Air, initially at 220 kPa and 450 K undergoes a polytropic state change to 374 kPa and 495 K. What is the polytropic exponent of this process? and Saturated water vapor is contained in a rigid container. Heat is then added until the the pressure and temperature become 861.818 MPa and 400 ?C, respectively. What was the initial temperature of the steam? ?C Solution PV n =C PV=nRT V= nRT/P P( nRT/P) n =C P 1 (T 1 /P 1 ) n =P 2 (T 2 /P 2 ) n (T 1 P 2 /T 2 P 1 ) n =P 2 /P 1 n= ln(P 2 /P 1 )/ln(T 1 P 2 /T 2 P 1 )= 1.218944 .

1. Air, initially at 220 kPa and 450 K undergoes a polytropic state change to 374 kPa and 495 K.
What is the polytropic exponent of this process?
and
Saturated water vapor is contained in a rigid container. Heat is then added until the the pressure
and temperature become 861.818 MPa and 400 ?C, respectively. What was the initial
temperature of the steam?
?C
Solution
PV n
=C
PV=nRT
V= nRT/P
P( nRT/P) n
=C
P 1 (T 1 /P 1 ) n
=P 2 (T 2 /P 2 ) n
(T 1 P 2 /T 2 P 1 ) n
=P 2 /P 1
n= ln(P 2 /P 1 )/ln(T 1 P 2 /T 2 P 1 )= 1.218944