WET COMPRESSION ANALYSIS INCLUDING VELOCITY SLIP EFFECTS

Injection of water droplets into industrial gas turbines in order to boost power output is now common practice. The intention is usually to saturate and cool the intake air, especially in hot and dry climates, but in many cases droplets carry over into the compressor and continue to evaporate. Evaporation within the compressor itself (often referred to as "overspray") is also central to several advanced wet cycles, including the Moist Air Turbine (MAT) and the so-called TO PHAT cycle. The resulting wet compression process affords a number of thermodynamic advantages, such as reduced compression work, and increased mass flow rate and specific heat capacity of the turbine flow. Against these benefits, many of the compressor stages will operate at significantly off-design flow angles, thereby compromising aerodynamic performance. The current paper describes wet compression calculations including velocity slip and many of the associated phenomena (e.g., blade deposition and Elm evaporation). The calculations also allow for a poly-dispersion of droplet sizes and droplet temperature relaxation effects (i.e., the full droplet energy equation is solved rather than assuming that droplets adopt the wet-bulb temperature). The latter is important for sprays produced by "flashing" since the resulting droplets are initially much hotter than the surrounding gas. The method has been applied to a "generic" twelve stage compressor to ascertain to the impact slip effects have on the wet compression process.