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ISSN Online: 2379-1748

ISBN Flash Drive: 978-1-56700-517-2

5-6th Thermal and Fluids Engineering Conference (TFEC)
May, 26–28, 2021 , Virtual

LOWER LIMIT ON THE THERMODYNAMIC COST TO MANUFACTURE HEAT ENGINES

Get access (open in a dialog) pages 485-494
DOI: 10.1615/TFEC2021.ens.036194

Abstract

A new approach to determine a lower limit on the thermodynamic cost of manufacturing a heat engine is presented and the relationship of that cost to the lifetime of the engine is discussed. A model system consisting of a piston-cylinder engine fabricated of a crystalline solid and filled with a monatomic ideal gas working fluid is considered. The thermodynamic cost of manufacture of the heat engine is taken to be the energy required to break the chemical bonds between atoms in the crystalline solid making up the piston-cylinder walls divided by the lifetime of the engine. The energy required to break the bonds between atoms making up the engine walls can be calculated as the product of the bond energy and the number of bonds. The lifetime of the heat engine is taken to be the time for high-energy working fluid atoms to impact on and break down the piston-cylinder walls. During operation of the engine, as the gas working fluid runs through its cycle, the fluid's atomic kinetic energy is represented with the Boltzmann distribution. A finite number of gas molecules at the high end of kinetic energy in the distribution will have sufficient energy to break the bonds between atoms in the walls of the piston cylinder and dislodge the atoms. Engine lifetime is then calculated as the time required for high-energy gas atoms to dislodge sufficient cylinder-wall atoms to undermine the structural integrity of the engine. The analysis shows engine lifetime, thermodynamic cost of manufacture and energy return on investment (EROI) to be extremely sensitive functions of engine cylinder material bond energy and working fluid temperature.
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