Effects of various coolants on flow and heat transfer characteristics in a round-tip pin-finned internal channel

This paper performs a numerical study regarding the effects of different kinds of coolants on flow and heat transfer in a pin-finned internal channel. A new pin-fin structure detached from one endwall with a round-tip is proposed which aims to increase the heat transfer enhancement. As a contrast, the investigation of the typical fully-attached pin-fin and the flat-tip detached pin-fin is also considered. In order to evaluate the reliability of the numerical method, an experiment of an internal channel with round-tip pin-fin arrays is conducted to serve as the reference, and all cases are carried out with the shear stress transport (SST) turbulence model. The effects of coolants including air, mist/air, steam, and mist/steam are analyzed with the Reynolds number ranging from 15, 000 to 50, 000. The results reveal that the round-tip pin-fin outperforms in heat transfer enhancement and pressure loss deterioration among all three pin-fin structures. With respect to Reynolds numbers, the averaged Nusselt numbers increase gradually for all coolants, and cases of mist/steam achieve the highest values, followed by cases of steam, mist/air, and air, respectively, but the differences between the mist coolants and pure coolants are not obvious as the Reynolds number is lower than 30, 000. In conclusion, cases of mist/steam obtain the best thermal performances, and the internal channel with round-tip pin-fin arrays using mist/steam as coolant is most favorable.