TITLE.PM5

298 ENGINEERING THERMODYNAMICS

dharm
/M-therm/th5-4.pm5

W

System

Atmosphere at

298 K

HE

1 kg water at

25°C to ice at

• 5°C

Q = 448.46 kJ

Q + W

Fig. 5.53

s 4 – s 1 = 1.6263 kJ/K

∴ W(min) = 298 × 1.6263 – 448.46 = 36.17 kJ. (Ans.)

Highlights

1. Clausius statement :
   “It is impossible for a self-acting machine working in a cyclic process, unaided by any external agency, to
   convey heat from a body at a lower temperature to a body at a higher temperature.”
   Kelvin-Planck statement :
   “It is impossible to construct an engine, which while operating in a cycle produces no other effect except to
   extract heat from a single reservoir and do equivalent amount of work”.
   Although above statements of second law of thermodynamic appear to be different, they are really equiva-
   lent in the sense that violation of either statement implies violation of other.


2. Perpetual motion machine of second kind (PMM2) is that imaginary machine which would continu-
   ously absorb heat from a single thermal reservoir and convert this heat completely into work. The effi-
   ciency of such a machine would be 100%.


3. Clausius inequality is given by,

Cycle

∑

F

HG

I

KJ

δQ

T^ ≤^0

“When a system performs a reversible cycle, then

Cycle

∑

F

HG

I

KJ

δQ

T = 0,