Heat is a form an energy. Energy flows from one point to another. Also, it may get stored. But what if I tell you heat is an energy which never gets stored!
Mind=Blown ???
ruko jara sabar karo....there is more ahead to get blown.
While performing (hopefully not making up) energy balance, the heat is shown being generated or consumed. This is also absolutely wrong!
What it is wrong? & How it should be? Let's dig it down.
Thermodynamic Energy Classification-
To understand about heat as an energy, we need to understand about energy. Thermodynamics classifies into two types-
1) Energy in transit- This type of energy does 𝗻𝗼𝘁 exclusively depend on
system properties like temperature or pressure.
- It is 𝗶𝗻𝗳𝗹𝘂𝗲𝗻𝗰𝗲𝗱 𝗯𝘆 𝘁𝗵𝗲 𝗽𝗮𝘁𝗵 𝗼𝗳 𝘁𝗵𝗲 𝗰𝗵𝗮𝗻𝗴𝗲 (not just the
initial and final states).
- Example: 𝗛𝗲𝗮𝘁 (𝗤) & 𝗪𝗼𝗿𝗸 (𝗪).
2) Energy in storage- This energy is 𝘀𝘁𝗮𝘁𝗲-𝗱𝗲𝗽𝗲𝗻𝗱𝗲𝗻𝘁—it depends 𝗼𝗻𝗹𝘆 on
the initial and final states of a system.
- It 𝗱𝗼𝗲𝘀 𝗻𝗼𝘁 𝗱𝗲𝗽𝗲𝗻𝗱 on the path of the change i.e. process (adiabatic,
isothermal,
isobaric, etc.).
- Example: 𝗜𝗻𝘁𝗲𝗿𝗻𝗮𝗹 𝗘𝗻𝗲𝗿𝗴𝘆 (Δ𝗨).
Deeper meaning of this-
The heat & work values will vary for each
unique process for which initial & final
states
are fixed but internal energy won't vary regardless of what path- adiabatic,
isothermal etc whichever you follow until you change initial & final states.
Now, let's discuss the motive of this discussion,
Elephant in the room-
Heat & Work are not associated to each state of the process (except
initial & final
state) & predominantly depends upon path followed to reach final state from initial
state.
Whereas Internal energy is dependent upon each individual state & not the
process.
Hence, Heat & Work are never part of
the system's state.
This implies that whatever
generation, consumption, accumulation
happens at individual state/s- Internal Energy is responsible.
Serious question when doing energy balance in heat transfer-
Answer- NO Majnu bhai, just mentioning it heat would be incorrect. Name it Thermal Energy.
Key Takeways-
Process Engineering Pun Break-
