Controlling and maximizing effective thermal properties by manipulating transient behaviors during energy-system cycles ☆

Abstract Transient processes generally constitute part of energy-system cycles. If skillfully manipulated, they actually are capable of assisting systems to behave beneficially to suit designers' needs. In the present study, behaviors related to both thermal conductivities ( κ ) and heat capacities ( c v ) are investigated. Three major findings validated by COMSOL simulations and micro-Hamiltonian-Oscillator analyses are reported: (1) effective κ and effective c v can be controlled to vary from their intrinsic material-property values to a few orders of magnitude larger; (2) a parameter, tentatively named as “nonlinear thermal bias”, is identified and can be used as a criterion in estimating energies transferred into the system during heating processes; (3) For bodies of fluids confined by a cold bottom and a hot top, it may be feasible to install a propeller that can be turned by a weak buoyancy force induced by the top-to-bottom heat conduction via the propeller, provided that densities of the propeller and the fluid are similar. Such a turning motion serves double purposes of performing the hydraulic work and increasing the effective κ of the propeller. Hence, hot-top-and-cold-bottom fluid-filled enclosures (e.g., oceans) that induce nearly no buoyancy flows may now, in principle, become energy-harnessing sources.