Non flow processes is classified as
(1). Constant volume process – Isocharic process
(2). Constant pressure process – Isobaric process.
(3) Constant temperature process - Isothermal process
(4). Reversible adiabatic process – Isentropic process
(5)). Polytropic process
(i). Constant Volume Process
V = C, dV = 0
dQ = dU+PdV/J
dQ = dU+PdV/J but dV = 0
dQ = dU
Integrating we get
Q12 = (U2-U1)
we know that for constant volume process
Q12 = mCv(T2-T1)
Cv - specific heat at constant volume = 0.713 KJ / Kg.K for air.
Q12 =(U2-U1) = mCv(T2-T1)
For constant volume process Work done = 0,Heat transfer = change in internal energy.
(ii). Constant pressure Process
P = C
dQ = dU+PdV/J
Integrating we get
Q12 = U2 –U1 + P [ V2 – V1] / 1000
= [U2 + P2 V2 / 1000 ] - [ U1 + P1 V1 / 1000 ]
Q12 = H2 – H1
H = U + PV / 1000
Enthalpy = Internal energy + Flow energy
But we know that for a constant pressure process
Q12 = m Cp (T2-T1)
Cp is specific heat at constant pressure. Cp =1KJ/Kg.K for air
Q12 = H2 – H1 = m Cp (T2-T1)
W = P (V2 –V1) / 1000
[U2 – U1] = m Cv(T2-T1)
For constant pressure process heat transfer = change in enthalpy.
(iii). Relation between Cp, Cv and R / J
From constant pressure process
Q12 = U2 –U1 + P [V2 – V1]
m Cp (T2-T1) = m Cv(T2-T1) + m R(T2 –T1) / J
Cp = Cv + R / J
Cp - Cv = R / J
(iv). Isothermal process,
dT = 0 , T2 = T1
we know that
P1V1/T1 = P2V2/T2
P1V1 = P2V2 [ since T2=T1]
PV = C
Hence isothermal process is also called as Hyperbolic process.
We know that
dQ = dU+PdV/J
dQ =PdV/J [ since dT = 0]
Heat transfer = Work done
Work done = 1∫2 P dV / J
PV = C
P = C / V
Substituting and integrating we get
W = P1V1 loge(V2/V1) / 1000
Q12 = W = P1V1 loge(V2/V1) / 1000
(v). Reversible Adiabatic Process
dQ = 0 , PVγ = C
We know that
dU = -PdV/J [ since dQ = 0 ]
change in internal energy = - work done
change in internal energy [ U2 – U1] = m Cv(T2-T1)
Workdone = 1∫2 P dV / J
We know that PVγ = C
P = C / Vγ
Substituting and integrating we get
W = P1V1 – P2V2 / [γ – 1 ] x 1000
(vi). Relation between P ,V and T
P2/ P1 = [V1 / V2 ] γ
T2 / T1 = [ P2/ P1 ] (γ -1 / γ)
T2 / T1 = [V1 / V2 ] γ -1
(vii). Polytropic Process
PVn = C
We know that
dQ = dU+PdV/J
integrating we get
Q12 = (U2-U1) + P1V1 – P2V2 / [n – 1 ]
= m Cv(T2-T1) + mR(T1-T2)/ [n – 1 ]
= m Cv(T2-T1) - mR(T2-T1)/ [n – 1 ]
= m Cv(T2-T1) – m Cv (γ – 1) (T2-T1)/ [n – 1]
= [ n- γ / n – 1] m Cv(T2-T1)
Q12 = [ n- γ / n – 1] ∆U
W = P1V1 – P2V2 / [n – 1 ] x 1000
[ U2 – U1] = m Cv(T2-T1)
(viii). Relation between P ,V and T
P2/ P1 = [V1 / V2 ] n
T2 / T1 = [ P2/ P1 ] (n -1 / n)
T2 / T1 = [V1 / V2 ] n-
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