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

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 (\(\kappa\)) and heat capacities (\(c_{v}\)) are analyzed. Along with solutions of the temperature and the flow velocity obtained by means of theories and simulations, three findings are reported herein: \((1)\) effective \(\kappa\) 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 and effective operating ranges of system temperatures; \((3)\) When a body of water, such as the immense ocean, is subject to the boundary condition of cold bottom and hot top, it may be feasible to manipulate transient behaviors of a solid propeller-like system such that the system can be turned by a weak buoyancy force, induced by the top-to-bottom heat conduction through the propeller, provided that the density of the propeller is selected to be close to that of the water. Such a turning motion serves both purposes of performing the hydraulic work and increasing the effective thermal conductivity of the system.