Thermal rectification permits a material to behave both as a conductor and an insulator simultaneously depending on the direction of heat transfer. For a material to exhibit thermal rectification it cannot be homogeneous, and its thermal conductivity should be dependent both on the local temperature in the material and the location. This requirement has generally led to the conclusion that only composite materials, such as layered walls, will exhibit thermal rectification. We propose a proof of concept study to demonstrate that thermal rectification can be induced in liquids that are generally homogeneous and not otherwise considered suitable. This will be shown by manipulating solid-fluid interfaces using either external forces through applied electric or magnetic fields, or by introducing surface forces, e.g. by rendering the surfaces hydrophobic or hydrophilic. We will use the method of molecular dynamics using a technique we have developed to investigate heat transfer at such solid-fluid interfaces and the resulting thermal rectification. We thus hope to demonstrate the possibility of thermal rectification for a wide range of liquids that are already deemed suitable for industrial applications.
Thermal rectification has important applications in the thermal management of electronics and thermoelectric devices. It can also contribute to improving sustainability solutions, such as solar water heaters that are now being increasingly used, where it is undesirable to loose heat at night. Other possible applications include biomedical ultrasound devices, thermal computers, energy saving and harvesting materials, and direction dependent insulating materials. Solids cannot be easily manipulated so it is difficult to tune, i.e., change, their rectification behavior. Liquids are more amenable to such tuning, which will enable the rectification to be dynamically changed. Thus a material could exhibit rectification when desirable; else the directionality of rectification could be inverted or even tuned off completely. This would allow many new devices to benefit from thermal rectification than is currently possible.
