Modeling of Heat Transfer in a Mist/Steam Impinging Jet

Abstract

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.

Simulation of Film Cooling Enhancement With Mist Injection

“…Models of collisions and coalescences will also be developed and incorporated into the future studies. Li et al modeled the mist cooling [22] using the experimental data from [13] and reported the major contribution for mist cooling enhancement was from the direct contact between droplets and the wall. In this paper, the direct droplet-wall contact heat transfer mechanism is not included, so the cooling results could be probably 50% under predicted.…”

Mist/steam heat transfer of multiple rows of impinging jets

“…The heat transfer between an individual droplet and wall is eventually related to the surface superheat, droplet diameter, impact velocity, and droplet surface tension. The comprehensive modeling and evaluations of q 00 1 , q 00 2 , and q 00 3 can be found in [7]. Depending on the mist flow conditions, heat conduction between the droplets and heated surface ðq 00 3 Þ and the subsequent liquid evaporation contribute about 80-99% to the total enhancement ðq 00 2 þ q 00 3 Þ.…”

“…Detailed mist/steam heat transfer mechanisms were investigated and analyzed by Li et al [7], in which the overall heat transfer of mist/steam is divided into three parts: heat transfer from the target wall to the steam flow ðq 00 1 Þ, heat transfer between steam and droplets (quenching effect, q 00 2 ), and heat transfer from wall to droplets ðq 0 3 Þ. Therefore, the enhancement ratio can be given as…”

“…Among these effects, it has been found that the direct droplet deposit and evaporation play a dominant role [7]. Not many studies have been found on the two-phase impingement heat transfer, especially on steam flow with droplets.…”

Simulation of Mist Film Cooling at Gas Turbine Operating Conditions

“…Li. et al [34] analytically showed that the brief contact between the droplet and the wall plays a major role in transferring heat. Rather than correctly model the droplet-wall interactions, the "trap" wall condition is applied for comparison.…”