A conceptual thermal actuation system driven by interface tension of nanofluids

In a system containing nanoporous materials and liquids, the well-known thermo-capillary effect can be amplified by the ultralarge specific surface area of the nanopores. With appropriate temperature change, the relative wetting-dewetting transition can cause the liquid to flow in or out of the nanopores, and part of the thermal energy is converted to significant mechanical output. A conceptual design of such a thermal actuation/energy conversion/storage system is investigated in this paper, whose working mechanism, i.e. the thermally dependent infiltration behaviors of liquids into nanopores, is analyzed using molecular dynamics simulations. The fundamental molecular characteristics, including the density profile, contact angle, and surface tension of the confined liquid molecules, are examined in considerable detail. The influences of pore size, solid phase and liquid species are elucidated, which couple with the thermal effect. The energy density, power density, and efficiency of the thermal actuation system are evaluated. An infiltration experiment on a zeolite/water system is performed to qualitatively validate these findings.