Thermogravitational Cycles: Theoretical Framework and Example of an Electric Thermogravitational Generator Based on Balloon Inflation/Deflation

• Main Authors: Kamel Aouane, Olivier Sandre, Ian J. Ford, Tim P. Elson, Chris Nightingale
• Format: Article
• Language: English
• Published: MDPI AG 2018-11-01
• Series: Inventions
• Subjects: thermogravitational cycle; thermogravitational electric generator; pure power cycle; Carnot; Rankine; and Brayton cycles; gravitational force; compression and expansion; waste heat; geothermal or solar energy harvesting
• Online Access: https://www.mdpi.com/2411-5134/3/4/79

Several studies have involved a combination of heat and gravitational energy exchanges to create novel heat engines. A common theoretical framework is developed here to describe thermogravitational cycles which have the same efficiencies as the Carnot, Rankine, or Brayton cycles. Considering a working fluid enclosed in a balloon inside a column filled with a transporting fluid, a cycle is composed of four steps. Starting from the top of the column, the balloon goes down by gravity, receives heat from a hot source at the bottom, then rises and delivers heat to a cold source at the top. Unlike classic power cycles which need external work to operate the compressor, thermogravitational cycles can operate as a “pure power cycle„ where no external work is needed to drive the cycle. To illustrate this concept, the prototype of a thermogravitational electrical generator is presented. It uses a hot source of average temperature near 57 °C and relies on the gravitational energy exchanges of an organic fluorinated fluid inside a balloon attached to a magnetic marble to produce an electromotive force of 50 mV peak to peak by the use of a linear alternator. This heat engine is well suited to be operated using renewable energy sources such as geothermal gradients or focused sunlight.