Thermal Equilibrium: Conditions and Application

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SUMMARY

This discussion centers on the concept of thermal equilibrium, specifically addressing whether a body can be considered in thermal equilibrium when parts of it are gaining and losing heat simultaneously. It is established that thermal equilibrium is defined by constant macroscopic state variables such as temperature, pressure, and density over time. However, in an isolated system, while a subsystem may exhibit steady-state conditions, it is not in true thermal equilibrium due to the inevitable heat flow that will vary over time until a uniform temperature is achieved. The example of human body temperatures illustrates this principle, where core and skin temperatures differ due to external heat exchange.

PREREQUISITES
  • Understanding of thermal equilibrium and its definitions
  • Knowledge of macroscopic state variables (temperature, pressure, density)
  • Familiarity with heat transfer concepts
  • Basic principles of thermodynamics
NEXT STEPS
  • Research the laws of thermodynamics and their implications on thermal systems
  • Explore the concept of steady-state conditions in thermodynamic systems
  • Learn about heat transfer mechanisms (conduction, convection, radiation)
  • Investigate the implications of temperature gradients in biological systems
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Students and professionals in physics, thermodynamics, and engineering, as well as anyone interested in understanding heat transfer and thermal dynamics in various systems.

tme92
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Can one say a body which has the conditions above mentioned be in thermal equilibrium? How does one apply the definition of temperature equilibrium to this situation?

(Physically I think it's possible for a body to be in this situation if some part of it receives heat from the outside and another loses heat)
 
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Interesting question. I guess it's a matter of what you mean by thermal equilibrium. In many textbooks they say thermal equilibrium is when the macroscopic state variables (temperature, pressure, density,...) of the system are constant over time. In this sense you can say that your system is at equilibrium. But if you consider the whole isolated system your subsystem belongs to, this is not at equilibrium. The flow of heat between all the parts of the isolated system cannot be steady forever, but will forcefully vary over time, and finally vanish when all the parts of the complete system will be at the same temperature (this because an infinite heat reservoir doesn't exist).
 


tme92 said:
Can one say a body which has the conditions above mentioned be in thermal equilibrium? How does one apply the definition of temperature equilibrium to this situation?

(Physically I think it's possible for a body to be in this situation if some part of it receives heat from the outside and another loses heat)

The body is not in equilibrium, but may have steady-state conditions. Our bodies have these conditions: core temperature 98.6 F, skin temperature closer to ambient air temperature.

All this means is that there is a steady flow of heat, and T(x,t) = T(x).
 

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