Thermal rectification in a fluid reservoir

An organized nonuniform mass distribution in solids leads to a monotonically varying thermal conductivity in a nanomaterial so that the heat flux is directionally dependent. We investigate through molecular dynamics simulations if the influence of an organized mass distribution in a fluid also leads to thermal rectification. Heat transfer is monitored in a water reservoir placed between two (hot and cold) silicon walls. The distribution of the fluid in the reservoirs is organized by applying an external force to each water molecule in a specified direction, creating a density gradient. This external force is smaller than the intermolecular forces in water, in most cases by much more than an order of magnitude. The simulations reveal that mass graded fluid-containing nanosystems can be engineered to possess an asymmetric axial thermal conductance that leads to greater heat flow in the direction of decreasing mass density. The rectification improves as the thermal conductivity is enhanced by increasing the fluid density adjacent to a hot wall, since doing so decreases the interfacial resistance and increases the heat flux.