Section 9

thoughtgreenpepperMechanics

Oct 27, 2013 (3 years and 9 months ago)

69 views

SECTION IX
-

INCREASE
-
IN
-
ENTROPY PRINCIPLE
(SECOND

LAW

OF

THERMODYNAMICS)





(i)





(ii)




If surrounding is a reservoir at temperature




(iii)





(iv)


altern
atively,




(v)




For a closed system:




(vi)




For an open system:





(vii)




If flow is uniform at all exits and inlets of the system, (vii) becomes





(vii
i)




If flow is steady and uniform at all exits and inlets of the system, (viii) becomes






(ix)




For unsteady flow systems, multiply (viii) by dt





(x)

Section IX


Increase
-
in
-
entropy Principle (Second Law …)

Page
43



If there are many reservoirs in the surrounding
s, then






(xi)




Use of the increase
-
in
-
entropy principle to show that the direction of heat transfer must be from
a higher
-
temperature body to a body at a lower temperature




Consider two bodies, one at temperature T
A

and the o
ther at temperature T
B

as shown below







let the only interaction between the two bodies be heat transfer


system of the two bodies is
an isolated system


Total entropy change: dS
tot

= dS
A

+ dB
B








Q
A

=
-

Q;

Q
B

=

Q





(Second Law)


T
A



T
B

Q.E.D.


Body A at T
A

Body B at T
B


Q

Boundary of isolated system