Question

2. (12 marks total) A number of gas turbine engines today have compressor intercooling provided by injecting liquid water into the air leaving the low pressure compressor. The intercooler in the sketch provides cooling partly by cold water injection and partly by heat transfer to the surroundings. A steady flow of air enters 1 mw the compressor at T = 20°C, P = 100 kPa and a relative humidity compressor intercooler of o. = 50% at a flow rate of 50 kg dry air/s. It leaves the compressor and enters the intercooler at T, = 250°C and P, = 600 kPa. Liquid water is injected into the intercooler at 20°C with a mass flow of 1.0 kg/s. In all of the calculations that follow, assume that water vapour in the air behaves as a perfect gas.

Answer 1

2 → - compression Intercooling Compression. Sd? Ti = 20c, po = 100 kpa, b = 50%, ma = 50 kg/s To = 2500, P2 = 600 kpor a) W (spacifie huwridelag of dis Catering the compresors) • W, = 0,622* Pue Pau atmospheric garsuse P Pa-Pro Pu - Vapour pressure Pa = 100 kpa · Pv = Relative Humidity x saluarsted steam pressure Pue = 0.5 * P. (100 kpa) → 0.5X100% Pv, = 50 kpa W, = 0,622 x 50 100 -50 [wi = 0.622 kg/kg of day air Ans b) ws( specific Hurridity of our leaving the compressor) W, = 0.622 x P ve O Pa-Pro PV= 0X Pz ~ 0.5 X600 i per Pvz = 300kpa W, = 0.629x 300 ~ 0.933 kg leg of day air 100-300 [Wa = 0,933 kg/kg of day air] Ans CScanned with CamScanner

Tema Dew point of the air leaving the compressor PV = nRT 600 XV, >50x 0.284 x (250+273) V = 19.50 m3 Dew point is to be calculated at Pu (Vapour pressure) Przx Y₂ = mB (Todewpoint) ; Rod Pra = 300kpa TD.p = 300X12.50 50X0.287 | Taew point = 261. 3240 c lang temparature of mårst air leaving Entercooler -90c W2 = 0.622 Pug PAVE - MRT PaPus Pus = $xPg PX 18.507 5øX0.253 PV3 = MRT3 ; $ PX12.5 = 50X0.287 x (90+273) - P₂ = 416.124 kpa. Py = 0.5% 416.724 3 Pue = 208.362 kpa (Yapour pressure (3) W Wz = 2208.362 1. 196 kg /kg of day air 208.362-100 W3 = 1, 196 kg / kg of day air Heat transfer = mcp dł (ni a mass flow) = 1*1.008 (T2 - T3) = 1.008 (250-90) | Heat tean-sfer = 1610 28 kW] Ta Y ^ 13 CS scanned with CamScanner