852 air enters a nozzle steadily at 200 kpa and 65c with a...

8–52 Air enters a nozzle steadily at 200 kPa and 65°C with a velocity of 35 m/s and exits at 95 kPa and 240 m/s. The heat loss from the nozzle to the surrounding medium at 17°C is estimated to be 3 kJ/kg. Determine (a) the exit temperature and (b) the exergy destroyed during this process. Answer: (a) 34.0°C, (b) 36.9 kJ/kg

Transcript

00:01 In this problem, we have air entering a nozzle at steadily at 200 kilopascals and 65 degrees c at a rate of 35 meters per second.

00:18 And it exits at 95 kilopascals and 240 meters per second.

00:24 The surrounding temperatures, the surrounding temperature is 17 degrees c.

00:30 And we estimate that the heat loss to this surroundings is 3 kilojoules per kilogram.

00:40 It's air, so we have an ideal gas constant of this.

00:45 And because we know two thermodynamic properties here, we can look up the anthropian and the standard entropy from tables.

00:54 And we know that there's no energy being stored in this system.

01:01 The rate of energy coming in has to be equal to the or minus the rate of energy going out has to be zero.

01:08 So they have to be equal to each other.

01:13 Because, again, there's no, well, there is no work being done.

01:23 So anyway, that gives us that the energy coming in is this, the flow of energy coming in, and the flow of energy going out.

01:31 And then we have in the fluid.

01:34 The energy going out in the heat, which i guess this would be, if you put an out on there.

01:45 So we can basically divide through, you know, multiply through by a differential time element and just get this in, well, divide through by this mass and get this all in a specific form.

01:57 So we have q -out plus delta h plus delta k -e is zero.

02:05 We know everything in here, except for h2...

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