Flow And Heat Transfer Characteristics Of Supercritical Nitrogen In Mini-tubes

Fluids with the state near the critical points-supercritical fluids show many tremendously strange characteristics, such as singularities in compressibility and viscosity, diminishing difference in vapor and liquid phases and so on which have attracted a lot of investigations both experimentally and theoretically for fundamental research.The already-existed results for the flow and heat transfer characteristics are mostly for the room-temperature fluids, and those for cryogenic fluids, e.g, nitrogen and helium, are rarely found. Firstly, summarized and analyzed the flow and heat transfer characteristics of the former literatures, and then designed the experimental setup, as well as illustrated the details.In the present study, experimental investigations of the heat transfer and fluid flow characteristics of supercritical nitrogen in a mini-tube of 2 mm in diameter and 220 mm in length are carried out, the effects of many influential factors on fluid flow and heat transfer are studied. Oscillate phenomena of local wall temperature is found in the experiment, and is analyzed on the effect of heat flux and mass flow rate. Meanwhile, the numerical analysis of the fluid flow and heat transfer characteristics of supercritical nitrogen is also conducted. It is found that the agreement between the experimental and numerical results is quite good and further simulated the velocity distribution at various inlet temperature and heat flux. Comparisons between numerical analysis and former literature results are also reached good agreement, and particularly analyzed the effect of different turbulence models and y+.Finally, the paper studied the flow and heat transfer characteristics in curved pipes and investigated the literatures world-wide. On the base of the numerical study of flow and heat transfer in mini-tube, simulated the condition of flow and heat transfer of supercritical nitrogen in curved pipes, and analyzed the temperature and velocity distribution, as well as the averaged heat transfer coefficient along the curved pipe.