Abstract
Gas turbines are always intended to give more specific work output for which continuous exposure to hot combustion gases is necessary. To increase the lifespan of the turbine blades active cooling should be applied to the High Pressure (HP) turbine blades. In the present work, a simple open cycle gas turbine is modeled to carry out thermodynamic analysis with different open loop steam cooling techniques: steam internal convection cooling (SICC), steam film cooling (SFC) and steam transpiration (STC) cooling. The effect of Turbine inlet temperature (TIT), Turbine blade temperature (T_b), and Compressor pressure ratio (CPR) on the coolant flow requirement and effect of T_b on the performance are estimated. The entire analysis is carried out with contemplation of variable specific heat (VSH) along with constant specific heats (CSH) for air and gas. Between VSH and CSH approaches, the former analysis leads to better performance from the first and second law efficiencies point of view. Irreversibility and Entropy generation rate are maximum in the combustor and they are less for VSH case in all cooling schemes and are decreased by 38.53%, 40.01%, and 40.40% for SICC, SFC and STC schemes respectively when compared with CSH(at TIT=1580 K, T_b=1123 K, CPR=19.1) analysis.
Highlights
The results of the parametric study to find the effect of operating parameters Turbine inlet temperature (TIT), Compressor pressure ratio (CPR) and Turbine blade temperature (Tb) on the coolant flow requirement for a simple gas turbine is evaluated and plotted
The minimum coolant requirement is found to be in the case of Steamtranspiration cooling (STC) with constant specific heat analysis
Among the three cooling schemes, STC is the best cooling option followed by steam film cooling (SFC) and steam internal convection cooling (SICC)
Summary
Thermodynamic model of simple gas turbine cycle plant with open loop steam cooling schemes. (ii) Isothermal effectiveness [7] as defined by the following equation is used for film and transpiration cooling concepts, which accounts for the reduced heat transfer from the gas to the blade. The coolant flows internally in the counterflow direction of the blade contour and after taking sufficient heat ejects out from the leading edge and forms a thin blanket of the stagnant layer (film) over the blade outer surface which reduces heat transfer from the gas to the blade In this case, the cooling is due to the joint action of internal convection and film formed over the surface and it’s film cooling. First and Second laws of thermodynamics applied to a cooled gas turbine lead to exergy balance equation as given by following expression: Eẋ Q + ∑ Eẋ i = ∑ Eẋ e + Eẋ w + İ (18). The hydrocarbon fuels (Cj Hk) specific chemical exergy is approximated as follows [24]:
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