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A gas is heat ed in a duct as it flows over a resistance heater. Consider a 101 kW electric heat ing syst em. The gas ent ers the heat ing section of the duct at 100 kPa and 27°C with a volume flow rate of 15 m³ /s. If heat is lost from the gas in the duct to the surroundings at a rate of 51 kW, the exit temperature of the gas is (Assume constant pressure, ideal gas, negligible change in kinetic and potential energies and constant specific heat: Cp = 1 kJ/kg. K; R = 0.5 kJ/kg K).
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- 37°C
- 76°C
- 53°C
- 32°C
Correct Option: D
| Cρ = 1 | ||
| kgK |
| R = 0.5 | ||
| kgK |
| ṁ = | = | = 10kg/s | ||
| RT1 | 0.5 × 300 |
By applying steady flow energy equation, (SFEE)
ṁh1 + Q̇ = ṁh2 + Ẇ
= 10 × 1 × 300 + ( -51) = 10 × 1 × T2 + (-101)
T2 = 305 K = 32°C
Hence, Exit temperature (T2) = 32°C.
