seven general property equation of the following thermodynamics processes: a. POLYTROPIC

Elements Of Electromagnetics
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ISBN:9780190698614
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Derive the seven general property equation of the following thermodynamics processes:

a. POLYTROPIC PROCESS

5. Polytropic Process
Polytropic process is an internally reversible process. The
from process definition:
previous four (4) processes discussed above is also a polytropic
PV" = C where n = any positive real number (n # k,1, and ∞.)
PV" = C
P = CV-"
process with various polytropic coefficient 'n'. Now, we define a
special case of polytropic process wherein ´n' is any positive real
number and n + k, 1, and . Thus also, we may have concluded
substituting to the integral and evaluating:
that Q + 0 also. And, as derived using the seven (7) general
A-
[V1-n
PV
= C
V-"dV = C
= PVn
equations, we have:
- n
v Any Process relation:
P2V2-P¡V1 _ mR(T2 – T1)
Wn =
1-n
1-n
PV
= C
P;V _ P¿V2
T2
Internal Energy:
=
Following the relation in the change in internal energy, we have
The relation between these three (3) parameters can be
an internal energy of:
simplified
AU = mC,(T2 – T1)
further to determine the relation between any of the two
v Heat Transferred:
desired
Following the relation of heat transfer, we have:
parameters using:
Q = AU + W,
mR(T2 – T,)
PV" = C where n = any positive real number (n # k,1, and co.)
Q = mC,(T2 – T;) +
1-n
PV™ = C
From properties of ideal gas, we have:
Deriving the pressure - volume relation:
P,V," = P,V2"
Cy
k -
; R = C„(k – 1)
一
Substituting from the above equation, we have:
mC, (k – 1)(T2 – T,)
Q = mC,(T2 – T1) +
Also to derive 'n', we may use:
1-n
(k -
= mc,(T, – T,) 1 + = mC,(T, – T,)
In
=n In
1-n
Note that the relation of heat transferred under polytropic
In
process has a special value for specific heat. That is the specific
In
heat under polytropic process, Cn, with an equivalent below:
Deriving the volume – temperature relation:
Cn = C,
;n# 1
; from
PV
relationship
And heat transferred under polytropic process will be:
Substituting to the previously derived pressure
- volume
Q = mC„(T2 – T,)
relation:
V Enthalpy:
Following the relation in the change in enthalpy, we have an
enthalpy of:
開
AH = mC,(Tz – T,)
V Entropy:
Deriving the pressure – temperature relation:
Following the guiding equation as represented by the to obtain
PV
; from relationship
AS,
Substituting the previously derived volume - temperature
dQ
mCndT
AS =
T
relation:
Evaluating the integral, we will have:
n-1
原-“
n-1
AS = mC„ln
1-n
Note that the other equivalent of T2/T; can be used also to
determine the value of AS. That is,
Simplifying, we will have:
n-1
一”
n-1
開-
v Work Non-flow:
Applying the integral to evaluate the work non-flow of the ideal
gas under polytropic process, we will again employ the use of:
v Work Steady flow:
W. = [° rav
PdV
For work steady flow, we follow the integral below:
W = -
VdP
from process definition:
PV" = C where n = any positive real number (n # k,1, and ∞.)
PV" = C
V
substituting to the integral and evaluating in below:
= -
1-n
Simplifying further we will arrive for the relation:
P,Vz-P,V,
= n
mR(T, – T,)
1-n
W, = n
1-n
Therefore, at polytropic process, we have a work on steady flow
system as:
w, = nW, = n
PdV
Transcribed Image Text:5. Polytropic Process Polytropic process is an internally reversible process. The from process definition: previous four (4) processes discussed above is also a polytropic PV" = C where n = any positive real number (n # k,1, and ∞.) PV" = C P = CV-" process with various polytropic coefficient 'n'. Now, we define a special case of polytropic process wherein ´n' is any positive real number and n + k, 1, and . Thus also, we may have concluded substituting to the integral and evaluating: that Q + 0 also. And, as derived using the seven (7) general A- [V1-n PV = C V-"dV = C = PVn equations, we have: - n v Any Process relation: P2V2-P¡V1 _ mR(T2 – T1) Wn = 1-n 1-n PV = C P;V _ P¿V2 T2 Internal Energy: = Following the relation in the change in internal energy, we have The relation between these three (3) parameters can be an internal energy of: simplified AU = mC,(T2 – T1) further to determine the relation between any of the two v Heat Transferred: desired Following the relation of heat transfer, we have: parameters using: Q = AU + W, mR(T2 – T,) PV" = C where n = any positive real number (n # k,1, and co.) Q = mC,(T2 – T;) + 1-n PV™ = C From properties of ideal gas, we have: Deriving the pressure - volume relation: P,V," = P,V2" Cy k - ; R = C„(k – 1) 一 Substituting from the above equation, we have: mC, (k – 1)(T2 – T,) Q = mC,(T2 – T1) + Also to derive 'n', we may use: 1-n (k - = mc,(T, – T,) 1 + = mC,(T, – T,) In =n In 1-n Note that the relation of heat transferred under polytropic In process has a special value for specific heat. That is the specific In heat under polytropic process, Cn, with an equivalent below: Deriving the volume – temperature relation: Cn = C, ;n# 1 ; from PV relationship And heat transferred under polytropic process will be: Substituting to the previously derived pressure - volume Q = mC„(T2 – T,) relation: V Enthalpy: Following the relation in the change in enthalpy, we have an enthalpy of: 開 AH = mC,(Tz – T,) V Entropy: Deriving the pressure – temperature relation: Following the guiding equation as represented by the to obtain PV ; from relationship AS, Substituting the previously derived volume - temperature dQ mCndT AS = T relation: Evaluating the integral, we will have: n-1 原-“ n-1 AS = mC„ln 1-n Note that the other equivalent of T2/T; can be used also to determine the value of AS. That is, Simplifying, we will have: n-1 一” n-1 開- v Work Non-flow: Applying the integral to evaluate the work non-flow of the ideal gas under polytropic process, we will again employ the use of: v Work Steady flow: W. = [° rav PdV For work steady flow, we follow the integral below: W = - VdP from process definition: PV" = C where n = any positive real number (n # k,1, and ∞.) PV" = C V substituting to the integral and evaluating in below: = - 1-n Simplifying further we will arrive for the relation: P,Vz-P,V, = n mR(T, – T,) 1-n W, = n 1-n Therefore, at polytropic process, we have a work on steady flow system as: w, = nW, = n PdV
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