Numerical Investigation of Heat Transfer Characteristics of scCO Flowing in a Vertically-Upward Tube with High Mass Flux.

In this work, the heat transfer characteristics of supercritical pressure CO in vertical heating tube with 10 mm inner diameter under high mass flux were investigated by using an SST - turbulent model. The influences of inlet temperature, heat flux, mass flux, buoyancy and flow acceleration on the heat transfer of supercritical pressure CO were discussed. Our results show that the buoyancy and flow acceleration effect based on single phase fluid assumption fail to explain the current simulation results. Here, supercritical pseudo-boiling theory is introduced to deal with heat transfer of scCO. scCO is treated to have a heterogeneous structure consisting of vapor-like fluid and liquid-like fluid. A physical model of scCO heat transfer in vertical heating tube was established containing a gas-like layer near the wall and a liquid-like fluid layer. Detailed distribution of thermophysical properties and turbulence in radial direction show that scCO heat transfer is greatly affected by the thickness of gas-like film, thermal properties of gas-like film and turbulent kinetic energy in the near-wall region. Buoyancy parameters < 10, < 5.6 × 10 and flow acceleration parameter < 3 × 10 in this paper, which indicate that buoyancy effect and flow acceleration effect has no influence on heat transfer of scCO under high mass fluxes. This work successfully explains the heat transfer mechanism of supercritical fluid under high mass flux.