help The exhaust nozzle of a jet engine adiabatically expands air at 300kPa and

Question

help

The exhaust nozzle of a jet engine adiabatically expands air at 300kPa and 200 degree C to l00kPa. Determine the air velocity at the exit when the inlet velocity is very low (can be neglected) and the nozzle isentropic efficiency is 90%. (Answer: 480m/s) R-134a is throttled from 1200kPa and 40 degree C to 200kPa. It is known that heat of 5kJ/kg is lost from R-134a to the surroundings at 20 degree C. Determine (a) the specific enthalpy of R-134a at the exit; (b) the temperature at exit; (c) the specific entropy of R-134a at the exit; and (d) the specific entropy generation. (Answer: 10323kJ/kg; -10.09 degree C; 0.403kJ/kgiC; 0.0257kJ/kg.K)

Explanation / Answer

From R-134a properties,

At 1200 kPa and 40 deg C we get h1 = 103.23 kJ/kg, s1 = 0.394 kJ/kg-K

At P2 = 200 kPa and h2 = h1 = 103.23 kJ/kg, we get T2 = -10.09 deg C, s2 = 0.403 kJ/kg-K

Hence,

a)

h2 = 103.23 kJ/kg

b)

T2 = -10.09 deg C

c)

s2 = 0.403 kJ/kg-K

d)

Entropy generation = s2 - s1 + Q / T_surr

= 0.403 - 0.394 + 5/(20+273)

= 0.0257 kJ/kg-K

Related Questions

Navigate

• Browse (All)
• Browse H
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.