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

• Published in: International communications in heat and mass transfer 2016-07, Vol.75, p.137-146
• Main Authors: Gao, Zhaojing, Shih, Tien-Mo, Merlitz, Holger, Chen, Zhong
• Format: Article
• Language: English
• Subjects: Buoyancy; Capacity; Conductivity; Enclosures; Estimating; Fluids; Heat transfer; Nonlinear thermal bias; Ocean energy; Propellers; Thermal conductivity; Thermal properties; Transient states
• ISSN: 0735-1933; 1879-0178
• DOI: 10.1016/j.icheatmasstransfer.2016.04.015

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 (cv) are investigated. Three major findings validated by COMSOL simulations and micro-Hamiltonian-Oscillator analyses are reported: (1) effective κ and effective cv 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.