240212 Solutions ECT

Pagina 1

PROBLEM 2: Data mw, t/h 50 cp,w, kJ/kgK 4,2 Tw,in, °C 100 T3, °C 90 p3 = p2, bar 25 p1 = p4, bar 5 eta,is,t 80% eta,me,t 96% eta,hy,p 75% eta,me,p 94% DTmin,PHE, °C 5 Tw,min, °C 50 Values from tables and chart Solution 1) Tw,in Tw,out reg 1 7 4 4 3 5 2 1≈2 3 4 x 2) Fluid name HEOS::R134a #1 #2 p, bar = 5 25 T, °C = 15,7 15,7 h, kJ/kg = 221,5 223,7 s, kJ/kgK = Density at condenser outlet: rho,1 = 1241 kg/m3 Enthalpy change across the pump: Dh,p = v * Dp / eta,hy,p = 2,1 kJ/kg 3) q,in = h3 - h2 = 225,3 kJ/kg Le,out = (h3 - h4) *eta,me = 26,4 kJ/kg Le,in = Dh,p / eta,me,p = 2,3 kJ/kg Le,net = 24,1 kJ/kg eta,e,net = 10,70% 5) Saturated liquid at evaporator inlet: 'x' hx = 317,8 kJ/kg Tx = 77,6 °C Brine temperature at evaporator outlet: Tw,x = Teva + DTmin,PHE = 82,6 °C mw = 13,89 kg/s Qeva+sh = mw * cp,w * (Tw,in - Tw,x) = 1016,3 kW mR134a = Qev+sh / (h3 - hx) = 7,75 kg/s check if the brine outlet temperature is above the salt deposition temperture (optional check) hy = 429,0 kJ/kg Qeva = mR134a * (hy - hx) = 861,8 kW Qpreh = mR134a * (hx - h2) = 730,2 kW Tw,out = Tw,x - Qpreh / (mw * cp,w) = 70,1 °C Q, kW TR134a, °C 2 0 15,7 x 730,2 77,6 y 1592,0 77,6 3 1746,6 90 6) Pe = mR134a * Le,net = 186,9 kW 0,0 20,0 40,0 60,0 80,0 100,0 120,0 0 500 1000 1500 2000 T, °C Q, kW Dhref 0,00 Dsref 0,000 #3 #4 #4,is 25 5 5 90 30,3 448,9 421,4 414,6 1,74 1,74 this temperature must be > the salt deposition temperature Tw, °C 70,1 82,6 97,4 100