Explain the terms:
Transient state,
Steady state, and
Temperature gradient.
Heat is received equally by all cross - sectional areas.
Let Q be the heat received from the adjacent cross-section on the hot side.
This heat is used in following parts:
(i) A part of total heat received is retained by the cross-section Qa.
(ii) A part of heat (Q1) is transferred to next cross-section towards cold end side. As a result, there is the flow of heat.
Since the temperature of various parts of the rod is increasing, the state is called transient state.
Steady state: As the temperature increases, the rate of loss of heat also increases.
After some time,
Q3= Qa and Q2 =0.
At this stage, the temperature of cross section attains a constant value. This stage is called steady state.
Temperature gradient: At a steady state, the temperature at a given cross-section is constant.
But, the temperature actually decreases along the length of the rod in a direction of flow of heat and is different in different directions.
The rate of change of temperature with distance in the direction of heat flow is called temperature gradient.
The temperature gradient at any point is represented by dθ/dx.
