EFFECT OF MATERIALS ON THE HEAT TRANSFER TO SUPERCRITICAL PRESSURE FLUIDS

Supercritical pressure fluids are widely used in many advanced single-phase thermosiphons as a working medium due to its high convective heat transfer efficiency and simpler design. However, the heat transfer in the pseudocritical region is very complex due to its steep variation of thermophysical properties and effect by the operating parameters. Under supercritical pressures, special heat transfer phenomenon can be observed in the heated tubes, three totally different heat transfer regimes present. As a result of the similarity between subcritical boiling phenomena and the deteriorated heat transfer behavior at supercritical pressure, scholars observed that heater with different materials but the same operating conditions, different types of free convection would be appeared by investigating the boiling-like phenomenon of carbon dioxide, which seems that boiling-like phenomena are specific to heater materials. The aim of this present study is to investigate the effects of thermophysical and chemical properties of heater materials upon heat transfer to supercritical water. In the present paper, two circular pipes with differential usual materials (AISI 321 and Inconel 600) are experimentally investigated by the electrically heating methods. The difference between AISI 321 and Inconel 600 in both enhanced and deteriorated heat transfer regimes are discussed respectively, then the heat transfer discrepancy caused by the materials analyzed. The results show that the heat transfer of supercritical pressure fluids dependent not only on the variation of the operating/boundary conditions but also on the materials of heating surface.