Air enters an uninsulated nozzle at 5 m/s, 500 kPa, and 50°C. The cross-sectional area of the inlet is 0.0002 m2. The air exits at a velocity of 120 m/s and a temperature of 48°C. Determine the heat transfer rate for the nozzle.

Question

Given: Air, P1 = 500 kPa; T1 = 50°C = 323 K; V1 = 5 m/s; A1 = 0.0002 m2; V2 = 120 m/s; T2 = 48°C = 321 K

What will be an ideal response?

Answer 1

For a nozzle, assume steady –state, steady-flow single-inlet, single-outlet flow, and assume that W?=?pe=0

As the temperature change is small, we will consider air to be an ideal gas with constant specific heats: h2 – h1 = cp (T2 – T1)

These assumptions result in the first law being (State 1 is inlet, State 2 is outlet)



where R = 0.287 kJ/kg-K. For air, take cp = 1.005 kJ/kg-K



This is a very small heat transfer rate, but so is the mass flow rate of the nozzle. A larger mass flow rate would cause the heat transfer rate to become larger.