Effect of mist concentration on the cooling effectiveness of a diffused hole mist cooling system
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Effect of mist concentration on the cooling effectiveness of a diffused hole mist cooling system Nishant Gandhi1 · S. Suresh1 Received: 25 October 2019 / Accepted: 7 April 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Cooling the blades of gas turbines is essential for extending the life of the blades. Conventional gas turbines use air-film cooling. With the increase in turbine inlet temperatures, novel cooling methods are required. Recently mist cooling started to gain prominence for high-capacity gas turbines. Mist cooling involves adding water droplets in the form of a fine mist to the air in conventional film cooled systems. This paper numerically investigates the performance of mist cooling at various mist concentrations for two different hole configurations. The cooling effectiveness for a coolant injection hole with diffusion angle of 10° and 15° was analyzed with mist concentration varied from 1 to 7%. The results show that with a low mist concentration of 1%, the cooling effectiveness improved drastically for both configurations. A maximum of 69% improvement was observed for 7% mist concentration and 10° diffused hole. Mist concentrations above 5% did not offer any significant improvements as with lower concentrations. Keywords Mist · Film cooling · Turbine blades List of symbols BR Blowing ratio C Concentration Cp Specific heat (J kg−1 K−1) D Diffusion coefficient (m2 s−1) d Diameter (mm, m) F Force (N) h Enthalpy (J kg−1) P Pressure (Pa) T Temperature (K) S Source term u Velocity (m s−1) Subscripts c Coolant g Gas p Particle w Wall
* S. Suresh [email protected] Nishant Gandhi [email protected] 1
Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli, Tiruchirappalli, Tamil Nadu, India
Greek characters α Injection angle (°) β Diffusion angle (°) ρ Density (kg m−3) η Adiabatic cooling effectiveness κ Turbulent kinetic energy (m2 s−2) 𝜖 Turbulent dissipation (m2 s−3) λ Thermal conductivity (W m−1 K−1) ν Kinematic viscosity (m2 s−1)
Introduction Gas turbines used in airplane and ship propulsion and power production operate under very harsh conditions. The turbine blades especially the first-stage rotor and stator are subject to extremely high temperatures and a corrosive environment. The turbine blades are at their peak operating limits. The thermal efficiency of the gas turbine is dependent on the turbine inlet temperature, and increasing the turbine inlet temperature increases the efficiency. However, this increase in turbine inlet temperature is limited by the material limits and blade design. Advances in material and technology have led to the development of turbines with inlet temperatures exceeding 1500 °C. To protect the blade from failure at these high temperatures, certain manufacturing and cooling methods must be employed. Modern gas turbine blades are
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manufactured from single-crystal materials, and superalloys have some form of thermal barrier coatings and employ som
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