Convection Heat Transfer of CO₂ at Supercritical Pressures in Microtubes

Abstract

Convection heat transfer of supercritical pressure CO2 in microtubes as well as characteristics of fluid flow and heat transfer were investigated. Alterations of physical properties of supercritical CO2 and the impact of buoyancy on the heat transfer were analyzed when the inlet Reynolds (Re) number of CO2, diameter of heat exchanger, and inlet Re of cooling water were changed. The temperatures of hot fluid in numerical simulations from several classical turbulence calculation models were compared with experimental results from the literature. The physical properties of CO2 changed significantly around the critical point, causing a distinct decline of buoyancy and strengthening of heat transfer.

A Review of Flow and Heat Transfer Characteristics of Supercritical Carbon Dioxide under Cooling Conditions in Energy and Power Systems

“…The mixed convection was the primary heat transfer mechanism in the SCO 2 cooling process. Yang et al [70] presented a simulation with a 0.4 mm inner diameter microtube. Near the SCO 2 critical point, changes in thermo-physical characteristics led to more significant buoyancy fluctuation, and buoyancy's impact on the heat transfer coefficient was substantial and complex.…”

Cooling Heat Transfer of Supercritical CO2 in Diverging and Converging Microtubes

“…Yang et al [10] numerically simulated the laminar mixed convective heat transfer of supercritical CO 2 in microtubes (D h = 0.5 mm) at different laying angles. Yang et al [11] numerically analyzed the change of physical properties of supercritical CO 2 and the buoyancy effect on heat transfer when the inlet Reynolds number of CO 2 , the diameter of the heat exchanger (0.4 D h 0.6 mm), and the inlet Reynolds number of the cooling water were changed.…”