Numerical study on heat transfer characteristics of supercritical CO2 in a vertical heating serpentine micro-tube

Abstract

Supercritical CO2 heat exchangers are used in many industries. In some applications, the channel may not be straight, but rather serpentine. The effects of mass flux (G = 100–200 kg/m2s) and heat flux (qw = 30–90 kW/m2) on the heat transfer of a vertical serpentine micro-tube (d = 1 mm) and the different effects of buoyancy and centrifugal force on the flow and heat transfer of a vertical serpentine micro-tube in the liquid-like region and the gas-like region are studied by numerical simulation. Under the same operating conditions, the heat transfer coefficient decreases with the increase of heat flux and increases with the increase of mass flux. The liquid-like region is greatly affected by buoyancy, resulting in the heat transfer coefficient of upward flow is significantly lower than that of downward flow, and the heat transfer coefficient fluctuates violently. The gas-like region is less affected by buoyancy, resulting in small difference between upward flow and downward flow heat transfer coefficients, and the heat transfer coefficient fluctuates less. At the turning point of the serpentine micro-tube, the centrifugal force mutation results in the weakened heat transfer of the local tube wall, and the weakened layer in the liquid-like region is larger than that in the gas-like region. These findings are important for understanding the effects of buoyancy and centrifugal force on flow and heat transfer in the liquid-like region and the gas-like region.