Heat transfer

Содержание и основные понятия

The energy is accidentally transferred from a warmer body to a lower hot one. Under different conditions, the transport provides collision of particles, flow of matter or electromagnetic radiation.
GEF · Grade 8
PIF · Baseline
Interactive model
Heat conductivity
assembly
radiation
thermal insulation
01
The physical picture
What happens and what boundaries the model has.
Main message
The energy is accidentally transferred from a warmer body to a lower hot one. Under different conditions, the transport provides collision of particles, flow of matter or electromagnetic radiation.
Heat conductivity is particularly visible in metals and is not accompanied by transport of the substance.
Convection arises in liquids and gases because of the difference between the density of hot and cold layers.
The radiation also spreads in a vacuum; its intensity depends on the temperature and properties of the surface.
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.
Q
=
c
m
Δ
T
Q=cm\Delta T
Q
=
c
m
Δ
T
Heat at temperature change
P
=
Q
t
P=\frac{Q}{t}
P
=
t
Q
​
Average heat transfer capacity
Review of the situation
Thermos reduces all three channels of loss: vacuum suppresses thermal conductivity and convection, mirror walls reflect thermal radiation.
04
Links and application
In the real world
Thermos reduces all three channels of loss: vacuum suppresses thermal conductivity and convection, mirror walls reflect thermal radiation.
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 the topic "Terp transfer" through the model, not just through the formula.
Outcome 2
To distinguish and correctly use the terms heat conductivity, convection, radiation.
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.
Heat conductivity
Transfer of internal energy during particle interaction without macroscopic transport of the substance.
assembly
Transmission of energy by liquid or gas flows.
radiation
Transport of energy by electromagnetic waves; does not require a material environment.
thermal insulation
Material or a system of measures to reduce unwanted heat transfer.
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.
Q
=
c
m
Δ
T
Q=cm\Delta T
Q
=
c
m
Δ
T
empirical law
Heat at temperature change.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
Q
∼
m
,
Q
∼
Δ
T
Q\sim m,\qquad Q\sim\Delta T
Q
∼
m
,
Q
∼
Δ
T
Experience with a homogeneous substance is found: the required heat is proportional to mass and temperature change.
c
=
Q
m
Δ
T
c=\frac{Q}{m\Delta T}
c
=
m
Δ
T
Q
​
The proportionality factor shall be applied as a specific heat capacity of the substance.
Q
=
c
m
Δ
T
Q=cm\Delta T
Q
=
c
m
Δ
T
The sign ΔT shows the direction of exchange: if Q is warmed positive, if cooled negative.
Conditions:
A homogeneous body, constant specific heat capacity in the range under consideration, no phase transition or chemical reaction.
Monitoring:
The dimensions of both parts shall coincide; the result shall be checked for sign, order and limit case.
P
=
Q
t
P=\frac{Q}{t}
P
=
t
Q
​
definition
Average heat transfer capacity.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
P
ср
=
переданная энергия
время передачи
P_{\text{ср}}=\frac{\text{переданная энергия}}{\text{время передачи}}
P
cf
​
=
time
Transfers
transferred
Energy
​
The average power is injected as the energy transferred per unit of time.
P
ср
=
Q
t
P_{\text{ср}}=\frac{Q}{t}
P
cf
​
=
t
Q
​
If the energy is transferred in the form of heat Q over the interval t, the definition shall take the specified form.
Conditions:
Q is the heat transmitted over the entire period t > 0; at the rate of heat transfer variable, the formula gives only the average power.
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
The formula cannot be transferred to any situation simply because of the overlap of letters. The key condition of this topic is that heat conductivity is particularly visible in metals and is not accompanied by transport of the substance.
How to Check the Mind
Convection occurs in liquids and gases because of the difference between the density of the heated and cold layers. Then check the units, vector direction, and behaviour of the result at zero or very large parameter.
Σ
Conclusion on the topic
Heat transfer
The energy is accidentally transferred from a warmer body to a lower hot one. Under different conditions, the transport provides collision of particles, flow of matter or electromagnetic radiation.
Heat conductivity is particularly visible in metals and is not accompanied by transport of the substance.
Convection arises in liquids and gases because of the difference between the density of hot and cold layers.
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.