TITLE.PM5

FIRST LAW OF THERMODYNAMICS 123

dharm

M-therm/th4-2.pm5

Expansion stroke. Process 2-1 :

Fig. 4.15
Work done by air on the piston, W2–1 = 100000 N-m (= 100 kJ)
Now, Q2–1 = (U 1 – U 2 ) + W
= – 37 + 100 kJ = 63 kJ
Hence, quantity of heat added to the system = 63 kJ. (Ans.)
+Example 4.8. A tank containing air is stirred by a paddle wheel. The work input to the
paddle wheel is 9000 kJ and the heat transferred to the surroundings from the tank is 3000 kJ.
Determine : (i)Work done ;
(ii)Change in internal energy of the system.
Solution. Refer Fig. 4.16.

Fig. 4.16