The addition of mist to a flow of steam or gas offers enhanced cooling for many applications, including cooling of gas turbine blades. The enhancement mechanisms include effects of mixing of mist with the gas phase and effects of evaporation of the droplets. An impinging mist flow is attractive for study because the impact velocity is relatively high and predictable. Water droplets, less than 15 μm diameter and at concentrations below 10 percent, are considered. The heat transfer is assumed to be the superposition of three components: heat flow to the steam, heat flow to the dispersed mist, and heat flow to the impinging droplets. The latter is modeled as heat flow to a spherical cap for a time dependent on the droplet size, surface tension, impact velocity and surface temperature. The model is used to interpret experimental results for steam invested with water mist in a confined slot jet. The model results follow the experimental data closely.

The flow field of a 2-D laminar confined impinging slot jet is investigated. Numerical results indicate that there exist two different solutions in some range of geometric and flow parameters. The two steady flow patterns are obtained under identical boundary conditions but only with different initial flow fields. Three different exit boundary conditions are investigated to eliminate artificial effects. The different flow patterns are observed to significantly affect the heat transfer. A flow visualization experiment is carried out to verify the computational results and both flow patterns are observed. The bifurcation mechanism is interpreted and discussed.

Closed loop steam has been chosen for cooling airfoils in heavy frame Advanced Turbine Systems (ATS) to improve efficiency. Enhanced cooling by the use of mist is considered to have potential to augment cooling by internal steam alone. Water droplets generally less than 10μm are added to 1.3 bar steam and injected through a row of four discrete round jets onto a heated surface. The Reynolds number is varied from 7500 to 22500 and the heat flux varied from 3.3 to 13.4 kW/m2. The mist increases the heat transfer coefficient along the stagnation line and downstream wanes in about 5 jet diameters. The heat transfer coefficient improves by 50 to 700 percent at the stagnation line for mist concentrations 0.75 to 3.5 percent by weight, depending on conditions. Off-axis maximum cooling occurs in most of the mist/steam flow but not in the steam-only flow. CFD simulation indicates that this off-axis cooling peak is caused by droplets’ interaction with the target walls.

This paper presents a new set of experimental data on the hydrodynamics of rotating bubble flow and is a continuation of previous gas-liquid rotating flow studies. The new data include the surface friction on both end walls of the vortex chamber, and static pressure distributions at the exit of swirl generator slots and on the inner surface of vortex chamber. The corotating disk technique was used to determine the friction momentum measured by the dynamometer. The air-liquid velocity was registered by the blade-anemometer with a light modulator fixed on its axis. The friction coefficient was found based on the conservation of rotational momentum and the assumption of constant air-liquid rotational velocity throughout the two-phase flow field. The ‘jump-like’ reductions in static pressure were registered on the border between the incoming jets and the bubble flow. A new correlation describing linear gas-liquid rotating velocity is given. The static pressure measurements are in reasonable agreement with the data predicted from the theoretical model.