velocities within 5 to 25 m/s.