NUMERICAL STUDY ON HEAT TRANSFER DETERIORATION OF n-DECANE DURING PYROLYSIS UNDER SUPERCRITICAL PRESSURE IN A VERTICAL TUBE

For accelerating hypersonic vehicles, it is important to understand the effects of various factors on heat transfer deterioration. The heat transfer characteristics of supercritical n-decane with pyrolysis were numerically simulated inside a vertical tube. The effects of flow direction, mass-flow rate, heat flux, inlet temperature, and flight acceleration on the heat transfer characteristics were investigated. When the inlet temperature was relatively low or the fluid was decelerated vertically upward, a typical M-shaped velocity distribution was formed, indicating the heat transfer deterioration. Furthermore, the decrease in wall heat flux, as well as the increase in mass-flow rate, inlet temperature and flight acceleration in the same direction as the flow makes the heat transfer deterioration gradually disappear. Finally, a new relationship was established between the heat flux and the flight acceleration and inlet temperature to determine critical heat flux under which heat transfer deterioration developed in the upward flow.