An insulated piston–cylinder device initially contains 1 m3 of air at 120 kPa and 17°C. Air is now heated for 15 min by a 200-W
resistance heater placed inside the cylinder. The pressure of air is maintained constant during this process. Determine the entropy change of air, assuming: (a) constant specific heats. (b) variable specific heats.
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Answer:
The time taken will be "1 hour 51 min". The further explanation is given below.
Explanation:
The given values are:
Number of required layers:
=
=
Diameter (d):
= 1.25 mm
Velocity (v):
= 40 mm/s
Now,
The area of one layer will be:
=
=
The area covered every \second will be:
=
=
=
The time required to deposit one layer will be:
=
=
The time required for one layer will be:
=
∴ Total times required for one layer will be:
=
=
So,
Number of layers = 152
Therefore,
Total time will be:
=
=
=