Heat transfer enhancement by mist/air two-phase flow in a high-temperature channel

TL;DR

This study experimentally investigates how mist/air two-phase flow enhances heat transfer in a high-temperature channel, demonstrating significant cooling improvements with small droplet amounts and analyzing effects of droplet size, flow rate, and heat flux.

Contribution

It provides new experimental data on mist/air cooling performance at high temperatures, highlighting the impact of droplet size and flow parameters on heat transfer enhancement.

Findings

Mist/air flow significantly improves heat transfer even with low droplet mass fractions.

Larger droplets cause more temperature reduction; smaller droplets improve temperature uniformity.

Cooling performance increases with mist/air mass ratio, extending downstream cooling effects.

Abstract

Mist/air two-phase flow is a promising cooling technique for many applications such as internal cooling of gas turbine blades. A significant enhancement of heat transfer can be achieved with a low mass fraction of droplets by utilizing the latent heat of the droplets. Using newly designed atomizers to accurately control the mist droplets, this study experimentally explores the heat transfer performance of mist/air flow in a high-temperature channel with a maximum temperature of 880 K. The effects of the mist/air mass ratio, droplet size, Reynolds number, and wall heat flux are studied. The results show that the cooling performance of the test section can be significantly improved by even adding a small amount of droplets. Considering mist droplets of different sizes, larger droplets can cause more remarkable temperature reduction, while smaller droplets can improve the uniformity of temperature distribution. For large droplets, the cooling effect in the upstream is more obvious than that in the downstream due to the interaction between the wall and the droplets, and with the increase of mist/air mass ratio, the area with obvious cooling extends downstream. The performance of mist/air cooling is tested by increasing the heat flux until the maximum temperature at the outlet reaches a predetermined value. Compared with air-only cooling, the increment in the wall heat flux by the mist/air cooling with a mass ratio of 3% can be up to 18.4%.