Film cooling with using the decomposition of an NH3 cooling stream as a chemical heat sink

The inlet temperatures of gas turbines are generally increasing over time, so conventional cooling methods are likely to approach their useful limits. It is therefore essential to investigate novel cooling methods. Based on the theory of heat transfer enhancement, a novel film cooling method for gas turbine blades using a chemical heat sink is proposed. In this method, the endothermic reaction of an NH3 cooling stream heated by the main gas stream takes place, reducing the convective heat transfer between the mainstream and the blades. Therefore, film cooling effectiveness is improved. To test the feasibility of the proposed method, numerical simulations were conducted, using the classical flat plate with a 30 degree angled cylindrical hole (diameter, D). Film cooling effectiveness at different blowing ratios (M = 0.5, 1.0, and 1.5) were computed and compared with the results of conventional cooling methods. The simulation results show that the proposed method can enhance film cooling effectiveness not only in the stream-wise direction, but also in the span-wise direction. The span-averaged film effectiveness is improved in the presence of a chemical heat sink, with the value of X/D (the ratio of downstream distance from the center of the film hole to the diameter of the film hole) increasing downstream of the film hole. The novel film cooling approach showed the best performance at M = 0.5.