The given figure depicts an indirectly fired gas turbine engine. In the gas turbine engine, air is compressed to a high pressure and then heat is added. The high pressure, high temperature air is then expanded during a turbine with power being extracted. To a first estimate, the compressor and turbine may be treated as adiabatic. In a typical gas turbine, the fuel is added to the air and combusted and it is really the combustion products that pass during the turbine. In the obliquely fired turbine, as is used in this problem, the air is heated with a heat exchanger which allows heat sources that could or else not be used (e.g. solar, coal, etc.). The net work out of the gas turbine engine is the work out of the turbine less the work into the compressor. In a real engine these devices are generally all coupled on a common shaft.
Since the work of compression decreases the total work out, anything you can do to decrease the compression work will increase the net work out. One way to do that is to cool the air being compressed. The attached diagram shows a proposed system where the compression is divided into two stages and liquid water is sprayed into the air to cool it between the two stages. It is proposed that this approach may increase power output and increase efficiency. Your task is to determine if this approach is thermodynamically feasible. You may neglect the pressure drops between components and within the heat exchanger and you can neglect kinetic energy. The subsequent design parameters are provided. For these design parameters, evaluate the effect of the water spray on efficiency (net work out divided by heat input) and net power out per kg/s of dry air coming into the turbine. Do this for a range of water spray inputs from 0 up to the amount needed to achieve 70% relative humidity at point
3.
Point 1
T= _20C______
P= _0.85 bar______
O = __50%_____
Point 2
P= __3.5 bar_____
Point 3
P= ___10.0 bar_____
Point 4
T=__1220K_______
Point 5
P= P1
Compressor A: ηisen = __0.87___ Compressor B: ηisen = _0.83____ Compressor C: ηisen = __0.93
