The thermodynamic limit of extractable kinetic energy buoyancy engine

Abstract

In this work, consideration is given to the thermodynamic limit of the kinetic energy extractable from the ascending or descending motion of a buoyancy engine for use in the contraction or expansion of its own chamber. From the laws of thermodynamics, a simple expression for thermodynamic efficiency was derived. It is shown that contrary to what might be expected, the efficiency is not dependent on the drag coefficient and then on the specific shape of the body but rather only on the normalized Reynolds number ReRet, where Ret is the terminal Reynolds number. The maximum efficiency was found to be ≃40% when the contraction or expansion takes place at ≈85% of the terminal velocity.