Problem 43P

Applying the Entropy Balance: Closed Systems

Air contained in a rigid, insulated tank fitted with a paddle wheel, initially at 300 K, 2 bar, and a volume of 2 m3, is stirred until its temperature is 500 K. Assuming the ideal gas model for the air, and ignoring kinetic and potential energy, determine (a) the final pressure, in bar, (b) the work, in kJ, and (c) the amount of entropy produced, in kJ/K. Solve using

(a) data from Table A-22.

(b) constant cv read from Table A-20 at 400 K.

Compare the results of parts (a) and (b).

Table A-20 Ideal Gas Specific Heats of Some Common Gases (kJ/kg · K)

Table A-22 Ideal Gas Properties of Air

a.)

Step 1 of 4

We have to find the final pressure, work done and the amount of entropy produced,for the air contained in a rigid, insulated tank fitted with a paddle wheel, initially at 300 K, 2 bar, and a volume of 2 m3 is stirred until its temperature is 500 K.

The final pressure can be found using ideal gas equation

Now, and

So,

Hence, =

= 2

= 3.33 bar

Therefore, the final pressure is 3.33 bar .