Question

Air at 7°C enters a turbojet engine at a rate of 16 kg/s and at a velocity of 220 m/s (relative to the engine). Air is heated in the combustion chamber at a rate 15,000 kJ/s, and it leaves the engine at 427°C. Determine the thrust produced by this turbojet engine.

Answer 1

Answer:

F=14.05 KN

Explanation:

Now from first law for open system

$h_1+\dfrac{V_1^2}{2}+Q=h_2+\dfrac{V_2^2}{2}+w$

In Turbojet net work out put is zero because ,power produce by turbine is consumed by compressor.

So w=0

Given mass flow rate =16 kg/s

$V_1=220 m/s$

Heat input Q=15000 KW  (Q=937.5 KJ/kg)

$h_1+\dfrac{V_1^2}{2}+Q=h_2+\dfrac{V_2^2}{2}$

$1.005\times (273+70)+\dfrac{220^2}{2000}+937.5=1.005\times (273+427)+\dfrac{V_2^2}{2000}$

So $V_2=1098.1 m/s$

So thrust

$F=\dot{m_a}(V_2-V_1)$

F=16(1098.32-220)

F=14.05 KN