Consider a column filled with a transporting medium and a balloon filled with a working fluid. Due to the hydrostatic pressure of the transporting medium, the pressure inside the column increases along the z axis (see figure). Initially, the balloon is inflated by the working fluid at temperature T and pressure P and located on top of the column. A thermogravitational cycle is decomposed into four ideal steps:
* 1→2: Descent of the balloon towards the bottom of the column. The working fluid undergoes adiabatic compression with its temperature increasing and its pressure reaching value P at the bottom (P>P).
* 2→3: While the ballon lays at the bottom, the working fluid receives heat from the hot source at temperature T and undergoes isobaric expansion at pressure P.
* 3→4: The balloon rises towards the column top. The working fluid undergoes adiabatic expansion with a drop in temperature and reaches pressure P after expansion when the balloon is on top.
* 4→1: Once arrived on top, the working fluid supplies heat to the cold source at temperature T while undergoing isobaric compression at pressure P.
For a thermogravitational cycle to occur, the balloon has to be denser than the transporting medium during 1→2 step and less dense during 3→4 step. If these conditions are not naturally satisfied by the working fluid, a weight can be attached to the balloon to increase its effective mass density.