How much work must be input by the paddle wheel in Fig. to raise the piston 5 in? The initial temperature is 100ºF.
Text Solution
Verified by ExpertsCHECK THE SOLUTION.
Sol. The first law, with Q = 0, is
W = Δ U or – PA Δ h – W paddle = mc v (T 2 – T 1 )
The pressure is found from a force balance on the piston:
P = 14.7 + 
= 18.18 psia
The mass of the air is found from the ideal-gas law:
M = 
= 
= 0.0255 lbm
The temperature T 2 is
T 2 = 
= 
= 840 ºR
Finally, the paddle-wheel work is found to be
W paddle = –PA Δ h – mc v (T 2 – T 1 ) = –(18.18)( π )(4) 2 (5/12) – (0.0255)(0.171)(788)(840–560)
= –1331 ft-lbf
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