The staged development of a horizontal pipe flow at supercritical pressure

The axial development of heat transfer to supercritical fluids in horizontal pipe has been studied both experimentally and numerically. It has been demonstrated that the flow and heat transfer exhibit a distinct three-stage development, including two entrance effect stages and an asymptotic development stage. Stage I is characterized by a rapid heat transfer coefficient reduction and is largely caused by the thermal boundary layer development. When the inlet temperature is close to the pseudo-critical value however, flow laminarisation also plays a role. Stage II is a special entrance effect, which has not been observed in flow and heat transfer at subcritical pressure condition. This is caused by the strong buoyancy effect, leading to stratification and secondary flow. Most interestingly the heat transfer of supercritical fluids in a horizontal flow can reach a pseudo-developed state stage III, where the flow and heat transfer is free from the influence of the entrance condition. This contrasts the common belief that the heat transfer of supercritical fluids can never reach an axially asymptotic condition because of the significant property variations. The existence of such a condition can be of great value for fluid-to-fluid similarity analyses.