how does unsteady state heat conduction differ from steady state heat conduction?

Question

chemical engineering question..

Answer 1

Steady state means that the temperture at any point does not change over time. In a continuous engineering process steady state is frequently a good assumption. At start up and shut down there will be transients, but many processes are steady state during operation.

For heat conduction specifically, a steady state process is concerned only with thermal conductivity (usually designated k with units of BTU/(hr-ft-deg F) or Watt/(m-deg C)). A transient condition must track the changing amount of heat stored in the material as the temperature changes. As such, the most important parmater becomes thermal diffusivity which is the ratio of thermal conductivity to volumetric thermal mass.

Answer 2

The spot temperatures changes over time in the unsteady case, while remains constant in the steady case. If there is a fixed thermal barrier between a hot and a cold zone, it will approach a steady state where there will be a time-independent function of temperature across the thickness of the barrier. However, if for example the temperature of the hot zone varied in time, then the temperature function across the thickness of the barrier will not be time-independent, and thus would be an example of an unsteady state heat conduction.

Answer 3

Unsteady State

Answer 4

Refer the book "Fundamentals of heat and mass transfer" by Incropera and Dewitt