Editing Thermal conduction (section)

===Steady-state conduction===
Steady-state conduction is the form of conduction that happens when the temperature difference(s) driving the conduction are constant, so that (after an equilibration time), the spatial distribution of temperatures (temperature field) in the conducting object does not change any further. Thus, all partial derivatives of temperature ''concerning space'' may either be zero or have nonzero values, but all derivatives of temperature at any point ''concerning time'' are uniformly zero. In steady-state conduction, the amount of heat entering any region of an object is equal to the amount of heat coming out (if this were not so, the temperature would be rising or falling, as thermal energy was tapped or trapped in a region).

For example, a bar may be cold at one end and hot at the other, but after a state of steady-state conduction is reached, the spatial gradient of temperatures along the bar does not change any further, as time proceeds. Instead, the temperature remains constant at any given cross-section of the rod normal to the direction of heat transfer, and this temperature varies linearly in space in the case where there is no heat generation in the rod.<ref>{{Cite book |title=Fundamentals of heat and mass transfer| date=2011|publisher=Wiley|last1=Bergman |first1=Theodore L. |last2=Lavine |first2=Adrienne S. |author2-link=Adrienne Lavine|last3=Incropera |first3=Frank P. |first4=David P. |last4=Dewitt |isbn=9780470501979 | edition=7th |location=Hoboken, NJ|oclc=713621645}}</ref>

In steady-state conduction, all the laws of direct current electrical conduction can be applied to "heat currents". In such cases, it is possible to take "thermal resistances" as the analog to [[electrical resistance]]s. In such cases, temperature plays the role of voltage, and heat transferred per unit time (heat power) is the analog of electric current. Steady-state systems can be modeled by networks of such thermal resistances in series and parallel, in exact analogy to electrical networks of resistors. See [[Lumped capacitance model#Thermal purely resistive circuits|purely resistive thermal circuits]] for an example of such a network.