2.3.2. Thermal Resistance

The boiling-induced nanoparticle deposition onto the interface of the solid and liquid phases seriously affects the interfacial thermal resistance (ITR) or Kapitsa resistance. The ITR can be modified by the wettability and morphology of the interface. For instance, the thermal conductance of different wettability interfaces functionalized with a self-assembled monolayer (SAM) has already been determined by the time-domain thermo-reflectance technique [59]. The authors reported that the ITR of a hydrophobic interface was near three-fold greater than that of a hydrophilic interface. Moreover, in the work performed by [5], the layer of carbon nanoparticles deposited onto the solid and liquid phases interface influenced the density of the working fluid, the heat transfer near the interface, and the ITR. The researchers numerically evaluated the ITR with changes in the intermolecular interactions between the fluid and the nanoparticles and those between the fluid and the surface. The researchers arrived at the following conclusions: (i) The nanoparticle layer deposited onto the solid–liquid interface decreased the ITR, which might become lower that the typical ITR value of a smooth heating surface, especially in the cases where the nanoparticles exhibit hydrophilicity. Additionally, it was common in the fullerene and amorphous nanoparticles. (ii) The considerable ITR decrease caused by the deposition layer enhanced the heat transfer from the heating surface to the nanoparticles, and, consequently, augmented the heat transfer of the nanoparticles. The key condition for the decrement in the ITR was the extraction, storing, and transport of the heat from the solid interface by the nanoparticles to the neighboring fluid outside the deposition layer. In addition to the heat flux increment, the temperature difference at the interface of the solid and liquid phases was decreased by the deposition of the nanoparticles. These alterations contributed to the ITR reduction. (iii) The deposit of nanoparticles onto the interface did not induce an appreciably extra thermal resistance as compared with the corresponding fluid layer, independently of the morphology of the nanoparticles. This was caused by the fact that the single layer of the nanoparticles was of such reduced dimensions that it could not be enough for producing the additional thermal resistance at the interface, although the thermal resistance of the used fullerene was high. (iv) The nanoparticle deposition changed

the density of the thermal fluid and the temperature gradient at the interface. The ITR decreased with increasing fluid density in the deposition layer. The changes in the fluid density in the interface nearby region and in its temperature gradient by the nanoparticle deposition were two major conditions affecting the ITR.
