The Stirling Cycle

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A thermodynamic machine that doesn't rely on internal combustion but instead receives heat input externally. This process still generates the typical pressure-volume cycle, allowing for modeling and calculating the achieved efficiency.

>Model

ID:(1485, 0)



The Stirling Cycle

Description

A thermodynamic machine that doesn't rely on internal combustion but instead receives heat input externally. This process still generates the typical pressure-volume cycle, allowing for modeling and calculating the achieved efficiency.

Variables

Symbol
Text
Variable
Value
Units
Calculate
MKS Value
MKS Units
$Q_C$
Q_C
Absorbed heat
J
$V_2$
V_2
Compressed volume
m^3
$W$
W
Effective work
J
$\eta$
eta
Efficiency
-
$V_1$
V_1
Expanded volume
m^3
$C_V$
C_V
Heat capacity at constant volume
J/kg
$Q$
Q
Heat contributed to the system
J
$Q_H$
Q_H
Heat supplied
J
$n$
n
Number of moles
mol
$T_1$
T_1
Temperature in state 1
K
$T_2$
T_2
Temperature in state 2
K
$R_C$
R_C
Universal gas constant
J/K mol
$W_{in}$
W_in
Work done on the system
J
$W_{out}$
W_out
Work performed by the system
J

Calculations


First, select the equation:   to ,  then, select the variable:   to 

Symbol
Equation
Solved
Translated

Calculations

Symbol
Equation
Solved
Translated

 Variable   Given   Calculate   Target :   Equation   To be used



Equations

When supplying the heat supplied ($Q_H$), the temperature of the gas increases from $T_2$ to $T_3$ in an isochoric process (at constant volume). This implies that we can utilize the relationship for ERROR:8085 with the heat capacity at constant volume ($C_V$) and the variación de Temperature ($\Delta T$), expressed by the equation:

$ dU = C_V \Delta T $



This results in the temperature in state 2 ($T_2$) and the temperature in state 3 ($T_3$) as follows:

$ Q_h = C_V ( T_2 - T_1 )$

(ID 15363)

By removing the absorbed heat ($Q_C$) when the volume ($V$) equals the compressed volume ($V_2$), the absolute temperature ($T$) increases from the temperature in state 1 ($T_1$) to the temperature in state 2 ($T_2$). This implies that we can use the relationship for ERROR:8085 with the heat capacity at constant volume ($C_V$) and the variación de Temperature ($\Delta T$), which is expressed by the equation:

$ dU = C_V \Delta T $



this leads us to the expression:

$ Q_c = C_V ( T_1 - T_2 )$

(ID 15364)

The work is calculated using the integral of the work done on the system ($W_{in}$) with the number of moles ($n$) and the pressure ($p$), integrated in the volume ($V$), from the expanded volume ($V_1$) to the compressed volume ($V_2$):

$ W = \displaystyle\int_{V_1}^{V_2}p\,dV$



If the pressure ($p$) is obtained using the universal gas constant ($R_C$), the number of moles ($n$), and the absolute temperature ($T$) with the gas equation

$ p V = n R_C T $



the integral for the absolute temperature ($T$) is equal to the temperature in state 1 ($T_1$).

$W = \displaystyle\int_{V_1}^{V_2} p dV = \displaystyle\int_{V_1}^{V_2} \displaystyle\frac{nRT_1}{V} dV = nRT_1\ln\left(\displaystyle\frac{V_2}{V_1}\right)$



Therefore,

$ W_{in} = n R_C T_1 \ln\left(\displaystyle\frac{ V_2 }{ V_1 }\right)$

(ID 15365)

The work is calculated using the integral of the work performed by the system ($W_{out}$) with the pressure ($p$), integrated in the volume ($V$), from the expanded volume ($V_1$) to the compressed volume ($V_2$):

$ W = \displaystyle\int_{V_1}^{V_2}p\,dV$



If the pressure ($p$) is obtained using the universal gas constant ($R_C$), the number of moles ($n$), and the absolute temperature ($T$) with the gas equation

$ p V = n R_C T $



the integral for the absolute temperature ($T$) is equal to the temperature in state 1 ($T_1$).

$W = \displaystyle\int_{V_1}^{V_2} p dV = \displaystyle\int_{V_1}^{V_2} \displaystyle\frac{nRT_2}{V} dV = nRT_2\ln\left(\displaystyle\frac{V_2}{V_1}\right)$



Therefore,

$ W_{out} = n R_C T_2 \ln\left(\displaystyle\frac{ V_2 }{ V_1 }\right)$

(ID 15366)

The efficiency ($\eta$) is defined as the ratio of the effective work ($W$) to the heat contributed to the system ($Q$):

$ \eta \equiv \displaystyle\frac{ W }{ Q } $



where the effective work ($W$) is related to the work performed by the system ($W_{out}$) and the work done on the system ($W_{in}$) through:

$ W \equiv W_{out} - W_{in} $



while the heat contributed to the system ($Q$) is associated with the heat supplied ($Q_H$), which is defined as:

$ Q \equiv W_{in} + Q_h $



As the work performed by the system ($W_{out}$) is related to the number of moles ($n$), the temperature in state 2 ($T_2$), the expanded volume ($V_1$), the compressed volume ($V_2$), and the universal gas constant ($R_C$) through:

$ W_{out} = n R_C T_2 \ln\left(\displaystyle\frac{ V_2 }{ V_1 }\right)$



and the work done on the system ($W_{in}$) is associated with the temperature in state 1 ($T_1$) through:

$ W_{in} = n R_C T_1 \ln\left(\displaystyle\frac{ V_2 }{ V_1 }\right)$



and the heat supplied ($Q_H$) is linked to the heat capacity at constant volume ($C_V$) by:

$ Q_h = C_V ( T_2 - T_1 )$



the efficiency ($\eta$) can be calculated, resulting in:

$ \eta = \displaystyle\frac{ T_2 - T_1 }{ T_1 + \displaystyle\frac{ C_V ( T_2 - T_1 )}{ n R_C \ln( V_2 / V_1 )}}$

(ID 15759)


Examples


ID:(1485, 0)