Enhancement of Heat Transfer in the Downstream Region of a Backward-Facing Step Using a Small Amount of Mist (1st Report; Study of Heat Transfer Enhancement)

Abstract

A Mist flow, an air flow with mixed water droplets, is suitable for rapid cooling by the latent heat of vaporizing water droplets. The technique using a small amount of fine mist is promising to partially cool the local region. The air flow which contains fine mist promotes heat transfer in some area. The cooled air by means of the evaporating mist augments the heat transfer on the duct wall. All the mist evaporates, and does not remain in the air flow. Therefore, this technique can be useful as well as the usual single phase air flow with heat transfer enhancement of a forced convection. This paper attempts to figure out how the heat transfer coefficient in the mist flow is affected by Reynolds number and heat flux on the duct wall. Experiments of heat transfer enhancement using the mist flow were carried out. It was found that the heat transfer coefficient increases when the mist is added, Reynolds number becomes larger and the added heat flux becomes smaller. The experimental results show that this technique is very promising to heat transfer enhancement.