Heat engines

Содержание и основные понятия

The heat engine cycled from the heater, part turned into mechanical work, and the rest passed over to the refrigerator. It was impossible to completely convert heat to work.
GEF · Grade 8
PIF · Baseline
Interactive model
Heater
working body
Fridge
SAP
Engine
01
The physical picture
What happens and what boundaries the model has.
Main message
The heat engine cycled from the heater, part turned into mechanical work, and the rest passed over to the refrigerator. It was impossible to completely convert heat to work.
The working body goes through a closed cycle and returns to its original state.
The PAC is always less than one because of the mandatory heat return to the refrigerator and the loss.
The heater temperature increase and the refrigerator temperature decrease increase the limit value.
How to reason
First, name the system and the interaction, then select the values, and only then write down the law. The formula works within the model's assumptions.
02
Laws and values
Symbols should be read as a relationship of values, not as a recipe for substitution.
A
=
Q
1
−
Q
2
A=Q_1-Q_2
A
=
Q
1
​
−
Q
2
​
cycle work
η
=
A
Q
1
⋅
100
%
\eta=\frac{A}{Q_1}\cdot100\%
η
=
Q
1
​
A
​
⋅
100%
Engine SAP
Review of the situation
If the engine received 1000 J and gave the refrigerator 650 J, it has 350 J and 35 % KPA.
04
Links and application
In the real world
If the engine received 1000 J and gave the refrigerator 650 J, it has 350 J and 35 % KPA.
Model verification
Compare the prediction with observation, evaluate the units, the order of magnitude and the influence of the factors not taken into account. Disparity does not always mean an error of law: often idealization is no longer sufficient.
C
What needs to be understood
Outcome 1
Explain the physical meaning of "Techniques" through the model, not just through the formula.
Outcome 2
Clear and correctly use terms: heater, work body, refrigerator.
Outcome 3
Indicate the conditions for the applicability of the law, verify units and limit cases.
T
Terms of the topic
The definition should indicate the physical meaning, not a substitute for a domestic synonym.
Heater
A higher-temperature body transmitting heat to the working body during the heater cycle.
working body
A system that is cycled to heat, does work and delivers part of the heat in the heater.
Fridge
In a heater, a body with a lower temperature, to which the working body gives part of the heat.
SAP
Ratio of useful energy or work to that spent; unlimited, usually expressed as a percentage.
Engine
A device that converts the energy of the source into mechanical work.
F
Origin and conclusion of the formulas
The fundamental law cannot be "proven" by algebras: for each record, it is stated whether it is a definition, an experimental law, or a model effect.
A
=
Q
1
−
Q
2
A=Q_1-Q_2
A
=
Q
1
​
−
Q
2
​
model effect
Working over a cycle.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
Δ
U
цикл
=
0
\Delta U_{\text{цикл}}=0
Δ
U
cycle
​
=
0
After the complete cycle, the working body returns to its original state, so its internal energy does not change.
Q
1
=
A
+
Q
2
Q_1=A+Q_2
Q
1
​
=
A
+
Q
2
​
Heat from the heater shall be used to work and to transfer the remainder to the refrigerator.
A
=
Q
1
−
Q
2
A=Q_1-Q_2
A
=
Q
1
​
−
Q
2
​
The engine shall operate at the same rate as the heat received and delivered.
Conditions:
The complete heater cycle; Q1 and Q2 indicate positive heat modules from the heater to the refrigerator.
Monitoring:
The dimensions of both parts shall coincide; the result shall be checked for sign, order and limit case.
η
=
A
Q
1
⋅
100
%
\eta=\frac{A}{Q_1}\cdot100\%
η
=
Q
1
​
A
​
⋅
100%
definition
Engine speed.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
η
=
полезная энергия
затраченная энергия
\eta=\frac{\text{полезная энергия}}{\text{затраченная энергия}}
η
=
spent
Energy
useful
Energy
​
The CAD is introduced as a share of energy spent, converted into a useful result.
E
пол
=
A
,
E
затр
=
Q
1
E_{\text{пол}}=A,\qquad E_{\text{затр}}=Q_1
E
Gender
​
=
A
,
E
morning
​
=
Q
1
​
For a thermal engine, work is useful, and the cost is heat from the heater.
η
=
A
Q
1
⋅
100
%
\eta=\frac{A}{Q_1}\cdot100\%
η
=
Q
1
​
A
​
⋅
100%
Multiplying the relationship by 100% translates the share into interest.
Conditions:
One engine cycle or stationary operation is considered; A and Q1 are measured over the same interval, Q1 > 0.
Monitoring:
The dimensions of both parts shall coincide; the result shall be checked for sign, order and limit case.
!
Model boundaries and typical errors
Error: Forget model condition
You can't put the formula on any situation just because it's a coincidence of letters. The key condition of this topic is that the working body goes through a closed cycle and goes back to its original state.
How to Check the Mind
The PAC is always less than one because of the mandatory heat return to the refrigerator and the loss. Then check the units, vector direction and behaviour of the result at zero or very large parameter.
Σ
Conclusion on the topic
Heat engines
The heat engine cycled from the heater, part turned into mechanical work, and the rest passed over to the refrigerator. It was impossible to completely convert heat to work.
The working body goes through a closed cycle and returns to its original state.
The PAC is always less than one because of the mandatory heat return to the refrigerator and the loss.
Any numerical result shall be accompanied by a unit, a sign and an explanation of its physical meaning.
The content is consistent with the FRP on Physics of the OS/OSS 2025 and the subject matter of the current lines of the PNP: I. M. Peryškin and co-authors (7–9), G. J. Mäkishev and coauthors (10–11), and with the lines "Engineers of the Future" and V. A. Kasyanov. The original texts are not reproduced, the text of the textbooks is not reproduced.