TITLE.PM5

SECOND LAW OF THERMODYNAMICS AND ENTROPY 297

dharm

/M-therm/th5-4.pm5

Fig. 5.52
The entropy change of the working fluid in the refrigerator would be zero, since it is operat-
ing in a cycle, i.e.,
(∆s)refrigerator = 0.
The entropy change of the atmosphere (positive),
(∆s)atm. = QWT+
∴ Entropy change of the universe
(∆s)univ. = (∆s)system + (∆s)refrigerator + (∆s)atm.

= (s 1 – s 4 ) + 0 + QWT+ = (s 1 – s 4 ) + QWT+

By the principle of increase of entropy

(∆s)univ. or isolated system ≥ 0

∴ ()ss

QW

14 −+T

L +

NM

O

QP^ ≥^0

∴ QWT+ ≥ (s 4 – s 1 )

W ≥ T (s 4 – s 1 ) – Q

W(min) = T (s 4 – s 1 ) – Q

Here Q = 448.46 kJ

T = 298 K