The lumped parameter analysis is considered when the process in which the internal resistance is assumed to be very small (i.e., negligible) when compared to surface convection resistance. The temperature in this process is considered to be uniform at a given time. In this, the whole solid, whose energy is transferred as lump because of negligible internal thermal conductance resistance hence called as lumped analysis.
It assumes a uniform temperature distribution throughout the solid body.
The surface conversion resistance is very significant compared with internal conduction resistance.