Heat Transfer Characteristics of Different Horizontal Wires in Pools of Liquid and Supercritical Carbon Dioxide

Abstract

The peculiar heat transfer mechanism of supercritical fluids has been studied for a long time, especially the flow and heat transfer in the tubes. Numerous experiments have demonstrated the three heat transfer modes of supercritical fluids: normal heat transfer, improved heat transfer and deteriorated heat transfer. The effects of the pressure, pipe diameter, mass flow rate, heat flux and flow direction also have been well studied in the experiments. From the perspective of theory, the pseudo-boiling theory noticed the similarities between the subcritical boiling and the supercritical fluid heat transfer, and explained the heat transfer mechanism. Another theory focuses the buoyancy and flow acceleration effect caused by the property change also made great success. However, the existing research still yields inconsistent results and more evidences are needed. In this work, the heat transfer characteristics from different horizontal wires immersed in both liquid and supercritical carbon dioxide are studied. For a wide range of bath temperatures (5 ∼ 60 °C) and pressures (5 ∼ 8 MPa), the heat transfer coefficients were measured with a quasi-steady increase and decrease of the heat generation rate. The surface temperature of the wires was derived from the measured resistance. Finally, the boiling curves of both the subcritical cases and supercritical cases were obtained. Meanwhile, the near-wall fluid fields were visualized using the high-speed camera. Different from the prior experiments, this pool-type experiment has avoided the complex turbulence flows, and provides clearer evidences of the different heat transfer modes of the supercritical fluids.