Optimization of liquid droplet injection in steam turbine blades: Loss reduction, droplet size control, and performance enhancement

In steam turbines, particularly in the low-pressure section, liquid droplet injection (LDI) is recognized as an advanced technique for regulating condensation. Instead of allowing large droplets to form, this method encourages condensation on the injected droplets, leading to finer and more uniform droplet formation. The purpose of this research is to minimize the occurrence of sudden, large droplets by promoting smaller, evenly distributed ones. To achieve this, the study investigates the droplet injection technique in detail and employs the TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) method to find the best injection strategy. The evaluation is based on several criteria, including mass flow rate, different entropy contributions (thermal, frictional, and phase change), total pressure loss coefficient (TPLC), droplet radius, liquid mass fraction (LMF), and kinetic energy. Results demonstrate that droplet injection has a strong influence on droplet radius, pressure losses, and phase change entropy. While the technique successfully decreases droplet size in certain cases, it consistently increases the liquid phase production across all tested scenarios. Injecting 1018 1/kg droplets with a mass fraction of 0.1% results in significant changes in various parameters: the average droplet radius at the output drops by 44.1%, phase change entropy falls by 76.1%, and the TPLC is reduced by 29.15%. Thermal entropy production and mass flow rate decrease by 10.96% and 2.8%, respectively, while the LMF at the outlet rises by 9.61%. Kinetic energy and frictional entropy production experience increases of 2.38% and 5.96%, respectively.