Simple realization of the polytropic process with a finite-sized reservoir

In many textbooks of thermodynamics, the polytropic process is usually introduced by defining its process equation rather than analyzing its actual origin. We realize a polytropic process of an ideal gas system when it is thermally contact with a reservoir whose heat capacity is a constant. This model can deepen students' understanding of typical thermodynamic processes, such as isothermal and adiabatic processes, in the teaching of thermodynamics. Moreover, it can inspire students to explore some interesting phenomena caused by the finiteness of the reservoir. The experimental implementation of the proposed model with realistic parameters is also discussed.