Gas slip flow and heat transfer over a semi-confined cylinder in proximity to a solid wall

A numerical simulation with second-order velocity slip and temperature jump models has been conducted to investigate gas slip flow and heat transfer over a semi-confined cylinder in proximity to a solid wall. The effects of rarefaction (characterized by Kn), convection (characterized by Re), compressibility (characterized by Ma), confinement (characterized by gap ratio d_gap/d_c), and temperature (characterized by cylinder-gas temperature ratio T_c/T_∞) on the drag coefficient (C_D) and Nusselt number (Nu) of a semi-confined cylinder have been comprehensively analyzed. It is found that: (1) with increasing Ma, the dominant effect determining the variation of C_D with Kn changes from rarefaction effect to compressibility effect, while the dominant effect determining the variation of Nu with Kn changes from temperature jump to velocity slip; (2) with increasing Ma, the variation of C_D with increasing Re changes from a monotonic decrease to a non-monotonic variation owing to the compressibility effect, while Nu increases monotonically with increasing Re owing to an enhanced convection effect; (3) with decreasing d_gap/d_c, C_D first increases, then decreases owing to the variation of gas velocity gradient and pressure surrounding the cylinder, while Nu first increases, then decreases, finally increases again owing to the variation of gas velocity and temperature gradient surrounding the cylinder; (4) with increasing T_c/T_∞, C_D and Nu increase owing to increases of gas dynamic viscosity and pressure, thermal conductivity and temperature gradient, respectively. Finally, dimensionless correlations for C_D and Nu of a semi-confined cylinder with comprehensive considerations of rarefaction, convection, compressibility, confinement, and temperature effects are proposed.