SECOND LAW OF THERMODYNAMICS

1. Isobaric ( P is constant)

Constant pressure on a T- s

Work done:

W = P(V2 - V1)

or

W= mR(T2-T1)

Unit : kJ

Heat flow:

Q = mCp ln (T2-T1)

Unit : kJ

The change of entropy is

s2 - s1 = mCp ln (T2/T1)

Unit : kJ/K

s2 - s1 = Cp ln (T2/T1)

Unit : kJ/kgK

2. Isometric (V is constant)

Constant volume on a T-s diagram

Heat flow =

Q = mC(T2-T1)

Unit : kJ

Change of entropy:

s2 - s1 = mCv ln (T2/T1)

Unit : kJ/K

s2 - s1 = Cv ln (T2/T1)

Unit : kJ/kgK

3. Isothermal (T is constant)

Constant temperature process on a T-s diagram

(the shaded area represents the heat supplied during the process)

Change of entropy:

s2 - s1 = R ln (v2/v1) = R ln (p1/p2)

Unit : kJ/kgK

s2 - s1 = mR ln (v2/v1) = mR ln (p1/p2)

Unit : kJ/K

4. Adiabatic 

Reversible adiabatic process on T-s diagram

from the non-flow equation:

W = mCv(T1 - T2)

or since, Cv = R/ γ-1

 W = mR(T1-T2)/γ-1

Or since PV = mRT

W= P1V1 - P2V2/ γ-1

Temperature, Pressure  and Volume for perfect gasses:
T2/T1 = (P2/P1)^γ-1/γ = (V1/V2)^γ-1

5. Polytropic Process

Reverse poly tropic process on a T-s diagram

Work done:

W = P1V1 - P2V2/ n-1

or since PV = mRT

W = mR(T1- T2)/ n-1

Change of entropy:

U2 - U1 = mCv(T2-T1)

Heat Flow:

Q = W + U2 - U1

Written by: Cahaya Athirah binti Mohammad Taufik