4. (a) What\'s the benefit of reheating- increase work or efficiency? (b) Where

Question

4. (a) What's the benefit of reheating- increase work or efficiency? (b) Where is it used between compressors or turbines? 5. An APU gas turbine for use on a large airliner uses air bleed from the compressor discharge for aircraft services such as cabin air, hydraulics, etc. This APU can provide 1.5 kg/s bleed air with remaining going through the system and generate 200 kW available shaft power. Calculate () total compressor air mass flow (I) the power available with no bleed air flow. The APU has the following operating conditions: Compressor PR.-3.8, Compressor isentropic efficiency-85%, combustion pressure loss 0.1 2bar, TIT 1050Kturbine isentropic efficiency-88%, compressor rotor mechanical efficiency-99%, mechanical efficiency(driven load-98%, ambient conditions 1 bar, 288K Use a T-s diagram and a Table for summarizing Pressure and Temperatures at conditions 1-4 a. Calculate TO2, using T1 and isentropic efficiency and PR b. Calculate PO2 c. Calculate PO3 using combustion pressure drop d. Use energy balance under bleed condition to find total compressor mass flow mtotal 200kW = nload [(mtotal-mbleed.Cpg.dTturbine-m total. .cpadTcompressorncomp-rotor)] e. Using the above energy balance with zero bleed, mbleed-O, find the total Power

Explanation / Answer

4)

a) In turbines with high expansion ratio, the moisture content of the steam leaving the turbine is high. This leads to corrosion of the blades and reduction in the nozzle and blade efficiency. The main purpose of the reheat system is to make use of the high temperature flue gasses to reduce the wetness of the steam by increasing the temperature and pressure of the steam entering the lower stages of turbines. This in turn leads to an increased overall efficiency

b) Ideally, reheating is done between the lower stages of turbine

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